Activation of p53 transcriptional activity requires ATM's kinase domain and multiple N-terminal serine residues of p53

UPS and Kinases-Gatekeepers of the G1/S Transition

The G1/S transition is a highly regulated and pivotal checkpoint in the cell cycle, where the cell decides whether to commit to DNA replication and subsequent division or enter a non-dividing state. This checkpoint serves as a critical control point for preventing uncontrolled cell proliferation and maintaining genomic stability. The major driving force underlying the G1/S transition is the sequential activation of Cyclin-dependent kinases (CDKs), which is regulated by the coordinated binding of Cyclin partners, as well as the phosphorylation and ubiquitin-mediated degradation of both Cyclin partners and Cyclin-dependent kinase inhibitors (CKIs). Various E3 ligase families govern the timely degradation of these regulatory proteins, with their activity intricately controlled by phosphorylation events. This coordination enables the cells to efficiently translate the environmental cues and molecular signaling inputs to determine their fate. We explore the evolution of three distinct models describing the G1/S transition, highlighting how the traditional linear model is being challenged by recent paradigm shifts and conflicting findings. These advances reveal emerging complexity and unresolved questions in the field, particularly regarding how the latest insights into coordinated phosphorylation and ubiquitination-dependent degradation integrate into contemporary models of the G1/S transition.

Immunosenescence promotes cancer development: from mechanisms to treatment strategies

The body's innate immune system plays a pivotal role in identifying and eliminating cancer cells. However, as the immune system ages, its functionality can deteriorate, becoming dysfunctional, inefficient, or even inactive-a condition referred to as immunosenescence. This decline significantly increases the risk of malignancies. While the pro-cancer effects of T-cell aging have been widely explored, there remains a notable gap in the literature regarding the impact of aging on innate immune cells, such as macrophages and neutrophils. This review seeks to address this gap, with emphasis on these cell types. Furthermore, although certain cancer immunotherapies, including immune checkpoint inhibitors (ICIs), have demonstrated efficacy across a broad spectrum of cancers, elderly patients are less likely to derive clinical benefit from these treatments. In some cases, they may even experience immune-related adverse events (irAEs). While senolytic strategies have shown promise in exerting anti-cancer effects, their adverse reactions and potential off-target effects present significant challenges. This review aims to elucidate the pro-cancer effects of immunosenescence, its implications for the efficacy and safety of ICIs, and potential anti-aging treatment strategies. In addition, optimizing anti-aging therapies to minimize adverse reactions and enhance therapeutic outcomes remains a critical focus for future research endeavors.

DNA damage causes ATM-dependent heterochromatin loss leading to nuclear softening, blebbing, and rupture

The nucleus must maintain stiffness to preserve its shape and integrity to ensure proper function. Defects in nuclear stiffness caused from chromatin and lamin perturbations produce abnormal nuclear shapes common in aging, heart disease, and cancer. Loss of nuclear shape via protrusions called blebs lead to nuclear rupture that is well established to cause nuclear dysfunction, including DNA damage. However, it remains unknown how increased DNA damage affects nuclear stiffness, shape, and ruptures, which could create a feedback loop. To determine whether increased DNA damage alters nuclear physical properties, we treated mouse embryonic fibroblast cells with DNA damage drugs cisplatin and bleomycin. DNA damage drugs caused increased nuclear blebbing and rupture in interphase nuclei within a few hours and independent of mitosis. Micromanipulation force measurements reveal that DNA damage decreased chromatin-based nuclear mechanics but did not change lamin-based strain stiffening at long extensions relative to wild type. Immunofluorescence measurements of DNA damage treatments reveal the mechanism is an ATM-dependent decrease in heterochromatin leading to nuclear weaken, blebbing, and rupture which can be rescued upon ATM inhibition treatment. Thus, DNA damage drugs cause ATM-dependent heterochromatin loss resulting in nuclear softening, blebbing, and rupture.

Cell cycle dysregulation in cancer

Cancer is a systemic manifestation of aberrant cell cycle activity and dysregulated cell growth. Genetic mutations can determine tumor onset by either augmenting cell division rates or restraining normal controls such as cell cycle arrest or apoptosis. As a result, tumor cells not only undergo uncontrolled cell division but also become compromised in their ability to exit the cell cycle accurately. Regulation of cell cycle progression is enabled by specific surveillance mechanisms known as cell cycle checkpoints, and aberrations in these signaling pathways often culminate in cancer. For instance, DNA damage checkpoints, which preclude the generation and augmentation of DNA damage in the G1, S, and G2 cell cycle phases, are often defective in cancer cells, allowing cell division in spite of the accumulation of genetic errors. Notably, tumors have evolved to become dependent on checkpoints for their survival. For example, checkpoint pathways such as the DNA replication stress checkpoint and the mitotic checkpoint rarely undergo mutations and remain intact because any aberrant activity could result in irreparable damage or catastrophic chromosomal missegregation leading to cell death. In this review, we initially focus on cell cycle control pathways and specific functions of checkpoint signaling involved in normal and cancer cells and then proceed to examine how cell cycle control and checkpoint mechanisms can provide new therapeutic windows that can be exploited for cancer therapy. SIGNIFICANCE STATEMENT: DNA damage checkpoints are often defective in cancer cells, allowing cell division in spite of the accumulation of genetic errors. Conversely, DNA replication stress and mitotic checkpoints rarely undergo mutations because any aberrant activity could result in irreparable damage or catastrophic chromosomal missegregation, leading to cancer cell death. This review focuses on the checkpoint signaling mechanisms involved in cancer cells and how an emerging understanding of these pathways can provide new therapeutic opportunities for cancer therapy.

Epistatic interactions between NMD and TRP53 control progenitor cell maintenance and brain size

Mutations in human nonsense-mediated mRNA decay (NMD) factors are enriched in neurodevelopmental disorders. We show that deletion of key NMD factor Upf2 in mouse embryonic neural progenitor cells causes perinatal microcephaly but deletion in immature neurons does not, indicating NMD's critical roles in progenitors. Upf2 knockout (KO) prolongs the cell cycle of radial glia progenitor cells, promotes their transition into intermediate progenitors, and leads to reduced upper-layer neurons. CRISPRi screening identified Trp53 knockdown rescuing Upf2KO progenitors without globally reversing NMD inhibition, implying marginal contributions of most NMD targets to the cell cycle defect. Integrated functional genomics shows that NMD degrades selective TRP53 downstream targets, including Cdkn1a, which, without NMD suppression, slow the cell cycle. Trp53KO restores the progenitor cell pool and rescues the microcephaly of Upf2KO mice. Therefore, one physiological role of NMD in the developing brain is to degrade selective TRP53 targets to control progenitor cell cycle and brain size.

DNA damage causes ATM-dependent heterochromatin loss leading to nuclear softening, blebbing, and rupture

The nucleus must maintain stiffness to protect the shape and integrity of the nucleus to ensure proper function. Defects in nuclear stiffness caused from chromatin and lamin perturbations produce abnormal nuclear shapes common in aging, heart disease, and cancer. Loss of nuclear shape via protrusions called blebs leads to nuclear rupture that is well-established to cause nuclear dysfunction, including DNA damage. However, it remains unknown how increased DNA damage affects nuclear stiffness, shape, and ruptures, which could create a negative feedback loop. To determine if increased DNA damage alters nuclear physical properties, we treated MEF cells with DNA damage drugs cisplatin and bleomycin. DNA damage drugs caused increased nuclear blebbing and rupture in interphase nuclei within a few hours and independent of mitosis. Micromanipulation force measurements reveal that DNA damage decreased chromatin-based nuclear mechanics but did not change lamin-based strain stiffening at long extensions relative to wild type. Immunofluorescence measurements of DNA damage treatments reveal the mechanism is an ATM-dependent decrease in heterochromatin leading to nuclear weaken, blebbing, and rupture which can be rescued upon ATM inhibition treatment. Thus, DNA damage drugs cause ATM-dependent heterochromatin loss resulting in nuclear softening, blebbing, and rupture.

Harmine alleviated STZ-induced rat diabetic nephropathy: A potential role via regulating AMPK/Nrf2 pathway and deactivating ataxia-telangiectasia mutated (ATM) signaling

Diabetic nephropathy (DN) is a serious kidney disorder driven by diabetes and affects people all over the world. One of the mechanisms promoting NF-κB-induced renal inflammation and injury has been theorized to be ATM signaling. On the other hand, AMPK, which can be activated by the naturally occurring alkaloid harmine (HAR), has been proposed to stop that action. As a result, the goal of this study was to evaluate the therapeutic effectiveness of HAR against streptozotocin (STZ)-induced DN in rats through AMPK-mediated inactivation of ATM pathways. Twenty male Wistar rats were grouped into 4 groups, as follow: CONT, DN, HAR (10 mg/kg), DN + HAR, where HAR was daily administered I.P. once for 2 weeks. The renal AMPK and PGC-1α expressions, as well as Sirt1 levels, were assessed. To ascertain the oxidative reactions, renal Nrf2 expression, HO-1, MDA, and TAC concentrations were measured. As parts of ATM pathways, ATM and p53 expressions, in addition to GSK-3β levels were determined. Renal expression of NEMO, TNF-α, and IL-6 levels were also estimated. Moreover, histopathological and immunohistochemical detection of Bcl-2, Bax, and caspase 3 were reported. Results indicated that HAR intake notably alleviated STZ-induced kidney damage by triggering AMPK and Sirt1, which in turn boosted PGC-1α, improved NRf2/HO-1 axis, and lowered ROS production. As a consequence, HAR blocked the ATM-triggered renal inflammation and minimized caspase-3 expression by repressing the Bax/Bcl2 ratio. Because of its ability to activate AMPK/Nrf2 axis, HAR may represent an emerging avenue for future DN therapy by blocking ATM pathways.

Flip a coin: cell senescence at the maternal-fetal interface†

During pregnancy, cell senescence at the maternal-fetal interface is required for maternal well-being, placental development, and fetal growth. However, recent reports have shown that aberrant cell senescence is associated with multiple pregnancy-associated abnormalities, such as preeclampsia, fetal growth restrictions, recurrent pregnancy loss, and preterm birth. Therefore, the role and impact of cell senescence during pregnancy requires further comprehension. In this review, we discuss the principal role of cell senescence at the maternal-fetal interface, emphasizing its "bright side" during decidualization, placentation, and parturition. In addition, we highlight the impact of its deregulation and how this "dark side" promotes pregnancy-associated abnormalities. Furthermore, we discuss novel and less invasive therapeutic practices associated with the modulation of cell senescence during pregnancy.

An integrative systems biology strategy to support the development of adverse outcome pathways (AOPs): a case study on radiation-induced microcephaly

Adverse Outcome Pathways (AOPs) are useful tools for assessing the potential risks associated with exposure to various stressors, including chemicals and environmental contaminants. They provide a framework for understanding the causal relationships between different biological events that can lead to adverse outcomes (AO). However, developing an AOP is a challenging task, particularly in identifying the molecular initiating events (MIEs) and key events (KEs) that constitute it. Here, we propose a systems biology strategy that can assist in the development of AOPs by screening publicly available databases, literature with the text mining tool AOP-helpFinder, and pathway/network analyses. This approach is straightforward to use, requiring only the name of the stressor and adverse outcome to be studied. From this, it quickly identifies potential KEs and literature providing mechanistic information on the links between the KEs. The proposed approach was applied to the recently developed AOP 441 on radiation-induced microcephaly, resulting in the confirmation of the KEs that were already present and identification of new relevant KEs, thereby validating the strategy. In conclusion, our systems biology approach represents a valuable tool to simplify the development and enrichment of Adverse Outcome Pathways (AOPs), thus supporting alternative methods in toxicology.

The old second messenger cAMP teams up with novel cell death mechanisms: potential translational therapeutical benefit for Alzheimer's disease and Parkinson's disease

Alzheimer's disease (AD) and Parkinson's disease (PD) represent the most prevalent neurodegenerative disorders severely impacting life expectancy and quality of life of millions of people worldwide. AD and PD exhibit both a very distinct pathophysiological disease pattern. Intriguingly, recent researches, however, implicate that overlapping mechanisms may underlie AD and PD. In AD and PD, novel cell death mechanisms, encompassing parthanatos, netosis, lysosome-dependent cell death, senescence and ferroptosis, apparently rely on the production of reactive oxygen species, and seem to be modulated by the well-known, "old" second messenger cAMP. Signaling of cAMP via PKA and Epac promotes parthanatos and induces lysosomal cell death, while signaling of cAMP via PKA inhibits netosis and cellular senescence. Additionally, PKA protects against ferroptosis, whereas Epac1 promotes ferroptosis. Here we review the most recent insights into the overlapping mechanisms between AD and PD, with a special focus on cAMP signaling and the pharmacology of cAMP signaling pathways.

In silico analysis prediction of HepTH1-5 as a potential therapeutic agent by targeting tumour suppressor protein networks

Many studies reported that the activation of tumour suppressor protein, p53 induced the human hepcidin expression. However, its expression decreased when p53 was silenced in human hepatoma cells. Contrary to Tilapia hepcidin TH1-5, HepTH1-5 was previously reported to trigger the p53 activation through the molecular docking approach. The INhibitor of Growth (ING) family members are also shown to directly interact with p53 and promote cell cycle arrest, senescence, apoptosis and participate in DNA replication and DNA damage responses to suppress the tumour initiation and progression. However, the interrelation between INGs and HepTH1-5 remains unknown. Therefore, this study aims to identify the mechanism and their protein interactions using in silico approaches. The finding revealed that HepTH1-5 and its ligands had interacted mostly on hotspot residues of ING proteins which involved in histone modifications via acetylation, phosphorylation, and methylation. This proves that HepTH1-5 might implicate in an apoptosis signalling pathway and preserve the protein structure and function of INGs by reducing the perturbation of histone binding upon oxidative stress response. This study would provide theoretical guidance for the design and experimental studies to decipher the role of HepTH1-5 as a potential therapeutic agent for cancer therapy. Communicated by Ramaswamy H. Sarma.

IL-1 and senescence: Friends and foe of EGFR neutralization and immunotherapy

Historically, senescence has been considered a safe program in response to multiple stresses in which cells undergo irreversible growth arrest. This process is characterized by morphological and metabolic changes, heterochromatin formation, and secretion of inflammatory components, known as senescence-associated secretory phenotype (SASP). However, recent reports demonstrated that anti-cancer therapy itself can stimulate a senescence response in tumor cells, the so-called therapy-induced senescence (TIS), which may represent a temporary bypass pathway that promotes drug resistance. In this context, several studies have shown that EGFR blockage, by TKIs or moAbs, promotes TIS by increasing IL-1 cytokine production, thus pushing cells into a "pseudo-senescent" state. Today, senotherapeutic agents are emerging as a potential strategy in cancer treatment thanks to their dual role in annihilating senescent cells and simultaneously preventing their awakening into a resistant and aggressive form. Here, we summarize classic and recent findings about the cellular processes driving senescence and SASP, and we provide a state-of-the-art of the anti-cancer strategies available so far that exploits the activation and/or blockade of senescence-based mechanisms.

Cellular Senescence and Ageing

Cellular senescence has become a subject of great interest within the ageing research field over the last 60 years, from the first observation in vitro by Leonard Hayflick and Paul Moorhead in 1961, to novel findings of phenotypic sub-types and senescence-like phenotype in post-mitotic cells. It has essential roles in wound healing, tumour suppression and the very first stages of human development, while causing widespread damage and dysfunction with age leading to a raft of age-related diseases. This chapter discusses these roles and their interlinking pathways, and how the observed accumulation of senescent cells with age has initiated a whole new field of ageing research, covering pathologies in the heart, liver, kidneys, muscles, brain and bone. This chapter will also examine how senescent cell accumulation presents in these different tissues, along with their roles in disease development. Finally, there is much focus on developing treatments for senescent cell accumulation in advanced age as a method of alleviating age-related disease. We will discuss here the various senolytic and senostatic treatment approaches and their successes and limitations, and the innovative new strategies being developed to address the differing effects of cellular senescence in ageing and disease.

Alternative Lengthening of Telomeres in Cancer Confers a Vulnerability to Reactivation of p53 Function

A subset of cancers across multiple histologies with predominantly poor outcomes use the alternative lengthening of telomeres (ALT) mechanism to maintain telomere length, which can be identified with robust biomarkers. ALT has been reported to be prevalent in high-risk neuroblastoma and certain sarcomas, and ALT cancers are a major clinical challenge that lack targeted therapeutic approaches. Here, we found ALT in a variety of pediatric and adult cancer histologies, including carcinomas. Patient-derived ALT cancer cell lines from neuroblastomas, sarcomas, and carcinomas were hypersensitive to the p53 reactivator eprenetapopt (APR-246) relative to telomerase-positive (TA+) models. Constitutive telomere damage signaling in ALT cells activated ataxia-telangiectasia mutated (ATM) kinase to phosphorylate p53, which resulted in selective ALT sensitivity to APR-246. Treatment with APR-246 combined with irinotecan achieved complete responses in mice xenografted with ALT neuroblastoma, rhabdomyosarcoma, and breast cancer and delayed tumor growth in ALT colon cancer xenografts, while the combination had limited efficacy in TA+ tumor models. A large number of adult and pediatric cancers present with the ALT phenotype, which confers a uniquely high sensitivity to reactivation of p53. These data support clinical evaluation of a combinatorial approach using APR-246 and irinotecan in ALT patients with cancer.

SIGNIFICANCE

This work demonstrates that constitutive activation of ATM in chemotherapy-refractory ALT cancer cells renders them hypersensitive to reactivation of p53 function by APR-246, indicating a potential strategy to overcome therapeutic resistance.

Senescence and cancer - role and therapeutic opportunities

Cellular senescence is a state of stable, terminal cell cycle arrest associated with various macromolecular changes and a hypersecretory, pro-inflammatory phenotype. Entry of cells into senescence can act as a barrier to tumorigenesis and, thus, could in principle constitute a desired outcome for any anticancer therapy. Paradoxically, studies published in the past decade have demonstrated that, in certain conditions and contexts, malignant and non-malignant cells with lastingly persistent senescence can acquire pro-tumorigenic properties. In this Review, we first discuss the major mechanisms involved in the antitumorigenic functions of senescent cells and then consider the cell-intrinsic and cell-extrinsic factors that participate in their switch towards a tumour-promoting role, providing an overview of major translational and emerging clinical findings. Finally, we comprehensively describe various senolytic and senomorphic therapies and their potential to benefit patients with cancer.

The entry of cells into senescence can act as a barrier to tumorigenesis; however, in certain contexts senescent malignant and non-malignant cells can acquire pro-tumorigenic properties. The authors of this Review discuss the cell-intrinsic and cell-extrinsic mechanisms involved in both the antitumorigenic and tumour-promoting roles of senescent cells, and describe the potential of various senolytic and senomorphic therapeutic approaches in oncology.

Cellular senescence is a natural barrier to tumorigenesis; senescent cells are widely detected in premalignant lesions from patients with cancer.

Cellular senescence is induced by anticancer therapy and can contribute to some treatment-related adverse events (TRAEs).

Senescent cells exert both protumorigenic and antitumorigenic effects via cell-autonomous and paracrine mechanisms.

Pharmacological modulation of senescence-associated phenotypes has the potential to improve therapy efficacy and reduce the incidence of TRAEs.

Exploring the role of senescence inducers and senotherapeutics as targets for anticancer natural products

During the last few decades, cancer has remained one of the deadliest diseases that endanger human health, emphasizing urgent drug discovery. Cellular senescence has gained a great deal of attention in recent years because of its link to the development of cancer therapy. Senescent cells are incapable of proliferating due to irreversibly inhibited the initiation of the cell cycle pathways. However, senescent cells aggregate in tissues and produce a pro-inflammatory secretome called senescence-associated secretory phenotype (SASP) that can cause serious harmful effects if not managed properly. There is mounting evidence that senescent cells lead to various phases of tumorigenesis in various anatomical sites, owing mostly to the paracrine activities of the SASP. Therefore, a new treatment field called senotherapeutics has been established. Senotherapeutics are newly developed anticancer agents that have been demonstrated to inhibit cancer effectively. In light of recent findings, several promising natural products have been identified as senescence inducers and senotherapeutics, including, miliusanes, epigallocatechin gallate, phloretin, silybin, resveratrol, genistein, sulforaphane, quercetin, allicin, fisetin, piperlongumine, berberine, triptolide, tocotrienols and curcumin analogs. Several of them have already been validated through preclinical trials and exert an enormous potential for clinical trials. This review article focuses on and summarises the latest advances on cellular senescence and its potential as a target for cancer treatment and highlights the well-known natural products as senotherapeutics for cancer treatment.

p53 at the crossroad of DNA replication and ribosome biogenesis stress pathways

Despite several decades of intense research focused on understanding function(s) and disease-associated malfunction of p53, there is no sign of any “mid-life crisis” in this rapidly advancing area of biomedicine. Firmly established as the hub of cellular stress responses and tumor suppressor targeted in most malignancies, p53’s many talents continue to surprise us, providing not only fresh insights into cell and organismal biology, but also new avenues to cancer treatment. Among the most fruitful lines of p53 research in recent years have been the discoveries revealing the multifaceted roles of p53-centered pathways in the fundamental processes of DNA replication and ribosome biogenesis (RiBi), along with cellular responses to replication and RiBi stresses, two intertwined areas of cell (patho)physiology that we discuss in this review. Here, we first provide concise introductory notes on the canonical roles of p53, the key interacting proteins, downstream targets and post-translational modifications involved in p53 regulation. We then highlight the emerging involvement of p53 as a key component of the DNA replication Fork Speed Regulatory Network and the mechanistic links of p53 with cellular checkpoint responses to replication stress (RS), the driving force of cancer-associated genomic instability. Next, the tantalizing, yet still rather foggy functional crosstalk between replication and RiBi (nucleolar) stresses is considered, followed by the more defined involvement of p53-mediated monitoring of the multistep process of RiBi, including the latest updates on the RPL5/RPL11/5 S rRNA-MDM2-p53-mediated Impaired Ribosome Biogenesis Checkpoint (IRBC) pathway and its involvement in tumorigenesis. The diverse defects of RiBi and IRBC that predispose and/or contribute to severe human pathologies including developmental syndromes and cancer are then outlined, along with examples of promising small-molecule-based strategies to therapeutically target the RS- and particularly RiBi- stress-tolerance mechanisms to which cancer cells are addicted due to their aberrant DNA replication, repair, and proteo-synthesis demands.

Albicanol modulates oxidative stress and the p53 axis to suppress profenofos induced genotoxicity in grass carp hepatocytes

The organophosphorus pesticide profenofos (PFF) is widely used as an environmental contaminant, and it can remain in water bodies causing serious harm to aquatic organisms. Albicanol is a sesquiterpenoid with potent antioxidant and antagonistic activities against heavy metal toxicity. However, the mechanism of PFF induced genotoxicity in fish hepatocytes and the role Albicanol can play in this process are unknown. In this study, the model was established by treating grass carp hepatocytes with PFF (150 μM) and/or Albicanol (5 × 10^-5 μg mL^-1) for 24 h. The results showed that PFF exposure arrested L8824 cells in the G1-S phase. PFF caused the increase of MDA level in L8824 cells, while the decrease of SOD, CAT and T-AOC levels caused oxidative stress. Elevated levels of γH2AX, tail moment, tail length, % DNA and 8-OHdG indicated that PFF caused DNA damage in L8824 cells. PFF inhibited the expression levels of cell cycle related regulatory genes (cyclin A, cyclin D, cyclin E, CDK2 and CDK4) by upregulating p53/p21 genes and activating the p53 signaling pathway. Albicanol was used to significantly reduce the above effects caused by PFF exposure on hepatocytes in grass carp. Albicanol could reduce the increase in the proportion of cells in the G1-S phase caused by PFF. In summary, Albicanol could inhibit the genotoxicity of L8824 cells resulted from PFF exposure by decreasing oxidative stress and the p53 pathway.

NAD+ depletion enhances reovirus-induced oncolysis in multiple myeloma

Cancer cell energy metabolism plays an important role in dictating the efficacy of oncolysis by oncolytic viruses. To understand the role of multiple myeloma metabolism in reovirus oncolysis, we performed semi-targeted mass spectrometry-based metabolomics on 12 multiple myeloma cell lines and revealed a negative correlation between NAD+ levels and susceptibility to oncolysis. Likewise, a negative correlation was observed between the activity of the rate-limiting NAD+ synthesis enzyme NAMPT and oncolysis. Indeed, depletion of NAD+ levels by pharmacological inhibition of NAMPT using FK866 sensitized several myeloma cell lines to reovirus-induced killing. The myelomas that were most sensitive to this combination therapy expressed a functional p53 and had a metabolic and transcriptomic profile favoring mitochondrial metabolism over glycolysis, with the highest synergistic effect in KMS12 cells. Mechanistically, U-¹³C-labeled glucose flux, extracellular flux analysis, multiplex proteomics, and cell death assays revealed that the reovirus + FK866 combination caused mitochondrial dysfunction and energy depletion, leading to enhanced autophagic cell death in KMS12 cells. Finally, the combination of reovirus and NAD+ depletion achieved greater antitumor effects in KMS12 tumors in vivo and patient-derived CD138+ multiple myeloma cells. These findings identify NAD+ depletion as a potential combinatorial strategy to enhance the efficacy of oncolytic virus-based therapies in multiple myeloma.

Senescence in chronic wounds and potential targeted therapies

Chronic wounds (e.g. diabetic wounds, pressure wounds, vascular ulcers, etc.) do not usually heal in a timely and orderly manner but rather last for years and may lead to irreversible adverse events, resulting in a substantial financial burden for patients and society. Recently, a large amount of evidence has proven that cellular senescence has a crucial influence on chronic nonhealing wounds. As a defensive mechanism, cell senescence is a manner of cell-cycle arrest with increased secretory phenotype to resist death, preventing cells from stress-induced damage in cancer and noncancer diseases. A growing amount of research has advanced the perception of cell senescence in various chronic wounds and focuses on pathological and physiological processes and therapies targeting senescent cells. However, previous reviews have failed to sum up novel understandings of senescence in chronic wounds and emerging strategies targeting senescence. Herein, we discuss the characteristics and mechanisms of cellular senescence and the link between senescence and chronic wounds as well as some novel antisenescence strategies targeting other diseases that may be applied for chronic wounds.

Skin Aging, Cellular Senescence and Natural Polyphenols

The skin, being the barrier organ of the body, is constitutively exposed to various stimuli impacting its morphology and function. Senescent cells have been found to accumulate with age and may contribute to age-related skin changes and pathologies. Natural polyphenols exert many health benefits, including ameliorative effects on skin aging. By affecting molecular pathways of senescence, polyphenols are able to prevent or delay the senescence formation and, consequently, avoid or ameliorate aging and age-associated pathologies of the skin. This review aims to provide an overview of the current state of knowledge in skin aging and cellular senescence, and to summarize the recent in vitro studies related to the anti-senescent mechanisms of natural polyphenols carried out on keratinocytes, melanocytes and fibroblasts. Aged skin in the context of the COVID-19 pandemic will be also discussed.

Innate immune response orchestrates phosphoribosyl pyrophosphate synthetases to support DNA repair

Ionizing radiation-induced DNA damages cause genome instability and are highly cytotoxic. Deoxyribonucleotide metabolism provides building blocks for DNA repair. Nevertheless, how deoxyribonucleotide metabolism is timely regulated to coordinate with DNA repair remains elusive. Here, we show that ionizing radiation results in TBK1-mediated phosphorylation of phosphoribosyl pyrophosphate synthetase (PRPS)1/2 at T228, thereby enhancing PRPS1/2 catalytic activity and promoting deoxyribonucleotide synthesis. DNA damage-elicited activation of cGAS/STING axis and ATM-mediated PRPS1/2 S16 phosphorylation are required for PRPS1/2 T228 phosphorylation under ionizing radiation. Furthermore, T228 phosphorylation overrides allosteric regulator-mediated effects and preserves PRPS1/2 with high activity. The expression of non-phosphorylatable PRPS1/2 mutants or inhibition of cGAS/STING axis counteracts ionizing radiation-induced PRPS1/2 activation, deoxyribonucleotide synthesis, and DNA repair, and further impairs cell viability. This study highlights a novel and important mechanism underlying an innate immune response-guided deoxyribonucleotide metabolism, which supports DNA repair.

Role of Cellular Senescence in Type II Diabetes

Cellular senescence is a cell fate that occurs in response to numerous types of stress and can promote tissue repair or drive inflammation and disruption of tissue homeostasis depending on the context. Aging and obesity lead to an increase in the senescent cell burden in multiple organs. Senescent cells release a myriad of senescence-associated secretory phenotype factors that directly mediate pancreatic β-cell dysfunction, adipose tissue dysfunction, and insulin resistance in peripheral tissues, which promote the onset of type II diabetes mellitus. In addition, hyperglycemia and metabolic changes seen in diabetes promote cellular senescence. Diabetes-induced cellular senescence contributes to various diabetic complications. Thus, type II diabetes is both a cause and consequence of cellular senescence. This review summarizes recent studies on the link between aging, obesity, and diabetes, focusing on the role of cellular senescence in disease processes.

Downregulation of both mismatch repair and non-homologous end-joining pathways in hypoxic brain tumour cell lines

Glioblastoma, a grade IV astrocytoma, has a poor survival rate in part due to ineffective treatment options available. These tumours are heterogeneous with areas of low oxygen levels, termed hypoxic regions. Many intra-cellular signalling pathways, including DNA repair, can be altered by hypoxia. Since DNA damage induction and subsequent activation of DNA repair mechanisms is the cornerstone of glioblastoma treatment, alterations to DNA repair mechanisms could have a direct influence on treatment success. Our aim was to elucidate the impact of chronic hypoxia on DNA repair gene expression in a range of glioblastoma cell lines. We adopted a NanoString transcriptomic approach to examine the expression of 180 DNA repair-related genes in four classical glioblastoma cell lines (U87-MG, U251-MG, D566-MG, T98G) exposed to 5 days of normoxia (21% O₂), moderate (1% O₂) or severe (0.1% O₂) hypoxia. We observed altered gene expression in several DNA repair pathways including homologous recombination repair, non-homologous end-joining and mismatch repair, with hypoxia primarily resulting in downregulation of gene expression. The extent of gene expression changes was dependent on hypoxic severity. Some, but not all, of these downregulations were directly under the control of HIF activity. For example, the downregulation of LIG4, a key component of non-homologous end-joining, was reversed upon inhibition of the hypoxia-inducible factor (HIF). In contrast, the downregulation of the mismatch repair gene, PMS2, was not affected by HIF inhibition. This suggests that numerous molecular mechanisms lead to hypoxia-induced reprogramming of the transcriptional landscape of DNA repair. Whilst the global impact of hypoxia on DNA repair gene expression is likely to lead to genomic instability, tumorigenesis and reduced sensitivity to anti-cancer treatment, treatment re-sensitising might require additional approaches to a simple HIF inhibition.

Roles of ATM and ATR in DNA double strand breaks and replication stress

The maintenance of genome integrity is critical for the faithful replication of the genome during cell division and for protecting cells from accumulation of DNA damage, which if left unrepaired leads to a loss of genetic information, a breakdown in cell function and ultimately cell death and cancer. ATM and ATR are master kinases that are integral to homologous recombination-mediated repair of double strand breaks and preventing accumulation of dangerous DNA structures and genome instability during replication stress. While the roles of ATM and ATR are heavily intertwined in response to double strand breaks, their roles diverge in the response to replication stress. This review summarises our understanding of the players and their mode of actions in recruitment, activation and activity of ATM and ATR in response to DNA damage and replication stress and discusses how controlling localisation of these kinases and their activators allows them to orchestrate a stress-specific response.

Blood Gene Expression Profile Study Revealed the Activation of Apoptosis and p53 Signaling Pathway May Be the Potential Molecular Mechanisms of Ionizing Radiation Damage and Radiation-Induced Bystander Effects

Radiotherapy is an effective treatment for local solid tumors, but the mechanism of damage to human body caused by radiation therapy needs further study. In this study, gene expression profiles of human peripheral blood samples exposed to different doses and rates of ionizing radiation (IR) were used for bioinformatics analysis to investigate the mechanism of IR damage and radiation-induced bystander effect (RIBE). Differentially expressed genes analysis, weighted gene correlation network analysis, functional enrichment analysis, hypergeometric test, gene set enrichment analysis, and gene set variation analysis were applied to analyze the data. Moreover, receiver operating characteristic curve analysis was performed to identify core genes of IR damage. Weighted gene correlation network analysis identified 3 modules associated with IR damage, 2 were positively correlated and 1 was negatively correlated. The analysis showed that the positively correlated modules were significantly involved in apoptosis and p53 signaling pathway, and ESR1, ATM, and MYC were potential transcription factors regulating these modules. Thus, the study suggested that apoptosis and p53 signaling pathway may be the potential molecular mechanisms of IR damage and RIBE, which could be driven by ESR1, ATM, and MYC.

Cellular senescence: a promising strategy for cancer therapy

Cellular senescence, a permanent state of cell cycle arrest, is believed to have originally evolved to limit the proliferation of old or damaged cells. However, it has been recently shown that cellular senescence is a physiological and pathological program contributing to embryogenesis, immune response, and wound repair, as well as aging and age-related diseases. Unlike replicative senescence associated with telomere attrition, premature senescence rapidly occurs in response to various intrinsic and extrinsic insults. Thus, cellular senescence has also been considered suppressive mechanism of tumorigenesis. Current studies have revealed that therapy-induced senescence (TIS), a type of senescence caused by traditional cancer therapy, could play a critical role in cancer treatment. In this review, we outline the key features and the molecular pathways of cellular senescence. Better understanding of cellular senescence will provide insights into the development of powerful strategies to control cellular senescence for therapeutic benefit. Lastly, we discuss existing strategies for the induction of cancer cell senescence to improve efficacy of anticancer therapy.

Identification of Candidate Genes and Pathways in Dexmedetomidine-Induced Cardioprotection in the Rat Heart by Bioinformatics Analysis

Dexmedetomidine (DEX), a highly selective alpha2 adrenergic receptor agonist, directly protects hearts against ischemia/reperfusion (I/R) injury. However, the detailed mechanism has not been fully elucidated. We studied differentially expressed mRNAs and miRNAs after DEX administration in rat hearts by comprehensive analysis. Additionally, bioinformatics analysis was applied to explore candidate genes and pathways that might play important roles in DEX-induced cardioprotection. The results of microarray analysis showed that 165 mRNAs and 6 miRNAs were differentially expressed after DEX administration. Through bioinformatics analysis using differentially expressed mRNAs, gene ontology (GO) terms including MAP kinase tyrosine/serine/threonine phosphatase activity and pathways including the p53 pathway were significantly enriched in the down-regulated mRNAs. Dusp1 and Atm were associated with the GO term of MAP kinase tyrosine/serine/threonine phosphatase activity and the p53 pathway, respectively. On the other hand, no significant pathway was found in the target mRNAs of deregulated miRNAs. The results indicated some possible key genes and pathways that seem to be of significance in DEX-induced cardioprotection, although miRNAs seem to be unlikely to contribute to cardioprotection induced by DEX.

Ageing, Cellular Senescence and Neurodegenerative Disease

Ageing is a major risk factor for developing many neurodegenerative diseases. Cellular senescence is a homeostatic biological process that has a key role in driving ageing. There is evidence that senescent cells accumulate in the nervous system with ageing and neurodegenerative disease and may predispose a person to the appearance of a neurodegenerative condition or may aggravate its course. Research into senescence has long been hindered by its variable and cell-type specific features and the lack of a universal marker to unequivocally detect senescent cells. Recent advances in senescence markers and genetically modified animal models have boosted our knowledge on the role of cellular senescence in ageing and age-related disease. The aim now is to fully elucidate its role in neurodegeneration in order to efficiently and safely exploit cellular senescence as a therapeutic target. Here, we review evidence of cellular senescence in neurons and glial cells and we discuss its putative role in Alzheimer's disease, Parkinson's disease and multiple sclerosis and we provide, for the first time, evidence of senescence in neurons and glia in multiple sclerosis, using the novel GL13 lipofuscin stain as a marker of cellular senescence.

Hallmarks of Cellular Senescence

Cellular senescence is a permanent state of cell cycle arrest that promotes tissue remodeling during development and after injury, but can also contribute to the decline of the regenerative potential and function of tissues, to inflammation, and to tumorigenesis in aged organisms. Therefore, the identification, characterization, and pharmacological elimination of senescent cells have gained attention in the field of aging research. However, the nonspecificity of current senescence markers and the existence of different senescence programs strongly limit these tasks. Here, we describe the molecular regulators of senescence phenotypes and how they are used for identifying senescent cells in vitro and in vivo. We also highlight the importance that these levels of regulations have in the development of therapeutic targets.

Ataxia-Telangiectasia Mutated Modulation of Carbon Metabolism in Cancer

The ataxia-telangiectasia mutated (ATM) protein kinase has been extensively studied for its role in the DNA damage response and its association with the disease ataxia telangiectasia. There is increasing evidence that ATM also plays an important role in other cellular processes, including carbon metabolism. Carbon metabolism is highly dysregulated in cancer due to the increased need for cellular biomass. A number of recent studies report a non-canonical role for ATM in the regulation of carbon metabolism. This review highlights what is currently known about ATM's regulation of carbon metabolism, the implication of these pathways in cancer, and the development of ATM inhibitors as therapeutic strategies for cancer.

Principal Aspects Regarding the Maintenance of Mammalian Mitochondrial Genome Integrity

Mitochondria have emerged as key players regarding cellular homeostasis not only due to their contribution regarding energy production through oxidative phosphorylation, but also due to their involvement in signaling, ion regulation, and programmed cell death. Indeed, current knowledge supports the notion that mitochondrial dysfunction is a hallmark in the pathogenesis of various diseases. Mitochondrial biogenesis and function require the coordinated action of two genomes: nuclear and mitochondrial. Unfortunately, both intrinsic and environmental genotoxic insults constantly threaten the integrity of nuclear as well as mitochondrial DNA. Despite the extensive research that has been made regarding nuclear genome instability, the importance of mitochondrial genome integrity has only recently begun to be elucidated. The specific architecture and repair mechanisms of mitochondrial DNA, as well as the dynamic behavior that mitochondria exert regarding fusion, fission, and autophagy participate in mitochondrial genome stability, and therefore, cell homeostasis.

Alterations of ubiquitin related proteins in the pathology and development of schizophrenia: Evidence from human and animal studies

Gene expression analyses in post-mortem schizophrenia brains suggest that a number of ubiquitin proteasome system (UPS) genes are associated with schizophrenia; however the status of UPS proteins in the schizophrenia brain is largely unknown. Ubiquitin related proteins are inherently involved in memory, neuronal survival and morphology, which are processes implicated in neurodevelopmental disorders such as schizophrenia. We examined levels of five UPS proteins (Protein Inhibitor of Activated STAT2 [PIAS2], F-Box and Leucine rich repeat protein 21 [FBXL21], Mouse Double Minute 2 homolog [MDM2], Ubiquitin Carboxyl-Terminal Hydrolase-L1 [UCHL1] and Ubiquitin Conjugating Enzyme E2D1 [UBE2D1]) involved in these neuronal processes, within the dorsolateral prefrontal cortex of post-mortem schizophrenia subjects and matched controls (n = 30/group), in addition to across neurodevelopmental time-points (juvenile, adolescent and adult stages of life), utilizing a well-established neurodevelopmental phencyclidine (PCP) animal model of schizophrenia. We observed significant reductions in PIAS2, FBXL21 and MDM2 in schizophrenia subjects compared to controls (p-values ranging from 0.002 to 0.004). In our developmental PCP model, MDM2 protein was significantly reduced in adult PCP-treated rats compared to controls (p = 0.034). Additionally, FBXL21 (p = 0.022) and UCHL1 (p = 0.022) were significantly decreased, whilst UBE2D1 was increased (p = 0.022), in juvenile phencyclidine-treated rats compared to controls. This is the first study reporting alterations of UPS proteins in post-mortem human schizophrenia subjects and in a neurodevelopmental model of schizophrenia. The findings from this study provide strong support for a role of these UPS proteins in the pathology and development of schizophrenia.

Approaches for Identifying Novel Targets in Precision Medicine: Lessons from DNA Repair

Genome stability is maintained by a number of elegant mechanisms, which sense and repair damaged DNA. Germline defects that compromise genomic integrity result in cancer predisposition, exemplified by rare syndromes caused by mutations in certain DNA repair genes. These individuals often exhibit other symptoms including progeria and neurodegeneration. Paradoxically, some of these deleterious genetic alterations provide novel therapeutic opportunities to target cancer cells; an excellent example of such an approach being the recent development of poly (ADP-ribose) polymerase inhibitors as the first 'synthetic lethal' medicine for patients with BRCA-mutant cancers. The therapeutic exploitation of synthetic lethal interactions has enabled a novel approach to personalised medicine based on continued molecular profiling of patient and tumour material. This profiling may also aid clinicians in the identification of specific drug resistance mechanisms following relapse, and enable appropriate modification of the therapeutic regimen. This chapter focuses on therapeutic strategies designed to target aspects of the DNA damage response, and examines emerging themes demonstrating mechanistic overlap between DNA repair and neurodegeneration.

Phosphorylation-Dependent Regulation of the DNA Damage Response of Adaptor Protein KIBRA in Cancer Cells

Multifunctional adaptor proteins encompassing various protein-protein interaction domains play a central role in the DNA damage response pathway. In this report, we show that KIBRA is a physiologically interacting reversible substrate of ataxia telangiectasia mutated (ATM) kinase. We identified the site of phosphorylation in KIBRA as threonine 1006, which is embedded within the serine/threonine (S/T) Q consensus motif, by site-directed mutagenesis, and we further confirmed the same with a phospho-(S/T) Q motif-specific antibody. Results from DNA repair functional assays such as the γ-H2AX assay, pulsed-field gel electrophoresis (PFGE), Comet assay, terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assay, and clonogenic cell survival assay using stable overexpression clones of wild-type (wt.) KIBRA and active (T1006E) and inactive (T1006A) KIBRA phosphorylation mutants showed that T1006 phosphorylation on KIBRA is essential for optimal DNA double-strand break repair in cancer cells. Further, results from stable retroviral short hairpin RNA-mediated knockdown (KD) clones of KIBRA and KIBRA knockout (KO) model cells generated by a clustered regularly interspaced short palindromic repeat (CRISPR)-Cas9 system showed that depleting KIBRA levels compromised the DNA repair functions in cancer cells upon inducing DNA damage. All these phenotypic events were reversed upon reconstitution of KIBRA into cells lacking KIBRA knock-in (KI) model cells. All these results point to the fact that phosphorylated KIBRA might be functioning as a scaffolding protein/adaptor protein facilitating the platform for further recruitment of other DNA damage response factors. In summary, these data demonstrate the imperative functional role of KIBRAper se(KIBRA phosphorylation at T1006 site as a molecular switch that regulates the DNA damage response, possibly via the nonhomologous end joining [NHEJ] pathway), suggesting that KIBRA could be a potential therapeutic target for modulating chemoresistance in cancer cells.

ATM and ATR signaling at a glance

ATM and ATR signaling pathways are well conserved throughout evolution and are central to the maintenance of genome integrity. Although the role of both ATM and ATR in DNA repair, cell cycle regulation and apoptosis have been well studied, both still remain in the focus of current research activities owing to their role in cancer. Recent advances in the field suggest that these proteins have an additional function in maintaining cellular homeostasis under both stressed and non-stressed conditions. In this Cell Science at a Glance article and the accompanying poster, we present an overview of recent advances in ATR and ATM research with emphasis on that into the modes of ATM and ATR activation, the different signaling pathways they participate in - including those that do not involve DNA damage - and highlight their relevance in cancer.

DNA-Repair Defects and Olaparib in Metastatic Prostate Cancer

BACKGROUND

Prostate cancer is a heterogeneous disease, but current treatments are not based on molecular stratification. We hypothesized that metastatic, castration-resistant prostate cancers with DNA-repair defects would respond to poly(adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibition with olaparib.

METHODS

We conducted a phase 2 trial in which patients with metastatic, castration-resistant prostate cancer were treated with olaparib tablets at a dose of 400 mg twice a day. The primary end point was the response rate, defined either as an objective response according to Response Evaluation Criteria in Solid Tumors, version 1.1, or as a reduction of at least 50% in the prostate-specific antigen level or a confirmed reduction in the circulating tumor-cell count from 5 or more cells per 7.5 ml of blood to less than 5 cells per 7.5 ml. Targeted next-generation sequencing, exome and transcriptome analysis, and digital polymerase-chain-reaction testing were performed on samples from mandated tumor biopsies.

RESULTS

Overall, 50 patients were enrolled; all had received prior treatment with docetaxel, 49 (98%) had received abiraterone or enzalutamide, and 29 (58%) had received cabazitaxel. Sixteen of 49 patients who could be evaluated had a response (33%; 95% confidence interval, 20 to 48), with 12 patients receiving the study treatment for more than 6 months. Next-generation sequencing identified homozygous deletions, deleterious mutations, or both in DNA-repair genes--including BRCA1/2, ATM, Fanconi's anemia genes, and CHEK2--in 16 of 49 patients who could be evaluated (33%). Of these 16 patients, 14 (88%) had a response to olaparib, including all 7 patients with BRCA2 loss (4 with biallelic somatic loss, and 3 with germline mutations) and 4 of 5 with ATM aberrations. The specificity of the biomarker suite was 94%. Anemia (in 10 of the 50 patients [20%]) and fatigue (in 6 [12%]) were the most common grade 3 or 4 adverse events, findings that are consistent with previous studies of olaparib.

CONCLUSIONS

Treatment with the PARP inhibitor olaparib in patients whose prostate cancers were no longer responding to standard treatments and who had defects in DNA-repair genes led to a high response rate. (Funded by Cancer Research UK and others; ClinicalTrials.gov number, NCT01682772; Cancer Research UK number, CRUK/11/029.).

Dimer monomer transition and dimer re-formation play important role for ATM cellular function during DNA repair

The ATM protein kinase, is a serine/threonine protein kinase that is recruited and activated by DNA double-strand breaks, mediates responses to ionizing radiation in mammalian cells. Here we show that ATM is held inactive in unirradiated cells as a dimer and phosphorylates the opposite strand of the dimer in response to DNA damage. Cellular irradiation induces rapid intermolecular autophosphorylation of serine 1981 that causes dimer dissociation and initiates cellular ATM kinase activity. ATM cannot phosphorylate the substrates when it could not undergo dimer monomer transition. After DNA repair, the active monomer will undergo dephosphorylation to form dimer again and dephosphorylation is critical for dimer re-formation. Our work reveals novel function of ATM dimer monomer transition and explains why ATM dimer monomer transition plays such important role for ATM cellular activity during DNA repair.

DNA damage response in adult stem cells

This review discusses the processes of DNA-damage-response and DNA-damage repair in stem and progenitor cells of several tissues. The long life-span of stem cells suggests that they may respond differently to DNA damage than their downstream progeny and, indeed, studies have begun to elucidate the unique stem cell response mechanisms to DNA damage. Because the DNA damage responses in stem cells and progenitor cells are distinctly different, stem and progenitor cells should be considered as two different entities from this point of view. Hematopoietic and mammary stem cells display a unique DNA-damage response, which involves active inhibition of apoptosis, entry into the cell-cycle, symmetric division, partial DNA repair and maintenance of self-renewal. Each of these biological events depends on the up-regulation of the cell-cycle inhibitor p21. Moreover, inhibition of apoptosis and symmetric stem cell division are the consequence of the down-regulation of the tumor suppressor p53, as a direct result of p21 up-regulation. A deeper understanding of these processes is required before these findings can be translated into human anti-aging and anti-cancer therapies. One needs to clarify and dissect the pathways that control p21 regulation in normal and cancer stem cells and define (a) how p21 blocks p53 functions in stem cells and (b) how p21 promotes DNA repair in stem cells. Is this effect dependent on p21s ability to inhibit p53? Such molecular knowledge may pave the way to methods for maintaining short-term tissue reconstitution while retaining long-term cellular and genomic integrity.

Glucose Tolerance in Mice is Linked to the Dose of the p53 Transactivation Domain

AIM

To test the transactivation domain-mediated control of glucose homeostasis by the tumor suppressor p53.

BACKGROUND

The tumor suppressor p53 has a critical role in maintenance of glucose homeostasis. Phosphorylation of Ser18 in the transaction domain of p53 controls the expression of Zpf385a, a zinc finger protein that regulates adipogenesis and adipose function. This results suggest that the transactivation domain of p53 is essential to the control of glucose homeostasis.

MATERIALS AND METHODS

Mice with mutations in the p53 transactivation domain were examined for glucose homeostasis as well as various metabolic parameters. Glucose tolerance and insulin tolerance tests were performed on age matched wild type and mutant animals. In addition, mice expressing increased dosage of p53 were also examined.

RESULTS

Mice with a mutation in p53Ser18 exhibit reduced Zpf385a expression in adipose tissue, adipose tissue-specific insulin resistance, and glucose intolerance. Mice with relative deficits in the transactivation domain of p53 exhibit similar defects in glucose homeostasis, while "Super p53" mice with an increased dosage of p53 exhibit improved glucose tolerance.

CONCLUSION

These data support the role of an ATM-p53 cellular stress axis that helps combat glucose intolerance and insulin resistance and regulates glucose homeostasis.

Role of cyclin B1 levels in DNA damage and DNA damage-induced senescence

The cyclin B1-Cdk1 complex is a key regulator of mitotic entry. A large number of proteins are phosphorylated by the cyclin B1-Cdk1 complex prior to mitotic entry. Regulation of the mitotic events is linked to the control of the activity of the cyclin B1-Cdk1 complex to make cells enter mitosis, arrest at G2-phase, or skip mitosis. The roles of cyclin B1 levels in DNA damage are described. The ATM/ATR pathway acts as a molecular switch for regulating cell fates, flipping between cell death via progress into mitosis and polyploidization via sustained G2 arrest upon DNA damage, where cyclin B1 degradation is important for inducing polyploidization. The decrease in cyclin B1 levels that is induced by DNA damage leads to polyploidization in DNA damage-induced senescence. A useful method for monitoring the expression level of cyclin B1 throughout cell cycle progression in living cells is also presented.

Role of JNK and p38 MAPK in Taiwanin A-induced cell death

AIM

The lignan compound Taiwanin A is cytotoxic for human cancer cells. Taiwanin A has been previously shown to damage microtubules, induce mitotic arrest and cause apoptosis in cancer cells. The goal of the current study is to identify intracellular signaling pathways that are involved in Taiwanin A-mediated apoptosis.

MAIN METHODS

We examined the activation of three mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinase (ERK), p38 and c-Jun N-terminal kinase (JNK), in HepG2 cells after Taiwanin A treatment. The role of MAPK activation in Taiwanin A-induced apoptosis was examined using Western blotting, caspase activity assays combined with specific MAPK inhibitors and shRNA treatment to knockdown JNK.

KEY FINDINGS

Taiwanin A activated all three MAPKs (ERK, p38 and JNK). Cytotoxicity was blocked by the p38 MAPK inhibitor SB203580 and the JNK inhibitor SP600125 but not by the ERK inhibitor PD98059. A combined treatment of SB203580 and SP600125 showed increased effects on the inhibition of Taiwanin A cytotoxicity, suggesting that both JNK and p38 play a role in Taiwanin A-induced apoptosis. Inhibition of p38 activity reduced Taiwanin A-induced p53 phosphorylation on Ser15. Direct interaction of Taiwanin A-activated p38 and p53 was demonstrated by immunoprecipitation. In addition, inhibition of JNK by SP600125 or silencing of the JNK scaffold protein JIP2 reduced phosphorylation of Bcl-2, which may help to promote anti-apoptotic pathways.

SIGNIFICANCE

We demonstrated for the first time that two distinct apoptotic pathways, the p38-p53 and JNK-Bcl-2 pathways, were triggered by the anti-microtubule compound Taiwanin A.

Pharmacological inhibition of ATM by KU55933 stimulates ATM transcription

Ataxia-telangiectasia mutated (ATM) kinase is a component of a signalling mechanism that determines the process of decision-making in response to DNA damage and involves the participation of multiple proteins. ATM is activated by DNA double-strand breaks (DSBs) through the Mre11–Rad50–Nbs1 (MRN) DNA repair complex, and orchestrates signalling cascades that initiate the DNA damage response. Cells lacking ATM are hypersensitive to insults, particularly genotoxic stress, induced through radiation or radiomimetic drugs. Here, we investigate the degree of ATM activation during time-dependent treatment with genotoxic agents and the effects of ATM on phospho-induction and localization of its downstream substrates. Additionally, we have demonstrated a new cell-cycle-independent mechanism of ATM gene regulation following ATM kinase inhibition with KU5593. Inhibition of ATM activity causes induction of ATM protein followed by oscillation and this mechanism is governed at the transcriptional level. Furthermore, this autoregulatory induction of ATM is also accompanied by a transient upregulation of p53, pATR and E2F1 levels. Since ATM inhibition is believed to sensitize cancer cells to genotoxic agents, this novel insight into the mechanism of ATM regulation might be useful for designing more precise strategies for modulation of ATM activity in cancer therapy.