UC San Diego

Changes in motogenic and mitogenic signaling pathways via epidermal growth factor receptors (EGFR) are characteristic of some cancer cells. We have shown that EGFR signaling can be fine-tuned by the G[alpha]- interacting vesicle-associated protein (GIV/Girdin), a multidomain molecule that modifies EGFR signal transduction pathways via interactions with heterotrimeric G proteins. GIV can assemble a complex with EGFR and G[alpha]i3, leading to prolongation of EGFR signaling from the plasma membrane and resulting in amplification of migratory signaling. Trafficking of activated EGFR through early endosomes is regulated by interactions between G[alpha]s and GIV to attenuate proliferation. In this study, we have pinpointed a heavily phosphorylated residue, S1674, near GIV's GEF domain that alters interaction with both G[alpha]i3 and G[alpha]s upon EGF stimulation. We showed that a nonphosphorylatable mutation at GIV's S1674 abolishes the binding of GIV to G[alpha]i3 and G[alpha]s. Using immunofluorescence, we found that the stay of activated EGFR in EEA1 early endosomes was prolonged, causing cells to proliferate more and migrate less than normal cells. However, in cells containing a phosphomimetic mutation, the binding of GIV to G[alpha]i3 and G[alpha]s is enhanced, resulting in increased migration and decreased proliferation in comparison to wild-type cells. The results of this study indicate that phosphorylation of GIV S1674 is important for modifying EGFR trafficking and signaling and for determining whether cells preferentially migrate or proliferate in response to EGFR stimulation. We hope that these findings may ultimately be useful in designing therapeutic agents capable of modifying abnormal cell growth that occurs in various cancers