Liver receptor homolog-1 (LRH-1) is a nuclear receptor previously known to have distinct functions during mouse development and essential roles in cholesterol homeostasis. Recently, a new role for LRH-1 has been discovered in tumor progression, giving LRH-1 potential transforming functions. In order to identify critical factors stimulating LRH-1 expression leading to deregulated cellular proliferation, we studied its expression and its regulation in several breast cancer cell lines. We observed that LRH-1 expression was increased in estrogen receptor (ER) α expressing cell lines, whereas weak-to-no expression was found in nonexpressing ERα cell lines. In MCF7, LRH-1 expression was highly induced after treatment with 17β-estradiol (E2). This transcriptional regulation was the result of a direct binding of the ER to the LRH-1 promoter, as demonstrated by gelshift and chromatin immunoprecipitation assays. Interestingly, siRNA-mediated inactivation of LRH-1 decreased the E2-dependent proliferation of MCF7 cells. Finally, LRH-1 protein expression was detected by immunohistochemistry in tumor cells of human mammary ductal carcinomas. Altogether, these data demonstrate that LRH-1 is transcriptionally regulated by the ER α and reinforce the hypothesis that LRH-1 could exert potential oncogenic effects during breast cancer formation.

The prevalence of metabolic syndrome (MetS) components including obesity, dyslipidemia, insulin resistance (IR), and hepatic steatosis is rapidly increasing in wealthy societies. It is accepted that inflammation/oxidative stress are involved in the initiation/evolution of the MetS features. The present work was designed to evaluate the effects of three major cellular ROS production systems on obesity, glucose tolerance, and hepatic steatosis development and on oxidative stress onset. To do so, 40 young male Sprague-Dawley rats were divided into 5 groups: 1-control group, 2-high fat (HF) group (60% energy from fat), 3-HF+ MitoQ (mitochondrial ROS scavenger), 4-HF+ Apocynin (NADPH oxidase inhibitor), 5-HF+ Allopurinol (xanthine oxidase inhibitor). After 8 weeks of these treatments, surrogate MetS, mitochondrial function, and oxidative stress markers were measured in blood and liver. As expected, rats that were fed the HF diet exhibited increased body weight, glucose intolerance, overt hepatic steatosis, and increased hepatic oxidative stress. The impacts of the studied ROS inhibitors on these aspects of the MetS were markedly different. MitoQ showed the most clinically relevant effects, attenuating body weight gain and glucose intolerance provoked by the HF diet. Both Apocynin and Allopurinol showed limited effects suggesting secondary roles of xanthine oxidase (XO) or NADPH oxidase-dependent ROS production in the onset of oxidative stress-dependent obesity, glucose intolerance, and hepatic steatosis process. Thus, MitoQ revealed the central role of mitochondrial oxidative stress in the development of MetS and suggested that mitochondria-targeted antioxidants may be worth considering as potentially helpful therapies for MetS features.

Receptor interacting protein 140 (RIP140) is a negative transcriptional regulator of nuclear hormone receptors that is required for the maintenance of energy homeostasis and ovulation. In this study, we investigated the mechanisms by which RIP140 expression is controlled by estrogens in breast cancer cells. We first analyzed by real time reverse transcription-polymerase chain reaction the regulation of RIP140 mRNA accumulation by estrogen receptor (ER) ligands in MCF-7 cells. We showed that the induction by estradiol (E2) was rapid and did not affect the apparent stability of the mRNA, suggesting a direct transcriptional regulation. To further study the underlying regulatory mechanisms, we then characterized the human RIP140 gene. We identified several noncoding exons with alternative splicing and localized the promoter region more than 100 kilobases upstream from the coding exon. Although we mapped a perfect consensus estrogen response element able to bind ERα in gel shift and in chromatin immunoprecipitation experiments, the effect of E2 on RIP140 gene transcription was very modest. This might result at least in part from the presence of an overlapping aryl hydrocarbon receptor (AhR) binding site, which interfered with the E2 response on both the transiently transfected reporter construct and the accumulation of the endogenous RIP140 mRNA. Altogether, our data indicate that the RIP140 gene exhibits a complex structure with several noncoding exons and supports transcriptional cross-talk and feedback involving the ERα and AhR nuclear receptors.

The nuclear receptor superfamily comprises ligand-regulated transcription factors that control various developmental and physiological pathways. These receptors share a common modular structure and regulate gene expression through the recruitment of a large set of coregulatory proteins. These transcription cofactors regulate, either positively or negatively, chromatin structure and transcription initiation. One of the first proteins to be identified as a hormone-recruited cofactor was RIP140. Despite its recruitment by agonist-liganded receptors, RIP140 exhibits a strong transcriptional repressive activity which involves several inhibitory domains and different effectors. Interestingly, the RIP140 gene, located on chromosome 21 in humans, is finely regulated at the transcriptional level by various nuclear receptors. In addition, the protein undergoes several post-translational modifications which control its repressive activity. Finally, experiments performed in mice devoid of the RIP140 gene indicate that this transcriptional cofactor is essential for female fertility and energy homeostasis. RIP140 therefore appears to be an important modulator of nuclear receptor activity which could play major roles in physiological processes and hormone-dependent diseases.