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：一个家族的Asp 1179突变和两个不相关的极端胰岛素抵抗家族的Leu 1193突变。在这些患者中，转化淋巴细胞的胰岛素结合和表面标记研究发现，细胞表面的胰岛素受体数量明显减少。转染了这两种突变cdna的COS 7细胞和大鼠1细胞的胰岛素结合也下降到正常的5-31%，突变胰岛素受体的酪氨酸激酶活性明显降低。虽然生物合成标记研究表明，这两个突变体受体合成为190-kDa前受体，但突变体的降解速度比野生型前受体快2倍。有趣的是，两种分子伴侣Hsc 70和Hsp 90与这些突变的细胞内β亚基gst融合蛋白的异常胰岛素受体前体和细胞内β亚基gst融合蛋白高亲和力结合。此外，微量注射抗hsp90抗体阻止了这些突变胰岛素前受体的降解，并将它们招募到细胞表面。这些结果表明，胰岛素受体激酶结构域的Asp 1179和Leu 1193突变是导致细胞表面胰岛素受体数量减少的唯一突变，分子伴侣对这些突变胰岛素受体的细胞内降解加速起重要作用。

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.