Pregnane X receptor and yin yang 1 contribute to the differential tissue expression and induction of CYP3A5 and CYP3A4

The Role of CYP3A in Health and Disease

CYP3A is an enzyme subfamily in the cytochrome P450 (CYP) superfamily and includes isoforms CYP3A4, CYP3A5, CYP3A7, and CYP3A43. CYP3A enzymes are indiscriminate toward substrates and are unique in that these enzymes metabolize both endogenous compounds and diverse xenobiotics (including drugs); almost the only common characteristic of these compounds is lipophilicity and a relatively large molecular weight. CYP3A enzymes are widely expressed in human organs and tissues, and consequences of these enzymes' activities play a major role both in normal regulation of physiological levels of endogenous compounds and in various pathological conditions. This review addresses these aspects of regulation of CYP3A enzymes under physiological conditions and their involvement in the initiation and progression of diseases.

Role of CYP3A5 in Modulating Androgen Receptor Signaling and Its Relevance to African American Men with Prostate Cancer

Androgen receptor signaling is crucial for prostate cancer growth and is positively regulated in part by intratumoral CYP3A5. As African American (AA) men often carry the wild type CYP3A5 and express high levels of CYP3A5 protein, we blocked the wild type CYP3A5 in AA origin prostate cancer cells and tested its effect on androgen receptor signaling. q-PCR based profiler assay identified several AR regulated genes known to regulate AR nuclear translocation, cell cycle progression, and cell growth. CYP3A5 processes several commonly prescribed drugs and many of these are CYP3A5 inducers or inhibitors. In this study, we test the effect of these commonly prescribed CYP3A5 inducers/inhibitors on AR signaling. The results show that the CYP3A5 inducers promoted AR nuclear translocation, downstream signaling, and cell growth, whereas CYP3A5 inhibitors abrogated them. The observed changes in AR activity is specific to alterations in CYP3A5 activity as the effects are reduced in the CYP3A5 knockout background. Both the inducers tested demonstrated increased cell growth of prostate cancer cells, whereas the inhibitors showed reduced cell growth. Further, characterization and utilization of the observation that CYP3A5 inducers and inhibitors alter AR signaling may provide guidance to physicians prescribing CYP3A5 modulating drugs to treat comorbidities in elderly patients undergoing ADT, particularly AA.

Role of vitamin D receptor in the regulation of CYP3A gene expression

Vitamin D₃ (VD₃) is a multifunctional nutrient which can be either synthesized or absorbed from the diet. It plays a pivotal role in systemic calcium and phosphate homeostasis, as well as in various physiological and pathological processes. VD₃ is converted to the active form, 1α,25-dihydroxyvitamin D₃ (1,25-D3), by cytochrome P450 2R1 (CYP2R1)/CYP27A1 and CYP27B1 sequentially, and deactivated by multiple enzymes including CYP3A4. On the other hand, 1,25-D3 is capable of activating the transcription of CYP3A genes in humans, mice and rats. The vitamin D receptor (VDR)-mediated transactivation of human CYP3A4 and CYP3A5 resembles that known for pregnane X receptor (PXR). Activated VDR forms a heterodimer with retinoid X receptor α (RXRα), recruits co-activators, translocates to the cell nucleus, binds to the specific vitamin D responsive elements (VDRE), and activates the gene transcription. In mice, intestinal Cyp3a11 mRNA levels, but not those of hepatic CYP3As, were induced by in vivo administration of VDR and PXR agonists. In rats, intestinal Cyp3a1 and Cyp3a2 mRNAs were induced by 1,25-D3 or lithocholic acid (LCA), whereas hepatic Cyp3a2, but not Cyp3a1 and Cyp3a9, was modulated to 1,25-D3 treatment. In general, the VDR-mediated regulation of CYP3A presents species and organ specificity.

DNA elements for constitutive androstane receptor- and pregnane X receptor-mediated regulation of bovine CYP3A28 gene

The regulation of cytochrome P450 3A (CYP3A) enzymes is established in humans, but molecular mechanisms of its basal and xenobiotic-mediated regulation in cattle are still unknown. Here, ~10 kbp of the bovine CYP3A28 gene promoter were cloned and sequenced, and putative transcription factor binding sites were predicted. The CYP3A28 proximal promoter (PP; -284/+71 bp) contained DNA elements conserved among species. Co-transfection of bovine nuclear receptors (NRs) pregnane X and constitutive androstane receptor (bPXR and bCAR) with various CYP3A28 promoter constructs into hepatoma cell lines identified two main regions, the PP and the distal fragment F3 (-6899/-4937 bp), that were responsive to bPXR (both) and bCAR (F3 fragment only). Site-directed mutagenesis and deletion of NR motif ER6, hepatocyte nuclear factor 1 (HNF-1) and HNF-4 binding sites in the PP suggested either the involvement of ER6 element in bPXR-mediated activation or the cooperation between bPXR and liver-enriched transcription factors (LETFs) in PP transactivation. A putative DR5 element within the F3 fragment was involved in bCAR-mediated PP+F3 transactivation. Although DNA enrichment by anti-human NR antibodies was quite low, ChIP investigations in control and RU486-treated BFH12 cells, suggested that retinoid X receptor α (RXRα) bound to ER6 and DR5 motifs and its recruitment was enhanced by RU486 treatment. The DR5 element seemed to be recognized mainly by bCAR, while no clear-cut results were obtained for bPXR. Present results point to species-differences in CYP3A regulation and the complexity of bovine CYP3A28 regulatory elements, but further confirmatory studies are needed.

The interleukin-17 G-197A polymorphism is associated with cyclosporine metabolism and transplant rejection in liver transplant recipients

Aim: This study aimed to investigate the effect of and mechanism involved in the IL-17 SNP on cyclosporine metabolism and outcomes of liver transplantation (LT). Materials & methods: The IL-17 genotype, IL-17 expression, postoperative outcome and cyclosporine concentration were reviewed in 106 LT recipients. The functional relevance of rs2275913 was evaluated by luciferase assay. Furthermore, L02 cells were treated with IL-17 recombinant protein or/and pregnane X receptor (PXR) knockdown lentiviruses, then the expression of PXR, CYP3A4, CYP3A5 and IL-17R were detected by PCR and western blotting. Result: The significant distribution difference at IL-17 locus G-197A was confirmed between patients with and without rejection (p = 0.035). Patients with acute rejection showed higher IL-17 level than those without rejection. Cyclosporine concentration was associated with the different IL-17 genotype (p < 0.05). Luciferase assay revealed that 197G genotype had higher luciferase activity than that in 197A genotype (p = 0.009). Furthermore, IL-17 recombinant protein remarkably promoted the expressions of PXR, CYP3A4 and CYP3A5 (p < 0.01), but not IL-17R. PXR knockdown significantly inhibited the mRNA levels of CYP3A4 and CYP3A5 but not IL-17R (p < 0.01), while IL-17 recombinant protein had no influence on the expressions of CYP3A4 and CYP3A5 when PXR was downregulated. Conclusion: This study revealed the possible association of IL-17 G-197A with cyclosporine metabolism and transplant rejection after LT, which might be partly related to the upregulations of CYP3A4/5 dependent on PXR.

Effect of panaxytriol on cytochrome P450 3A4 via the pregnane X receptor regulatory pathway

Panaxytriol (PXT) is one of the major effective components of red ginseng and Shenmai injection. The present study aimed to explore the effect of PXT on cytochrome P450 3A4 (CYP3A4) based on the pregnane X receptor (PXR)-CYP3A4 regulatory pathway in HepG2 cells and hPXR-overexpressing HepG2 cells treated with PXT for different time periods using quantitative polymerase chain reaction, Western blot, and dual-luciferase reporter gene assays. PXT could upregulate the levels of PXR and CYP3A4 mRNA in HepG2 cells treated with PXT for 1 hr, with no impact on the expression of their protein levels. The expression levels of both PXR and CYP3A4 mRNA and protein in HepG2 cells treated with PXT for 24 hr increased in a concentration-dependent manner. The effects of PXT on the expression of PXR and CYP3A4 mRNA and protein in hPXR-overexpressing HepG2 cells were similar to those in HepG2 cells. Moreover, the influence trend of PXT on CYP3A4 was consistent with that of PXR in HepG2 cells and hPXR-overexpressing HepG2 cells. The dual-luciferase reporter gene assay in HepG2 cells further demonstrated that PXT treatment for specific time periods could significantly induce the expression of CYP3A4 mediated by the PXR regulatory pathway.

C2H2-Type Zinc Finger Proteins: Evolutionarily Old and New Partners of the Nuclear Hormone Receptors

Nuclear hormone receptors (NRs) are evolutionarily conserved ligand-dependent transcription factors. They are essential for human life, mediating the actions of lipophilic molecules, such as steroid hormones and metabolites of fatty acid, cholesterol, and external toxic compounds. The C2H2-type zinc finger proteins (ZNFs) form the largest family of the transcription factors in humans and are characterized by multiple, tandemly arranged zinc fingers. Many of the C2H2-type ZNFs are conserved throughout evolution, suggesting their involvement in preserved biological activities, such as general transcriptional regulation and development/differentiation of organs/tissues observed in the early embryonic phase. However, some C2H2-type ZNFs, such as those with the Krüppel-associated box (KRAB) domain, appeared relatively late in evolution and have significantly increased family members in mammals including humans, possibly modulating their complicated transcriptional network and/or supporting the morphological development/functions specific to them. Such evolutional characteristics of the C2H2-type ZNFs indicate that these molecules influence the NR functions conserved through evolution, whereas some also adjust them to meet with specific needs of higher organisms. We review the interaction between NRs and C2H2-type ZNFs by focusing on some of the latter molecules.

Differential Regulation of CYP3A4 and CYP3A5 and its Implication in Drug Discovery

BACKGROUND

Cancer cells use several mechanisms to resist the cytotoxic effects of drugs, resulting in tumor progression and invasion. One such mechanism capitalizes on the body's natural defense against xenobiotics by increasing the rate of xenobiotic efflux and metabolic inactivation. Xenobiotic metabolism typically involves conversion of parent molecules to more soluble and easily excreted derivatives in reactions catalyzed by Phase I and Phase II drug metabolizing enzymes.

METHODS

We performed a structured search of peer-reviewed literature on P450 (CYP) 3A, with a focus on CYP3A4 and CYP3A5.

RESULTS

Recent reports indicate that components of the xenobiotic response system are upregulated in some diseases, including many cancers. Such components include the pregnane X receptor (PXR), CYP3A4 and CYP3A5 enzymes. The CYP3A enzymes are a subset of the numerous enzymes that are transcriptionally activated following the interaction of PXR and many ligands.

CONCLUSION

Intense research is ongoing to understand the functional ramifications of aberrant expression of these components in diseased states with the goal of designing novel drugs that can selectively target them.