Dexamethasone-Mediated Up-Regulation of HumanCYP2A6Involves the Glucocorticoid Receptor and Increased Binding of Hepatic Nuclear Factor 4α to the Proximal Promoter

Abstract

Human cytochrome P450 2A6 (CYP2A6) metabolizes various clinically relevant compounds, including nicotine-and tobaccospecific procarcinogens; however, transcriptional regulation of this gene is poorly understood. We investigated the role of the glucocorticoid receptor (GR) in transcriptional regulation of CYP2A6. Dexamethasone (DEX) increased CYP2A6 mRNA and protein levels in human hepatocytes in primary culture. This effect was attenuated by the GR receptor antagonist mifepristone (RU486; 17␤-hydroxy-11␤-[4-dimethylamino phenyl]-17␣-[1-propynyl]estra-4,9-dien-3-one), suggesting that induction of CYP2A6 by DEX was mediated by the GR. In gene reporter assays, DEX caused dose-dependent increases in luciferase activity that was also prevented by RU486 and progressive truncations of the CYP2A6 promoter delineated DEX-responsiveness to a Ϫ95 to ϩ12 region containing an hepatic nuclear factor 4 (HNF4) ␣ response element (HNF4-RE). Mutation of the HNF4-RE abrogated HNF4␣-and DEX-mediated transactivation of CYP2A6. In addition, overexpression of HNF4␣ increased CYP2A6 transcriptional activity by 3-fold. DEX increased HNF4␣ mRNA levels by 4-fold; however, the amount of HNF4␣ nuclear protein was unaltered. Electrophoretic mobility shift, chromatin immunoprecipitation (ChIP), and streptavidin DNA binding assays revealed that DEX increased binding of HNF4␣ to the HNF4-RE and that an interaction of GR and HNF4␣ occurred at this site. Moreover, ChIP assays indicated that histone H4 acetylation of the CYP2A6 proximal promoter chromatin was increased by DEX that may allow for increased binding of HNF4␣ to the HNF4-RE in human hepatocytes. These findings indicate that increased expression of CYP2A6 by DEX is mediated by the GR via a nonconventional transcriptional mechanism involving interaction of HNF4␣ with an HNF4-RE rather than a glucocorticoid response element.

Phase I Study of the Investigational NEDD8-Activating Enzyme Inhibitor Pevonedistat (TAK-924/MLN4924) in Patients with Advanced Solid Tumors

“…It did, however, decrease the frequency of nausea, vomiting, and myalgias. Because pevonedistat is a substrate of CYP3A4, we evaluated whether concurrent use of dexamethasone, a known, albeit weak, inducer of CYP3A activity via glucocorticoid receptor-mediated transcriptional upregulation (38), would increase pevonedistat systemic clearance, resulting in lower systemic exposure. On the basis of a limited sample size and after dose normalization ( Supplementary Fig.…”

Human CYP2A6 is regulated by nuclear factor-erythroid 2 related factor 2

“…To understand the regulators of CYP2A6 expression, we have studied transcriptional factors regulating CYP2A6 expression and found that pregnane X receptor [8] and estrogen receptor [9] are involved in the CYP2A6 regulation. In addition, a recent study reported the involvement of glucocorticoid receptor in the regulation of CYP2A6 [10].…”

Downregulation of 15-lipoxygenase 2 by glucocorticoid receptor in prostate cancer cells

“…The siRNAs of GR was previously shown to specifically abolish expression of GR (21) and RU486 was shown to inhibit the function of 15-LOX-2 (22,23). The luciferase assays showed that the treatment with siRNAs of GR was able to reverse the inhibitory effect of GR on promoter activities of LF4 and LF7, GR reduced luciferase activities of LF4 and LF7 to 60.73%±2.09 and 56.11±2.94, respectively, but these were up to 86.17±3.60 and 138.57±3.03, respectively after the treatment with siRNAs of GR.…”