The genomic analysis of the impact of steroid receptor coactivators ablation on hepatic metabolism

Members of the steroid receptor coactivator (SRC) family, which include SRC-1 (NcoA-1/p160), SRC-2(TIF2/GRIP1/NcoA-2) and SRC-3(pCIP/RAC3/ACTR/pCIP/ AIB1/TRAM1), are critical mediators of steroid receptor action. Gene ablation studies previously identified SRC-1 and SRC-2 as being involved in the control of energy homeostasis. A more precise identification of the molecular pathways regulated by these coactivators is crucial for understanding the role of steroid receptor coactivators in the control of energy homeostasis and obesity. A genomic approach using microarray analysis was employed to identify the subsets of genes that are altered in the livers of SRC-1-/-, SRC-2-/-, and SRC-3-/- mice. Microarray analysis demonstrates that gene expression changes are specific and nonoverlapping for each SRC member in the liver. The overall pattern of altered gene expressions in the SRC-1-/- mice was up-regulation, whereas SRC-2-/- mice showed an overall down-regulation. Several key regulatory enzymes of energy metabolism were significantly altered in the liver of SRC-2-/- mice, which are consistent with the prior observation that SRC-2-/- mice have increased energy expenditure. This study demonstrates that the molecular targets of SRC-2 regulation in the murine liver stimulate fatty acid degradation and glycolytic pathway, whereas fatty acid, cholesterol, and steroid biosynthetic pathways are down-regulated.     

A structural and in vitro characterization of asoprisnil: a selective progesterone receptor modulator

Selective progesterone receptor modulators (SPRMs) have been suggested as therapeutic agents for treatment of gynecological disorders. One such SPRM, asoprisnil, was recently in clinical trials for treatment of uterine fibroids and endometriosis. We present the crystal structures of progesterone receptor (PR) ligand binding domain complexed with asoprisnil and the corepressors nuclear receptor corepressor (NCoR) and SMRT. This is the first report of steroid nuclear receptor crystal structures with ligand and corepressors. These structures show PR in a different conformation than PR complexed with progesterone (P4). We profiled asoprisnil in PR-dependent assays to understand further the PR-mediated mechanism of action. We confirmed previous findings that asoprisnil demonstrated antagonism, but not agonism, in a PR-B transfection assay and the T47D breast cancer cell alkaline phosphatase activity assay. Asoprisnil, but not RU486, weakly recruited the coactivators SRC-1 and AIB1. However, asoprisnil strongly recruited the corepressor NCoR in a manner similar to RU486. Unlike RU486, NCoR binding to asoprisnil-bound PR could be displaced with equal affinity by NCoR or TIF2 peptides. We further showed that it weakly activated T47D cell gene expression of Sgk-1 and PPL and antagonized P4-induced expression of both genes. In rat leiomyoma ELT3 cells, asoprisnil demonstrated partial P4-like inhibition of cyclooxygenase (COX) enzymatic activity and COX-2 gene expression. In the rat uterotrophic assay, asoprisnil demonstrated no P4-like ability to oppose estrogen. Our data suggest that asoprisnil differentially recruits coactivators and corepressors compared to RU486 or P4, and this specific cofactor interaction profile is apparently insufficient to oppose estrogenic activity in rat uterus.