Alpha-tocopherol downregulates the expression of GPIIb promoter in HEL cells.
Alpha-tocopherol is known to inhibit platelet aggregation but the mechanism responsible for this has not been elucidated. Glycoprotein IIb (GPIIb) is the alpha-subunit of the platelet membrane protein GPIIb/IIIa, which functions as a specific receptor for platelet aggregation. Human erythroleukemia (HEL) cells are megakaryocytelike and express the megakaryocyte-specific GPIIb gene. To understand the molecular mechanism of alpha-tocopherol on antiaggregation, we analyzed the effect of physiologically relevant concentrations of alpha-tocopherol on the expression of human GPIIb promoter in HEL cells. The enhancement of tetradecanoylphoerbol-12,13-acetate (TPA)-mediated transient and optimal expression of plasmids was achieved by adding 10(-7)-M TPA in the medium 24 h before lipofection. Transient expression of GPIIb promoter was determined in transfected cells pretreated with various concentrations of alpha-tocopherol. Our data shows that the GPIIb promoter activity was downregulated to 55, 23, 27, 20, and 15% in the presence of 10, 20, 40, 80, and 120 microg/ml of alpha-tocopherol, respectively, as compared with that in the absence of alpha-tocopherol. The downregulation of alpha-tocopherol on the TPA-mediated GPIIb promoter activity may result in a reduction of GPIIb protein expression and thus contribute to antiplatelet aggregation.
Department of Biology, National Cheng Kung University, Tainan, Taiwan, ROC. sjchang@mail.ncku.edu.tw
S J
SJ
Chang
J S
JS
Lin
H H
HH
Chen
D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D017930:Genes, Reporter; D006801:Humans; D004915:Leukemia, Erythroblastic, Acute; D008533:Megakaryocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D010974:Platelet Aggregation / Q000187:drug effects; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000235:genetics*; D010980:Platelet Membrane Glycoproteins; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D015183:Restriction Mapping; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured; D014810:Vitamin E / Q000494:pharmacology*
D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; C032193:glycoprotein receptor GPIb-IX; D014810:Vitamin E; D015500:Chloramphenicol O-Acetyltransferase; D013755:Tetradecanoylphorbol Acetate