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Human pregnane X receptor compromises the function of p53 and promotes malignant transformation.

ABSTRACT: The pregnane X receptor (PXR) is well established as a nuclear receptor that has a central role in xenobiotic metabolism and disposition. However, emerging evidence suggests that PXR is also a regulator of apoptosis, promoting a malignant phenotype both in vitro and in vivo. The tumor suppressor p53 can be activated in the presence of DNA damage and induce cell cycle arrest to allow for DNA repair or, ultimately, apoptosis to suppress tumor formation. We previously identified p53 as a novel PXR-associated protein by using a mass spectrometric approach. In the current study, we identified a novel inhibitory effect of PXR on p53, revealing an anti-apoptotic function of PXR in colon carcinogenesis. PXR expression reduced p53 transactivation and the expression of its downstream target genes involved in cell cycle arrest and apoptosis by decreasing p53 recruitment to the promoter regions of these genes. Consistent with the inhibitory effect of PXR on p53, elevated PXR levels decreased doxorubicin- or nutlin-3a-mediated toxicity and promoted malignant transformation in colon cancer cells. Our findings show for the first time that PXR expression modulates p53 target gene promoter binding and contributes to the downregulation of p53 function in human colon cancer cells. These results define the functional significance of PXR expression in modulating p53-mediated mechanisms of tumor suppression.

SUBMITTER: Robbins D

PROVIDER: S-EPMC4979430 | biostudies-literature | 2016

REPOSITORIES: biostudies-literature

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Human pregnane X receptor compromises the function of p53 and promotes malignant transformation.

Robbins D D Cherian M M Wu J J Chen T T

Cell death discovery 20160418

The pregnane X receptor (PXR) is well established as a nuclear receptor that has a central role in xenobiotic metabolism and disposition. However, emerging evidence suggests that PXR is also a regulator of apoptosis, promoting a malignant phenotype both in vitro and in vivo. The tumor suppressor p53 can be activated in the presence of DNA damage and induce cell cycle arrest to allow for DNA repair or, ultimately, apoptosis to suppress tumor formation. We previously identified p53 as a novel PXR- ...[more]

PMID: 27547448

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Project description:The xenobiotic receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are activated by structurally diverse chemicals to regulate the expression of target genes, and they have overlapping regulation in terms of ligands and target genes. Receptor-selective agonists are, therefore, critical for studying the overlapping function of PXR and CAR. An early effort identified 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl)oxime (CITCO) as a selective human CAR (hCAR) agonist, and this has since been widely used to distinguish the function of hCAR from that of human PXR (hPXR). The selectivity was demonstrated in a green monkey kidney cell line, CV-1, in which CITCO displayed >100-fold selectivity for hCAR over hPXR. However, whether the selectivity observed in CV-1 cells also represented CITCO activity in liver cell models was not hitherto investigated. In this study, we showed that CITCO: 1) binds directly to hPXR; 2) activates hPXR in HepG2 cells, with activation being blocked by an hPXR-specific antagonist, SPA70; 3) does not activate mouse PXR; 4) depends on tryptophan-299 to activate hPXR; 5) recruits steroid receptor coactivator 1 to hPXR; 6) activates hPXR in HepaRG cell lines even when hCAR is knocked out; and 7) activates hPXR in primary human hepatocytes. Together, these data indicate that CITCO binds directly to the hPXR ligand-binding domain to activate hPXR. As CITCO has been widely used, its confirmation as a dual agonist for hCAR and hPXR is important for appropriately interpreting existing data and designing future experiments to understand the regulation of hPXR and hCAR. SIGNIFICANCE STATEMENT: The results of this study demonstrate that 6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-(3,4-dichlorobenzyl)oxime (CITCO) is a dual agonist for human constitutive androstane receptor (hCAR) and human pregnane X receptor (hPXR). As CITCO has been widely used to activate hCAR, and hPXR and hCAR have distinct and overlapping biological functions, these results highlight the value of receptor-selective agonists and the importance of appropriately interpreting data in the context of receptor selectivity of such agonists.

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Human pregnane X receptor compromises the function of p53 and promotes malignant transformation.

Publications

Human pregnane X receptor compromises the function of p53 and promotes malignant transformation.

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