Sensitivity of cells to ATR and CHK1 inhibitors requires hyperactivation of CDK2 rather than endogenous replication stress or ATM dysfunction

DNA damage activates cell cycle checkpoint proteins ATR and CHK1 to arrest cell cycle progression, providing time for repair and recovery. Consequently, inhibitors of ATR (ATRi) and CHK1 (CHK1i) enhance damage-induced cell death. Intriguingly, both CHK1i and ATRi alone elicit cytotoxicity in some cell lines. Sensitivity has been attributed to endogenous replications stress, but many more cell lines are sensitive to ATRi than CHK1i. Endogenous activation of the DNA damage response also did not correlate with drug sensitivity. Sensitivity correlated with the appearance of γH2AX, a marker of DNA damage, but without phosphorylation of mitotic markers, contradicting suggestions that the damage is due to premature mitosis. Sensitivity to ATRi has been associated with ATM mutations, but dysfunction in ATM signaling did not correlate with sensitivity. CHK1i and ATRi circumvent replication stress by reactivating stalled replicons, a process requiring a low threshold activity of CDK2. In contrast, γH2AX induced by single agent ATRi and CHK1i requires a high threshold activity CDK2. Hence, phosphorylation of different CDK2 substrates is required for cytotoxicity induced by replication stress plus ATRi/CHK1i as compared to their single agent activity. In summary, sensitivity to ATRi and CHK1i as single agents is elicited by premature hyper-activation of CDK2.

Deep Next Generation Sequencing Identifies Somatic Mutational Signature in Egyptian Colorectal Cancer Patients

Background: Colorectal cancer (CRC) incidence is progressively increasing in Egypt. Unfortunately, there is inadequate knowledge of the acquired somatic mutations in Egyptian CRC patients which limit our understanding of its progression. To the best of our knowledge, our study is the first to sequence multiple-gene panel to identify the somatic mutation pattern associated with CRC disease progression in a cohort of Egyptian patients. Custom 72 genes, which are frequently associated with CRC, were sequenced using Qiaseq UMI-based targeted DNA panel in 120 fresh tissues classified into; inflammatory bowel disease (IBD; n=20), colonic polyp (CP; n=38) and CRC (n=62) as well as 20 biopsies with non-specific colitis served as a control group (n=20). Results: Using Ingenuity Variant Analysis (IVA), we revealed that APC, TP53 & ATM genes harbored the highly frequent CRC-specific somatic mutations (15, 11 & 6, respectively). We also identified common somatic mutations (predictors) that were associated with disease progression from colitis to CRC; APC (c.1742delA (65%)), TP53 (c.121delG (58%), c.215C>G (52%)), ATM (c.640delT (16%)), IGF2 (c.677delG (56%)), RET (c.2071G>A (37%)), ACVR2A (c.1310delA (26%)), PIK3CA (c.1173A>G (16%)) & KIT (c.1621A>C (13%)). Furthermore, pathway analysis using Ingenuity Pathway Analysis (IPA) showed that Wnt/βcatenin, ATM signaling, RTK-RAS and TGF-β were the most altered pathways in the CRC group (73%. 72%, 40% & 36%, respectively).Conclusion: In this data set, we shed the light on the most frequent somatic mutations and the most altered pathways that are crucial for understanding colorectal cancer predisposition and developing personalized therapies for the Egyptian CRC patients.

NLRP3 controls ATM activation in response to DNA damage

ABSTRACTThe DNA damage response (DDR) is essential to preserve genomic integrity and acts as a barrier to cancer. The ATM pathway orchestrates the cellular response to DNA double strand breaks (DSBs), and its attenuation is frequent during tumorigenesis. Here, we show that NLRP3, a Pattern Recognition Receptor known for its role in the inflammasome complex formation, interacts with the ATM kinase to control the early phase of DDR, independently of its inflammasome activity. NLRP3 down-regulation in human bronchial epithelial cells impairs ATM pathway activation as shown by an altered ATM substrate phosphorylation profile, and due to impaired p53 activation, confers resistance to acute genomic stress. Moreover, we found that NLRP3 is down-regulated in Non-Small Cell Lung Cancer (NSCLC) tissues and NLRP3 expression is correlated with patient overall survival. NLRP3 re-expression in NSCLC cells restores appropriate ATM signaling. Our findings identify a non-immune function for NLRP3 in genome integrity surveillance and strengthen the concept of a functional link between innate immunity and DNA damage sensing pathways.

Gene expression is associated with virulence in murine macrophages infected withLeptospiraspp

Leptospiragenus contains species that affect human health with varying degrees of pathogenicity. In this context, we aimed to evaluate the differences in modulation of host gene expression by strains ofLeptospirawith varied virulence degrees. Our data showed a high number of differentilly expressed transcripts in murine macrophages following 6h of infection with both virulent and culture-attenuatedL. interrogansand to a lesser degree, with the saprophyte strainL. biflexa. That suggests that certain genes are modulated byLeptospirainfection independent of their degree of virulence, whether others are virulence and species associated. Pathway analysis indicated that Apoptosis, ATM Signaling and Cell Cycle: G2/M DNA Damage Checkpoint Regulation were exclusively regulated following infection with the virulent strain. Results demonstrated that species and virulence play a role during host response toLeptosppiraspp in murine macrophages.Author summaryLeptospirosis is an infectious disease that is transmitted from animals to humans. It is a re-emerging neglected zoonosis that is found in a range of environments worldwide, most notably tropical regions prone to flooding. This bacteria is found in soil and water and are eliminated in the urine by rats, their natural host reservoir. Through skin contacts with the bacteria people or animals can get infected however the infection process is still poorly understood, such as the fact that different strains can cause different severity of illness. In this study, we aimed to evaluate the differences in modulation of host gene expression by strains ofLeptospiravarying in virulence. After transcriptomic analysis, the results showed a high number of differentially expressed genes after 6h of infection by virulent and attenuatedL. interrogans, and to a lesser extent withL. biflexasaprophytic lineage. This suggests that RNAs are modulated after infection byLeptospirain macrophages, in a species and virulence related manner. It is hoped that the data produced will contribute to further our understanding on the pathogenesis of leptospirosis.

Mutant huntingtin impairs PNKP and ATXN3, disrupting DNA repair and transcription

How huntingtin (HTT) triggers neurotoxicity in Huntington’s disease (HD) remains unclear. We report that HTT forms a transcription-coupled DNA repair (TCR) complex with RNA polymerase II subunit A (POLR2A), ataxin-3, the DNA repair enzyme polynucleotide-kinase-3'-phosphatase (PNKP), and cyclic AMP-response element-binding (CREB) protein (CBP). This complex senses and facilitates DNA damage repair during transcriptional elongation, but its functional integrity is impaired by mutant HTT. Abrogated PNKP activity results in persistent DNA break accumulation, preferentially in actively transcribed genes, and aberrant activation of DNA damage-response ataxia telangiectasia-mutated (ATM) signaling in HD transgenic mouse and cell models. A concomitant decrease in Ataxin-3 activity facilitates CBP ubiquitination and degradation, adversely impacting transcription and DNA repair. Increasing PNKP activity in mutant cells improves genome integrity and cell survival. These findings suggest a potential molecular mechanism of how mutant HTT activates DNA damage-response pro-degenerative pathways and impairs transcription, triggering neurotoxicity and functional decline in HD.