βPix-a enhances the activity of phospholipase Cγ1 by binding SH3 domain in breast cancer

Phospholipase C-gamma 1 (PLC gamma 1) plays a critical role in cell growth and proliferation by generating the second messengers, diacylglycerol and 1, 4, 5-inositol triphosphate. To investigate the roles of Src homology domain 2 and domain 3 of PLC gamma 1 in PLC gamma 1-mediated cell signaling, we characterized some proteins binding to these domains in the MCF7 and MDA-MB-231 breast cancer cell lines. Of the several proteins that bind to glutathione-S-transferase-SH2/SH2/SH3, we identified an 85 kDa protein that binds to the SH3 domain of PLC gamma 1 as the guanine nucleotide exchange factor, p21-activated protein kinase-interacting exchange factor-a (beta Pix-a). beta Pix-a co-immunoprecipitated with PLC gamma 1 in breast cancer tissues extracts and in MCF7 and MDA-MB-231 cell extracts. In addition, PDGF-stimulated PLC gamma 1 activity was elevated in beta Pix-a-overexpressing NIH3T3 cells. Our results suggest that beta Pix-a binds to the Src homology domain 3 of PLC gamma 1 and promotes tumor growth in breast cancer by enhancing the activity PLC gamma 1. (c) 2004 Wiley-Liss, Inc.