Sustained CHK2 activity, but not ATM activity, is critical to maintain a G1 arrest after DNA damage in untransformed cells

The histone acetyltransferase CBP participates in regulating the DNA damage response through ATM after double-strand breaks

BACKGROUND

Spatial and temporal control of DNA damage response pathways after DNA damage is crucial for maintenance of genomic stability. Ataxia telangiectasia mutated (ATM) protein plays a central role in DNA damage response pathways. The chain of events following induction of DNA damage that results in full activation of ATM is still evolving. Here we set out to explore the role of CREB-binding protein (CBP), a histone acetyltransferase (HAT), in DNA damage response, particularly in the ATM activation pathway.

RESULTS

In response to DNA damage, CBP is stabilized and is recruited at sites of DNA double-strand breaks where it acetylates ATM and promotes its kinase activity. Cells deficient in CBP display an impairment in DNA double-strand break repair and high sensitivity to chemo- and radiotherapy. Importantly, re-expressing CBP's HAT domain in CBP-deficient cells restores the DNA repair capability, demonstrating the essential role of CBP's HAT domain in repairing DNA double-strand breaks.

CONCLUSIONS

Together, our findings shed the light on CBP as a key participant in the ATM activation pathway and in the subsequent repair of DNA double-strand breaks, which may serve as a potential target to modulate the cellular response to DNA damaging agents in cancer.

DNA damage checkpoints balance a tradeoff between diploid- and polyploid-derived arrest failures

The DNA damage checkpoint system ensures genomic integrity by preventing the division of damaged cells. This system operates primarily through theG 1 ∕ S andG 2 ∕ M checkpoints, which are susceptible to failure; how these checkpoints coordinate quantitatively to ensure optimal cellular outcomes remains unclear. In this study, we exposed non-cancerous human cells to exogenous DNA damage and used single-cell imaging to monitor spontaneous arrest failure. We discovered that cells fail to arrest in two major paths, resulting in two types with distinct characteristics, including ploidy, nuclear morphology, and micronuclei composition. Computational simulations and experiments revealed strengthening one checkpoint reduced one mode of arrest failure but increased the other, leading to a critical tradeoff for optimizing total arrest failure rates. Our findings suggest optimal checkpoint strengths for minimizing total error are inherently suboptimal for any single failure type, elucidating the systemic cause of genomic instability and tetraploid-like cells in response to DNA damage.

Advances in the mechanism of CDK4/6 inhibitor resistance in HR+/HER2- breast cancer

Among women, breast cancer is the most prevalent form of a malignant tumour. Among the subtypes of breast cancer, hormone receptor (HR) positive and human epidermal growth factor receptor (HER2) negative kinds make up the biggest proportion. The advent of cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, which are dependent on cell cycle proteins, has greatly enhanced the prognosis of patients with advanced HR+/HER2- breast cancer. This is a specific treatment that stops the growth of cancer cells by preventing them from dividing. Nevertheless, the drug resistance of the disease unavoidably impacts the effectiveness of treatment and the prognosis of patients. This report provides a thorough analysis of the current research advancements about the resistance mechanism of CDK4/6 inhibitors in HR+/HER2- breast cancer. It presents an in-depth discussion from numerous viewpoints, such as aberrant cell cycle regulation and changes in signalling pathways. In response to the drug resistance problem, subsequent treatment strategies are also being explored, including switching to other CDK4/6 inhibitor drugs, a combination of novel endocrine therapeutic agents, an optimal combination of targeted therapies and switching to chemotherapy. An in-depth study of the resistance mechanism can assist in identifying creative tactics that can overcome or postpone drug resistance, alleviate the problem of restricted treatment strategies following drug resistance and enhance the prognosis of patients.

Cigarette smoke extract induces malignant transformation and DNA damage via c-MET phosphorylation in human bronchial epithelial cells

Cigarette smoke, a complex mixture produced by tobacco combustion, contains a variety of carcinogens and can trigger DNA damage. Overactivation of c-MET, a receptor tyrosine kinase, may cause cancer and cellular DNA damage, but the underlying mechanisms are unknown. In this work, we investigated the mechanisms of cigarette smoke extract (CSE) induced malignant transformation and DNA damage in human bronchial epithelial cells (BEAS-2B). The results demonstrated that CSE treatment led to up-regulated mRNA expression of genes associated with the c-MET signaling pathway, increased expression of the DNA damage sensor protein γ-H2AX, and uncontrolled proliferation in BEAS-2B cells. ATR, ATR, and CHK2, which are involved in DNA damage repair, as well as the phosphorylation of c-MET and a group of kinases (ATM, ATR, CHK1, CHK2) involved in the DNA damage response were all activated by CSE. In addition, CSE activation promotes the phosphorylation modification of ATR, CHK1 proteins associated with DNA damage repair. The addition of PHA665752, a specific inhibitor of c-MET, or knock-down with c-MET both attenuated DNA damage, while overexpression of c-MET exacerbated DNA damage. Thus, c-MET phosphorylation may be involved in CSE-induced DNA damage, providing a potential target for intervention in the prevention and treatment of smoking-induced lung diseases.

Daunorubicin induces GLI1‑dependent apoptosis in colorectal cancer cell lines

Daunorubicin, also known as daunomycin, is a DNA‑targeting anticancer drug that is used as chemotherapy, mainly for patients with leukemia. It has also been shown to have anticancer effects in monotherapy or combination therapy in solid tumors, but at present it has not been adequately studied in colorectal cancer (CRC). In the present study, from a screening using an FDA‑approved drug library, it was found that daunorubicin suppresses GLI‑dependent luciferase reporter activity. Daunorubicin also increased p53 levels, which contributed to both GLI1 suppression and apoptosis. The current detailed investigation showed that daunorubicin promoted the β‑TrCP‑mediated ubiquitination and proteasomal degradation of GLI1. Moreover, a competition experiment using BODIPY‑cyclopamine, a well‑known Smo inhibitor, suggested that daunorubicin does not bind to Smo in HCT116 cells. Administration of daunorubicin (2 mg/kg, ip, qod, 15 days) into HCT116 xenograft mice profoundly suppressed tumor progress and the GLI1 level in tumor tissues. Taken together, the present results revealed that daunorubicin suppresses canonical Hedgehog pathways in CRC. Ultimately, the present study discloses a new mechanism of daunorubicin's anticancer effect and might provide a rationale for expanding the clinical application of daunorubicin.

Molecular portraits of cell cycle checkpoint kinases in cancer evolution, progression, and treatment responsiveness

Cell cycle dysregulation is prerequisite for cancer formation. However, it is unknown whether the mode of dysregulation affects disease characteristics. Here, we conduct comprehensive analyses of cell cycle checkpoint dysregulation using patient data and experimental investigations. We find that ATM mutation predisposes the diagnosis of primary estrogen receptor (ER)+/human epidermal growth factor (HER)2- cancer in older women. Conversely, CHK2 dysregulation induces formation of metastatic, premenopausal ER+/HER2- breast cancer (P = 0.001) that is treatment-resistant (HR = 6.15, P = 0.01). Lastly, while mutations in ATR alone are rare, ATR/TP53 co-mutation is 12-fold enriched over expected in ER+/HER2- disease (P = 0.002) and associates with metastatic progression (HR = 2.01, P = 0.006). Concordantly, ATR dysregulation induces metastatic phenotypes in TP53 mutant, not wild-type, cells. Overall, we identify mode of cell cycle dysregulation as a distinct event that determines subtype, metastatic potential, and treatment responsiveness, providing rationale for reconsidering diagnostic classification through the lens of the mode of cell cycle dysregulation..

The Landscape and Therapeutic Targeting of BRCA1, BRCA2 and Other DNA Damage Response Genes in Pancreatic Cancer

Genes participating in the cellular response to damaged DNA have an important function to protect genetic information from alterations due to extrinsic and intrinsic cellular insults. In cancer cells, alterations in these genes are a source of genetic instability, which is advantageous for cancer progression by providing background for adaptation to adverse environments and attack by the immune system. Mutations in BRCA1 and BRCA2 genes have been known for decades to predispose to familial breast and ovarian cancers, and, more recently, prostate and pancreatic cancers have been added to the constellation of cancers that show increased prevalence in these families. Cancers associated with these genetic syndromes are currently treated with PARP inhibitors based on the exquisite sensitivity of cells lacking BRCA1 or BRCA2 function to inhibition of the PARP enzyme. In contrast, the sensitivity of pancreatic cancers with somatic BRCA1 and BRCA2 mutations and with mutations in other homologous recombination (HR) repair genes to PARP inhibitors is less established and the subject of ongoing investigations. This paper reviews the prevalence of pancreatic cancers with HR gene defects and treatment of pancreatic cancer patients with defects in HR with PARP inhibitors and other drugs in development that target these molecular defects.

Mechanism of apoptosis activation by Curcumin rescued mutant p53Y220C in human pancreatic cancer

The mutant p53Y220C (mutp53Y220C) is frequently observed in numerous tumors, including pancreatic cancer. The mutation creates a crevice in the DNA binding core domain and makes p53 a thermally unstable non-functional protein that assists tumor progression and confers resistance to chemotherapeutic drugs. Restoring mutp53 function to its wild type by selectively targeting this crevice with small molecules is a pivotal strategy to promote apoptosis. In this study, we have shown through different biophysical and cell-based studies that curcumin binds and rescues mutp53Y220C to an active wild-type conformation and restores its apoptotic transcription function in BxPC-3-pancreatic cancer cells. In addition, the curcumin-rescued-p53Y220C (CRp53) showed significant hyperphosphorylation at Ser15, Ser20, and acetylation at Lys382 with an 8-fold increase in transcription activity in the BxPC-3 cell lines. We also observed that the active CRp53 escapes Mdm2-mediated proteasomal degradation and the majority of the proteins were localized inside the nucleus with an increased half-life and transcription restoration compared to untreated BxPC-3 cells. By label-free proteomics analysis, we observed that upon curcumin treatment almost 227 proteins were dysregulated with the majority of them being transcriptional targets of p53. Based on our studies, it reflects that apoptosis in pancreatic cancer cells is mediated by curcumin-rescued mutant p53Y220C.

Diallyl Disulfide Induces Chemosensitization to Sorafenib, Autophagy, and Cell Cycle Arrest and Inhibits Invasion in Hepatocellular Carcinoma

Hepatocellular carcinoma is the seventh most common type of cancer in the world, with limited treatment options. A promising strategy to treat cancer is to associate chemotherapeutics and plant bioactive compounds. Here, we examined whether diallyl disulfide (DADS; 50-200 μM) and sorafenib (SORA; 8 μM), either alone or in combination, were toxic to hepatocellular carcinoma cells (HepG2) in vitro. We assessed whether DADS and/or SORA induced cell death (LIVE/DEAD assay and autophagy) and cell cycle changes (flow cytometry), altered expression of key genes and proteins (RT-qPCR and Western blot), and modulated tumorigenesis signatures, such as proliferation (clonogenic assay), migration (wound healing), and invasion (inserts). The DADS + SORA combination elicited autophagic cell death by upregulating LC3 and NRF2 expression and downregulating FOS and TNF expression; induced the accumulation of cells in the G1 phase which thereby upregulated the CHEK2 expression; and inhibited invasion by downregulating the MMP2 expression. Predictive analysis indicated the participation of the MAPK pathway in the reported results. The DADS + SORA combination suppressed both cell invasion and clonogenic survival, which indicated that it dampened tumor growth, proliferation, invasion, and metastatic potential. Therefore, the DADS + SORA combination is a promising therapy to develop new clinical protocols.

Cell cycle-dependent radiosensitivity in mouse zygotes

Mammalian zygotes are hypersensitive to radiation exposure compared with later-stage embryos and somatic cells, which may be due to an unusual DNA damage response (DDR). DNA damage checkpoints are an essential part of the DDR, allowing for faithful replication of cells. Although the DDR and radiosensitivity of somatic cells are dependent on the cell cycle phase, it remains largely unclear how the irradiation of zygotes at different phases affects cell cycle progression and preimplantation development. Here, mouse zygotes were irradiated with 10 Gy γ-rays at all four cell cycle phases. DNA damage checkpoints were activated by γ-irradiation at the G2 phase, but not at the G1, S, and M phases. The absence of DNA damage checkpoints at the G1 and M phases seems to be due to the low abundance of phosphorylated CHK2, which plays a key role in checkpoint activation in response to ionizing radiation. The cause of the inoperative S phase checkpoint may lie downstream of CHK2 activation. The inactive DNA damage checkpoints at the G1 and S phases contributed to micronucleus formation in the subsequent 2-cell stage, whereas irradiation at the M phase led to the highest incidence of chromatin bridges. The low developmental rates of embryos irradiated at the G1, S, and M phases suggest that embryos with these two types of chromatin abnormalities are prone to developmental failure. Taken together, these results suggest that the radiosensitivity of zygotes can be ascribed to a defective DDR at the G1, S, and M phases.