Strous G J, van Kerkhof P, Govers R, Ciechanover A, Schwartz A L
Department of Cell Biology, Faculty of Medicine and Institute of Biomembranes, Utrecht University, Heidelberglaan 100, 3584 CX Utrecht, The Netherlands.
EMBO J. 1996 Aug 1;15(15):3806-12.
The ubiquitin-dependent protein degradation system has recently been implicated in downregulation of signal transducing receptors. Growth hormone receptor (GHR) cDNA was transfected into Chinese hamster ovary cells, which exhibit a temperature-sensitive defect in ubiquitin conjugation (CHO-ts20), as well as into wild-type cells (CHO-E36). Upon binding of growth hormone (GH), two GHR polypeptides dimerize and initiate signal transduction. In CHO-E36 and in CHO-ts20 at the permissive temperature the GHR was ubiquitinated and degraded in a GH-dependent fashion. However, at the non-permissive temperature in CHO-ts20 cells, neither GH-dependent uptake nor degradation of the GHR was observed, while in CHO-E36 cells both GHR uptake and degradation were accelerated. Incubation of CHO-E36 cells with inhibitors of endosomal/lysosomal function (NH4Cl, bafilomycin A1) markedly reduced ligand-induced GHR degradation. Our results indicate that a functional ubiquitin conjugating system is required for GH-induced endocytosis and that degradation of both the exoplasmic and cytoplasmic portions of the GHR occurs within the endosomal/lysosomal compartment.
泛素依赖性蛋白质降解系统最近被认为与信号转导受体的下调有关。将生长激素受体（GHR）cDNA转染到中国仓鼠卵巢细胞中，这些细胞在泛素缀合方面表现出温度敏感缺陷（CHO-ts20），以及转染到野生型细胞（CHO-E36）中。生长激素（GH）结合后，两个GHR多肽二聚化并启动信号转导。在CHO-E36和处于允许温度的CHO-ts20中，GHR以GH依赖性方式被泛素化并降解。然而，在CHO-ts20细胞的非允许温度下，未观察到GHR的GH依赖性摄取和降解，而在CHO-E36细胞中，GHR的摄取和降解均加速。用内体/溶酶体功能抑制剂（NH4Cl、巴弗洛霉素A1）孵育CHO-E36细胞可显著降低配体诱导的GHR降解。我们的结果表明，功能性泛素缀合系统是GH诱导的内吞作用所必需的，并且GHR的胞外和胞质部分的降解发生在内体/溶酶体区室中。
