Waterman H, Levkowitz G, Alroy I, Yarden Y
Department of Biological Regulation, The Weizmann Institute of Science, Rehovot 76100, Israel.
J Biol Chem. 1999 Aug 6;274(32):22151-4. doi: 10.1074/jbc.274.32.22151.
Ligand-induced activation of surface receptors, including the epidermal growth factor receptor (EGFR), is followed by a desensitization process involving endocytosis and receptor degradation. c-Cbl, a tyrosine phosphorylation substrate shared by several signaling pathways, accelerates desensitization by recruiting EGFR and increasing receptor polyubiquitination. Here we demonstrate that the RING type zinc finger of c-Cbl is essential for ubiquitination and subsequent desensitization of EGFR. Mutagenesis of a single cysteine residue impaired the ability of c-Cbl to enhance both down-regulation and ubiquitination of EGFR in living cells, although the mutant retained binding to the activated receptor. Consequently, the mutant form of c-Cbl acquired a dominant inhibitory function and lost the ability to inhibit signaling downstream to EGFR. In vitro reconstitution of EGFR ubiquitination implies that the RING finger plays an essential direct role in ubiquitin ligation. Our results attribute to the RING finger of c-Cbl a causative role in endocytic sorting of EGFR and desensitization of signal transduction.
包括表皮生长因子受体（EGFR）在内的表面受体的配体诱导激活之后会发生脱敏过程，该过程涉及内吞作用和受体降解。c-Cbl是几种信号通路共有的酪氨酸磷酸化底物，它通过招募EGFR并增加受体多聚泛素化来加速脱敏。在此我们证明，c-Cbl的RING型锌指对于EGFR的泛素化及随后的脱敏是必不可少的。单个半胱氨酸残基的诱变损害了c-Cbl在活细胞中增强EGFR下调和泛素化的能力，尽管该突变体仍保留与活化受体的结合。因此，c-Cbl的突变形式获得了显性抑制功能，并失去了抑制EGFR下游信号传导的能力。EGFR泛素化的体外重建表明，RING指在泛素连接中起重要的直接作用。我们的结果表明，c-Cbl的RING指在EGFR的内吞分选和信号转导脱敏中起因果作用。
