Antagonistic Effects of Oxidized Low Density Lipoprotein and α-Tocopherol on CD36 Scavenger Receptor Expression in Monocytes

• Published in: The Journal of biological chemistry 2006-03, Vol.281 (10), p.6489-6497
• Main Authors: Munteanu, Adelina, Taddei, Michele, Tamburini, Ilaria, Bergamini, Ettore, Azzi, Angelo, Zingg, Jean-Marc
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M508799200

Vitamin E deficiency increases expression of the CD36 scavenger receptor, suggesting specific molecular mechanisms and signaling pathways modulated by α-tocopherol. We show here that α-tocopherol down-regulated CD36 expression (mRNA and protein) in oxidized low density lipoprotein (oxLDL)-stimulated THP-1 monocytes, but not in unstimulated cells. Furthermore, α-tocopherol treatment of monocytes led to reduction of fluorescent oxLDL-3,3′-dioctadecyloxacarbocyanine perchlorate binding and uptake. Protein kinase C (PKC) appears not to be involved because neither activation of PKC by phorbol 12-myristate 13-acetate nor inhibition by PKC412 was affected by α-tocopherol. However, α-tocopherol could partially prevent CD36 induction after stimulation with a specific agonist of peroxisome proliferator-activated receptor-γ (PPARγ; troglitazone), indicating that this pathway is susceptible to α-tocopherol action. Phosphorylation of protein kinase B (PKB) at Ser473 was increased by oxLDL, and α-tocopherol could prevent this event. Expression of PKB stimulated the CD36 promoter as well as a PPARγ element-driven reporter gene, whereas an inactive PKB mutant had no effect. Moreover, coexpression of PPARγ and PKB led to additive induction of CD36 expression. Altogether, our results support the existence of PKB/PPARγ signaling pathways that mediate CD36 expression in response to oxLDL. The activation of CD36 expression by PKB suggests that both lipid biosynthesis and fatty acid uptake are stimulated by PKB.