Therefore, CCRP might be a common co-chaperone that regulates not only intracellular localization but also trans-activation activity of many nuclear receptors. However, these regulations by CCRP have not been investigated in organs and tissues such as liver in vivo. Here we generated CCRP KO mice and utilized them to examine the in vivo roles of CCRP in CAR activation in the livers. CCRP KO mice were treated with PB, from the livers of which samples were prepared for Western blot, real time PCR, cDNA microarray and chromatin immunoprecipitation assays. Demonstrating that CCRP regulates not only intracellular localization of CAR but also its ability to activate the Cyp2b10 gene, we will develop the hypothesis that CCRP determines both CAR-dependent and -independent gene expression in the livers. Since CCRP is present in both cytoplasm and nucleus in the livers, CCRP can regulate CAR activity in either or both compartments. Co-chaperone regulation in the cytoplasm has been intensively investigated in nuclear receptors. For example: FK506 binding protein 51 and 52, TPR proteins within the immunophilin family, mediate the interaction between GR with HSP90 to facilitate ligand binding. Liganded GR replaces FKBP51 with FKBP52 to translocate into the nucleus. This role of FKBP52 was confirmed in a cell line derived from FKBP52 KO mice, although the corresponding GR-FKBP52 complex could not be found in the cytoplasm of rat livers. Hepatitis B virus X-associated protein 2, also known as AIP or ARA9, the other immunophilin type of TPR protein, promotes interaction between aryl hydrocarbon receptor and HSP90 to translocate AHR from the cytoplasm into the nucleus after ligand binding in transformed cells such as Hepa1 cells. Global knock out of XAP2 was embryonic lethal. Liver-specific XAP2 KO mouse was produced ; however, neither an AHR-XAP2 complex nor intracellular localization has been confirmed before or after ligand treatments in the livers. Global CCRP KO mice grow normally and as to CCRP in the livers in vivo, it appears to constitute a regulatory Cycloheximide Small Molecules inhibitor system that optimizes nuclear CAR accumulation by its ability of repressing this accumulation. In addition to CAR, CCRP also interacted with GR, mineralocorticoid receptor, progesterone receptor, estrogen receptor, androgen receptor and pregnane X receptor. CCRP regulates interactions between PR and HSP90, and GR and HSP70. In the cases of PXR, over-expression of CCRP increased the cytoplasmic level of PXR-CCRP-HSP90 complex and retained it in the cytoplasm of HepG2 cell. Besides nuclear receptors, CCRP also interacted with p53 to inhibit its interaction with mouse double minute 2 homologue in COS1 cells. Therefore, CCRP may be a common co-chaperone and the roles it plays in the cytoplasm may go far beyond CAR to many other nuclear receptors as well as signaling molecules. CCRP is now found to engage in diverse regulations in the nucleus, one of which is epigenetic regulation. Only in the presence of CCRP does the histone of Cyp2b10 promoter remain methylated before PB treatment and demethylated after treatment.