A CELL-DENSITY SENSING FACTOR REGULATES THE LIFETIME OF A CHEMOATTRACTANT-INDUCED G-ALPHA-GTP CONFORMATION

Starving Dictyostelium discoideum cells monitor the local density of o ther starving cells by simultaneously secreting and sensing CMF. CMF r egulates signal transduction through the chemoattractant cAMP receptor , cAR1. cAR1 activates a heterotrimeric G protein by stimulating G alp ha 2 to release GDP and bind GTP. We show here that the rate of cAMP-s timulated GTP hydrolysis in membranes from cells exposed to CMF is rou ghly 4 times slower than in membranes from untreated cells, even thoug h the rate of GTP binding is the same. This hydrolysis is abolished in cells lacking G alpha 2. Our data thus suggest that CMF regulates cAM P signal transduction in part by prolonging the lifetime of the G alph a 2-GTP complex. (C) 1997 Federation of European Biochemical Societies .