Chromosomal instability drives metastasis through a cytosolic DNA response

Modelling chromosome structural and copy number changes to understand cancer genomes

Cancer cells differ from healthy cells by genetic information that is massively altered not only by point mutations and small insertions and deletions, but also by large scale changes such as chromosomal rearrangements as well as gains and losses of individual chromosomes or entire chromosome sets. How exactly large-scale chromosomal abnormalities contribute to tumorigenesis has been difficult to study. Remarkable progress has been recently made thanks to in vitro models that mimic large-scale chromosomal aberrations and allow their systematic analysis. The obtained findings reveal that genomic alterations strongly affect the cellular physiology and, importantly, instigate further genomic instability. This suggests that these model systems might provide novel insights by recapitulating the processes that occur during tumorigenesis.

Local, transient tensile stress on the nuclear membrane causes membrane rupture

Cancer cell migration through narrow constrictions generates compressive stresses on the nucleus that deform it and cause rupture of nuclear membranes. Nuclear membrane rupture allows uncontrolled exchange between nuclear and cytoplasmic contents. Local tensile stresses can also cause nuclear deformations, but whether such deformations are accompanied by nuclear membrane rupture is unknown. Here we used a direct force probe to locally deform the nucleus by applying a transient tensile stress to the nuclear membrane. We found that a transient (∼0.2 s) deformation (∼1% projected area strain) in normal mammary epithelial cells (MCF-10A cells) was sufficient to cause rupture of the nuclear membrane. Nuclear membrane rupture scaled with the magnitude of nuclear deformation and the magnitude of applied tensile stress. Comparison of diffusive fluxes of nuclear probes between wild-type and lamin-depleted MCF-10A cells revealed that lamin A/C, but not lamin B2, protects the nuclear membranes against rupture from tensile stress. Our results suggest that transient nuclear deformations typically caused by local tensile stresses are sufficient to cause nuclear membrane rupture.

CINSARC signature as a prognostic marker for clinical outcome in sarcomas and beyond

Prognostication is a key issue for sarcoma patients' care as it triggers the therapeutic approach including chemotherapy, which is still not standard for localized patients. Current prognostic evaluation, based on the FNCLCC grading system, has recently been improved by the CINSARC signature outperforming histology-based grading system by identifying high-risk patients in every grade, even in those considered as low. CINSARC is an expression-based signature related to mitosis and chromosome integrity with prognostic value in a wide range of cancers additional to sarcoma. First developed with frozen material, CINSARC is now coupled with NanoString technology allowing evaluation from FFPE blocks used in clinical practice. Consequently, CINSARC is currently evaluated in clinical trials with a dual objective of demonstrating the benefit of chemotherapy in sarcoma patients and testing its response prediction. Considering its overarching value in oncology, its development is welcome in any cancers where the prognostication needs to be improved.

An Analysis of the Expression and Association with Immune Cell Infiltration of the cGAS/STING Pathway in Pan-Cancer

Recent evidence shows that cyclic GMP-AMP synthase (cGAS)/stimulator of interferon (IFN) genes (STING) signaling is essential for antitumor immunity by inducing the production of type I IFN and thus activating both innate and adaptive immunity based on gene knockout mouse models. However, the extensive detection of the expression of cGAS/STING signaling in human cancer and mining the roles of this signaling pathway in human cancer immunity have not been performed until now. In this study, we revealed that four key molecules (cGAS, STING, TANK binding kinase 1 [TBK1], and IFN regulatory factor 3 [IRF3]) in the cGAS/STING signaling are highly expressed in cancer tissues, and the expression levels of these genes are negatively correlated with their methylation levels in most of the detected cancer types. We also showed that highly upregulated cGAS/STING signaling is negatively correlated with the infiltration of immune cells in some tumor types, and consistent with these findings, we showed that a high level of cGAS/STING signaling predicts a poor prognosis in patients with certain cancers. This study suggests that it is necessary to deeply and fully evaluate the function of cGAS/STING signaling in cancer immunity and cancer progression before the application of the STING agonist-based anticancer immune therapy in the clinic.

DNA-stimulated cell death: implications for host defence, inflammatory diseases and cancer

The immune system detects disturbances in homeostasis that occur during infection, sterile tissue damage and cancer. This initiates immune responses that seek to eliminate the trigger of immune activation and to re-establish homeostasis. At the same time, these mechanisms can also play a crucial role in the progression of disease. The occurrence of DNA in the cytosol constitutes a potent trigger for the innate immune system, governing the production of key inflammatory cytokines such as type I interferons and IL-1β. More recently, it has become clear that cytosolic DNA also triggers other biological responses, including various forms of programmed cell death. In this article, we review the emerging literature on the pathways governing DNA-stimulated cell death and the current knowledge on how these processes shape immune responses to exogenous and endogenous challenges.

NLRX1 regulates TNF-α-induced mitochondria-lysosomal crosstalk to maintain the invasive and metastatic potential of breast cancer cells

An increased level of proinflammatory cytokines, including TNF-α in tumor microenvironment regulates the bioenergetic capacity, immune evasion and survival of cancer cells. Emerging evidences suggest that mitochondrial immune signaling proteins modulates mitochondrial bioenergetic capacity, in addition to the regulation of innate immune response. The optimal oxidative phosphorylation (OxPhos) capacity is required for the maintenance of functional lysosomes and autophagy flux. NLRX1, a mitochondrial NOD family receptor protein, regulates mitochondrial function during apoptosis and tissue injury. However, its role in regulation of mitochondrial and lysosomal function to modulate autophagy flux during inflammatory conditions is not understood. In the current study, we investigated the role of NLRX1 in modulating TNF-α induced autophagy flux and mitochondrial turnover and its implication in regulating the invasive and metastatic capability of breast cancer cells. Expression analyses of clinical breast cancer samples and meta-analysis of multiple public databases revealed that NLRX1 expression is significantly increased in basal-like and metastatic breast carcinoma as compared to non-basal-like and primary breast cancer. Depletion of NLRX1 expression in triple-negative breast cancer cells, altered the organization and activity of OxPhos complexes in presence of TNF-α. NLRX1 depletion further impaired lysosomal function and hence the turnover of damaged mitochondria through mitophagy in presence of TNF-α. Importantly, loss of NLRX1 decreased OxPhos-dependent cell proliferation and migration ability of triple-negative breast cancer cells in presence of TNF-α. These evidences suggest an essential role of NLRX1 in maintaining the crosstalk of mitochondrial metabolism and lysosomal function to regulate invasion and metastasis capability of breast cancer cells.

Approaches towards Longevity: Reprogramming, Senolysis, and Improved Mitotic Competence as Anti-Aging Therapies

Mainstream approaches that are currently used as anti-aging therapies primarily explore the senescence and epigenetic drift aging hallmarks and they are at two ends of the spectrum. While senolytic therapies include either the selective elimination of senescent cells or the disruption of their secretome with the use of drugs or natural compounds, cellular reprogramming uses genetic manipulation to revert cells all the way back to pluripotency. Here, we describe the progress that has been made on these therapies, while highlighting the major challenges involved. Moreover, based on recent findings elucidating the impact of mitotic shutdown and aneuploidy in cellular senescence, we discuss the modulation of mitotic competence as an alternative strategy to delay the hallmarks of aging. We propose that a regulated rise in mitotic competence of cells could circumvent certain limitations that are present in the senolytic and reprogramming approaches, by acting to decelerate senescence and possibly restore the epigenetic landscape.

The immunological consequences of radiation-induced DNA damage

Historically, our understanding of the cytotoxicity of radiation has centred on tumour cell-autonomous mechanisms of cell death. Here, tumour cell death occurs when a threshold number of radiation-induced non-reparable double-stranded DNA breaks is exceeded. However, in recent years, the importance of immune mechanisms of cell death has been increasingly recognised, as well as the impact of radiotherapy on non-malignant cellular components of the tumour microenvironment. Conserved antiviral pathways that detect foreign nucleic acid in the cytosol and drive downstream interferon (IFN) responses via the cyclic guanosine monophosphate-adenosine monophosphate synthase/stimulator of IFN genes (cGAS/STING) pathway are key components of the immune response to radiation-induced DNA damage. In preclinical models, acute induction of a type 1 IFN response is important for both direct and abscopal tumour responses to radiation. Inhibitors of the DNA damage response show promise in augmenting this inflammatory IFN response. However, a substantial proportion of tumours show chronic IFN signalling prior to radiotherapy, which paradoxically drives immunosuppression. This chronic IFN signalling leads to treatment resistance, and heterotypic interactions between stromal fibroblasts and tumour cells contribute to an aggressive tumour phenotype. The effect of radiotherapy on myeloid cell populations, particularly tumour-associated macrophages, has an additional impact on the immune tumour microenvironment. It is not yet clear how the above preclinical findings translate into a human context. Human tumours show greater intratumoural genomic heterogeneity and more variable levels of chromosomal instability than experimental murine models. High-quality translational studies of immunological changes occurring during radiotherapy that incorporate intrinsic tumour biology will enable a better understanding of the immunological consequences of radiation-induced DNA damage in patients. Copyright © 2019 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

High PLK4 expression promotes tumor progression and induces epithelial‑mesenchymal transition by regulating the Wnt/β‑catenin signaling pathway in colorectal cancer

Polo‑like kinase 4 (PLK4) has been identified as an oncogene, which is overexpressed in various types of human cancer; however, its role in colorectal cancer (CRC) development remains unknown. The present study demonstrated that PLK4 protein expression was upregulated in CRC tissues compared with in normal tissues through western blotting. In addition, immunohistochemical analysis of 39 CRC specimens further demonstrated that PLK4 protein expression was upregulated in 64.1% (25/39) of samples. Increased PLK4 expression was closely associated with enhanced tumor size (P=0.031), lymph node metastasis (P=0.016) and TNM stage (P=0.001). Subsequently, cell viability, wound scratch, migration and invasion assays were conducted in vitro, and nude mice CRC xenograft models were generated. The results demonstrated that knockdown of PLK4 in CRC cells resulted in significant decreases in cell viability and proliferation, and decreased the protein expression levels of N‑cadherin and snail, which are biomarkers of epithelial‑mesenchymal transition. Furthermore, PLK4 knockdown inactivated the Wnt/β‑catenin pathway in CRC cells in vitro and in vivo, and suppressed the growth of xenograft tumors in nude mice. In conclusion, these results suggested that PLK4 may promote the carcinogenesis and metastasis of CRC, thus indicating that PLK4 may be considered a molecular target for CRC treatment.

Cell-Free eccDNAs: A New Type of Nucleic Acid Component for Liquid Biopsy?

Extrachromosomal circular DNAs (eccDNAs) are circular DNAs that are originated from chromosomes, but are independent from chromosomal DNA. The eccDNAs are commonly found in various tissues and cell types, and in both normal and diseased conditions. Due to their highly heterogeneous origins and being widely spread in nearly all eukaryotes, the eccDNAs are believed to reflect the genome's plasticity and instability. With the assistance of next-generation sequencing, more eccDNAs have been characterized at the molecular level. Recently, eccDNAs have been reported as cell-free DNAs in the circulation system. Importantly, these circulating eccDNAs have shown some evidence with disease associations, suggesting their potential utility as a new type of biomarker for disease detection, treatment assessment and progress surveillance. However, many challenges need to be addressed before implementing the eccDNAs as a new source of genetic material for liquid biopsy.

BRCA2 deficiency instigates cGAS-mediated inflammatory signaling and confers sensitivity to tumor necrosis factor-alpha-mediated cytotoxicity

Loss of BRCA2 affects genome stability and is deleterious for cellular survival. Using a genome-wide genetic screen in near-haploid KBM-7 cells, we show that tumor necrosis factor-alpha (TNFα) signaling is a determinant of cell survival upon BRCA2 inactivation. Specifically, inactivation of the TNF receptor (TNFR1) or its downstream effector SAM68 rescues cell death induced by BRCA2 inactivation. BRCA2 inactivation leads to pro-inflammatory cytokine production, including TNFα, and increases sensitivity to TNFα. Enhanced TNFα sensitivity is not restricted to BRCA2 inactivation, as BRCA1 or FANCD2 inactivation, or hydroxyurea treatment also sensitizes cells to TNFα. Mechanistically, BRCA2 inactivation leads to cGAS-positive micronuclei and results in a cell-intrinsic interferon response, as assessed by quantitative mass-spectrometry and gene expression profiling, and requires ASK1 and JNK signaling. Combined, our data reveals that micronuclei induced by loss of BRCA2 instigate a cGAS/STING-mediated interferon response, which encompasses re-wired TNFα signaling and enhances TNFα sensitivity.

The loss of homologous recombination (HR) genes such as BRCA1 and BRCA2 is deleterious to the survival of normal cells, yet it is tolerated in cancer cells. Here the authors identify TNFα signaling as a determinant of viability in BRCA2- inactivated cancer cells.

Identification of key genes and specific pathways potentially involved in androgen-independent, mitoxantrone-resistant prostate cancer

Background

Resistance to mitoxantrone (MTX), an anthracenedione antineoplastic agent used in advanced and metastatic androgen-refractory prostate cancer (PCa), seriously limits therapeutic success.

Methods

Xenografts from two human PCa cell lines (VCaP and CWR22) were established in male severe combined immunodeficiency mice, and MTX was administered, with or without concurrent castration, three times a week until tumors relapsed. Microarray technology was used to screen for differentially expressed genes (DEGs) in androgen-independent, MTX-resistant PCa xenografts. Gene expression profiles of MTX-treatment xenografts and their respective parental cell lines were performed using an Agilent whole human genome oligonucleotide microarray and analyzed using Ingenuity Pathway Analysis software.

Results

A total of 636 genes were differentially expressed (fold change ≥1.5; P<0.05) in MTX-resistant castration-resistant prostate cancer (CRPC) xenografts. Of these, 18 were selected to be validated and showed that most of these genes exhibited a transcriptional profile similar to that seen in the microarray (Pearson’s r=0.87). Western blotting conducted with a subset of genes deregulated in MTX-resistant CRPC tumors was shown through network analysis to be involved in androgen synthesis, drug efflux, ATP synthesis, and vascularization.

Conclusion

The present data provide insight into the genetic alterations underlying MTX resistance in androgen-independent PCa and highlight potential targets to improve therapeutic outcomes.

Mechanistic link between DNA damage sensing, repairing and signaling factors and immune signaling

Previously, DNA damage sensing, repairing and signaling machineries were thought to mainly suppress genomic instability in response to genotoxic stress. Emerging evidence indicates a crosstalk between DNA repair machinery and the immune system. In this chapter, we attempt to decipher the molecular choreography of how factors, including ATM, BRCA1, DNA-PK, FANCA/D2, MRE11, MUS81, NBS1, RAD51 and TREX1, of multiple DNA metabolic processes are directly or indirectly involved in suppressing cytosolic DNA sensing pathway-mediated immune signaling. We provide systematic details showing how different DDR factors' roles in modulating immune signaling are not direct, but are rather a consequence of their inherent ability to sense, repair and signal in response to DNA damage. Unexpectedly, most DDR factors negatively impact the immune system; that is, the immune system shows defective signaling if there are defects in DNA repair pathways. Thus, in addition to their known DNA repair and replication functions, DDR factors help prevent erroneous activation of immune signaling. A more precise understanding of the mechanisms by which different DDR factors function in immune signaling can be exploited to redirect the immune system for both preventing and treating autoimmunity, cellular senescence and cancer in humans.

The diverse consequences of aneuploidy

Aneuploidy, or imbalanced chromosome number, has profound effects on eukaryotic cells. In humans, aneuploidy is associated with various pathologies, including cancer, which suggests that it mediates a proliferative advantage under these conditions. Here, we discuss physiological changes triggered by aneuploidy, such as altered cell growth, transcriptional changes, proteotoxic stress, genomic instability and response to interferons, and how cancer cells adapt to the changing aneuploid genome.

Cytokinesis defects and cancer

Whole-genome and centrosome duplication as a consequence of cytokinesis failure can drive tumorigenesis in experimental model systems. However, whether cytokinesis failure is in fact an important cause of human cancers has remained unclear. In this Review, we summarize evidence that whole-genome-doubling events are frequently observed in human cancers and discuss the contribution that cytokinesis defects can make to tumorigenesis. We provide an overview of the potential causes of cytokinesis failure and discuss how tetraploid cells that are generated through cytokinesis defects are used in cancer as a transitory state on the route to aneuploidy. Finally, we discuss how cytokinesis defects can facilitate genetic diversification within the tumour to promote cancer development and could constitute the path of least resistance in tumour evolution.

Circulating tumor cells (CTCs) for the noninvasive monitoring and personalization of non-small cell lung cancer (NSCLC) therapies

Growing evidences for tumor heterogeneity confirm that single-tumor biopsies frequently fail to reveal the widespread mutagenic profile of tumor. Repeated biopsies are in most cases unfeasible, especially in advanced cancers. We describe here how circulating tumor cells (CTCs) isolated from minimally invasive blood sample might inform us about intratumor heterogeneity, tumor evolution and treatment resistance. We also discuss the advances of CTCs research, most notably in molecularly selected non-small cell lung cancer (NSCLC) patients, highlighting challenges and opportunities related to personalized therapy.

Replication stress: Driver and therapeutic target in genomically instable cancers

Genomically instable cancers are characterized by progressive loss and gain of chromosomal fragments, and the acquisition of complex genomic rearrangements. Such cancers, including triple-negative breast cancers and high-grade serous ovarian cancers, typically show aggressive behavior and lack actionable driver oncogenes. Increasingly, oncogene-induced replication stress or defective replication fork maintenance is considered an important driver of genomic instability. Paradoxically, while replication stress causes chromosomal instability and thereby promotes cancer development, it intrinsically poses a threat to cellular viability. Apparently, tumor cells harboring high levels of replication stress have evolved ways to cope with replication stress. As a consequence, therapeutic targeting of such compensatory mechanisms is likely to preferentially target cancers with high levels of replication stress and may prove useful in potentiating chemotherapeutic approaches that exert their effects by interfering with DNA replication. Here, we discuss how replication stress drives chromosomal instability, and the cell cycle-regulated mechanisms that cancer cells employ to deal with replication stress. Importantly, we discuss how mechanisms involving DNA structure-specific resolvases, cell cycle checkpoint kinases and mitotic processing of replication intermediates offer possibilities in developing treatments for difficult-to-treat genomically instable cancers.

Risks of aneuploidy induction from chemical exposure: Twenty years of collaborative research in Europe from basic science to regulatory implications

Although Theodor Boveri linked abnormal chromosome numbers and disease more than a century ago, an in-depth understanding of the impact of mitotic and meiotic chromosome segregation errors on cell proliferation and diseases is still lacking. This review reflects on the efforts and results of a large European research network that, from the 1980's until 2004, focused on protection against aneuploidy-inducing factors and tackled the following problems: 1) the origin and consequences of chromosome imbalance in somatic and germ cells; 2) aneuploidy as a result of environmental factors; 3) dose-effect relationships; 4) the need for validated assays to identify aneugenic factors and classify them according to their modes of action; 5) the need for reliable, quantitative data suitable for regulating exposure and preventing aneuploidy induction; 6) the need for mechanistic insight into the consequences of aneuploidy for human health. This activity brought together a consortium of experts from basic science and applied genetic toxicology to prepare the basis for defining guidelines and to encourage regulatory activities for the prevention of induced aneuploidy. Major strengths of the EU research programmes on aneuploidy were having a valuable scientific approach based on well-selected compounds and accurate methods that allow the determination of precise dose-effect relationships, reproducibility and inter-laboratory comparisons. The work was conducted by experienced scientists stimulated by a fascination with the complex scientific issues surrounding aneuploidy; a key strength was asking the right questions at the right time. The strength of the data permitted evaluation at the regulatory level. Finally, the entire enterprise benefited from a solid partnership under the lead of an inspired and stimulating coordinator. The research programme elucidated the major modes of action of aneugens, developed scientifically sound assays to assess aneugens in different tissues, and achieved the international validation of relevant assays with the goal of protecting human populations from aneugenic chemicals. The role of aneuploidy in tumorigenesis will require additional research, and the study of effects of exposure to multiple agents should become a priority. It is hoped that these reflections will stimulate the implementation of aneuploidy testing in national and OECD guidelines.

The frequencies of micronuclei, nucleoplasmic bridges and nuclear buds as biomarkers of genomic instability in patients with urothelial cell carcinoma

Bladder urothelial cell carcinoma (UCC) is an increasingly prevalent cancer worldwide, and thus, gaining a better understanding of its identifiable risk factors is a global priority. This study addressed this public health need with the understanding that cancer-initiating events, such as chromosome breakage, loss and rearrangement, can be reasonably used as biomarkers to evaluate an individual’s cancer risk. Overall, forty bladder cancer patients and twenty controls were evaluated for genomic instability. To the best of the investigators’ knowledge, this is the first study to perform micronucleus (MN) assays simultaneously in urothelial exfoliated cells (UEC), buccal exfoliated cells (BEC), and peripheral blood lymphocytes (PBL) in first-diagnosed, non-smoker bladder UCC patients. Additionally, the frequency of nucleoplasmic bridges (NPBs) and nuclear buds (NBUDs) in PBL was evaluated. The MN frequencies in UEC, BEC, and PBL, as well as the frequencies of NPBs and NBUDs, were significantly higher in patients than in controls. In conclusion, MN assays, particularly in UEC, may be used to identify individuals who are at high risk of developing UCC, as single or as additional triage test to UroVysion FISH test. Our results further validate the efficacy of biomarkers, such as MN, NPBs, and NBUDs, as predictors of genomic instability.

Aurora B kinase activity-dependent and -independent functions of the chromosomal passenger complex in regulating sister chromatid cohesion

The chromosomal passenger complex (CPC) is a master regulator of mitosis. CPC consists of inner centromere protein (INCENP), Survivin, Borealin, and the kinase Aurora B and plays key roles in regulating kinetochore-microtubule attachments and spindle assembly checkpoint signaling. However, the role of CPC in sister chromatid cohesion, mediated by the cohesin complex, remains incompletely understood. Here, we show that Aurora B kinase activity contributes to centromeric cohesion protection partly through promoting kinetochore localization of the kinase Bub1. Interestingly, disrupting the interaction of INCENP with heterochromatin protein 1 (HP1) in HeLa cells selectively weakens cohesion at mitotic centromeres without detectably reducing the kinase activity of Aurora B. Thus, through this INCENP-HP1 interaction, the CPC also protects centromeric cohesion independently of Aurora B kinase activity. Moreover, the requirement for the INCENP-HP1 interaction in centromeric cohesion protection can be bypassed by tethering HP1 to centromeres or by depleting the cohesin release factor Wapl. We provide further evidence suggesting that the INCENP-HP1 interaction protects centromeric cohesion by promoting the centromere localization of Haspin, a protein kinase that antagonizes Wapl activity at centromeres. Taken together, this study identifies Aurora B kinase activity-dependent and -independent roles for the CPC in regulating centromeric cohesion during mitosis in human cells.

Cisplatin-induced immune modulation in ovarian cancer mouse models with distinct inflammation profiles

The backbone of ovarian cancer treatment is platinum-based chemotherapy and aggressive surgical debulking. New therapeutic approaches using immunotherapy via immune checkpoint blockade, which have demonstrated clinical efficacy in other tumor types, have been less promising in ovarian cancer. To increase their clinical efficacy, checkpoint inhibitors are now being tested in clinical trials in combination with chemotherapy. Here, we evaluated the impact of cisplatin on tumor immunogenicity and its in vivo roles when used alone or in combination with anti-PD-L1, in two novel murine ovarian cancer cell models. The 2F8 and its platinum-resistant derivative 2F8cis model, display distinct inflammatory profiles and chemotherapy sensitivities, and mirror the primary and recurrent human disease, respectively. Acute and chronic exposure to cisplatin enhances tumor immunogenicity by increasing calreticulin, MHC class I, antigen presentation and T-cell infiltration. Cisplatin also upregulates PD-L1 expression in vitro and in vivo, demonstrating a dual, paradoxical immune modulatory effect and supporting the rationale for combination with immune checkpoint blockade. One of the pathways activated by cisplatin treatment is the cGAS/STING pathway. Chronic cisplatin treatment led to upregulation of cGAS and STING proteins in 2F8cis compared to parental 2F8 cells, while acute exposure to cisplatin further increases cGAS and STING levels in both 2F8 and 2F8cis cells. Overexpression of cGAS/STING modifies tumor immunogenicity by upregulating PD-L1, MHC I and calreticulin in tumor cells. Anti-PD-L1 alone in a platinum-sensitive model or with cisplatin in a platinum-resistant model increases survival. These studies have high translational potential in ovarian cancer.

Hypermethylation of DMTN promotes the metastasis of colorectal cancer cells by regulating the actin cytoskeleton through Rac1 signaling activation

Background

Colorectal cancer (CRC) is one of the most common digestive malignant tumors, and DMTN is a transcriptionally differentially expressed gene that was identified using CRC mRNA sequencing data from The Cancer Genome Atlas (TCGA). Our preliminary work suggested that the expression of DMTN was downregulated in CRC, and the Rac1 signaling pathway was significantly enriched in CRC tissues with low DMTN expression. However, the specific functions and underlying molecular mechanisms of DMTN in the progression of CRC and the upstream factors regulating the downregulation of the gene remain unclear.

Methods

DMTN expression was analyzed in CRC tissues, and the relationship between DMTN expression and the clinicopathological parameters was analyzed. In vitro and in vivo experimental models were used to detect the effects of DMTN dysregulation on invasion and metastasis of CRC cells. GSEA assay was performed to explore the mechanism of DMTN in invasion and metastasis of CRC. Westernblot, Co-IP and GST-Pull-Down assay were used to detect the interaction between DMTN and ARHGEF2, as well as the activation of the RAC1 signaling. Bisulfite genomic sequence (BSP) assay was used to test the degree of methylation of DMTN gene promoter in CRC tissues.

Results

We found that the expression of DMTN was significantly decreased in CRC tissues, and the downregulation of DMTN was associated with advanced progression and poor survival and was regarded as an independent predictive factor of CRC patient prognosis. The overexpression of DMTN inhibited, while the knockdown of DMTN promoted, invasion and metastasis in CRC cells. Moreover, hypermethylation and the deletion of DMTN relieved binding to the ARHGEF2 protein, activated the Rac1 signaling pathway, regulated actin cytoskeletal rearrangements, and promoted the invasion and metastasis of CRC cells.

Conclusion

Our study demonstrated that the downregulation of DMTN promoted the metastasis of colorectal cancer cells by regulating the actin cytoskeleton through RAC1 signaling activation, potentially providing a new therapeutic target to enable cancer precision medicine for CRC patients.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0958-1) contains supplementary material, which is available to authorized users.

Nanoscale extracellular vesicle-derived DNA is superior to circulating cell-free DNA for mutation detection in early-stage non-small-cell lung cancer

Background

The comparison between relatively intact nanoscale extracellular vesicle-derived DNA (nEV-DNA) and fragmented circulating cell-free DNA (cfDNA) in mutation detection among patients with non-small-cell lung cancer (NSCLC) has not been carried out yet, and thus deserves investigation.

Patients and methods

Both nEV-DNA and cfDNA was obtained from 377 NSCLC patients with known EGFR mutation status and 69 controls. The respective EGFRE19del/T790M/L858R mutation status was interrogated with amplification-refractory-mutation-system-based PCR assays (ARMS-PCR).

Results

Neither nEV-DNA nor cfDNA levels show a strong correlation with tumor volumes. There is no correlation between cfDNA and nEV-DNA levels either. The detection sensitivity of nEV-DNA and cfDNA using ARMS-PCR in early-stage NSCLC was 25.7% and 14.2%, respectively, with 96.6% and 91.7% specificity, respectively. In late-stage NSCLC, both nEV-DNA and cfDNA show ∼80% sensitivity and over 95% specificity.

Conclusions

nEV-DNA is superior to cfDNA for mutation detection in early-stage NSCLC using ARMS-PCR. However, the advantages vanish in late-stage NSCLC.

Genomic loss of heterozygosity and survival in the REAL3 trial

Background

Homologous recombination deficiency (HRD) measured using a genomic signature for loss of heterozygosity (LOH) predicts benefit from rucaparib in ovarian cancer. We hypothesized that some oesophagogastric cancers will have high-LOH which would be prognostic in patients treated with platinum chemotherapy.

Methods

Diagnostic biopsy DNA from patients treated in the REAL3 trial was sequenced using the Foundation Medicine T5 next-generation sequencing (NGS) assay. An algorithm quantified the percentage of interrogable genome with LOH. Multidimensional optimization was performed to identify a cut-off dichotomizing the population into LOH-high and low groups associated with differential survival outcomes.

Results

Of 158 available samples, 117 were successfully sequenced; LOH was derived for 74 of these. A cut-off of 21% genomic LOH defined an LOH-high subgroup (n=10, 14% of population) who had median overall survival (OS) of 18.3 months (m) versus 11m for the LOH-low group (HR 0.55 95% CI 0.19-0.97, p= 0.10). Progression free survival (PFS) for LOH-high and LOH-low groups was 10.7m and 7.3m (HR 0.61 (95% CI 0.21 – 1.09, p=0.09). Sensitivity analysis censoring operated patients (n=4), demonstrated OS of 18.3m vs. 10.2m (HR 0.43, 95% CI (0.20-0.92), p=0.02; PFS was 10.5m vs. 7.2m (HR 0.55, (95% CI 0.26-1.17), p=0.09 for LOH-high and LOH-low.

Conclusion

HRD assessment using an algorithmically derived LOH signature on a standard NGS panel identifies oesophagogastric cancer patients with high LOH who have prolonged survival when treated with platinum chemotherapy. Validation work will determine the signature's predictive value in patients treated with a PARP inhibitor and with platinum chemotherapy.

PRL-3 Promotes Ubiquitination and Degradation of AURKA and Colorectal Cancer Progression via Dephosphorylation of FZR1

The oncogenic phosphatase PRL-3 is highly expressed in metastatic colorectal cancer but not in nonmetastatic colorectal cancer or noncolorectal cancer metastatic cancers. Although the proinvasive capacity of PRL-3 has been validated in multiple types of cancer, its impact on colorectal cancer progression and the underlying mechanisms remain poorly understood. Here, we report that overexpressed PRL-3 stimulates G₂-M arrest, chromosomal instability (CIN), self-renewal, and growth of colorectal cancer cells in xenograft models, while colorectal cancer cell proliferation is decreased. PRL-3-induced G₂-M arrest was associated with decreased expression of Aurora kinase A (AURKA). PRL-3-promoted slow proliferation, CIN, self-renewal, and growth in xenografts were counteracted by ectopic expression of AURKA. Conversely, knockdown of PRL-3 resulted in low proliferation, S-phase arrest, impaired self-renewal, increased apoptosis, and diminished xenograft growth independently of AURKA. Analysis of colorectal cancer specimens showed that expression of PRL-3 was associated with high status of CIN and poor prognosis, which were antagonized by expression of AURKA. PRL-3 enhanced AURKA ubiquitination and degradation in a phosphatase-dependent fashion. PRL-3 interacted with AURKA and FZR1, a regulatory component of the APC/C^FZR1 complex. Destabilization of AURKA by PRL-3 required PRL-3-mediated dephosphorylation of FZR1 and assembly of the APC/C^FZR1 complex. Our study suggests that PRL-3-regulated colorectal cancer progression is collectively determined by distinct malignant phenotypes and further reveals PRL-3 as an essential regulator of APC/C^FZR1 in controlling the stability of AURKA. SIGNIFICANCE: Dephosphorylation of FZR1 by PRL-3 facilitates the activity of APC/C^FZR1 by destabilizing AURKA, thus influencing aggressive characteristics and overall progression of colorectal cancer.

STING Promotes Homeostasis via Regulation of Cell Proliferation and Chromosomal Stability

Given the integral role of stimulator of interferon genes (STING, TMEM173) in the innate immune response, its loss or impairment in cancer is thought to primarily affect antitumor immunity. Here we demonstrate a role for STING in the maintenance of cellular homeostasis through regulation of the cell cycle. Depletion of STING in human and murine cancer cells and tumors resulted in increased proliferation compared with wild-type controls. Microarray analysis revealed genes involved in cell-cycle regulation are differentially expressed in STINGko compared with WT MEFs. STING-mediated regulation of the cell cycle converged on NFκB- and p53-driven activation of p21. The absence of STING led to premature activation of cyclin-dependent kinase 1 (CDK1), early onset to S-phase and mitosis, and increased chromosome instability, which was enhanced by ionizing radiation. These results suggest a pivotal role for STING in maintaining cellular homeostasis and response to genotoxic stress. SIGNIFICANCE: These findings provide clear mechanistic understanding of the role of STING in cell-cycle regulation, which may be exploited in cancer therapy because most normal cells express STING, while many tumor cells do not.See related commentary by Gius and Zhu, p. 1295.

The molecular origins and pathophysiological consequences of micronuclei: New insights into an age-old problem

Micronuclei (MN), the small nucleus-like bodies separated from the primary nucleus, can exist in cells with numerical and/or structural chromosomal aberrations in apparently normal tissues and more so in tumors in humans. While MN have been observed for over 100 years, they were merely and constantly considered as passive indicators of chromosome instability (CIN) for a long time. Relatively little is known about the molecular origins and biological consequences of MN. Rapid technological advances are helping to close these gaps. Very recent studies provide exciting evidence that MN act as key platform for chromothripsis and a trigger of innate immune response, suggesting that MN could affect cellular functions by both genetic and nongenetic means. These previously unappreciated findings have reawakened widespread interests in MN. In this review, the diverse mechanisms leading to MN generation and the complex fate profiles of MN are discussed, together with the evidence for their contribution to CIN, inflammation, senescence and cell death. Moreover, we put this knowledge together into a speculative perspective on how MN may be responsible for cancer development and how their presence may influence the choice of treatment. We suggest that the heterogeneous responses to MN may function physiological to ensure the arrestment, elimination and immune clearance of damaged cells, but pathologically, may enable the survival and oncogenic transformation of cells bearing CIN. These insights not only underscore the complexity of MN biology, but also raise a host of new questions and provide fertile ground for future research.

Role of the cGAS-STING pathway in cancer development and oncotherapeutic approaches

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway mediates anti-microbial innate immunity by inducing the production of type I interferons (IFNs) and inflammatory cytokines upon recognition of microbial DNA. Recent studies reveal that self-DNA from tumors and by-products of genomic instability also activates the cGAS-STING pathway and either promotes or inhibits tumor development. This has led to the development of cancer therapeutics using STING agonists alone and in combination with conventional cancer treatment or immune checkpoint targeting. On the other hand, for cancers lacking the cGAS-STING pathway and thus a regular innate immunity response, oncolytic virus therapy has been shown to have therapeutic potential. We here review and discuss the dichotomous roles of the cGAS-STING pathway in cancer development and therapeutic approaches.

Tolerance of Chromosomal Instability in Cancer: Mechanisms and Therapeutic Opportunities

Chromosomal instability (CIN) is the result of ongoing changes in the number (aneuploidy) and structure of chromosomes. CIN is induced by chromosome missegregation in mitosis and leads to karyotypic diversity within the cancer cell population, thereby adding to intratumor heterogeneity. Regardless of the overall pro-oncogenic function of CIN, its onset is typically detrimental for cell fitness and thus tumors must develop CIN-tolerance mechanisms in order to propagate. There is overwhelming genetic and functional evidence linking mutations in the tumor suppressor TP53 with CIN-tolerance. However, the pathways leading to p53 activation following chromosome missegregation remain controversial. Recently, additional mechanisms have been identified in CIN-surveillance, resulting in a more complex network of pathways acting independently or in cooperation with p53. Tolerance might also be achieved by modifying aspects of the cancer cell physiology in order to attenuate CIN or by adaptation to the consequences of aneuploid karyotypes. In this review, we summarize the current knowledge about p53-dependent and -independent mechanisms of CIN-tolerance in cancer, the adaptations observed in CIN cells buffering CIN levels, its consequences for cellular homeostasis, and the potential of exploiting these adaptations in order to design new cancer therapies.

Expression analysis of a panel of cancer-testis antigens in bladder cancer

AIM

Cancer-testis antigens (CTAs) have specific expression in gametogenic tissues and aberrant expression in cancers. Materials & methods: We assessed expression of five testis-specific genes namely KIF2B, CST8, TMEM225, RBM46, OAZ3 in bladder cancer tissues, adjacent non-neoplastic tissues and urinary cell pellets (UCPs) of bladder cancer patients compared with nonmalignant conditions.

RESULTS

Expressions of all CTAs were higher in UCPs of bladder cancer patients compared with nonmalignant conditions. RBM46 expression in UCPs was higher in patients with recurrent tumors compared with primary tumors and in patients without hematuria compared with those having hematuria. TMEM225 expression in tumoral tissues was higher in high-grade tumors compared with low-grade tumors.

CONCLUSION

Expression analysis of CTAs in UCP might provide diagnostic information about bladder cancer.

The DNA damage response in immunotherapy and radiation

Purpose

Deficiencies in DNA damage repair (DDR) and response represent a common alteration in tumors, and exploitation of this feature using therapeutics has become more prominent.

Methods and materials

Recent work has highlighted the important interaction between DDR defects, as well as DDR targeting agents such as radiation and the immunogenicity of the tumor. This relationship emphasizes the potential for combination therapeutics with immune checkpoint inhibitors (ICI). Somatic mutations and DDR defects are some of the strongest predictors of response to ICI.

Results

This review highlights the interplay among DDR pathways, ionizing radiation, and ICI efficacy. The mechanisms of radiation immunogenicity, including the cytosolic DNA sensing cGAS/STING pathways, are also described.

Conclusions

A greater mechanistic understanding of the complex interaction between the DNA damage response and the immune system will expand the therapeutic potential of immunotherapy for patients with advanced cancer.

From Colitis to Cancer: An Evolutionary Trajectory That Merges Maths and Biology

Patients with inflammatory bowel disease have an increased risk of developing colorectal cancer, and this risk is related to disease duration, extent, and cumulative inflammation burden. Carcinogenesis follows the principles of Darwinian evolution, whereby somatic cells acquire genomic alterations that provide them with a survival and/or growth advantage. Colitis represents a unique situation whereby routine surveillance endoscopy provides a serendipitous opportunity to observe somatic evolution over space and time in vivo in a human organ. Moreover, somatic evolution in colitis is evolution in the ‘fast lane': the repeated rounds of inflammation and mucosal healing that are characteristic of the disease accelerate the evolutionary process and likely provide a strong selective pressure for inflammation-adapted phenotypic traits. In this review, we discuss the evolutionary dynamics of pre-neoplastic clones in colitis with a focus on how measuring their evolutionary trajectories could deliver a powerful way to predict future cancer occurrence. Measurements of somatic evolution require an interdisciplinary approach that combines quantitative measurement of the genotype, phenotype and the microenvironment of somatic cells–paying particular attention to spatial heterogeneity across the colon–together with mathematical modeling to interpret these data within an evolutionary framework. Here we take a practical approach in discussing how and why the different “evolutionary ingredients” can and should be measured, together with our viewpoint on subsequent translation into clinical practice. We highlight the open questions in the evolution of colitis-associated cancer as a stimulus for future work.

Suppression of STING Associated with LKB1 Loss in KRAS-Driven Lung Cancer

KRAS-driven lung cancers frequently inactivate TP53 and/or STK11/LKB1, defining tumor subclasses with emerging clinical relevance. Specifically, KRAS-LKB1 (KL)-mutant lung cancers are particularly aggressive, lack PD-L1, and respond poorly to immune checkpoint blockade (ICB). The mechanistic basis for this impaired immunogenicity, despite the overall high mutational load of KRAS-mutant lung cancers, remains obscure. Here, we report that LKB1 loss results in marked silencing of stimulator of interferon genes (STING) expression and insensitivity to cytoplasmic double-strand DNA (dsDNA) sensing. This effect is mediated at least in part by hyperactivation of DNMT1 and EZH2 activity related to elevated S-adenylmethionine levels and reinforced by DNMT1 upregulation. Ectopic expression of STING in KL cells engages IRF3 and STAT1 signaling downstream of TBK1 and impairs cellular fitness, due to the pathologic accumulation of cytoplasmic mitochondrial dsDNA associated with mitochondrial dysfunction. Thus, silencing of STING avoids these negative consequences of LKB1 inactivation, while facilitating immune escape. SIGNIFICANCE: Oncogenic KRAS-mutant lung cancers remain treatment-refractory and are resistant to ICB in the setting of LKB1 loss. These results begin to uncover the key underlying mechanism and identify strategies to restore STING expression, with important therapeutic implications because mitochondrial dysfunction is an obligate component of this tumor subtype.See related commentary by Corte and Byers, p. 16.This article is highlighted in the In This Issue feature, p. 1.

SAMHD1 and the innate immune response to cytosolic DNA during DNA replication

Cytosolic DNA of endogenous or exogenous origin is sensed by the cGAS-STING pathway to activate innate immune responses. Besides microbial DNA, this pathway detects self-DNA in the cytoplasm of damaged or abnormal cells and plays a central role in antitumor immunity. The mechanism by which cytosolic DNA accumulates under genotoxic stress conditions is currently unclear, but recent studies on factors mutated in the Aicardi-Goutières syndrome cells, such as SAMHD1, RNase H2 and TREX1, are shedding new light on this key process. In particular, these studies indicate that the rupture of micronuclei and the release of ssDNA fragments during the processing of stalled replication forks and chromosome breaks represent potent inducers of the cGAS-STING pathway.

Activating the Nucleic Acid-Sensing Machinery for Anticancer Immunity

Nucleic acid sensing pathways have likely evolved as part of a broad pathogen sensing strategy intended to discriminate infectious agents and initiate appropriate innate and adaptive controls. However, in the absence of infectious agents, nucleic acid sensing pathways have been shown to play positive and negative roles in regulating tumorigenesis, tumor progression and metastatic spread. Understanding the normal biology behind these pathways and how they are regulated in malignant cells and in the tumor immune environment can help us devise strategies to exploit nucleic acid sensing to manipulate anti-cancer immunity.

Analysis of the role of GSK3 in the mitotic checkpoint

The mitotic checkpoint ensures proper chromosome segregation; defects in this checkpoint can lead to aneuploidy, a hallmark of cancer. The mitotic checkpoint blocks progression through mitosis as long as chromosomes remain unattached to spindle microtubules. Unattached kinetochores induce the formation of a mitotic checkpoint complex (MCC) composed of Mad2, BubR1, Bub1 and Bub3 which inhibits anaphase onset. Spindle toxins induce prolonged mitotic arrest by creating persistently unattached kinetochores which trigger MCC formation. We find that the multifunctional ser/thr kinase, glycogen synthase kinase 3 (GSK3) is required for a strong mitotic checkpoint. Spindle toxin-induced mitotic arrest is relieved by GSK3 inhibitors SB 415286 (SB), RO 318220 (RO) and lithium chloride. Similarly, targeting GSK3β with knockout or RNAi reduced mitotic arrest in the presence of Taxol. GSK3 was required for optimal localization of Mad2, BubR1, and Bub1 at kinetochores and for optimal assembly of the MCC in spindle toxin-arrested cells. The WNT- and PI3K/Akt signaling pathways negatively regulate GSK3β activity. Inhibition of WNT and PI3K/Akt signaling, in the presence of Taxol, induced a longer mitotic arrest compared to Taxol alone. Our observations provide novel insight into the regulation of the mitotic checkpoint and its connection to growth-signaling pathways.

Roles for the IKK-Related Kinases TBK1 and IKKε in Cancer

While primarily studied for their roles in innate immune response, the IκB kinase (IKK)-related kinases TANK-binding kinase 1 (TBK1) and IKKε also promote the oncogenic phenotype in a variety of cancers. Additionally, several substrates of these kinases control proliferation, autophagy, cell survival, and cancer immune responses. Here we review the involvement of TBK1 and IKKε in controlling different cancers and in regulating responses to cancer immunotherapy.

A Markov chain for numerical chromosomal instability in clonally expanding populations

Cancer cells frequently undergo chromosome missegregation events during mitosis, whereby the copies of a given chromosome are not distributed evenly among the two daughter cells, thus creating cells with heterogeneous karyotypes. A stochastic model tracing cellular karyotypes derived from clonal populations over hundreds of generations was recently developed and experimentally validated, and it was capable of predicting favorable karyotypes frequently observed in cancer. Here, we construct and study a Markov chain that precisely describes karyotypic evolution during clonally expanding cancer cell populations. The Markov chain allows us to directly predict the distribution of karyotypes and the expected size of the tumor after many cell divisions without resorting to computationally expensive simulations. We determine the limiting karyotype distribution of an evolving tumor population, and quantify its dependency on several key parameters including the initial karyotype of the founder cell, the rate of whole chromosome missegregation, and chromosome-specific cell viability. Using this model, we confirm the existence of an optimal rate of chromosome missegregation probabilities that maximizes karyotypic heterogeneity, while minimizing the occurrence of nullisomy. Interestingly, karyotypic heterogeneity is significantly more dependent on chromosome missegregation probabilities rather than the number of cell divisions, so that maximal heterogeneity can be reached rapidly (within a few hundred generations of cell division) at chromosome missegregation rates commonly observed in cancer cell lines. Conversely, at low missegregation rates, heterogeneity is constrained even after thousands of cell division events. This leads us to conclude that chromosome copy number heterogeneity is primarily constrained by chromosome missegregation rates and the risk for nullisomy and less so by the age of the tumor. This model enables direct integration of karyotype information into existing models of tumor evolution based on somatic mutations.

Chromosomal instability (CIN) is a hallmark of cancer and it results from persistent chromosome segregation errors during cell division. CIN has been shown to play a key role in drug resistance and tumor metastasis. While our understanding of CIN on the cellular level has grown over the past decade, our ability to predict the behavior of tumors containing billions of cells remains limited due to the paucity of adequate mathematical models. Here, we develop a Markov-chain model that is capable of providing exact solutions for long-term chromosome copy number distributions during tumor growth. Using this model we confirm the presence of optimal chromosome missegregation rates that balance genomic heterogeneity required for tumor evolution and survival. Interestingly, we show that chromosome copy number heterogeneity is primarily influenced by the rate of chromosome segregation errors rather than the age of the tumor. At chromosome missegregation rates frequently observed in cancer, tumors can acquire maximal genomic heterogeneity after a few hundred cell divisions. This model enables the integration of selection imparted by CIN into existing models of tumor evolution based on somatic mutations to explore their mutual effects.

Cytosolic DNA Sensing in Organismal Tumor Control

Besides constituting a first layer of defense against microbial challenges, the detection of cytosolic DNA is fundamental for mammalian organisms to control malignant transformation and tumor progression. The accumulation of DNA in the cytoplasm can initiate the proliferative inactivation (via cellular senescence) or elimination (via regulated cell death) of neoplastic cell precursors. Moreover, cytosolic DNA sensing is intimately connected to the secretion of cytokines that support innate and adaptive antitumor immunity. Here, we discuss the molecular mechanisms whereby cytosolic DNA enables cell-intrinsic and -extrinsic oncosuppression, and their relevance for the development of novel therapeutic approaches that reinstate anticancer immunosurveillance.

The Multifaceted Role of Chromosomal Instability in Cancer and Its Microenvironment

Chromosomal instability (CIN) is a hallmark of human cancer, and it is associated with poor prognosis, metastasis, and therapeutic resistance. CIN results from errors in chromosome segregation during mitosis, leading to structural and numerical chromosomal abnormalities. In addition to generating genomic heterogeneity that acts as a substrate for natural selection, CIN promotes inflammatory signaling by introducing double-stranded DNA into the cytosol, engaging the cGAS-STING anti-viral pathway. These multipronged effects distinguish CIN as a central driver of tumor evolution and as a genomic source for the crosstalk between the tumor and its microenvironment, in the course of immune editing and evasion.

Copy number signatures and mutational processes in ovarian carcinoma

The genomic complexity of profound copy number aberrations has prevented effective molecular stratification of ovarian cancers. Here, to decode this complexity, we derived copy number signatures from shallow whole-genome sequencing of 117 high-grade serous ovarian cancer (HGSOC) cases, which were validated on 527 independent cases. We show that HGSOC comprises a continuum of genomes shaped by multiple mutational processes that result in known patterns of genomic aberration. Copy number signature exposures at diagnosis predict both overall survival and the probability of platinum-resistant relapse. Measurement of signature exposures provides a rational framework to choose combination treatments that target multiple mutational processes.

Non-canonical NF-κB Antagonizes STING Sensor-Mediated DNA Sensing in Radiotherapy

The NF-κB pathway plays a crucial role in supporting tumor initiation, progression, and radioresistance of tumor cells. However, the role of the NF-κB pathway in radiation-induced anti-tumor host immunity remains unclear. Here we demonstrated that inhibiting the canonical NF-κB pathway dampened the therapeutic effect of ionizing radiation (IR), whereas non-canonical NF-κB deficiency promoted IR-induced anti-tumor immunity. Mechanistic studies revealed that non-canonical NF-κB signaling in dendritic cells (DCs) was activated by the STING sensor-dependent DNA-sensing pathway. By suppressing recruitment of the transcription factor RelA onto the Ifnb promoter, activation of the non-canonical NF-κB pathway resulted in decreased type I IFN expression. Administration of a specific inhibitor of the non-canonical NF-κB pathway enhanced the anti-tumor effect of IR in murine models. These findings reveal the potentially interactive roles for canonical and non-canonical NF-κB pathways in IR-induced STING-IFN production and provide an alternative strategy to improve cancer radiotherapy.

Ribonucleotide Excision Repair Is Essential to Prevent Squamous Cell Carcinoma of the Skin

Because of imperfect discrimination against ribonucleoside triphosphates by the replicative DNA polymerases, large numbers of ribonucleotides are incorporated into the eukaryotic nuclear genome during S-phase. Ribonucleotides, by far the most common DNA lesion in replicating cells, destabilize the DNA, and an evolutionarily conserved DNA repair machinery, ribonucleotide excision repair (RER), ensures ribonucleotide removal. Whereas complete lack of RER is embryonically lethal, partial loss-of-function mutations in the genes encoding subunits of RNase H2, the enzyme essential for initiation of RER, cause the SLE-related type I interferonopathy Aicardi-Goutières syndrome. Here, we demonstrate that selective inactivation of RER in mouse epidermis results in spontaneous DNA damage and epidermal hyperproliferation associated with loss of hair follicle stem cells and hair follicle function. The animals developed keratinocyte intraepithelial neoplasia and invasive squamous cell carcinoma with complete penetrance, despite potent type I interferon production and skin inflammation. These results suggest that compromises to RER-mediated genome maintenance might represent an important tumor-promoting principle in human cancer.Significance: Selective inactivation of ribonucleotide excision repair by loss of RNase H2 in the murine epidermis results in spontaneous DNA damage, type I interferon response, skin inflammation, and development of squamous cell carcinoma. Cancer Res; 78(20); 5917-26. ©2018 AACR.

Preserving replication fork integrity and competence via the homologous recombination pathway

Flaws in the DNA replication process have emerged as a leading driver of genome instability in human diseases. Alteration to replication fork progression is a defining feature of replication stress and the consequent failure to maintain fork integrity and complete genome duplication within a single round of S-phase compromises genetic integrity. This includes increased mutation rates, small and large scale genomic rearrangement and deleterious consequences for the subsequent mitosis that result in the transmission of additional DNA damage to the daughter cells. Therefore, preserving fork integrity and replication competence is an important aspect of how cells respond to replication stress and avoid genetic change. Homologous recombination is a pivotal pathway in the maintenance of genome integrity in the face of replication stress. Here we review our recent understanding of the mechanisms by which homologous recombination acts to protect, restart and repair replication forks. We discuss the dynamics of these genetically distinct functions and their contribution to faithful mitoticsegregation.

Copy number signatures and mutational processes in ovarian carcinoma

The genomic complexity of profound copy number aberrations has prevented effective molecular stratification of ovarian cancers. Here, to decode this complexity, we derived copy number signatures from shallow whole-genome sequencing of 117 high-grade serous ovarian cancer (HGSOC) cases, which were validated on 527 independent cases. We show that HGSOC comprises a continuum of genomes shaped by multiple mutational processes that result in known patterns of genomic aberration. Copy number signature exposures at diagnosis predict both overall survival and the probability of platinum-resistant relapse. Measurement of signature exposures provides a rational framework to choose combination treatments that target multiple mutational processes.