Item

Abstract

This study investigates interaction of bombesin receptors with heterotrimeric guanosine triphosphate (GTP)-binding proteins (G proteins) and monomeric small molecular weight GTP-binding proteins (smg proteins), respectively, in plasma membranes (PM) of rat pancreatic acinar cells. Addition of bombesin to isolated PM stimulated the incorporation of the photoaffinity analogue [alpha-^rasP]GTP-gamma-azidoanilide into G_i proteins of 40-41 kDa and reduced the pertussis toxin-induced ADP ribosylation of three 40-41 kDa proteins, which had been previously identified as G_i1, G_i2, and G_i3 (30). In PM isolated from bombesin-prestimulated acinar cells, binding of [alpha-^rasP]-GTP to PM proteins of 21-22 kDa and of a monoclonal antibody against p21^ras proteins was increased. Two-dimensional separation of PM proteins revealed the presence of 18 or 19 differently charged smg proteins. The p21^ras proteins could be separated into two differently charged proteins with isoelectric points of 5.58 and 5.79. In microsomal membranes (MM), [alpha-³²P]GTP binding to yet unidentified 21-22 kDa smg proteins was decreased compared with membranes from unstimulated acinar cells. The data suggest that G_i proteins as well as p21^ras proteins are involved in bombesin receptor-mediated signal transduction in the PM. Furthermore, 21-22 kDa smg proteins in MM might play a role in bombesin-induced stimulation of intracellular pathways that lead to enzyme secretion from pancreatic acinar cells.