The mechanism of degradation of mutant insulin receptors.

我们发现了两个新的胰岛素受体基因杂合错义突变：一个家族中的Asp 1179突变和两个极端胰岛素抵抗无关家族中的Leu 1193突变。在这些患者中，通过转化淋巴细胞的胰岛素结合和表面标记研究发现细胞表面胰岛素受体的数量显著减少。胰岛素与转染两种突变cDNA的COS 7细胞和Rat-1细胞的结合也降低到正常的5-31%，突变胰岛素受体显示出明显降低的酪氨酸激酶活性。尽管生物合成标记研究显示两种突变受体都是以190-kDa前受体的形式合成的，但突变前受体的降解速率比野生型前受体快2倍。有趣的是，两种分子伴侣，Hsc 70和Hsp 90以高亲和力结合细胞中这些异常的胰岛素受体前体和具有这些突变的细胞内β亚基GST融合蛋白。此外，显微注射抗Hsp 90抗体阻止这些突变的胰岛素前受体的降解，并将它们募集到细胞表面。这些结果表明，在胰岛素受体激酶结构域的天冬氨酸1179和亮氨酸1193突变是独特的，在引起细胞表面上的胰岛素受体的数量减少，分子伴侣起着重要的作用，加速这些突变的胰岛素受体的细胞内降解。

We indentified two novel heterozygous missense mutations of the insulin receptor gene : the Asp 1179 mutation in one family and the Leu 1193 mutation in two unrelated families with extreme insulin resistance. In these patients, the number of insulin receptors on the cell surfacc was found to be markedly decreased by insulin binding and surface labeling studies in transformedlymphocytes. Insulin binding to the transfected COS 7 cells and Rat-1 cells with both mutant cDNAs was also decreased to 5-31% of normal, and the mutant insulin receptors showed a markedly decreased tyrosine kinase activity. Although biosynthetic labeling studies revealed the both mutant receptors were synthesized as 190-kDa proreceptors, the degradation rate of the mutant proreccptors ws 2-fold faster than that of the wild type proreceptors. Interestingly, two molecular chaperones, Hsc 70 and Hsp 90 bound with high affinity to these abnormal insulin receptor precursors in cells and intracellular beta-subunit GST-fusion proteins with these mutations. Furthermore, microinjection of anti-Hsp 90 antibody prevented the degradation of these mutant insulin proreceptors and recruited them to the cell surface. These results suggest that Asp 1179 an Leu 1193 mutations in the insulin receptor kinase domain are unique in causing decreased insulin receptor number on the cell surface and that molecular chaperons play an important role for the accelerated intracellular degradation of these mutant insulin receptors.