The mechanism of the G0/G1 cell cycle phase arrest induced by activation of PXR in human cells

Context: Pregnane X receptor (PXR) is an important transcriptional regulator that plays important roles in the cell metabolism and cell growth by regulating the transcriptional of a sort of metabolizing enzymes. Objective: To investigate whether rifampicin effected HepG2 cells growth and the inhibition was due to the G0/G1 phase arrest. Methods: PXR-knockdown experiments using RNAi showed that the cell cycle phase arrest mediated by rifampicin based on activation of PXR. The results also indicated that cell phase arrest by rifampicin could protect cells form UVB-induced DNA damage. Retinoid X receptor alpha (RXR alpha) expression level in cells is another key factor for cell cycle phase arrest mediated by rifampicin. Both over expression and lacking expression of RXR alpha in cell reduced the cell arrest efficiency mediated by rifampicin. In the study, we found that rifampicin inhibited HepG2 cells growth and demonstrated that the inhibition is due to the G0/G1 phase arrest through flow cytometry analysis. Conclusion: The results showed that RXR alpha promote cell cycle phase transition rate of HepG2. Competitive bind of rifampicin-activated PXR with RXRa is one main reason to arrest cell cycle phase through inhibiting combination of RXR alpha with other partners. Rifampicin could promote cell growth rate when RXR alpha expressed more excessively than PXR in cells. (C) 2011 Published by Elsevier Masson SAS.