title: Cyclin-dependent kinase 2 negatively regulates human pregnane X receptor-mediated CYP3A4 gene expression in HepG2 liver carcinoma cells.
abstract: The human pregnane X receptor (hPXR) regulates the expression of critical drug metabolism enzymes. One of such enzymes, cytochrome P450 3A4 (CYP3A4), plays critical roles in drug metabolism in hepatocytes that are either quiescent or passing through the cell cycle. It has been well established that the expression of P450, such as CYP3A4, is markedly reduced during liver development or regeneration. Numerous studies have implicated cellular signaling pathways in modulating the functions of nuclear receptors, including hPXR. Here we report that inhibition of cyclin-dependent kinases (Cdks) by kenpaullone and roscovitine (two small molecule inhibitors of Cdks that we identified in a screen for compounds that activate hPXR) leads to activation of hPXR-mediated CYP3A4 gene expression in HepG2 human liver carcinoma cells. Consistent with this finding, activation of Cdk2 attenuates the activation of CYP3A4 gene expression. In vitro kinase assays revealed that Cdk2 directly phosphorylates hPXR. A phosphomimetic mutation of a putative Cdk phosphorylation site, Ser(350), significantly impairs the function of hPXR, whereas a phosphorylation-deficient mutation confers resistance to Cdk2. Using HepG2 that has been stably transfected with hPXR and the CYP3A4-luciferase reporter, enriched in different phases of the cell cycle, we found that hPXR-mediated CYP3A4 expression is greatly reduced in the S phase. Our results indicate for the first time that Cdk2 negatively regulates the activity of hPXR, and suggest an important role for Cdk2 in regulating hPXR activity and CYP3A4 expression in hepatocytes passing through the cell cycle, such as those in fetal or regenerating adult liver.
authors.affiliation: Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
authors.forename: Wenwei
authors.initials: W
authors.lastname: Lin
authors.forename: Jing
authors.initials: J
authors.lastname: Wu
authors.forename: Hanqing
authors.initials: H
authors.lastname: Dong
authors.forename: David
authors.initials: D
authors.lastname: Bouck
authors.forename: Fu-Yue
authors.initials: FY
authors.lastname: Zeng
authors.forename: Taosheng
authors.initials: T
authors.lastname: Chen
mesh_terms: D001552:Benzazepines / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D051357:Cyclin-Dependent Kinase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D051544:Cytochrome P-450 CYP3A / Q000096:biosynthesis* / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000235:genetics; D022781:Hepatocytes / Q000201:enzymology; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008113:Liver Neoplasms / Q000201:enzymology* / Q000235:genetics; D009154:Mutation; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid / Q000378:metabolism*; D012038:Regeneration / Q000187:drug effects / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics
chemical_list: D001552:Benzazepines; D007211:Indoles; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid; C119620:kenpaullone; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2
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