Regulation of scavenger receptor expression in smooth muscle cells by protein kinase C: a role for oxidative stress.
Phorbol esters increase scavenger-receptor mRNA expression and receptor activity in smooth muscle cells (SMCs). Our present results demonstrate that activation of protein kinase C (PKC) mediates this increase in receptor expression. This conclusion is based on the findings that (1) phorbol esters induced translocation of PKC-alpha from the cytosol to the membrane fraction; (2) PKC inhibitors blocked the effect of phorbol esters on receptor expression; (3) diacylglycerol, a physiological PKC agonist, enhanced scavenger-receptor activity; and (4) in cotransfected human SMCs, constitutively active PKC-alpha stimulated the expression of a reporter gene under control of the scavenger-receptor promoter. Phorbol ester treatment of SMCs increased intracellular reactive oxygen, and the increase in receptor activity was reduced 30% by the antioxidant N-acetyl cysteine (NAC), suggesting a role for reactive oxygen in phorbol ester-mediated receptor regulation. Furthermore, direct treatment of SMCs with reactive oxygen species increased scavenger-receptor activity. In rabbit SMCs, 100 micromol/L H2O2 alone slightly increased scavenger-receptor mRNA and protein expression. In combination, 100 micromol/L H2O2 and 10 micromol/L vanadate, which promotes formation of OH and enhances the inhibition of protein tyrosine phosphatase by H2O2, increased scavenger-receptor mRNA expression 25-fold in rabbit SMCs and 8-fold in human SMCs. NAC reduced the effect of H2O2 and vanadate by 93%. The increase in SMC scavenger-receptor expression occurs at the level of gene transcription. Receptor mRNA half-life was unchanged after treatment with either phorbol esters or reactive oxygen (approximately 14.5 hours), and induction by phorbol esters increased SMC scavenger-receptor mRNA transcription, as determined by nuclear run-on assay. Multiple cytokines and growth factors that contribute to the generation of reactive oxygen species are present in atherosclerotic lesions. These factors may all contribute to the upregulation of SMC scavenger-receptor activity and therefore to the formation of smooth muscle foam cells.
Mietus-Snyder
M
M
Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94141-9100, USA.
Friera
A
A
Glass
C K
CK
Pitas
R E
RE
D000818:Animals; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008156:Luciferases / Q000235:genetics; D008565:Membrane Proteins; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D018384:Oxidative Stress; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D011817:Rabbits; D017382:Reactive Oxygen Species; D011971:Receptors, Immunologic / Q000235:genetics*; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D011993:Recombinant Fusion Proteins; D051122:Scavenger Receptors, Class B; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D015854:Up-Regulation
D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D011971:Receptors, Immunologic; D018110:Receptors, Lipoprotein; D051116:Receptors, Scavenger; D011993:Recombinant Fusion Proteins; C454739:Scarb1 protein, mouse; D051122:Scavenger Receptors, Class B; D006861:Hydrogen Peroxide; D008156:Luciferases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate