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Elhadd T, Bashir M, Baager KA, Ali HA, Almohannadi DHS, Dabbous Z, Malik RA, Abou-Samra AB. Mitigation of hypoglycemia during Ramadan using the flash glucose monitoring system following dose adjustment of insulin and sulphonylurea in patients taking multiple glucose-lowering therapies (The PROFAST-IT Study). Diabetes Res Clin Pract 2021; 172:108589. [PMID: 33316309 DOI: 10.1016/j.diabres.2020.108589] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/26/2020] [Revised: 11/17/2020] [Accepted: 11/27/2020] [Indexed: 11/26/2022]
Abstract
BACKGROUND AND HYPOTHESIS Patients with type-2 diabetes mellitus (T2DM) on multiple glucose-lowering therapies who fast during Ramadan are at increased risk of hypoglycemia. We have assessed the utility of the flash glucose monitoring system after adjusting the dose of insulin and sulphonylureas to mitigate the risk of hypoglycemia in patients with T2DM who fast during Ramadan. PATIENTS AND METHODS Patients with T2DM on either basal insulin or a sulphonylurea and at least 2 other glucose-lowering agents received structured education and adjustment of insulin or sulphonylurea dose according to the PROFAST Ramadan protocol. Glucose variability and episodes of hypoglycemia were assessed using the flash glucose monitoring system (Free Style Libre) before and during Ramadan. RESULTS A total of 33 patients with T2DM (on sulphonylurea (SU+) (n = 21), on basal insulin (BI+) (n = 12) aged 50.8 ± 1.6 years with a diabetes duration of 13.1 ± 6.5 years were studied. The average sensor glucose was 154 ± 34 mg/dl (8.5 ± 1.88 mmol/l) with 65.2% in the target range before Ramadan and the average sensor glucose was 156 ± 36 mg/dl (8.6 ± 2.0 mmol/l) with 67.1% in the target range during Ramadan. The incidence of hypoglycemia in the whole group (2.9 v 2.9) and in the SU+ (3.7 vs 3.0) and BI+ (1.7 vs 2.9) groups and eHbA1c (P = 0.56, P = 0.93), average glucose (P = 0.56, P = 0.92) and time within range (P = 0.63, P = 0.73) did not change in the SU+ and BI+ groups, respectively, before and during Ramadan. CONCLUSION Structured education with adjustment of the dose of glucose lowering medication alongside use of the FGMS can effectively mitigate the increased risk of hypoglycemia in patients with T2DM on multiple glucose-lowering therapies who fast during Ramadan.
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Affiliation(s)
- Tarik Elhadd
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Qatar.
| | - Mohamed Bashir
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Qatar
| | - Khaled A Baager
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Qatar
| | - Hamda A Ali
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Qatar
| | | | - Zainab Dabbous
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Qatar
| | - Rayaz A Malik
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Doha & Weill Cornell Medicine-Qatar, Doha, Qatar
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Bashir M, Naem E, Taha F, Konje JC, Abou-Samra AB. Outcomes of type 1 diabetes mellitus in pregnancy; effect of excessive gestational weight gain and hyperglycaemia on fetal growth. Diabetes Metab Syndr 2019; 13:84-88. [PMID: 30641818 DOI: 10.1016/j.dsx.2018.08.030] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Accepted: 08/27/2018] [Indexed: 01/01/2023]
Abstract
AIMS To study pregnancy outcomes in patients with type 1 diabetes mellitus (T1DM) and the factors associated with poor outcomes. METHODS A retrospective study of 110 patients with T2DM who attended our diabetes in pregnancy clinic at the Women's Wellness and Research centre, Doha, between March 2015 and December 2016 and 1419 normoglycaemic controls. RESULTS There was no difference in age, weight, and BMI between the two groups. The incidence of macrosomia, shoulder dystocia and stillbirth were similar in the two groups while that of pre-term labour, pre-eclampsia, Caesarean section (CS), large for gestational age (LGA), neonatal ICU (NICU) admission and neonatal hypoglycaemia were significantly higher in the T1DM than in the control group. From a multivariate regression analysis, excessive gestational weight gain was associated with increased risk of LGA (OR 4.53; 95% CI [1.42-14.25]). Last trimester HBA1c was associated with increased risk for macrosomia [OR 2.46, 95% CI [1.03-5.86)]; LGA [ OR 3.25, 95% CI [1.65-6.40)]; increased risk for C-section (OR 1.96, 95% CI [1.12-3.45]), and increased risk of NICU admission (OR 2.46, 95% CI [1.04-5.86]). The changes in HBA1C between the first and last trimester HBA1c was associated with a reduction in the risk of LGA [OR 0.46, 95% CI [(0.28-0.75)] CONCLUSION: T1DM in pregnancy is associated with adverse pregnancy outcomes compared to the general population. Reducing gestational weight gain and improving glycaemic control might improve pregnancy outcomes.
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Affiliation(s)
- Mohammed Bashir
- Qatar Metabolic Institute, Hamad Medical Corporation, Doha, Qatar.
| | - Emad Naem
- Qatar Metabolic Institute, Hamad Medical Corporation, Doha, Qatar
| | - Faten Taha
- Department of Obstetrics and Gynaecology, Women's Wellness and Research Centre, Hamad Medical Corporation, Doha, Qatar
| | - Justin C Konje
- Women's Clinical Services Management Group (WCMG), Sidra Medicine, Doha, Qatar
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3
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Bashir M, Dabbous Z, Baagar K, Elkhatib F, Ibrahim A, Brich SA, Abdel-Rahman ME, Konje JC, Abou-Samra AB. Type 2 diabetes mellitus in pregnancy: The impact of maternal weight and early glycaemic control on outcomes. Eur J Obstet Gynecol Reprod Biol 2018; 233:53-57. [PMID: 30572188 DOI: 10.1016/j.ejogrb.2018.12.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Revised: 12/03/2018] [Accepted: 12/07/2018] [Indexed: 11/18/2022]
Abstract
OBJECTIVES To study the pregnancy outcomes in women with type 2 diabetes mellitus (T2DM) and to relate these to maternal risk factors. METHODS We conducted a retrospective study of 419 women with T2DM (index group)- who attended our diabetes in pregnancy clinic at the Hamad Women's Hospital, Doha, between March 2015 and December 2016 -and 1419 normoglycaemic women (control group). RESULTS Compared with the controls, T2DM women were older (mean age 34.7 ± 6.9 vs 29.6 ± 5.5 years; p < 0.001) and had a higher BMI (34.5 ± 6.7 vs 28.8 ± 6.1 kg/m2; p < 0.001). The incidence of macrosomia, shoulder dystocia and stillbirth were similar in the two groups, while that of pre-term labour, pre-eclampsia, caesarean section (CS), large for gestational age (LGA), neonatal ICU (NICU) admission, and neonatal hypoglycaemia were significantly higher in the T2DM compared to the control group (p < 0.05). Multivariate regression analysis showed that first trimester HbA1C was associated with an increased risk of LGA (OR 1.17; 95% CI [1.01-1.36]), pre-eclampsia (OR 1.26; 95% CI [1.02-1.54]), neonatal hypoglycaemia (OR 1.32; 95% CI 1.10-1.60) and NICU admission (OR 1.32; 95% CI 1.10-1.60). Pre-pregnancy BMI was associated with increased risk of LGA (OR 1.04; 95%CI [1.00-1.08]), macrosomia (OR 1.06; 95%CI [1.00-1.12]) and CS (OR 1.05; 95% CI [1.01-1.09]). Last trimester HbA1c was associated with an increased risk of LGA [OR 1.53, 95% CI [1.13-2.10)] and CS (OR 1.37, 95% CI [1.01-1.87]). CONCLUSION T2DM is associated with adverse pregnancy outcomes compared to the normal control in Qatar. Maternal obesity and glycaemic control before and during pregnancy are the main determinants of pregnancy outcomes in women with T2DM.
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MESH Headings
- Adult
- Case-Control Studies
- Cesarean Section/statistics & numerical data
- Diabetes Mellitus, Type 2/complications
- Diabetes Mellitus, Type 2/drug therapy
- Diabetes Mellitus, Type 2/physiopathology
- Female
- Fetal Macrosomia/epidemiology
- Fetal Macrosomia/etiology
- Gestational Weight Gain
- Glycated Hemoglobin/administration & dosage
- Glycated Hemoglobin/analysis
- Humans
- Hypoglycemia/epidemiology
- Hypoglycemia/etiology
- Hypoglycemic Agents/therapeutic use
- Infant, Newborn
- Infant, Newborn, Diseases/epidemiology
- Infant, Newborn, Diseases/etiology
- Insulin/therapeutic use
- Intensive Care Units, Neonatal/statistics & numerical data
- Metformin/therapeutic use
- Obesity/complications
- Obstetric Labor, Premature/epidemiology
- Obstetric Labor, Premature/etiology
- Pre-Eclampsia/epidemiology
- Pre-Eclampsia/etiology
- Pregnancy
- Pregnancy in Diabetics/drug therapy
- Pregnancy in Diabetics/physiopathology
- Qatar
- Retrospective Studies
- Risk Factors
- Young Adult
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Affiliation(s)
- Mohammed Bashir
- Qatar Metabolic Institute, Hamad Medical Corporation, Doha, Qatar.
| | - Zeinab Dabbous
- Qatar Metabolic Institute, Hamad Medical Corporation, Doha, Qatar
| | - Khaled Baagar
- Qatar Metabolic Institute, Hamad Medical Corporation, Doha, Qatar
| | - Fadi Elkhatib
- Department of Obstetrics and Gynaecology, Women's Hospital, Hamad Medical Corporation, Doha, Qatar
| | - Amin Ibrahim
- Department of Obstetrics and Gynaecology, Women's Hospital, Hamad Medical Corporation, Doha, Qatar
| | - Sanam-Alhouda Brich
- Department of Obstetrics and Gynaecology, Women's Hospital, Hamad Medical Corporation, Doha, Qatar
| | - Manar E Abdel-Rahman
- Department of Biostatistics, College of Health Science, Qatar University, Doha, Qatar
| | - Justin C Konje
- Women's Clinical Services Management Group (WCMG), Sidra Medicine, Doha, Qatar
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Elhadd T, Dabbous Z, Bashir M, Elzouki A, Ghadban W, Baagar K, Benjamin S, Hassanien M, Saeed AAM, Dukhan K, Malik RA, Abou-Samra AB. Incidence of hypoglycaemia in patients with type-2 diabetes taking multiple glucose lowering therapies during Ramadan: the PROFAST Ramadan Study. J Diabetes Metab Disord 2018; 17:309-314. [PMID: 30918866 DOI: 10.1007/s40200-018-0374-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 11/09/2018] [Indexed: 11/26/2022]
Abstract
Objective To assess the incidence of hypoglycemia in people with type-2 diabetes mellitus (T2DM) on three or more anti-diabetic medications during Ramadan. Study design methods We have studied people with T2DM on three or more glucose-lowering drugs during Ramadan of H1438 (May-June 2017). The dose of each drug was adjusted according to a pre-specified protocol. The incidence of symptomatic or blood glucose confirmed hypoglycemia was recorded during the study. Results We enrolled 228 people with T2DM; 181 completed the study, and data on hypoglycaemia was available in 172 subjects. There were 115 males and 66 females, (mean age ± SD) 53.6 ± 9.7 years, diabetes duration 10 ± 6 yrs. The incidence of hypoglycaemia was 16.3% (28/172). Univariable logistic regression analysis showed that the risk of hypoglycaemia was increased in Arab subjects compared to Qatari; in those with longer duration of diabetes; and in those on four or more anti-diabetic medications compared to those on three anti-diabetic medications. Conclusion Despite the tailored advice, there is a high incidence of hypoglycemia in people with T2DM taking multiple glucose lowering therapies whilst fasting during Ramadan. Guidelines should address the increased complexity in anti-diabetic medications in patients who fast during Ramadan. Healthcare providers should individualize the modifications in anti-diabetic medications during Ramadan.
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Affiliation(s)
- Tarik Elhadd
- 1Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Modular Building, Doha, Qatar
| | - Zeinab Dabbous
- 1Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Modular Building, Doha, Qatar
| | - Mohammed Bashir
- 1Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Modular Building, Doha, Qatar
| | - Abdulnasir Elzouki
- 1Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Modular Building, Doha, Qatar
| | - Wissam Ghadban
- 1Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Modular Building, Doha, Qatar
| | - Khaled Baagar
- 1Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Modular Building, Doha, Qatar
| | - Silas Benjamin
- 1Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Modular Building, Doha, Qatar
| | | | - Abazar A M Saeed
- 1Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Modular Building, Doha, Qatar
| | - Khaled Dukhan
- 1Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Modular Building, Doha, Qatar
| | | | - Abdul-Badie Abou-Samra
- 1Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Modular Building, Doha, Qatar
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Bashir M, Elhadd T, Ali H, Baagar K, Abdel Hakam IA, Al-Mohanadi DHS, Naem E, Al Abdulla A, Mohammed K, Abou-Samra AB. A pilot study using flash continuous glucose monitoring in patients with type-2 diabetes on multiple anti-diabetic agents during Ramadan. Diabetes Metab Syndr 2018; 12:965-968. [PMID: 29895446 DOI: 10.1016/j.dsx.2018.06.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Accepted: 06/05/2018] [Indexed: 11/17/2022]
Abstract
BACKGROUND This study aims to examine the incidence of hypoglycaemia, based on activity, during Ramadan in patients with type 2 diabetes mellitus who were on were on three or more anti-diabetic medications. METHODS Type 2 diabetes patients who fasted during Ramadan and were on three or more anti-diabetic medications were studied for two weeks using flash glucose monitoring. The patients were asked to document all episodes of hypoglycaemia and were classified as active or sedentary according to their daytime activity. RESULTS The study included 16 patients of whom 10 were active and 6 were sedentary. There were 13 males and 3 females; mean age was 53.4 ± 6.4 years; mean diabetes duration was 15 ± 5.9 years, and mean HbA1C was 7.9 ± 1.3%. Over the two weeks; there were 7.9 episodes of hypoglycaemia recorded per patient; 50% of which were asymptomatic. There was no difference at baseline in age, BMI, HBA1C, diabetes duration, and anti-diabetic medications between the active and sedentary groups. The active group had better glucose control; median blood glucose was (7.1 (5.1-8.5) vs 10.6 (9.6-11.5) mmol p < 0.01), mean estimated HBA1C was (6.2 ± 1.2% vs 8.3 ± 1.0%; p = 0.047). The active group had more episodes of hypoglycaemia compared to the sedentary group (11.6 vs 1.8 hypo episode per patient/two weeks; p = 0.019); most of which were asymptomatic. CONCLUSION Patients with type 2 diabetes mellitus who are on three or more anti-diabetic medications should be warned about the increased risk of asymptomatic hypoglycaemia during Ramadan. Anti-diabetic medication adjustments during Ramadan should take into account the degree of activity. Flash glucose monitoring system can help patients to fast safely during Ramadan and detect asymptomatic hypoglycaemia.
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Affiliation(s)
- Mohammed Bashir
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Doha, Qatar.
| | - Tarik Elhadd
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Doha, Qatar
| | - Hamda Ali
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Doha, Qatar
| | - Khaled Baagar
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Doha, Qatar
| | - Ibrahim A Abdel Hakam
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Doha, Qatar
| | - Dabia H S Al-Mohanadi
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Doha, Qatar
| | - Emad Naem
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Doha, Qatar
| | - Amina Al Abdulla
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Doha, Qatar
| | - Kawsar Mohammed
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Doha, Qatar
| | - Abdul-Badie Abou-Samra
- Qatar Metabolic Institute, Department of Medicine, Hamad Medical Corporation, Doha, Qatar
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Abstract
The corticotropin-releasing factor (CRF) receptor type 1 (CRFR1) contains five potential N-glycosylation sites: N38, N45, N78, N90, and N98. Cells expressing CRFR1 were treated with tunicamycin to block receptor glycosylation. The nonglycosylated receptor did not bind the radioligand and had a decreased cAMP stimulation potency in response to CRF. To determine which of the polysaccharide chain(s) is/are involved in ligand interaction, the polysaccharide chains were deleted using site-directed mutagenesis of the glycosylation consensus, N-X-S/T. Two sets of mutations were performed for each glycosylation site: N to Q and S/T to A, respectively. The single mutants Q38, Q45, Q78, Q90, Q98, A40, A47, A80, A92, and A100 and the double mutants A40/A47 and A80/A100 were well expressed, bound CRF, sauvagine (SVG), and urotensin-I (UTS-I) with a normal affinity, and increased cAMP accumulation with a high efficiency. In contrast, the combined mutations A80/A92/A100, A40/A80/A92/A100, and A40/A47/A80/A92/A100 had low levels of expression, did not bind the radioligand, and had a decreased cAMP stimulation. These data indicate the requirement for three or more polysaccharide chains for normal CRFR1 function.
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Affiliation(s)
- I Q Assil
- Endocrine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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7
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Abstract
Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) binding to their common receptor stimulates second messenger accumulation, receptor phosphorylation, and internalization. LLC-PK(1) cells expressing a green fluorescent protein-tagged PTH/PTHrP receptor show time- and dose-dependent receptor internalization. The internalized receptors colocalize with clathrin-coated pits. Internalization is stimulated by PTH analogs that bind to and activate the PTH/PTHrP receptor. Cell lines expressing a mutant protein kinase A regulatory subunit that is resistant to cAMP and/or a mutant receptor (DSEL mutant) that does not activate phospholipase C internalize their receptors normally. In addition, internalization of the wild-type receptor and the DSEL mutant is stimulated by the PTH analog [Gly(1),Arg(19)]hPTH-(1-28), which does not stimulate phospholipase C. Forskolin, IBMX, and the active phorbol ester, phorbol-12-myristate-13-acetate, did not promote receptor internalization or increase PTH-induced internalization. These data indicate that ligand-induced internalization of the PTH/PTHrP receptor requires both ligand binding and receptor activation but does not involve stimulation of adenylate cyclase/protein kinase A or phospholipase C/protein kinase C.
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Affiliation(s)
- H A Tawfeek
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street, Boston, MA 02114, USA
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8
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Abstract
The methionine residues in Tyr-corticotropin-releasing factor (CRF) and Tyr-sauvagine radioligands are subject to oxidation, which renders them biologically inactive. Therefore [Tyr(0,) Gln(1,) Leu(17)]sauvagine (YQLS), in which the methionine was replaced with leucine was synthesized and labeled with (125)Iodine using chloramine-T. Mass spectroscopy revealed that chloramine-T-treatment did not oxidize YQLS. (125)I-YQLS bound with high affinity to cells expressing the murine CRF receptor 1 (CRFR1), CRF receptor 2 (CRFR2), and the mouse brain regions known to express both CRF receptors. (125)I-YQLS chemically cross-linked to CRFR1. In conclusion, (125)I-YQLS is oxidation-resistant, high affinity radioligand that can be chemically cross-linked to the CRF receptors.
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Affiliation(s)
- I Q Assil
- Endocrine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
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9
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Assil IQ, Qi LJ, Arai M, Shomali M, Abou-Samra AB. Juxtamembrane region of the amino terminus of the corticotropin releasing factor receptor type 1 is important for ligand interaction. Biochemistry 2001; 40:1187-95. [PMID: 11170443 DOI: 10.1021/bi001758y] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The functional properties of the amino terminus (NT) of the corticotropin releasing factor (CRF) receptor type 1 (R1) were studied by use of murine (m) CRFR1 and rat (r) parathyroid hormone (PTH)/parathyroid hormone-related peptide receptor (PTH1R) chimeras. The chimeric receptor CXP, in which the NT of mCRFR1 was annealed to the TMs of PTH1R, and the reciprocal hybrid, PXC, bound radiolabeled analogues of sauvagine and PTH(3--34), respectively. Neither hybrid bound radiolabeled CRF or PTH(1--34). CRF and PTH(1--34) weakly stimulated intracellular cAMP accumulation in COS-7 cells transfected with PXC and CXP, respectively. Thus the NT is required for ligand binding and the TMs are required for agonist-stimulated cAMP accumulation. Replacing individual intercysteine segments of PXC with their mCRFR1 counterparts did not rescue CRF or sauvagine radioligand binding or stimulation of cAMP accumulation. Replacement of residues 1--31 of mCRFR1 with their PTH1R counterparts resulted in a chimeric receptor, PEC, which had normal CRFR1 functional properties. In addition, a series of chimeras (F1PEC--F6PEC) were generated by replacement of the NT intercysteine residues of PEC with their PTH1R counterparts. Only F1PEC, F2PEC, and F3PEC showed detectable CRF and sauvagine radioligand binding. All of the PEC chimeras except F5PEC increased cAMP accumulation. These data indicate that the Cys(68)(-)Glu(109) domain is important for binding and that the Cys(87)(-)Cys(102) region plays an important role in CRFR1 activation.
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MESH Headings
- Amino Acid Sequence
- Amphibian Proteins
- Animals
- COS Cells
- Cyclic AMP/metabolism
- Ligands
- Membrane Proteins/chemistry
- Membrane Proteins/genetics
- Membrane Proteins/metabolism
- Membrane Proteins/physiology
- Mice
- Mice, Inbred BALB C
- Molecular Sequence Data
- Mutagenesis, Insertional
- Peptide Fragments/chemistry
- Peptide Fragments/genetics
- Peptide Fragments/metabolism
- Peptide Fragments/physiology
- Peptide Hormones
- Peptides/pharmacology
- Protein Structure, Tertiary/genetics
- Proto-Oncogene Proteins c-myc/genetics
- Rats
- Receptor, Parathyroid Hormone, Type 1
- Receptors, Corticotropin-Releasing Hormone/chemistry
- Receptors, Corticotropin-Releasing Hormone/genetics
- Receptors, Corticotropin-Releasing Hormone/metabolism
- Receptors, Corticotropin-Releasing Hormone/physiology
- Receptors, Parathyroid Hormone/chemistry
- Receptors, Parathyroid Hormone/genetics
- Receptors, Parathyroid Hormone/metabolism
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/metabolism
- Structure-Activity Relationship
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Affiliation(s)
- I Q Assil
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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10
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Arai M, Assil IQ, Abou-Samra AB. Characterization of three corticotropin-releasing factor receptors in catfish: a novel third receptor is predominantly expressed in pituitary and urophysis. Endocrinology 2001; 142:446-54. [PMID: 11145609 DOI: 10.1210/endo.142.1.7879] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The present study reports the isolation of three complementary DNA (cDNA) clones encoding distinct subtypes of CRF receptors from the diploid catfish (cf) species, Ameiurus nebulosus. The first clone encodes a 446-amino acid protein (cfCRF-R1) that is highly homologous to mouse (m) CRF-R1 (93% identical). The cfCRF-R1 messenger RNA is highly expressed in the brain, and its distribution pattern correlates well with that of mammalian CRF-R1, except for weak expression in the pituitary. When transiently expressed in COS-7 cells, cfCRF-R1 bound CRF, urotensin I, and sauvagine with similar affinities. The second full-length cDNA, which was cloned from catfish heart, encodes a 406-amino acid protein that showed homology to murine CRF-R2 (88%) and when expressed in COS-7 cells preferentially bound sauvagine. The highest level of cfCRF-R2 expression was observed in the heart. The third full-length cDNA clone, which encodes a 428-amino acid protein, is structurally closer to cfCRF-R1 (85%) than to cfCRF-R2 (80%). This novel CRF receptor (cfCRF-R3) bound CRF with a 5-fold higher affinity than urotensin I and sauvagine and was expressed in the pituitary gland, urophysis, and brain. The presence of three different CRF receptors, each with distinct tissue distribution and ligand binding properties, suggests a complex CRF/urotensin I system.
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Affiliation(s)
- M Arai
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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11
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Williams LJ, Abou-Samra AB. The transcription factors SP1 and MAZ regulate expression of the parathyroid hormone/parathyroid hormone-related peptide receptor gene. J Mol Endocrinol 2000; 25:309-19. [PMID: 11116210 DOI: 10.1677/jme.0.0250309] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor regulates extracellular calcium concentrations and is therefore important for mineral homeostasis. ROS 17/2.8 cells, a rat osteoblast-like osteosarcoma cell line, express the PTH/PTHrP receptor and provide a good model for examining the transcriptional regulation of its gene. The rat PTH/PTHrP receptor gene has two promoters, U1 and U3, which were shown to be important for its expression. Using extracts from ROS 17/2.8 cells, we have demonstrated two regions (termed FP1 and FP2) of nuclear protein/DNA interaction within promoter sequences previously shown to be important for the activity of the U3 promoter. Nuclear extracts from rat 2 fibroblasts, which do not express the PTH/PTHrP receptor, produced one site of protein/DNA interaction which was found at a position on the promoter identical to the position of FP1 produced by a ROS 17/2.8 nuclear extract. Mutation of these two sites of protein/DNA interaction resulted in reduced U3 promoter activity. Furthermore, we have demonstrated that the transcription factors SP1 and MAZ regulate U3 promoter expression and have shown their functional significance using mutational analysis. These data demonstrate that SP1 and MAZ bind to the PTH/PTHrP receptor promoter and that they are involved in cell-specific expression of its gene product.
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Affiliation(s)
- L J Williams
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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12
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Abstract
The receptor for parathyroid hormone (PTH) and PTH-related peptide (PTHrP) is a G-protein-coupled receptor with four potential sites for N-linked glycosylation. The contribution of the oligosaccharide moieties to cell surface expression, ligand binding, and signal transduction was investigated. Site-directed mutagenesis of the rat PTH/PTHrP receptor cDNA was performed at single or combination of the four potential glycosylation sites to determine the effect of the putative carbohydrate chains on the activities of the receptor. The results revealed that all four potential N-glycosylation sites in the PTH/PTHrP receptor are glycosylated. Receptors missing a single or multiple glycosylation consensus but with at least one intact glycosylation site expressed sufficiently and functioned normally. In contrast, the nonglycosylated receptor, in which all four glycosylation sites were mutated, is deficient in these functions. These data indicate important roles for N-linked glycosylation in PTH/PTHrP receptor functions.
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Affiliation(s)
- A T Zhou
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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13
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Karperien M, Farih-Sips H, Hendriks JA, Lanske B, Papapoulos SE, Abou-Samra AB, Löwik CW, Defize LH. Identification of a retinoic acid-inducible element in the murine PTH/PTHrP (parathyroid hormone/parathyroid hormone-related peptide) receptor gene. Mol Endocrinol 1999; 13:1183-96. [PMID: 10406468 DOI: 10.1210/mend.13.7.0313] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
We have shown previously that the PTH/PTHrP (PTH-related peptide) receptor mRNA becomes expressed very early in murine embryogenesis, i.e. during the formation of extraembryonic endoderm. Retinoic Acid (RA) is a potent inducer of extraembryonic endoderm formation and PTH/PTHrP-receptor expression in embryonal carcinoma (EC) and embryonal stem (ES) cells. Using the P19 EC cell line, we have characterized promoter elements of the murine PTH/PTHrP-receptor gene that are involved in this RA-induced expression. The data show that RA-induced expression of the PTH/ PTHrP-receptor gene is mediated by the downstream P2 promoter. Analysis of promoter reporter constructs in transiently transfected P19 cells treated with RA identified an enhancer region between nucleotides -2714 and -2702 upstream of the P2 transcription start site that is involved in the RA effect. This region matches a consensus hormone response element consisting of a direct repeat with an interspacing of 1 bp (R-DR1). The R-DR1 efficiently binds retinoic acid receptor-alpha (RARalpha)-retinoid X receptor-alpha (RXRalpha) and chicken ovalbumin upstream promoter (COUP)-transcription factor I (TFI)-RXRalpha heterodimers and RXRalpha and COUP-TFI homodimers in a bandshift assay using extracts of transiently transfected COS-7 cells. RA differentiation of P19 EC cells strongly increases protein binding to the R-DR1 in a band-shift assay. This is caused by increased expression of RXR (alpha, beta, or gamma) and by the induction of expression of RARbeta and COUP TFI/TFII, which bind to the R-DR1 as shown by supershifting antibodies. The presence of RXR (alpha, beta, or gamma) in the complexes binding to the R-DR1 suggests that RXR homodimers are involved in RA-induced expression of the PTH/PTHrP-receptor gene. The importance of the R-DR1 for RA-induced expression of PTH/ PTHrP-receptor was shown by an inactivating mutation of the R-DR1, which severely impairs RA-induced expression of PTH/PTHrP-receptor promoter reporter constructs. Since this mutation does not completely abolish RA-induced expression of PTH/PTHrP-receptor promoter reporter constructs, sequences other than the R-DR1 might also be involved in the RA effect. Finally, we show that the RA-responsive promoter region is also able to induce expression of a reporter gene in extraembryonic endoderm of 7.5 day-old transgenic mouse embryos.
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Affiliation(s)
- M Karperien
- Department of Endocrinology, Leiden University Medical Center, The Netherlands.
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14
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Giannoukos G, Williams LJ, Chilco PJ, Abou-Samra AB. Characterization of an element within the rat parathyroid hormone/parathyroid hormone-related peptide receptor gene promoter that enhances expression in osteoblastic osteosarcoma 17/2.8 cells. Biochem Biophys Res Commun 1999; 258:336-40. [PMID: 10329388 DOI: 10.1006/bbrc.1999.0641] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Parathyroid hormone (PTH) and PTH-related peptide (PTHrP) mediate their actions via a common G-protein-coupled receptor. High levels of PTH/PTHrP receptor expression have been detected in many tissues including bone and kidney. This study has demonstrated specific PTH/PTHrP receptor expression from the U3 promoter in the osteoblastic osteosarcoma ROS 17/2.8 cell line, which expresses the endogenous PTH/PTHrP receptor, compared to rat 2 fibroblasts which do not express the endogenous PTH/PTHrP receptor gene. Transient transfection studies revealed cell-specific expression of a construct containing 4391 bp of DNA upstream of exon U3 of the PTH/PTHrP receptor gene fused to a luciferase reporter gene. Deletion mapping of the 5' region of U3 revealed that a construct containing 206 bp upstream of U3 confers cell-specific expression. These data suggest that cell-specific expression in ROS 17/2.8 involves cell-specific elements within the PTH/PTHrP receptor promoter.
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Affiliation(s)
- G Giannoukos
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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15
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Abstract
The PTH/PTH-related peptide (PTHrP) receptor is predicted to span the plasma membrane seven times with an amino-terminal extracellular extension and a cytoplasmic carboxyl-terminal tail. To assess this prediction, we inserted 10- or 9-amino acid epitope tags from c-myc or hemophilus influenza hemaglutinin (HA), which are recognized by the monoclonal antibodies 9E10 and 12Ca5, respectively, in different extracellular and cytoplasmic regions of the receptor and examined the immunoreactivity of the epitopes in intact and permeabilized cells. The data show that the epitopes were well tolerated when introduced into the E2 region of the extracellular amino-terminus (E2-myc and E2-HA), in the first extracellular loop (EL1), in the second and third cytoplasmic loops (CL2c and CL3), or in the carboxyl-terminal tail (T-myc). Receptors tagged at these locations were well expressed, bound PTH with high affinity, and increased cAMP accumulation with a good efficiency. Receptors tagged in the second and third extracellular loops (EL2c and EL3c) or the first cytoplasmic loop (CL1c) bound the PTH radioligand with a low affinity, stimulated cAMP accumulation with a low efficiency, and had low expression levels. The receptors tagged on presumed extracellular regions, E2-myc, E2-HA, EL1, EL2c, and EL3c, were readily detected on the surface of intact cells with the monoclonal antibody against the epitope tag. In contrast, receptors tagged with the c-myc epitope in the cytoplasmic loops (CL1c, CL2c, and CL3) or in the carboxyl-terminal tail (T-myc) did not show any 9E10 binding in intact cells. These receptors, however, were well expressed on the cell surface, as detected by the binding of the monoclonal antibody, 12Ca5, to the HA tag that was introduced into the E2 region of these constructs. The c-myc epitopes, however, became accessible after permeabilization of the cell membrane. In conclusion, these data provide experimental evidence for the sidedness of the extracellular and cytoplasmic domains of the PTH/PTHrP receptor.
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Affiliation(s)
- L Y Xie
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston 02114, USA
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16
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Qi LJ, Leung AT, Xiong Y, Marx KA, Abou-Samra AB. Extracellular cysteines of the corticotropin-releasing factor receptor are critical for ligand interaction. Biochemistry 1997; 36:12442-8. [PMID: 9376348 DOI: 10.1021/bi970997r] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The corticotropin-releasing factor receptor (CRF-R) contains six conserved cysteines in its amino-terminal domain (C30, C44, C54, C68, C87, and C102) and one cysteine in its first and second extracellular loops (C188 and C258, respectively). Additionally, several other cysteines are located in the transmembrane domains (C128, C211, C233, and C364) and first intracellular loop (C150). Reduction of disulfide bonds with DTT decreased CRF binding to detergent-solubilized membranes, suggesting an important role for disulfide bonds in ligand recognition. Therefore, site-directed mutagenesis was used to introduce single and paired Cys (C) to Ser (S) or Ala (A) mutations. A silent nine amino acid tag from c myc was introduced in the amino terminus of the mouse CRF-R. With the exception of C258S and C188S/C258S mutations, all C to S or to A receptor mutants had good surface expression that was at least 52.5% of control. C30S, C54S, and C30S/C54S mutations had good CRF binding and CRF-stimulated cAMP accumulation. No CRF binding was detected for the C44S, C68S, C87S, C102S, C188S, C258S, C30S/C44S, C30S/C68S, C54S/C68S, C87S/C102S, and C188S/C258S mutants, while CRF-stimulated cAMP accumulation occurred with high EC50 values. In particular, receptors carrying double mutations, C44S/C102S and C68S/C87S, had an improved signaling property as compared to receptors carrying the respective single cysteine mutations. These data, together with the effects of DTT on CRF binding, indicate that disulfide bridges are important for receptor functions. Functional data from single and paired cysteine mutations suggest potential pairings between C44 and C102, C68 and C87, and C188 and C258 that are critical for ligand-receptor interactions.
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Affiliation(s)
- L J Qi
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA
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17
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Jongen JW, Willemstein-van Hove EC, van der Meer JM, Bos MP, Jüppner H, Segre GV, Abou-Samra AB, Feyen JH, Herrmann-Erlee MP. Down-regulation of the receptor for parathyroid hormone (PTH) and PTH-related peptide by PTH in primary fetal rat osteoblasts. J Bone Miner Res 1996; 11:1218-25. [PMID: 8864895 DOI: 10.1002/jbmr.5650110905] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We studied the effects of parathyroid hormone (PTH) on PTH parathyroid hormone related peptide (PTHrP) receptor mRNA level, PTHrP binding and PTH-stimulated cyclic adenosine monophosphate (cAMP) accumulation in osteoblasts, derived from fetal rat calvariae (ROB). Cells isolated during 10-70 minutes of collagenase treatment were seeded at a density of 25,000 cells/cm2 and cultured for 4 days. These cells show a fast increase in cAMP production after stimulation for 5 minutes with 20 nM bovine parathyroid hormone(1-34) (bPTH(1-34)). When ROB are incubated with bPTH(1-34) (0.04-40nM) for 24 h, a dose-dependent decrease of the PTH/PTHrP receptor mRNA level, PTHrP binding, and PTH-stimulated cAMP accumulation can be observed. Pretreatment of ROB with a high concentration of bPTH(1-34) (40 nM) leads within 15 minutes to a decrease in PTH-stimulated cAMP accumulation. However, it takes > or = 3 h before a significant decrease in PTH/PTHrP receptor mRNA level can be observed. Also a significant decrease in PTHrP binding is observed after only 4 h of incubation with bPTH(1-34). Compared with bPTH(1-34), pretreatment of ROB with bPTH(3-34) (40 and 100 nM) for 24 h causes smaller decreases in PTH-stimulated cAMP accumulation, PTHrP binding, and in the PTH/PTHrP receptor mRNA level. We investigated the possible involvement of the protein kinase A signaling pathway in the regulation of the PTH/PTHrP receptor mRNA expression. Both forskolin and (Bu)2cAMP decreased PTHrP binding and PTH/PTHrP mRNA levels. These observations suggest that chronic activation of the PKA signaling pathway may down-regulate PTH/PTHrP receptor expression and thus hormone responsiveness in "normal" osteoblasts. In short, we found that the decrease of the PTH-stimulated cAMP accumulation after long-term pretreatment with bPTH(1-34) is correlated with both PTH/PTHrP receptor mRNA level and PTHrP binding. These data also suggest that the initial desensitization (< 30 minutes) of PTH-stimulated cAMP responsiveness by pretreatment with a high concentration of bPTH(1-34) (40 nM) is not dependent on the number of available PTH/PTHrP receptors. The protein kinase A signaling pathway is involved in the regulation of the PTH/PTHrP receptor, but, regarding the effect of bPTH(3-34), other signaling systems are also involved.
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Affiliation(s)
- J W Jongen
- Laboratory of Cell Biology and Histology, University of Leiden, The Netherlands
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18
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Lanske B, Karaplis AC, Lee K, Luz A, Vortkamp A, Pirro A, Karperien M, Defize LH, Ho C, Mulligan RC, Abou-Samra AB, Jüppner H, Segre GV, Kronenberg HM. PTH/PTHrP receptor in early development and Indian hedgehog-regulated bone growth. Science 1996; 273:663-6. [PMID: 8662561 DOI: 10.1126/science.273.5275.663] [Citation(s) in RCA: 897] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The PTH/PTHrP receptor binds to two ligands with distinct functions: the calcium-regulating hormone, parathyroid hormone (PTH), and the paracrine factor, PTH-related protein (PTHrP). Each ligand, in turn, is likely to activate more than one receptor. The functions of the PTH/PTHrP receptor were investigated by deletion of the murine gene by homologous recombination. Most PTH/PTHrP receptor (-/-) mutant mice died in mid-gestation, a phenotype not observed in PTHrP (-/-) mice, perhaps because of the effects of maternal PTHrP. Mice that survived exhibited accelerated differentiation of chondrocytes in bone, and their bones, grown in explant culture, were resistant to the effects of PTHrP and Sonic hedgehog. These results suggest that the PTH/PTHrP receptor mediates the effects of Indian Hedgehog and PTHrP on chondrocyte differentiation.
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Affiliation(s)
- B Lanske
- Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA
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19
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Xie LY, Leung A, Segre GV, Yamamoto I, Abou-Samra AB. Downregulation of the PTH/PTHrP receptor by vitamin D3 in the osteoblast-like ROS 17/2.8 cells. Am J Physiol 1996; 270:E654-60. [PMID: 8928773 DOI: 10.1152/ajpendo.1996.270.4.e654] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on the expression of the parathyroid hormone (PTH)/PTH-related peptide (rP) receptor protein and mRNA in ROS 17/2.8 cells were studied. Treatment of ROS 17/2.8 cells with 1,25(OH)2D3 caused time- and dose-dependent suppression of PTH/PTHrP receptor number and immunoreactivity. The effects required more than 24 h incubation with 1,25(OH)2D3 and were maximal by 72 h. The cells did not recover their PTH/PTHrP receptors even after 4 days of treatment with control medium. Treatment with low concentrations of 1,25(OH)2D3 (0.1 M) dramatically decreased the PTH/PTHrP receptor mRNA levels, which were maximal after 24 h of incubation. The half-life of the PTH/PTHrP receptor transcript, 6-8 h, was similar in control and 1,25(OH)2D3-treated cells, suggesting that 1,25(OH)2D3 acts in controlling transcription of the PTH/PTHrP receptor gene but does not change the degradation rate of the PTH/PTHrP receptor transcripts. These data indicate that 1,25(OH)2D3 has a potent inhibitory effect on the expression of the PTH/PTHrP receptor protein and mRNA in ROS 17/2.8 cells.
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Affiliation(s)
- L Y Xie
- Endocrine Unit, Massachusetts General Hospital, Boston 02114, USA
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20
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Abstract
The hypothalamic-pituitary-adrenal axis is an essential physiological system in many species. CRF, the major neuropeptide regulating ACTH secretion, is highly conserved in its primary sequence. Evolutionary conservation of the CRF sequence suggests that the CRF receptor (CRF-R) complementary DNA and examined its properties. The avian CRF-R complementary DNA encodes a 420-amino acid protein that is 87-88% identical to those of human, rat, and mouse. Most sequence divergence occurs in the putative signal peptide and the extracellular amino-terminus of the receptor. Five additional amino acids are inserted in the amino-terminus of the cCRF-R. When expressed in COS-7 cells, the cCRF-R binds the CRF and urotensin I radioligands with high affinities. Urotensin I competes for binding to the chicken CRF-R, expressed in COS-7 cells, with an apparent affinity 20 times higher than that of CRF. Both urotensin I and sauvagine were more effective in stimulating cAMP accumulation in COS-7 cells transfected with the cCRF-R than CRF. The effects of CRF and urotensin I on inositol phosphate accumulation were also tested. Urotensin I was an effective as CRF in stimulating inositol phosphate accumulation in COS-7 cells transfected with the cCRF-R. These data suggest that the sequence of the CRF-R is highly conserved from avian to mammalian species and that, despite its high sequence homology to the type A mammalian CRF-R, the ligand binding properties of cCRF-R are similar to those of the type B CRF-R i.e. a higher affinity for urotensin I than for CRF.
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Affiliation(s)
- J Yu
- Endocrine Unit, Massachusetts General Hospital, Boston 02114, USA
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21
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Guo J, Iida-Klein A, Huang X, Abou-Samra AB, Segre GV, Bringhurst FR. Parathyroid hormone (PTH)/PTH-related peptide receptor density modulates activation of phospholipase C and phosphate transport by PTH in LLC-PK1 cells. Endocrinology 1995; 136:3884-91. [PMID: 7649096 DOI: 10.1210/endo.136.9.7649096] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We showed previously that a single species of cloned PTH/PTH-related peptide (PTHrP) receptors, when stably expressed in LLC-PK1 kidney cells, couples to multiple second messenger signals and biological responses. To address the linkages of individual messenger signals to specific biological responses in these cells, we examined the relations among PTH/PTHrP receptor expression, PTH-activated phospholipase C (PLC) and adenylyl cyclase, and PTH-regulated phosphate transport in LLC-PK1 cells that stably express cloned rat PTH/PTHrP receptors. Among 18 such subclones, PTH stimulation of intracellular cAMP accumulation was nearly equivalent, despite differences in receptor density ranging from 20,000-400,000 sites/cell. In contrast, activation of PLC by PTH was directly and continuously dependent upon receptor density. PTH-stimulated phosphate uptake also was strongly dependent upon receptor expression, correlated well with PLC activity, was mimicked by active phorbol esters but not by cAMP analogs or forskolin, and was strikingly inhibited by the protein kinase C inhibitor, staurosporine. The peptide analog [Arg2]human PTH-(1-34), which significantly stimulated cAMP accumulation but failed to activate PLC, also did not increase phosphate uptake. We conclude that in LLC-PK1 cells, PTH-modulated PLC activation, unlike adenylyl cyclase activation, is strongly dependent upon PTH/PTHrP receptor density. This feature is reflected in the analogous relation between receptor density and PTH regulation of phosphate uptake, which appears to be mediated via a PKC-dependent pathway in these transfected cells. The results suggest that regulation of PTH/PTHrP receptor expression on target cells may provide a mechanism for altering the character as well as the magnitude of the signaling response to the hormone.
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Affiliation(s)
- J Guo
- Endocrine Unit, Massachusetts General Hospital, Boston 02114, USA
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22
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Jongen JW, Willemstein-Van Hove EC, Van der Meer JM, Bos MP, Jüppner H, Segre GV, Abou-Samra AB, Feyen JH, Herrmann-Erlee MP. Down-regulation of the receptor for parathyroid hormone (PTH) and PTH-related peptide by transforming growth factor-beta in primary fetal rat osteoblasts. Endocrinology 1995; 136:3260-6. [PMID: 7628359 DOI: 10.1210/endo.136.8.7628359] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We studied the effects of transforming growth factor-beta 2 (TGF beta 2) on the level of PTH/PTH-related peptide-(PTHrP) receptor messenger RNA (mRNA), PTHrP binding, and PTH-stimulated cAMP accumulation in cultured osteoblasts derived from fetal rat calvariae (ROB). When ROB were pretreated with TGF beta 2 at concentrations ranging from 1-100 pM for 24 h, dose-dependent decreases in the level of PTH/PTHrP receptor mRNA, PTHrP binding, and PTH-stimulated cAMP accumulation were observed. For the PTH/PTHrP receptor mRNA level and PTH-stimulated cAMP accumulation, the half-maximal effective concentration was approximately 4 pM. For the inhibition of PTHrP binding, the half-maximal effective concentration was much higher. A 50% decrease in both PTH/PTHrP receptor mRNA level and PTH-stimulated cAMP accumulation was obtained when ROB were treated with 100 pM TGF beta 2 for 4 h. A comparable decrease in PTHrP binding was only observed after 24 h of incubation with 100 pM TGF beta 2. Actinomycin D induced a rapid decrease in the PTH/PTHrP receptor mRNA level (70% after 4 h), indicating a half-life for the receptor mRNA of 2-3 h. Under the same conditions, PTHrP binding and PTH-stimulated cAMP accumulation did not change. When ROB were treated with cycloheximide for the same period, only a small decrease in PTHrP binding (20%) was observed, suggesting that PTH/PTHrP receptors do not have a rapid turnover. Cycloheximide also reduced PTH-stimulated cAMP production; after coincubation of cycloheximide with TGF beta 2, this inhibition was smaller than that in ROB cultures treated with TGF beta 2 exclusively. From these observations we conclude that TGF beta 2 induces a decrease in steady state levels of PTH/PTHrP receptor mRNA that results in decreased PTHrP receptor binding. The PTH-stimulated cAMP accumulation is at least to some extent independent of the PTH/PTHrP receptor availability. Furthermore, there is a high turnover of PTH/PTHrP receptor mRNA, whereas turnover of the receptor protein is much slower. Finally, protein synthesis is required for TGF beta 2-induced desensitization of cAMP responsiveness to PTH.
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Affiliation(s)
- J W Jongen
- Laboratory of Cell Biology and Histology, University of Leiden, The Netherlands
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23
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Nabhan C, Xiong Y, Xie LY, Abou-Samra AB. The alternatively spliced type II corticotropin-releasing factor receptor, stably expressed in LLCPK-1 cells, is not well coupled to the G protein(s). Biochem Biophys Res Commun 1995; 212:1015-21. [PMID: 7626087 DOI: 10.1006/bbrc.1995.2071] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Two alternatively spliced corticotropin-releasing factor receptor (CRF-R) cDNAs, type I and type II, were recently isolated from a human cDNA library. The two cDNAs are identical except that the type II cDNA encodes an additional 29 amino acid inserted in the first putative cytoplasmic loop. Since the first cytoplasmic loop is highly conserved in all the members of the hCRF receptor family we have examined whether the presence of the 29 amino acid cassette in CRF-RII influences G protein coupling in LLCPK-1 cells stably expressing the type I and type II hCRF receptors. Whether measured in intact cells or in membrane preparations, LLCPK-1 cells stably expressing CRF-RII have a 4-5 fold lower binding affinity. Maximal CRF-stimulated cAMP accumulation in LLCPK-1 cells stably expressing CRF-RI was 10-15-fold higher than that in LLCPK-1 cells expressing CRF-RII. The EC50 for CRF-stimulated cAMP accumulation in hCRF-RI-expressing cells was in the range of 0.5 +/- 0.2 nM. In contrast, the EC50 for CRF-stimulated cAMP accumulation in hCRF-RII expressing cells was 7.7 +/- 0.2 nM. hCRF increased phosphoinositide turnover in LLCPK-1 cells stably expressing CRF-RI but not in those expressing CRF-RII; this effect required hCRF concentrations of 100 nM and higher. In membrane preparations, GTP-gamma-S inhibited hCRF binding to CRF-RI and shifted the binding Kd from 4.5 nM to 16.7 nM. Conversely, GTP-gamma-S did not influence hCRF binding to CRF-RII in broken cell membranes. Additionally, CRF-stimulated adenylate cyclase activity in cell membranes expressing CRF-RI was potentiated by GTP, whereas CRF-stimulated adenylate cyclase activity in cell membranes expressing CRF-RII was insensitive to GTP. These data indicate that CRF-RII is not well coupled to the G protein. Since the only difference between the CRF-RII and CRF-RI is the insert in the first putative cytoplasmic loop, these data indicate that the first cytoplasmic loop plays a crucial role in hCRF receptor coupling to the G protein.
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Affiliation(s)
- C Nabhan
- Endocrine Unit, Massachusetts General Hospital, Boston 02114, USA
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24
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Orloff JJ, Kats Y, Urena P, Schipani E, Vasavada RC, Philbrick WM, Behal A, Abou-Samra AB, Segre GV, Jüppner H. Further evidence for a novel receptor for amino-terminal parathyroid hormone-related protein on keratinocytes and squamous carcinoma cell lines. Endocrinology 1995; 136:3016-23. [PMID: 7789327 DOI: 10.1210/endo.136.7.7789327] [Citation(s) in RCA: 80] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
PTH and PTH-related peptides (PTHrPs) interact with a common PTH/PTHrP receptor (type I), which is expressed in many tissues, including bone and kidney. Amino-terminal PTH and PTHrPs also recognize receptors in several nonclassical PTH target tissues, and in some of these, the signaling mechanisms differ qualitatively from those of the classical type I receptor. In normal keratinocytes and squamous carcinoma cell lines, PTH and PTHrP stimulate a rise in intracellular calcium, but not cAMP, suggesting the existence of an alternate, type II PTH/PTHrP receptor. SqCC/Y1 squamous carcinoma cells stably expressing the type I receptor displayed sensitive intracellular cAMP responses to PTHrP and PTH, indicating that these cells express functional GS proteins and that the type I receptor is capable of signaling through adenylyl cyclase in this cell line. Therefore, the endogenous type II receptor in SqCC/Y1 cells differs from the cloned type I receptor. We next examined whether messenger RNA (mRNA) from keratinocytes and squamous cell lines could hybridize to a human type I PTH/PTHrP receptor complementary DNA [1.9 kilobases (kb)]. No type I receptor mRNA (2.3 kb) was detected in polyadenylated RNA from any of the squamous cell lines. However, squamous cell lines did express several mRNA transcripts that hybridized with the type I receptor probe, yet were smaller (1 and 1.5 kb) or larger (3.5-5 kb) than the cloned receptor mRNA. The predominant mRNA in two squamous carcinoma cell lines and normal keratinocytes was a 1-kb transcript. Northern analysis with five different region-specific probes that span the entire coding region of the human type I receptor was used to map homologous regions within each of the transcripts. Several of the transcripts identified in squamous lines are also present in polyadenylated RNA from SaOS-2 human bone cells, but a unique 1-kb transcript hybridizing to probe 2 (nucleotides 490-870) was observed only in squamous cells. The smaller 1- and 1.5-kb transcripts did not hybridize to probes corresponding to the extreme 5'- and 3'-coding regions of the type I receptor complementary DNA. Ribonuclease protection analysis employing riboprobes that correspond to the five region-specific DNA probes revealed strong RNA signals of the expected size in SaOS-2 cells, but no hybridization with squamous cell RNA. Several smaller, but minor, bands that were unique to squamous cells were observed with riboprobe 2 only, suggesting partial homology of this region with the type I receptor.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- J J Orloff
- Division of Endocrinology and Metabolism, West Haven Veterans Affairs Medical Center, Connecticut 06516, USA
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25
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Ureña P, Mannstadt M, Hruby M, Ferreira A, Schmitt F, Silve C, Ardaillou R, Lacour B, Abou-Samra AB, Segre GV. Parathyroidectomy does not prevent the renal PTH/PTHrP receptor down-regulation in uremic rats. Kidney Int 1995; 47:1797-805. [PMID: 7643551 DOI: 10.1038/ki.1995.248] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
In a recent study we demonstrated that the PTH/PTHrP receptor (PTH-R) mRNA was markedly down-regulated in the remnant kidney of uremic rats with severe secondary hyperparathyroidism. Among the factors potentially implicated in this down-regulation, to date only PTH has been demonstrated to modulate PTH-R expression. Here, we examined the effect of thyroparathyroidectomy (TPTX) on the renal expression of PTH-R in rats with normal renal function or with chronic renal failure (CRF) induced by 5/6 nephrectomy. Four groups of rats were studied: control, TPTX, CRF, and CRF + TPTX. Moderate-degree renal failure was documented by mean (+/- SD) creatinine clearances (microliter/min/100 g body wt) of 259 +/- 40 and 212 +/- 45 in CRF and CRF + TPTX rats, compared with 646 +/- 123 and 511 +/- 156 in control and TPTX rats, respectively. Plasma phosphorus, calcitriol, and ionized calcium were significantly lower in CRF and CRF + TPTX than in control animals. Plasma ionized calcium and calcitriol were also lower in TPTX than in control rats. Plasma PTH levels (pg/ml) were increased in CRF rats (41.8 +/- 29.4), and markedly decreased in TPTX (10.1 +/- 7.8) and CRF + TPTX (8.0 +/- 3.8) rats compared with control rats (21.7 +/- 7.5). Northern blot analysis showed that the level of the steady-state PTH-R mRNA in the kidney of CRF and CRF + TPTX rats was markedly decreased compared with that of control rats, the ratios of PTH-R mRNA/beta-actin mRNA being 0.28 +/- 0.04 and 0.27 +/- 0.03 versus 0.54 +/- 0.05, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- P Ureña
- INSERM Unité 90, Hôpital Necker, Paris, France
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26
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Xiong Y, Xie LY, Abou-Samra AB. Signaling properties of mouse and human corticotropin-releasing factor (CRF) receptors: decreased coupling efficiency of human type II CRF receptor. Endocrinology 1995; 136:1828-34. [PMID: 7720627 DOI: 10.1210/endo.136.5.7720627] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
CRF is the primary neuroregulator of the function of the hypothalamic-pituitary-adrenal axis. We have recently cloned a mouse CRF receptor (mCRF-R) complementary DNA (cDNA) from an AtT-20 cell cDNA library by polymerase chain reaction. To compare the functions of mCRF-R to those of the human type I and type II CRF receptors (hCRF-RI and hCRF-RII), cDNAs were cloned into the expression vector pcDNA1 and transfected into COS-7 cells. CRF binding and CRF-stimulated cAMP accumulation as well as phosphoinositide hydrolysis were measured. Scatchard analysis of the binding of 125I-labeled [Tyr0]r/hCRF ([125I]CRF) to COS-7 cells expressing mCRF-R and hCRF-RI cDNAs revealed the same apparent Kd (9 nM). In contrast, the apparent binding Kd for hCRF-RII was 20 nM CRF. Maximal stimulatory concentrations (1 microM) of rat/human CRF-(1-41) (r/hCRF) increased cAMP accumulation in COS-7 cells transfected with mCRF-R, hCRF-RI, and hCRF-RII cDNA plasmid (10 micrograms each) from basal values of 8-19 pmol/10(5) cells.15 min to 84 +/- 10, 87 +/- 16, and 45 +/- 16 pmol/10(5) cells.15 min, respectively. The EC50 values of r/hCRF-stimulated cAMP accumulation in COS-7 cells expressing mCRF-R and hCRF-RI cDNAs were similar at 0.4 +/- 0.2 and 0.7 +/- 0.2 nM, respectively. Conversely, the EC50 of r/hCRF-stimulated cAMP accumulation in hCRF-RII-transfected COS-7 cells was 47.5 +/- 18.9 nM. As the level of expression of hCRF-RII was lower than that of hCRF-RI, we compared r/hCRF-stimulated cAMP accumulation in COS-7 cells expressing low and high levels of hCRF-RI. The EC50 for r/hCRF-stimulated cAMP accumulation in COS-7 cells transfected with hCRF-RI did not change when receptor expression was varied by a factor of 1- to 8.4-fold. In contrast, the EC50 for r/hCRF-stimulated cAMP accumulation mediated by hCRF-RII was at least 100-fold higher than that mediated by the hCRF-RI in COS-7 cells, which suggests poor coupling between hCRF-RII and adenylate cyclase. Inositol phosphate (IP) levels were also determined in mCRF-R, hCRF-RI, and hCRF-RII cDNA-transfected COS-7 cells stimulated with increasing concentrations of r/hCRF. r/hCRF-stimulated IPs accumulation was dose dependent in COS-7 cells expressing mCRF-R and hCRF-RI using 100 and 1000 nM r/hCRF. Concentrations of 10 (or less) nM r/hCRF had no effect on IP generation. hCRF-RII did not mediate stimulation of IP even at 1000 nM r/hCRF.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- Y Xiong
- Endocrine Unit, Massachusetts General Hospital, Boston 02114, USA
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27
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Iida-Klein A, Guo J, Xie LY, Jüppner H, Potts JT, Kronenberg HM, Bringhurst FR, Abou-Samra AB, Segre GV. Truncation of the carboxyl-terminal region of the rat parathyroid hormone (PTH)/PTH-related peptide receptor enhances PTH stimulation of adenylyl cyclase but not phospholipase C. J Biol Chem 1995; 270:8458-65. [PMID: 7721741 DOI: 10.1074/jbc.270.15.8458] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The functional role of the rat parathyroid hormone(PTH)/PTH-related peptide (PTHrP) receptor's carboxyl-terminal region was characterized by comparing the binding and signaling properties of receptors that have 78 and 111 amino acid deletions (R513 and R480, respectively), with those of the 591-amino acid wild-type (WT) receptor. R480 and R513 have 4- and 1.5-fold lower apparent Kd values for rat PTH-(1-34) (rPTH), compared with the WT receptor (WT, 1.81 +/- 0.19 nM; R513, 1.24 +/- 0.12 nM; R480, 0.48 +/- 0.05 nM, mean +/- S.E.). PTH (100 nM)-stimulated cAMP accumulation and polyphosphoinositide hydrolysis both correlated positively with receptor expression. However, whereas PTH-stimulated polyphosphoinositide hydrolysis was indistinguishable among WT and either truncated mutant at comparable levels of expressed receptors, maximal PTH-stimulated cAMP accumulation was 4-6- and 2-3-fold higher in cells expressing R480 and R513, respectively. Furthermore, pretreatment of COS-7 cells with 100 ng/ml of pertussis toxin (PTX) enhanced PTH-stimulated cAMP accumulation in cells expressing the WT receptor, but failed to do so in cells expressing either R480 or R513. Thus, sequences in the PTH/PTHrP receptor's carboxyl-terminal tail lower the affinity of the WT receptor for agonist; directly interact with, or indirectly facilitate the interaction of the receptor with a PTX-sensitive G protein that inhibits adenylyl cyclase; and decrease the efficacy with which the receptor interacts with Gs.
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Affiliation(s)
- A Iida-Klein
- Endocrine Unit, Massachusetts General Hospital, Boston 02114, USA
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28
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Abou-Samra AB, Goldsmith PK, Xie LY, Jüppner H, Spiegel AM, Segre GV. Down-regulation of parathyroid (PTH)/PTH-related peptide receptor immunoreactivity and PTH binding in opossum kidney cells by PTH and dexamethasone. Endocrinology 1994; 135:2588-94. [PMID: 7988447 DOI: 10.1210/endo.135.6.7988447] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Recent data have shown that PTH down-regulation of its receptor on opossum kidney (OK) cells is not associated with any change in the steady state level of the PTH/PTH-related peptide (PTHrP) receptor messenger RNA. For analysis of down-regulation of the PTH/PTHrP receptor in OK cells, the present work uses a specific receptor anti-serum, SR-2, that is useful for detection and quantification of PTH/PTHrP receptor immunoreactivity on intact cells bearing the opossum PTH/PTHrP receptor. SR-2 specifically binds to COS-7 cells transiently expressing the opossum PTH/PTHrP receptor complementary DNA (OK-O), to LLCPK1 cells stably expressing the recombinant opossum PTH/PTHrP receptor (AOK cells), and to OK cells expressing endogenous PTH/PTHrP receptors, but not to mock-transfected COS-7 cells or untransfected LLCPK1 cells. SR-2 binding was also linearly correlated with PTH binding in COS-7 cells transfected with different amounts of OK-O plasmid DNA. Treatment with PTH (100 nM) for 4 and 6 h did not significantly down-regulate the PTH/PTHrP receptor immunoreactivity, although PTH binding was decreased to 51% and 49% of control, respectively, and PTH-stimulated cAMP accumulation was decreased to 27% and 28% of control, respectively. Treatment with PTH (100 nM) for 24 and 48 h significantly decreased PTH binding to 51% and 60% of control and decreased PTH/PTHrP receptor immunoreactivity to 68% and 58% of control, respectively. Incubation of OK cells with 0.1 nM to 1 microM PTH for 4 h did not down-regulate the PTH/PTHrP receptor immunoreactivity, although PTH binding was decreased dramatically. Scatchard blot analysis revealed that the binding affinity was decreased by 7-fold in OK cells treated with PTH for 4 h without change in receptor number. Conversely, treatment of OK cells with PTH for 24 h resulted in a parallel decrease in both receptor number and receptor immunoreactivity without any change in receptor binding affinity. Treatment of OK cells with dexamethasone (0.1 nM to 1 microM) had no effect on PTH binding or PTH/PTHrP receptor immunoreactivity. Incubation of OK cells with both dexamethasone (1 microM) and PTH (0.1 nM to 1 microM), however, caused a significantly greater down-regulation of both PTH binding and PTH/PTHrP receptor immunoreactivity than in cells treated with PTH alone. These data indicate that during the first 4 h of exposure of OK cells to PTH, PTH/PTHrP receptors remain on the cell surface but have lowered affinity to bind the ligand and that dexamethasone potentiates the effect of PTH on PTH/PTHrP receptor down-regulation in OK cells.
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Affiliation(s)
- A B Abou-Samra
- Endocrine Unit, Massachusetts General Hospital, Boston 02114
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29
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Gelbert L, Schipani E, Jüppner H, Abou-Samra AB, Segre GV, Naylor S, Drabkin H, Heath H. Chromosomal localization of the parathyroid hormone/parathyroid hormone-related protein receptor gene to human chromosome 3p21.1-p24.2. J Clin Endocrinol Metab 1994; 79:1046-8. [PMID: 7962272 DOI: 10.1210/jcem.79.4.7962272] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The human PTH/PTH-related peptide (PTH/PTHrP) receptor could be involved in hereditary disorders of PTH or PTHrP action. Knowledge of the gene's chromosomal location would allow studies linking it to specific disease traits. Therefore, we mapped the human PTH/PTHrP receptor gene by polymerase chain reaction of human/rodent somatic cell hybrid panels using oligonucleotide primers designed to amplify a portion of the gene from genomic DNA. The PTH/PTHrP gene was unambiguously assigned to the short arm of human chromosome 3, in the region designated 3p21.1-p24.2. Analysis of a second chromosome 3-specific mapping panel suggests that the gene is located near the 3p21.2-p21.3 boundary. The availability of highly polymorphic markers located in this region will permit exploration of the PTH/PTHrP receptor locus in genetic linkage searches for the causes of bone, calcium, and other potential disorders.
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Affiliation(s)
- L Gelbert
- Department of Human Genetics, University of Utah Health Sciences Center, Salt Lake City 84132
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30
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Lee C, Gardella TJ, Abou-Samra AB, Nussbaum SR, Segre GV, Potts JT, Kronenberg HM, Jüppner H. Role of the extracellular regions of the parathyroid hormone (PTH)/PTH-related peptide receptor in hormone binding. Endocrinology 1994; 135:1488-95. [PMID: 7523099 DOI: 10.1210/endo.135.4.7523099] [Citation(s) in RCA: 88] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The PTH/PTH-related peptide receptor is a member of a newly discovered family of G-protein-coupled receptors. Strikingly conserved features among these receptors include the positioning of eight extracellular cysteines and several other residues that are located predominantly within the membrane-embedded region. Deletion mutants or receptors with point mutations of the highly conserved cysteine residues were transiently expressed in COS-7 cells to evaluate PTH binding and PTH-stimulated cAMP production. Deletion of residues 61-105, which are encoded by exon E2 in the PTH/PTH-related peptide receptor gene, did not affect receptor function. An epitope derived from Haemophilus influenza hemagglutinin was, therefore, introduced into this portion of most receptors to allow the independent assessment of cell surface expression. PTH binding capacity was not reduced by the deletion of residues 258-278 in the first extracellular loop. Receptors with deletion of either residues 31-47 in the amino-terminal extension or residues 431-440 in the third extracellular loop failed to bind PTH, although expression of the receptor on the cell surface was only marginally reduced. Most other receptor mutants, including those in which each of the six cysteines in the amino-terminus was replaced by serines, failed to be processed and/or expressed appropriately, whereas the substitution of cysteine-281 or -351 had a less severe effect. The combined replacement of both cysteines concomitantly increased PTH binding and cell surface expression, suggesting the formation of a disulfide bond between these two residues. Our data indicate that residues near the amino-terminus and within the third extracellular loop are necessary for ligand binding, whereas more than 25% of the receptor's extracellular region appears not to be involved.
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Affiliation(s)
- C Lee
- Department of Medicine, Massachusetts General Hospital, Boston 02114
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31
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Gardella TJ, Jüppner H, Wilson AK, Keutmann HT, Abou-Samra AB, Segre GV, Bringhurst FR, Potts JT, Nussbaum SR, Kronenberg HM. Determinants of [Arg2]PTH-(1-34) binding and signaling in the transmembrane region of the parathyroid hormone receptor. Endocrinology 1994; 135:1186-94. [PMID: 8070362 DOI: 10.1210/endo.135.3.8070362] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Previously, we reported that [Arg2]PTH-(1-34) bound to the rat osteosarcoma cell line, ROS 17/2.8, with 2-fold higher apparent affinity than it did to the opossum kidney cell line, OK, yet the analog was only a weak partial agonist for cAMP stimulation with ROS 17/2.8 cells, whereas it was a full cAMP agonist with OK cells. These results suggested that the rat and opossum PTH receptors differ in a region recognized by the hormone's amino-terminus. In this report we show that the cloned PTH receptors derived from ROS 17/2.8 and OK cells, expressed in COS-7 cells, also displayed altered responses to [Arg2]PTH-(1-34). Thus, [Arg2]PTH-(1-34) bound to the cloned rat PTH receptor with 7-fold higher affinity than it did to the cloned opossum PTH receptor, and in cAMP stimulation assays, it was a much weaker agonist with the rat receptor than it was with the opossum receptor. Studies with rat/opossum PTH receptor chimeras suggested that the membrane-spanning region of the receptor contributed to the different binding and signaling responses to [Arg2]PTH-(1-34). Point mutation analysis identified three sites in or near the extracellular ends of transmembrane domains V and VI, which specifically affected [Arg2]PTH-(1-34) binding and signaling.
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Affiliation(s)
- T J Gardella
- Endocrine Unit, Massachusetts General Hospital, Boston
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32
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Okano K, Wu S, Huang X, Pirola CJ, Juppner H, Abou-Samra AB, Segre GV, Iwasaki K, Fagin JA, Clemens TL. Parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptor and its messenger ribonucleic acid in rat aortic vascular smooth muscle cells and UMR osteoblast-like cells: cell-specific regulation by angiotensin-II and PTHrP. Endocrinology 1994; 135:1093-9. [PMID: 8070351 DOI: 10.1210/endo.135.3.8070351] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
PTH-related protein (PTHrP) is produced in vascular smooth muscle, where it is believed to act as a local vasorelaxant by activating either the classical PTH or a unique PTHrP receptor. We used a newly cloned complementary DNA encoding the rat PTH/PTHrP receptor to study the expression of its messenger RNA (mRNA) in primary aortic vascular smooth muscle cells (VSMC) and in UMR-106 osteoblast-like cells under basal conditions and in response to treatment with agonists. Both cell types expressed a 2.4-kilobase PTH/PTHrP receptor mRNA transcript and exhibited hormone-induced desensitization of PTHrP-(1-34)NH2-stimulated cAMP. In VSMC, angiotensin-II, which induces PTHrP expression, also rapidly (30 min) desensitized the cAMP response and down-regulated (75-90%) receptor mRNA within 1 h. Treatment of cells with phorbol 12-myristate 13-acetate (0.1 microM) mimicked these effects, whereas neither PTHrP-(1-34)NH2, forskolin, nor (Bu)2cAMP altered receptor mRNA expression. By contrast, in UMR-106 cells, PTHrP-(1-34)NH2 induced time- and dose-dependent decreases in receptor mRNA that were preceded by pronounced desensitization (cAMP and ligand binding) of cell surface receptors. These effects were mimicked by (Bu)2cAMP and forskolin, but not by phorbol 12-myristate 13-acetate, suggesting that both receptor mRNA down-regulation and receptor desensitization in UMR cells were mediated through a protein kinase-A pathway. We suggest that VSMC and UMR cells express a common receptor, which is subject to cell-specific regulation. Such diversity in the PTH/PTHrP receptor regulatory mechanisms provides a means for restricting the length and duration of the cellular response to hormone in a cell/tissue-specific manner.
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Affiliation(s)
- K Okano
- Department of Medicine, Cedars-Sinai Research Institute, Cedars-Sinai Medical Center, Los Angeles, California 90048
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33
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Bergwitz C, Abou-Samra AB, Hesch RD, Jüppner H. Rapid desensitization of parathyroid hormone dependent adenylate cyclase in perifused human osteosarcoma cells (SaOS-2). Biochim Biophys Acta 1994; 1222:447-56. [PMID: 8038214 DOI: 10.1016/0167-4889(94)90053-1] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The pulsatile but not the continuous application of parathyroid hormone (PTH) increase bone mass in vivo. To study the effects of intermittent hormonal administration on bone-derived cells in vitro, we established a perifusion system using the human osteosarcoma cell line SaOS-2. Cells were grown in suspension culture attached to collagen beads and were then loaded into a 3 ml syringe for perifusion experiments. The application of PTH(1-34) resulted in a dose-dependent increase of cAMP release by SaOS-2 cells into the effluent medium. Cyclic AMP accumulation was rapidly desensitized by approx. 80% after 30 min of continuous exposure to PTH(1-34) (10(-7) M), while cells remained responsive to forskolin. The recovery of PTH responsiveness required at least 2 h of hormone-free perifusion. Desensitization in the experimental setting was dose-dependent (EC50 = 1 x 10(-10) M PTH(1-34)). Neither 8Br-cAMP (2 x 10(-4) M) nor PMA(1 x 10(-7) M) had an effect on the PTH(1-34)-induced desensitization of the adenylate cyclase. Radioreceptor assays showed that [125I]-[Tyr36]hPTHrP(1-36)amide binding to SaOS-2 cells was decreased by 60-70% by PTH(1-34) (1 x 10(-6) M), bPTH(1-84) (1.8 x 10(-6) M) and bPTH(3-34) (2 x 10(-6) M), whereas 8Br-cAMP (2 x 10(-4) M) had no effect on radioligand binding. PMA (1 x 10(-7) M) appeared to slightly increase [125I]PTHrP binding. This observation is consistent with a small (3-fold) increase in PTH-induced cAMP release as a result of PMA pre-treatment. Receptor internalization was dose-dependent EC50 = 3 x 10(-7) M PTH(1-34)). The maximal effect occurred after 10-30 min and was largely reversible within 2 h. Monensin (3 x 10(-5) M) inhibited the recovery from receptor internalization. We conclude that a perifusion system using SaOS-2 cells is a suitable model to study the effect of discontinuous application of PTH on cAMP release. A rapid, homologous desensitization of PTH(1-34) stimulated cAMP accumulation has been observed that does not appear to involve protein kinase A or C.
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Affiliation(s)
- C Bergwitz
- Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston 02114
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34
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Karperien M, van Dijk TB, Hoeijmakers T, Cremers F, Abou-Samra AB, Boonstra J, de Laat SW, Defize LH. Expression pattern of parathyroid hormone/parathyroid hormone related peptide receptor mRNA in mouse postimplantation embryos indicates involvement in multiple developmental processes. Mech Dev 1994; 47:29-42. [PMID: 7524627 DOI: 10.1016/0925-4773(94)90093-0] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
In this paper we describe the cloning of the mouse Parathyroid Hormone/Parathyroid Hormone related Peptide Receptor (PTH/PTHrPR) cDNA and expression of its mRNA during mouse postimplantation development from day 5.5 until day 15.5 post coitum (p.c.). In support of a model from previous studies, in which parietal endoderm differentiation is regulated by the interaction of the PTH/PTHrPR and Parathyroid Hormone related Peptide (PTHrP), high levels of PTH/PTHrPR mRNA levels were detected in developing parietal endoderm from day 5.5 p.c. and onwards. In the embryo proper, PTH/PTHrPR mRNA expression was mainly detected at sites of epithelium/mesenchyme interactions, starting at day 9.5 p.c. in the epithelium of the intestine and later in the mesenchyme of the lung, the epithelium of meso- and metanephric tubuli, the dermis and at all sites where bone formation takes place. The complexity of the PTH/PTHrPR expression pattern suggests tight developmental regulation and indicates multiple roles in embryogenesis for the receptor and its ligands, not only in extraembryonic tissue but also in the formation of various organs.
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MESH Headings
- Animals
- Blotting, Northern
- Cloning, Molecular
- DNA/analysis
- DNA/genetics
- Embryo, Mammalian/chemistry
- Embryonic Development/physiology
- Embryonic and Fetal Development/genetics
- Embryonic and Fetal Development/physiology
- Endoderm/chemistry
- Female
- In Situ Hybridization
- Intestines/chemistry
- Intestines/embryology
- Lung/chemistry
- Lung/embryology
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Inbred CBA
- Pregnancy
- RNA/analysis
- RNA/genetics
- RNA, Messenger/analysis
- RNA, Messenger/genetics
- Receptor, Parathyroid Hormone, Type 1
- Receptors, Parathyroid Hormone/genetics
- Receptors, Parathyroid Hormone/physiology
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Affiliation(s)
- M Karperien
- Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Utrecht
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35
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O'Connell NA, Kumar A, Chatzipanteli K, Mohan A, Agarwal RK, Head C, Bornstein SR, Abou-Samra AB, Gwosdow AR. Interleukin-1 regulates corticosterone secretion from the rat adrenal gland through a catecholamine-dependent and prostaglandin E2-independent mechanism. Endocrinology 1994; 135:460-7. [PMID: 8013385 DOI: 10.1210/endo.135.1.8013385] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Studies from this and other laboratories have shown that interleukin-1 alpha (IL-1 alpha) stimulates corticosterone and prostaglandin (PG) release from primary cultures of rat adrenal cells. A previous report from our laboratory (1) indicated involvement of the alpha-adrenergic system in IL-1 alpha-stimulated corticosterone secretion from primary cultures of rat adrenal cells. The present experiments were conducted to determine the role of catecholamines and eicosanoids in IL-1-stimulated corticosterone release from primary rat adrenal cells. Primary adrenal cells were incubated for 24 h at 37 C with IL-1 alpha (10 nM), medium, or the appropriate agonist. After incubation, the supernatant was removed and assayed for epinephrine, prostaglandin E2 (PGE2), and corticosterone concentrations. At this time, untreated adrenal cells were fixed for immunohistochemical staining with a specific antirat tyrosine hydroxylase antibody. The results indicate that the primary adrenal cells contained 3.1 +/- 0.45% tyrosine hydroxylase-positive cells. On the ultrastructural level, the chromaffin cells were found to be in direct cellular contact with cortical cells. IL-1 alpha significantly increased (P < 0.05) epinephrine, PGE2, and corticosterone levels above those in medium-treated controls from primary adrenal cells. In the presence of the alpha-adrenergic antagonist phentolamine (10 microM), IL-1 alpha-stimulated (P < 0.05) corticosterone release was inhibited, whereas IL-1 alpha-induced PGE2 release was not affected. Conversely, the presence of the cyclooxygenase inhibitor indomethacin (10 microM) significantly inhibited IL-1 alpha-induced PGE2 secretion without altering the effect of IL-1 alpha on corticosterone release. Inhibitors of the 5-lipoxygenase system (10 microM CGS 8518) and the lipoxygenase and cytochrome P450 monooxygenase systems (10 microM nordihydroguaiaretic acid) did not effect IL-1 alpha-induced corticosterone or PGE2 release. These observations indicate that IL-1 alpha stimulates corticosterone release through an alpha-adrenergic mechanism that is independent of PGE2 release from primary rat adrenal cells.
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36
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McCauley LK, Beecher CA, Melton ME, Werkmeister JR, Jüppner H, Abou-Samra AB, Segre GV, Rosol TJ. Transforming growth factor-beta1 regulates steady-state PTH/PTHrP receptor mRNA levels and PTHrP binding in ROS 17/2.8 osteosarcoma cells. Mol Cell Endocrinol 1994; 101:331-6. [PMID: 9397968 DOI: 10.1016/0303-7207(94)90250-x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The effect of transforming growth factor beta1 (TGF-beta1) on the expression of mRNA for the parathyroid hormone receptor and binding of iodinated parathyroid hormone-related protein in ROS 17/2.8 osteosarcoma cells was evaluated. TGF-beta1 stimulated a 2-7-fold increase in steady state mRNA levels for the parathyroid hormone receptor at a maximal dose of 5 ng/ml, with increased levels of expression at 6 h of TGF-beta1-incubation, and peak levels at 8-24 h. Receptor binding studies revealed a significant increase in PTHrP-specific binding with TGF-beta1 doses as low as 0.5 ng/ml and a 55% increase in numbers of receptors with no alteration in binding affinity with 5.0 ng/ml TGF-beta1. Time course studies indicated that receptor binding was increased at 24 h with peak levels reached at 48 h of treatment. PTH-stimulated cAMP levels were significantly increased in ROS 17/2.8 cells treated with TGF-beta1 (0.5 ng/ml) for 48 h. These data indicate that TGF-beta1 upregulates steady-state mRNA, ligand binding and PTH/PTHrP receptor signaling in rat osteosarcoma cells. The effects of TGF-beta1 on bone may be attributed in part to regulation of the PTH/PTHrP receptor at the molecular level.
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Affiliation(s)
- L K McCauley
- Department of Periodontology / Prevention and Geriatrics, The University of Michigan, Ann Arbor 48109-1078, USA
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37
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Fukayama S, Schipani E, Jüppner H, Lanske B, Kronenberg HM, Abou-Samra AB, Bringhurst FR. Role of protein kinase-A in homologous down-regulation of parathyroid hormone (PTH)/PTH-related peptide receptor messenger ribonucleic acid in human osteoblast-like SaOS-2 cells. Endocrinology 1994; 134:1851-8. [PMID: 8137752 DOI: 10.1210/endo.134.4.8137752] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Homologous down-regulation of PTH/PTH-related peptide (PTHrP) receptor expression occurs in several PTH-responsive osteoblastic cell lines, but the mechanisms responsible are not well understood. We have used wild-type SaOS-2 human osteoblastic cells, in which homologous PTH/PTHrP receptor down-regulation occurs within 4 h, and a mutant cAMP-resistant subclone (Ca4A strain), to investigate the mechanisms by which PTH/PTHrP receptor mRNA is regulated. SaOS-2 cells expressed a single 2.2- to 2.5-kilobase transcript of PTH/PTHrP receptor mRNA, as assessed by Northern blot analysis of total RNA with a cDNA probe encoding the human PTH/PTHrP receptor. Homologous down-regulation of this PTH/PTHrP receptor mRNA first became significant when SaOS-2 cells had been treated with human (h) PTH-(1-34) (10(-7) M) for 8-12 h. By 24 h, steady state levels of PTH/PTHrP receptor mRNA were reduced by about 50%. This effect was mimicked by both (Bu)2cAMP (DBcAMP; 0.5 mM) and forskolin (Fsk; 10(-5) M). In contrast, down-regulation of PTH/PTHrP receptor mRNA by hPTH-(1-34), DBcAMP or Fsk was almost completely blocked in cAMP-resistant Ca4A cells. Short term (4-6 h) treatment with hPTH-(1-34), DBcAMP, or Fsk did not reduce steady state levels of PTH/PTHrP receptor mRNA in either SaOS-2 or Ca4A cells, although down-regulation was induced by 4-6 h of treatment with active phorbol esters such as 12-O-tetradecanoyl phorbol-13-acetate (200 nM) or phorbol-12,13-didecanoate (200 nM). Neither thapsigargin (1 microM) nor ionomycin (200 nM), both of which stimulate calcium transients in these cells, altered PTH/PTHrP receptor mRNA expression. Treatment with hPTH-(39-84) and hPTH-(53-84), which do not activate either cAMP-dependent protein kinase or protein kinase-C, but do stimulate 45Ca2+ uptake in these cells, did not alter PTH/PTHrP receptor mRNA expression. In the presence of actinomycin-D (1 microgram/ml), down-regulation of PTH/PTHrP receptor mRNA by hPTH-(1-34) was not observed. Cycloheximide (10 micrograms/ml) did not block down-regulation of PTH/PTHrP receptor mRNA induced by hPTH-(1-34). We conclude that homologous down-regulation of PTH/PTHrP receptor mRNA in SaOS-2 cells occurs later than the decline in functional surface receptors via a mechanism that does not involve enhanced mRNA degradation or new protein synthesis, but is dependent upon cAMP/cAMP-dependent protein kinase.
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Affiliation(s)
- S Fukayama
- Endocrine Unit, Massachusetts General Hospital, Boston 02114
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38
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Ureña P, Kubrusly M, Mannstadt M, Hruby M, Trinh MM, Silve C, Lacour B, Abou-Samra AB, Segre GV, Drüeke T. The renal PTH/PTHrP receptor is down-regulated in rats with chronic renal failure. Kidney Int 1994; 45:605-11. [PMID: 8164450 DOI: 10.1038/ki.1994.79] [Citation(s) in RCA: 115] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Hypocalcemia, hyperphosphatemia, and resistance to the action of PTH are well characterized features in the setting of advanced chronic renal failure (CRF). Although the underlying mechanisms are ill-understood, clinical and experimental evidence points to both PTH receptor down-regulation and post-receptor abnormalities in their pathogenesis. In the present study we have examined the effect of advanced CRF in rats on the renal expression of PTH/PTHrP receptor (PTH-R). CRF was created by a standard two-step operation (5/6 nephrectomy). Four weeks thereafter, 19 uremic rats were compared with 23 sham-operated rats. Uremic rats had higher mean (+/- SD) plasma creatinine levels than control rats, 164 +/- 107 microM versus 43 +/- 5 microM, respectively. They also had higher plasma phosphorus and iPTH levels, 4.70 +/- 1.71 mM versus 2.59 +/- 0.37 mM and 561 +/- 336 versus 27 +/- 18 pg/ml, respectively. Mean plasma total calcium and blood ionized calcium were significantly lower in uremic than in control rats, 2.13 +/- 0.06 mM versus 2.61 +/- 0.10 mM and 1.07 +/- 0.11 versus 1.31 +/- 0.06 mM, respectively. Mean plasma calcitriol concentration was also significantly lower in uremic than in control rats, 39.8 +/- 14.6 and 80.4 +/- 15.2 pg/ml, respectively. Nine out of the 19 rats were examined for renal PTH-R gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- P Ureña
- INSERM Unité 90, Hôpital Necker, Paris, France
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39
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Jüppner H, Schipani E, Bringhurst FR, McClure I, Keutmann HT, Potts JT, Kronenberg HM, Abou-Samra AB, Segre GV, Gardella TJ. The extracellular amino-terminal region of the parathyroid hormone (PTH)/PTH-related peptide receptor determines the binding affinity for carboxyl-terminal fragments of PTH-(1-34). Endocrinology 1994; 134:879-84. [PMID: 8299582 DOI: 10.1210/endo.134.2.8299582] [Citation(s) in RCA: 109] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The recombinant human PTH/PTH-related peptide (PTHrP) receptor, when transiently expressed in COS-7 cells, binds [Nle8,18,Tyr34] bovine PTH-(7-34)amide [PTH-(7-34)], human PTH-(10-34)amide [PTH-(10-34)], and bovine PTH-(15-34)amide [PTH-(15-34)] with at least 50-fold higher affinity than does the rat receptor homolog. In contrast, PTH-(1-34) binding affinities are similar for both receptor homologs. To map those areas of the PTH/PTHrP receptors that determine the binding specificity for carboxyl-terminal fragments of PTH-(1-34), we constructed chimeric rat/human PTH/PTHrP receptors. These bound PTH-(1-34) with normal affinity and, therefore, must have an overall conformation that resembles that of native receptors. Chimeras with the amino-terminal extracellular domain of the human PTH/PTHrP receptor have a considerably higher binding affinity for PTH-(7-34), PTH-(10-34), and PTH-(15-34) than do the reciprocal receptor constructs in which the amino-terminal region is from the rat PTH/PTHrP receptor. The opossum PTH/PTHrP receptor homolog also binds PTH-(7-34) with higher affinity than the rat receptor, and studies of rat/opossum chimeras confirm the importance of the amino-terminal extracellular domain in determining the PTH-(7-34) binding specificity. Mutant rat and human PTH/PTHrP receptors in which either residues 61-105 of the extracellular region or most of the intracellular tail were deleted have PTH-(7-34) binding characteristics indistinguishable from those of either wild-type receptor. These findings indicate that the amino-terminal extracellular region of the PTH/PTHrP receptor contains a domain(s) that largely determines the binding affinity of amino-terminally truncated PTH analogs. This region, therefore, is likely to constitute a site for ligand-receptor interaction.
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Affiliation(s)
- H Jüppner
- Department of Pediatrics, Massachusetts General Hospital, Boston
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40
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Ureña P, Iida-Klein A, Kong XF, Jüppner H, Kronenberg HM, Abou-Samra AB, Segre GV. Regulation of parathyroid hormone (PTH)/PTH-related peptide receptor messenger ribonucleic acid by glucocorticoids and PTH in ROS 17/2.8 and OK cells. Endocrinology 1994; 134:451-6. [PMID: 8275958 DOI: 10.1210/endo.134.1.8275958] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
To study mechanisms controlling the expression of PTH/PTH-related peptide (PTHrP) receptors in ROS 17/2.8 and OK cells, we investigated the regulation of PTH/PTHrP receptor availability and receptor mRNA levels by glucocorticoids and PTH. Treatment of ROS 17/2.8 cells with dexamethasone (1 microM) for 2, 4, and 6 days increased specific binding of PTH to 148 +/- 12%, 203 +/- 10%, and 344 +/- 9% (mean +/- SD), respectively, compared to that in untreated control cells. PTH-stimulated cAMP accumulation also increased with dexamethasone treatment (1 microM) from 230 +/- 15%, 382 +/- 9%, and 820 +/- 9% after 2, 4 and 6 days, respectively, compared to that in untreated cells. Treatment of ROS 17/2.8 cells with [Nle8,Nle18,Tyr34]bovine PTH-(1-34) amide (NlePTH; 100 nM) alone or together with dexamethasone (1 microM), however, markedly decreased PTH binding and PTH-stimulated cAMP accumulation. Northern blot analysis showed that dexamethasone dramatically increased steady state levels of PTH/PTHrP receptor mRNA in a time- and dose-dependent manner, which did not occur when NlePTH (100 nM) was added concomitantly to the cultures. As previously reported, daily NlePTH treatment of ROS 17/2.8 cells reduced PTH/PTHrP receptor availability and PTH-stimulated cAMP accumulation markedly within 2 days, which remained at these low levels during continued PTH treatment. In contrast, the identical treatment reduced steady state levels of PTH/PTHrP receptor mRNA in ROS 17/2.8 transiently and to only a slight extent, which then returned to pretreatment levels. Treatment of OK cells with NlePTH (100 nM) for 1, 2, and 4 days decreased PTH binding to 56 +/- 6%, 44 +/- 4%, and 64 +/- 4% (mean +/- SD) and PTH-stimulated cAMP accumulation to 42 +/- 6%, 19 +/- 4%, and 21 +/- 3% (mean +/- SD), respectively, compared to values in untreated control cells. The same treatment, however, had no significant effect on steady state levels of PTH/PTHrP receptor transcripts. In contrast to its effects in ROS 17/2.8 cells, dexamethasone (1 microM) treatment of OK cells for 1-4 days did not affect PTH binding, nor did it significantly affect steady state levels of PTH/PTHrP receptor mRNA, although the latter was slightly lowered by dexamethasone treatment. PTH-stimulated cAMP accumulation was unchanged after 1-day treatment with dexamethasone and modestly rose to 142 +/- 4% of the control value by day 4 of glucocorticoid exposure.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- P Ureña
- Endocrine Unit, Massachusetts General Hospital, Boston 02114
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41
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Gwosdow AR, O'Connell NA, Abou-Samra AB. Interleukin-1 increases protein kinase A activity by a cAMP-independent mechanism in AtT-20 cells. Am J Physiol 1994; 266:E79-84. [PMID: 7508195 DOI: 10.1152/ajpendo.1994.266.1.e79] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
A recent study from this laboratory has shown that the inflammatory mediator, interleukin-1 alpha (IL-1 alpha), stimulates protein kinase A (PKA) activity and adrenocorticotropic hormone (ACTH) secretion from AtT-20 cells without any detectable increase in intracellular cAMP accumulation. The present studies were conducted to determine if cAMP is involved in IL-1 alpha activation of PKA and if PKA is responsible for IL-1 alpha-induced ACTH release from AtT-20 cells. The data are consistent with a novel mechanism of PKA activation that does not involve cAMP. Inhibition of adenylate cyclase with 2'5'-dideoxyadenosine (2'5'-DDA) did not affect IL-1 alpha-induced increases in PKA activity and ACTH secretion. In contrast, CRF-stimulated PKA activity and ACTH secretion were inhibited by 2'5'-DDA. Additional evidence was obtained using the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). IBMX did not alter IL-1 alpha-induced PKA activity or ACTH secretion, yet IBMX potentiated CRF-induced cAMP accumulation. Inhibition of PKA with the PKA inhibitor, H-8, blocked activation of PKA and ACTH secretion by both IL-1 alpha and CRF in AtT-20 cells. These observations demonstrate that 1) the mechanism of IL-1 alpha activation of PKA is independent of adenylate cyclase or cAMP and 2) PKA is used by IL-1 alpha to induce ACTH secretion from AtT-20 cells.
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Affiliation(s)
- A R Gwosdow
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston 02114
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42
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Ureña P, Kong XF, Abou-Samra AB, Jüppner H, Kronenberg HM, Potts JT, Segre GV. Parathyroid hormone (PTH)/PTH-related peptide receptor messenger ribonucleic acids are widely distributed in rat tissues. Endocrinology 1993; 133:617-23. [PMID: 8393771 DOI: 10.1210/endo.133.2.8393771] [Citation(s) in RCA: 193] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
PTH/PTH-related peptide (PTHrP) receptor mRNAs are widely distributed in rat tissues. PTH and PTHrP, a peptide responsible for hypercalcemia associated with cancers, bind equivalently to common receptors that initially were cloned from rat bone and opossum renal cell cDNA libraries. In this study we used rat PTH/PTHrP receptor cDNA to probe for receptor expression in different rat tissues by Northern blot analysis. PTH/PTHrP receptor transcripts are highly expressed in PTH target tissues, kidney and bone. Receptor transcripts, however, also are expressed in many other tissues, including aorta, adrenal gland, bladder, brain, cerebellum, breast, heart, ileum, liver, lung, skeletal muscle, ovary, placenta, skin, spleen, stomach, uterus, and testes. The major transcript in most tissues is 2.3-2.5 kilobases in size. At least two larger mRNAs are observed in kidney and liver, and smaller transcripts are found in kidney, skin, and testes. The most abundant testicular transcript is 1.4-1.5 kilobases in size, and it hybridizes with two different cDNA probes that encode portions of the receptor sequence from the putative fourth transmembrane domain to its C-terminal end. It does not hybridize, however, with a probe encoding the first 107 residues of the receptor sequence. Although, PTH/PTHrP receptor mRNAs are highly expressed in kidney and bone, classic PTH targets that are associated with calcium homeostasis, their wide tissue distribution suggests that PTH and/or PTHrP have other physiological roles, particularly in these other tissues. The mechanisms leading to tissue-specific expression of PTH/PTHrP receptor transcripts of different sizes and the functions of these mRNAs remain to be determined.
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Affiliation(s)
- P Ureña
- Endocrine Unit, Massachusetts General Hospital, Boston 02114
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43
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Schipani E, Karga H, Karaplis AC, Potts JT, Kronenberg HM, Segre GV, Abou-Samra AB, Jüppner H. Identical complementary deoxyribonucleic acids encode a human renal and bone parathyroid hormone (PTH)/PTH-related peptide receptor. Endocrinology 1993; 132:2157-65. [PMID: 8386612 DOI: 10.1210/endo.132.5.8386612] [Citation(s) in RCA: 121] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Identical complementary DNAs (cDNAs) that encode a 593-amino acid human PTH (PTH)/PTH-related peptide (PTHrP) receptor were isolated by hybridization techniques from two cDNA libraries which had been constructed from human kidney and human osteoblast-like osteosarcoma cells (SaOS-2). Northern blot analysis of total RNA from human bone- and kidney-derived tissue revealed one single major messenger RNA species of about 2.5 kilobases in both tissues. The human PTH/PTHrP receptor has 91% and 81% identity, respectively, with the previously cloned rat and opossum receptors, indicating a high degree of conservation among mammals. Despite this striking degree of amino-acid conservation, the human PTH/PTHrP receptor has several unique biological properties when transiently expressed in COS-7 cells. The apparent dissociation constants for [Nle8,18,Tyr34] bovine PTH(1-34) amide [bPTH(1-34)] are similar for the human and the rat receptor (approximately 8 vs. approximately 15 nM) whereas [Tyr36]PTHrP(1-36) amide has a slightly lower affinity for the human (15-40 nM) than for the rat receptor (approximately 15 nM). Both ligands stimulate efficiently and with similar efficacy the accumulation of intracellular cAMP. The affinities for the antagonists [Nle8,18,Tyr34] bPTH(3.34) amide [bPTH(3-34)] and in particular for [Nle8,18,Tyr34] bPTH(7-34) amide [bPTH(7-34)] are considerably higher for the human receptor, e.g. approximately 8 nM vs. 30 nM for bPTH(3-34) and approximately 100 nM vs. 5000 nM for bPTH(7-34), respectively. Similar biological findings were previously attributed to differences in species- and/or organ-specific PTH/PTHrP receptors. The expression of the recombinant, highly homologous rat and human receptors in a uniform environment indicate that the moderate differences in the primary receptor structure have profound consequences for the receptor binding affinity of amino-terminally truncated PTH analogs. Furthermore, the molecular cloning of identical cDNAs encoding a human PTH/PTHrP receptor from the two major target organs for PTH, bone and kidney, provides strong evidence for one single PTH/PTHrP receptor in both organs, although additional and/or alternatively spliced receptors cannot be excluded.
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Affiliation(s)
- E Schipani
- Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston 02114
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44
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Abstract
We characterized cells that express parathyroid hormone/parathyroid hormone related peptide (PTH/PTHrP) receptor mRNA in bones of fetal and postnatal rats by in situ hybridization. During endochondral development of fetal bones, PTH/PTHrP receptor transcripts were highly expressed both in maturing chondrocytes and in osteoblasts in the periosteum and ossification center, but not in fully hypertrophic chondrocytes. Similar to the localization in the fetal bones, PTH/PTHrP receptor mRNA expression was highly localized to maturing chondrocytes in the articular cartilage and growth plate, and to osteoblasts in the femur of young rats. In both young and fetal rats, transcripts for Type X collagen were localized to hypertrophic chondrocytes, mostly between chondrocytes and bone cells both of which express PTH/PTHrP receptor mRNA. Transcripts for PTH/PTHrP receptors and alkaline phosphatase co-localized in the bone of young rats, but they did not co-localize in fetal bones at the early stages of endochondral ossification. These results show that PTH/PTHrP receptor mRNA is expressed in a cell-type and stage-specific manner during skeletal development.
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Affiliation(s)
- K Lee
- Endocrine Unit, Massachusetts General Hospital, Boston 02114
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45
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Bringhurst FR, Juppner H, Guo J, Urena P, Potts JT, Kronenberg HM, Abou-Samra AB, Segre GV. Cloned, stably expressed parathyroid hormone (PTH)/PTH-related peptide receptors activate multiple messenger signals and biological responses in LLC-PK1 kidney cells. Endocrinology 1993; 132:2090-8. [PMID: 8386606 DOI: 10.1210/endo.132.5.8386606] [Citation(s) in RCA: 157] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
PTH elicits multiple second messenger signals in target cells. This signaling diversity may reflect coupling of a single species of PTH receptors to multiple effectors, the action of different subtypes of PTH receptors, or both. We recently reported the expression cloning, from rat and opossum cells, of closely related cDNAs encoding receptors for PTH [and PTH-related peptide (PTHRP)]. To determine if these cloned PTH/PTHRP receptors can activate multiple intracellular effectors when present at near-physiological levels in intact target cells, we have stably expressed the rat and opossum PTH/PTHRP receptor cDNAs in LLC-PK1 porcine renal epithelial cells. These cells lack endogenous PTH/PTHRP receptors, but do express abundant calcitonin receptors and many features of a proximal tubular phenotype. Subclones of transfected LLC-PK1 cells exhibited high affinity binding (Kd, 1-5 nM) of [Nle8.18,Tyr34]bovine PTH-(1-34)amide (PTH) and dose-dependent activation by PTH of both cAMP accumulation (EC50, 1 nM) and increased release of cytosolic free calcium from intracellular stores (EC50, > or = 20-50 nM) across a wide range of receptor expression. Expressed rat and opossum receptors exhibited similar properties, except for a 5-fold lower binding affinity of the rat receptor for PTH-(7-34). Stimulation by PTH of both cAMP accumulation and elevated cytosolic free calcium was augmented in cells expressing higher numbers of PTH/PTHRP receptors. Like calcitonin, PTH (1-100 nM) reduced the rate of cell proliferation and augmented the rate of inorganic phosphate transport after 24 and 5 h of preincubation, respectively. The growth effect was mimicked by cAMP analogs, forskolin, phorbol esters, and calcium ionophores. Regulation of phosphate transport, however, was mimicked by phorbols, but not by cAMP analogs or forskolin. We conclude that LLC-PK1 cells provide a useful model in which to study the function of cloned PTH/PTHRP receptors. In these cells, a single species of cloned PTH/PTHRP receptors, stably expressed at near-physiological numbers, activates multiple second messenger responses and regulates subsequent biological responses, including at least one (phosphate transport) that is mediated by mechanisms independent of cAMP.
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Affiliation(s)
- F R Bringhurst
- Endocrine Unit, Massachusetts General Hospital, Boston 02114
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46
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Abstract
Studies from this and other laboratories have shown that interleukin-1 (IL-1) stimulates ACTH secretion directly from AtT-20 cells. The present studies were conducted to determine the signal transduction mechanisms activated by IL-1 to stimulate ACTH release. IL-1 significantly (P < 0.05) elevated ACTH release after incubation periods of 4, 8, and 24 h. IL-1-induced ACTH release was not additive to that of CRF, cholera toxin, 8-bromo-cAMP, or forskolin. In contrast, IL-1 and the phorbol ester phorbol 12-myristate 13-acetate together produced a greater increase (P < 0.05) in ACTH release than either agent alone. IL-1 did not stimulate cAMP accumulation at any time period between 5 min and 24 h and did not affect cAMP accumulation induced by CRF, cholera toxin, or forskolin. The lack of additivity between IL-1 and CRF, cholera toxin, 8-bromo-cAMP, and forskolin suggests that IL-1 stimulates ACTH release by a pathway that shares some common step(s) with CRF. Because IL-1 did not affect cAMP accumulation, the effect of IL-1 on protein kinase A (PKA) was investigated. IL-1 began to increase (P < 0.05) PKA activity at 15 min and remained elevated for 2 h before returning to control levels. IL-1 stimulation of PKA and the lack of additivity between IL-1 and CRF, forskolin, and cholera toxin indicate that PKA is the intracellular mediator used by IL-1 to stimulate ACTH release in AtT-20 cells.
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Affiliation(s)
- A R Gwosdow
- Endocrine Unit, Massachusetts General Hospital, Boston 02114
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47
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Abou-Samra AB, Jüppner H, Khalifa A, Karga H, Kong XF, Schiffer-Alberts D, Xie LY, Segre GV. Parathyroid hormone (PTH) stimulates adrenocorticotropin release in AtT-20 cells stably expressing a common receptor for PTH and PTH-related peptide. Endocrinology 1993; 132:801-5. [PMID: 7678801 DOI: 10.1210/endo.132.2.7678801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Complementary DNA encoding a rat bone PTH/PTHrP receptor was stably expressed in the murine corticotroph cell line, AtT-20. Several clones, expressing variable numbers of PTH/PTHrP receptors, were developed. In contrast to the relatively low binding affinity (apparent Kd = 15 nM) observed in COS-7 cells transiently expressing the PTH/PTHrP receptor, all AtT-20 stable transfectants bound [Nle8,18,Tyr34]bPTH(1-34)NH2 (NlePTH) with an affinity that was indistinguishable from that observed in ROS 17/2.8 cells expressing native PTH/PTHrP receptors. Additionally, NlePTH dramatically increased cAMP accumulation and ACTH release in AtT-20 cells expressing the PTH/PTHrP receptor with an ED50 of 0.6 +/- 0.3 and 0.3 +/- 0.1 nM, respectively. The high binding affinity and the high efficacy of NlePTH in stimulating cAMP accumulation and ACTH release indicate that the PTH/PTHrP receptor is efficiently coupled to the intracellular signalling system responsible for stimulation of ACTH release in AtT-20 cells. No additivity of cAMP accumulation or of ACTH release was observed when these cells were treated with maximally active concentrations of both NlePTH and CRF. This suggests that the receptors for both of these hormones share the same intracellular effectors, and that intracellular signaling in AtT-20 cells is not compartmentalized. Additionally, the ability of NlePTH to stimulate ACTH release in AtT-20 cells, a function that is normally performed by CRF, demonstrates promiscuity between activated receptors and distal biological functions.
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Affiliation(s)
- A B Abou-Samra
- Endocrine Unit, Massachusetts General Hospital, Boston 02114
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48
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van de Stolpe A, Karperien M, Löwik CW, Jüppner H, Segre GV, Abou-Samra AB, de Laat SW, Defize LH. Parathyroid hormone-related peptide as an endogenous inducer of parietal endoderm differentiation. J Cell Biol 1993; 120:235-43. [PMID: 8380175 PMCID: PMC2119495 DOI: 10.1083/jcb.120.1.235] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Parathyroid hormone related peptide (PTHrP), first identified in tumors from patients with the syndrome of "Humoral Hypercalcemia of Malignancy," can replace parathyroid hormone (PTH) in activating the PTH-receptor in responsive cells. Although PTHrP expression is widespread in various adult and fetal tissues, its normal biological function is as yet unknown. We have examined the possible role of PTHrP and the PTH/PTHrP-receptor in early mouse embryo development. Using F9 embryonal carcinoma (EC) cells and ES-5 embryonic stem (ES) cells as in vitro models, we demonstrate that during the differentiation of these cells towards primitive and parietal endoderm-like phenotypes, PTH/PTHrP-receptor mRNA is induced. This phenomenon is correlated with the appearance of functional adenylate cyclase coupled PTH/PTHrP-receptors. These receptors are the mouse homologues of the recently cloned rat bone and opossum kidney PTH/PTHrP-receptors. Addition of exogenous PTH or PTHrP to RA-treated EC or ES cells is an efficient replacement for dBcAMP in inducing full parietal endoderm differentiation. Endogenous PTHrP is detectable at very low levels in undifferentiated EC and ES cells, and is upregulated in their primitive and parietal endoderm-like derivatives as assessed by immunofluorescence. Using confocal laser scanning microscopy on preimplantation mouse embryos, PTHrP is detected from the late morula stage onwards in developing trophectoderm cells, but not in inner cell mass cells. In blastocyst stages PTHrP is in addition found in the first endoderm derivatives of the inner cell mass. Together these results indicate that the PTH/PTHrP-receptor signalling system serves as a para- or autocrine mechanism for parietal endoderm differentiation in the early mouse embryo, thus constituting the earliest hormone receptor system involved in embryogenesis defined to date.
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Affiliation(s)
- A van de Stolpe
- Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Utrecht
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Abstract
Corticotropin-releasing factor (CRF) stimulates adrenocorticotropin (ACTH) release via the adenylate cyclase/cAMP-dependent protein kinase system. Because calcium is necessary for receptor-mediated release of ACTH, we have examined the effect of CRF on 45Ca2+ uptake in a corticotroph cell line model, AtT-20. Treatment of AtT-20 cells with CRF (10(-9)-10(-6) M) resulted in dose- and time-dependent increases in 45Ca2+ uptake, up to 2.2-fold above control values. The effect was statistically significant at 1 min and persisted for at least 10 min. Treatment with forskolin (1-30 microM), 8-Br-cAMP (0.5 mM), cholera toxin (CT, 100 ng/ml) and K+ (20 mM) also increased cell-associated 45Ca2+. The effect of K+ was completely blocked by nifedipine (100 microM), whereas the effects of CRF (10(-8) M) were only partially inhibited by this calcium channel antagonist. These data suggested a role of voltage-dependent calcium channels in 45Ca2+ uptake. Short term pretreatment (1-2 h) of AtT-20 cells with CRF (10(-8) M) significantly desensitized both CRF-stimulated cAMP accumulation and ACTH release, but did not attenuate CRF-stimulated 45Ca2+ uptake. Pretreatment with CRF (10(-8) M) for 4 h did not alter CT- or forskolin-stimulated cAMP accumulation and ACTH release. This suggests that the molecular mechanisms of desensitization are proximal to adenylate cyclase. Conversely, long term pretreatment (24 h) of AtT-20 cells with CRF (10(-8) M) induced significant desensitization of CRF-stimulated 45Ca2+ uptake. These results indicate that CRF stimulates calcium uptake in AtT-20 cells via cAMP-dependent and cAMP-independent mechanisms, and that the cellular mechanisms involved in desensitization of cAMP accumulation and ACTH release and those involved in desensitization of calcium uptake are qualitatively different.
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Affiliation(s)
- K Tojo
- Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston 02114
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Uneno S, Yamamuro T, Jüppner H, Abou-Samra AB, Keutmann HT, Potts JT, Segre GV. Solubilization of functional receptors for parathyroid hormone and parathyroid hormone-related peptide from clonal rat osteosarcoma cells, ROS17/2.8. Calcif Tissue Int 1992; 51:382-6. [PMID: 1333876 DOI: 10.1007/bf00316884] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
ROS17/2.8 cells, a cell line derived from a rat osteosarcoma, have abundant receptors for parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTHrP). A particulate membrane fraction was prepared from these cells and it was solubilized using relatively mild conditions with digitonin (0.25%), a nonionic detergent. When radioligands of both PTH and PTHrP were incubated with this membrane fraction in the absence of any protease inhibitor at 15 degrees C, approximately 75% of these radioligands were degraded within 2 hours. This degradative activity was inhibited more effectively by bacitracin than by any of several other protease inhibitors tested. The digitonin-solubilized PTH/PTHrP receptors were radiolabeled in the presence of bacitracin using radioiodinated [Tyr36]PTHrP(1-36) amide (PTHrP(1-36)) and N-hydroxysuccinimidyl-4-azidobenzoate (HSAB), as cross-linker. When an aliquot of the reaction solution was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography, a broad band was observed that had an apparent molecular size of 90,000 daltons (M(r) = 90 kD). This band was no longer seen when the binding was conducted in the presence of 10(-6) M of unlabeled PTHrP(1-36), and it was decreased in density when binding was conducted in the presence of 10(-6) M of unlabeled [Nle8,18, Tyr34] bovine PTH(1-34) amide (NlePTH). The solubilized receptors retained their capacity to bind the radioligand after partial purification by wheat-germ agglutinin affinity-chromatography. The use of relatively mild detergent conditions thus offers a means to solubilize receptors that retain their capacity to bind PTH and PTHrP.
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Affiliation(s)
- S Uneno
- Department of Medicine, Massachusetts General Hospital, Boston
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