Haglund Kaisa, Schmidt Mirko H H, Wong Esther Sook Miin, Guy Graeme R, Dikic Ivan
Institute for Biochemistry II, Building 75, Goethe University Medical School, Theodor-Stern-Kai 7, 605 90 Frankfurt am Main, Germany.
EMBO Rep. 2005 Jul;6(7):635-41. doi: 10.1038/sj.embor.7400453.
The ubiquitin ligase Cbl mediates ubiquitination of activated receptor tyrosine kinases (RTKs) and interacts with endocytic scaffold complexes, including CIN85/endophilins, to facilitate RTK endocytosis and degradation. Several mechanisms regulate the functions of Cbl to ensure the fine-tuning of RTK signalling and cellular homeostasis. One regulatory mechanism involves the binding of Cbl to Sprouty2, which sequesters Cbl away from activated epidermal growth factor receptors (EGFRs). Here, we show that Sprouty2 associates with CIN85 and acts at the interface between Cbl and CIN85 to inhibit EGFR downregulation. The CIN85 SH3 domains A and C bind specifically to proline-arginine motifs present in Sprouty2. Intact association between Sprouty2, Cbl and CIN85 is required for inhibition of EGFR endocytosis as well as EGF-induced differentiation of PC12 cells. Moreover, Sprouty4, which lacks CIN85-binding sites, does not inhibit EGFR downregulation, providing a molecular explanation for functional differences between Sprouty isoforms. Sprouty2 therefore acts as an inducible inhibitor of EGFR downregulation by targeting both the Cbl and CIN85 pathways.
泛素连接酶Cbl介导活化的受体酪氨酸激酶（RTK）的泛素化，并与包括CIN85/内吞素在内的内吞支架复合物相互作用，以促进RTK的内吞作用和降解。多种机制调节Cbl的功能，以确保RTK信号传导和细胞内稳态的精细调节。一种调节机制涉及Cbl与Sprouty2的结合，后者将Cbl从活化的表皮生长因子受体（EGFR）中隔离出来。在此，我们表明Sprouty2与CIN85相关联，并在Cbl和CIN85之间的界面起作用，以抑制EGFR的下调。CIN85的SH3结构域A和C特异性结合Sprouty2中存在的脯氨酸-精氨酸基序。抑制EGFR内吞作用以及EGF诱导的PC12细胞分化需要Sprouty2、Cbl和CIN85之间完整的关联。此外，缺乏CIN85结合位点的Sprouty4不抑制EGFR的下调，这为Sprouty亚型之间的功能差异提供了分子解释。因此，Sprouty2通过靶向Cbl和CIN85途径，作为EGFR下调的诱导性抑制剂。
