RIP140 (receptor-interacting protein 140) is a transcriptional co-repressor that regulates diverse genes such as those responsive to hormones and involved in metabolic processes. The expression of RIP140 is regulated by multiple hormonal activities in adipose tissue and cancer cell lines. However, it is unclear whether and how RIP140 is regulated post-transcriptionally. Using 5′RACE (rapid amplification of 5′ cDNA ends), we have identified a novel 5′ splice variant of RIP140 mRNA in mouse brain and P19 cells. A target sequence for miRNA (microRNA) mir-346 was found in the 5′UTR (5′-untranslated region) of RIP140 mRNA; this miRNA is also expressed endogenously in mouse brain and P19 cells. Gain- and loss-of-function studies demonstrated that mir-346 elevates RIP140 protein levels by facilitating association of its mRNA with the polysome fraction. Furthermore, the activity of mir346 does not require Ago-2 (Argonaute 2). The expression of mir-346 enhances the gene repressive activity of RIP140. This is the first report demonstrating post-transcriptional regulation of RIP140 mRNA, involving the enhancing effect of a specific miRNA that targets RIP140's 5′UTR.

Endotoxin tolerance dampens responses to subsequent Toll-like receptor stimulation, but the molecular details of this process are still being defined. Wei and colleagues show that endotoxin tolerance requires degradation of the coactivator RIP140. Tolerance to endotoxins that is triggered by prior exposure to Toll-like receptor (TLR) ligands provides a mechanism with which to dampen inflammatory cytokines. The receptor-interacting protein RIP140 interacts with the transcription factor NF-κB to regulate the expression of genes encoding proinflammatory cytokines. Here we found lipopolysaccharide stimulation of kinase Syk–mediated tyrosine phosphorylation of RIP140 and interaction of the NF-κB subunit RelA with RIP140. These events resulted in more recruitment of the E3 ligase SCF to tyrosine-phosphorylated RIP140, which degraded RIP140 to inactivate genes encoding inflammatory cytokines. Macrophages expressing nondegradable RIP140 were resistant to the establishment of endotoxin tolerance for specific 'tolerizable' genes. Our results identify RelA as an adaptor with which SCF fine tunes NF-κB target genes by targeting the coactivator RIP140 and show an unexpected role for RIP140 degradation in resolving inflammation and endotoxin tolerance.

Receptor interacting protein 140 (RIP140), a ligand‐dependent corepressor for nuclear receptors, can be modified by arginine methylation. Three methylated arginine residues, at Arg‐240, Arg‐650, and Arg‐948, were identified by mass spectrometric analysis. Site‐directed mutagenesis studies demonstrated the functionality of these arginine residues. The biological activity of RIP140 was suppressed by protein arginine methyltransferase 1 (PRMT1) due to RIP140 methylation, which reduced the recruitment of histone deacetylases to RIP140 and facilitated its nuclear export by enhancing interaction with exportin 1. A constitutive negative (Arg/Ala) mutant of RIP140 was resistant to the effect of PRMT1, and a constitutive positive (Arg/Phe) mutation mimicked the effect of arginine methylation. The biological activities of the wild type and the mutant proteins were examined in RIP140‐null MEF cells. This study uncovered a novel means to inactivate, or suppress, RIP140, and demonstrated protein arginine methylation as a critical type of modification for corepressor.

Cells form stress granules (SGs) in response to environmental stresses, which constitute cytoplasmic domains where mRNAs are stored and translation is halted. Although several components are found in SGs, it is poorly understood as to how SGs are formed and dissolved. We identified growth factor receptor-bound protein 7 (Grb7), an RNA-binding, translational regulator, as an integral component of SGs, which directly interacts with Hu antigen R (HuR) and is required for cells to form SGs. When stress is terminated, Grb7 is hyperphosphorylated by focal adhesion kinase (FAK), loses its ability to directly interact with HuR and is dissociated from SG components, thereby disrupting SGs in recovering cells. Consistently, dominant-negative hypophospho mutants of FAK and Grb7 significantly attenuate SG disassembly during recovery. FAK activation followed by its phosphorylating Grb7 constitutes a cell-autonomous signalling pathway that regulates the disassembly of SGs and translational stimulation during recovery. This is the first reported pathway actively regulating the dynamics of SGs.

κ-opioid receptor (KOR) is detected pre- and postsynaptically, but the subcellular localization, translation, and regulation ofkormRNA in presynaptic compartments of sensory neurons remain elusive.In situhybridization detected axonal distribution ofkormRNA in primary neurons of dorsal root ganglia (DRG). The MS2-fused GFP trackedkormRNA transport from DRG neuronal soma to axons, requiring its 5′ and 3′ UTRs. In Campenot chambers, axonal translation ofkormRNA was demonstrated for DRG neurons, which depended on its 5′ UTR and was stimulated by KCl depolarization. KCl depolarization of DRG neurons rendered redistribution ofkormRNA from the postpolysomal fraction to the translationally active polysomal fraction. This study provided evidence for mRNA transport and regulation of presynaptic protein synthesis of nonstructural proteins like KOR in primary sensory neurons and demonstrated a mechanism of KCl depolarization-stimulated axonal mRNA redistribution for localized translational regulation.