DIFFERENTIAL MODULATION OF BOMBESIN-STIMULATED PHOSPHOLIPASE C-BETA AND MITOGEN-ACTIVATED PROTEIN-KINASE ACTIVITY BY [D-ARG(1),D-PHE(5),D-TRP(7,9),LEU(11)] SUBSTANCE-P

Mitogenic stimulation of Swiss 3T3 fibroblasts with bombesin results i n receptor-mediated activation of a complex array of effecters, includ ing phospholipase C beta and mitogen-activated protein (MAP) kinase. I ncubation of Swiss 3T3 fibroblasts with the 11-amino acid [D-Arg(1),D- Phe(5),D-Trp(7,9),Leu(11)]substance P peptide inhibited bombesin-stimu lated cell proliferation and phospholipase C beta activation even at h igh bombesin concentrations. The peptide did not inhibit the activatio n of phospholipase C beta by a GTPase-deficient form of the G(q)-like protein, G(16), indicating that the peptide does ndt inhibit phospholi pase C beta and is acting at a point upstream of the activated form of the G protein alpha subunit. The peptide inhibited MAP kinase activat ion at low bombesin concentrations, but unlike phospholipase C beta, t his inhibition could be overcome with 30 nM bombesin, In control Swiss 3T3 cells, bombesin did not measurably activate has or Raf-1 above ba sal levels. Following incubation of the cells with the [D-Arg(1),D-Phe (5),D-Trp(7,9),Leu(11)]substance P peptide, 50 nM bombesin activated R af-1 4-6-fold over basal levels. Platelet-derived growth factor stimul ated activities of PLC, Ras, Raf-1, and MAP kinase were unaltered afte r incubation of Swiss 3T3 cells with the [D-Arg(1),D-Phe(5),D-Trp(7,9) ,Leu(11)]substance P peptide, as was platelet-derived growth factor-st imulated growth of the Swiss 3T3 cells. Thus, the peptide behaves as a n antagonist that differentially inhibited phospholipase C beta and MA P kinase signal transduction pathways. The growth arrest observed with the peptide indicates that the bombesin-stimulated activation of MAP kinase is not sufficient to support mitogenesis in Swiss 3T3 cells.