Pregnane X receptor and human malignancy.

Pregnane X Receptor (PXR) is a member of the nuclear receptor superfamily, expressed in liver, intestine and other tissues. PXR exerts transcriptional regulation by binding to its DNA response elements as an heterodimer with Retinoid X Receptor (RXR). This nuclear receptor is implicated in the homeostasis of numerous endobiotics, such as glucose, lipids, steroids and bile acids. Additionally, the activation of PXR induces expression of drug metabolizing enzymes (DMEs) and transporters, including multidrug resistance protein 1 (MDR1), leading to regulation of xenobiotic metabolism and drug-drug interactions. New roles for PXR have been established in inflammatory bowel disease, bone homeostasis, liver steatosis, antifibrogenesis and oxidative stress. PXR has, additionally, a multifactorial impact on cancer, either by directly affecting cell proliferation and apoptosis or by inducing chemotherapy resistance, in colon, breast, prostate, and endometrial cancer, and in osteosarcoma. PXR polymorphisms may also have clinical significance in certain types of cancer and their treatment. Further studies are needed in order to clarify the mechanisms involved in PXR-regulated carcinogenesis. PXR down-regulation could be considered as a novel therapeutic approach to overcome chemoresistance, while future research should be mainly focused on modulating PXR status in order to increase chemotherapy effectiveness and finally improve cancer patient prognosis.