title: Protein kinase C-mediated negative-feedback inhibition of unstimulated and bombesin-stimulated polyphosphoinositide hydrolysis in Swiss-mouse 3T3 cells.
abstract: Bombesin-related peptides stimulate a rapid increase in polyphosphoinositide hydrolysis in Swiss-mouse 3T3 cells. These peptides generate an increase in the efflux of 45Ca2+ from pre-labelled cells, a response consistent with an inositol trisphosphate-mediated mobilization of intracellular Ca2+. The bombesin-stimulated release of cellular 45Ca2+ is inhibited by tumour-promoting phorbol esters (e.g. 12-O-tetradecanoylphorbol 13-acetate, TPA). Although there are several possible sites of action at which this effect might occur, our results indicate that TPA induces an uncoupling of bombesin-stimulated hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) without decreasing cellular binding of bombesin. In cultured cells, protein kinase C can be down-modulated by a prolonged incubation of the cells with phorbol esters. Such pretreatment greatly decreased the inhibitory effect of TPA on bombesin-stimulated PIP2 hydrolysis, suggesting that this action of the phorbol ester is mediated via protein kinase C. Since diacylglycerol is an endogenous activator of protein kinase C and a direct product of PIP2 hydrolysis, these results suggest that protein kinase C inhibition of polyphosphoinositide hydrolysis may function as a negative-feedback pathway. Cells in which protein kinase C has been down-modulated show elevated basal and bombesin-stimulated production of inositol phosphates, providing evidence that such a feedback loop limits polyphosphoinositide turnover in both unstimulated and mitogen-stimulated cells.
authors.affiliation: A.F.R.C. Institute of Animal Physiology, Babraham, Cambridge, U.K.
authors.forename: K D
authors.initials: KD
authors.lastname: Brown
authors.forename: D M
authors.initials: DM
authors.lastname: Blakeley
authors.forename: M H
authors.initials: MH
authors.lastname: Hamon
authors.forename: M S
authors.initials: MS
authors.lastname: Laurie
authors.forename: A N
authors.initials: AN
authors.lastname: Corps
mesh_terms: D000818:Animals; D001839:Bombesin / Q000494:pharmacology*; D002132:Calcium Radioisotopes; D002478:Cells, Cultured; D006868:Hydrolysis; D051379:Mice; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D002132:Calcium Radioisotopes; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D001839:Bombesin