Role of post-translational modifications in a function of pregnane X receptor

Abstract

The pregnane X receptor (PXR) is a broad spectrum entero-hepatic xenobiotic ?sensor? and master-regulator of drug inducible gene expression. In addition, PXR controls the expression of numerous genes involved in the metabolism of endobiotics and plays an important role in the development of specific forms of cancer. Importantly, the xenosensor PXR is often responsible for clinically important drug-drug interactions as well as for undesirable side effects underlying important physiological functions of this nuclear receptor. All PXR functions have been attributed to ligand activation. However, the activity of PXR is also modulated in a ligand-independent manner implying cross-talk between other cell signaling pathways and PXR. The transcriptional activity of PXR is modulated through post-translational modification of this receptor. This thesis is focused on PXR phosphorylation, and in particular on the study of specific target residues. The theoretical background concentrates on xenobiotic and endobiotic functions of this nuclear receptor, its target genes and its post-translational modifications. In the methodological section, methods of studying protein-protein interaction and binding to DNA were developed and optimized. Then, the putative phosphorylation sites T248, Y249 and T422 were determined by in silico consensus kinase site prediction analysis. The roles of these residues in the function of PXR were examined with a particular focus on PXR transcriptional activity, promoter- binding activity, and interaction with the common heterodimerization partner retinoid X receptor alpha (RXR?). Our finding would shows an important mechanistic link between the xenobiotic metabolism gene expression controlled by PXR and cellular signaling pathways.