Sawa T, Imamura T, Haruta T, Sasaoka T, Ishiki M, Takata Y, Takada Y, Morioka H, Ishihara H, Usui I, Kobayashi M
First Department of Medicine, Toyama Medical and Pharmaceutical University, Japan.
Biochem Biophys Res Commun. 1996 Jan 17;218(2):449-53. doi: 10.1006/bbrc.1996.0080.
We have examined the binding specificities of Hsp70 family molecular chaperones, BiP and Hsp70/Hsc70, to wild-type or mutant insulin receptors. BiP bound to proreceptor of wild-type insulin receptor, but not to mature receptor. A mutant insulin receptor, which lacked 47 amino acid residues (delta Ex13 IR) corresponding to exon 13 of insulin receptor gene, accumulated in the endoplasmic reticulum as uncleaved proreceptor with immature oligosaccharide chains. This deletion mutant bound to BiP more tightly than wild type. Introduction of two types of mutations, Asp1179 or Leu1193, into delta Ex13 IR led to accelerated degradation, and these double mutants bound weakly to BiP. In contrast, Ser735 insulin receptor was normally transported to the plasma membrane and normally bound to BiP. Furthermore, Asp1179, Leu1193 insulin receptors and delta Ex13 IR combination mutant with either Asp1179 or Leu1193 bound more tightly to Hsp70/Hsc70 compared with wild-type, Ser735, and delta Ex13 IR. These results suggest that the binding specificity of mutant insulin receptors to two molecular chaperones, i.e., BiP and Hsp70/Hsc70, plays an important role for their posttranslational processing that may lead to the accumulation in the endoplasmic reticulum or the degradation of insulin receptors.
我们研究了热休克蛋白70（Hsp70）家族分子伴侣BiP和Hsp70/Hsc70与野生型或突变型胰岛素受体的结合特异性。BiP与野生型胰岛素受体的前体受体结合，但不与成熟受体结合。一种突变型胰岛素受体，缺少对应于胰岛素受体基因第13外显子的47个氨基酸残基（ΔEx13 IR），以内切未成熟寡糖链的未切割前体受体形式在内质网中积累。这种缺失突变体与BiP的结合比野生型更紧密。在ΔEx13 IR中引入两种突变，Asp1179或Leu1193，导致加速降解，并且这些双突变体与BiP的结合较弱。相比之下，Ser735胰岛素受体正常转运到质膜并正常与BiP结合。此外，与野生型、Ser735和ΔEx13 IR相比，Asp1179、Leu1193胰岛素受体以及带有Asp1179或Leu1193的ΔEx13 IR组合突变体与Hsp70/Hsc70的结合更紧密。这些结果表明，突变型胰岛素受体与两种分子伴侣BiP和Hsp70/Hsc70的结合特异性在其翻译后加工中起重要作用，这可能导致胰岛素受体在内质网中积累或降解。
