title: Identification and interplay of sequence specific DNA binding proteins involved in regulation of human Pregnane and Xenobiotic Receptor gene.
abstract: Pregnane and Xenobiotic Receptor (PXR), a member of nuclear receptor superfamily, acts as a 'xenosensor' in our body and modulates a network of genes involved in xenobiotic metabolism and elimination. Expression levels of PXR in certain metabolic disorders including cancer are reported to be altered and its induced expression is associated with the development of resistance towards chemotherapy and adverse drug-drug interactions. Though the transcriptional regulation of PXR target genes have been elucidated in significant details, the structure and functional control of PXR promoter itself remains inadequately explored. In this work, we identify a Composite Element (CE) located within the proximal PXR promoter region that consists of multiple overlapping cis-elements and demonstrated that CE interacts specifically with some critical nuclear proteins. Subsequent DNA-protein interaction studies revealed mutually exclusive interactions on CE occurring between Sp1 and two unidentified DNA binding proteins with molecular masses of 50 and 54kDa. Here, we report the identification of 54kDa CE binding protein as a heterogeneous nuclear ribonucleoprotein K (hnRNPK) and demonstrate the effect of hnRNP K and Sp1 on PXR promoter transcriptional activity. Overall, the study indicates that PXR gene is tightly regulated to maintain a low receptor level.
authors.affiliation: Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi 110067, India.
authors.forename: Mallampati
authors.initials: M
authors.lastname: Saradhi
authors.affiliation: Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi 110067, India.
authors.forename: Sangeeta
authors.initials: S
authors.lastname: Kumari
authors.affiliation: Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi 110067, India.
authors.forename: Manjul
authors.initials: M
authors.lastname: Rana
authors.affiliation: Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi 110067, India.
authors.forename: Gauranga
authors.initials: G
authors.lastname: Mukhopadhyay
authors.affiliation: Special Centre for Molecular Medicine, Jawaharlal Nehru University, New Delhi 110067, India. Electronic address: rktyagi@yahoo.com.
authors.forename: Rakesh K
authors.initials: RK
authors.lastname: Tyagi
mesh_terms: D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D005786:Gene Expression Regulation; D056945:Hep G2 Cells; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D006801:Humans; D000077297:Pregnane X Receptor; D011401:Promoter Regions, Genetic / Q000235:genetics; D011987:Receptors, Steroid / Q000235:genetics* / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D012261:Ribonucleoproteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid; D012261:Ribonucleoproteins; C072074:HNRNPK protein, human
keywords: ChIP; Cis-elements; EMSA; Gene regulation; Pregnane X Receptor; Promoter-reporter assays; Sp1; Transcription factors; hnRNPK