Oxidized low density lipoproteins stimulate galactosyltransferase activity, ras activation, p(44) mitogen activated protein kinase and c-fos expression in aortic smooth muscle cells

Previously, our laboratory has shown that oxidized low density lipoproteins (Ox-LDL) can exert a concentration-dependent stimulation in the proliferation of aortic smooth muscle cells, ''a hallmark in the pathogenesis of atherosclerosis'' (Chatterjee,S. (1992) Mel. Cell, Biochem., 111, 143-147), Here we report a novel aspect of Ox-LDL-mediated signal transduction, We demonstrate that in aortic smooth muscle cells, Ox-LDL stimulates the activity of a UDP-galactose:glucosylceramide beta 1-->4 galactosyltransferase (GalT-2) and phosphorylation/activation of p(44) mitogen-activated protein (MAP) kinase (p(44) MAPK). The activity of GalT-2 increased about 2-fold within 2.5-5 min of incubation of cells with Ox-LDL (10 mu g/ml), After 5 min of incubation of cells with Ox-LDL, but not LDL, there was a 2-fold increase in the activity of p(44) MAPK, Phosphoamino acid analysis employing thin layer chromatography revealed that the tyrosine and threonine moieties of,44 MAPK was phosphorylated by Ox-LDL. D-1-Phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP; a potent inhibitor of GalT-2) impaired the Ox-LDL mediated induction of p(44) MAPK activity and the phosphorylation of tyrosine and threonine residues in p(44) MAPK, This phenomenon was bypassed by the simultaneous addition of lactosylceramide. The upstream and downstream parameters in MAP kinase signaling pathways were investigated next, We found that Ox-LDL stimulated (9-fold) the loading of GTP on Pas, Interestingly, Ox-LDL specifically induced c-fos mRNA expression (6.5-fold) in these cells, as compared to the control, Thus, one of the biochemical mechanisms in Ox-LDL mediated induction in the proliferation in aortic smooth muscle cells may involve GalT-2 activation, lactosylceramide production, Pas GTP loading, activation of the kinase cascade, and c-fos expression.