Cyclin-dependent kinase 2 down-regulates expression of drug-metabolizing enzymes UGT1A1 and CYP3A4 through phosphorylation of nuclear receptor PXR

我们研究了UGT 1A 1和CYP 3A 4等药物代谢酶的表达如何受细胞周期相关信号的调节。CDK 2的活性形式（磷酸化CDK 2）分别在2 h和4 h达到峰值，这些水平在8 h下降，而UGT 1A 1和CYP 2B 6在0 h至6 h以极低水平存在，并在8 h开始蓄积。CDK 2抑制剂roscovitine可增强UGT 1A 1和CYP 3A 4的表达，而抑制转染S350 D PXR的细胞中UGT 1A 1和CYP 3A 4的表达。PXR的丝氨酸350磷酸化突变体在细胞核中检测到，并失去与RXR的结合，并与辅激活剂SRC-2，而不是SRC-1共转染恢复PXR活性。这些结果表明，roscovitine通过抑制CDK 2刺激UGT 1A 1和CYP 3A 4的表达，CDK 2使PXR在丝氨酸-350处磷酸化，从而抑制细胞核中的反式激活。

We investigated how the expression of drug-metabolizing enzymes including UGT1A1and CYP3A4 is regulated by cell signals associated with cell-cycle progression. While the active form of CDK2(phospho-CDK2) peaked at 2 h and 4 h, respectively, and these levels dropped at 8 h, UGT1A1 and CYP2B6 were present at very low levels at 0 h to 6 h and started accumulating at 8 h. While CDK2 inhibitor roscovitine enhanced the expression of UGT1A1 and CYP3A4, it suppressed the expression of UGT1A1 and CYP3A4 in the cells transfected with S350D PXR. Phosphomimetic mutant at serine-350 of PXR was detected in the nuclei and lost the binding with RXR, and co-transfection with co-activator SRC-2 but not SRC-1 recovered PXR activity. These results indicate that roscovitine stimulated expression of UGT1A1 and CYP3A4 through inhibiting CDK2, which phosphorylated PXR at serine-350 to suppress the transactivation in the nuclei.