The nuclear receptor transcriptional coregulator RIP140

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

The RIP140 Gene Is a Transcriptional Target of E2F1

RIP140 is a transcriptional coregulator involved in energy homeostasis and ovulation which is controlled at the transcriptional level by several nuclear receptors. We demonstrate here that RIP140 is a novel target gene of the E2F1 transcription factor. Bioinformatics analysis, gel shift assay, and chromatin immunoprecipitation demonstrate that the RIP140 promoter contains bona fide E2F response elements. In transiently transfected MCF-7 breast cancer cells, the RIP140 promoter is transactivated by overexpression of E2F1/DP1. Interestingly, RIP140 mRNA is finely regulated during cell cycle progression (5-fold increase at the G1/S and G2/M transitions). The positive regulation by E2F1 requires sequences located in the proximal region of the promoter (−73/+167), involves Sp1 transcription factors, and undergoes a negative feedback control by RIP140. Finally, we show that E2F1 participates in the induction of RIP140 expression during adipocyte differentiation. Altogether, this work identifies the RIP140 gene as a new transcriptional target of E2F1 which may explain some of the effect of E2F1 in both cancer and metabolic diseases

Retinoic Acid Mediates Long-Paced Oscillations in Retinoid Receptor Activity: Evidence for a Potential Role for RIP140

Mechanisms that underlie oscillatory transcriptional activity of nuclear receptors (NRs) are incompletely understood. Evidence exists for rapid, cyclic recruitment of coregulatory complexes upon activation of nuclear receptors. RIP140 is a NR coregulator that represses the transactivation of agonist-bound nuclear receptors. Previously, we showed that RIP140 is inducible by all-trans retinoic acid (RA) and mediates limiting, negative-feedback regulation of retinoid signaling.Here we report that in the continued presence of RA, long-paced oscillations of retinoic acid receptor (RAR) activity occur with a period ranging from 24 to 35 hours. Endogenous expression of RIP140 and other RA-target genes also oscillate in the presence of RA. Cyclic retinoid receptor transactivation is ablated by constitutive overexpression of RIP140. Further, depletion of RIP140 disrupts cyclic expression of the RA target gene HOXA5. Evidence is provided that RIP140 may limit RAR signaling in a selective, non-redundant manner in contrast to the classic NR coregulators NCoR1 and SRC1 that are not RA-inducible, do not cycle, and may be partially redundant in limiting RAR activity. Finally, evidence is provided that RIP140 can repress and be induced by other nuclear receptors in a manner that suggests potential participation in other NR oscillations.We provide evidence for novel, long-paced oscillatory retinoid receptor activity and hypothesize that this may be paced in part, by RIP140. Oscillatory NR activity may be involved in mediating hormone actions of physiological and pathological importance

CARM1 mediates the ligand-independent and tamoxifen-resistant activation of the estrogen receptor α by cAMP

The estrogen receptor α (ERα) is activated as a transcription factor by both estrogen and a large variety of other extracellular signals. The mechanisms of this ligand-independent activation, notably by cAMP signaling, are still largely unknown. We now close the gap in the signaling pathway between cAMP and ERα. Whereas the direct phosphorylation of ERα by the cAMP-activated protein kinase A (PKA) is dispensable, the phosphorylation of the coactivator-associated arginine methyltransferase 1 (CARM1) by PKA at a single serine is necessary and sufficient for direct binding to the unliganded hormone-binding domain (HBD) of ERα, and the interaction is necessary for cAMP activation of ERα. Sustained PKA activity promoting a constitutive interaction may contribute to tamoxifen resistance of breast tumors. Binding and activation involve a novel regulatory groove of the ERα HBD. As a result, depending on the activating signal, ERα recruits different coactivator complexes to regulate alternate sets of target genes

Rôle de RIP140 dans la signalisation hormonale

Les récepteurs nucléaires forment une superfamille de facteurs de transcription, qui contrôlent de nombreux aspects du métabolisme cellulaire et dont l’activité est réglée par un grand nombre de ligands et de cofacteurs transcriptionnels. RIP140 (receptor interacting protein of 140 kDa), un des premiers corégulateurs identifiés, est une protéine atypique qui, si elle interagit avec les récepteurs nucléaires en présence de ligands agonistes, exerce un contrôle négatif sur leur activité transcriptionnelle. Les mécanismes responsables de cette transrépression sont complexes et impliquent plusieurs domaines, recrutant différents partenaires tels que les protéines HDAC (histone désacétylase) et CtBP (C-terminal binding protein). Le contrôle de l’expression du gène RIP140 dans les cellules de cancers hormonodépendants semble intéressant, car il implique des possibilités de boucles de régulations multiples. Enfin, l’étude du rôle biologique de RIP140 suggère qu’il est impliqué dans le contrôle hormonal de processus fondamentaux tels que l’ovulation et la thermogenèse.Nuclear hormone receptors belong to a superfamily of ligand-activated transcription factors which regulate fundamental physiological processes. Their activity is controlled by a large number of coregulatory proteins which are, in most cases, recruited by nuclear receptors in the presence of ligand. RIP140 (receptor interacting protein of 140 kDa) was one of the first transcription cofactors to be identified almost ten years ago. This molecule is an atypical cofactor which interacts with agonist-liganded nuclear receptors but negatively regulates their transactivation potential. RIP140 exhibits nine leucine-rich motifs (LxxLL) which mediate the specific docking on the nuclear receptor ligand-binding domain. Transcription repression exerted by this cofactor implicates different mechanisms. Not only it involves a competition with coactivators such as those belonging to the p160 family, but also relies on active intrinsic repression through at least four different domains which allow recruitement of downstream repressors such as histone deacetylases (HDACs) or C-terminal binding proteins (CtBPs). The biological role of RIP140 has been investigated by disrupting the gene in mice. The lack of RIP140 expression in ovaries prevents follicle rupture and ovulation, rising to female infertility. In addition, this cofactor is also required for the control of fat storage and utilization through the regulation of genes involved in thermogenesis. Finally, RIP140 could play a role in the hormonal control of cancer cell proliferation by negatively regulating the activity of estrogen and retinoic acid receptors which are key actors in cancer growth. Interestingly, both estrogens and retinoic acid regulate RIP140 gene expression, revealing an increased level of complexity. In conclusion, RIP140 is an atypical transcription inhibitor which, by repressing nuclear hormone receptor activity, plays fundamental physiopathological roles

Receptor-interacting protein 140 is a repressor of the androgen receptor activity.: AR repression by RIP140

International audienceThe androgen receptor (AR) is a ligand-activated transcription factor that controls growth and survival of prostate cancer cells. In the present study, we investigated the regulation of AR activity by the receptor-interacting protein 140 (RIP140). We first showed that RIP140 could be coimmunoprecipitated with the receptor when coexpressed in 293T cells. This interaction appeared physiologically relevant because chromatin immunoprecipitation assays revealed that, under R1881 treatment, RIP140 could be recruited to the prostate-specific antigen encoding gene in LNCaP cells. In vitro glutathione S-transferase pull-down assays provided evidence that the carboxy-terminal domain of AR could interact with different regions of RIP140. By means of fluorescent proteins, we demonstrated that ligand-activated AR was not only able to translocate to the nucleus but also to relocate RIP140 from very structured nuclear foci to a diffuse pattern. Overexpression of RIP140 strongly repressed AR-dependent transactivation by preferentially targeting the ligand binding domain-dependent activity. Moreover, disruption of RIP140 expression induced AR overactivation, thus revealing RIP140 as a strong AR repressor. We analyzed its mechanism of transrepression and first demonstrated that different regions of RIP140 could mediate AR-dependent repression. We then showed that the carboxy-terminal end of RIP140 could reverse transcriptional intermediary factor 2-dependent overactivation of AR. The use of mutants of RIP140 allowed us to suggest that C-terminal binding protein played no role in RIP140-dependent inhibition of AR activity, whereas histone deacetylases partly regulated that transrepression. Finally, we provided evidence for a stimulation of RIP140 mRNA expression in LNCaP cells under androgen treatment, further emphasizing the role of RIP140 in androgen signaling

Tissue-specific expression of receptor-interacting protein in aging mouse

Receptor-interacting protein (RIP) is a well-characterized coregulator for nuclear receptors. Here, we report the expression of RIP as two isoforms with molecular weights of 140 kDa and 137 kDa in liver and kidney, but only as one isoform of 140 kDa in lung, adipose tissue, prostate and testis of mice. The levels of both the isoforms decreased in liver and kidney of old mice compared with adult mice. The expression of RIP140 in kidney was relatively lower in old males than females. In contrast, adipose tissue showed remarkably higher levels of RIP140 in old than adult mice of both sexes. Thus, the expression of RIP varied with the type of tissue, sex and age of mice, suggesting differences in its function as a coregulator