Nuclear receptor CAR requires early growth response 1 to activate the human cytochrome P450 2B6 gene.
The nuclear receptor CAR (constitutive active/androstane receptor) is a drug-sensing transcription factor, regulating the hepatic genes that encode various drug-metabolizing enzymes. We have now characterized the novel regulatory mechanism by which the signal molecule EGR1 (early growth response 1) determines CAR-mediated activation of the human CYP2B6 (cytochrome P450 2B6) gene. The CYP2B6 enzyme metabolizes commonly used therapeutics and also activates pro-drugs. The CAR directly binds to the distal enhancer element of the CYP2B6 promoter, which is essential in converging to its drug-sensing function onto promoter activity. However, this binding alone is not sufficient to activate the CYP2B6 promoter; the promoter requires EGR1 to enable CAR to activate the CYP2B6 promoter. Upon stimulation by protein kinase C, EGR1 directly binds to the proximal promoter and coordinates the nearby HNF4alpha (hepatocyte-enriched nuclear factor 4alpha) with CAR at the distal enhancer element to activate the promoter. Thus, synergy of drug activation and the stimulation of cellular signal are necessary for CAR to activate the CYP2B6 gene.
Inoue
Kaoru
K
Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, NIEHS, National Institutes of Health, Research Triangle Park, North Carolina 27709, USA.
Negishi
Masahiko
M
D002460:Cell Line; D000090702:Constitutive Androstane Receptor; D065702:Cytochrome P-450 CYP2B6; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D051766:Early Growth Response Protein 1 / Q000378:metabolism*; D004789:Enzyme Activation; D051557:Hepatocyte Nuclear Factor 4 / Q000378:metabolism; D006801:Humans; D008954:Models, Biological; D008957:Models, Genetic; D011401:Promoter Regions, Genetic; D011493:Protein Kinase C / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D020218:Response Elements; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
D000090702:Constitutive Androstane Receptor; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; C496592:HNF4A protein, human; D051557:Hepatocyte Nuclear Factor 4; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D003577:Cytochrome P-450 Enzyme System; C585599:CYP2B6 protein, human; D065702:Cytochrome P-450 CYP2B6; D011493:Protein Kinase C