Receptor specificity of growth factor-stimulated synthesis of 3-phosphorylated inositol lipids in Swiss 3T3 cells

Abstract

We have investigated synthesis of 3-phosphorylated inositol lipids in growth factor-stimulated Swiss 3T3 cells. Those growth factors tested which act via tyrosine kinase-containing receptors (platelet-derived growth factor (PDGF), insulin growth factor I (IGF-I), epidermal growth factor (EGF), and basic fibroblast growth factor (bFGF)) caused the rapid synthesis of [32P]PtdIns(3,4)P2 and [32P]PtdIns(3,4,5)P3 (PtdIns is phosphatidylinositol) in [32P]Pi-prelabeled cells and the appearance of an inositol lipid 3-OH kinase in antiphosphotyrosine immunoprecipates. In contrast, those growth factors tested which act via G-protein-coupled receptors (bombesin, vasopressin, prostaglandin E1) were unable to stimulate either of the above responses. Furthermore, while PDGF was able to increase the formation of PtdIns(3,4)P2 and PtdIns(3,4,5)P3 in streptolysin-permeabilized cells, guanosine 5′-3-(thio)triphosphate and guanyl-5′-yl imidodiphosphate were not. These results suggest that Swiss 3T3 cells possess the machinery for tyrosine kinase but not G-protein-mediated activation of PtdIns(4, 5)P2 3-OH kinase; a situation which is the inverse to that recently described for human neutrophils. The tyrosine kinase-containing receptors differed markedly in their relative abilities to elevate the levels of [32P] PtdIns(3,4,5)P3 (ranked in the order PDGF ≥ IGF-I > EGF > bFGF), [32P]Ptd-OH (PDGF > EGF > bFGF; undetectable for IGF-I), and [32P]PtdIns4P (EGF > bFGF > PDGF; undetectable for IGF-I) in [32P]Pi-prelabeled cells. These differences are epitomized by IGF-I, which was the joint most powerful stimulus for [32P] PtdIns(3,4,5)P3 formation, but was unable to stimulate a measurable accumulation of [32P]Ptd-OH (and hence, by deduction, was unable to stimulate phospholipase C). These results indicate that there is a differential ability among the tyrosine kinase-containing receptors present in a single cell to recruit phospholipase C and PtdIns(4, 5)P2 3-OH kinase into their signalling complexes and further emphasizes the notion that the rapid synthesis of PtdIns(3,4,5)P3 may be a signalling event.