DNA binding and transactivation properties of the Schistosoma mansoni constitutive androstane receptor homologue.
SmCAR (Schistosoma mansoni constitutive androstane receptor) is a schistosome homologue of the CAR/PXR/VDR group of nuclear receptors. The P box sequence in the DNA binding domain (DBD) of SmCAR, which is essential in determining the DNA binding specificity of nuclear receptors, is different from its vertebrate homologues. Previous data demonstrates that SmCAR binds to a hormone response element containing a single half site AGTGCA as a monomer. SmRXR1 and SmRXR2 are two S. mansoni homologues of vertebrate retinoid X receptors (RXRs). RXRs usually heterodimerize with various nuclear receptors. Yeast-two hybrid analyses, in vitro pull-down and co-immunoprecipitation assays demonstrated that SmCAR interacts with SmRXR1 but not SmRXR2. Using chimeras consisting of the DBD of SmCAR and the ligand binding domain (LBD) of mouse (m) CAR, we show that despite a different P box, SmCAR DBD shares DNA binding specificity with mCAR. However, the SmCAR DBD does exhibit some of the DNA binding properties specific to SmCAR. Studies of the chimeras also demonstrated that the SmCAR DBD is able to heterodimerize with the DBD of human RXR, allowing high affinity DNA binding. Based on this study and previous results, we conclude that SmCAR may recognize its cognate hormone response element via two mechanisms: binding to DNA monomerically or heterodimerizing with SmRXR1. We also demonstrate that a transcription activation function-1 (AF-1) is located in the SmCAR A/B domain.
Hu
Rong
R
Department of Microbiology and Immunology, School of Medicine, State University of New York, Buffalo, NY 14214, USA.
Niles
Edward G
EG
LoVerde
Philip T
PT
D000818:Animals; D045744:Cell Line, Tumor; D000090702:Constitutive Androstane Receptor; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D019281:Dimerization; D004440:Ecdysone / Q000235:genetics; D005786:Gene Expression Regulation; D015801:Helminth Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000378:metabolism*; D020218:Response Elements; D047488:Retinoid X Receptors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012550:Schistosoma mansoni / Q000235:genetics* / Q000378:metabolism*; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D015533:Transcriptional Activation; D020798:Two-Hybrid System Techniques
D000090702:Constitutive Androstane Receptor; D004268:DNA-Binding Proteins; D015801:Helminth Proteins; D008024:Ligands; D018160:Receptors, Cytoplasmic and Nuclear; D047488:Retinoid X Receptors; D014157:Transcription Factors; D004440:Ecdysone; D004247:DNA