Stat3-mediated transformation of NIH-3T3 cells by the constitutively active Q205L G alpha(o) protein

Expression of Q205L G alpha(o) (G alpha(o)*), an alpha subunit of heterotri meric guanine nucleotide-binding proteins (G proteins) that lacks guanosine triphosphatase (GTPase) activity in NIH-3T3 cells, results in transformati on. Expression of G alpha(o)* in NIH-3T3 cells activated signal transducer and activator of transcription 3 (Stat3) but not mitogen-activated protein (MAP) kinases 1 or 2, Coexpression of dominant negative Stat3 inhibited G a lpha(o)*-induced transformation of NIH-3T3 cells and activation of endogeno us Stat3, Furthermore, G alpha(o)* expression increased activity of the tyr osine kinase c-Src, and the G alpha(o)*-induced activation of Stat3 was blo cked by expression of Csk (carboxyl-terminal Src kinase), which inactivates c-Src. The results indicate that Stat3 can function as a downstream effect or for G alpha(o)* and mediate its biological effects.