Expression of the α-tocopherol transfer protein gene is regulated by oxidative stress and common single-nucleotide polymorphisms.
Vitamin E (α-tocopherol) is the major lipid-soluble antioxidant in most animal species. By controlling the secretion of vitamin E from the liver, the α-tocopherol transfer protein regulates whole-body distribution and levels of this vital nutrient. However, the mechanism(s) that regulates the expression of this protein is poorly understood. Here we report that transcription of the TTPA gene in immortalized human hepatocytes is induced by oxidative stress and by hypoxia, by agonists of the nuclear receptors PPARα and RXR, and by increased cAMP levels. The data show further that induction of TTPA transcription by oxidative stress is mediated by an already-present transcription factor and does not require de novo protein synthesis. Silencing of the cAMP response element-binding (CREB) transcription factor attenuated transcriptional responses of the TTPA gene to added peroxide, suggesting that CREB mediates responses of this gene to oxidative stress. Using a 1.9-kb proximal segment of the human TTPA promoter together with a site-directed mutagenesis approach, we found that single-nucleotide polymorphisms that are commonly found in healthy humans dramatically affect promoter activity. These observations suggest that oxidative stress and individual genetic makeup contribute to vitamin E homeostasis in humans. These findings may explain the variable responses to vitamin E supplementation observed in human clinical trials.
Department of Nutrition, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
Lynn
L
Ulatowski
Department of Nutrition, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
Cara
C
Dreussi
Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
Noa
N
Noy
Department of Epidemiology and Biostatistics, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
Jill
J
Barnholtz-Sloan
Glickman Urological Institute, Cleveland Clinic Foundation, Cleveland, OH 44195, USA.
Eric
E
Klein
Department of Nutrition, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA; Department of Pharmacology, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA. Electronic address: dxm178@case.edu.
Danny
D
Manor
D000818:Animals; D001665:Binding Sites; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D056726:Genetic Association Studies; D006801:Humans; D008099:Liver / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009928:Organ Specificity; D018384:Oxidative Stress; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic; D015533:Transcriptional Activation
C115163:CREB1 protein, human; D002352:Carrier Proteins; D017362:Cyclic AMP Response Element-Binding Protein; C017763:alpha-tocopherol transfer protein