Vitamin E Isoforms Differentially Regulate Intercellular Adhesion Molecule-1 Activation of PKCα in Human Microvascular Endothelial Cells (173.25)

Abstract

Abstract Leukocytes bind to ICAM-1 on endothelial cells during leukocyte transendothelial migration. ICAM-1 is reported to activate endothelial cell xanthine oxidase (XO), protein kinase C(PKC) and ERK1/2, but the PKC isoform and the pathway involving these signals is not known. PKCα can be directly regulated by vitamin E, but it is not known whether vitamin E regulates ICAM-1 activation of PKC. Therefore, we identified an ICAM-1 signaling pathway and determined whether these signals are regulated by the vitamin E isoforms d-α-tocopherol and d-γ-tocopherol. In primary cultures of TNFα-stimulated human microvascular endothelial cells, ICAM-1 crosslinking activated the PKC isoform PKCα but not PKCβ. ICAM-1-activated XO stimulated ERK1/2 activation that then induced activation of PKCα. ICAM-1 crosslinking did not induce oxidative activation of PKCα. D-α-tocopherol inhibited ICAM-1 activation of PKCα but not the upstream signal ERK1/2. The d-α-tocopherol inhibition of PKCα was ablated by the addition of d-γ-tocopherol. In summary, ICAM-1 activation of XO and ERK1/2 stimulates endothelial PKCα without oxidation of PKCα. ICAM-1 activation of PKCα is inhibited by d-α-tocopherol and this inhibition is ablated by d-γ-tocopherol. These data are consistent with PKCα antagonist and agonist functions of d-α-tocopherol and d-γ-tocopherol, respectively, during ICAM-1 signaling.