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（IGFBPs）结合的生长因子。IGFBP-1是IGFBPs中的一种，已知其在生物体液中被磷酸化，但其磷酸化的生理意义尚未阐明。本研究通过免疫印迹和阴离子交换层析分离胎鼠和脐带血清中IGFBP-1的磷酸化异构体，检测到一种非磷酸化和四种磷酸化IGFBP-1。在中期分娩的胎儿血液样本中，胎儿血液中非磷酸化IGFBP-1的百分比高于母亲。同样，足月分娩的AFD婴儿中非磷酸化IGFBP-1的百分比高于SFD婴儿。因此，在本发明中，IGFBP-1的非磷酸化和磷酸化异构体的比例随着胎儿的生长而变化。结合研究表明，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IGFBP-1可增强培养滋养层细胞对IGF-I介导的^3 H-AIB的摄取，而磷酸化IGFBP-1可抑制培养滋养层细胞对IGF-I的摄取。因此，磷酸化和非磷酸化的IGFBP-1具有不同的生化性质，对IGF-I的作用也不同。

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.