The resultant ligand bound PXR translocates to the nucleus the place it forms a heterodimer with one more nuclear receptor referred to as retinoic acid receptor.
The extent of PXR mediated gene transcription is increased by coactivators, such because the p160/SRC family of coactivators, like steroid co activator 1, and peroxisome proliferator activated receptor ? coactivator Docetaxel 1, and decreased by corepressors, such as nuclear receptor corepressor protein, sterol regulatory element binding protein 1, and silencing mediator of retinoid and thyroid hormone receptors, particularly the SMRT isoform. PXR transcriptional activity is also inuenced by other nuclear receptors or transcription factors. As examples, hepatocyte nuclear factor 4 and glucocorticoid receptor have been shown to increase PXR transcriptional activity. In contrast, small heterodimer partner suppresses PXR activity. The reader is referred to recent reviews on the details of the molecular mechanism of PXR activation and the interplay between PXR with other nuclear receptors.
PXR is expressed predominantly in liver, although it has also been detected in various extrahepatic tissues, including small intestines, E7080 colon, kidney, brain capillaries, and mammary tissue. In addition, studies with human specimens have shown localization of PXR in mammary and endometrial tumors. Interestingly, a tissue specic PXR activator has been identied. With the use of PXR humanized mice, it has been shown that rifaximin is a gut specic activator of human PXR. Chemical activation NSCLC of PXR may also be species dependent. Whereas rifampicin activates human PXR, it does not activate rodent PXR. By comparison, PCN activates rodent PXR, whereas it has little or no effect on human PXR activity. Other compounds have also been identied as agonists and antagonists of PXR.
Among the approximately 20 individual chemical constituents that have been identied in C. forkohlii extract, the best characterized is forskolin, which is a diterpene present in the root of the plant. Forskolin activates adenylate cyclase, increases cAMP levels, and stimulates the protein kinase A signaling pathway. Various herbal preparations of C. forkohlii Docetaxel are available, including extracts standardized to 10% forskolin. An alcoholic extract of C. forkohlii of undened chemical composition has been reported to activate mouse PXR based on the experimental nding indicating that the extract increases Cyp3a11 messenger RNA expression in primary hepatocytes isolated from wild type mice, whereas it has little or no effect on Cyp3a11 mRNA expression in hepatocytes isolated from PXR knockout mice.
As mentioned previously, Cyp3a11 is a gene subject to regulation by PXR. It is not known which individual chemical constituent is directly responsible for or contributes to the activation of mouse PXR by C. forkohlii extract.
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