The H3 histone variant CENP-A is an epigenetic marker critical for the centromere identity and function. However, the precise regulation of the spatiotemporal deposition and propagation of CENP-A at centromeres during the cell cycle is still poorly understood. Here, we show that CENP-A is phosphorylated at Ser68 during early mitosis by Cdk1. Our results demonstrate that phosphorylation of Ser68 eliminates the binding of CENP-A to the assembly factor HJURP, thus preventing the premature loading of CENP-A to the centromere prior to mitotic exit. Because Cdk1 activity is at its minimum at the mitotic exit, the ratio of Cdk1/PP1α activity changes in favor of Ser68 dephosphorylation, thus making CENP-A available for centromeric deposition by HJURP. Thus, we reveal that dynamic phosphorylation of CENP-A Ser68 orchestrates the spatiotemporal assembly of newly synthesized CENP-A at active centromeres during the cell cycle.

Interferon regulatory factor 8 (IRF8) is known to affect the innate immune response, for example, by regulating the differentiation and function of immune cells. However, whether IRF8 can influence cardiac hypertrophy is unknown. Here we show that IRF8 levels are decreased in human dilated/hypertrophic cardiomyopathic hearts and in murine hypertrophic hearts. Mice overexpressing Irf8 specifically in the heart are resistant to aortic banding (AB)-induced cardiac hypertrophy, whereas mice lacking IRF8 either globally or specifically in cardiomyocytes develop an aggravated phenotype induced by pressure overload. Mechanistically, we show that IRF8 directly interacts with NFATc1 to prevent NFATc1 translocation and thus inhibits the hypertrophic response. Inhibition of NFATc1 ameliorates the cardiac abnormalities in IRF8−/− mice after AB. In contrast, constitutive activation of NFATc1 nullifies the protective effects of IRF8 on cardiac hypertrophy in IRF8-overexpressing mice. Our results indicate that IRF8 is a potential therapeutic target in pathological cardiac hypertrophy.

The tandem Tudor-like domain-containing protein Spindlin1 has been reported to be a meiotic spindle-associated protein. Here we report that Spindlin1 is not associated with the spindle in mouse embryonic fibroblast cells during mitotic divisions. In interphase cells, Spindlin1 specifically localizes to the nucleoli. Moreover, Spindlin1 is a histone methylation effector protein that specifically recognizes H3K4 methylation. Finally, Spindlin1 localizes to the active ribosomal DNA (rDNA) repeats, and Spindlin1 facilitates the expression of rRNA genes.

The transcription factor NF-κB plays critical roles in many biological processes, especially immunity. The signaling to NF-κB activation is subtly regulated to avoid harmful immune effects. In this report, we identified ubiquitin-specific protease 2 isoform a (USP2a) as a novel negative regulator in Toll-like receptors/IL-1β- and Sendai virus (SeV)-induced NF-κB activation. Overexpression of USP2a inhibited IL-1β- and SeV-induced NF-κB activation and transcription of inflammatory cytokines, whereas the knockdown or knockout of USP2a had opposite effects. USP2a-deficient cells exhibited potentiated ubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6) upon stimulation by IL-1β and SeV. Furthermore, USP2a was constitutively associated with TRAF6, and removed K63-linked polyubiquitin chains of TRAF6 induced by IL-1β and SeV stimulation. The residues of USP2a important for their role were also identified. Because of the importance of TRAF6 in multiple pathways leading to NF-κB activation, these findings provide a general regulatory mechanism for NF-κB activation triggered by different stimuli.

SummaryGenes of the mixed lineage leukemia (MLL) family regulate transcription by methylating histone H3K4. Six members of the MLL family exist in humans, including SETD1A, SETD1B and MLL1-MLL4. Each of them plays non-redundant roles in development and disease genesis. MLL1 regulates the cell cycle and the oscillation of circadian gene expression. Its fusion proteins are involved in leukemogenesis. Here, we studied the role of MLL1 in innate immunity and found it selectively regulates the activation of genes downstream of NF-kB mediated by tumor necrosis factor (TNFa) and lipopolysaccharide (LPS). Real-time PCR and genome-wide gene expression profile analysis proved that the deficiency of MLL1 reduced the expression of a group of genes downstream of nuclear factor kB (NF-kB). However, the activation of NF-kB itself was not affected. The MLL1 complex is found both in the nucleus and cytoplasm and is associated with NF-kB. CHIP assays proved that the translocation of MLL1 to chromatin was dependent on NF-kB. Our results suggest that MLL1 is recruited to its target genes by activated NF-kB and regulates their transcription.