Modulation of phosphorylation of tocopherol and phosphatidylinositol by hTAP1/SEC14L2-mediated lipid exchange

Jean-Marc Zingg, Roksan Libinaki, Mohsen Meydani, Angelo Azzi

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21 Citations (Scopus)

Abstract

The vitamin E derivative, alpha-tocopheryl phosphate (alphaTP), is detectable in cultured cells, plasma and tissues in small amounts, suggesting the existence of enzyme(s) with alpha-tocopherol (alphaT) kinase activity. Here, we characterize the production of alphaTP from alphaT and [gamma-32P]-ATP in primary human coronary artery smooth muscle cells (HCA-SMC) using separation by thin layer chromatography (TLC) and subsequent analysis by Ultra Performance Liquid Chromatography (UPLC). In addition to alphaT, although to a lower amount, also gammaT is phosphorylated. In THP-1 monocytes, gammaTP inhibits cell proliferation and reduces CD36 scavenger receptor expression more potently than alphaTP. Both alphaTP and gammaTP activate the promoter of the human vascular endothelial growth factor (VEGF) gene with similar potency, whereas alphaT and gammaT had no significant effect. The recombinant human tocopherol associated protein 1 (hTAP1, hSEC14L2) binds both alphaT and alphaTP and stimulates phosphorylation of alphaT possibly by facilitating its transport and presentation to a putative alphaT kinase. Recombinant hTAP1 reduces the in vitro activity of the phosphatidylinositol-3-kinase gamma (PI3Kgamma) indicating the formation of a stalled/inactive hTAP1/PI3Kgamma heterodimer. The addition of alphaT, betaT, gammaT, deltaT or alphaTP differentially stimulates PI3Kgamma, suggesting facilitated egress of sequestered PI from hTAP1 to the enzyme. It is suggested that the continuous competitive exchange of different lipophilic ligands in hTAPs with cell enzymes and membranes may be a way to make these lipophiles more accessible as substrates for enzymes and as components of specific membrane domains.
Original languageEnglish
Article numbere101550
Number of pages10
JournalPLoS ONE
Volume9
Issue number7
DOIs
Publication statusPublished - 2014

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