Mori S, Heldin C H, Claesson-Welsh L
Ludwig Institute for Cancer Research, Biomedical Center, Uppsala, Sweden.
J Biol Chem. 1993 Jan 5;268(1):577-83.
We have recently reported that the platelet-derived growth factor beta-receptor undergoes polyubiquitination as a consequence of ligand binding and that a mutant beta-receptor lacking the carboxyl-terminal 98 amino acid residues of the receptor (CT98 mutant) does not undergo this posttranslational modification (Mori, S., Heldin, C.-H., and Claesson-Welsh, L. (1992) J. Biol. Chem. 267, 6429-6434). In this paper, we report that a mutant beta-receptor in which the carboxyl-terminally located Tyr-1009 and Tyr-1021, which are potential autophosphorylation sites, were simultaneously changed to phenylalanine residues by site-directed mutagenesis (Y1009F/Y1021F mutant) showed only 15% efficiency in ligand-induced ubiquitination compared with the wild-type receptor. Ligand-stimulated degradation of the receptor-bound ligand, as well as of the receptor itself, was partially impaired in the cells expressing the ubiquitination-deficient receptor mutants (CT98 and Y1009F/Y1021F). Furthermore, the ubiquitination-deficient receptors possessed an amplified mitogenic activity, as judged by a [3H]thymidine incorporation assay. These data suggest that ligand-induced ubiquitination plays a negative regulatory role in mitogenic signaling of the platelet-derived growth factor beta-receptor, possibly by promoting the efficient degradation of the ligand-activated receptor.
我们最近报道，血小板衍生生长因子β受体因配体结合而发生多聚泛素化，并且缺失受体羧基末端98个氨基酸残基的β受体突变体（CT98突变体）不会发生这种翻译后修饰（森，S.，赫尔丁，C.-H.，和克莱松-威尔士，L.（1992年）《生物化学杂志》267卷，6429 - 6434页）。在本文中，我们报道，通过定点诱变将羧基末端的潜在自磷酸化位点酪氨酸-1009和酪氨酸-1021同时替换为苯丙氨酸残基的β受体突变体（Y1009F/Y1021F突变体），与野生型受体相比，在配体诱导的泛素化中仅表现出15%的效率。在表达泛素化缺陷受体突变体（CT98和Y1009F/Y1021F）的细胞中，配体刺激的受体结合配体以及受体本身的降解部分受损。此外，通过[3H]胸苷掺入试验判断，泛素化缺陷受体具有增强的促有丝分裂活性。这些数据表明，配体诱导的泛素化在血小板衍生生长因子β受体的促有丝分裂信号传导中起负调节作用，可能是通过促进配体激活受体的有效降解来实现的。
