7 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 a ctivation of adenylyl cyclase and erk2 null cells are aggregation-defi cient. In this manuscript, we show that the Dictyostelium MAP kinase E RK2 is rapidly and transiently activated in response to the chemoattra ctant cAMP. This response requires cAMP receptors, but is independent of the coupled G alpha 2 subunit and the only known G beta subunit. Th ese data indicate that ligand-mediated receptor activation of adenylyl cyclase requires two receptor-dependent pathways, one of which requir es heterotrimeric G proteins, including G alpha 2 and the only known G beta subunit, and the second of which requires ERK2. Our results sugg est that ERK2 may be activated by a novel receptor-mediated pathway.