F. Mitchell, L. Heasley, N. Qian
Apr 14, 1995
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2
Influential Citations
42
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Journal
The Journal of Biological Chemistry
Abstract
Mitogenic stimulation of Swiss 3T3 fibroblasts with bombesin results in receptor-mediated activation of a complex array of effectors, including phospholipase Cβ and mitogen-activated protein (MAP) kinase. Incubation of Swiss 3T3 fibroblasts with the 11-amino acid [D-Arg1, D-Phe5, D-Trp7,9,Leu11]substance P peptide inhibited bombesin-stimulated cell proliferation and phospholipase Cβ activation even at high bombesin concentrations. The peptide did not inhibit the activation of phospholipase Cβ by a GTPase-deficient form of the Gq-like protein, G16, indicating that the peptide does not inhibit phospholipase Cβ and is acting at a point upstream of the activated form of the G protein α subunit. The peptide inhibited MAP kinase activation at low bombesin concentrations, but unlike phospholipase Cβ, this inhibition could be overcome with 30 n M bombesin. In control Swiss 3T3 cells, bombesin did not measurably activate Ras or Raf-1 above basal levels. Following incubation of the cells with the [D-Arg1, D-Phe5, D-Trp7,9,Leu11]substance P peptide, 50 n M bombesin activated Raf-1 4-6-fold over basal levels. Platelet-derived growth factor-stimulated activities of PLC, Ras, Raf-1, and MAP kinase were unaltered after incubation of Swiss 3T3 cells with the [D-Arg1, D-Phe5, D-Trp7,9,Leu11]substance P peptide, as was platelet-derived growth factor-stimulated growth of the Swiss 3T3 cells. Thus, the peptide behaves as an antagonist that differentially inhibited phospholipase Cβ and MAP 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.