Ca²⁺-mediated activation of ERK in hepatocytes by norepinephrine and prostaglandin F_2α: role of calmodulin and src kinases

Abstract

Abstract Background Previous studies have shown that several agents that stimulate heptahelical G-protein coupled receptors activate the extracellular signal regulated kinases ERK1 (p44mapk) and ERK2 (p42mapk) in hepatocytes. The molecular pathways that convey their signals to ERK1/2 are only partially clarified. In the present study we have explored the role of Ca2+ and Ca2+-dependent steps leading to ERK1/2 activation induced by norepinephrine and prostaglandin (PG)F2α. Results Pretreatment of the cells with the Ca2+ chelators BAPTA-AM or EGTA, as well as the Ca2+ influx inhibitor gadolinium, resulted in a partial decrease of the ERK response. Furthermore, the calmodulin antagonists W-7, trifluoperazine, and J-8 markedly decreased ERK activation. Pretreatment with KN-93, an inhibitor of the multifunctional Ca2+/calmodulin-dependent protein kinase, had no effect on ERK activation. The Src kinase inhibitors PP1 and PP2 partially diminished the ERK responses elicited by both norepinephrine and PGF2α. Conclusion The present data indicate that Ca2+ is involved in ERK activation induced by hormones acting on G protein-coupled receptors in hepatocytes, and suggest that calmodulin and Src kinases might play a role in these signaling pathways.