Gastrin induces c-fos gene transcription via multiple signaling pathways

We previously observed that the trophic actions of gastrin (G17) on the AR4 2J rat acinar cell line are mediated by mitogen-activated protein kinase (M APK)-induced c-fos gene transcription via protein kinase C (PKC)-dependent and -independent pathways. In this study, we further investigated the signa ling pathways that target c-fos in response to G17. G17 led to a sixfold in duction in luciferase activity in cells transfected with plasmids containin g the -356+109 sequence of the murine c-fos promoter, which includes the Si s-inducible element (SIE), serum response element (SRE), and the Ca2+/cAMP response element (CRE) regulatory elements. Addition of either the selectiv e PKC inhibitor GF-109203X or the MAPK/extracellular signal-regulated kinas e inhibitor PD-98059 resulted in an 80% reduction in luciferase activity. G 17 induced the transcriptional activity of both Elk-l and Sap-la, transcrip tion factors that bind to the E26 transformation specific (Ets) DNA sequenc e of the SRE, and this effect was inhibited by both GF-109203X and PD-98059 . Point mutations in the Ets sequence led to a 4-fold induction of c-fos tr anscription stimulated by G17 and to a 1.3-fold induction in response to ep idermal growth factor (EGF). In contrast, mutations in the CA rich G (CArG) sequence of the SRE prevented transcriptional activation by both G17 and E GF. G17 induction of the Ets mutant construct was unaffected by either GF-1 09203X or PD-98059. Because activation of the SRE involves the small GTP-bi nding protein Rho A, we examined the role of Rho A in G17 induction of c-fo s transcription. Inactivation of Rho A by either the specific inhibitor C3 or by expression of a dominant negative Rho A gene inhibited G17 induction of both the wild-type and the Ets mutant constructs by 60%. C3 also inhibit ed G17-stimulated AR42J cell proliferation. Thus G17 targets the c-fos prom oter CArG sequence via Rho A-dependent pathways, and Rho A appears to play an important role in the regulation of the trophic action of G17.