title: Vitamin E isoforms differentially regulate intercellular adhesion molecule-1 activation of PKCα in human microvascular endothelial cells.
abstract: OBJECTIVE
  ICAM-1-dependent leukocyte recruitment in vivo is inhibited by the vitamin E isoform d-α-tocopherol and elevated by d-γ-tocopherol. ICAM-1 is reported to activate endothelial cell signals including protein kinase C (PKC), but the PKC isoform and the mechanism for ICAM-1 activation of PKC are not known. It is also not known whether ICAM-1 signaling in endothelial cells is regulated by tocopherol isoforms. We hypothesized that d-α-tocopherol and d-γ-tocopherol differentially regulate ICAM-1 activation of endothelial cell PKC.
  
  
  RESULTS
  ICAM-1 crosslinking activated the PKC isoform PKCα but not PKCβ in TNFα-pretreated human microvascular endothelial cells. ICAM-1 activation of PKCα was blocked by the PLC inhibitor U73122, ERK1/2 inhibitor PD98059, and xanthine oxidase inhibitor allopurinol. ERK1/2 activation was blocked by inhibition of XO and PLC but not by inhibition of PKCα, indicating that ERK1/2 is downstream of XO and upstream of PKCα during ICAM-1 signaling. During ICAM-1 activation of PKCα, the XO-generated ROS did not oxidize PKCα. Interestingly, 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.
  
  
  CONCLUSIONS
  Crosslinking ICAM-1 stimulated XO/ROS which activated ERK1/2 that then activated PKCα. ICAM-1 activation of PKCα was inhibited by d-α-tocopherol and this inhibition was ablated by the addition of d-γ-tocopherol. These tocopherols regulated ICAM-1 activation of PKCα without altering the upstream signal ERK1/2. Thus, we identified a mechanism for ICAM-1 activation of PKC and determined that d-α-tocopherol and d-γ-tocopherol have opposing regulatory functions for ICAM-1-activated PKCα in endothelial cells.
authors: Allergy-Immunology Division, Northwestern University Feinberg School of Medicine, Chicago, Illinois, United States of America.
authors: Hiam
authors: H
authors: Abdala-Valencia
authors: Sergejs
authors: S
authors: Berdnikovs
authors: Joan M
authors: JM
authors: Cook-Mills
mesh_terms: D003545:Cysteine / Q000737:chemistry; D042783:Endothelial Cells / Q000166:cytology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism*; D008168:Lung / Q000166:cytology; D008833:Microcirculation; D010100:Oxygen / Q000737:chemistry; D010766:Phosphorylation; D020033:Protein Isoforms; D051571:Protein Kinase C-alpha / Q000378:metabolism*; D014810:Vitamin E / Q000737:chemistry*; D014969:Xanthine Oxidase / Q000378:metabolism
chemical_list: D020033:Protein Isoforms; D018799:Intercellular Adhesion Molecule-1; D014810:Vitamin E; D014969:Xanthine Oxidase; D051571:Protein Kinase C-alpha; D048049:Extracellular Signal-Regulated MAP Kinases; D003545:Cysteine; D010100:Oxygen