Fatty acids inhibit growth-factor-induced diacylglycerol kinase or activation in vascular smooth-muscle cells

We have previously shown that unsaturated fatty acids amplify platelet-deri ved-growth-factor (PDGF)-induced protein kinase C (PKC) activation in vascu lar smooth-muscle cells (VSMCs), Diacylglycerol-induced PKC activation is n ormally terminated by diacylglycerol kinases (DGKs), We thus hypothesized t hat fatty acids act by inhibiting a DGK, Fractionation of VSMC extracts dem onstrated that the DGK. a isoform was the major DGK activity present. PDGF markedly increased the DGK activity of cultured cells. An inhibitor selecti ve for the DGK a isoform, R59949 [3-{2-[4-(bis-(4-fluorophenyl}methylene]-p iperidin-1-yl)ethyl)-2,3-dihydro-2-thioxo-4(1H)-quinazolinone], abolished t he growth-factor-induced increase in DGK activity, but had little effect on basal activity. PDGF thus selectively activates DGK alpha. Epidermal growt h factor and a-thrombin stimulated total DGK activity similarly to PDGF. Ac tivation by epidermal growth factor was sensitive to R59949, again suggesti ng involvement of DGK alpha. However, the alpha -thrombin-induced activity was unaffected by this agent, Unsaturated fatty acids inhibited growth-fact or-induced DGK alpha activation, but had no effect on basal activity. Fatty acids also amplified the PDGF-induced increase in cell diacylglycerol cont ent. These results indicate that inhibition of DGK alpha contributes to fat ty-acid-induced amplification of PKC activation, increased levels of fatty acids in diabetes may thus contribute to chronic PKC activation associated with this disorder.