Heritable loss‐of‐function mutations in genes encoding key regulators of DNA repair and genome stability can result in degenerative progeroid and/or cancer predisposition syndromes; however, such ...mutations have never been found to affect the Chk1 protein kinase, despite its central role in DNA damage signalling and checkpoint activation. Remarkably, two recent reports now demonstrate that heritable, gain‐of‐function mutations within the Chk1 C‐terminal regulatory domain can cause female infertility in humans. In vitro, oocytes from individuals heterozygous for such mutant Chk1 alleles fail to undergo the first mitotic division after fertilization owing to arrest in G2 phase of the cell cycle. This arrest results from inhibition of the master regulator of mitosis, the cyclin‐dependent kinase CDK1, through the same molecular mechanisms that are engaged by activated Chk1 to impose G2 checkpoint arrest in somatic cells bearing DNA damage. Remarkably, the failure of this first zygotic division in heterozygotes in vitro can be rescued through treatment with selective Chk1 inhibitor drugs, allowing development of apparently normal blastocysts and offering hope that a pharmacological solution to this cause of infertility may be possible.
Germline mutations in DNA damage response genes often underlie cancer predisposition and/or progeroid syndromes; however, no such mutations had been observed to affect the DNA damage‐activated protein kinase Chk1. Now, two recent reports identify heritable, gain‐of‐function mutations of Chk1 as a cause of human female infertility due to zygote arrest. Remarkably, this arrest can be relieved in vitro using Chk1 kinase inhibitor drugs, raising the prospect of a pharmacological treatment.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Formaldehyde is an aliphatic monoaldehyde and is a highly reactive environmental human carcinogen. Whereas humans are continuously exposed to exogenous formaldehyde, this reactive aldehyde is a ...naturally occurring biological compound that is present in human plasma at concentrations ranging from 13 to 97 micromol/L. It has been well documented that DNA-protein crosslinks (DPC) likely play an important role with regard to the genotoxicity and carcinogenicity of formaldehyde. However, little is known about which DNA damage response pathways are essential for cells to counteract formaldehyde. In the present study, we first assessed the DNA damage response to plasma levels of formaldehyde using chicken DT40 cells with targeted mutations in various DNA repair genes. Here, we show that the hypersensitivity to formaldehyde is detected in DT40 mutants deficient in the BRCA/FANC pathway, homologous recombination, or translesion DNA synthesis. In addition, FANCD2-deficient DT40 cells are hypersensitive to acetaldehyde, but not to acrolein, crotonaldehyde, glyoxal, and methylglyoxal. Human cells deficient in FANCC and FANCG are also hypersensitive to plasma levels of formaldehyde. These results indicate that the BRCA/FANC pathway is essential to counteract DPCs caused by aliphatic monoaldehydes. Based on the results obtained in the present study, we are currently proposing that endogenous formaldehyde might have an effect on highly proliferating cells, such as bone marrow cells, as well as an etiology of cancer in Fanconi anemia patients.
DNA damage is a key factor both in the evolution and treatment of cancer. Genomic instability is a common feature of cancer cells, fuelling accumulation of oncogenic mutations, while radiation and ...diverse genotoxic agents remain important, if imperfect, therapeutic modalities. Cellular responses to DNA damage are coordinated primarily by two distinct kinase signaling cascades, the ATM-Chk2 and ATR-Chk1 pathways, which are activated by DNA double-strand breaks (DSBs) and single-stranded DNA respectively. Historically, these pathways were thought to act in parallel with overlapping functions; however, more recently it has become apparent that their relationship is more complex. In response to DSBs, ATM is required both for ATR-Chk1 activation and to initiate DNA repair via homologous recombination (HRR) by promoting formation of single-stranded DNA at sites of damage through nucleolytic resection. Interestingly, cells and organisms survive with mutations in ATM or other components required for HRR, such as BRCA1 and BRCA2, but at the cost of genomic instability and cancer predisposition. By contrast, the ATR-Chk1 pathway is the principal direct effector of the DNA damage and replication checkpoints and, as such, is essential for the survival of many, although not all, cell types. Remarkably, deficiency for HRR in BRCA1- and BRCA2-deficient tumors confers sensitivity to cisplatin and inhibitors of poly(ADP-ribose) polymerase (PARP), an enzyme required for repair of endogenous DNA damage. In addition, suppressing DNA damage and replication checkpoint responses by inhibiting Chk1 can enhance tumor cell killing by diverse genotoxic agents. Here, we review current understanding of the organization and functions of the ATM-Chk2 and ATR-Chk1 pathways and the prospects for targeting DNA damage signaling processes for therapeutic purposes.
3•Atmospheric ice crystals accrete in aircraft engines, causing blockage and damage3•A novel three-layer thermodynamic model is shown for ice growth on engine surfaces3•The surface may be warm or ...cold, and is subject to a flux of mixed phase particles3•Three simple methods are given for the in-depth thermal response of the substrate3•The model is validated against experimental data from an ice crystal wind tunnel
Ingestion of high-altitude ice particles can be hazardous to aircraft engines in flight. Ice accretion may occur in the compression system, leading to blockage of the core gas path, blade damage and/or engine flameout. Numerous engine powerloss events since 1990 have been attributed to this mechanism. An expansion in engine certification requirements to incorporate ice crystal conditions has spurred efforts to develop analytical models for phenomenon. A necessary component of a complete icing simulation is a thermodynamic accretion model. In this paper, a new model for ice crystal icing is developed through adaptation of the Extended Messinger Model (EMM) from supercooled water conditions to mixed phase conditions (ice crystals and supercooled water). The new model is termed the Extended Messinger Model -Crystals (EMM-C). Continuity and energy balances are performed using the local flow conditions and impinging mass fluxes of ice and water. For accretions grown on a warm engine surface, initially above freezing temperature, a novel three-layer (water-ice-water) accretion structure is proposed, and the underlying equations described. Finally, predictions from the EMM-C model are compared to experimental results generated in an ice crystal wind tunnel. Compared with current literature icing models, EMM-C provides a tractable framework for modelling engine icing through allowing mixed phase accretions on warm surfaces.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Higher cutting speeds are desired for an enhanced manufacturing productivity. However, this is limited by the increased wear rate at the elevated cutter-chip interface temperature. To achieve the ...optimal cutting speed and cutter design for a prolonged tool life, a high fidelity thermal model is indispensable. In this paper, the thermal distribution for a multi-component system of cutter, workpiece and chip is modelled in a single mesh with realistic geometries and thermal boundary conditions. Directly modelling the multi-component system avoids the problem of inter-component heat partitioning. In order to dispense the computational cost of a 3D transient simulation, a multi-component system in a thermal equilibrium is modelled in a quasi-static way, i.e. heat taken away by the moving material is treated as advection heat transfer in the flow. This reduced-order model is achievable by imposing a mapping boundary condition dealing with temperature continuity and velocity discontinuity at the shear plane such that the numerical error in heat flux crossing the curly air-material boundaries is eliminated. After validation against Ivester et al. (2000)’s experimental data, a wide range of cutting speeds, shear zone and friction zone thicknesses are investigated. This quasi-static model was found to perform better than Lalwani et al. (2009)’s semi-empirical tuned analytical model in predicting the maximum interface temperature, while also applying non-linear material properties and realistic thermal boundaries. It was found that heat partitioning into the tool was over-predicted by using this empirical formula and the maximum temperature at the tool-chip interface was sensitive to the friction zone geometry. Furthermore, convective and radiative surface heat loss was found to be insignificant when compared to the heat taken away by the moving material. Therefore, a high-fidelity thermal distribution can be calculated within several seconds using a quasi-static 2D model. This reduced order model can not only be used to optimise the cutter design, but also to model the thermal distribution of any multi-component system with moving components in a thermal equilibrium.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Aurora B kinase activity is required for successful cell division. In this paper, we show that Aurora B is phosphorylated at serine 331 (Ser331) during mitosis and that phosphorylated Aurora B ...localizes to kinetochores in prometaphase cells. Chk1 kinase is essential for Ser331 phosphorylation during unperturbed prometaphase or during spindle disruption by taxol but not nocodazole. Phosphorylation at Ser331 is required for optimal phosphorylation of INCENP at TSS residues, for Survivin association with the chromosomal passenger complex, and for complete Aurora B activation, but it is dispensable for Aurora B localization to centromeres, for autophosphorylation at threonine 232, and for association with INCENP. Overexpression of Aurora B(S331A), in which Ser331 is mutated to alanine, results in spontaneous chromosome missegregation, cell multinucleation, unstable binding of BubR1 to kinetochores, and impaired mitotic delay in the presence of taxol. We propose that Chk1 phosphorylates Aurora B at Ser331 to fully induce Aurora B kinase activity. These results indicate that phosphorylation at Ser331 is an essential mechanism for Aurora B activation.
Claspin was discovered as a Chk1‐interacting protein necessary for Chk1 phosphorylation and activation by the upstream kinase, ATR, in response to DNA synthesis inhibition in Xenopus oocyte extracts. ...Subsequent investigations have defined a molecular model in which Claspin acts as an adaptor or scaffold protein to facilitate activation of Chk1 by ATR within a multiprotein complex that forms on single‐stranded DNA at stalled replication forks and sites of DNA damage. Interestingly, Claspin is an unstable protein whose degradation via the proteasome is tightly regulated via ubiquitination and controlled by multiple ubiquitin ligases and deubiquitinases. As a result, Claspin levels fluctuate during the cell cycle, contributing to the regulation of checkpoint proficiency and playing a key role in terminating checkpoint‐mediated cell cycle arrest. In addition to its role in signalling genotoxic stress, Claspin is required to maintain normal rates of replication fork progression during unperturbed DNA replication and may contribute to the regulation of replication origin firing. Consistent with this, Claspin can bind directly to DNA, with particular affinity for branched or forked molecules, and it interacts with multiple protein components of the replisome. As expected for a protein with key roles in checkpoint signalling and genome duplication, aberrations of Claspin expression and structure have been observed in cancer. Claspin is furthermore targeted to facilitate viral replication and plays a role in suppressing cellular DNA synthesis in response to nongenotoxic endoplasmic reticulum stress. Here, we review the functions and regulation of Claspin with a focus on areas of active research.
Claspin is an adaptor molecule that facilitates activation of the checkpoint effector kinase, Chk1, by its upstream activator ATR within a multiprotein complex that forms at sites of DNA damage or stalled replication. Claspin is also thought to play an important role in normal replication, and may be a target for certain nongenotoxic stress signalling pathways that inhibit DNA synthesis.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Charge regulation of nonpolar colloids Hallett, James E; Gillespie, David A J; Richardson, Robert M ...
Soft matter,
2018, Volume:
14, Issue:
3
Journal Article
Peer reviewed
Open access
Individual colloids often carry a charge as a result of the dissociation (or adsorption) of weakly-ionized surface groups. The magnitude depends on the precise chemical environment surrounding a ...particle, which in a concentrated dispersion is a function of the colloid packing fraction η. Theoretical studies have suggested that the effective charge Z
in regulated systems could, in general, decrease with increasing η. We test this hypothesis for nonpolar dispersions by determining Z
(η) over a wide range of packing fractions (10
≤ η ≤ 0.3) using a combination of small-angle X-ray scattering and electrophoretic mobility measurements. All dispersions remain entirely in the fluid phase regime. We find a complex dependence of the particle charge as a function of the packing fraction, with Z
initially decreasing at low concentrations before finally increasing at high η. We attribute the non-monotonic density dependence to a crossover from concentration-independent screening at low η, to a high packing fraction regime in which counterions outnumber salt ions and electrostatic screening becomes η-dependent. The efficiency of charge stabilization at high concentrations may explain the unusually high stability of concentrated nanoparticle dispersions which has been reported.
The spindle checkpoint delays anaphase onset in cells with mitotic spindle defects. Here, we show that Chk1, a component of the DNA damage and replication checkpoints, protects vertebrate cells ...against spontaneous chromosome missegregation and is required to sustain anaphase delay when spindle function is disrupted by taxol, but not when microtubules are completely depolymerized by nocodazole. Spindle checkpoint failure in Chk1-deficient cells correlates with decreased Aurora-B kinase activity and impaired phosphorylation and kinetochore localization of BubR1. Furthermore, Chk1 phosphorylates Aurora-B and enhances its catalytic activity in vitro. We propose that Chk1 augments spindle checkpoint signaling and is required for optimal regulation of Aurora-B and BubR1 when kinetochores produce a weakened signal. In addition, Chk1-deficient cells exhibit increased resistance to taxol. These results suggest a mechanism through which Chk1 could protect against tumorigenesis through its role in spindle checkpoint signaling.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Background The anticoagulant treatment of acute deep venous thrombosis (DVT) has been historically directed toward the prevention of recurrent venous thromboembolism. However, such treatment ...imperfectly protects against late manifestations of the postthrombotic syndrome. By restoring venous patency and preserving valvular function, early thrombus removal strategies can potentially decrease postthrombotic morbidity. Objective A committee of experts in venous disease was charged by the Society for Vascular Surgery and the American Venous Forum to develop evidence-based practice guidelines for early thrombus removal strategies, including catheter-directed pharmacologic thrombolysis, pharmacomechanical thrombolysis, and surgical thrombectomy. Methods Evidence-based recommendations are based on a systematic review and meta-analysis of the relevant literature, supplemented when necessary by less rigorous data. Recommendations are made according to the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology, incorporating the strength of the recommendation (strong: 1; weak: 2) and an evaluation of the level of the evidence (A to C). Results On the basis of the best evidence currently available, we recommend against routine use of the term “proximal venous thrombosis” in favor of more precise characterization of thrombi as involving the iliofemoral or femoropopliteal venous segments (Grade 1A). We further suggest the use of early thrombus removal strategies in ambulatory patients with good functional capacity and a first episode of iliofemoral DVT of <14 days in duration (Grade 2C) and strongly recommend their use in patients with limb-threatening ischemia due to iliofemoral venous outflow obstruction (Grade 1A). We suggest pharmacomechanical strategies over catheter-directed pharmacologic thrombolysis alone if resources are available and that surgical thrombectomy be considered if thrombolytic therapy is contraindicated (Grade 2C). Conclusions Most data regarding early thrombus removal strategies are of low quality but do suggest patient-important benefits with respect to reducing postthrombotic morbidity. We anticipate revision of these guidelines as additional evidence becomes available.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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