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Postnatal maturation of calcium signaling in islets of Langerhans from neonatal mice. Cell Calcium 2020; 94:102339. [PMID: 33422769 DOI: 10.1016/j.ceca.2020.102339] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2020] [Revised: 12/20/2020] [Accepted: 12/21/2020] [Indexed: 01/02/2023]
Abstract
Pancreatic islet cells develop mature physiological responses to glucose and other fuels postnatally. In this study, we used fluorescence imaging techniques to measure changes in intracellular calcium ([Ca2+]i) to compare islets isolated from mice on postnatal days 0, 4, and 12 with islets from adult CD-1 mice. In addition, we used publicly available RNA-sequencing data to compare expression levels of key genes in β-cell physiology with [Ca2+]i data across these ages. We show that islets isolated from mice on postnatal day 0 displayed elevated [Ca2+]i in basal glucose (≤4 mM) but lower [Ca2+]i responses to stimulation by 12-20 mM glucose compared to adult. Neonatal islets displayed more adult-like [Ca2+]i in basal glucose by day 4 but continued to show lower [Ca2+]i responses to 16 and 20 mM glucose stimulation up to at least day 12. A right shift in glucose sensing (EC50) correlated with lower fragment-per-kilobase-of-transcript-per-million-reads-mapped (FPKM) of Slc2a2 (glut2) and Actn3 and increased FPKM for Galk1 and Nupr1. Differences in [Ca2+]i responses to additional stimuli were also observed. Calcium levels in the endoplasmic reticulum were elevated on day 0 but became adult-like by day 4, which corresponded with reduced expression in Atp2a2 (SERCA2) and novel K+-channel Ktd17, increased expression of Pml, Wfs1, Thada, and Herpud1, and basal [Ca2+]i maturing to adult levels. Ion-channel activity also matured rapidly, but RNA sequencing data mining did not yield strong leads. In conclusion, the maturation of islet [Ca2+]i signaling is complex and multifaceted; several possible gene targets were identified that may participate in this process.
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Romero-Lorca A, Gaibar M, Armesilla AL, Fernandez-Santander A, Novillo A. Differential expression of PMCA2 mRNA isoforms in a cohort of Spanish patients with breast tumor types. Oncol Lett 2018; 16:6950-6959. [PMID: 30546427 PMCID: PMC6256341 DOI: 10.3892/ol.2018.9540] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 05/29/2018] [Indexed: 01/01/2023] Open
Abstract
The present study examined the mRNA expression levels of different isoforms of the plasma membrane calcium ATPase 2 (PMCA2) gene generated by alternative splicing at the first intracellular loop (site A) and C-terminal region (site C) in 85 human breast cancer tumor and 69 adjacent non-tumor tissues. Associations were identified between the expression of PMCA2 splice isoforms and the following clinical variables: Estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) status, tumor size, staging and histological classification, and lymph node status. Transcripts including splice site A or splice site C were amplified by reverse transcription-quantitative polymerase chain reaction using PMCA2 isoform-specific primers. Tumor and adjacent tissues were determined to express the different PMCA2 splice isoforms 2w, 2× and 2z (site A), and 2b (site C). The mRNA levels for these variants indicated high biological variability, but increased expression was observed in breast tumor tissues, compared with in adjacent tissues. Significantly increased PMCA2×/b expression levels were detected in breast tumor tissues histologically classified as lobulillar, compared with in ductal-types breast tumor tissues (P<0.028). Furthermore, PMCA2z expression was significantly associated with PR status (P<0.024, compared with in PR-negative tumor tissues), and PMCA2w expression was significantly associated with ER status (P<0.048, increased in ER-positive tumor tissues, compared with ER-negative tumor tissues). Finally, PMCA2b was overexpressed in HER2-positive tumor tissues, compared with in HER2-negative tumor tissues (P<0.014). The data demonstrated the differential mRNA expression of a number of splice site A and C variants of PMCA2 in breast tumor and adjacent tissues, depending on tumor hormone receptor status and histological classification. In agreement with previous data, PMCA2b was overexpressed in HER2-positive tumor tissues, indicating that high mRNA levels of this variant could be a marker of poor prognosis.
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Affiliation(s)
- Alicia Romero-Lorca
- Department of Basic Biomedical Sciences, Faculty of Biomedical and Health Sciences, Universidad Europea de Madrid, Villaviciosa de Odón, Madrid 28670, Spain
| | - Maria Gaibar
- Department of Basic Biomedical Sciences, Faculty of Biomedical and Health Sciences, Universidad Europea de Madrid, Villaviciosa de Odón, Madrid 28670, Spain
| | - Angel Luis Armesilla
- Faculty of Science and Engineering, School of Pharmacy, University of Wolverhampton, Wolverhampton, West Midlands WV1 1LY, UK
| | - Ana Fernandez-Santander
- Department of Basic Biomedical Sciences, Faculty of Biomedical and Health Sciences, Universidad Europea de Madrid, Villaviciosa de Odón, Madrid 28670, Spain
| | - Apolonia Novillo
- Department of Basic Biomedical Sciences, Faculty of Biomedical and Health Sciences, Universidad Europea de Madrid, Villaviciosa de Odón, Madrid 28670, Spain
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Bardy G, Virsolvy A, Quignard JF, Ravier MA, Bertrand G, Dalle S, Cros G, Magous R, Richard S, Oiry C. Quercetin induces insulin secretion by direct activation of L-type calcium channels in pancreatic beta cells. Br J Pharmacol 2015; 169:1102-13. [PMID: 23530660 DOI: 10.1111/bph.12194] [Citation(s) in RCA: 75] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2012] [Revised: 03/01/2013] [Accepted: 03/21/2013] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE Quercetin is a natural polyphenolic flavonoid that displays anti-diabetic properties in vivo. Its mechanism of action on insulin-secreting beta cells is poorly documented. In this work, we have analysed the effects of quercetin both on insulin secretion and on the intracellular calcium concentration ([Ca(2+)]i) in beta cells, in the absence of any co-stimulating factor. EXPERIMENTAL APPROACH Experiments were performed on both INS-1 cell line and rat isolated pancreatic islets. Insulin release was quantified by the homogeneous time-resolved fluorescence method. Variations in [Ca(2+)]i were measured using the ratiometric fluorescent Ca(2+) indicator Fura-2. Ca(2+) channel currents were recorded with the whole-cell patch-clamp technique. KEY RESULTS Quercetin concentration-dependently increased insulin secretion and elevated [Ca(2+)]i. These effects were not modified by the SERCA inhibitor thapsigargin (1 μmol·L(-1)), but were nearly abolished by the L-type Ca(2+) channel antagonist nifedipine (1 μmol·L(-1)). Similar to the L-type Ca(2+) channel agonist Bay K 8644, quercetin enhanced the L-type Ca(2+) current by shifting its voltage-dependent activation towards negative potentials, leading to the increase in [Ca(2+)]i and insulin secretion. The effects of quercetin were not inhibited in the presence of a maximally active concentration of Bay K 8644 (1 μmol·L(-1)), with the two drugs having cumulative effects on [Ca(2+)]i. CONCLUSIONS AND IMPLICATIONS Taken together, our results show that quercetin stimulates insulin secretion by increasing Ca(2+) influx through an interaction with L-type Ca(2+) channels at a site different from that of Bay K 8644. These data contribute to a better understanding of quercetin's mechanism of action on insulin secretion.
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Affiliation(s)
- G Bardy
- Département de Pharmacologie Médicale et Toxicologie, Hôpital Lapeyronie, CHRU de Montpellier, Montpellier, France
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Johnson JS, Kono T, Tong X, Yamamoto WR, Zarain-Herzberg A, Merrins MJ, Satin LS, Gilon P, Evans-Molina C. Pancreatic and duodenal homeobox protein 1 (Pdx-1) maintains endoplasmic reticulum calcium levels through transcriptional regulation of sarco-endoplasmic reticulum calcium ATPase 2b (SERCA2b) in the islet β cell. J Biol Chem 2014; 289:32798-810. [PMID: 25271154 DOI: 10.1074/jbc.m114.575191] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Although the pancreatic duodenal homeobox 1 (Pdx-1) transcription factor is known to play an indispensable role in β cell development and secretory function, recent data also implicate Pdx-1 in the maintenance of endoplasmic reticulum (ER) health. The sarco-endoplasmic reticulum Ca(2+) ATPase 2b (SERCA2b) pump maintains a steep Ca(2+) gradient between the cytosol and ER lumen. In models of diabetes, our data demonstrated loss of β cell Pdx-1 that occurs in parallel with altered SERCA2b expression, whereas in silico analysis of the SERCA2b promoter revealed multiple putative Pdx-1 binding sites. We hypothesized that Pdx-1 loss under inflammatory and diabetic conditions leads to decreased SERCA2b levels and activity with concomitant alterations in ER health. To test this, siRNA-mediated knockdown of Pdx-1 was performed in INS-1 cells. The results revealed reduced SERCA2b expression and decreased ER Ca(2+), which was measured using fluorescence lifetime imaging microscopy. Cotransfection of human Pdx-1 with a reporter fused to the human SERCA2 promoter increased luciferase activity 3- to 4-fold relative to an empty vector control, and direct binding of Pdx-1 to the proximal SERCA2 promoter was confirmed by chromatin immunoprecipitation. To determine whether restoration of SERCA2b could rescue ER stress induced by Pdx-1 loss, Pdx1(+/-) mice were fed a high-fat diet. Isolated islets demonstrated an increased spliced-to-total Xbp1 ratio, whereas SERCA2b overexpression reduced the Xbp1 ratio to that of wild-type controls. Together, these results identify SERCA2b as a novel transcriptional target of Pdx-1 and define a role for altered ER Ca(2+) regulation in Pdx-1-deficient states.
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Affiliation(s)
| | | | - Xin Tong
- Cellular and Integrative Physiology and
| | | | - Angel Zarain-Herzberg
- the Departamento de Bioquimica, Facultad de Medicina, National Autonomous University of México, México City, 04510 México
| | - Matthew J Merrins
- the Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, and Department of Biomolecular Chemistry, University of Wisconsin Madison School of Medicine and Public Health, Madison, Wisconsin 53705
| | - Leslie S Satin
- the Department of Pharmacology and Brehm Center for Diabetes Research, University of Michigan Medical School, Ann Arbor, Michigan 48105
| | - Patrick Gilon
- the Pôle d'Endocrinologie, Diabète et Nutrition, Institut de Recherche Expérimentale et Clinique, Université Catholique de Louvain, Brussels, 1348 Belgium, and
| | - Carmella Evans-Molina
- From the Departments of Biochemistry and Molecular Biology, Medicine, and Cellular and Integrative Physiology and the Herman B. Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, Indiana 46202, the Roudebush Veterans Affairs Medical Center, Indianapolis, Indiana 46202
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Kosiorek M, Zylinska L, Zablocki K, Pikula S. Calcineurin/NFAT signaling represses genes Vamp1 and Vamp2 via PMCA-dependent mechanism during dopamine secretion by Pheochromocytoma cells. PLoS One 2014; 9:e92176. [PMID: 24667359 PMCID: PMC3965406 DOI: 10.1371/journal.pone.0092176] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Accepted: 02/19/2014] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Plasma membrane Ca(2+)-ATPases (PMCA) extrude Ca(2+) ions out of the cell and contribute to generation of calcium oscillations. Calcium signaling is crucial for transcriptional regulation of dopamine secretion by neuroendocrine PC12 cells. Low resting [Ca(2+)]c in PC12 cells is maintained mainly by two Ca(2+)-ATPases, PMCA2 and PMCA3. Recently, we found that Ca(2+) dependent phosphatase calcineurin was excessively activated under conditions of experimental downregulation of PMCA2 or PMCA3. Thus, the aim of this study was to explain if, via modulation of the Ca(2+)/calcineurin-dependent nuclear factor of activated T cells (NFAT) pathway, PMCA2 and PMCA3 affect intracellular signaling in pheochromocytoma/neuronal cells/PC12 cells. Secondly, we tested whether this might influence dopamine secretion by PC12 cells. RESULTS PMCA2- and PMCA3-deficient cells displayed profound decrease in dopamine secretion accompanied by a permanent increase in [Ca(2+)]c. Reduction in secretion might result from changes in NFAT signaling, following altered PMCA pattern. Consequently, activation of NFAT1 and NFAT3 transcription factors was observed in PMCA2- or PMCA3-deficient cells. Furthermore, chromatin immunoprecipitation assay indicated that NFATs could be involved in repression of Vamp genes encoding vesicle associated membrane proteins (VAMP). CONCLUSIONS PMCA2 and PMCA3 are crucial for dopamine secretion in PC12 cells. Reduction in PMCA2 or PMCA3 led to calcium-dependent activation of calcineurin/NFAT signaling and, in consequence, to repression of the Vamp gene and deterioration of the SNARE complex formation in PC12 cells.
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Affiliation(s)
- Michalina Kosiorek
- Department of Biochemistry, Nencki Institute of Experimental Biology, PAS, Warsaw, Poland
- Laboratory of Neurogenetics, Department of Neurodegenerative Disorders, Mossakowski Medical Research Centre PAS, Warsaw, Poland
- * E-mail: (MK); (SP)
| | - Ludmila Zylinska
- Department of Molecular Neurochemistry, Medical University, Lodz, Poland
| | - Krzysztof Zablocki
- Department of Biochemistry, Nencki Institute of Experimental Biology, PAS, Warsaw, Poland
| | - Slawomir Pikula
- Department of Biochemistry, Nencki Institute of Experimental Biology, PAS, Warsaw, Poland
- * E-mail: (MK); (SP)
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Brozzi F, Lajus S, Diraison F, Rajatileka S, Hayward K, Regazzi R, Molnár E, Váradi A. MyRIP interaction with MyoVa on secretory granules is controlled by the cAMP-PKA pathway. Mol Biol Cell 2012; 23:4444-55. [PMID: 22993210 PMCID: PMC3496617 DOI: 10.1091/mbc.e12-05-0369] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Myosin- and Rab-interacting protein is not a classic receptor for MyoVa on large, dense-core secretory granules (SGs), but it aids in PKA-dependent phosphorylation of MyoVa-associated proteins on SGs in endocrine and neuroendocrine cells. Myosin- and Rab-interacting protein (MyRIP), which belongs to the protein kinase A (PKA)–anchoring family, is implicated in hormone secretion. However, its mechanism of action is not fully elucidated. Here we investigate the role of MyRIP in myosin Va (MyoVa)-dependent secretory granule (SG) transport and secretion in pancreatic beta cells. These cells solely express the brain isoform of MyoVa (BR-MyoVa), which is a key motor protein in SG transport. In vitro pull-down, coimmunoprecipitation, and colocalization studies revealed that MyRIP does not interact with BR-MyoVa in glucose-stimulated pancreatic beta cells, suggesting that, contrary to previous notions, MyRIP does not link this motor protein to SGs. Glucose-stimulated insulin secretion is augmented by incretin hormones, which increase cAMP levels and leads to MyRIP phosphorylation, its interaction with BR-MyoVa, and phosphorylation of the BR-MyoVa receptor rabphilin-3A (Rph-3A). Rph-3A phosphorylation on Ser-234 was inhibited by small interfering RNA knockdown of MyRIP, which also reduced cAMP-mediated hormone secretion. Demonstrating the importance of this phosphorylation, nonphosphorylatable and phosphomimic Rph-3A mutants significantly altered hormone release when PKA was activated. These data suggest that MyRIP only forms a functional protein complex with BR-MyoVa on SGs when cAMP is elevated and under this condition facilitates phosphorylation of SG-associated proteins, which in turn can enhance secretion.
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Affiliation(s)
- Flora Brozzi
- Centre for Research in Biomedicine, Faculty of Health and Life Sciences, University of the West of England, Bristol BS16 1QY, United Kingdom
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7
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Persaud SJ, Liu B, Jones PM. Functional analysis of human islets of Langerhans maintained in culture. Methods Mol Biol 2012; 806:55-71. [PMID: 22057445 DOI: 10.1007/978-1-61779-367-7_5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Islets of Langerhans isolated from experimental animals, such as mice and rats, have contributed much to our understanding of the mechanisms by which pancreatic β-cells secrete insulin in a regulated manner, and this knowledge is important in identifying potential novel therapies for Type 2 diabetes. However, although many of the signal transduction pathways identified in rodent islets are common to humans, some critical differences have been demonstrated experimentally. It is, therefore, essential that experiments are performed using islets isolated from human pancreas to provide robust data defining whether the key observations made in rodents are also applicable to the human situation. The rate-limiting factor in this area of research is the supply of high-quality human islets isolated from pancreases retrieved from organ donors, and the protocols described in this chapter aim to provide methods of maximising information that can be obtained when human islets are maintained in culture.
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Alzugaray ME, García ME, Del Zotto HH, Raschia MA, Palomeque J, Rossi JP, Gagliardino JJ, Flores LE. Changes in islet plasma membrane calcium-ATPase activity and isoform expression induced by insulin resistance. Arch Biochem Biophys 2009; 490:17-23. [DOI: 10.1016/j.abb.2009.07.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2009] [Revised: 07/29/2009] [Accepted: 07/30/2009] [Indexed: 11/25/2022]
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Abstract
Ca2+-ATPases (pumps) are key actors in the regulation of Ca2+ in eukaryotic cells and are thus essential to the correct functioning of the cell machinery. They have high affinity for Ca2+ and can efficiently regulate it down to very low concentration levels. Two of the pumps have been known for decades (the SERCA and PMCA pumps); one (the SPCA pump) has only become known recently. Each pump is the product of a multigene family, the number of isoforms being further increased by alternative splicing of the primary transcripts. The three pumps share the basic features of the catalytic mechanism but differ in a number of properties related to tissue distribution, regulation, and role in the cellular homeostasis of Ca2+. The molecular understanding of the function of the pumps has received great impetus from the solution of the three-dimensional structure of one of them, the SERCA pump. These spectacular advances in the structure and molecular mechanism of the pumps have been accompanied by the emergence and rapid expansion of the topic of pump malfunction, which has paralleled the rapid expansion of knowledge in the topic of Ca2+-signaling dysfunction. Most of the pump defects described so far are genetic: when they are very severe, they produce gross and global disturbances of Ca2+ homeostasis that are incompatible with cell life. However, pump defects may also be of a type that produce subtler, often tissue-specific disturbances that affect individual components of the Ca2+-controlling and/or processing machinery. They do not bring cells to immediate death but seriously compromise their normal functioning.
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10
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Jahanshahi P, Wu R, Carter JD, Nunemaker CS. Evidence of diminished glucose stimulation and endoplasmic reticulum function in nonoscillatory pancreatic islets. Endocrinology 2009; 150:607-15. [PMID: 18818288 PMCID: PMC2646533 DOI: 10.1210/en.2008-0773] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Pulsatility is a fundamental feature of pancreatic islets and a hallmark of hormone secretion. Isolated pancreatic islets endogenously generate rhythms in secretion, metabolic activity, and intracellular calcium ([Ca(2+)](i)) that are important to normal physiological function. Few studies have directly compared oscillatory and nonoscillatory islets to identify possible differences in function. We investigated the hypothesis that the loss of these oscillations is a leading indicator of islet dysfunction by comparing oscillatory and nonoscillatory mouse islets for multiple parameters of function. Nonoscillatory islets displayed elevated basal [Ca(2+)](i) and diminished [Ca(2+)](i) response and insulin secretory response to 3-28 mm glucose stimulation compared with oscillatory islets, suggesting diminished glucose sensitivity. We investigated several possible mechanisms to explain these differences. No differences were observed in mitochondrial membrane potential, estimated ATP-sensitive potassium channel and L-type calcium channel activity, or cell death rates. Nonoscillatory islets, however, showed a reduced response to the sarco(endo)plasmic reticulum calcium ATPase inhibitor thapsigargin, suggesting a disruption in calcium homeostasis in the endoplasmic reticulum (ER) compared with oscillatory islets. The diminished ER calcium homeostasis among nonoscillatory islets was also consistent with the higher cytosolic calcium levels observed in 3 mm glucose. Inducing mild damage with low-dose proinflammatory cytokines reduced islet oscillatory capacity and produced similar effects on glucose-stimulated [Ca(2+)](i), basal [Ca(2+)](i), and thapsigargin response observed among untreated nonoscillatory islets. Our data suggest the loss of oscillatory capacity may be an early indicator of diminished islet glucose sensitivity and ER dysfunction, suggesting targets to improve islet assessment.
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Affiliation(s)
- Pooya Jahanshahi
- Department of Medicine, Division of Endocrinology and Metabolism, University of Virginia, Charlottesville, VA 22908-1413, USA
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Szewczyk MM, Pande J, Grover AK. Caloxins: a novel class of selective plasma membrane Ca2+ pump inhibitors obtained using biotechnology. Pflugers Arch 2007; 456:255-66. [PMID: 17909851 DOI: 10.1007/s00424-007-0348-6] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2007] [Accepted: 09/06/2007] [Indexed: 12/22/2022]
Abstract
Plasma membrane Ca2+ pumps (PMCA) extrude cellular Ca2+ with a high affinity and hence play a major role in Ca2+ homeostasis and signaling. Caloxins (selective extracellular PMCA inhibitors) would aid in elucidating the physiology of PMCA. PMCA proteins have five extracellular domains (exdoms). Our hypotheses are: 1) peptides that bind selectively to each exdom can be invented by screening a random peptide library, and 2) a peptide can modulate PMCA activity by binding to one of the exdoms. The first caloxin 2a1, selected for binding exdom 2 was selective for PMCA (Ki=529 microM). It has been used to examine the physiological role of PMCA. PMCA isoforms are encoded by four genes. PMCA isoform expression differs in various cell types, with PMCA1 and 4 being the most widely distributed. There are differences between PMCA1-4 exdom 1 sequences, which may be exploited for inventing isoform selective caloxins. Using exdom 1 of PMCA4 as a target, modified screening procedures and mutagenesis led to the high-affinity caloxin 1c2 (Ki=2.3 microM for PMCA4). It is selective for PMCA4 over PMCA1, 2, or 3. We hope that caloxins can be used to discern the roles of individual PMCA isoforms in Ca2+ homeostasis and signaling. Caloxins may also become clinically useful in cardiovascular diseases, neurological disorders, retinopathy, cancer, and contraception.
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Affiliation(s)
- Magdalena M Szewczyk
- Department of Biology, McMaster University, HSC 4N41, 1200 Main Street W, Hamilton, ON L8N3Z5, Canada
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12
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Talarico EF, Mangini NJ. Alternative splice variants of plasma membrane calcium-ATPases in human corneal epithelium. Exp Eye Res 2007; 85:869-79. [PMID: 17931625 DOI: 10.1016/j.exer.2007.08.023] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2007] [Revised: 08/27/2007] [Accepted: 08/28/2007] [Indexed: 10/22/2022]
Abstract
Plasma membrane calcium-ATPases (PMCAs) play a critical role in regulating intracellular calcium concentration. Four genes encode PMCA proteins with alternative splicing of transcripts at three sites (A, B and C) serving to increase isoform diversity. Our previous work shows that all four PMCAs are expressed and have specific locations in human corneal epithelium (hCE). The present work examined which splice variants of PMCAs are expressed in hCE. Total RNA was extracted from hCE scraped from cadaver corneas of five different donors (two females and three males, age range 55-76 years). RT-PCR was performed using PMCA isoform-specific primers designed to amplify transcripts that included either splice site A or splice sites B and C. PMCA cDNAs were sequenced or cloned, and then sequenced. There was uniformity in the PMCA1 and PMCA4 expression profile among the five donors. Specifically, every donor expressed PMCA4 transcripts (4x at site A and 4b at site B/C). Every donor also expressed PMCA1 transcripts at sites B/C, specifically PMCA1b and PMCA1kb. In contrast, PMCA2 and PMCA3 expression varied; PCR DNAs were detected in two of five donors. One donor expressed PMCA2a and a novel PMCA2 variant we termed PMCA2((i)). PMCA3a transcript was demonstrated in a different donor. Finally, for all the donors, bands encoding site A transcripts for PMCA4 were obtained but no PCR transcripts were detected at site A for PMCA1, PMCA2 and PMCA3. This investigation showed that hCE expressed multiple splice variants of PMCA isoforms. Furthermore, this study documented the expression of the PMCA1k variant (PMCA1kb) previously only described in intestine and pancreatic beta cells and describes a novel PMCA2((i)) variant. Finally, this study suggests that the molecular configuration of PMCA1, PMCA2 and PMCA3 in the region of splice site A in hCE must be different than in other tissues since the same primers that produced site A transcripts in several other tissues were ineffective in priming PCR in hCE.
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Affiliation(s)
- Ernest F Talarico
- Department of Anatomy and Cell Biology, Indiana University School of Medicine-Northwest, Gary, IN 46408-1197, USA.
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Abstract
Pancreatic beta-cells maintain glucose homeostasis by their regulated Ca(2+)-dependent secretion of insulin. Several cellular mechanisms control intracellular Ca(2+) levels, but their relative significance in mouse beta-cells is not fully known. We used photometry to measure the dynamics of cytosolic Ca(2+) ([Ca(2+)](i)) clearance after brief, depolarization-induced Ca(2+) entry. Treatment with thapsigargin or cyclopiazonic acid, inhibitors of the sarco-endoplasmic reticulum Ca(2+)-ATPase (SERCA) pumps, nearly doubled the peak and slowed the decay of the depolarization-induced Ca(2+) transients. The remaining thapsigargin-insensitive decay was slowed further by inhibition of the plasma membrane Ca(2+)-ATPase (PMCA) and plasma membrane Na(+)/Ca(2+) exchanger (NCX) via alkalization of the bath solution, by adding lanthanum, or by substitution of Na(+) with Li(+). Mitochondrial Ca(2+) uptake contributed little to clearance in thapsigargin-pretreated cells. Together, the SERCA, PMCA, and NCX transport mechanisms accounted for 89 to 97% of clearance in normal solutions. We developed a quantitative model for the dynamic role of removal mechanisms over a wide range of [Ca(2+)](i). According to our model, 50 to 64% of initial Ca(2+) removal is via the SERCA pump, whereas the NCX contributes 21-30% of the extrusion at high [Ca(2+)](i), and the PMCA contributes 21-27% at low [Ca(2+)](i).
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Affiliation(s)
- Liangyi Chen
- Department of Physiology & Biophysics, School of Medicine, University of Washington, Seattle 98195-7290, USA.
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Lee WJ, Roberts-Thomson SJ, Holman NA, May FJ, Lehrbach GM, Monteith GR. Expression of plasma membrane calcium pump isoform mRNAs in breast cancer cell lines. Cell Signal 2002; 14:1015-22. [PMID: 12359307 DOI: 10.1016/s0898-6568(02)00049-9] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The plasma membrane Ca(2+) ATPase (PMCA) is an important regulator of free intracellular calcium, with dynamic regulation in the rat mammary gland during lactation. Recent studies suggest that Ca(2+) plays a role in cellular proliferation. To determine if PMCA expression is altered in tumorigenesis, we compared relative levels of PMCA1 mRNA. We found that the relative expression of PMCA1 mRNA is increased, by approximately 270% and 170%, in MCF-7 and MDA-MB-231 human breast cancer cell lines deprived of serum for 72 h, respectively, compared to the similarly treated MCF-10A human mammary gland epithelial cell line. Characterization of PMCA mRNA isoforms revealed that PMCA1b and PMCA4 mRNA are expressed in MCF-7, MDA-MB-231, SK-BR-3, ZR-75-1 and BT-483 breast cancer cell lines. We also detected PMCA2 mRNA expression in all the breast cancer cell lines examined. However, PMCA3 mRNA was only detected in BT-483 cells. Our results suggest that PMCA expression may be altered in breast cancer cell lines, suggesting altered Ca(2+) regulation in these cell lines. Our results also indicate that breast cancer cell lines can express mRNAs for a variety PMCA isoforms.
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Affiliation(s)
- Won Jae Lee
- School of Pharmacy, The University of Queensland, St Lucia, Brisbane, Queensland 4072, Australia
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Arredouani A, Guiot Y, Jonas JC, Liu LH, Nenquin M, Pertusa JA, Rahier J, Rolland JF, Shull GE, Stevens M, Wuytack F, Henquin JC, Gilon P. SERCA3 ablation does not impair insulin secretion but suggests distinct roles of different sarcoendoplasmic reticulum Ca(2+) pumps for Ca(2+) homeostasis in pancreatic beta-cells. Diabetes 2002; 51:3245-53. [PMID: 12401716 DOI: 10.2337/diabetes.51.11.3245] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Two sarcoendoplasmic reticulum Ca(2+)-ATPases, SERCA3 and SERCA2b, are expressed in pancreatic islets. Immunocytochemistry showed that SERCA3 is restricted to beta-cells in the mouse pancreas. Control and SERCA3-deficient mice were used to evaluate the role of SERCA3 in beta-cell cytosolic-free Ca(2+) concentration ([Ca(2+)](c)) regulation, insulin secretion, and glucose homeostasis. Basal [Ca(2+)](c) was not increased by SERCA3 ablation. Stimulation with glucose induced a transient drop in basal [Ca(2+)](c) that was suppressed by inhibition of all SERCAs with thapsigargin (TG) but unaffected by selective SERCA3 ablation. Ca(2+) mobilization by acetylcholine was normal in SERCA3-deficient beta-cells. In contrast, [Ca(2+)](c) oscillations resulting from intermittent glucose-stimulated Ca(2+) influx and [Ca(2+)](c) transients induced by pulses of high K(+) were similarly affected by SERCA3 ablation or TG pretreatment of control islets; their amplitude was increased and their slow descending phase suppressed. This suggests that, during the decay of each oscillation, the endoplasmic reticulum releases Ca(2+) that was pumped by SERCA3 during the upstroke phase. SERCA3 ablation increased the insulin response of islets to 15 mmol/l glucose. However, basal and postprandial plasma glucose and insulin concentrations in SERCA3-deficient mice were normal. In conclusion, SERCA2b, but not SERCA3, is involved in basal [Ca(2+)](c) regulation in beta-cells. SERCA3 becomes operative when [Ca(2+)](c) rises and is required for normal [Ca(2+)](c) oscillations in response to glucose. However, a lack of SERCA3 is insufficient in itself to alter glucose homeostasis or impair insulin secretion in mice.
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Affiliation(s)
- Abdelilah Arredouani
- Unité d'Endocrinologie et Métabolisme, University of Louvain Faculty of Medicine, Brussels, Belgium
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16
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Armbrecht HJ, Boltz MA, Hodam TL. Differences in intestinal calcium and phosphate transport between low and high bone density mice. Am J Physiol Gastrointest Liver Physiol 2002; 282:G130-6. [PMID: 11751166 DOI: 10.1152/ajpgi.00175.2001] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The purpose of this study was to determine whether there are differences in intestinal Ca and phosphate transport in mice having different peak bone densities. Intestinal transport was measured in C57BL/6 (C57, low bone density) and C3H/He (C3H, high bone density) female mice. Unidirectional (mucosal to serosal) transport of Ca was 58% higher in C3H compared with C57 mice, as measured by everted duodenal sacs. The capacity of the duodenal mucosa to take up Ca was also higher in the C3H mice. This uptake highly correlated with Ca transport across the intestine. 1,25-Dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], which stimulates intestinal Ca absorption, markedly stimulated unidirectional Ca transport and uptake to similar levels in both strains of mice. On the other hand, unidirectional phosphate transport in C3H mice was only 36% that of C57 mice. mRNA levels of the plasma membrane Ca pump were 90% higher in the duodenum of C3H mice. There was no difference between strains in duodenal calbindin or 24-hydroxylase mRNA levels. Regarding vitamin D metabolism, there was no difference in serum 1,25(OH)(2)D(3) levels or in renal 1alpha-hydroxylase mRNA levels. The combination of high intestinal Ca transport and low phosphate transport may contribute to the high peak bone density seen in the C3H relative to the C57 mouse.
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Affiliation(s)
- H J Armbrecht
- Geriatric Research, Education, and Clinical Center, St. Louis Veterans Administration Medical Center, Missouri 63125, USA.
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17
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Kamagate A, Herchuelz A, Bollen A, Van Eylen F. Expression of multiple plasma membrane Ca(2+)-ATPases in rat pancreatic islet cells. Cell Calcium 2000; 27:231-46. [PMID: 10858669 DOI: 10.1054/ceca.2000.0116] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
When stimulated by glucose, the pancreatic beta-cell displays large oscillations of intracellular free Ca2+ concentration ([Ca2+]i). To control [Ca2+]i, the beta-cell must be equipped with potent mechanisms for Ca2+ extrusion. We studied the expression of the plasma membrane Ca(2+)-ATPases (PMCA) in three insulin secreting preparations (a pure beta-cell preparation, RINm5F cells and pancreatic islet cells), using reverse-transcribed PCR, RNase protection assay and Western blotting. The four main isoforms, PMCA1, PMCA2, PMCA3 and PMCA4 were expressed in the three preparations. Six alternative splice mRNA variants, characterized at splice sites A, B and C were detected in the three preparations (rPMCA1xb, 2yb, 2wb, 3za, 3zc, 4xb), plus two additional variants in pancreatic islet cells (PMCA4za, 1xkb). The latter variant corresponded to a novel variant of rat PMCA1 gene lacking the exon coding for the 10th transmembrane segment, at splice site B. At the mRNA and protein level, five variants predominated (1xb, 2wb, 3za, 3zc, 4xb), whilst one additional isoform (4za), predominated at the protein level only. This provides the first evidence for the presence of PMCA2 and PMCA3 isoforms at the protein level in non-neuronal tissue. Hence, the pancreatic beta-cell is equipped with multiple PMCA isoforms with possible differential regulation, providing a full range of PMCAs for [Ca2+]i regulation.
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Affiliation(s)
- A Kamagate
- Laboratory of Pharmacology, Brussels Free University School of Medicine, Belgium
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18
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Reinhardt TA, Horst RL. Ca2+-ATPases and their expression in the mammary gland of pregnant and lactating rats. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:C796-802. [PMID: 10199809 DOI: 10.1152/ajpcell.1999.276.4.c796] [Citation(s) in RCA: 153] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The transcellular Ca2+ fluxes required for milk production must be rigorously regulated to maintain the low cytosolic Ca2+ concentrations critical to cell function. Ca2+-ATPases play a critical role in the maintenance of this cellular Ca2+ homeostasis. Using RT-PCR and sequencing, we identified six Ca2+ pumps in lactating mammary tissue. Three plasma membrane Ca2+-ATPases (PMCAs) were found (PMCA1b, PMCA2b, and PMCA4b). Two sarco (endo)plasmic reticulum Ca2+-ATPases (SERCAs) were identified (SERCA2 and SERCA3), and the rat homologue to the yeast Golgi Ca2+-ATPase RS-10 was also found. The pattern of mRNA expression of each of these pumps was examined in rat mammary tissue from the 7th day of pregnancy to the 21st day of lactation. Northern blots revealed increased mRNA expression for all Ca2+ pumps by the 14th day of lactation, and transcripts continued to increase through the 18th day of lactation. PMCA1b, PMCA4b, SERCA2, and SERCA3 showed the lowest levels of expression. RS-10 transcripts were more abundant than SERCA2, SERCA3, PMCA1b, and PMCA4b. RS-10 was the only pump to increase in expression before parturition. PMCA2b was the most abundant transcript found in lactating mammary tissue. At peak lactation, expression of PMCA2b approached that of actin. The high expression, high affinity for Ca2+, and high activity at low calmodulin concentrations exhibited by PMCA2b suggest that it is uniquely suited for maintenance of Ca2+ homeostasis in the lactating mammary gland. The pattern of expression and abundance of RS-10 suggest that it is a candidate for the Golgi Ca2+-ATPase shown to be important in maintaining the Golgi Ca2+ concentration required for casein synthesis and micelle formation.
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Affiliation(s)
- T A Reinhardt
- Metabolic Diseases and Immunology Research Unit, National Animal Disease Center, Agricultural Research Service, United States Department of Agriculture, Ames, Iowa 50010, USA.
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19
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Niki I, Hidaka H. Roles of intracellular Ca2+ receptors in the pancreatic beta-cell in insulin secretion. Mol Cell Biochem 1999; 190:119-24. [PMID: 10098978 DOI: 10.1023/a:1006997822987] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Ca2+ is the central second messenger in the regulation of insulin release from the pancreatic beta-cell; and intracellular Ca2+ -binding proteins, classified into two groups, the EF hand proteins and the Ca2+/phospholipid binding proteins, are considered to mediate Ca2+ signaling. A number of Ca binding proteins have been suggested to participate in the secretory machinery in the beta-cell. Calmodulin, the ubiquitous EF hand protein, is the predominant intracellular Ca2+ receptor that modulates insulin release via the multiplicity of its binding to target proteins including protein kinases. Other Ca binding proteins such as calcyclin and the Ca2+/phospholipid binding proteins may also be suggested to be involved. Ca2+ influx from the extracellular space appears to be responsible for exocytosis of insulin via Ca2+ -dependent protein/protein interactions. On the other hand, intracellular Ca2+ mobilization resulting in secretory granule movement may be controlled by Ca2+/calmodulin-dependent protein phosphorylation. Thus, Ca2+ exerts versatile effects on the secretory cascade via binding to specific binding proteins in the pancreactic beta-cells.
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Affiliation(s)
- I Niki
- Department of Pharmacology, Nagoya University School of Medicine, Japan
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20
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Monteith GR, Wanigasekara Y, Roufogalis BD. The plasma membrane calcium pump, its role and regulation: new complexities and possibilities. J Pharmacol Toxicol Methods 1998; 40:183-90. [PMID: 10465152 DOI: 10.1016/s1056-8719(99)00004-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Significant progress has been achieved in elucidating the role of the plasma membrane Ca2(+)-ATPase in cellular Ca2+ homeostasis and physiology since the enzyme was first purified and physiology since the enzyme was first purified and cloned a number of years ago. The simple notion that the PM Ca2(+)-ATPase controls resting levels of [Ca2+]CYT has been challenged by the complexity arising from the finding of four major isoforms and splice variants of the Ca2+ pump, and the finding that these are differentially localized in various organs and subcellular regions. Furthermore, the isoforms exhibit differential sensitivities to Ca2+, calmodulin, ATP, and kinase-mediated phosphorylation. The latter pathways of regulation can give rise to activation or inhibition of the Ca2+ pump activity, depending on the kinase and the particular Ca2+ pump isoform. Significant progress is being made in elucidating subtle and more profound roles of the PM Ca2(+)-ATPase in the control of cellular function. Further understanding of these roles awaits new studies in both transfected cells and intact organelles, a process that will be greatly aided by the development of new and selective Ca2+ pump inhibitors.
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Affiliation(s)
- G R Monteith
- School of Pharmacy, University of Queensland, St. Lucia, Australia
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21
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Caride AJ, Chini EN, Homma S, Penniston JT, Dousa TP. mRNA encoding four isoforms of the plasma membrane calcium pump and their variants in rat kidney and nephron segments. THE JOURNAL OF LABORATORY AND CLINICAL MEDICINE 1998; 132:149-56. [PMID: 9708576 DOI: 10.1016/s0022-2143(98)90010-5] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
To survey the presence of the four different isoforms of the plasma membrane calcium pump (PMCA) and their alternative splicing variants in the rat kidney, three major zones (cortex, outer medulla, and inner medulla) were macrodissected and probed for the presence of mRNA encoding these isoforms and their variants at the splicing site C by using reverse transcription-polymerase chain reaction (RT-PCR). Both the cortex and the outer medulla showed PMCA 1b, 2b, 3(a and c), and 4b. Semiquantitative comparisons indicated that isoform 2b is more abundant in the cortex than in the outer medulla and conversely, that isoform 3 (a and c) is more abundant in the outer medulla than in the cortex. The inner medulla showed only mRNA for isoforms 1b and 4b. The nephron segments present in the cortex and outer medulla were microdissected and analyzed by RT-PCR. Isoforms 1b, 2b, and 4b were found in all nephron segments but were found more frequently in tubular segments with high rates of Ca2+ reabsorption, suggesting that these isoforms may be involved in transepithelial transport. On the other hand, mRNA encoding isoform 3 (a and c) was most abundant in descending thin limb of Henle but was detected also in glomeruli and cortical thin ascending limb. Its distinct localization suggests that this isoform might have another function, such as in intracellular signalling.
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Affiliation(s)
- A J Caride
- Department of Biochemistry and Molecular Biology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA
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22
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Filoteo AG, Elwess NL, Enyedi A, Caride A, Aung HH, Penniston JT. Plasma membrane Ca2+ pump in rat brain. Patterns of alternative splices seen by isoform-specific antibodies. J Biol Chem 1997; 272:23741-7. [PMID: 9295318 DOI: 10.1074/jbc.272.38.23741] [Citation(s) in RCA: 122] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The expression at the protein level of plasma membrane calcium pump (PMCA) isoforms in rat brain was detected by new antibodies that distinguished the four gene products and their alternatively spliced variants. All four gene products were distributed throughout hippocampus, cortex, and cerebellum, but the alternate splices showed more distinct distribution patterns. The b splice of isoform 1 was not detectable in any of the brain regions, which makes it unlikely that this isoform performs an essential housekeeping role as is frequently proposed. The b splices of isoforms 3 and 4, although expressed in all three regions, showed evidence of proteolysis, which removed a portion of the carboxyl terminus. In contrast, isoform 2b retained its full length, indicating that PMCA2b is more resistant to proteolysis than the other b forms. Whereas substantial amounts of isoforms 1a, 2a, and 3a were expressed in all regions, 4a was found only in frontal cortex. The distinct patterns of expression of the PMCA isoforms in brain suggest that some of them play a special role in intracellular Ca regulation.
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Affiliation(s)
- A G Filoteo
- Department of Biochemistry and Molecular Biology, Mayo Foundation, Rochester, Minnesota 55905, USA
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23
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White KE, Gesek FA, Nesbitt T, Drezner MK, Friedman PA. Molecular dissection of Ca2+ efflux in immortalized proximal tubule cells. J Gen Physiol 1997; 109:217-28. [PMID: 9041450 PMCID: PMC2220068 DOI: 10.1085/jgp.109.2.217] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/1996] [Accepted: 11/14/1996] [Indexed: 02/03/2023] Open
Abstract
Plasma membrane Ca(2+)-ATPase (PMCA) and the Na+/Ca2+ exchanger participate in regulating cell function by maintaining proper intracellular Ca2+ concentrations ([Ca2+]i). In renal epithelial cells these proteins have been additionally implicated in cellular calcium absorption. The purpose of the present studies was to determine the Ca2+ extrusion mechanisms in cells derived from the proximal tubule. Homology-based RT-PCR was used to amplify PMCA transcripts from RNA isolated from mouse cell lines originating from the S1, S2, and S3 proximal tubule segments. S1, S2, and S3 cells exhibited only PMCA1 and PMCA4 products. PCR product identity was confirmed by sequence analysis. Northern analysis of proximal tubule cell RNAs revealed appropriate transcripts of 7.5 and 5.5 kb for PMCA1 and 8.5 and 7.5 kb for PMCA4, but were negative for PMCA2 and PMCA3. Western analysis with a monoclonal antibody to PMCA showed that all proximal cell lines expressed a reacting plasma membrane protein of 140 kD, the reported PMCA molecular mas. Na+/Ca2+ exchanger (NCX1) mRNA expression, analyzed by RT-PCR, protein expression by Western analysis, and functional exchange activity were uniformly absent from all proximal tubule cell lines. These observations support the idea that immortalized cells derived from the proximal tubule express PMCA1 and PMCA4, which may serve as the primary mechanism of cellular Ca2+ efflux.
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Affiliation(s)
- K E White
- Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA
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24
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Váradi A, Molnár E, Ostenson CG, Ashcroft SJ. Isoforms of endoplasmic reticulum Ca(2+)-ATPase are differentially expressed in normal and diabetic islets of Langerhans. Biochem J 1996; 319 ( Pt 2):521-7. [PMID: 8912690 PMCID: PMC1217799 DOI: 10.1042/bj3190521] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Glucose-dependent sequestration of Ca2+ into endoplasmic reticulum and its subsequent release play an important role in the control of intracellular Ca2+ concentration, which regulates insulin secretion in pancreatic beta-cells. The active uptake of cytosolic Ca2+ into endoplasmic reticulum is mediated by sarco-(endo)plasmic reticulum Ca(2+)-ATPases (SERCAs). We found, using RT-PCR with isoform-specific primers, that SERCA 2 and SERCA 3 mRNAs are co-expressed in human and rat islets of Langerhans and in the RINm5F beta-cell line. Immunochemical analysis also revealed the existence of two SERCA proteins with molecular masses of 110 and 115 kDa in beta-cell membranes. The 115 kDa protein was identified as SERCA 2b by its reaction with an isoform-specific antibody and the 110 kDa protein most probably corresponds to SERCA 3. The presence of two functionally different SERCA isoforms raises the possibility that they are located in distinct Ca2+ stores. There is evidence that altered Ca2+ handling in the beta-cell may contribute to the decreased insulin secretion seen in non-insulin dependent diabetes mellitus (NIDDM). We therefore investigated SERCA 2 and SERCA 3 mRNA expression by quantitative RT-PCR in islets prepared from Goto-Kakizaki (GK) rats, a non-obese spontaneous model of NIDDM. We found a significant reduction (about 68%) in SERCA 3 isoform expression. Since SERCA 2 expression was not significantly reduced, these genes are independently regulated and probably play distinct roles in islets of Langerhans. The marked decrease of SERCA 3 expression may constitute a defect in Ca2+ signalling in GK rat islets which could be a component of NIDDM.
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Affiliation(s)
- A Váradi
- University of Oxford, Nuffield Department of Clinical Biochemistry, John Radcliffe Hospital Headington, UK
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