Adenosine diphosphate (ADP)-ribosylation is a post-translational protein modification implicated in the regulation of a range of cellular processes. A family of proteins that catalyse ADP-ribosylation reactions are the poly(ADPribose) (PAR) polymerases (PARPs). PARPs covalently attach an ADP-ribose nucleotide to target proteins and some PARP family members can subsequently add additional ADP-ribose units to generate a PAR chain. The hydrolysis of PAR chains is catalysed by PAR glycohydrolase (PARG). PARG is unable to cleave the mono(ADP-ribose) unit directly linked to the protein and although the enzymatic activity that catalyses this reaction has been detected in mammalian cell extracts, the protein(s) responsible remain unknown. Here, we report the homozygous mutation of the c6orf130 gene in patients with severe neurodegeneration, and identify C6orf130 as a PARP-interacting protein that removes mono(ADP-ribosyl)ation on glutamate amino acid residues in PARP-modified proteins. X-ray structures and biochemical analysis of C6orf130 suggest a mechanism of catalytic reversal involving a transient C6orf130 lysyl-(ADP-ribose) intermediate. Furthermore, depletion of C6orf130 protein in cells leads to proliferation and DNA repair defects. Collectively, our data suggest that C6orf130 enzymatic activity has a role in the turnover and recycling of protein ADP-ribosylation, and we have implicated the importance of this protein in supporting normal cellular function in humans.

There are controversial claims that the embryonic stem cell (ESC) pluripotency factor OCT4 is activated in somatic cells, but there is no evidence it plays a functional role in these cells. Herein we demonstrate that smooth muscle cell (SMC)-specific conditional knockout of Oct4 within Apoe−/− mice resulted in increased lesion size and changes consistent with decreased plaque stability including a thinner fibrous cap, increased necrotic core, and increased intra-plaque hemorrhage. Results of SMC-lineage tracing studies showed that these changes were likely due to marked reductions in SMC number within lesions including impaired SMC migration and investment within the fibrous cap. Re-activation of Oct4 within SMCs was associated with hydroxymethylation of the Oct4 promoter and was HIF1α- and KLF4-dependent. Results provide the first direct evidence that OCT4 plays a functional role in somatic cells and highlight the importance of further investigation of possible OCT4 functions in normal and diseased somatic cells.

The phosphorylated inositol moiety is viewed as a fundamental signaling entity that the cell utilizes to generate combinatorially complex arrays of communication pathways with multiple functions (1). To list just a few examples, a 1,4,5-trisphosphate configuration yields a molecule (Ins(1,4,5)P 3 ) 2 that gates intracellular Ca 2ϩ channels (2). The 3,4,5,6-tetrakisphosphate of inositol (Ins(3,4,5,6)P 4 ) inhibits Cl Ϫ channel conductance (3). An inositol ring with six phosphates (InsP 6 ) enhances the activity of Dbp5, a key component of a molecular ratchet that winches mRNA out of the nucleus (4). Many additional biological activities have been attributed to these and other inositol phosphates (5-7).In the early 1990s, two groups working independently discovered a novel subgroup of the inositol phosphate signaling family in which diphosphate groups are added to Ins(1,3,4,5,6)P 5 and InsP 6 (8, 9), forming compounds that are now generally described as "inositol pyrophosphates" or "diphosphoinositol polyphosphates" (see Fig. 1) (10). These molecules have been reported to regulate vesicle trafficking (11), transcription (12), chemotaxis (13), telomere maintenance (14, 15), apoptosis (16, 17), and DNA repair (18) and to mediate environmental stress responses (19 -22). One of these inositol pyrophosphates, PP-InsP 5 , has been shown to directly phosphorylate-specific target proteins in a kinaseindependent manner (23).The importance of inositol pyrophosphates has meant that the molecular identification of all of the enzymes that synthesize and metabolize this group of molecules has been one of the key goals of this field of research in recent years. For example, the family of kinases that synthesize PP-InsP 4 and PP-InsP 5 (see Fig. 1) has already been cloned (24 -26). Specific phosphatases that hydrolyze the inositol pyrophosphates have also been cloned (27-29). However, the molecular identity of PPIP5K (E.C. 2.7.1.155; see Fig. 1), the enzyme that phosphorylates PPInsP 5 to (PP) 2 -InsP 4 , 3 has eluded researchers for 14 years. It has been observed in mammalian cell extracts (8, 9, 30, 31) but has not previously been cloned. Yet (PP) 2 -InsP 4 is a molecule of * This work was supported by grants from the Intramural Research Program of the NIEHS/National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

DYRK1A (the dual specificity tyrosine phosphorylation-regulated kinase 1A) plays an important role in body growth and brain physiology. Overexpression of this kinase has been associated with the development of Down syndrome in both human and animal models, whereas single copy loss-of-function of DYRK1A leads to increased apoptosis and decreased brain size. Although more than a dozen of DYRK1A targets have been identified, the molecular basis of its involvement in neuronal development remains unclear. Here we show that DYRK1A and another pro-survival member of the DYRK family, DYRK3, promote cell survival through phosphorylation and activation of SIRT1, an NAD ؉ -dependent protein deacetylase that is essential in a variety of physiological processes including stress response and energy metabolism. DYRK1A and DYRK3 directly phosphorylate SIRT1 at Thr 522 , promoting deacetylation of p53. A SIRT1 phosphorylation mimetic (SIRT1 T522D) displays elevated deacetylase activity, thus inhibiting cell apoptosis. Conversely, a SIRT1 dephosphorylation mimetic (SIRT1 T522V) fails to mediate DYRK-induced deacetylation of p53 and cell survival. We show that knockdown of endogenous DYRK1A and DYRK3 leads to hypophosphorylation of SIRT1, sensitizing cells to DNA damage-induced cell death. We also provide evidence that phosphorylation of Thr 522 activates SIRT1 by promoting product release, thereby increasing its enzymatic turnover. Taken together, our findings provide a novel mechanism by which two anti-apoptotic DYRK members promote cell survival through direct modification of SIRT1. These findings may have important implications in understanding the molecular mechanisms of tumorigenesis, Down syndrome, and aging.

Topoisomerase 2 (TOP2) DNA transactions are essential for life, and proceed via formation of the TOP2 cleavage complex (TOP2cc), a covalent enzyme-DNA reaction intermediate that is vulnerable to trapping by potent anticancer TOP2 drugs. How genotoxic TOP2 DNA-protein crosslinks are resolved is unclear. Here, we show that the SUMO ligase ZATT (ZNF451) is a multifunctional DNA repair factor that controls cellular responses to TOP2 damage. ZATT binding to TOP2cc facilitates a proteasome-independent Tyrosyl-DNA phosphodiesterase 2 (TDP2) hydrolase activity on stalled TOP2cc. The ZATT SUMO ligase activity further promotes TDP2 interactions with SUMOylated TOP2, regulating efficient TDP2 recruitment through a "split-SIM" SUMO2 engagement platform. These findings uncover a ZATT–TDP2 catalyzed and SUMO2-modulated pathway for direct resolution of TOP2cc.

Nsp15, a uridine specific endoribonuclease conserved across coronaviruses, processes viral RNA to evade detection by host defense systems. Crystal structures of Nsp15 from different coronaviruses have shown a common hexameric assembly, yet how the enzyme recognizes and processes RNA remains poorly understood. Here we report a series of cryo-EM reconstructions of SARS-CoV-2 Nsp15, in both apo and UTP-bound states. The cryo-EM reconstructions, combined with biochemistry, mass spectrometry, and molecular dynamics, expose molecular details of how critical active site residues recognize uridine and facilitate catalysis of the phosphodiester bond. Mass spectrometry revealed the accumulation of cyclic phosphate cleavage products, while analysis of the apo and UTP-bound datasets revealed conformational dynamics not observed by crystal structures that are likely important to facilitate substrate recognition and regulate nuclease activity. Collectively, these findings advance understanding of how Nsp15 processes viral RNA and provide a structural framework for the development of new therapeutics.

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SUMMARY Store-operated Ca2+ entry (SOCE) and Ca2+ release-activated Ca2+ currents (Icrac) are strongly suppressed during mitosis, the only known physiological situation in which Ca2+ store depletion is uncoupled from the activation of Ca2+ influx. We found that the ER Ca2+ sensor, STIM1, failed to rearrange into near-plasma membrane puncta in mitotic cells, a critical step in the SOCE activation pathway. We also found that STIM1 from mitotic cells is recognized by the phosphospecific MPM-2 antibody, suggesting that STIM1 is phosphorylated during mitosis. Removal of 10 MPM-2-recognition sites by truncation at amino acid 482 abolished MPM-2 recognition of mitotic STIM1, and significantly rescued STIM1 rearrangement and SOCE responses in mitosis. We identified S486 and S668 as mitosis-specific phosphorylation sites, and STIM1 containing mutations of these sites to alanine also significantly rescued mitotic SOCE. Therefore, phosphorylation of STIM1 at S486 and S668, and possibly other sites, underlies suppression of SOCE during mitosis.