Synergism between two growth regulatory pathways: cooperative transformation of NIH3T3 cells by G alpha 12 and c-raf-1.

The alpha-subunit of the heterotrimeric G-protein, G12, has been shown to induce cellular transformation when overexpressed or oncogenically activated in rodent fibroblasts. To investigate the interaction between Galpha12 transforming pathway and the Ras-Raf-MAPK pathway, we examined the ability of mitogenic signaling molecules in cooperating with Galpha12 in transforming NIH3T3 fibroblasts. We observed a striking cooperative effect on focus-forming ability when Galpha12 and c-raf-1 cDNAs were co-transfected into NIH3T3 cells. NIH3T3 cells coexpressing both Galpha12 and c-raf-1 resulted in the constitutive activation of the mitogenic-activated protein kinase (MAPK). In addition, the levels of GTP-bound Ras were elevated in Galpha12 transformed NIH3T3 cells. Our results provide a model for studying the effects of simultaneous activation of two distinct growth regulatory pathways in cellular transformation.