Molecular mechanisms of insulin signal transduction and diabetes mellitus

一些细胞因子和生长因子受体的外畴已被发现在血浆中循环。因此，怀疑人血清中存在可溶性IR。此外，向血浆中分泌可溶性IRα的转基因小鼠表现出慢性高血糖。在此，我们建立了新的酶联免疫吸附测定（ELISA）系统来测量IR的外结构域（α-亚基和β-亚基的一部分）和IR的全长。利用这些ELISA系统，我们报道了可溶性hlRα与部分hIRβ的细胞外区域存在于人血浆中，而不是作为整个IR或完整的hlRβ，并且其血浆水平在血糖升高的患者中升高。IR的外结构域至少部分地被高血糖状态相关机制所破坏。我们和其他人之前报道了Gaq蛋白偶联受体（gaqpcr）的激活也刺激了几种细胞系中GLUT4的易位和葡萄糖摄取。在这里，我们报道了gaqpcr的激活也促进了160 KDa的Akt底物AS160 （Rab GTPase激活蛋白（GAP））被5'-AMP激活蛋白激酶（AMPK）磷酸化。利用siRNA敲低AMPKα1亚基抑制AS160磷酸化可促进GLUT4在细胞内的囊泡保留，但不影响Gaq刺激的GLUT4易位的翻倍增加。这些结果表明AS160是胰岛素和GaqPCR激活刺激的GLUT4囊泡运输的共同介质。AS160调节GLUT4囊泡在细胞内的分布及其在细胞内的滞留。

The ectodomains of receptors for several cytokines and growth factors have been found to circulate in plasma. Thus, the existence of soluble IR in human serum has been suspected.Furthermore, transgenic mice secreting soluble IRα into the plasma showed chronic hyperglycemia. Here, we established novel enzyme-linked immunosorbent assay (ELISA) systems to measure both the ectodomain (α-subunit and a part of β-subunit) of IR and full length of IR.With these ELISA systems, we report that soluble hlRα with parts of extracellular region of hIRβ, but not as a whole IR or with intact hlRβ, is present in human plasma and that its plasma level is elevated in patients with elevated blood glucose. The ectodomain of IR may be cleaved, at least in part, by hyperglycemic state-associated mechanisms.We and others previously reported that the activation of Gaq protein- coupled receptors (GaqPCRs) also stimulates GLUT4 translocation and glucose uptake in several cell lines. Here, we report that the activation of GaqPCRs also promoted the phosphorylation of AS160, Akt substrate of 160 KDa which is Rab GTPase activating protein (GAP), by 5'-AMP activated protein kinase (AMPK). The suppression of AS160 phosphorylation by AMPKα1 subunit knockdown using siRNA promoted GLUT4 vesicle retention at intracellular compartments, but did not affect a fold increase of the Gaq- stimulated GLUT4 translocation. These results suggest that AS160 is a common mediator of the GLUT4 vesicle trafficking stimulated by insulin and by the activation of GaqPCR. The AS160 regulates the intracellular distribution of the GLUT4 vesicles and its retention inside the cells.