Direct interaction of SOS1 ras exchange protein with the SH3 domain of phospholipase C-γ1

A recent report that microinjection of the SH3 domain of PLC-gamma 1 could induce DNA synthesis raised the functional importance of the SH3 domain of PLC-gamma 1 in mitogenic signaling. In this report, we provide evidence that SOS1, a p2Ras-specific guanine nucleotide exchange factor, directly binds to the SH3 domain of PLC-gamma 1, and that the SH3 domain of 1 is involved in SOS1-mediated p21Ras activation. SOS1 was coprecipitated with the GST-fused SH3 domain of PLC-gamma 1 in vitro. The interaction between SOS1 and the PLC-gamma 1 SH3 domain is mediated by direct physical interaction. The carboxyl-terminal proline-rich domain of SOS1 is involved in the interaction with the PLC-gamma 1 SH3 domain. Moreover, PLC-gamma 1 could be co-immunoprecipitated with SOS1 antibody in cell lysates. From transient expression studies, we could demonstrate that the SH3 domain of PLC-gamma 1 is necessary for the association with SOS1 in vivo. Intriguingly, overexpression of the SH3 domain of PLC-gamma 1, lipase-inactive PLC-gamma 1, or wild-type PLC-gamma 1 elevated p21Ras activity and ERK activity when compared with vector transfected cells. The PLC-gamma 1 mutant lacking the SH3 domain could not activate p21Ras. p21Ras activities in cell lines overexpressing either PLC-gamma 1 or the SH2-SH2-SH3 domain of PLC-gamma 1 were elevated about 2-fold compared to vector transfected cells. This study is the first to demonstrate that the PLC-gamma 1 SH3 domain enhances p21Ras activity, and that the SH3 domain of PLC-gamma 1 may be involved in the SOS1-mediated signaling pathway.