[Pregnane X receptor promotes programmed cell death protein 4 expression in HepG2 cells]

Area of Science:

• Molecular Biology
• Cell Biology
• Pharmacology

Background:

• The pregnane X receptor (PXR) is a nuclear receptor involved in xenobiotic metabolism and cellular defense.
• Programmed cell death proteins (PDCDs) play critical roles in regulating apoptosis and cell survival.
• The interplay between PXR and PDCDs, particularly PDCD4, in liver cells remains incompletely understood.

Purpose of the Study:

• To elucidate the role of PXR in regulating programmed cell death proteins (PDCDs) in HepG2 human liver cancer cells.
• To investigate the molecular mechanisms underlying PXR-mediated regulation of PDCDs, focusing on PDCD4.
• To determine if PDCD4 is a direct target gene of PXR.

Main Methods:

• HepG2 cells were treated with PXR agonists (rifampicin, SR12813) or DMSO control.
• Cells were infected with PXR-expressing adenovirus (VP-PXR) or Mock adenovirus.
• mRNA levels of PDCD2, PDCD4, PDCD5, PDCD6, and miRNA21 were quantified by qRT-PCR.
• PDCD4 protein levels were assessed by Western blotting.
• Bioinformatic analysis was used to identify potential PXR-responsive elements (PXREs) in the PDCD4 promoter.

Main Results:

• PXR activation by rifampicin and SR12813 significantly increased PDCD4 mRNA and protein expression.
• Rifampicin treatment also led to decreased PDCD2 mRNA expression.
• Overexpression of PXR via adenovirus significantly upregulated PDCD4 and MDR1 mRNA.
• PDCD4 upregulation by PXR agonists was independent of miRNA21 expression changes.
• Bioinformatic analysis predicted PXRE motifs in the 5'-flanking region of the PDCD4 gene.

Conclusions:

• PXR activation in HepG2 cells upregulates PDCD4 expression.
• PDCD4 is likely a direct transcriptional target of PXR in these cells.
• The PXR-mediated regulation of PDCD4 occurs independently of the miRNA21 pathway.