Lower Expression of HNF4α and PGC1α Might Impair Rifampicin-mediated CYP3A4 Induction under Conditions Where PXR Is Overexpressed in Human Fetal Liver Cells

Abstract

Pregnane X receptor (PXR) mRNA was detected in HepG2 cells by RT-PCR, but not in human fetal liver (HFL) cells. CYP3A4 was induced by rifampicin (RIF), mifepristone (RU486), clotrimazole (CTZ), and dexamethasone (DEX) in HepG2 cells, while these PXR ligands with the exception of DEX did not induce CYP3A4 mRNA expression in HFL cells. Ad-PXR infection increased mRNA levels of PXR and CYP3A4 in both cells despite the absence of PXR ligands. Similar results were observed in reporter gene assays. However, in HFL cells, RIF-mediated CYP3A4 induction was insufficient compared with HepG2 cells, despite PXR overexpression. The expression levels of five coactivators (HNF4α, PGC1α, SRC1, CBP, and P300) related to CYP3A4 expression in HepG2, HFL cells, and human adult liver were analyzed by RT-PCR. Expression levels of HNF4α and PGC1α in HFL cells were downregulated to 20% of those in the human adult liver. On the other hand, the expression level of HNF4α in HepG2 cells was higher than that in HFL cells, although PGC1α expression level was almost the same as that in HFL cells. HNF4α mRNA expression level in HepG2 cells was 57% of that in human adult liver, and the level in HFL cells was 30% of that in HepG2 cells. These results suggested that lower expression of HNF4α and PGC1α may impair RIF-mediated CYP3A4 induction under conditions of PXR overexpression in HFL cells.

Oleanolic Acid-Mediated Inhibition of Pregnane X Receptor and Constitutive Androstane Receptor Attenuates Rifampin-Isoniazid Cytotoxicity

“…Previous studies showed that full activation of PXR under RIF induction was dependent on the coregulation of RXRα, HNF4α, SRC-1, and PGC-1α . Thus, we assessed the coregulation of these coactivators by PXR on CYP3A4 promoter activity in the presence of RIF and OA.…”

“…Previous studies showed that full activation of PXR under RIF induction was dependent on the coregulation of RXRα, HNF4α, SRC-1, and PGC-1α. 26 Thus, we assessed the coregulation of these coactivators by PXR on CYP3A4 promoter activity in the presence of RIF and OA. Full-length human RXRα, HNF4α, SRC-1, and PGC-1α expression constructs were cotransfected with human PXR/vector control and CYP3A4 promoter constructs into HepG2 cells.…”

“…The fully activation of PXR functions depends on the ligands binding to the ligand-binding domain which located in the receptor, interaction with coregulators such as RXRα, HNF4α, SRC-1, and PGC-1α, and binding to the specific responsive element within the promoters of target genes. 26 When no ligand binding, PXR forms a complex with corepressors such as NCoR and inhibits transcriptional activity. Meanwhile, ligand binding results in dissociation of PXR from the corepressor and recruitment of coactivator proteins.…”

Development of a highly reproducible system to evaluate inhibition of cytochrome P450 3A4 activity by natural medicines

“…The cDNA was used to carry out real-time polymerase chain reaction (PCR) using SYBR ® Premix ExTaq (TaKaRa Bio) in order to measure mRNA levels of CYP3A4 and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The amplification reactions were performed with specific primers for CYP3A4 (forward: 5'-CTGTGTTTCCAAGAGAAGTTAC-3' and reverse: TGCATCAATTTCCTCCTGCAG-3'), and GAPDH (forward: 5'-CATGGGTGTGAACCATGAGAA-3' and reverse: 5'-GGTCATGAGTCCTTCCACGAT-3') (19). Quantitative values were obtained above the threshold PCR cycle number (Ct) at which the increase in signal associated with an exponential growth in PCR products was detected using Thermal Cycler Dice TM TP800 (TaKaRa Bio).…”

Associations between Pregnane X Receptor and Breast Cancer Growth and Progression

“…Activators of PXR, which include some anticancer drugs, induce a conformational change resulting in dissociation of corepressors and recruitment of coactivators [ 19 ]. Coactivators that have been identified include steroid receptor coactivators (SRCs) 1, 2 and 3, peroxisome proliferator activated receptor gamma coactivator 1-alpha (PGC-1α), forkhead box O 1 transcription factor (FOXO1), protein arginine methyltransferase (PRMT) and p300 [ 2 , 29 , 30 ]. Thus, activity of PXR can be influenced by a number of factors including and excluding direct activators or inhibitors.…”