title: Modulation of phosphorylation of tocopherol and phosphatidylinositol by hTAP1/SEC14L2-mediated lipid exchange.
abstract: The vitamin E derivative, alpha-tocopheryl phosphate (αTP), is detectable in cultured cells, plasma and tissues in small amounts, suggesting the existence of enzyme(s) with α-tocopherol (αT) kinase activity. Here, we characterize the production of αTP from αT and [γ-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 αT, although to a lower amount, also γT is phosphorylated. In THP-1 monocytes, γTP inhibits cell proliferation and reduces CD36 scavenger receptor expression more potently than αTP. Both αTP and γTP activate the promoter of the human vascular endothelial growth factor (VEGF) gene with similar potency, whereas αT and γT had no significant effect. The recombinant human tocopherol associated protein 1 (hTAP1, hSEC14L2) binds both αT and αTP and stimulates phosphorylation of αT possibly by facilitating its transport and presentation to a putative αT kinase. Recombinant hTAP1 reduces the in vitro activity of the phosphatidylinositol-3-kinase gamma (PI3Kγ) indicating the formation of a stalled/inactive hTAP1/PI3Kγ heterodimer. The addition of αT, βT, γT, δT or αTP differentially stimulates PI3Kγ, 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.
authors.affiliation: Vascular Biology Laboratory, JM USDA-Human Nutr. Res. Ctr. On Aging, Tufts University, Boston, Massachusetts, United States of America.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Zingg
authors.affiliation: Dept. Biochem. and Mol. Biology, Monash University, Melbourne, VIC, Australia.
authors.forename: Roksan
authors.initials: R
authors.lastname: Libinaki
authors.affiliation: Vascular Biology Laboratory, JM USDA-Human Nutr. Res. Ctr. On Aging, Tufts University, Boston, Massachusetts, United States of America.
authors.forename: Mohsen
authors.initials: M
authors.lastname: Meydani
authors.affiliation: Vascular Biology Laboratory, JM USDA-Human Nutr. Res. Ctr. On Aging, Tufts University, Boston, Massachusetts, United States of America.
authors.forename: Angelo
authors.initials: A
authors.lastname: Azzi
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D003331:Coronary Vessels / Q000166:cytology / Q000378:metabolism*; D006801:Humans; D050356:Lipid Metabolism / Q000502:physiology*; D008074:Lipoproteins / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D024505:Tocopherols / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D008074:Lipoproteins; D010716:Phosphatidylinositols; C432422:SEC14L2 protein, human; D015534:Trans-Activators; D019869:Phosphatidylinositol 3-Kinases; C523442:PIK3R3 protein, human; D024505:Tocopherols