Nuclear receptor PXR is predominantly expressed in liver and intestine. Expression of PXR is observed to be dysregulated in various metabolic disorders indicating its involvement in disease development. However, information available on mechanisms of PXR self-regulation is fragmentary. The present investigation identifies some of the regulatory elements responsible for its tight regulation and low cellular expression. Here, we report that the PXR-promoter is a target for some key transcription factors like PU.1/Ets-1, Pax5, LEF-1 and c-Jun. Interestingly, we observed that PXR-promoter responsiveness to Pax5, LEF-1 and c-Jun, is considerably enhanced by Ets transcription factors (PU.1 and Ets-1). Co-transfection of cells with Ets-1, LEF-1 and c-Jun increased PXR-promoter activity by 5-fold and also induced expression of endogenous human PXR. Site-directed mutagenesis and transfection studies revealed that two Ets binding sites and two of the three LEF binding sites in the PXR-promoter are functional and have a positive effect on PXR transcription. Results suggest that expression of Ets family members, in conjunction with Pax5, LEF-1 and c-Jun, lead to coordinated up-regulation of PXR gene transcription. Insights obtained on the regulation of PXR gene have relevance in offering important cues towards normal functioning as well as development of several metabolic disorders via PXR signaling.
Keywords: Gene regulation; Pregnane and Xenobiotic Receptor; Promoter-reporter assays; Transcription factors; cis-elements.
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