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The multi-subunit translation initiation factor eIF2B is a control node for protein synthesis. eIF2B activity is canonically modulated through stress-responsive phosphorylation of its substrate eIF2. The eIF2B regulatory subcomplex is evolutionarily related to sugar-metabolizing enzymes, but the biological relevance of this relationship was unknown. To identify natural ligands that might regulate eIF2B, we conduct unbiased binding- and activity-based screens followed by structural studies. We find that sugar phosphates occupy the ancestral catalytic site in the eIF2Bα subunit, promote eIF2B holoenzyme formation and enhance enzymatic activity towards eIF2. A mutant in the eIF2Bα ligand pocket that causes Vanishing White Matter disease fails to engage and is not stimulated by sugar phosphates. These data underscore the importance of allosteric metabolite modulation for proper eIF2B function. We propose that eIF2B evolved to couple nutrient status via sugar phosphate sensing with the rate of protein synthesis, one of the most energetically costly cellular processes., The activity of translation initiation factor eIF2B is known to be modulated through stress-responsive phosphorylation of its substrate eIF2. Here, the authors uncover the regulation of eIF2B by the binding of sugar phosphates, suggesting a link between nutrient status and the rate of protein synthesis.

p53 is primarily known as a downstream transcriptional effector in the DNA damage-response cascade. We report that endogenous p53 rapidly accumulates at DNA damage sites within 2 s of UVA microirradiation. The kinetics of p53 recruitment mimics those of known DNA damage-response proteins, such as Ku70 and poly(- ADP-ribose) polymerase (PARP), and precedes recruitment of Nbs1, 53BP1, and DDB1. Mutations in the DNA-binding and C-terminal domains significantly suppress this rapid recruitment. The C-terminal domain of p53 contains key residues for PARP interaction that are required for rapid recruitment of p53 to DNA damage sites, as is PARP-dependent modification. The presence of p53 at damage sites influences the recruitment kinetics of 53BP1 and DDB1 and directs the choice of nonhomologous end joining repair (NHEJ) and nucleotide excision repair. Mutations that suppressed rapid recruitment of p53 promoted error-prone alternative end-joining (alt-NHEJ) and inhibited nucleotide excision repair. Our finding that p53 is a critical early responder to DNA damage stands in contrast with its extensively studied role as a downstream transcriptional regulator in DNA damage repair. We highlight an unrecognized role of p53 in directing DNA repair dynamics and integrity and suggest a parallel mode of p53 tumor suppression apart from its function as a transcription factor. Ministry of Education (MOE) National Medical Research Council (NMRC) National Research Foundation (NRF) Published version D.P.L. and T.L.F.H. were supported by A*STAR core funding. M.P.S. and Y.-H.W. were supported by the Mechanobiology Institute at the National University of Singapore, and, more recently, by a Cancer Prevention and Research Institute of Texas grant at the University of Texas Medical Branch. W.L.T. and M.Y.L. were supported by funding from the National Medical Research Council, Singapore (OFIRG17may-061, OFIRG19nov-0106, CTGIIT18may-0012, NMRC/OFLCG/002-2018), the National Research Foundation, Singapore (NRF-NRFF2015-04, NRF-CRP22- 2019-0003, NRF-CRP23-2019-0004), and the Singapore Ministry of Education under its Research Centers of Excellence initiative.

Nicotinamide adenine dinucleotide (NAD) levels decline during aging, contributing to physical and metabolic dysfunction. The NADase CD38 plays a key role in age-related NAD decline. Whether the inhibition of CD38 increases lifespan is not known. Here, we show that the CD38 inhibitor 78c increases lifespan and healthspan of naturally aged mice. In addition to a 10% increase in median survival, 78c improved exercise performance, endurance, and metabolic function in mice. The effects of 78c were different between sexes. Our study is the first to investigate the effect of CD38 inhibition in naturally aged animals.

Centrosomes are major microtubule-organizing centers composed of centrioles surrounded by an extensive proteinacious layer called the pericentriolar material (PCM). In Caenorhabditis elegans embryos, the mitotic PCM expands by Polo-like kinase 1 (PLK-1) phosphorylation-accelerated assembly of SPD-5 molecules into supramolecular scaffolds. However, how PLK-1 phosphorylation regulates SPD-5 assembly is not known. We found that a mutant version of SPD-5 that is insensitive to PLK-1 phosphorylation (SPD-54A) could localize to PCM but was unable to rescue the reduction in PCM size and density when wild-type SPD-5 levels were decreased. In vitro, purified SPD-54A self-assembled into functional supramolecular scaffolds over long time scales, suggesting that phosphorylation only controls the rate of SPD-5 scaffold assembly. Furthermore, the SPD-5 scaffold, once assembled, remained intact and supported microtubule nucleation in the absence of PLK-1 activity in vivo. We conclude that PLK-1 is required for rapid assembly of the PCM scaffold but not for scaffold maintenance or function. Based on this idea, we developed a theoretical model that adequately predicted PCM growth rates in different mutant conditions in vivo. We propose that PLK-1 phosphorylation-dependent conversion of SPD-5 into an assembly-competent form underlies PCM formation in vivo and that the rate of this conversion determines final PCM size and density., Summary: Polo-like kinase phosphorylation determines proper centrosome scaffold size and density, but not function or maintenance, in Caenorhabditis elegans embryos.

The integrated stress response (ISR) attenuates the rate of protein synthesis while inducing expression of stress proteins in cells. Various insults activate kinases that phosphorylate the GTPase eIF2 leading to inhibition of its exchange factor eIF2B. Vanishing White Matter (VWM) is a neurological disease caused by eIF2B mutations that, like phosphorylated eIF2, reduce its activity. We show that introduction of a human VWM mutation into mice leads to persistent ISR induction in the central nervous system. ISR activation precedes myelin loss and development of motor deficits. Remarkably, long-term treatment with a small molecule eIF2B activator, 2BAct, prevents all measures of pathology and normalizes the transcriptome and proteome of VWM mice. 2BAct stimulates the remaining activity of mutant eIF2B complex in vivo, abrogating the maladaptive stress response. Thus, 2BAct-like molecules may provide a promising therapeutic approach for VWM and provide relief from chronic ISR induction in a variety of disease contexts., eLife digest Cells must be able to respond to their changing environment in order to survive. When cells encounter particularly unfavorable conditions, they often react by activating a so-called ‘stress’ response. A group of proteins collectively known as eIF2B helps to regulate this response. In a severe neurological condition called Vanishing White Matter (VWM), the genes that produce the eIF2B proteins contain mutations that make eIF2B less active. As a result, certain cells in people with VWM are always stressed. Six years ago, researchers discovered a molecule that boosts the activity of eIF2B. In 2018, they found that it also works on various mutant forms of eIF2B found in VWM. The molecule had so far only been tested in biochemical laboratory experiments. Now, Wong et al. – including some of the researchers involved in the 2018 study – have tested whether an improved version of the molecule treats VWM in mice. The trial treatment successfully halted all signs of the disease in the mice. The molecule blunted the persistent stress response of the cells in the brain and spinal cord, primarily in a cell type that is severely affected by the human form of VWM. Cells in other parts of the body were spared. Overall, the results of the experiments suggest that an eIF2B activator may prove to be an effective treatment for VWM in humans. It could similarly be used to treat other conditions that activate this abnormal cell stress response. The molecule Wong et al. used is not suitable for use in humans, so work is continuing to find a suitable variant.

The Integrated Stress Response (ISR) attenuates the rate of protein synthesis while inducing expression of stress proteins in cells. Various insults activate kinases that phosphorylate the GTPase eIF2 leading to inhibition of its exchange factor eIF2B. Vanishing White Matter (VWM) is a neurological disease caused by eIF2B mutations that, like phosphorylated eIF2, reduce its activity. We show that introduction of a human VWM mutation into mice leads to persistent ISR induction in the central nervous system. ISR activation precedes myelin loss and development of motor deficits. Remarkably, long-term treatment with a novel eIF2B activator, 2BAct, prevents all measures of pathology and normalizes the transcriptome and proteome of VWM mice. 2BAct stimulates the remaining activity of mutant eIF2B complexin vivo, abrogating the maladaptive stress response. Thus, 2BAct-like molecules may provide a promising therapeutic approach for VWM and provide relief from chronic ISR induction in a variety of other disease contexts.

eIF2B is a dedicated guanine nucleotide exchange factor for eIF2, the GTPase that is essential to initiate mRNA translation. The integrated stress response (ISR) signaling pathway inhibits eIF2B activity, attenuates global protein synthesis and upregulates a set of stress-response proteins. Partial loss-of-function mutations in eIF2B cause a neurodegenerative disorder called Vanishing White Matter Disease (VWMD). Previously, we showed that the small molecule ISRIB is a specific activator of eIF2B (Sidrauski et al., 2015). Here, we report that various VWMD mutations destabilize the decameric eIF2B holoenzyme and impair its enzymatic activity. ISRIB stabilizes VWMD mutant eIF2B in the decameric form and restores the residual catalytic activity to wild-type levels. Moreover, ISRIB blocks activation of the ISR in cells carrying these mutations. As such, ISRIB promises to be an invaluable tool in proof-of-concept studies aiming to ameliorate defects resulting from inappropriate or pathological activation of the ISR.

Giving an old organelle the old heave-ho Centrioles are ancient cellular organelles that build centrosomes, the major microtubule-organizing centers in animal cells. Duplication of centrioles is tightly controlled to ensure that each dividing cell has precisely two centrosomes. Human cancer cells often have extra centrosomes, which has been hypothesized to confer a proliferative advantage. Wong et al. developed small molecules (centrinones) that allowed them to reversibly “delete” centrioles from cells (see the Perspective by Stearns). Surprisingly, cancer cells continued to divide in the absence of centrosomes, whereas normal cells stopped dividing. Science , this issue p. 1155 ; see also p. 1091

Aneuploidy, a state of karyotype imbalance, is a hallmark of cancer. Changes in chromosome copy number have been proposed to drive disease by modulating the dosage of cancer driver genes and by promoting cancer genome evolution. Given the potential of cells with abnormal karyotypes to become cancerous, do pathways that limit the prevalence of such cells exist? By investigating the immediate consequences of aneuploidy on cell physiology, we identified mechanisms that eliminate aneuploid cells. We find that chromosome mis-segregation leads to further genomic instability that ultimately causes cell-cycle arrest. We further show that cells with complex karyotypes exhibit features of senescence and produce pro-inflammatory signals that promote their clearance by the immune system. We propose that cells with abnormal karyotypes generate a signal for their own elimination that may serve as a means for cancer cell immunosurveillance. By examining the immediate consequences of chromosome mis-segregation, Santaguida et al. show that aneuploidy causes genomic instability and the evolution of cells with complex karyotypes. Such cells undergo senescence and produce pro-inflammatory cytokines that promote their clearance by natural killer cells. Keywords: aneuploidy; cancer; immune system; genome instability; senescence, National Institutes of Health (U.S.) (Grant CA206157), National Institutes of Health (U.S.) (Grant GM118066), National Institute of General Medical Sciences (U.S.) (Grant T32GM007753)

SummaryAssembly of SAS-6 dimers to form the centriolar cartwheel requires the ZYG-1/Plk4 kinase. Here, we show that ZYG-1 recruits SAS-6 to the mother centriole independently of its kinase activity; kinase activity is subsequently required for cartwheel assembly. We identify a direct interaction between ZYG-1 and the SAS-6 coiled coil that explains its kinase activity-independent function in SAS-6 recruitment. Perturbing this interaction, or the interaction between an adjacent segment of the SAS-6 coiled coil and SAS-5, prevented SAS-6 recruitment and cartwheel assembly. SAS-6 mutants with alanine substitutions in a previously described ZYG-1 target site or in 37 other residues, either phosphorylated by ZYG-1 in vitro or conserved in closely related nematodes, all supported cartwheel assembly. We propose that ZYG-1 binding to the SAS-6 coiled coil recruits the SAS-6-SAS-5 complex to the mother centriole, where a ZYG-1 kinase activity-dependent step, whose target is unlikely to be SAS-6, triggers cartwheel assembly.

Centrosomes are major microtubule-organizing centers composed of centrioles surrounded by an extensive proteinacious layer called the pericentriolar material (PCM). In C. elegans embryos, the mitotic PCM expands by Polo-kinase (PLK-1) phosphorylation-accelerated assembly of SPD-5 molecules into supramolecular scaffolds. However, how PLK-1 phosphorylation regulates SPD-5 assembly is not known. We found that a mutant version of SPD-5 that is insensitive to PLK-1 phosphorylation (SPD-54A) could localize to PCM but was unable to rescue the reduction in PCM size and density when wild-type SPD-5 levels were decreased. In vitro, purified SPD-54A self-assembled into functional supramolecular scaffolds over long time scales, suggesting that phosphorylation only controls the rate of SPD-5 scaffold assembly. Furthermore, the SPD-5 scaffold, once assembled, remained intact and supported microtubule nucleation in the absence of PLK-1 activity in vivo. We conclude that Polo Kinase is required for rapid assembly of the PCM scaffold but not for scaffold maintenance or function. Based on this idea, we developed a theoretical model that adequately predicted PCM growth rates in different mutant conditions in vivo. We propose that PLK-1 phosphorylation-dependent conversion of SPD-5 into an assembly-competent form underlies PCM formation in vivo and that the rate of this conversion determines final PCM size and density.

Centrioles organise centrosomes and template cilia and flagella. Several centriole and centrosome proteins have been linked to microcephaly (MCPH), a neuro-developmental disease associated with small brain size. CPAP (MCPH6) and STIL (MCPH7) are required for centriole assembly, but it is unclear how mutations in them lead to microcephaly. We show that the TCP domain of CPAP constitutes a novel proline recognition domain that forms a 1:1 complex with a short, highly conserved target motif in STIL. Crystal structures of this complex reveal an unusual, all-β structure adopted by the TCP domain and explain how a microcephaly mutation in CPAP compromises complex formation. Through point mutations, we demonstrate that complex formation is essential for centriole duplication in vivo. Our studies provide the first structural insight into how the malfunction of centriole proteins results in human disease and also reveal that the CPAP–STIL interaction constitutes a conserved key step in centriole biogenesis. DOI: http://dx.doi.org/10.7554/eLife.01071.001, eLife digest Organisms—and individual tissues—grow and develop by dividing their cells. However, the process of cell division does not have to be symmetric, and the fates of the cells can be very different if cellular contents, including RNAs or proteins, are exclusively retained in the ‘mother’ or passed to her ‘daughter’. Organelles known as centrioles can play an important part in influencing whether cell division is symmetric or asymmetric. Centrioles contain ordered assemblies of various proteins, and mutations in some of these proteins can cause developmental defects in humans. For example, mutations in the centriolar proteins CPAP and STIL cause a syndrome known as microcephaly, in which the brain is smaller than normal. Although CPAP and STIL are known to bind each other, how they interact on a molecular level to form centrioles—and how this interaction is disrupted in microcephaly—is not well understood. Cottee et al. have now used structural and biochemical assays to explore how these two proteins bind to each other, and have identified specific amino acid residues that enable this interaction. These residues are highly conserved across many organisms, and a mutation in one of them has previously been associated with microcephaly in humans. Now, Cottee et al. demonstrate that this mutation weakens the interaction between CPAP and STIL in vitro. To explore these processes in vivo, Cottee et al. studied mutant fruit flies in which the interactions between CPAP and STIL were weaker than normal, and found that these mutations prevented the normal formation of centrioles. Furthermore, there was a striking correlation between the ability to form centrioles in fruit flies and the ability of CPAP and STIL to bind each other, based on the structural model and in vitro binding studies. Cumulatively, these findings reinforce the importance of CPAP and STIL in centriole formation, and suggest that one reason for the development of microcephaly may be defects in the proper formation of centrioles. DOI: http://dx.doi.org/10.7554/eLife.01071.002

Aurora kinases are essential for cell division and are frequently misregulated in human cancers. Based on their potential as cancer therapeutics, a plethora of small molecule Aurora kinase inhibitors have been developed, with a subset having been adopted as tools in cell biology. Here, we fill a gap in the characterization of Aurora kinase inhibitors by using biochemical and cell-based assays to systematically profile a panel of 10 commercially available compounds with reported selectivity for Aurora A (MLN8054, MLN8237, MK-5108, MK-8745, Genentech Aurora Inhibitor 1), Aurora B (Hesperadin, ZM447439, AZD1152-HQPA, GSK1070916), or Aurora A/B (VX-680). We quantify the in vitro effect of each inhibitor on the activity of Aurora A alone, as well as Aurora A and Aurora B bound to fragments of their activators, TPX2 and INCENP, respectively. We also report kinome profiling results for a subset of these compounds to highlight potential off-target effects. In a cellular context, we demonstrate that immunofluorescence-based detection of LATS2 and histone H3 phospho-epitopes provides a facile and reliable means to assess potency and specificity of Aurora A versus Aurora B inhibition, and that G2 duration measured in a live imaging assay is a specific readout of Aurora A activity. Our analysis also highlights variation between HeLa, U2OS, and hTERT-RPE1 cells that impacts selective Aurora A inhibition. For Aurora B, all four tested compounds exhibit excellent selectivity and do not significantly inhibit Aurora A at effective doses. For Aurora A, MK-5108 and MK-8745 are significantly more selective than the commonly used inhibitors MLN8054 and MLN8237. A crystal structure of an Aurora A/MK-5108 complex that we determined suggests the chemical basis for this higher specificity. Taken together, our quantitative biochemical and cell-based analyses indicate that AZD1152-HQPA and MK-8745 are the best current tools for selectively inhibiting Aurora B and Aurora A, respectively. However, MK-8745 is not nearly as ideal as AZD1152-HQPA in that it requires high concentrations to achieve full inhibition in a cellular context, indicating a need for more potent Aurora A-selective inhibitors. We conclude with a set of “good practice” guidelines for the use of Aurora inhibitors in cell biology experiments.

Centrosomes are the major microtubule-organizing centers in animal cells. Centrosomes catalyze microtubule assembly to accelerate formation of the bipolar mitotic spindle that segregates chromosomes during cell division. To analyze the effect of centrosome removal in normal and cancer cells, we developed centrinone, a potent, specific and cellularly-active inhibitor of the protein kinase polo-like kinase 4 (Plk4), which is essential for centrosome duplication (Wong et al., 2015, Science 348:1155-60). Centrosome-less cells take longer to execute mitosis, and trigger a mitotic stress signaling pathway that results in p53 stabilization and apoptosis and/or senescence of the resulting daughter cells. Failure to form a spindle can also lead to apoptosis during mitosis or exit from mitosis without chromosome segregation (mitotic slippage). In a genome-wide CRISPR/Cas9 loss-of-function screen for resistance to centrinone, we had previously shown that loss of the ubiquitin ligase TRIM37 makes spindle assembly more robust to centrosome removal (Meitinger et al., 2016, J Cell Biol. 214:155-66), raising the possibility that high levels of TRIM37 might increase sensitivity to centrosome removal. Here, we describe the use of single-cell live imaging assays to identify determinants of vulnerability of cancer cells to centrosome removal. Among a panel of 37 tested cell lines, neuroblastoma-derived cell lines were the most sensitive to centrosome removal, exhibiting high levels of apoptosis and rapid loss of viability following treatment with centrinone. We found that sensitivity to centrosome removal correlated with TRIM37 expression levels. Upon centrosome depletion, cells with high TRIM37 levels, particularly neuroblastoma cells, exhibited greatly increased mitotic duration and frequency of mitotic failure. p53 positive neuroblastoma cell lines exhibited apoptosis resulting from mitotic stress-mediated p53 activation and from mitotic failure. Surprisingly, p53 negative neuroblastoma cell lines, which are unable to sense mitotic stress, were also highly sensitive to centrosome removal, with cell death in this case resulting from high rates of mitotic failure. TRIM37 deletion restored the ability of cells to proliferate in centrinone. Thus, centrosome removal via Plk4 inhibition appears to be a promising strategy for therapeutic treatment of neuroblastomas and potentially other cancers with high levels of TRIM37 expression. Citation Format: Franz Meitinger, Robert L. Davis, Ruth Kabeche, John V. Anzola, Yao Liang Wong, Andrew K. Shiau, Arshad Desai, Karen Oegema. TRIM37 expression levels dictate susceptibility to centrosome removal, supporting Plk4 inhibition as a potential new strategy for targeting neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4130.

Kinesin-1 is a microtubule-based motor comprising two heavy chains (KHCs) and two light chains (KLCs). Motor activity is precisely regulated to avoid futile ATP consumption and to ensure proper intracellular localization of kinesin-1 and its cargoes. The KHC tail inhibits ATPase activity by interacting with the enzymatic KHC heads, and the tail also binds microtubules. Here, we present a role for the KLCs in regulating both the head- and microtubule-binding activities of the kinesin-1 tail. We show that KLCs reduce the affinity of the head-tail interaction over tenfold and concomitantly repress the tail’s regulatory activity. We also show that KLCs inhibit tail-microtubule binding by a separate mechanism. Inhibition of head-tail binding requires steric and electrostatic factors. Inhibition of tail-microtubule binding is largely electrostatic, pH dependent, and mediated partly by a highly negatively charged linker region between the KHC-interacting and cargo-binding domains of the KLCs. Our data support a model wherein KLCs promote activation of kinesin-1 for cargo transport by simultaneously suppressing tail-head and tail-microtubule interactions. KLC-mediated inhibition of tail-microtubule binding may also influence diffusional movement of kinesin-1 on microtubules, and kinesin-1’s role in microtubule transport/sliding.

Centrioles are ancient organelles that build centrosomes, the major microtubule-organizing centers of animal cells. Extra centrosomes are a common feature of cancer cells. To investigate the importance of centrosomes in the proliferation of normal and cancer cells, we developed centrinone, a reversible inhibitor of Polo-like kinase 4 (Plk4), a serine-threonine protein kinase that initiates centriole assembly. Centrinone treatment caused centrosome depletion in human and other vertebrate cells. Centrosome loss irreversibly arrested normal cells in a senescence-like G1 state by a p53-dependent mechanism that was independent of DNA damage, stress, Hippo signaling, extended mitotic duration, or segregation errors. In contrast, cancer cell lines with normal or amplified centrosome numbers could proliferate indefinitely after centrosome loss. Upon centrinone washout, each cancer cell line returned to an intrinsic centrosome number "set point." Thus, cells with cancer-associated mutations fundamentally differ from normal cells in their response to centrosome loss.

We have used electron paramagnetic resonance and fluorescence spectroscopy to study the interaction between the kinesin-1 head and its regulatory tail domain. The interaction between the tails and the enzymatically active heads has been shown to inhibit intrinsic and microtubule-stimulated ADP release. Here, we demonstrate that the probe mobility of two different spin-labeled nucleotide analogs in the kinesin-1 nucleotide pocket is restricted upon binding of the tail domain to kinesin-1 heads. This conformational restriction is distinct from the microtubule-induced changes in the nucleotide pocket. Unlike myosin V, this tail-induced restriction occurs independent of nucleotide state. We find that the head-tail interaction that causes the restriction only weakly stabilizes Mg(2+) in the nucleotide pocket. The conformational restriction also occurs when a tail construct containing a K922A point mutation is used. This mutation eliminates the tail's ability to inhibit ADP release, indicating that the tail does not inhibit nucleotide ejection from the pocket by simple steric hindrance. Together, our data suggest that the observed head-tail interaction serves as a scaffold to position K922 to exert its inhibitory effect, possibly by interacting with the nucleotide alpha/beta-phosphates in a manner analogous to the arginine finger regulators of some G proteins.

SummaryCells keep their energy balance and avoid oxidative stress by regulating mitochondrial movement, distribution, and clearance. We report here that two Parkinson's disease proteins, the Ser/Thr kinase PINK1 and ubiquitin ligase Parkin, participate in this regulation by arresting mitochondrial movement. PINK1 phosphorylates Miro, a component of the primary motor/adaptor complex that anchors kinesin to the mitochondrial surface. The phosphorylation of Miro activates proteasomal degradation of Miro in a Parkin-dependent manner. Removal of Miro from the mitochondrion also detaches kinesin from its surface. By preventing mitochondrial movement, the PINK1/Parkin pathway may quarantine damaged mitochondria prior to their clearance. PINK1 has been shown to act upstream of Parkin, but the mechanism corresponding to this relationship has not been known. We propose that PINK1 phosphorylation of substrates triggers the subsequent action of Parkin and the proteasome.PaperFlick