G-PROTEINS OF THE G(Q) FAMILY COUPLE THE H-2 HISTAMINE-RECEPTOR TO PHOSPHOLIPASE-C

In several cell systems histamine has been shown to stimulate both ade nylyl cyclase and phospholipase C through activation of a G protein-co upled H-2 receptor. To analyze the bifurcating signal emanating from t he activated H-2 receptor and to identify the G proteins involved, H-1 and H-2 histamine receptors were functionally expressed in baculoviru s-infected insect cells, Histamine challenge lead to concentration-dep endent cAMP formation and Ca2+ mobilization in Sf9 cells infected with a virus encoding the H-2 receptor, whereas H-1 receptor stimulation o nly resulted in pronounced phospholipase C activation, To analyze the G protein coupling pattern of histamine receptors, activated G protein s were labeled with [alpha-32P]GTP azidoanilide and identified by sele ctive immunoprecipitation. In insect cell membranes expressing H-1 his tamine receptors, histamine led to incorporation of the label into alp ha-(32)like proteins, whereas activation of the H-2 receptor resulted in labeling of a(q)- and alpha(s)-like G protein alpha-subunits. In CO S cells transfected with H-2 receptor complementary DNA, histamine cau sed concentration-dependent accumulation of cAMP and inositol phosphat es; the latter effect was insensitive to pertussis toxin treatment. Hi stamine stimulation led to a pronounced increase in inositol phosphate production when complementary DNAs coding for alpha(q), alpha(11), al pha(14), or alpha(15) G protein alpha-subunits were cotransfected. Thi s increase was specific for G(q) family members, as overexpression of alpha(12) or alpha(s) did not enhance histamine-stimulated phospholipa se C activation. In membranes of guinea pig heart, addition of [alpha- P-32]GTP azidoanilide resulted in labeling of alpha(q) and alpha(11) v ia the activated H-1 and also via H-2 receptors. These data demonstrat e that dual signaling of the activated H-2 histamine receptor is media ted by coupling of the receptor to G(s) and G(q) family members.