DUAL ROLE OF CAMP AND INVOLVEMENT OF BOTH G-PROTEINS AND RAS IN REGULATION OF ERK2 IN DICTYOSTELIUM-DISCOIDEUM

Dictyostelium discoideum expresses two Extracellular signal Regulated Kinases, ERK1 and ERK2, which are involved in growth, multicellular de velopment and regulation of adenylyl cyclase. Binding of extracellular cAMP to cAMP receptor 1, a G-protein coupled cell surface receptor, t ransiently stimulates phosphorylation, activation and nuclear transloc ation of ERK2. Activation of ERK2 by cAMP is dependent on heterotrimer ic G-proteins, since activation of ERK2 is absent in cells lacking the GaA subunit. The small G-protein rasD also activates ERK2. In cells o verexpressing a mutated, constitutively active rasD, ERK2 activity is elevated prior to cAMP stimulation. Intracellular cAMP and cAMP-depend ent protein kinase (PKA) are essential for adaptation of the ERK2 resp onse. This report shows that multiple signalling pathways are involved in regulation of ERK2 activity in D. discoideum.