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The CCR4-NOT complex acts as a central player in the control of mRNA turnover and mediates accelerated mRNA degradation upon HDAC inhibition. Here, we explored acetylation-induced changes in the composition of the CCR4-NOT complex by purification of the endogenously tagged scaffold subunit NOT1 and identified RNF219 as an acetylation-regulated cofactor. We demonstrate that RNF219 is an active RING-type E3 ligase which stably associates with CCR4-NOT via NOT9 through a short linear motif (SLiM) embedded within the C-terminal low-complexity region of RNF219. By using a reconstituted six-subunit human CCR4-NOT complex, we demonstrate that RNF219 inhibits deadenylation through the direct interaction of the α-helical SLiM with the NOT9 module. Transcriptome-wide mRNA half-life measurements reveal that RNF219 attenuates global mRNA turnover in cells, with differential requirement of its RING domain. Our results establish RNF219 as an inhibitor of CCR4-NOT-mediated deadenylation, whose loss upon HDAC inhibition contributes to accelerated mRNA turnover., The CCR4-NOT complex is a key regulator of eukaryotic mRNA deadenylation. Here the authors identified the E3 ubiquitin ligase RNF219 as an acetylation-regulated cofactor of the complex, which inhibits mRNA decay through a direct interaction with NOT9.

SIRT7 is an NAD+-dependent protein deacetylase that regulates cell growth and proliferation. Previous studies have shown that SIRT7 is required for RNA polymerase I (Pol I) transcription and pre-rRNA processing. Here, we took a proteomic approach to identify novel molecular targets and characterize the role of SIRT7 in non-nucleolar processes. We show that SIRT7 interacts with numerous proteins involved in transcriptional regulation and RNA metabolism, the majority of interactions requiring ongoing transcription. In addition to its role in Pol I transcription, we found that SIRT7 also regulates transcription of snoRNAs and mRNAs. Mechanistically, SIRT7 promotes the release of P-TEFb from the inactive 7SK snRNP complex and deacetylates CDK9, a subunit of the elongation factor P-TEFb, which activates transcription by phosphorylating serine 2 within the C-terminal domain (CTD) of Pol II. SIRT7 counteracts GCN5-directed acetylation of lysine 48 within the catalytic domain of CDK9, deacetylation promoting CTD phosphorylation and transcription elongation.

Activation of γ-aminobutyric A receptors (GABAARs) in the subependymal zone (SEZ) induces hyperpolarization and osmotic swelling in precursors, thereby promoting surface expression of the epidermal growth factor receptor (EGFR) and cell cycle entry. However, the mechanisms underlying the GABAergic modulation of cell swelling are unclear. Here, we show that GABAARs colocalize with the water channel aquaporin (AQP) 4 in prominin-1 immunopositive (P+) precursors in the postnatal SEZ, which include neural stem cells. GABAAR signaling promotes AQP4 expression by decreasing serine phosphorylation associated with the water channel. The modulation of AQP4 expression by GABAAR signaling is key to its effect on cell swelling and EGFR expression. In addition, GABAAR function also affects the ability of neural precursors to swell in response to an osmotic challenge in vitro and in vivo. Thus, the regulation of AQP4 by GABAARs is involved in controlling activation of neural stem cells and water exchange dynamics in the SEZ.

SummaryTumor necrosis factor-α (TNF-α) is the most potent proinflammatory cytokine in mammals. The degradation of TNF-α mRNA is critical for restricting TNF-α synthesis and involves a constitutive decay element (CDE) in the 3′ UTR of the mRNA. Here, we demonstrate that the CDE folds into an RNA stem-loop motif that is specifically recognized by Roquin and Roquin2. Binding of Roquin initiates degradation of TNF-α mRNA and limits TNF-α production in macrophages. Roquin proteins promote mRNA degradation by recruiting the Ccr4-Caf1-Not deadenylase complex. CDE sequences are highly conserved and are found in more than 50 vertebrate mRNAs, many of which encode regulators of development and inflammation. In macrophages, CDE-containing mRNAs were identified as the primary targets of Roquin on a transcriptome-wide scale. Thus, Roquin proteins act broadly as mediators of mRNA deadenylation by recognizing a conserved class of stem-loop RNA degradation motifs.