Bombesin, diacylglycerols, and phorbol esters rapidly stimulate the phosphorylation of an Mr = 80,000 protein kinase C substrate in permeabilized 3T3 cells. Effect of guanine nucleotides.
We have used digitonin permeabilization to study the mechanism of bombesin-induced activation of protein kinase C in Swiss 3T3 cells. Protein kinase C-mediated phosphorylations in permeabilized cells were identified using phorbol esters and diacylglycerols. Addition of phorbol 12,13-dibutyrate (PDBu) in the presence of [gamma-32P]ATP and digitonin caused a marked and rapid time- and dose-dependent increase in the phosphorylation of an Mr 80,000 cellular protein (maximum stimulation = 12.6 +/- 1.6-fold after 1 min, EC50 = 27 nM). 1-oleoyl-2-acetylglycerol substituted for PDBu in stimulating the phosphorylation of Mr 80,000 protein (EC50 = 13 microM). Bombesin also caused a striking increase in the phosphorylation of Mr 80,000 protein with a time course similar to that observed with PDBu. This phosphorylation was mimicked by mammalian bombesin-like peptides and blocked by the bombesin antagonists [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P and [Leu13 psi (CH2NH)Leu14]bombesin. Down-regulation of protein kinase C in intact cells by prolonged exposure to PDBu prevented Mr 80,000 protein phosphorylation upon subsequent bombesin addition in digitonin-permeabilized cells. Comigration on one- and two-dimensional gel electrophoresis and phosphopeptide mapping confirmed that the Mr 80,000 protein phosphorylated in permeabilized cells was indistinguishable from the Mr 80,000 protein which is the major protein kinase C substrate in intact cells. The GDP analogue guanosine-5'-O-(2-thiodiphosphate) (GDP beta S) caused a 70% inhibition of the bombesin-induced phosphorylation of Mr 80,000 protein but had no effect on the phosphorylation induced by PDBu. Bombesin stimulated Mr 80,000 protein phosphorylation in permeabilized cells in a dose-dependent manner (EC50 = 4 nM), and GDP beta S shifted the bombesin dose response curve to higher bombesin concentrations (EC50 = 14 nM). These results demonstrate for the first time a growth factor receptor-mediated activation of protein kinase C in permeabilized cells and provide functional evidence for the involvement of a G protein in the transmembrane signaling pathway that mediates the stimulation of protein kinase C by bombesin in Swiss 3T3 cells.
Erusalimsky
J D
JD
Imperial Cancer Research Fund, London, United Kingdom.
Friedberg
I
I
Rozengurt
E
E
D000818:Animals; D001839:Bombesin / Q000494:pharmacology*; D002460:Cell Line; D004075:Diglycerides / Q000494:pharmacology*; D004789:Enzyme Activation; D005989:Glycerides / Q000494:pharmacology*; D006150:Guanine Nucleotides / Q000494:pharmacology*; D008970:Molecular Weight; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*
D004075:Diglycerides; D005989:Glycerides; D006150:Guanine Nucleotides; D010703:Phorbol Esters; D011506:Proteins; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; D001839:Bombesin