PHOSPHORYLATION-DEPENDENT ASSOCIATION OF WRN WITH RPA IS REQUIRED FOR RECOVERY OF REPLICATION FORKS STALLED AT SECONDARY DNA STRUCTURES

The WRN protein mutated in the hereditary premature aging disorder Werner syndrome plays a vital role in handling, processing, and restoring perturbed replication forks. One of its most abundant partners, Replication Protein A (RPA), has been shown to robustly enhance WRN helicase activity in specific cases when tested in vitro. However, the significance of RPA-binding to WRN at replication forks in vivo has remained largely unexplored. In this study, we have identified several conserved phosphorylation sites in the acidic domain of WRN that are targeted by Casein Kinase 2 (CK2). Surprisingly, these phosphorylation sites are essential for the interaction between WRN and RPA, both in vitro and in human cells. By characterizing a CK2-unphosphorylatable WRN mutant that lacks the ability to bind RPA, we have determined that the WRN-RPA complex plays a critical role in fork recovery after replication stress whereas the WRN-RPA interaction is not necessary for the processing of replication forks or preventing DNA damage when forks stall or collapse. When WRN fails to bind RPA, fork recovery is impaired, leading to the accumulation of single-stranded DNA gaps in the parental strands, which are further enlarged by the structure-specific nuclease MRE11. Notably, RPA-binding by WRN and its helicase activity are crucial for countering the persistence of G4 structures after fork stalling. Therefore, our findings reveal for the first time a novel role for the WRN-RPA interaction to facilitate fork restart, thereby minimizing G4 accumulation at single-stranded DNA gaps and suppressing accumulation of unreplicated regions that may lead to MUS81-dependent double-strand breaks requiring efficient repair by RAD51 to prevent excessive DNA damage.

Re-sensitization to pembrolizumab following PSMA-CD3 T-cell redirection therapy with JNJ-081 in a patient with mismatch repair-deficient metastatic castration-resistant prostate cancer: a case report

While checkpoint inhibitor therapy has revolutionized the treatment landscape of some solid tumors, it has shown limited efficacy in metastatic castration-resistant prostate cancers (mCRPC). A small (~3-5%) but clinically distinct subset of mCRPC tumors have a DNA mismatch repair deficiency (dMMR) and develop a hypermutation phenotype with elevated tumor mutational burden and high microsatellite instability (MSI-H). Retrospective analyses have shown dMMR/MSI-H status to be a predictive biomarker for response to pembrolizumab in prostate tumors. Here, in this report, we present a case of a patient with mCRPC harboring a somatic dMMR who had progressed on pembrolizumab after an initial response. He enrolled on a clinical trial with JNJ-081, a prostate-specific membrane antigen-CD3 bispecific T-cell engager antibody and experienced a partial response with course complicated by cytokine release syndrome. On progression, he was reinitiated on pembrolizumab and experienced an exceptional second response, with his prostate-specific antigen falling from a high of 20.01 to undetectable after 6 weeks and remaining undetectable for >11 months. To our knowledge, this represents the first reported case of bispecific T-cell engager-mediated re-sensitization to checkpoint inhibitor therapy in any cancer.

Combining histological grade, TILs, and the PD-1/PD-L1 pathway to identify immunogenic tumors and de-escalate radiotherapy in early breast cancer: a secondary analysis of a randomized clinical trial

BACKGROUND

The implementation of immunological biomarkers for radiotherapy (RT) individualization in breast cancer requires consideration of tumor-intrinsic factors. This study aimed to investigate whether the integration of histological grade, tumor-infiltrating lymphocytes (TILs), programmed cell death protein-1 (PD-1), and programmed death ligand-1 (PD-L1) can identify tumors with aggressive characteristics that can be downgraded regarding the need for RT.

METHODS

The SweBCG91RT trial included 1178 patients with stage I-IIA breast cancer, randomized to breast-conserving surgery with or without adjuvant RT, and followed for a median time of 15.2 years. Immunohistochemical analyses of TILs, PD-1, and PD-L1 were performed. An activated immune response was defined as stromal TILs ≥10% and PD-1 and/or PD-L1 expression in ≥1% of lymphocytes. Tumors were categorized as high-risk or low-risk using assessments of histological grade and proliferation as measured by gene expression. The risk of ipsilateral breast tumor recurrence (IBTR) and benefit of RT were then analyzed with 10 years follow-up based on the integration of immune activation and tumor-intrinsic risk group.

RESULTS

Among high-risk tumors, an activated immune infiltrate was associated with a reduced risk of IBTR (HR 0.34, 95% CI 0.16 to 0.73, p=0.006). The incidence of IBTR in this group was 12.1% (5.6-25.0) without RT and 4.4% (1.1-16.3) with RT. In contrast, the incidence of IBTR in the high-risk group without an activated immune infiltrate was 29.6% (21.4-40.2) without RT and 12.8% (6.6-23.9) with RT. Among low-risk tumors, no evidence of a favorable prognostic effect of an activated immune infiltrate was seen (HR 2.0, 95% CI 0.87 to 4.6, p=0.100).

CONCLUSIONS

Integrating histological grade and immunological biomarkers can identify tumors with aggressive characteristics but a low risk of IBTR despite a lack of RT boost and systemic therapy. Among high-risk tumors, the risk reduction of IBTR conferred by an activated immune infiltrate is comparable to treatment with RT. These findings may apply to cohorts dominated by estrogen receptor-positive tumors.

PP4 inhibition sensitizes ovarian cancer to NK cell-mediated cytotoxicity via STAT1 activation and inflammatory signaling

BACKGROUND

Increased infiltration of T cells into ovarian tumors has been repeatedly shown to be predictive of enhanced patient survival. However, despite the evidence of an active immune response in ovarian cancer (OC), the frequency of responses to immune checkpoint blockade (ICB) therapy in OC is much lower than other cancer types. Recent studies have highlighted that deficiencies in the DNA damage response (DDR) can drive increased genomic instability and tumor immunogenicity, which leads to enhanced responses to ICB. Protein phosphatase 4 (PP4) is a critical regulator of the DDR; however, its potential role in antitumor immunity is currently unknown.

RESULTS

Our results show that the PP4 inhibitor, fostriecin, combined with carboplatin leads to increased carboplatin sensitivity, DNA damage, and micronuclei formation. Using multiple OC cell lines, we show that PP4 inhibition or PPP4C knockdown combined with carboplatin triggers inflammatory signaling via Nuclear factor kappa B (NF-κB) and signal transducer and activator of transcription 1 (STAT1) activation. This resulted in increased expression of the pro-inflammatory cytokines and chemokines: CCL5, CXCL10, and IL-6. In addition, IFNB1 expression was increased suggesting activation of the type I interferon response. Conditioned media from OC cells treated with the combination of PP4 inhibitor and carboplatin significantly increased migration of both CD8 T cell and natural killer (NK) cells over carboplatin treatment alone. Knockdown of stimulator of interferon genes (STING) in OC cells significantly abrogated the increase in CD8 T-cell migration induced by PP4 inhibition. Co-culture of NK-92 cells and OC cells with PPP4C or PPP4R3B knockdown resulted in strong induction of NK cell interferon-γ, increased degranulation, and increased NK cell-mediated cytotoxicity against OC cells. Stable knockdown of PP4C in a syngeneic, immunocompetent mouse model of OC resulted in significantly reduced tumor growth in vivo. Tumors with PP4C knockdown had increased infiltration of NK cells, NK T cells, and CD4⁺ T cells. Addition of low dose carboplatin treatment led to increased CD8⁺ T-cell infiltration in PP4C knockdown tumors as compared with the untreated PP4C knockdown tumors.

CONCLUSIONS

Our work has identified a role for PP4 inhibition in promoting inflammatory signaling and enhanced immune cell effector function. These findings support the further investigation of PP4 inhibitors to enhance chemo-immunotherapy for OC treatment.

Oxidative Damage Induced Telomere Mediated Genomic Instability in Cells from Ataxia Telangiectasia Patients

Our cellular genome is susceptible to cytotoxic lesions which include single strand breaks and double strand breaks among other lesions. Ataxia telangiectasia mutated (ATM) protein was one of the first DNA damage sensor proteins to be discovered as being involved in DNA repair and as well as in telomere maintenance. Telomeres help maintain the stability of our chromosomes by protecting the ends from degradation. Cells from ataxia telangiectasia (AT) patients lack ATM and accumulate chromosomal alterations. AT patients display heightened susceptibility to cancer. In this study, cells from AT patients (called as AT -/- and AT +/- cells) were characterized for genome stability status and it was observed that AT -/- cells show considerable telomere attrition. Furthermore, DNA damage and genomic instability were compared between normal (AT +/+ cells) and AT -/- cells exhibiting increased frequencies of spontaneous DNA damage and genomic instability markers. Both AT -/- and AT +/- cells were sensitive to sodium arsenite (1.5 and 3.0 μg/ml) and ionizing radiation-induced (2 Gy, gamma rays) oxidative stress. Interestingly, telomeric fragments were detected in the comet tails as revealed by comet-fluorescence in situ hybridization analysis, suggestive of telomeric instability in AT -/- cells upon exposure to sodium arsenite or radiation. Besides, there was an increase in the number of chromosome alterations in AT -/- cells following arsenite treatment or irradiation. In addition, complex chromosome aberrations were detected by multicolor fluorescence in situ hybridization in AT -/- cells in comparison to AT +/- and normal cells. Telomere attrition and chromosome alterations were detected even at lower doses of sodium arsenite. Peptide nucleic acid - FISH analysis revealed defective chromosome segregation in cells lacking ATM proteins. The data obtained in this study substantiates the role of ATM in telomere stability under oxidative stress.

Identification of natural product 3, 5-diiodotyrosine as APOBEC3B inhibitor to prevent somatic mutation accumulation and cancer progression

BACKGROUND

The development of cancer is largely dependent on the accumulation of somatic mutations, indicating the potential to develop cancer chemoprevention agents targeting mutation drivers. However, ideal cancer chemoprevention agents that can effectively inhibit the mutation drivers have not been identified yet.

METHODS

The somatic mutation signatures and expression analyses of APOBEC3B were performed in patient with pan-cancer. The computer-aided screening and skeleton-based searching were performed to identify natural products that can inhibit the activity of APOBEC3B. 4-nitroquinoline-1-oxide (4-NQO)-induced spontaneous esophageal squamous cell carcinoma (ESCC) and azoxymethane/dextran sulfate sodium (AOM/DSS)-induced spontaneous colon cancer mouse models were conducted to investigate the influences of APOBEC3B inhibitor on the prevention of somatic mutation accumulation and cancer progression.

RESULTS

Here, we discovered that the cytidine deaminase APOBEC3B correlated somatic mutations were widely observed in a variety of cancers, and its overexpression indicated poor survival. SMC247 (3, 5-diiodotyrosine), as a source of kelp iodine without side effects, could strongly bind APOBEC3B (K_D=65 nM) and effectively inhibit its deaminase activity (IC₅₀=1.69 µM). Interestingly, 3, 5-diiodotyrosine could significantly reduce the clusters of mutations, prevent the precancerous lesion progression, and prolong the survival in 4-NQO-induced spontaneous ESCC and AOM/DSS-induced spontaneous colon cancer mouse models. Furthermore, 3, 5-diiodotyrosine could reduce colitis, increase the proportion and function of T lymphocytes via IL-15 in tumor microenvironment. The synergistic cancer prevention effects were observed when 3, 5-diiodotyrosine combined with PD-1/PD-L1 blockade.

CONCLUSIONS

This is the first prove-of-concept study to elucidate that the natural product 3, 5-diiodotyrosine could prevent somatic mutation accumulation and cancer progression through inhibiting the enzymatic activity of APOBEC3B. In addition, 3, 5-diiodotyrosine could reduce the colitis and increase the infiltration and function of T lymphocytes via IL-15 in tumor microenvironment. 3, 5-diiodotyrosine combined with PD-1/PD-L1 blockade could elicit synergistic cancer prevention effects, indicating a novel strategy for both prevent the somatic mutation accumulation and the immune-suppressive microenvironment exacerbation.

Canonical DNA Repair Pathways Influence R-Loop-Driven Genome Instability

DNA repair defects create cancer predisposition in humans by fostering a higher rate of mutations. While DNA repair is quite well characterized, recent studies have identified previously unrecognized relationships between DNA repair and R-loop-mediated genome instability. R-loops are three-stranded nucleic acid structures in which RNA binds to genomic DNA to displace a loop of single-stranded DNA. Mutations in homologous recombination, nucleotide excision repair, crosslink repair, and DNA damage checkpoints have all now been linked to formation and function of transcription-coupled R-loops. This perspective will summarize recent literature linking DNA repair to R-loop-mediated genomic instability and discuss how R-loops may contribute to mutagenesis in DNA-repair-deficient cancers.

Monopolar spindle 1 (MPS1) protein-dependent phosphorylation of RecQ-mediated genome instability protein 2 (RMI2) at serine 112 is essential for BLM-Topo III α-RMI1-RMI2 (BTR) protein complex function upon spindle assembly checkpoint (SAC) activation during mitosis

Genomic instability and a predisposition to cancer are hallmarks of Bloom syndrome, an autosomal recessive disease arising from mutations in the BLM gene. BLM is a RecQ helicase component of the BLM-Topo III α-RMI1-RMI2 (BTR) complex, which maintains chromosome stability at the spindle assembly checkpoint (SAC). Other members of the BTR complex include Topo IIIa, RMI1, and RMI2. All members of the BTR complex are essential for maintaining the stable genome. Interestingly, the BTR complex is posttranslationally modified upon SAC activation during mitosis, but its significance remains unknown. In this study, we show that two proteins that interact with BLM, RMI1 and RMI2, are phosphorylated upon SAC activation, and, like BLM, RMI1, and RMI2, are phosphorylated in an MPS1-dependent manner. An S112A mutant of RMI2 localized normally in cells and was found in SAC-induced coimmunoprecipitations of the BTR complex. However, in RMI2-depleted cells, an S112A mutant disrupted the mitotic arrest upon SAC activation. The failure of cells to maintain mitotic arrest, due to lack of phosphorylation at Ser-112, results in high genomic instability characterized by micronuclei, multiple nuclei, and a wide distribution of aberrantly segregating chromosomes. We found that the S112A mutant of RMI2 showed defects in redistribution between the nucleoplasm and nuclear matrix. The phosphorylation at Ser-112 of RMI2 is independent of BLM and is not required for the stability of the BTR complex, BLM focus formation, and chromatin targeting in response to replication stress. Overall, this study suggests that the phosphorylation of the BTR complex is essential to maintain a stable genome.

Rad51, friend or foe?

A protein long recognized for its role in DNA repair has now paradoxically been implicated in DNA damage.

Regulation of Rad17 protein turnover unveils an impact of Rad17-APC cascade in breast carcinogenesis and treatment

Aberrant regulation of DNA damage checkpoint function leads to genome instability that in turn can predispose cellular tissues to become cancerous. Previous works from us and others demonstrated the role of Rad17 in either activation or termination of DNA damage checkpoint function. In the current study, we have revealed the unexpected accumulation of Rad17 in various types of breast cancer cell lines as well as human breast cancer tissues. We observed that Rad17 protein turnover rate in breast epithelial cells is much faster than in breast cancer cells, where the turnover of Rad17 is regulated by the Cdh1/APC pathway. We further observed that Rad17-mediated checkpoint function is modulated by proteolysis. Stabilization of Rad17 disrupts cellular response to chemotherapeutic drug-induced DNA damage and enhances cellular transformation. In addition, manipulation of Rad17 by RNA interference or stabilization of Rad17 significantly sensitize breast cancer cell to various chemotherapeutic drugs. Our present results indicate the manipulation of Rad17 proteolysis could be a valuable approach to sensitize breast cancer cell to the chemotherapeutic treatment despite of the critical role in governing DNA damage response and cellular recovery from genotoxic stress.

Physiological and oncogenic Aurora-A pathway

Aurora family of protein kinases have emerged as crucial factors of, not only mitosis and cytokinesis, but also human carcinogenesis. Among these family members is Aurora-A that is frequently overexpressed in varieties of human cancer. Both in vitro and in vivo studies demonstrated that Aurora-A induces tumorigenesis through genome instability. These studies have further shown that cell signaling cross-talk between Aurora-A and other cellular proteins are essential for fully-transformed phenotypes. This review summarizes recent progress of Aurora-A-associated carcinogenesis.