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Hypoxia alters phosphorylation status of insulin‐like growth factor ( IGF )‐binding protein‐1 and attenuates biological activities of IGF ‐ I in H ep G 2 cell cultures
Author(s) -
Tsunawaki Tomonori,
Sakai Keiji,
Momomura Mai,
Wachi Yuichi,
Matsuzawa Yukiko,
Iwashita Mitsutoshi
Publication year - 2013
Publication title -
journal of obstetrics and gynaecology research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.597
H-Index - 50
eISSN - 1447-0756
pISSN - 1341-8076
DOI - 10.1111/jog.12078
Subject(s) - phosphorylation , receptor , growth factor , cell growth , insulin like growth factor , fetal bovine serum , biology , cell culture , microbiology and biotechnology , cell , endocrinology , medicine , biochemistry , genetics
Aim Insulin‐like growth factor ( IGF )‐ I is known to stimulate fetal growth. One of the IGF ‐binding proteins, IGFBP ‐1, suppresses IGF ‐ I activity, and thereby inhibits fetal growth. Because hypoxic stress in the uterus is known to cause fetal growth restriction, we examined the effects of hypoxia on IGFBP ‐1 production and phosphorylation status. Methods Because liver is a main IGFBP ‐1 production site in the fetus, we used a hepatoma cell line, H ep G 2 cells, that secrete a large amount of IGFBP ‐1, express IGF ‐ I receptors and model fetal liver metabolism in vitro . IGFBP ‐1 was analyzed by sodium dodecylsulfate polyacrylamide gel electrophoresis ( PAGE ) following immunoblotting, and IGFBP ‐1 phosphorylation status was analyzed by native PAGE following immunoblotting. Results Total concentrations of IGFBP ‐1 in media were higher and the highly phosphorylated isoforms were dominant in low oxygen conditions. Phosphorylation of IGF ‐ I receptor by IGF ‐ I was attenuated in low oxygen conditions. IGF ‐ I ‐induced phosphorylation of insulin receptor substrate‐1 ( IRS ‐1) was attenuated in low oxygen conditions as well. However, attenuated phosphorylation of IGF ‐ I receptor and IRS ‐1 were not observed in low oxygen conditions if the cells were stimulated with LR 3 IGF ‐ I that has a similar binding affinity to IGF ‐ I receptor but much less binding affinity to IGFBP ‐1 compared to those of native IGF ‐ I . While IGF ‐ I ‐induced cell proliferation was also inhibited in low oxygen conditions, LR 3 IGF ‐ I ‐stimulated cell proliferation was not inhibited. These findings indicate that low oxygen conditions inhibit IGF ‐ I action by increasing IGFBP ‐1, especially phosphorylated IGFBP ‐1, which inhibits IGF ‐ I action. Conclusion This study has indicated that hypoxia‐induced IGFBP ‐1 production in the fetus may be a conserved physiological mechanism for restricting IGF ‐ I ‐stimulated fetal growth.