Formisano P, Najjar S M, Gross C N, Philippe N, Oriente F, Kern-Buell C L, Accili D, Gorden P
Diabetes Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.
J Biol Chem. 1995 Oct 13;270(41):24073-7. doi: 10.1074/jbc.270.41.24073.
pp120/HA4 is a hepatocyte membrane glycoprotein phosphorylated by the insulin receptor tyrosine kinase. In this study, we have investigated the role of pp120/HA4 in insulin action. Transfection of antisense pp120/HA4 cDNA in H35 hepatoma cells resulted in inhibition of pp120/HA4 expression and was associated with a 2-3-fold decrease in the rate of insulin internalization. Furthermore, insulin internalization in NIH 3T3 fibroblasts co-transfected with insulin receptors and pp120/HA4 was increased 2-fold compared with cells expressing insulin receptors alone. In contrast, no effect on internalization was observed in cells overexpressing a naturally occurring splice variant of pp120/HA4 that lacks the phosphorylation sites in the intracellular domain. Insulin internalization was also unaffected in cells expressing three site-directed mutants of pp120/HA4 in which the sites of phosphorylation by the insulin receptor kinase had been removed (Y488F, Y488F/Y513F, and S503A). Our data suggest that pp120/HA4 is part of a complex of proteins required for receptor-mediated internalization of insulin. It is possible that this function is regulated by insulin-induced phosphorylation of the intracellular domain of pp120/HA4.
pp120/HA4是一种由胰岛素受体酪氨酸激酶磷酸化的肝细胞膜糖蛋白。在本研究中，我们研究了pp120/HA4在胰岛素作用中的作用。在H35肝癌细胞中转染反义pp120/HA4 cDNA导致pp120/HA4表达受到抑制，并与胰岛素内化速率降低2至3倍相关。此外，与单独表达胰岛素受体的细胞相比，共转染胰岛素受体和pp120/HA4的NIH 3T3成纤维细胞中的胰岛素内化增加了2倍。相反，在过表达缺乏细胞内结构域磷酸化位点的pp120/HA4天然剪接变体的细胞中，未观察到对内化的影响。在表达pp120/HA4的三个位点定向突变体（其中胰岛素受体激酶的磷酸化位点已被去除（Y488F、Y488F/Y513F和S503A））的细胞中，胰岛素内化也未受影响。我们的数据表明，pp120/HA4是胰岛素受体介导的内化所需蛋白质复合物的一部分。这种功能可能受胰岛素诱导的pp120/HA4细胞内结构域磷酸化的调节。
