title: Src kinase mediates the regulation of phospholipase C-gamma activity by glycosphingolipids.
abstract: Glucosylceramide-based glycosphingolipids have been previously demonstrated to regulate negatively the formation of inositol 1,4,5-trisphosphate by phospholipase C-gamma1. In the present study, the depletion of endogenous glucosylceramide by D-t-EtDO-P4 in cultured ECV304 cells induced autophosphorylation of Src kinase at tyrosine residue 418 within the catalytic loop and dephosphorylation of Src kinase at tyrosine residues 529 within the carboxyl-terminal regulatory region. Phosphotransferase activities of Src kinase were also induced in the glucosylceramide-depleted cells. c-Src kinase activity and phosphorylations at Src Tyr-418 and epidermal growth factor (EGF) receptor Tyr-1068 were significantly enhanced by bradykinin in response to 100 nm D-t-EtDO-P4 compared with control cells. The phosphorylation and dephosphorylation on Tyr-418 and Tyr-529 residues of c-Src were reversed by treatment of 4-amino-5-(4-chlorophenyl)-7-t-butyl(pyrazolo)[3,4-d]pyrimidine (PP2), an inhibitor of Src kinase, in control cells. Glucosylceramide-depleted cells resisted treatment with PP2, and both phosphorylation of Tyr-418 and dephosphorylation of Tyr-529 induced by depletion of glucosylceramide were maintained. Compared with untreated cells, tyrosine phosphorylation of phospholipase C-gamma1 was enhanced by EGF stimulation in glucosylceramide-depleted cells, associated with enhanced tyrosine phosphorylation of the EGF receptor at Tyr-1068 and Tyr-1086 stimulated by EGF. The Src inhibitor, PP2, significantly blocked EGF-induced tyrosine phosphorylation of phospholipase C-gamma1 in control cells, whereas in glucosylceramide-depleted cells, suppression of Src kinase activity by PP2 toward EGF-induced tyrosine phosphorylation of phospholipase C-gamma1 was less significant. Thus the activation of Src kinase by depletion of glucosylceramide-based glycosphingolipids in cultured ECV304 cells is a critical up-stream event in the activation of phospholipase C-gamma1.
authors.affiliation: Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109-0676, USA.
authors.forename: Liming
authors.initials: L
authors.lastname: Shu
authors.forename: James A
authors.initials: JA
authors.lastname: Shayman
mesh_terms: D000595:Amino Acid Sequence; D001920:Bradykinin / Q000494:pharmacology; D002478:Cells, Cultured; D006028:Glycosphingolipids / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011743:Pyrimidines / Q000494:pharmacology; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000378:metabolism*; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: C412373:AG 1879; D006028:Glycosphingolipids; D010446:Peptide Fragments; D011743:Pyrimidines; D019061:src-Family Kinases; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D001920:Bradykinin