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...

Similarities in physiological roles of LXR (liver X receptors) and co-repressor RIP140 (receptor-interacting protein 140) in regulating energy homoeostasis and lipid and glucose metabolism suggest that the effects of LXR could at least partly be mediated by recruitment of the co-repressor RIP140. In the present study, we have elucidated the molecular basis for regulation of LXR transcriptional activity by RIP140. LXR is evenly localized in the nucleus and neither the N-terminal domain nor the LBD (ligand-binding domain) is necessary for nuclear localization. Both LXR subtypes, LXRalpha and LXRbeta, interact with RIP140 and co-localize in diffuse large nuclear domains. Interaction and co-localization are dependent on the LBD of the receptor. The C-terminal domain of RIP140 is sufficient for full repressive effect. None of the C-terminal NR (nuclear receptor)-boxes is required for the co-repressor activity, whereas the NR-box-like motif as well as additional elements in the C-terminal region are required for full repressive function. The C-terminal NR-box-like motif is necessary for interaction with LXRbeta, whereas additional elements are needed for strong interaction with LXRalpha. In conclusion, our results suggest that co-repression of LXR activity by RIP140 involves an atypical binding mode of RIP140 and a repression element in the RIP140 C-terminus.

No abstract

No abstract