Regulation of Subnuclear Localization Is Associated with a Mechanism for Nuclear Receptor Corepression by RIP140

Abstract

Regulation of gene transcription by nuclear receptors involves association with numerous coregulators.Receptor-interacting protein 140 (RIP140) is a corepressor that negatively regulates the ligand-induced activity of several nuclear receptors, including the glucocorticoid receptor (GR). In the present study, we have characterized the role of the intranuclear localization of RIP140 in its corepressor activity. In the absence of ligand-activated GR, RIP140 is localized in small nuclear foci targeted by a 40-amino-acid-long sequence. Although the focus-targeting domain overlaps with a binding sequence for the corepressor CtBP (C-terminal binding protein), interaction with CtBP is not involved in the localization. RIP140 foci do not correspond to PML bodies but partly colocalize with domains harboring the corepressor SMRT. Upon ligand binding, GR and RIP140 are redistributed to large nuclear domains distinct from the RIP140 foci. The redistribution requires regions of RIP140 with corepressor activity, as well as the DNA-binding domain of GR. Furthermore, we show that full RIP140 corepressor activity is contributed both by C-terminal receptor-binding LXXLL motifs and interaction with the CtBP corepressor. In conclusion, our results suggest that the corepressor function of RIP140 is multifaceted and involves binding to nuclear receptors, as well as additional functions mediated by the formation and intranuclear relocalization of a repressive protein complex.Nuclear hormone receptors are ligand-regulated transcription factors that may either activate or repress gene transcription. Transcriptional activation by nuclear receptors is dependent on the recruitment of numerous coregulator proteins to the receptors (for a review, see reference 18). These encompass ATP-dependent chromatin-remodeling proteins, proteins with histone acetyltransferase activity, and protein complexes involved in recruitment of the basal transcriptional machinery, including RNA polymerase II. Ligand-induced gene activation by nuclear receptors has been suggested to constitute a switch from a repressed state that is maintained by receptor interaction with corepressor proteins such as SMRT and NCoR, recruiting histone deacetylases (HDACs), to an activated state induced by coactivator proteins such as p160/SRC-1 proteins that have histone acetylase activity or recruit proteins that do. The C-terminal ligand-binding domain (LBD) of the receptor is the main docking site for the coregulators (1). Many coregulators have specific LXXLL motifs (NR boxes) that are involved in the interaction with the receptor LBDs (7, 13, 24).Receptor-interacting protein 140 (RIP140), also called nuclear receptor-interacting protein 1 (Nrip1), is a unique coregulator of nuclear receptors (3). It acts mainly as a corepressor reducing gene transcription but, in contrast to other corepressors that interact with unliganded or antagonist-activated receptors, RIP140 interacts with ligand-activated receptors. RIP140 has a restricted number of target proteins that only includes som...

Functional interactions with Pit-1 reorganize co-repressor complexes in the living cell nucleus

“…This indicated that, although the mutant Pit-1 retained its ability to interact with the co-repressor complex, DNA-binding activity was necessary to establish the final positioning of the Pit-1/corepressor complexes in the cell nucleus. Similar results have been reported for qualitative imaging studies of the RIP140 corepressor and a GR DNA-binding-domain mutant (Tazawa et al, 2003).…”

“…This implies that most Pit-1/co-repressor interactions occur outside the spherical focal bodies. Interestingly, our linear regression models revealed that Pit-1 expression caused a graded dispersal of YFP-SMRT foci in the cell population instead of the 'all or none' dispersal implied by previous qualitative imaging studies of co-repressors and nuclear receptors (Tazawa et al, 2003;Wu et al, 2001). These are the first statistical data supporting the hypothesis that DNAbinding factors position co-repressor complexes in specific subnuclear domains, moving co-repressor protein out of spherical foci and into more widely distributed nuclear compartments.…”

“…Similar results were reported for receptor-interacting protein 140 (RIP140), another co-repressor protein that is redistributed from spherical foci to a diffuse pattern through physical interactions with the nonligand-bound glucocorticoid receptor (GR). This dispersal of RIP140 also correlated with repression (Tazawa et al, 2003). In combination with these results, our imaging and functional studies indicate that transcriptional repression correlates with the dispersal of co-repressor complexes by DNA-binding factors in living cells.…”

Nuclear receptor corepressor RIP140 regulates fat accumulation

“…Expression of UCP1 has been shown to be induced in WAT in transgenic mice by introduction of an activated form of PPAR␦ (20) and also in human white adipocytes in culture as a result of expression of PGC-1␣ and activation by ligands for PPAR␥ (52). RIP140 is capable of interacting directly with all of these receptors in a liganddependent manner and of repressing their transcriptional activity (34,35,53). Although endogenous high-affinity ligands have not yet been identified for the PPAR␥ and PPAR␦ isoforms, it is apparent that the availability of PPAR␣ ligands such as oleylethanolamide may influence the regulation of body weight (54).…”

Activity and subcellular compartmentalization of peroxisome proliferator-activated receptor α are altered by the centrosome-associated protein CAP350

“…Nuclear compartmentalization plays an important role in gene regulation, and many transcription factors, including steroid and nuclear hormone receptors such as the glucocorticoid, estrogen, thyroid and retinoic acid receptors, and nuclear receptor coregulatory molecules such as GRIP-1, SMRT, SRC-1, and RIP140, have been shown to accumulate in discrete foci distributed throughout the nucleoplasm (Carmo-Fornesca, 2002;Doucas, 2002;Hendzel et al, 2001;Zilliacus et al, 2001;Tazawa et al, 2003;van Steensel et al, 1995). The identity, composition and function of these foci remain to be elucidated.…”