Cdc42Binds To γCOP Of The Coatomer Complex To Upregulate The EGFR Protein Level And Promote EGFR Nuclear Transport And Cellular Transformation

Cdc42is a Ras-related small GTP-binding protein that works as molecularswitches cycling between an active GTP-bound state and an inactive GDP-boundstate and plays a role of bridge in intracellular signal transduction pathways. It alsoplays an important role in cytoskeletal reorganization, the morphology of cell, cellpolarity and cell migration. It involves the regulation of normal cell proliferation,differentiation, apoptosis, and is closely related to the tumorigenesis, invasion andmetastasis. A variety of extracellular stimuli, including epidermal growth factor(EGF), can activate Cdc42. Previous studies showed that the Cdc42mutant, Cdc42(F28L), capable of spontaneous GDP-GTP exchange (referred to as “fast cycling”),transformed NIH3T3cells, but the specific mechanisms are not well understood.To further investigate the molecular mechanism of cell transformation caused byCdc42, we mutated two lysine residues to serine within its C-terminal region in theCdc42(F28L) background. The mutant eliminated the binding of Cdc42to the γCOPof coatomer protein complex, one of its binding partners. We found that cells stablyexpressing the Cdc42(F28Lss) mutant grow much slower than the cells expressingCdc42(F28L), even though both Cdc42mutants share similar cell localization and canproduce filopodia. Additionally，the Cdc42(F28Lss) mutant failed to accumulateEGFR protein like Cdc42(F28L), consistent with Cdc42(F28L)-dependent EGFinduced ERK, JNK and PI-3K activation not being sustained by Cdc42(F28Lss). Inaddition, we show that the Cdc42(F28L) can lead to Src gene overexpression,contributes to more EGFR to enter the nucleus, these promote cell malignanttransformation and tumorigenesis, however, Cdc42(F28Lss) does not cause thesephenotypes.