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Induced CYP3A4 Expression in Confluent Huh7 Hepatoma Cells as a Result of Decreased Cell Proliferation and Subsequent PXR Activation.


Mol Pharmacol. 2012 Dec 21;


Authors: Sivertsson L, Edebert I, Porsmyr Palmertz M, Ingelman-Sundberg M, Neve EP


Abstract

We have previously shown that confluent growth of the human hepatoma cell line Huh7 substantially induces the CYP3A4 mRNA, protein and activity levels. Here, the mechanisms behind were investigated and a transcriptome analysis revealed significant up-regulation of liver specific functions, whereas pathways related to proliferation and cell cycle were down-regulated in the confluent cells. Reporter analysis revealed that the CYP3A4 gene was transcriptionally activated during confluence in a process involving PXR. PXR expression was increased and PXR protein accumulated in the nuclei during confluent growth. The PXR ligand rifampicin further increased the expression of CYP3A4 and siRNA mediated knock-down of PXR in confluent cells resulted in decreased CYP3A4 expression. CDK2, a known modulator of the cell cycle and a negative regulator of PXR, was higher expressed in proliferating control cells. Trypsinization of the confluent cells and replating them subconfluent resulted in a decrease in CYP3A4 and PXR expression back to levels observed in subconfluent control cells whereas the CDK2 levels increased. Knock-down of CDK2 in proliferating control cells increased the CYP3A4 and PXR protein levels. Moreover, the CDK inhibitor roscovitine stimulated the expression of CYP3A4. A phosphorylation-deficient mutation (S350A) in the PXR protein significantly induced the CYP3A4 transcription. In conclusion, the data strongly suggest that the increased CYP3A4 expression in confluent Huh7 cells is caused by the endogenous induction of PXR as a result of cell-cell contact inhibited proliferation and subsequent decreased CDK2 activities indicating an endogenous, non-ligand dependent regulation of PXR and CYP3A4 possibly of physiological and pharmacological significance.

PMID: 23264496 [PubMed - as supplied by publisher]