Site-specific IGFBP-1 hyper-phosphorylation in fetal growth restriction: clinical and functional relevance.
Phosphorylation enhances IGFBP-1 binding to IGF-I, thereby limiting the bioavailability of IGF-I that may be important in fetal growth. Our goal in this study was to determine whether changes in site-specific IGFBP-1 phosphorylation were unique to fetal growth restriction. To establish a link, we compared IGFBP-1 phosphorylation (sites and degree) in amniotic fluid from FGR (N = 10) and controls (N = 12). The concentration of serine phosphorylated IGFBP-1 showed a negative correlation with birth weight in FGR (P = 0.049). LC-MS/MS analysis revealed all four previously identified phosphorylation sites (Ser98, Ser101, Ser119, and Ser169) to be common to FGR and control groups. Relative phosphopeptide intensities (LC-MS) between FGR and controls demonstrated 4-fold higher intensity for Ser101 (P = 0.026), 7-fold for Ser98/Ser101 (P = 0.02), and 23-fold for Ser169 (P = 0.002) in the FGR group. Preliminary BIAcore data revealed 4-fold higher association and 1.7-fold lower dissociation constants for IGFBP-1/IGF-I in FGR. A structural model of IGFBP-1 bound to IGF-I indicates that all the phosphorylation sites are on relatively mobile regions of the IGFBP-1 sequence. Residues Ser98, Ser101, and Ser169 are close to structured regions that are involved in IGF-I binding and, therefore, could potentially make direct contact with IGF-I. On the other hand, residue Ser119 is in the middle of the unstructured linker that connects the N- and C-terminal domains of IGFBP-1. The model is consistent with the assumption that residues Ser98, Ser101, and Ser169 could directly interact with IGF-I, and therefore phosphorylation at these sites could change IGF-I interactions. We suggest that site-specific increase in IGFBP-1 phosphorylation limits IGF-I bioavailability, which directly contributes to the development of FGR. This study delineates the potential role of higher phosphorylation of IGFBP-1 in FGR and provides the basis to substantiate these findings with larger sample size.
Department of Pediatrics, University of Western Ontario, Ontario, Canada.
Majida
M
Abu Shehab
Javad
J
Khosravi
Victor K M
VK
Han
Brian H
BH
Shilton
Madhulika B
MB
Gupta
D000653:Amniotic Fluid / Q000737:chemistry*; D001682:Biological Availability; D005260:Female; D005317:Fetal Growth Retardation / Q000378:metabolism*; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007700:Kinetics; D008958:Models, Molecular; D010748:Phosphopeptides / Q000378:metabolism; D010766:Phosphorylation; D011247:Pregnancy; D011485:Protein Binding; D025941:Protein Interaction Mapping / Q000379:methods; D020033:Protein Isoforms / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D018709:Statistics, Nonparametric; D053719:Tandem Mass Spectrometry
C032231:IGFBP1 protein, human; D018970:Insulin-Like Growth Factor Binding Protein 1; D010748:Phosphopeptides; D020033:Protein Isoforms; D012694:Serine; D007334:Insulin-Like Growth Factor I