Physiological significance of IGFBP-1 phosphorylation on fetal growth

胰岛素样生长因子- i （IGF-I）是一种与特异性高亲和力结合蛋白（igfbp）循环结合的生长因子。igfbp之一IGFBP-1已知在生物体液中被磷酸化，然而，该分子磷酸化的生理意义尚未阐明。本研究探讨了IGFBP-1磷酸化对胎儿生长的影响。采用免疫印迹法和阴离子交换色谱法分离了胎鼠和脐带血清中磷酸化的IGFBP-1异构体，检测到1个非磷酸化和4个磷酸化的IGFBP-1。在中期分娩的血液样本中，胎儿血液中非磷酸化IGFBP-1的百分比高于母亲。同样，AFD婴儿中非磷酸化IGFBP-1的百分比高于足月分娩的SFD婴儿。因此，IGFBP-1非磷酸化和磷酸化异构体的比例随胎儿生长而变化。通过结合研究评估，磷酸化IGFBP-1对IGF-I的亲和力比非磷酸化IGFBP-1高4倍。非磷酸化的IGFBP-1增强培养的滋养细胞对IGF-I介导的^3H-AIB的摄取，而磷酸化的IGFBP-1在这些IGFBP-1同种异构体存在的情况下与IGF-I孵育时抑制细胞。因此，磷酸化和非磷酸化的IGFBP-1具有不同的生化特性，对igf -1的修饰作用也不同。

Insulin-like growth factor-I (IGF-I) is one of growth factors that circulates bound to specific, high affinity binding proteins (IGFBPs). One of IGFBPs, IGFBP-1 is known to be phosphorylated in biological fluid, however, the physiological significance of phosphorylation on this molecle is not elucidated. We investigated the effect of phosphorylation of IGFBP-1 on fetal growth in this study.The isomers of phosphorylated IGFBP-1 in fetal rats and cord sera are separated by immunoblot and anion ion exchange chromatography in which one nonphosphorylated and four phosphorylated IGFBP-1 are detected. In pared blood samples from mid-term delivery, percentage of nonphosphorylated IGFBP-1 is higher in fetal blood compared to those in mother. Similarly, percentage of nonphosphorylated IGFBP-1 is elevated in AFD infants than in SFD infants from term delivery. Thus, the proportion of nonphosphorylated and phosphorylated isomers of IGFBP-1 varies corresponding to fetal growth.The affinity of phosphorylated IGFBP-1 for IGF-I is 4-fold higher than those of nonphosphorylated IGFBP-1 when evaluated by binding study.Nonphosphorylated IGFBP-1 enhances IGF-I-mediated ^3H-AIB uptake by cultured trophoblast cells while phosphorylated IGFBP-1 inhibits when cells are incubated with IGF-I under the presence of these isoforms of IGFBP-1.Thus, phosphorylated and nonphosphorylated IGFBP-1 have differant biochemical property and modify IGF-I action differntly.