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Chen AW, Biggar K, Nygard K, Singal S, Zhao T, Li C, Nathanielsz PW, Jansson T, Gupta MB. IGFBP-1 hyperphosphorylation in response to nutrient deprivation is mediated by activation of protein kinase Cα (PKCα). Mol Cell Endocrinol 2021; 536:111400. [PMID: 34314739 PMCID: PMC8634829 DOI: 10.1016/j.mce.2021.111400] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/20/2021] [Revised: 07/13/2021] [Accepted: 07/19/2021] [Indexed: 02/06/2023]
Abstract
Fetal growth restriction (FGR) is associated with decreased nutrient availability and reduced insulin-line growth factor (IGF)-I bioavailability via increased IGF binding protein (IGFBP)-1 phosphorylation. While protein kinase C (PKC) is implicated in IGFBP-1 hyperphosphorylation in nutrient deprivation, the mechanisms remain unclear. We hypothesised that the interaction of PKCα with protein kinase CK2β and activation of PKCα under leucine deprivation (L0) mediate fetal hepatic IGFBP-1 hyperphosphorylation. Parallel Reaction Monitoring Mass Spectrometry (PRM-MS) followed by PKCα knockdown demonstrated the PKCα isoform interacts with IGFBP-1 and CK2β under L0. Pharmacological PKCα activation with phorbol 12-myristate 13-acetate (PMA) increased whereas inhibition with bisindolylmaleimide II (Bis II) decreased IGFBP-1 phosphorylation (Ser101/119/169, Ser98 + 101 and Ser169 + 174), respectively. Furthermore, PMA mimicked L0-induced PKCα translocation and IGFBP-1 expression. PKCα expression was increased in baboon fetal liver in FGR, providing biological relevance in vivo. In summary, we report a novel nutrient-sensitive mechanism for PKCα in mediating IGFBP-1 hyperphosphorylation in FGR.
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Affiliation(s)
- Allan W Chen
- Department of Biochemistry, University of Western Ontario, London, ON, Canada
| | - Kyle Biggar
- Institute of Biochemistry, Carleton University, Ottawa, ON, Canada
| | - Karen Nygard
- Biotron Integrated Microscopy Facility, University of Western Ontario, London, ON, Canada
| | - Sahil Singal
- Department of Biochemistry, University of Western Ontario, London, ON, Canada
| | - Tiffany Zhao
- Department of Biochemistry, University of Western Ontario, London, ON, Canada
| | - Cun Li
- University of Wyoming, Laramie, WY, USA; Southwest National Primate Research Center, San Antonio, TX, USA
| | - Peter W Nathanielsz
- University of Wyoming, Laramie, WY, USA; Southwest National Primate Research Center, San Antonio, TX, USA
| | - Thomas Jansson
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Madhulika B Gupta
- Department of Biochemistry, University of Western Ontario, London, ON, Canada; Department of Pediatrics, University of Western Ontario, London, ON, Canada; Children's Health Research Institute, London, ON, Canada.
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Lin YW, Weng XF, Huang BL, Guo HP, Xu YW, Peng YH. IGFBP-1 in cancer: expression, molecular mechanisms, and potential clinical implications. Am J Transl Res 2021; 13:813-832. [PMID: 33841624 PMCID: PMC8014352 DOI: pmid/33841624] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Accepted: 12/09/2020] [Indexed: 02/05/2023]
Abstract
Insulin-like growth factor binding protein-1 (IGFBP-1) belongs to the insulin-like growth factor (IGF) system, which plays an indispensable role in normal growth and development, and in the pathophysiology of various tumors. IGFBP-1 has been shown to be associated with the risk of various tumors, and has a vital function in regulating tumor behaviors such as proliferation, migration, invasion and adhesion through different molecular mechanisms. The biological actions of IGFBP-1 in cancer are found to be related to its phosphorylation state, and the IGF-dependent and -independent mechanisms. In this review, we provided an overview of IGFBP-1 in normal physiology, and its aberrantly expression and the underlying molecular mechanisms in a range of common tumors, as well as discussed the potential clinical implications of IGFBP-1 as diagnostic or prognostic biomarkers in cancer.
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Affiliation(s)
- Yi-Wei Lin
- Department of Clinical Laboratory Medicine, The Cancer Hospital of Shantou University Medical CollegeShantou, Guangdong, People’s Republic of China
- Precision Medicine Research Center, Shantou University Medical CollegeShantou, Guangdong, People’s Republic of China
| | - Xue-Fen Weng
- Department of Clinical Laboratory Medicine, The Cancer Hospital of Shantou University Medical CollegeShantou, Guangdong, People’s Republic of China
- Precision Medicine Research Center, Shantou University Medical CollegeShantou, Guangdong, People’s Republic of China
| | - Bin-Liang Huang
- Department of Clinical Laboratory Medicine, The Cancer Hospital of Shantou University Medical CollegeShantou, Guangdong, People’s Republic of China
- Precision Medicine Research Center, Shantou University Medical CollegeShantou, Guangdong, People’s Republic of China
| | - Hai-Peng Guo
- Department of Head and Neck Surgery, The Cancer Hospital of Shantou University Medical CollegeShantou 515041, People’s Republic of China
| | - Yi-Wei Xu
- Department of Clinical Laboratory Medicine, The Cancer Hospital of Shantou University Medical CollegeShantou, Guangdong, People’s Republic of China
- Precision Medicine Research Center, Shantou University Medical CollegeShantou, Guangdong, People’s Republic of China
| | - Yu-Hui Peng
- Department of Clinical Laboratory Medicine, The Cancer Hospital of Shantou University Medical CollegeShantou, Guangdong, People’s Republic of China
- Precision Medicine Research Center, Shantou University Medical CollegeShantou, Guangdong, People’s Republic of China
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Vallikkannu N, Lam WK, Omar SZ, Tan PC. Insulin-like growth factor binding protein 1, Bishop score, and sonographic cervical length: tolerability and prediction of vaginal birth and vaginal birth within 24 hours following labour induction in nulliparous women. BJOG 2016; 124:1274-1283. [DOI: 10.1111/1471-0528.14175] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/15/2016] [Indexed: 11/27/2022]
Affiliation(s)
- N Vallikkannu
- Department of Obstetrics and Gynaecology; Faculty of Medicine; University of Malaya; Kuala Lumpur Malaysia
| | - WK Lam
- Department of Obstetrics and Gynaecology; Faculty of Medicine; University of Malaya; Kuala Lumpur Malaysia
| | - SZ Omar
- Department of Obstetrics and Gynaecology; Faculty of Medicine; University of Malaya; Kuala Lumpur Malaysia
| | - PC Tan
- Department of Obstetrics and Gynaecology; Faculty of Medicine; University of Malaya; Kuala Lumpur Malaysia
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Malkani N, Jansson T, Gupta MB. IGFBP-1 hyperphosphorylation in response to leucine deprivation is mediated by the AAR pathway. Mol Cell Endocrinol 2015; 412:182-95. [PMID: 25957086 PMCID: PMC5563670 DOI: 10.1016/j.mce.2015.04.031] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 04/28/2015] [Accepted: 04/30/2015] [Indexed: 02/07/2023]
Abstract
Insulin-like growth factor-1 (IGF-I) is the key regulator of fetal growth. IGF-I bioavailability is markedly diminished by IGF binding protein-1 (IGFBP-1) phosphorylation. Leucine deprivation strongly induces IGFBP-1 hyperphosphorylation, and plays an important role in fetal growth restriction (FGR). FGR is characterized by decreased amino acid availability, which activates the amino acid response (AAR) and inhibits the mechanistic target of rapamycin (mTOR) pathway. We investigated the role of AAR and mTOR in mediating IGFBP-1 secretion and phosphorylation in HepG2 cells in leucine deprivation. mTOR inhibition (rapamycin or raptor + rictor siRNA), or activation (DEPTOR siRNA) demonstrated a role of mTOR in leucine deprivation-induced IGFBP-1 secretion but not phosphorylation. When the AAR was blocked (U0126, or ERK/GCN2 siRNA), both IGFBP-1 secretion and hyperphosphorylation (pSer101/pSer119/pSer169) due to leucine deprivation were prevented. CK2 inhibition by TBB also attenuated IGFBP-1 phosphorylation in leucine deprivation. These results suggest that the AAR and mTOR independently regulate IGFBP-1 secretion and phosphorylation in response to decreased amino acid availability.
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Affiliation(s)
- Niyati Malkani
- Department of Biochemistry, University of Western Ontario, London, Ontario N6A 5C1, Canada
| | - Thomas Jansson
- Department of Obstetrics & Gynecology, University of Colorado, Anschutz Medical Campus, Aurora, Colorado, USA
| | - Madhulika B Gupta
- Department of Biochemistry, University of Western Ontario, London, Ontario N6A 5C1, Canada; Department of Pediatrics, University of Western Ontario, London, Canada; Children's Health Research Institute, University of Western Ontario, London, ON, Canada.
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Heng YJ, Liong S, Permezel M, Rice GE, Di Quinzio MKW, Georgiou HM. Human cervicovaginal fluid biomarkers to predict term and preterm labor. Front Physiol 2015; 6:151. [PMID: 26029118 PMCID: PMC4429550 DOI: 10.3389/fphys.2015.00151] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Accepted: 04/27/2015] [Indexed: 01/06/2023] Open
Abstract
Preterm birth (PTB; birth before 37 completed weeks of gestation) remains the major cause of neonatal morbidity and mortality. The current generation of biomarkers predictive of PTB have limited utility. In pregnancy, the human cervicovaginal fluid (CVF) proteome is a reflection of the local biochemical milieu and is influenced by the physical changes occurring in the vagina, cervix and adjacent overlying fetal membranes. Term and preterm labor (PTL) share common pathways of cervical ripening, myometrial activation and fetal membranes rupture leading to birth. We therefore hypothesize that CVF biomarkers predictive of labor may be similar in both the term and preterm labor setting. In this review, we summarize some of the existing published literature as well as our team's breadth of work utilizing the CVF for the discovery and validation of putative CVF biomarkers predictive of human labor. Our team established an efficient method for collecting serial CVF samples for optimal 2-dimensional gel electrophoresis resolution and analysis. We first embarked on CVF biomarker discovery for the prediction of spontaneous onset of term labor using 2D-electrophoresis and solution array multiple analyte profiling. 2D-electrophoretic analyses were subsequently performed on CVF samples associated with PTB. Several proteins have been successfully validated and demonstrate that these biomarkers are associated with term and PTL and may be predictive of both term and PTL. In addition, the measurement of these putative biomarkers was found to be robust to the influences of vaginal microflora and/or semen. The future development of a multiple biomarker bed-side test would help improve the prediction of PTB and the clinical management of patients.
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Affiliation(s)
- Yujing J Heng
- Department of Pathology, Harvard Medical School and Beth Israel Deaconess Medical Center Boston, MA, USA
| | - Stella Liong
- Department of Obstetrics and Gynaecology, University of Melbourne Melbourne, VIC, Australia ; Mercy Perinatal Research Centre, Mercy Hospital for Women Heidelberg, VIC, Australia
| | - Michael Permezel
- Department of Obstetrics and Gynaecology, University of Melbourne Melbourne, VIC, Australia ; Mercy Perinatal Research Centre, Mercy Hospital for Women Heidelberg, VIC, Australia
| | - Gregory E Rice
- University of Queensland Centre for Clinical Research Herston, QLD, Australia
| | - Megan K W Di Quinzio
- Department of Obstetrics and Gynaecology, University of Melbourne Melbourne, VIC, Australia ; Mercy Perinatal Research Centre, Mercy Hospital for Women Heidelberg, VIC, Australia
| | - Harry M Georgiou
- Department of Obstetrics and Gynaecology, University of Melbourne Melbourne, VIC, Australia ; Mercy Perinatal Research Centre, Mercy Hospital for Women Heidelberg, VIC, Australia
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The role and regulation of IGFBP-1 phosphorylation in fetal growth restriction. J Cell Commun Signal 2015; 9:111-23. [PMID: 25682045 DOI: 10.1007/s12079-015-0266-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2014] [Accepted: 01/21/2015] [Indexed: 12/18/2022] Open
Abstract
Fetal growth restriction (FGR) increases the risk of perinatal complications and predisposes the infant to developing metabolic, cardiovascular, and neurological diseases in childhood and adulthood. The pathophysiology underlying FGR remains poorly understood and there is no specific treatment available. Biomarkers for early detection are also lacking. The insulin-like growth factor (IGF) system is an important regulator of fetal growth. IGF-I is the primary regulator of fetal growth, and fetal circulating levels of IGF-I are decreased in FGR. IGF-I activity is influenced by a family of IGF binding proteins (IGFBPs), which bind to IGF-I and decrease its bioavailability. During fetal development the predominant IGF-I binding protein in fetal circulation is IGFBP-1, which is primarily secreted by the fetal liver. IGFBP-1 binds IGF-I and thereby inhibits its bioactivity. Fetal circulating levels of IGF-I are decreased and concentrations of IGFBP-1 are increased in FGR. Phosphorylation of human IGFBP-1 at specific sites markedly increases its binding affinity for IGF-I, further limiting IGF-I bioactivity. Recent experimental evidence suggests that IGFBP-1 phosphorylation is markedly increased in the circulation of FGR fetuses suggesting an important role of IGFBP-1 phosphorylation in the regulation of fetal growth. Understanding of the significance of site-specific IGFBP-1 phosphorylation and how it is regulated to contribute to fetal growth will be an important step in designing strategies for preventing, managing, and/or treating FGR. Furthermore, IGFBP-1 hyperphosphorylation at unique sites may serve as a valuable biomarker for FGR.
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Phosphorylated IGFBP-1 in predicting successful vaginal delivery in post-term pregnancy. Arch Gynecol Obstet 2014; 292:45-52. [PMID: 25524535 PMCID: PMC4435902 DOI: 10.1007/s00404-014-3577-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Accepted: 12/03/2014] [Indexed: 11/15/2022]
Abstract
Purpose To estimate whether phosphorylated IGFBP-1 (phIGFBP-1) in cervical secretion in term and post-term pregnancies can predict spontaneous onset of labor or vaginal delivery. Methods A prospective cohort study of 167 women in singleton term and post-term pregnancies, was conducted at 1st Department of Obstetrics and Gynecology, Medical University of Warsaw, between 2013 and 2014. phIGFBP-1 test (Actim Partus Medix Biochemica), ultrasound cervix assessment and Bishop score were analyzed in the study group. Spontaneous onset of labor was the primary and vaginal delivery was the secondary outcome. Results In 32.5 % of patients, spontaneous uterine contractions appeared. 67.5 % of women delivered vaginally, 32.5 % had cesarean section. phIGFBP-1 test predicted spontaneous onset of labor (sensitivity 0.69, specificity of 0.42) and successful vaginal delivery (0.67, 0.48). In the prediction of spontaneous delivery onset ultrasound cervical assessment and phIBFBP-1 had comparable sensitivity and in the prediction of successful vaginal birth all three tests had comparable sensitivity. The time from preinduction to spontaneous onset of delivery was significantly shorter in women with positive phIGFBP-1 test (13.65 ± 6.7 vs 20.75 ± 2.6 h; p = 0.006). Conclusion A test for phIGFBP1 presence might be an additional tool for predicting both spontaneous onset of labor and successful vaginal delivery in post-term pregnancies.
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Tsunawaki T, Sakai K, Momomura M, Wachi Y, Matsuzawa Y, Iwashita M. Hypoxia alters phosphorylation status of insulin-like growth factor (IGF)-binding protein-1 and attenuates biological activities of IGF-I in HepG2 cell cultures. J Obstet Gynaecol Res 2013; 39:1367-73. [DOI: 10.1111/jog.12078] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Accepted: 01/23/2013] [Indexed: 11/28/2022]
Affiliation(s)
- Tomonori Tsunawaki
- Department of Obstetrics and Gynecology; School of Medicine; Kyorin University; Tokyo Japan
| | - Keiji Sakai
- Department of Obstetrics and Gynecology; School of Medicine; Kyorin University; Tokyo Japan
| | - Mai Momomura
- Department of Obstetrics and Gynecology; School of Medicine; Kyorin University; Tokyo Japan
| | - Yuichi Wachi
- Department of Obstetrics and Gynecology; School of Medicine; Kyorin University; Tokyo Japan
| | - Yukiko Matsuzawa
- Department of Obstetrics and Gynecology; School of Medicine; Kyorin University; Tokyo Japan
| | - Mitsutoshi Iwashita
- Department of Obstetrics and Gynecology; School of Medicine; Kyorin University; Tokyo Japan
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Abu Shehab M, Iosef C, Wildgruber R, Sardana G, Gupta MB. Phosphorylation of IGFBP-1 at discrete sites elicits variable effects on IGF-I receptor autophosphorylation. Endocrinology 2013; 154:1130-43. [PMID: 23354097 DOI: 10.1210/en.2012-1962] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We previously demonstrated that hypoxia and leucine deprivation cause hyperphosphorylation of IGF-binding protein-1 (IGFBP-1) at discrete sites that markedly enhanced IGF-I affinity and inhibited IGF-I-stimulated cell growth. In this study we investigated the functional role of these phosphorylation sites using mutagenesis. We created three IGFBP-1 mutants in which individual serine (S119/S169/S98) residues were substituted with alanine and S101A was recreated for comparison. The wild-type (WT) and mutant IGFBP-1 were expressed in Chinese hamster ovary cells and IGFBP-1 in cell media was isolated using isoelectric-focusing-free-flow electrophoresis. BIACore analysis indicated that the changes in IGF-I affinity for S98A and S169A were moderate, whereas S119A greatly reduced the affinity of IGFBP-1 for IGF-I (100-fold, P < .0001). Similar results were obtained with S101A. The IGF-I affinity changes of the mutants were reflected in their ability to inhibit IGF-I-induced receptor autophosphorylation. Employing receptor-stimulation assay using IGF-IR-overexpressing P6 cells, we found that WT-IGFBP-1 inhibited IGF-IRβ autophosphorylation (~2-fold, P < .001), possibly attributable to sequestration of IGF-I. Relative to WT, S98A and S169A mutants did not inhibit receptor autophosphorylation. S119A, on the other hand, greatly stimulated the receptor (2.3-fold, P < .05). The data with S101A matched S119A. In summary, we show that phosphorylation at S98 and S169 resulted in milder changes in IGF-I action; nonetheless most dramatic inhibitory effects on the biological activity of IGF-I were due to IGFBP-1 phosphorylation at S119. Our results provide novel demonstration that IGFBP-1 phosphorylation at S119 can enhance affinity for IGF-I possibly through stabilization of the IGF-IGFBP-1 complex. These data also propose that the synergistic interaction of distinct phosphorylation sites may be important in eliciting more pronounced effects on IGF-I affinity that needs further investigation.
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10
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Abstract
AbstractInsulin-like growth factors (IGFs) and their binding proteins play an essential role in regulating animal growth and metabolism. The initial portion of the current review focuses on the physiological effects of the IGFs and delineates their role as regulators of animal growth and metabolism. The role of IGFs as mediators of growth hormone effects, as insulin-like metabolic regulators and as foetal growth regulators is discussed. The remainder of the review is devoted to the IGF binding proteins, their modulation of IGF action and their role in foetal and postnatal regulation of growth.
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Brik M, Hernández AIM, Pedraz CC, Perales A. Phosphorylated insulin-like growth factor binding protein-1 and cervical measurement in women with threatening preterm birth. Acta Obstet Gynecol Scand 2010; 89:268-74. [PMID: 19961279 DOI: 10.3109/00016340903443668] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE To assess the efficacy of the cervical phosphorylated insulin-like growth factor binding protein-1 (pIGFBP-1) in combination with cervical length measurement for the prediction of preterm delivery. DESIGN Observational prospective study. SETTING University Hospital, Spain. SAMPLE A total of 276 women between 24 and 34 weeks gestational age complaining of uterine contractions and intact membranes. METHODS Transvaginal scan to assess cervical length and cervical swabs for pIGFBP-1 detection. MAIN OUTCOME MEASURES Prevalence of preterm delivery within 48 hours and 7 days, delivery at < 32, < 34 weeks, admission-to-delivery interval by cervical length and the presence of pIGFBP-1. Results. The prevalence of preterm delivery at < 34 weeks was 14.1% (39/276) and 7.6% (21/276) at < 32 weeks. Cervical pIGFBP-1 was positive in 38.7% (107/276), whereas cervical length < 15 mm was present in 7.2% (20/276) and was > 30 mm for 64.8% (179/276) of the women. The presence of a positive pIGFBP-1 appeared useful for prediction of delivery before 32 (likelihood ratio (LR) = 2.21, confidence interval (CI): 1.63-3.00) and 34 weeks (LR = 1.76, CI: 1.25-2.41), respectively. Receiver operating characteristic curves were significant for cervical length and pIGFBP-1 for prediction of delivery at < 34 weeks, < 32 weeks, < 48 hours and < 7 days. Combining pIGFBP-1 and cervical length had a median interval that was shorter when both were positive as compared to only one positive or both negative, but the CIs overlapped. CONCLUSIONS Both cervical length measurement and pIGFBP-1 are useful for prediction of spontaneous preterm delivery. A pIGFBP-1 positive result associated with cervical length does not improve preterm delivery prediction rates.
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Affiliation(s)
- Maia Brik
- Obstetrics Department, University Hospital La Fe, 3(a) planta, Av. Campanar 21, 46009 Valencia, Spain.
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12
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Nissum M, Abu Shehab M, Sukop U, Khosravi JM, Wildgruber R, Eckerskorn C, Han VKM, Gupta MB. Functional and complementary phosphorylation state attributes of human insulin-like growth factor-binding protein-1 (IGFBP-1) isoforms resolved by free flow electrophoresis. Mol Cell Proteomics 2009; 8:1424-35. [PMID: 19193607 DOI: 10.1074/mcp.m800571-mcp200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Fetal growth restriction (FGR) is a common disorder in which a fetus is unable to achieve its genetically determined potential size. High concentrations of insulin-like growth factor-binding protein-1 (IGFBP-1) have been associated with FGR. Phosphorylation of IGFBP-1 is a mechanism by which insulin-like growth factor-I (IGF-I) bioavailability can be modulated in FGR. In this study a novel strategy was designed to determine a link between IGF-I affinity and the concomitant phosphorylation state characteristics of IGFBP-1 phosphoisoforms. Using free flow electrophoresis (FFE), multiple IGFBP-1 phosphoisoforms in amniotic fluid were resolved within pH 4.43-5.09. The binding of IGFBP-1 for IGF-I in each FFE fraction was determined with BIAcore biosensor analysis. The IGF-I affinity (K(D)) for different IGFBP-1 isoforms ranged between 1.12e-08 and 4.59e-07. LC-MS/MS characterization revealed four phosphorylation sites, Ser(P)(98), Ser(P)(101), Ser(P)(119), and Ser(P)(169), of which Ser(P)(98) was new. Although the IGF-I binding affinity for IGFBP-1 phosphoisoforms across the FFE fractions did not correlate with phosphopeptide intensities for Ser(P)(101), Ser(P)(98), and Ser(P)(169) sites, a clear association was recorded with Ser(P)(119). Our data demonstrate that phosphorylation at Ser(119) plays a significant role in modulating affinity of IGFBP-1 for IGF-I. In addition, an altered profile of IGFBP-1 phosphoisoforms was revealed between FGR and healthy pregnancies that may result from potential site-specific phosphorylation. This study provides a strong basis for use of this novel approach in establishing the linkage between phosphorylation of IGFBP-1 and FGR. This overall strategy will also be broadly applicable to other phosphoproteins with clinical and functional significance.
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Affiliation(s)
- Mikkel Nissum
- BD Diagnostics, Am Klopferspitz 19a, 82152 Planegg, Germany
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Tanir HM, Sener T, Yildiz Z. Cervical phosphorylated insulin-like growth factor binding proteın-1 for the prediction of preterm delivery in symptomatic cases with intact membranes. J Obstet Gynaecol Res 2009; 35:66-72. [DOI: 10.1111/j.1447-0756.2008.00833.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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14
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Khosravi J, Krishna RG, Bodani U, Diamandi A, Khaja N, Kalra B, Kumar A. Immunoassay of serine-phosphorylated isoform of insulin-like growth factor (IGF) binding protein (IGFBP)-1. Clin Biochem 2006; 40:86-93. [PMID: 17005169 DOI: 10.1016/j.clinbiochem.2006.07.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2006] [Revised: 06/29/2006] [Accepted: 07/21/2006] [Indexed: 11/17/2022]
Abstract
OBJECTIVES Development of an ELISA for phosphorylated isoform of IGFBP-1. Serine phosphorylation is an important regulator of IGFBP-1 bioactivity, but specific immunoassays for its measurement are currently lacking. DESIGN AND METHODS Assay design was based on a novel approach of first capturing the phosphorylated and non-phosphorylated IGFBP-1 by an anti-IGFBP-1 antibody and then selectively detecting the phosphorylated form by an anti-phosphoserine antibody. Method development involved pair-wise evaluation of the candidate antibodies and determinations of analytical performance and specificity. Specificity was monitored by reactivity with dephosphorylated IGFBP-1, with antibodies against other phosphorylated residues that are not expressed, and by comparative analysis of sample containing different IGFBP-1 phosphorylation profile. RESULTS Analytical evaluation demonstrated acceptable performance; detection limit 0.3 microg/L, dynamic range 1.56-100 microg/L; intra- and inter-assay CVs 2.1-8.6%; mean recovery (+/-SD) 97.8+/-9.2%, and mean recovery of sample dilution 93.4+/-6.0%. The phosphorylated and total IGFBP-1 medians in non-pregnant adult serum, which mostly contain the highly phosphorylated isoform, were 11.9 and 18.6 microg/L, respectively, and the sample values were tightly correlated (r=0.99). As expected, the corresponding medians in 1st trimester (17.4 and 63.0 microg/L) and 2nd trimester (30.9 and 75.8) samples with altered IGFBP-1 phosphorylation were significantly different (p<0.001). Similarly, a fraction (1.29%) of total IGFBP-1 (13.3 mg/L) in amniotic fluids was found to be phosphorylated (0.172 mg/L). There was no reactivity with dephosphorylated IGFBP-1. CONCLUSIONS The present ELISA is highly specific for the phosphorylated isoform of IGFBP-1 and its availability should help expedite further investigations of IGFBP-1 phosphorylation.
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Affiliation(s)
- Javad Khosravi
- Diagnostic Systems Laboratories (Canada) Inc., Toronto, Ontario, Canada M5G 1L7.
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15
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Nayak NR, Giudice LC. Comparative Biology of the IGF System in Endometrium, Decidua, and Placenta, and Clinical Implications for Foetal Growth and Implantation Disorders. Placenta 2003; 24:281-96. [PMID: 14626217 DOI: 10.1053/plac.2002.0906] [Citation(s) in RCA: 71] [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: 12/17/2022]
Abstract
The insulin like growth factors and their binding proteins appear to play a central role during implantation and establishment of pregnancy in all species studied. Although there are similarities among species in the cell types that express IGFs and IGFBPs and their regulation during implantation and pregnancy, there are also significant differences. Understanding of the role of the IGF system in placental function in the human is of immense clinical importance, because serious complications of pregnancy such as intrauterine growth restriction and pre-eclampsia are thought to be associated with alterations in IGF system during early pregnancy and later in gestation. Research in laboratory and domestic animals, including transgenic and gene targeting studies in mice, has significantly improved our understanding of the role of IGF system in placental and foetal development. This paper reviews the diversity in the expression and regulation of IGF system in the decidua and placenta at the foetal-maternal interface in the human and different animal species, which may benefit in directing future studies in understanding of various complications of human pregnancy.
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Affiliation(s)
- N R Nayak
- Department of Gynecology and Obstetrics, Center for Research on Women's Health and Reproductive Medicine, Stanford University Medical Center, Stanford, CA 94305-5317, USA
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Bhatia S, Faessen GH, Carland G, Balise RL, Gargosky SE, Druzin M, El-Sayed Y, Wilson DM, Giudice LC. A longitudinal analysis of maternal serum insulin-like growth factor I (IGF-I) and total and nonphosphorylated IGF-binding protein-1 in human pregnancies complicated by intrauterine growth restriction. J Clin Endocrinol Metab 2002; 87:1864-70. [PMID: 11932331 DOI: 10.1210/jcem.87.4.8418] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
In cord blood and late gestation maternal serum, IGF-I is positively correlated with birth weight, whereas IGF-binding protein-1 (IGFBP-1) is inversely correlated with birth weight. Our goal was to determine whether maternal serum or amniotic fluid concentrations of IGF-I, IGFBP-1, or nonphosphorylated IGFBP-1 (npIGFBP-1) in early gestation predict later fetal growth abnormalities. Maternal serum was collected prospectively across gestation (5-40 wk) from 749 pregnant subjects. Amniotic fluid was collected after amniocentesis during wk 15-26 from 207 subjects. We compared median serum concentrations of IGF-I, IGFBP-1, and npIGFBP-1 in 38 subjects who delivered growth-restricted infants with the control group of 236 subjects with normal weight infants for each gestational age grouping, wk 5-12, 13-23, and 24-34. In the control group median IGF-I concentrations were 14.8, 11, and 15.6 nmol/liter for wk 5-12, 13-23, and 24-34, respectively, compared with 13.7, 14.3, and 10.6 nmol/liter in the intrauterine growth restriction (IUGR) group. Median IGFBP-1 concentrations were 8.5, 30.4, and 24.4 nmol/liter, respectively, in controls, compared with 11.4, 28.6, and 25.5 nmol/liter in the IUGR group. Median npIGFBP-1 concentrations were 6.9, 22, and 17.4 nmol/liter, respectively, in controls, compared with 5.0, 32.1, and 24.2 nmol/liter in the IUGR group. In the control group the median amniotic fluid IGFBP-1 level was 13,160 nmol/liter, and the median npIGFBP-1 level was 15,970 nmol/liter; in the IUGR group these levels were 13,440 and 18,440 nmol/liter, respectively. No clinically useful differences were found between the IUGR and control groups. Our results do not support the use of maternal serum IGF-I or IGFBP-1 or amniotic fluid IGFBP-1 or npIGFBP-1 early in gestation to predict later fetal growth restriction.
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Affiliation(s)
- S Bhatia
- Department of Gynecology and Obstetrics, Stanford University Medical Center, Stanford, California 94305, USA
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17
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Zumkeller W. Current topic: the role of growth hormone and insulin-like growth factors for placental growth and development. Placenta 2000; 21:451-67. [PMID: 10940195 DOI: 10.1053/plac.2000.0505] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- W Zumkeller
- Department of Pediatrics, Martin-Luther-University Halle-Wittenberg, Germany.
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18
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Kalme T, Loukovaara M, Koistinen R, Koistinen H, Angervo M, Leinonen P, Seppälä M. Estradiol increases the production of sex hormone-binding globulin but not insulin-like growth factor binding protein-1 in cultured human hepatoma cells. Fertil Steril 1999; 72:325-9. [PMID: 10439005 DOI: 10.1016/s0015-0282(99)00229-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
OBJECTIVE To study the effects of E2 on insulin-like growth factor binding protein-1 (IGFBP-1) and sex hormone-binding globulin (SHBG) production with cultured human HepG2 hepatoma cells. DESIGN Experimental cell culture. SETTING Academic medical center. PATIENT(S) None. INTERVENTION(S) Addition of E2 to cell culture medium. MAIN OUTCOME MEASURE(S) Intracellular and released concentrations of IGFBP-1 and SHBG. RESULT(S) Estradiol did not affect the intracellular or extracellular IGFBP-1 concentration, whereas the intracellular SHBG concentration increased significantly in response to 0.5-2.5 microM of E2. CONCLUSION(S) Whereas the two binding proteins share a number of regulatory factors, their regulation by E2 is dissimilar in human hepatoma cells. Estradiol does not affect the intracellular or secreted IGFBP-1 concentration, but it does increase the production of SHBG.
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Affiliation(s)
- T Kalme
- Department of Obstetrics and Gynecology, Helsinki University Central Hospital, Finland
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19
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Phosphorylated Isoforms of Insulin-Like Growth Factor Binding Protein-1 in the Cervix as a Predictor of Cervical Ripeness. Obstet Gynecol 1999. [DOI: 10.1097/00006250-199908000-00017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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20
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Watanabe H, Narai A, Shimizu M. Purification and cDNA cloning of a protein derived from Flammulina velutipes that increases the permeability of the intestinal Caco-2 cell monolayer. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 262:850-7. [PMID: 10411648 DOI: 10.1046/j.1432-1327.1999.00440.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A new protein that decreases transepithelial electrical resistance (TEER) in the human intestinal Caco-2 cell monolayer was found in a water-soluble fraction of the mushroom Flammulina velutipes. This protein, termed TEER-decreasing protein (TDP), is not cytotoxic and does not induce cell detachment, but rapidly increases the tight junctional permeability for water-soluble marker substances such as Lucifer Yellow CH (Mr 457) through the paracellular pathway. TDP was isolated and purified from the aqueous extract of F. velutipes by chromatographic means. Purified TDP was found to be a simple, nonglycosylated protein without intermolecular disulfide bonds, and the apparent molecular mass as estimated by SDS/PAGE and gel filtration is 30 kDa. It was revealed that the N-terminal amino-acid sequence of purified TDP is identical to the recently reported N-terminal sequence of flammutoxin, a membrane-perturbing hemolytic protein, for which the complete primary structure has not yet been reported [Tomita, T., Ishikawa, D., Noguchi, T., Katayama, E., and Hashimoto, Y. (1998) Biochem. J. 333, 24794-24799]. The cDNA coding for TDP was cloned by 5' and 3' rapid amplification of cDNA ends. The ORF encodes a protein with 272 amino-acid residues showing no homology to known proteins. Relevant studies using TDP cDNA will provide insight into the structure-function relationships of membrane pore-forming toxins.
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Affiliation(s)
- H Watanabe
- Department of Applied Biological Chemistry, The University of Tokyo, Japan
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21
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Iwashita M, Sakai K, Kudo Y, Takeda Y. Phosphoisoforms of insulin-like growth factor binding protein-1 in appropriate-for-gestational-age and small-for-gestational-age fetuses. Growth Horm IGF Res 1998; 8:487-93. [PMID: 10985761 DOI: 10.1016/s1096-6374(98)80302-x] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We analysed phosphoisoforms of insulin-like growth factor binding protein-1 (IGFBP-1) in maternal and cord sera from preterm and term fetus with different growth status. Phosphoisoforms were separated by non-SDS-polyacrylamide gel electrophoresis and detected by immunoblot. Phosphoisoforms were also analysed by anion exchange chromatography on HPLC. The proportion of non-phosphorylated IGFBP-1 to total IGFBP-1 was significantly higher in preterm fetus than in their mothers, however, the relative amounts of each IGFBP-1 isoforms were similar between preterm and term fetus. The levels of non-phosphorylated IGFBP-1 were similar between appropriate for gestational age (AGA) and small for gestational age (SGA) fetus at term, however, phosphorylated isoforms of IGFBP-1 were increased in SGA fetus compared to those of AGA fetus and the proportion of non-phosphorylated IGFBP-1 to total IGFBP-1 was lower in SGA fetus than those in AGA fetus. Thus, the profiles of non-phosphorylated and phosphorylated IGFBP-1 in the fetus varies corresponding to fetal growth suggesting that not only total amounts of IGFBP-1 but also the proportion of phosphoisoforms of IGFBP-1 is important for fetal growth.
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Affiliation(s)
- M Iwashita
- Department of Obstetrics and Gynecology, Tokyo Women's Medical College, Japan. iwashita@bnn-net-or-jp
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22
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Peterkofsky B, Gosiewska A, Wilson S, Kim YR. Phosphorylation of rat insulin-like growth factor binding protein-1 does not affect its biological properties. Arch Biochem Biophys 1998; 357:101-10. [PMID: 9721188 DOI: 10.1006/abbi.1998.0797] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Insulin-like growth factors (IGFs) I and II stimulate growth and expression of specific genes through binding to cell membrane receptors. IGF binding proteins also bind IGF-I with higher affinity than the receptor. They are found in the circulation and tissues and can modulate IGF actions. Human IGFBP-1 is phosphorylated on serine residues, which increases its affinity for IGF-I. An acidic, presumably phosphorylated, form of human IGFBP-1 inhibits IGF-I-stimulated DNA synthesis in cultured cells, while a less acidic, unphosphorylated form potentiates this function. Phosphorylation of human IGFBP-3, however, does not affect its affinity for IGF-I. Previously we found that multiple forms of rat IGFBP-1 are obtained by anion-exchange chromatography, raising the possibility that it also is phosphorylated, which led us to examine its properties. Phosphopeptide analysis of 32P-labeled, immunoprecipitated rat IGFBP-1 synthesized by H-4-II-EC3 rat hepatoma cells indicated that it is phosphorylated on two sites that were deduced to be ser107 and ser132 in the central nonconserved domain. Dephosphorylation of purified phosphorylated rat IGFBP-1 did not affect its affinity for IGF-I or its specific binding activity, and the dephosphorylated form inhibited DNA synthesis in 3T3 cells. Incubation of cells labeled with radioactive proline in the presence of monensin and brefeldin A, which inhibit secretion at different sites, led to intracellular accumulation of the least phosphorylated form of rat IGFBP-1, but prevented further phosphorylation. The results suggested that phosphorylation occurs at two sites in cells, the cis-Golgi and the trans-Golgi network. In summary, these studies have shown that rat IGFBP-1 is phosphorylated on two sites by reactions that occur in different secretory organelles and that similar to human IGFBP-3, but unlike human IGFBP-1, phosphorylation does not affect its affinity for IGF-I.
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Affiliation(s)
- B Peterkofsky
- Laboratory of Biochemistry, National Cancer Institute, Bethesda, Maryland 20982-4255, USA.
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23
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Yu J, Iwashita M, Kudo Y, Takeda Y. Phosphorylated insulin-like growth factor (IGF)-binding protein-1 (IGFBP-1) inhibits while non-phosphorylated IGFBP-1 stimulates IGF-I-induced amino acid uptake by cultured trophoblast cells. Growth Horm IGF Res 1998; 8:65-70. [PMID: 10990446 DOI: 10.1016/s1096-6374(98)80323-7] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The effects of phosphorylated insulin-like growth factor-binding protein (pIGFBP-1) and non-phosphorylated (npIGFBP-1) IGFBP-1 on amino acid uptake induced by IGF-I were studied using cultured trophoblast cells. Trophoblast cells obtained from term pregnancy were incubated with indicated concentrations of pIGFBP-1 or npIGFBP-1 for 24 h and further incubated with 10 nM IGF-I for 3 h. Cells were then incubated with 3H-alpha-amino isobutyric acid (3H-AIB) for 30 min. Both pIGFBP-1 and npIGFBP-1 alone had no effect on 3H-AIB uptake; however, pIGFBP-1 inhibited IGF-I-stimulated 3H-AIB uptake with an ED50 of 0.26 nM while npIGFBP-1 potentiated 3H-AIB uptake with an ED50 of 0.27 nM. Maternal IGF-I promotes fetal growth by stimulating nutrient transport in the placenta. As shown in this study, pIGFBP-1 inhibits while npIGFBP-1 stimulates this IGF-I action in the placenta. Thus, it is suggested that IGFBP-1 phosphoisoforms are also involved in fetal growth by modulating IGF-I action in the placenta.
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Affiliation(s)
- J Yu
- Department of Obstetrics and Gynecology, Tokyo Women's Medical College, Japan
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24
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Martina NA, Kim E, Chitkara U, Wathen NC, Chard T, Giudice LC. Gestational age-dependent expression of insulin-like growth factor-binding protein-1 (IGFBP-1) phosphoisoforms in human extraembryonic cavities, maternal serum, and decidua suggests decidua as the primary source of IGFBP-1 in these fluids during early pregnancy. J Clin Endocrinol Metab 1997; 82:1894-8. [PMID: 9177402 DOI: 10.1210/jcem.82.6.3974] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) are important regulators of fetal and maternal tissue development during pregnancy. Posttranslational modification of IGFBP-1 yields up to six IGFBP-1 phosphovariants and a nonphosphorylated form, which in vitro, have some different properties. Nonphospho IGFBP-1 has less affinity for IGFs than the phospho isoforms and also may have IGF-independent actions. Herein, we have investigated the complement of IGFBP-1 phosphoisoforms present in extraembryonic coelomic (EEC) fluid, amniotic fluid (AF), and maternal serum (MS) throughout human gestation. Also, to determine potential tissue source(s) of IGFBP-1 in these fluids, we have quantified IGFBP-1 and examined IGFBP-1 phosphoisoforms in conditioned media (CM) from maternal decidua, fetal liver, and fetal kidney explants throughout gestation. Western immunodetection revealed that IGFBP-1, present in EEC and AF in early pregnancy and in CM from early pregnancy decidua, is primarily in the nonphosphorylated form. MS in this period contains primarily the nonphospho form and, as in nonpregnant adults, the highly phosphorylated form of IGFBP-1. The phosphorylation profile of IGFBP-1 in AF, MS, and decidua CM changes as pregnancy progresses. All the IGFBP-1 phosphoisoforms ultimately are produced by decidua and are present in midgestation MS, and all but the most highly phosphorylated form are present in AF. In late gestation, MS contains primarily the highly phosphorylated form. In contrast, profiles in CM from explants of fetal liver and kidney at different gestational ages remain unchanged. Nonphosphorylated IGFBP-1 is the primary form in fetal kidney CM, whereas fetal liver CM contains all IGFBP-1 phosphoisoforms. Concentrations of IGFBP-1 in fetal liver and kidney CM are significantly lower (482 +/- 146 and 120 +/- 32 ng/mL x 100 mg wet wt tissue, respectively) than in decidua CM (11,417 +/- 2,358 ng/mL x 100 mg wet wt tissue). The data cumulatively suggest that maternal decidua is the primary source of IGFBP-1 in EEC, AF, and MS in early pregnancy and that fetal liver and kidney are not likely significant contributors. The presence of nonphospho IGFBP-1 in AF, EEC, and MS suggests an important role for this isoform during early gestation.
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Affiliation(s)
- N A Martina
- Department of Gynecology and Obstetrics, Stanford University Medical Center, California 94305-5317, USA
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25
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Abstract
Insulin-like growth factor (IGF) binding proteins (IGFBPs) play a key role in regulating the availability of IGFs in the circulation and the extracellular environment. Three of these proteins-IGFBP-1, IGFBP-3 and IGFBP-5-are known to be serine-phosphorylated in their central domains, and the others have possible target sites for serine/threonine kinases. Whereas nonphosphorylated IGFBP-1 may potentiate IGF action in certain cells, phosphorylation increases its affinity for IGFs, and converts the protein to an inhibitory form. The highly phosphorylated protein predominates in the circulation, where it may acutely regulate IGF bioavailability. IGFBP-3 is also secreted as a phosphoprotein, and can be phosphorylated in vitro by protein kinases A and C, and casein kinase II. De-phosphorylation has no effect on IGF-binding, but may increase its ability to bind to the acid-labile subunit and to associate with cell surfaces. Although no specific functions have yet been ascribed to phosphorylated forms of the other IGFBPs, current evidence supports the proposal that IGFBP phosphorylation plays an important role in the regulation of IGFBP function.
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Affiliation(s)
- J A Coverley
- Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St. Leonards, NSW, Australia.
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26
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Abstract
AbstractAccurate measurement of insulin-like growth factor (IGF) binding protein-1 (IGFBP-1) is important for precise definition of its physiological roles and potential diagnostic values. Because altered phosphorylation results in altered IGFBP-1 immunoreactivity, current assays may significantly underestimate or fail to detect physiological changes in the IGFBP-1 concentrations. We developed three ELISAs (ELISA 1–3) using a common capture but three different detection antibodies. IGFBP-1 in serum, synovial fluid (SF), cerebrospinal fluid (CSF), and amniotic fluid (AF) were measured before and after treatment with alkaline phosphatase (ALP). Among the methods, only ELISA-1 was unaffected by IGFBP-1 phosphorylation and generated identical results before and after ALP treatment. The serum and SF values by ELISA-2 and -3 were lower by ∼4- to 10-fold, but increased after ALP treatment to within 66–98% of those by ELISA-1. The medians in AF, and to a lesser extent in CSF, by all methods were similar and did not change significantly after dephosphorylation. ELISA-1 showed excellent correlation with ELISA-2, ELISA-3, and a commercial IGFBP-1 IRMA only after ALP-treated samples were analyzed by the comparative methods. ELISA-1 is highly specific for IGFBP-1 and demonstrated acceptable analytical performance characteristics.
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Affiliation(s)
- M Javad Khosravi
- Diagnostic Systems Laboratories (Canada) Inc., Toronto, ON, Canada
- Department of Clinical Biochemistry, University of Toronto, Toronto, ON, Canada
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27
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Westwood M, Gibson JM, White A. Purification and characterization of the insulin-like growth factor-binding protein-1 phosphoform found in normal plasma. Endocrinology 1997; 138:1130-6. [PMID: 9048619 DOI: 10.1210/endo.138.3.5020] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Our previous work has shown that, in the normal circulation, insulin-like growth factor-binding protein-1 (IGFBP-1) is present as a single highly phosphorylated species. In this study, we have purified this previously uncharacterized isoform of IGFBP-1 to determine its ligand-binding affinity and the potential significance of highly phosphorylated IGFBP-I. Immunoaffinity chromatography was used to isolate IGFBP-1 from normal human plasma and from human hepatoma (Hep G2) cell medium as an alternative source of the IGFBP-1 phosphoform in the circulation. The affinity of this highly phosphorylated IGFBP-1 was compared with that of nonphosphorylated IGFBP-1 and recombinant human (rh) IGFBP-3 by equilibrium binding to IGF-II and IGF-II. Anion exchange (IEX) HPLC, nondenaturing electrophoresis, alkaline phosphatase treatment, and ligand-binding studies indicated that the highly phosphorylated IGFBP-1 from HepG2 cells was comparable with IGFBP-1 from plasma. In binding to IGF-I, the plasma phosphoform of IGFBP-1 was found to have a higher affinity (2.3 +/- 1.1 x 10(10) M-1) than nonphosphorylated IGFBP-1 (2.5 +/- 1.7 x 10(9) M-1, P < 0.002). However, when binding to IGF-II, phosphorylation had no affect on the affinity of IGFBP-1 (3.6 +/- 2 x 10(9) M-1 vs. 1.8 +/- 3 x 10(9) M-1, P not significant). Therefore, in the circulation, IGF-I has a considerably higher affinity than IGF-II for IGFBP-1 (P < 0.02). The affinity of phosphorylated IGFBP-1 from plasma (2.3 +/- 1.1 x 10(10) M-1) also was significantly higher than the affinity of IGFBP-3 for IGF-I (5.6 +/- 4.2 x 10(9) M-1, P < 0.005). These data suggest that the highly phosphorylated IGFBP-1 in the normal circulation will preferentially bind IGF-I rather than IGF-II, whereas in pregnancy, the affinity of IGFBP-1 for IGF-I will be reduced because of the appearance of non- and lesser-phosphorylated forms. This lends support to the theory that changes in IGFBP-1 phosphorylation may influence the modulatory effects of IGFBP-1 on IGF bioavailability.
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Affiliation(s)
- M Westwood
- Department of Medicine, University of Manchester, United Kingdom.
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28
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Abstract
The phosphorylation of insulin-like growth factor binding protein-I (IGFBP-1) alters its binding affinity for insulin-like growth factor I (IGF-I) and thus regulates the bioavailability of IGF-I for binding to the IGF-I receptor. The kinase(s) responsible for the phosphorylation of IGFBP-1 has not been identified. This study was designed to characterize the IGFBP-1 kinase activity in HepG2 human hepatoma cells, a cell line that secretes IGFBP-1 primarily as phosphorylated isoforms. IGFBP-1 kinase activity was partially purified from detergent extracts of the cells by phosphocellulose chromatography and gel filtration. Two kinases of approximate M(r) 150,000 (peak I kinase) and M(r) 50,000 (peak II kinase) were identified. Each kinase phosphorylated IGFBP-1 at serine residues that were phosphorylated by intact HepG2 cells. The kinases were distinct based on their differential sensitivity to inhibition by heparin (IC50 = 2.5 and 16.5 micrograms/ml, peak I and II kinase, respectively) and inhibition by the isoquinoline sulfonamide CKI-7 (IC50 = 50 microM and 100 microM, peak I and II kinase, respectively). In addition, a tenfold molar excess of nonradioactive GTP relative to [gamma-32P]ATP lowered the incorporation of 32P into IGFBP-1 by 80% when the reaction was catalyzed by the peak I kinase, whereas GTP had no effect on the reaction catalyzed by the peak II kinase. In the presence of polylysine, IGFBP-1 was radiolabeled by the partially purified kinase activity when [gamma-32P]GTP served as the phosphate donor indicating the presence of casein kinase II activity. Furthermore, IGFBP-1 was phosphorylated by purified casein kinase I and casein kinase II at sites phosphorylated by the peak I and II kinases. Our data suggest that at least two kinases could be responsible for the phosphorylation of IGFBP-1 in intact HepG2 cells and that the kinases are related to the casein kinase family of protein kinases.
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Affiliation(s)
- D P Ankrapp
- Department of Medicine, University of North Carolina, Chapel Hill 27599, USA
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