Chk2 Modulates Bmi1-Deficiency-Induced Renal Aging and Fibrosis via Oxidative Stress, DNA Damage, and p53/TGFß1-Induced Epithelial-Mesenchymal Transition.

Renal aging may lead to fibrosis and dysfunction, yet underlying mechanisms remain unclear. We explored whether deficiency of the Polycomb protein Bmi1 causes renal aging via DNA damage response (DDR) activation, inducing renal tubular epithelial cell (RTEC) senescence and epithelial-mesenchymal transition (EMT). Bmi1 knockout mice exhibited oxidative stress, DDR activation, RTEC senescence, senescence-associated secretory phenotype (SASP), and age-related fibrosis in kidneys. Bmi1 deficiency impaired renal structure and function, increasing serum creatinine/urea, reducing creatinine clearance, and decreasing cortical thickness and glomerular number. However, knockout of the serine-threonine kinase Chk2 alleviated these aging phenotypes. Transcriptomics identified transforming growth factor beta 1 (TGFß1) upregulation in Bmi1-deficient RTECs, but TGFß1 was downregulated upon Chk2 knockout. The tumor suppressor protein p53 transcriptionally activated TGFß1, promoting EMT in RTECs. Bmi1 knockout or oxidative stress (induced with H2O2) increased TGFß1 expression, and EMT in RTECs and was partly reversed by p53 inhibition. Together, Bmi1 deficiency causes oxidative stress and DDR-mediated RTEC senescence/SASP, thus activating p53 and TGFß1 to induce EMT and age-related fibrosis. However, blocking DDR (via Chk2 knockout) or p53 ameliorates these changes. Our study reveals mechanisms whereby Bmi1 preserves renal structure and function during aging by suppressing DDR and p53/TGFß1-mediated EMT. These pathways represent potential targets for detecting and attenuating age-related renal decline.

Triple-Negative Breast Cancer and Emerging Therapeutic Strategies: ATR and CHK1/2 as Promising Targets.

Worldwide, breast cancer is the most frequently diagnosed malignancy in women, with triple-negative breast cancer (TNBC) being the most aggressive molecular subtype. Due to the dearth of effective therapeutic options for TNBC, novel agents targeting key mechanisms and pathways in cancer cells are continuously explored; these include ATR inhibitors, which target the ATR kinase involved in the DNA damage response (DDR) pathway, and CHK1/2 inhibitors, which target the Checkpoint Kinase 1/2 (CHK1/2) involved in cell cycle arrest and DNA repair. ATR and CHK1/2 inhibitors show potential as prospective treatments for TNBC by focusing on the DDR and interfering with cell cycle regulation in cancer cells. Preliminary preclinical and clinical findings suggest that when combined with chemotherapy, ATR and CHK1/2 inhibitors demonstrate significant anti-proliferative efficacy against TNBC. In this article, we introduce ATR and CHK1/2 inhibitors as promising therapeutic approaches for the management of TNBC. Preclinical and clinical studies performed evaluating ATR and CHK1/2 inhibitors for the treatment of TNBC and associated challenges encountered in this context to date are reviewed.

The Link between Autosomal Dominant Polycystic Kidney Disease and Chromosomal Instability: Exploring the Relationship.

In autosomal dominant polycystic kidney disease (ADPKD) with germline mutations in a PKD1 or PKD2 gene, innumerable cysts develop from tubules, and renal function deteriorates. Second-hit somatic mutations and renal tubular epithelial (RTE) cell death are crucial features of cyst initiation and disease progression. Here, we use established RTE lines and primary ADPKD cells with disease-associated PKD1 mutations to investigate genomic instability and DNA damage responses. We found that ADPKD cells suffer severe chromosome breakage, aneuploidy, heightened susceptibility to DNA damage, and delayed checkpoint activation. Immunohistochemical analyses of human kidneys corroborated observations in cultured cells. DNA damage sensors (ATM/ATR) were activated but did not localize at nuclear sites of damaged DNA and did not properly activate downstream transducers (CHK1/CHK2). ADPKD cells also had the ability to transform, as they achieved high saturation density and formed colonies in soft agar. Our studies indicate that defective DNA damage repair pathways and the somatic mutagenesis they cause contribute fundamentally to the pathogenesis of ADPKD. Acquired mutations may alternatively confer proliferative advantages to the clonally expanded cell populations or lead to apoptosis. Further understanding of the molecular details of aberrant DNA damage responses in ADPKD is ongoing and holds promise for targeted therapies.

A novel role for the ROS-ATM-Chk2 axis mediated metabolic and cell cycle reprogramming in the M1 macrophage polarization.

Reactive oxygen species (ROS) play a pivotal role in macrophage-mediated acute inflammation. However, the precise molecular mechanism by which ROS regulate macrophage polarization remains unclear. Here, we show that ROS function as signaling molecules that regulate M1 macrophage polarization through ataxia-telangiectasia mutated (ATM) and cell cycle checkpoint kinase 2 (Chk2), vital effector kinases in the DNA damage response (DDR) signaling pathway. We further demonstrate that Chk2 phosphorylates PKM2 at the T95 and T195 sites, promoting glycolysis and facilitating macrophage M1 polarization. In addition, Chk2 activation increases the Chk2-dependent expression of p21, inducing cell cycle arrest for subsequent macrophage M1 polarization. Finally, Chk2-deficient mice infected with lipopolysaccharides (LPS) display a significant decrease in lung inflammation and M1 macrophage counts. Taken together, these results suggest that inhibiting the ROS-Chk2 axis can prevent the excessive inflammatory activation of macrophages, and this pathway can be targeted to develop a novel therapy for inflammation-associated diseases and expand our understanding of the pathophysiological functions of DDR in innate immunity.

Functional analysis of chromatin-associated proteins in Sordaria macrospora reveals similar roles for RTT109 and ASF1 in development and DNA damage response.

We performed a functional analysis of two potential partners of ASF1, a highly conserved histone chaperone that plays a crucial role in the sexual development and DNA damage resistance in the ascomycete Sordaria macrospora. ASF1 is known to be involved in nucleosome assembly and disassembly, binding histones H3 and H4 during transcription, replication and DNA repair and has direct and indirect roles in histone recycling and modification as well as DNA methylation, acting as a chromatin modifier hub for a large network of chromatin-associated proteins. Here, we functionally characterized two of these proteins, RTT109 and CHK2. RTT109 is a fungal-specific histone acetyltransferase, while CHK2 is an ortholog to PRD-4, a checkpoint kinase of Neurospora crassa that performs similar cell cycle checkpoint functions as yeast RAD53. Through the generation and characterization of deletion mutants, we discovered striking similarities between RTT109 and ASF1 in terms of their contributions to sexual development, histone acetylation, and protection against DNA damage. Phenotypic observations revealed a developmental arrest at the same stage in Δrtt109 and Δasf1 strains, accompanied by a loss of H3K56 acetylation, as detected by western blot analysis. Deletion mutants of rtt109 and asf1 are sensitive to the DNA damaging agent methyl methanesulfonate, but not hydroxyurea. In contrast, chk2 mutants are fertile and resistant to methyl methanesulfonate, but not hydroxyurea. Our findings suggest a close functional association between ASF1 and RTT109 in the context of development, histone modification, and DNA damage response, while indicating a role for CHK2 in separate pathways of the DNA damage response.

In silico and structure-based evaluation of deleterious mutations identified in human Chk1, Chk2, and Wee1 protein kinase.

Checkpoint kinases Chk1, Chk2, Wee1 are playing a key role in DNA damage response and genomic integrity. Cancer-associated mutations identified in human Chk1, Chk2, and Wee1 were retrieved to understand the function associated with the mutation and also alterations in the folding pattern. Therefore, an attempt has been made to identify deleterious effect of variants using in silico and structure-based approach. Variants of uncertain significance for Chk1, Chk2, and Wee1 were retrieved from different databases and four prediction servers were employed to predict pathogenicity of mutations. Further, Interpro, I-Mutant 3.0, Consurf, TM-align, and have (y)our protein explained were used for comprehensive study of the deleterious effects of variants. The sequences of Chk1, Chk2, and Wee1 were analyzed using Clustal Omega, and the three-dimensional structures of the proteins were aligned using TM-align. The molecular dynamics simulations were performed to explore the differences in folding pattern between Chk1, Chk2, Wee1 wild-type, and mutant protein and also to evaluate the structural integrity. Thirty-six variants in Chk1, 250 Variants in Chk2, and 29 in Wee1 were categorized as pathogenic using in silico prediction tools. Furthermore, 25 mutations in Chk1, 189 in Chk2, and 14 in Wee1 were highly conserved, possessing deleterious effect and also influencing the protein structure and function. These identified mutations may provide underlying genetic intricacies to serve as potential targets for therapeutic inventions and clinical management.

DON induced DNA damage triggers absence of p53-mediated G2 arrest and apoptosis in IPEC-1 cells.

Deoxynivalenol (DON) stands among the prevalent mycotoxins, and usually contaminates cereal foods and animal feed, leading to human and animal clinical poisoning symptoms such as abdominal pain, diarrhea, and vomiting. To date, the mechanism of toxicity of DON in different mammalian cells is not fully elucidated. In this study, we explored the detrimental impacts of DON on porcine intestinal epithelial cells (IPEC-1), serving as a representative model for porcine intestinal epithelial cells. After treating cells with DON for 24 h, DON can significantly inhibit the activity of cells, induce the production of reactive oxygen species (ROS), significantly reduce the content of glutathione and the activity of catalase, and increase the activity of superoxide dismutase and malondialdehyde, leading to an imbalance in intracellular redox status. In addition, DON can induce DNA double-strand breaks, and decrease mitochondrial membrane potential. Furthermore, DON can promote the release of Cyt C through changes in mitochondrial permeability through inhibit the expression of B-cell lymphoma 2 (Bcl-2) proteins, leading to apoptosis through the mitochondrial pathway. On the other hand, we found that DON can cause IPEC-1 cells G2 phase cycle arrest. Different with our pervious study, DON induces cell cycle arrest in the G2 phase only by activating the ATM-Chk2-Cdc 25 C pathway, but cannot regulate the cell cycle arrest via the ATM-p53 pathway. These results indicate that DON can induce the same toxic phenotype in different cells, but its toxic mechanism is different. All these provide a rationale for revealing DON induced cytotoxicity and intestinal diseases.

Prolonged Cell Cycle Arrest in Response to DNA damage in Yeast Requires the Maintenance of DNA Damage Signaling and the Spindle Assembly Checkpoint.

Cells evoke the DNA damage checkpoint (DDC) to inhibit mitosis in the presence of DNA double-strand breaks (DSBs) to allow more time for DNA repair. In budding yeast, a single irreparable DSB is sufficient to activate the DDC and induce cell cycle arrest prior to anaphase for about 12 to 15 hours, after which cells "adapt" to the damage by extinguishing the DDC and resuming the cell cycle. While activation of the DNA damage-dependent cell cycle arrest is well-understood, how it is maintained remains unclear. To address this, we conditionally depleted key DDC proteins after the DDC was fully activated and monitored changes in the maintenance of cell cycle arrest. Degradation of Ddc2ATRIP, Rad9, Rad24, or Rad53CHK2 results in premature resumption of the cell cycle, indicating that these DDC factors are required both to establish and to maintain the arrest. Dun1 is required for establishment, but not maintenance of arrest, whereas Chk1 is required for prolonged maintenance but not for initial establishment of the mitotic arrest. When the cells are challenged with 2 persistent DSBs, they remain permanently arrested. This permanent arrest is initially dependent on the continuous presence of Ddc2 and Rad53; however, after 15 hours both proteins become dispensable. Instead, the continued mitotic arrest is sustained by spindle-assembly checkpoint (SAC) proteins Mad1, Mad2, and Bub2 but not by Bub2's binding partner Bfa1. These data suggest that prolonged cell cycle arrest in response to 2 DSBs is achieved by a handoff from the DDC to specific components of the SAC. Furthermore, the establishment and maintenance of DNA damage-induced cell cycle arrest requires overlapping but different sets of factors.

Silence of URI in gastric cancer cells promotes cisplatin-induced DNA damage and apoptosis.

URI, a prefoldin family member, has been implicated roles in cancer development. We have previously shown that URI can attenuate DNA damage in gastric cancer cells treated with potassium dichromate. The aim of this study was to investigate how URI involves cisplatin-induced DNA damage response (DDR) in gastric cancer cells and its possible mechanism relating to the ATM/CHK2 pathway. Here, MGC-803 and SGC-7901 gastric cancer cells were treated with different concentrations of cisplatin. Comet assay was used to detect DNA damage and the results confirmed the dose-effect of cisplatin-induced DNA damage in gastric cancer cells. URI knockdown cell lines were established with siRNA transfection. Cell viability and proliferation were detected by counting kit 8 (CCK-8) and 5-ethynyl-2'-deoxyuridine (EdU) assays respectively. Apoptosis and cell cycle were analyzed by flow cytometry. The results indicated that URI knockdown increased the sensitivity of cells to cisplatin by inhibiting proliferation and promoting apoptosis. The levels of P-ATM, P-CHK2 and γH2AX were detected by Western blot. Increased levels of P-ATM, P-CHK2, and γH2AX were observed in cisplatin treated cells, indicating that cisplatin induced a DNA damage response (DDR). URI knockdown in cisplatin-treated cells significantly decreased the levels of P-ATM and P-CHK2 at 12 hours, but not at 0 and 6 hours after drug withdrawal, while significantly increased γH2AX levels were detected at 6 hours, but not at 0 and 12 hours after drug withdrawal compared with the control cells. However, the levels of γH2AX were significantly increased in URI knockdown cells after cisplatin treatment for 12 hours. The cell cycle analysis showed that the number of cells entering S phase was significantly reduced and the cells were arrested in the G1 phase in URI-silenced cisplatin-exposed cells, indicating that cell cycle progression was inhibited. In conclusion, our results suggest that URI is involved in the cisplatin-induced DNA damage response via the ATM/CHK2 pathway, and silencing URI can increase cisplatin-induced DNA damage and enhance drug sensitivity in gastric cancer cells.

Chk2 deletion rescues Bmi1 deficiency-induced mandibular osteoporosis by blocking DNA damage response pathway.

OBJECTIVES: Bmi1 deficiency has been proved to be able to cause mandibular osteoporosis through suppressing oxidative stress. However, the role of DNA damage response pathway in this pathogenesis had not been well understood. In this study, we investigate whether mandibular osteoporosis induced by Bmi1 deficiency could be rescued by blocked DNA damage response pathway. METHODS: The protein expression levels of antioxidant enzymes and DNA damage and damage response pathway molecules in mandibular tissue were examined using Western blots. Double knockout mice that lacked both Bmi1 and Chk2 were generated and their mandibular phenotypes were compared at 6 weeks old to wild-type, Chk2-/-, and Bmi1-/- mice using radiograph, micro-CT, histopathology, cellular and molecular techniques. RESULTS: Bmi1 deficiency induces oxidative stress and DNA damage and activates DNA damage response pathways in mouse mandibles. Chk2 deletion rescued mandibular osteoporosis through promoting formation of osteoblastic bone as well as decreasing osteoclastic bone resorption. Mechanistically, Chk2 deletion suppressed oxidative stress, DNA damage, as well as cell senescence. In addition, it boosted proliferation of bone marrow mesenchymal stem cells (BM-MSCs) that derived from mandible through blocking the DNA damage response pathway. CONCLUSION: Abolish the expression of Chk2 could rescue Bmi1 deficiency-related mandibular osteoporosis through promoting BM-MSC proliferation and osteoblastic bone formation, reducing osteoclastic bone resorption, decreasing oxidative stress, inhibiting damage of DNA and associated response pathways, suppressing cell senescence as well as senescence-associated secretory phenotype (SASP). These findings offer a theoretical basis for using Chk2 or p53 inhibitors to prevent and treat age-related mandibular osteoporosis.

Could Inhibiting the DNA Damage Repair Checkpoint Rescue Immune-Checkpoint-Inhibitor-Resistant Endometrial Cancer?

Endometrial cancer (EC) is increasingly undermining female health worldwide, with poor survival rates for advanced or recurrent/metastatic diseases. The application of immune checkpoint inhibitors (ICIs) has opened a window of opportunity for patients with first-line therapy failure. However, there is a subset of patients with endometrial cancer who remain insensitive to immunotherapy alone. Therefore, it is necessary to develop new therapeutic agents and further explore reliable combinational strategies to optimize the efficacy of immunotherapy. DNA damage repair (DDR) inhibitors as novel targeted drugs are able to generate genomic toxicity and induce cell death in solid tumors, including EC. Recently, growing evidence has demonstrated the DDR pathway modulates innate and adaptive immunity in tumors. In this review, we concentrate on the exploration of the intrinsic correlation between DDR pathways, especially the ATM-CHK2-P53 pathway and the ATR-CHK1-WEE1 pathway, and oncologic immune response, as well as the feasibility of adding DDR inhibitors to ICIs for the treatment of patients with advanced or recurrent/metastatic EC. We hope that this review will offer some beneficial references to the investigation of immunotherapy and provide a reasonable basis for "double-checkpoint inhibition" in EC.

Baicalein Induces G2/M Cell Cycle Arrest Associated with ROS Generation and CHK2 Activation in Highly Invasive Human Ovarian Cancer Cells.

Ovarian cancer is a lethal gynecological cancer because drug resistance often results in treatment failure. The CHK2, a tumor suppressor, is considered to be an important molecular target in ovarian cancer due to its role in DNA repair. Dysfunctional CHK2 impairs DNA damage-induced checkpoints, reduces apoptosis, and confers resistance to chemotherapeutic drugs and radiation therapy in ovarian cancer cells. This provides a basis for finding new effective agents targeting CHK2 upregulation or activation to treat or prevent the progression of advanced ovarian cancer. Here, the results show that baicalein (5,6,7-trihydroxyflavone) treatment inhibits the growth of highly invasive ovarian cancer cells, and that baicalein-induced growth inhibition is mediated by the cell cycle arrest in the G2/M phase. Baicalein-induced G2/M phase arrest is associated with an increased reactive oxygen species (ROS) production, DNA damage, and CHK2 upregulation and activation. Thus, baicalein modulates the expression of DNA damage response proteins and G2/M phase regulatory molecules. Blockade of CHK2 activation by CHK2 inhibitors protects cells from baicalein-mediated G2/M cell cycle arrest. All the results suggest that baicalein has another novel growth inhibitory effect on highly invasive ovarian cancer cells, which is partly related to G2/M cell cycle arrest through the ROS-mediated DNA breakage damage and CHK2 activation. Collectively, our findings provide a molecular basis for the potential of baicalein as an adjuvant therapeutic agent in the treatment of metastatic ovarian cancer.

Nanoparticle-Mediated PRDX2 Inhibition for Specific Targeting of CHK2-Null Colorectal Cancer.

Synthetic lethality is a pragmatic targeted cancer therapy approach in which cancer cells harboring genetic alterations are exploited for the specific killing of cancer cells. Earlier, we have established a synthetic lethal (SL) interaction between two genes that are CHK2 and PRDX2 in colorectal cancer (CRC) cells. The SL interaction between CHK2 and PRDX2 resulted in selective targeting of CHK2-defective CRC cells. N-Carbamoyl alanine (NCA) is a PRDX2 inhibitor and is a peptide-like organic compound, which degrades after oral administration in harsh gastric pH. To overcome the limitations of NCA, a chitosan-based nanocarrier was developed for the entrapment of NCA. In this study, we targeted the SL interaction between PRDX2 and CHK2 using NCA-loaded chitosan nanoparticles (NCA-Chit NPs) to selectively inhibit the CHK2-null HCT116 cells. NCA-Chit NPs were assessed for various physicochemical characterizations such as the hydrodynamic diameter (size), zeta potential, and polydispersity index using a Zetasizer. Additionally, morphological studies for the shape and size of NPs were confirmed by transmission electron microscopy, scanning electron microscopy, and atomic force microscopy. Cellular uptake of NPs was confirmed using confocal microscopy, which exhibited that nanoparticles were able to internalize into the HCT116 cells. Blank Chit NPs were found to be cytocompatible as they did not exert any cytotoxic effects on hTERT, L929, and Caco-2 cells (intestinal epithelial cells). Importantly, NCA-Chit NPs were quite hemocompatible also. In the form of an NCA-chitosan nanoformulation, the efficacy was enhanced by about 8 times compared to free form of NCA towards selective killing of CHK2-null HCT116 cells as compared to HCT116 cells. The chitosan-based nanoformulation for NCA was developed to augment the efficacy of the NCA for enhanced cell death of colorectal cancer cells having CHK2 defects.

Minor Kinases with Major Roles in Cytokinesis Regulation.

Cytokinesis, the conclusive act of cell division, allows cytoplasmic organelles and chromosomes to be faithfully partitioned between two daughter cells. In animal organisms, its accurate regulation is a fundamental task for normal development and for preventing aneuploidy. Cytokinesis failures produce genetically unstable tetraploid cells and ultimately result in chromosome instability, a hallmark of cancer cells. In animal cells, the assembly and constriction of an actomyosin ring drive cleavage furrow ingression, resulting in the formation of a cytoplasmic intercellular bridge, which is severed during abscission, the final event of cytokinesis. Kinase-mediated phosphorylation is a crucial process to orchestrate the spatio-temporal regulation of the different stages of cytokinesis. Several kinases have been described in the literature, such as cyclin-dependent kinase, polo-like kinase 1, and Aurora B, regulating both furrow ingression and/or abscission. However, others exist, with well-established roles in cell-cycle progression but whose specific role in cytokinesis has been poorly investigated, leading to considering these kinases as "minor" actors in this process. Yet, they deserve additional attention, as they might disclose unexpected routes of cell division regulation. Here, we summarize the role of multifunctional kinases in cytokinesis with a special focus on those with a still scarcely defined function during cell cleavage. Moreover, we discuss their implication in cancer.

Role of genetic variations of DNA damage response pathway genes and heat-shock proteins in increased head and neck cancer risk.

Aim: The present study was designed to evaluate the role of DNA damage response pathway genes and heat-shock proteins in head and neck cancer (HNC) risk. Methods: For this purpose, two study cohorts were used. Cohort 1 (blood samples of 250 HNC patients and 250 controls) was used for polymorphism screening of selected genes using tetra-primer amplification refractory mutation system-polymerase chain (Tetra-ARMS PCR). Cohort 2 (200 HNC tumors and adjacent controls) was used for expression analysis, using quantitative PCR. Results: Analysis showed that mutant allele frequency of selected polymorphisms was found associated with increased HNC risk. Expression analysis showed the significant deregulation of selected genes in patients. Conclusion: The present study showed that selected genes (CHK1, CHK2, HSP70 and HSP90) can act as good diagnostic/prognostic markers in HNC.

The present study is designed to identify the selected genes of DNA damage response pathway and heat-shock proteins as diagnostic/prognostic markers of head and neck cancer (HNC). To do this, DNA was isolated from blood samples and RNA isolated from the tissue samples of HNC patients. The mutation and expression level of selected genes was tested, and selected genes showed good diagnostic/prognostic values for HNC patients.

RYBP Sensitizes Cancer Cells to PARP Inhibitors by Regulating ATM Activity.

Ring1 and YY1 Binding Protein (RYBP) is a member of the non-canonical polycomb repressive complex 1 (PRC1), and like other PRC1 members, it is best described as a transcriptional regulator. Previously, we showed that RYBP, along with other PRC1 members, is also involved in the DNA damage response. RYBP inhibits recruitment of breast cancer gene 1(BRCA1) complex to DNA damage sites through its binding to K63-linked ubiquitin chains. In addition, ataxia telangiectasia mutated (ATM) kinase serves as an important sensor kinase in early stages of DNA damage response. Here, we report that overexpression of RYBP results in inhibition in both ATM activity and recruitment to DNA damage sites. Cells expressing RYBP show less phosphorylation of the ATM substrate, Chk2, after DNA damage. Due to its ability to inhibit ATM activity, we find that RYBP sensitizes cancer cells to poly-ADP-ribose polymerase (PARP) inhibitors. Although we find a synergistic effect between PARP inhibitor and ATM inhibitor in cancer cells, this synergy is lost in cells expressing RYBP. We also show that overexpression of RYBP hinders cancer cell migration through, at least in part, ATM inhibition. We provide new mechanism(s) by which RYBP expression may sensitize cancer cells to DNA damaging agents and inhibits cancer metastasis.

Checkpoint Kinase 2 Inhibition Can Reverse Tamoxifen Resistance in ER-Positive Breast Cancer.

Breast cancer is a heterogeneous disease. Tamoxifen is frequently used to treat ER-positive breast cancer. Our team has identified a novel splice variant of NCOR2, BQ323636.1 (BQ), that mediates tamoxifen resistance. However, the upstream factors that modulate BQ expression are not apparent. This study reveals that tamoxifen treatment causes induction of DNA damage which can enhance BQ expression. We show that DNA damage can activate the ATM/CHK2 and ATR/CHK1 signalling cascades and confirm that ATM/CHK2 signalling is responsible for enhancing the protein stability of BQ. siRNA or a small inhibitor targeting CHK2 resulted in the reduction in BQ expression through reduced phosphorylation and enhanced poly-ubiquitination of BQ. Inhibition of CHK2 by CCT241533 could reverse tamoxifen resistance in vitro and in vivo. Using clinical samples in the tissue microarray, we confirmed that high p-CHK2 expression was significantly associated with high nuclear BQ expression, tamoxifen resistance and poorer overall and disease-specific survival. In conclusion, tamoxifen treatment can enhance BQ expression in ER-positive breast cancer by activating the ATM/CHK2 axis. Targeting CHK2 is a promising approach to overcoming tamoxifen resistance in ER-positive breast cancer.

Phosphoproteomics reveals that cinobufotalin promotes intrahepatic cholangiocarcinoma cell apoptosis by activating the ATM/CHK2/p53 signaling pathway.

Intrahepatic cholangiocarcinoma (ICC) is a malignant tumor that originates from bile duct's epithelial cells and is usually characterized by insidious symptoms and poor prognosis. Cinobufotalin (CB), an active ingredient obtained from the Traditional Chinese Medicine ChanSu, is purported to exhibit a wide range of antitumorigenic activities. However, the mechanism by which it achieves such pharmacological effects remains elusive. Here, we disclosed the mechanism of action by which CB inhibits ICC cells. Initial experiments revealed that the proliferation of RBE and HCCC-9810 cells was significantly inhibited by CB with IC50 values of 0.342 µM and 0.421 µM respectively. CB induced the expression of caspase-3 subsequently leading to the apoptosis of ICC cells. Phosphoproteomics revealed that the phosphorylation of many proteins associated with DNA damage response increased. Kinase-substrate enrichment analysis revealed that ATM was activated after CB treatment, while CDK1 was inactivated. Activated ATM increased p-CHK2-T68 and p-p53-S15, which promoted the expression of FAS, DR4 and DR5 and triggered cell apoptosis. In summary, this work reveals the role of CB in inducing DNA damage and cell apoptosis involved in the activation of the ATM/CHK2/p53 signaling pathway, and indicates that CB may serve as a chemotherapeutic drug candidate for ICC treatment.

Dexamethasone promotes osteoblast apoptosis through the Chk2/p53 signaling pathway.

BACKGROUND: Glucocorticoids (GCs) are widely used to treat inflammatory or autoimmune diseases. However, several studies have reported that the use of GCs can lead to numerous complications, the most serious of which are osteoporosis and osteonecrosis of the femoral head (ONFH). Osteoblast apoptosis has been identified as an important event in the development of GC-induced osteoporosis and ONFH. However, the mechanisms underlying the regulation of these processes have not yet been explored. OBJECTIVES: To observe the effect of dexamethasone (Dex) on the apoptosis of osteoblasts and explore its mechanism, as well as provide a new therapeutic idea for GC­induced osteoporosis and ONFH. MATERIAL AND METHODS: Cell proliferation and apoptosis of MC3T3-E1 cells after Dex treatment were determined using the CellTiter-Glo® Luminescent Cell Viability Assay kit and Annexin V-FITC/PI Double Staining Apoptosis Detection Kit, respectively. The expression of caspase-3/cleaved caspase-3 and poly(ADP-ribose) polymerase (PARP)/cleaved PARP in MC3T3-E1 cells after Dex treatment was determined with western blotting. The expression of p53 and checkpoint kinase 2 (Chk2) in MC3T3-E1 cells after Dex treatment was analyzed using western blotting and polymerase chain reaction (PCR). The effects of p53 knockdown and Chk2 knockdown on Dex-induced apoptosis of MC3T3-E1 cells were also characterized. RESULTS: Dexamethasone remarkably inhibited cell growth and induced the apoptosis of MC3T3-E1 cells. We also observed that Dex induced osteoblast apoptosis by promoting p53 expression. The regulatory effect of Dex on p53 expression is mediated by the upregulation of Chk2, which interacted with p53 and inhibited p53 degradation. The knockdown of p53 alleviated Dex-induced MC3T3-E1 cell apoptosis by decreasing the expression of cleaved caspase-3 and cleaved PARP. CONCLUSIONS: We demonstrated that Dex increased Chk2 protein expression, which stabilized the protein expression of p53, and in turn promoted osteoblast apoptosis.

Involvement of DNA Damage Response via the Ccndbp1-Atm-Chk2 Pathway in Mice with Dextran-Sodium-Sulfate-Induced Colitis.

The dextran sodium sulfate (DSS)-induced colitis mouse model has been widely utilized for human colitis research. While its mechanism involves a response to double-strand deoxyribonucleic acid (DNA) damage, ataxia telangiectasia mutated (Atm)-checkpoint kinase 2 (Chk2) pathway activation related to such response remains unreported. Recently, we reported that cyclin D1-binding protein 1 (Ccndbp1) activates the pathway reflecting DNA damage in its knockout mice. Thus, this study aimed to examine the contribution of Ccndbp1 and the Atm-Chk2 pathway in DSS-induced colitis. We assessed the effect of DSS-induced colitis on colon length, disease activity index, and histological score and on the Atm-Chk2 pathway and the subsequent apoptosis in Ccndbp1-knockout mice. DSS-induced colitis showed distal colon-dominant Atm and Chk2 phosphorylation, increase in TdT-mediated dUTP-biotin nick end labeling and cleaved caspase 3-positive cells, and histological score increase, causing disease activity index elevation and colon length shortening. These changes were significantly ameliorated in Ccndbp1-knockout mice. In conclusion, Ccndbp1 contributed to Atm-Chk2 pathway activation in the DSS-induced colitis mouse model, causing inflammation and apoptosis of mucosal cells in the colon.