Activation of c-fos promoter by Gbetagamma-mediated signaling: involvement of Rho and c-Jun N-terminal kinase.

Abstract

Several extracellular stimuli mediated by G protein-coupled receptors activate c-fos promoter. Recently, we and other groups have demonstrated that signals from G protein-coupled receptors stimulate mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAPK. The activation of these three MAPKs is mediated in part by the G protein betagamma subunit (Gbetagamma). In this study, we characterized the signals from Gbetagamma to c-fos promoter using transient transfection of c-fos luciferase into human embryonal kidney 293 cells. Activation of m2 muscarinic acetylcholine receptor and overexpression of Gbetagamma, but not constitutively active Galphai2, stimulated c-fos promoter activity. The c-fos promoter activation by m2 receptor and Gbetagamma was inhibited by beta-adrenergic receptor kinase C-terminal peptide (betaARKct), which functions as a Gbetagamma antagonist. MEK1 inhibitor PD98059 and kinase-deficient mutant of JNK kinase, but not p38 MAPK inhibitor SB203580, attenuated the m2 receptor- and Gbetagamma-induced c-fos promoter activation. Activated mutants of Ras and Rho stimulated the c-fos promoter activity, and the dominant negative mutants of Ras and Rho inhibited the c-fos promoter activation by m2 receptor and Gbetagamma. Moreover, c-fos promoter activation by m2 receptor, Gbetagamma, and active Rho, but not active Ras, was inhibited by botulinum C3 toxin. These data indicated that both Ras- and Rho-dependent signaling pathways are essential for c-fos promoter activation mediated by Gbetagamma.