Seven helix chemoattractant receptors transiently stimulate mitogen-activated protein kinase in Dictyostelium. Role of heterotrimeric G proteins.

Mitogen-activated protein (MAP) kinases are involved in controlling a cell's responses to a variety of stimuli and can be activated by both protein tyrosine kinase and G protein-coupled receptors. It was shown previously that Dictyostelium MAP kinase ERK2 is required for normal activation of adenylyl cyclase and erk2 null cells are aggregation-deficient. In this manuscript, we show that the Dictyostelium MAP kinase ERK2 is rapidly and transiently activated in response to the chemoattractant cAMP. This response requires cAMP receptors, but is independent of the coupled G alpha2 subunit and the only known G beta subunit. These data indicate that ligand-mediated receptor activation of adenylyl cyclase requires two receptor-dependent pathways, one of which requires heterotrimeric G proteins, including G alpha2 and the only known G beta subunit, and the second of which requires ERK2. Our results suggest that ERK2 may be activated by a novel receptor-mediated pathway.