Starving cancer cells to enhances DNA damage and immunotherapy response.

Prostate cancer (PCa) poses significant challenges in treatment, particularly when it progresses to a metastatic, castrate-resistant state. Conventional therapies, including chemotherapy, radiotherapy, and hormonal treatments, often fail due to toxicities, off-target effects, and acquired resistance. This research perspective defines an alternative therapeutic strategy focusing on the metabolic vulnerabilities of PCa cells, specifically their reliance on non-essential amino acids such as cysteine. Using an engineered enzyme cyst(e)inase to deplete the cysteine/cystine can induce oxidative stress and DNA damage in cancer cells. This depletion elevates reactive oxygen species (ROS) levels, disrupts glutathione synthesis, and enhances DNA damage, leading to cancer cell death. The combinatorial use of cyst(e)inase with agents targeting antioxidant defenses, such as thioredoxins, further amplifies ROS accumulation and cytotoxicity in PCa cells. Overall, in this perspective provides a compressive overview of the previous work on manipulating amino acid metabolism and redox balance modulate the efficacy of DNA repair-targeted and immune checkpoint blockade therapies in prostate cancer.

Dysregulation of base excision repair factors associated with low tumor immunogenicity in head and neck cancer: implication for immunotherapy.

Background: Head and neck squamous carcinoma (HNSCC) is caused by different exogenous risk factors including smoking cigarettes, alcohol consumption, and HPV infection. Base excision repair (BER) is the frontline to repair oxidative DNA damage, which is initiated by the DNA N-glycosylase proteins (OGG1) and other BER factors including DNA polymerase ß (POLB). Objective: Explore whether BER genes' (OGG1, POLB) overexpression in HNSCC alters genomic integrity, immunogenicity, and its role in prognostic value. Design: RNA sequencing (RNA-Seq) and clinical information (age, gender, histological grade, survival status, and stage) of 530 patients of HNSCC were retrieved from the Cancer Genome Atlas. Patients' data are categorized HPV positive or negative to analyze the tumor data including the tumor stage, POLB, and OGG1 gene expression. Methods: RNA-Seq of HNSCC data retrieved and mutation count and aneuploidy score were compared using an unpaired t-test. The TIMER algorithm was used to calculate the tumor abundance of six infiltrating immune cells (CD4+ T cells, CD8+ T cells, B cells, neutrophils, macrophages, and dendritic cells) based on RNA-Seq expression profile data. The correlation between the POLB, OGG1, and immune cells was calculated by Spearman correlation analysis using TIMER 2.0. Results: Our data analysis reveals that BER genes frequently overexpressed in HNSCC tumors and increase mutation count. In addition, OGG1 and POLB overexpression are associated with low infiltration of immune cells, low immune checkpoint gene expression (PD-1, cytotoxic T-lymphocyte antigen 4, program death ligand 1, and program death ligand 2), and innate immune signaling genes. Furthermore, dysregulated BER factors in Human papillomavirus (HPV) positive tumors had better overall survival. Conclusion: Our analysis suggests that dysregulation of the BER genes panel might be a potential prognosis marker and/or an attractive target for an immune checkpoint blockade in HNSCC cancers. However, our observation still requires further experimental-based scientific validation studies.

Inhibition of DHODH Enhances Replication-Associated Genomic Instability and Promotes Sensitivity in Endometrial Cancer.

Endometrial carcinoma (EC) is the most common gynecological malignancy in the United States. De novo pyrimidine synthesis pathways generate nucleotides that are required for DNA synthesis. Approximately 38% of human endometrial tumors present with an overexpression of human dihydroorotate dehydrogenase (DHODH). However, the role of DHODH in cancer cell DNA replication and its impact on modulating a treatment response is currently unknown. Here, we report that endometrial tumors with overexpression of DHODH are associated with a high mutation count and chromosomal instability. Furthermore, tumors with an overexpression of DHODH show significant co-occurrence with mutations in DNA replication polymerases, which result in a histologically high-grade endometrial tumor. An in vitro experiment demonstrated that the inhibition of DHODH in endometrial cancer cell lines significantly induced replication-associated DNA damage and hindered replication fork progression. Furthermore, endometrial cancer cells were sensitive to the DHODH inhibitor either alone or in combination with the Poly (ADP-ribose) polymerase 1 inhibitor. Our findings may have important clinical implications for utilizing DHODH as a potential target to enhance cytotoxicity in high-grade endometrial tumors.

Cysteine depletion sensitizes prostate cancer cells to agents that enhance DNA damage and to immune checkpoint inhibition.

BACKGROUND: Prostate Cancer (PCa) represents one of the most commonly diagnosed neoplasms in men and is associated with significant morbidity and mortality. Therapy resistance and significant side effects of current treatment strategies indicate the need for more effective agents to treat both androgen-dependent and androgen-independent PCa. In earlier studies, we demonstrated that depletion of L-cysteine/cystine with an engineered human enzyme, Cyst(e)inase, increased intracellular ROS levels and inhibited PCa growth in vitro and in vivo. The current study was conducted to further explore the mechanisms and potential combinatorial approaches with Cyst(e)inase for treatment of PCa. METHODS: DNA single strand breaks and clustered oxidative DNA damage were evaluated by alkaline comet assay and pulsed field gel electrophoresis, respectively. Neutral comet assay and immunofluorescence staining was used to measure DNA double strand breaks. Cell survival and reactive oxygen species level were measured by crystal violet assay and DCFDA staining, respectively. Western blot was used to determine protein expression. FACS analyses were preformed for immune cell phenotyping. Allograft and xenograft tumor models were used for assessing effects on tumor growth. RESULTS: PCa cells treated with Cyst(e)inase lead to DNA single and double strand breaks resulted from clustered oxidative DNA damage (SSBs and DSBs). Cyst(e)inase in combination with Auranofin, a thioredoxin reductase inhibitor, further increased intracellular ROS and DNA DSBs and synergistically inhibited PCa cell growth in vitro and in vivo. A combination of Cyst(e)inase with a PARP inhibitor (Olaparib) also increased DNA DSBs and synergistically inhibited PCa cell growth in vitro and in vivo without additional ROS induction. Knockdown of BRCA2 in PCa cells increased DSBs and enhanced sensitivity to Cyst(e)inase. Finally, Cyst(e)inase treatment altered tumor immune infiltrates and PD-L1 expression and sensitized PCa cells to anti-PD-L1 treatment. CONCLUSIONS: The current results demonstrate the importance of oxidative DNA damage either alone or in combination for Cyst(e)inase-induced anticancer activity. Furthermore, cysteine/cystine depletion alters the tumor immune landscape favoring enhanced immune checkpoint inhibition targeting PD-L1. Thus, combinatorial approaches with Cyst(e)inase could lead to novel therapeutic strategies for PCa.

Role of Base Excision Repair in Innate Immune Cells and Its Relevance for Cancer Therapy.

Innate immunity is critical for immediate recognition and elimination of invading pathogens or defense against cancer cell growth. Dysregulation of innate immune systems is associated with the pathogenesis of different types of inflammatory diseases, including cancer. In addition, the maintenance of innate immune cells' genomic integrity is crucial for the survival of all organisms. Oxidative stress generated from innate immune cells may cause self-inflicted DNA base lesions as well as DNA damage on others neighboring cells, including cancer cells. Oxidative DNA base damage is predominantly repaired by base excision repair (BER). BER process different types of DNA base lesions that are presented in cancer and innate immune cells to maintain genomic integrity. However, mutations in BER genes lead to impaired DNA repair function and cause insufficient genomic integrity. Moreover, several studies have implicated that accumulation of DNA damage leads to chromosomal instability that likely activates the innate immune signaling. Furthermore, dysregulation of BER factors in cancer cells modulate the infiltration of innate immune cells to the tumor microenvironment. In the current review, the role of BER in cancer and innate immune cells and its impact on innate immune signaling within the tumor microenvironment is summarized. This is a special issue that focuses on DNA damage and cancer therapy to demonstrate how BER inhibitor or aberrant repair modulates innate inflammatory response and impact immunotherapy approaches. Overall, the review provides substantial evidence to understand the impact of BER in innate immune response dynamics within the current immune-based therapeutic strategy.

Defective DNA polymerase beta invoke a cytosolic DNA mediated inflammatory response.

Base excision repair (BER) has evolved to maintain the genomic integrity of DNA following endogenous and exogenous agent induced DNA base damage. In contrast, aberrant BER induces genomic instability, promotes malignant transformation and can even trigger cancer development. Previously, we have shown that deoxyribo-5'-phosphate (dRP) lyase deficient DNA polymerase beta (POLB) causes replication associated genomic instability and sensitivity to both endogenous and exogenous DNA damaging agents. Specifically, it has been established that this loss of dRP lyase function promotes inflammation associated gastric cancer. However, the way that aberrant POLB impacts the immune signaling and inflammatory responses is still unknown. Here we show that a dRP lyase deficient variant of POLB (Leu22Pro, or L22P) increases mitotic dysfunction associated genomic instability, which eventually leads to a cytosolic DNA mediated inflammatory response. Furthermore, poly(ADP-ribose) polymerase 1 inhibition exacerbates chromosomal instability and enhances the cytosolic DNA mediated inflammatory response. Our results suggest that POLB plays a significant role in modulating inflammatory signaling, and they provide a mechanistic basis for future potential cancer immunotherapies.

Significance of base excision repair to human health.

Oxidative and alkylating DNA damage occurs under normal physiological conditions and exogenous exposure to DNA damaging agents. To counteract DNA base damage, cells have evolved several defense mechanisms that act at different levels to prevent or repair DNA base damage. Cells combat genomic lesions like these including base modifications, abasic sites, as well as single-strand breaks, via the base excision repair (BER) pathway. In general, the core BER process involves well-coordinated five-step reactions to correct DNA base damage. In this review, we will uncover the current understanding of BER mechanisms to maintain genomic stability and the biological consequences of its failure due to repair gene mutations. The malfunction of BER can often lead to BER intermediate accumulation, which is genotoxic and can lead to different types of human disease. Finally, we will address the use of BER intermediates for targeted cancer therapy.

Human ALKBH6 Is Required for Maintenance of Genomic Stability and Promoting Cell Survival During Exposure of Alkylating Agents in Pancreatic Cancer.

Alpha-ketoglutarate-dependent dioxygenase (ALKBH) is a DNA repair gene involved in the repair of alkylating DNA damage. There are nine types of ALKBH (ALKBH1-8 and FTO) identified in humans. In particular, certain types of ALKBH enzymes are dioxygenases that directly reverse DNA methylation damage via transfer of a methyl group from the DNA adduct onto α-ketoglutarate and release of metabolic products including succinate and formaldehyde. Here, we tested whether ALKBH6 plays a significant role in preventing alkylating DNA damage and decreasing genomic instability in pancreatic cancer cells. Using an E. coli strain deficient with ALKB, we found that ALKBH6 complements ALKB deficiency and increases resistance after alkylating agent treatment. In particular, the loss of ALKBH6 in human pancreatic cancer cells increases alkylating agent-induced DNA damage and significantly decreases cell survival. Furthermore, in silico analysis from The Cancer Genome Atlas (TCGA) database suggests that overexpression of ALKBH6 provides better survival outcomes in patients with pancreatic cancer. Overall, our data suggest that ALKBH6 is required to maintain the integrity of the genome and promote cell survival of pancreatic cancer cells.

Combinatorial Approaches to Enhance DNA Damage following Enzyme-Mediated Depletion of L-Cys for Treatment of Pancreatic Cancer.

Pancreatic ductal adenocarcinoma (PDAC) represents one of the deadliest forms of cancer with very few available therapeutic options. We previously reported that an engineered human enzyme, cyst(e)inase, which degrades L-cysteine (L-Cys) and cystine, inhibits growth of multiple cancer cells, including PDAC both in vitro and in vivo. Here, we show that cyst(e)inase treatment leads to increased clustered oxidative DNA damage, DNA single-strand breaks, apurinic/apyrimidinic sites, and DNA double-strand breaks (DSBs) in PDAC cells sensitive to intracellular depletion of L-Cys that is associated with reduced survival. BRCA2-deficient PDAC cells exhibited increased DSBs and enhanced sensitivity to cyst(e)inase. The blocking of a second antioxidant pathway (thioredoxin/thioredoxin reductase) using auranofin or inhibiting DNA repair using the poly (ADP-ribose) polymerase (PARP) inhibitor, olaparib, led to significant increases in DSBs following cyst(e)inase treatment in all PDAC cells examined. Cyst(e)inase plus olaparib also synergistically inhibited growth of sensitive and resistant PDAC cells in both xenograft and allograft tumor models. Collectively, these results demonstrate an important role for oxidative DNA damage and ultimately DNA DSBs in the anticancer action of cyst(e)inase. The data further show the potential for combining agents that target alternate antioxidant pathways or by targeting DNA repair pathways or genetic liabilities in DNA repair pathways to enhance the therapeutic action of cyst(e)inase for PDAC.

Cold Storage Effects on Fitness of the Whitefly Parasitoids Encarsia sophia and Eretmocerus hayati.

Successful biological control of the whitefly Bemisia tabaci involves the mass rearing of biocontrol agents in large numbers for field release. Cold storage of the biocontrol agents is often necessary to provide a sufficient number of biocontrol agents during an eventual pest outbreak. In this study, the fitness of two whitefly parasitoids Encarsia sophia Girault and Dodd (Hymenoptera: Aphelinidae) and Eretmocerus hayati Zolnerowich and Rose (Hymenoptera: Aphelinidae) was evaluated under fluctuating cold storage temperatures. The emergence rate of old pupae of either species was not affected when stored at 12, 10, 8 and 6 °C for 1 week. Cold storage had no effect on the longevity of the emerging adult En. sophia except young pupae stored at 4 °C, while Er. hayati was negatively affected after 2 weeks of storage time at all temperatures. Parasitism by adults emerging from older pupae stored at 12 °C for 1 week was equivalent to the control. Combined with the results for the emergence time, we suggest that the old pupal stage of En. sophia and Er. hayati could be stored at 12 and 10 °C, respectively (transferred every 22 h to 26 ± 1 °C for 2 h), for 1 week, with no or little adverse effect.

Overexpression of NEIL3 associated with altered genome and poor survival in selected types of human cancer.

Base excision repair, which is initiated by the DNA N-glycosylase proteins, is the frontline for repairing potentially mutagenic DNA base damage. Several base excision repair genes are deregulated in cancer and affect cellular outcomes to chemotherapy and carcinogenesis. Endonuclease VIII-like 3 (NEIL3) is a DNA glycosylase protein that is involved in oxidative and interstrand crosslink DNA damage repair. Our previous work has showed that NEIL3 is required to maintain replication fork integrity. It is unknown whether NEIL3 overexpression could contribute to cancer phenotypes, and its prognostic value and use as potential drug target remain unexplored. Our analysis of cancer genomics data sets reveals that NEIL3 frequently undergoes overexpression in several cancers. Furthermore, patients who exhibited NEIL3 overexpression with pancreatic adenocarcinoma, lung adenocarcinoma, lower grade glioma, kidney renal clear cell carcinoma, and kidney papillary cell carcinoma had worse overall survival. Importantly, NEIL3 overexpressed tumors accumulate mutation and chromosomal variations. Furthermore, NEIL3 overexpressed tumors exhibit simultaneous overexpression of homologous recombination genes (BRCA1/2) and mismatch repair genes (MSH2/MSH6). However, NEIL3 overexpression is negatively correlated with tumor overexpressing nucleotide excision repair genes (XPA, XPC, ERCC1/2). Our results suggest that NEIL3 might be a potential prognosis marker for high-risk patients, and/or an attractive therapeutic target for selected cancers.

Mutation in DNA Polymerase Beta Causes Spontaneous Chromosomal Instability and Inflammation-Associated Carcinogenesis in Mice.

DNA polymerase beta (Pol ß) is a key enzyme in the base excision repair (BER) pathway. Pol ß is mutated in approximately 40% of human tumors in small-scale studies. The 5´-deoxyribose-5-phosphate (dRP) lyase domain of Pol ß is responsible for DNA end tailoring to remove the 5' phosphate group. We previously reported that the dRP lyase activity of Pol ß is critical to maintain DNA replication fork stability and prevent cellular transformation. In this study, we tested the hypothesis that the human gastric cancer associated variant of Pol ß (L22P) has the ability to promote spontaneous chromosomal instability and carcinogenesis in mice. We constructed a Pol ß L22P conditional knock-in mouse model and found that L22P enhances hyperproliferation and DNA double strand breaks (DSBs) in stomach cells. Moreover, mouse embryonic fibroblasts (MEFs) derived from L22P mice frequently induce abnormal numbers of chromosomes and centrosome amplification, leading to chromosome segregation errors. Importantly, L22P mice exhibit chronic inflammation accompanied by stomach tumors. These data demonstrate that the human cancer-associated variant of Pol ß can contribute to chromosomal instability and cancer development.

Aberrant DNA Polymerase Beta Enhances H. pylori Infection Induced Genomic Instability and Gastric Carcinogenesis in Mice.

H. pylori is a significant risk factor of gastric cancer that induces chronic inflammation and oxidative DNA damage to promote gastric carcinoma. Base excision repair (BER) is required to maintain the genome integrity and prevent oxidative DNA damage. Mutation in DNA polymerase beta (Pol ß) impacts BER efficiency and has been reported in approximately 30-40% of gastric carcinoma tumors. In this study, we examined whether reduced BER capacity associated with mutation in the POLB gene, along with increased DNA damage generated by H. pylori infection, accelerates gastric cancer development. By infecting a Pol ß mutant mouse model that lacks dRP lyase with H. pylori, we show that reactive oxygen and nitrogen species (RONS) mediated DNA damage is accumulated in Pol ß mutant mice (L22P). In addition, H. pylori infection in Leu22Pro (L22P) mice significantly increases inducible nitric oxide synthesis (iNOS) mediated chronic inflammation. Our data show that L22P mice exhibited accelerated H. pylori induced carcinogenesis and increased tumor incidence. This work shows that Pol ß mediated DNA repair under chronic inflammation conditions is an important suppressor of H. pylori induced stomach carcinogenesis.

Molecular Mechanisms of H. pylori-Induced DNA Double-Strand Breaks.

Infections contribute to carcinogenesis through inflammation-related mechanisms. H. pylori infection is a significant risk factor for gastric carcinogenesis. However, the molecular mechanism by which H. pylori infection contributes to carcinogenesis has not been fully elucidated. H. pylori-associated chronic inflammation is linked to genomic instability via reactive oxygen and nitrogen species (RONS). In this article, we summarize the current knowledge of H. pylori-induced double strand breaks (DSBs). Furthermore, we provide mechanistic insight into how processing of oxidative DNA damage via base excision repair (BER) leads to DSBs. We review recent studies on how H. pylori infection triggers NF-κB/inducible NO synthase (iNOS) versus NF-κB/nucleotide excision repair (NER) axis-mediated DSBs to drive genomic instability. This review discusses current research findings that are related to mechanisms of DSBs and repair during H. pylori infection.

Loss of NEIL3 DNA glycosylase markedly increases replication associated double strand breaks and enhances sensitivity to ATR inhibitor in glioblastoma cells.

DNA endonuclease eight-like glycosylase 3 (NEIL3) is one of the DNA glycosylases that removes oxidized DNA base lesions from single-stranded DNA (ssDNA) and non-B DNA structures. Approximately seven percent of human tumors have an altered NEIL3 gene. However, the role of NEIL3 in replication-associated repair and its impact on modulating treatment response is not known. Here, we report that NEIL3 is localized at the DNA double-strand break (DSB) sites during oxidative DNA damage and replication stress. Loss of NEIL3 significantly increased spontaneous replication-associated DSBs and recruitment of replication protein A (RPA). In contrast, we observed a marked decrease in Rad51 on nascent DNA strands at the replication fork, suggesting that HR-dependent repair is compromised in NEIL3-deficient cells. Interestingly, NEIL3-deficient cells were sensitive to ataxia-telangiectasia and Rad3 related protein (ATR) inhibitor alone or in combination with PARP1 inhibitor. This study elucidates the mechanism by which NEIL3 is critical to overcome oxidative and replication-associated genotoxic stress. Our findings may have important clinical implications to utilize ATR and PARP1 inhibitors to enhance cytotoxicity in tumors that carry altered levels of NEIL3.

Dynamics of Base Excision Repair at the Maternal-Fetal Interface in Pregnancies Complicated by Preeclampsia.

Preeclampsia (PE) (gestational proteinuric hypertension) is the leading cause of maternal and perinatal mortality worldwide. Although placental endothelial dysfunction and oxidative stress are known to contribute to PE, the exact pathological basis for this disorder remains unclear. Previously, we demonstrated that DNA damage at the maternal-fetal interface is more common in the placentas of women with PE than normotensive controls. In this study, we utilized an in vivo comparative study, including 20 preeclamptic women and 8 healthy control subjects, and an in vitro hypoxia/reperfusion model to mimic the effects of oxidative stress at the maternal-fetal interface. We tracked the spatial pattern of expression of 2 base excision repair proteins, 8-oxoguanine glycosylase (OGG1) and apurinic/apyrimidinic endonuclease-1 (APE1), at the maternal-fetal interface in response to oxidative stress. In vivo, we found a significant increase in OGG1 and APE1 concentrations in PE placental tissues as compared to normotensive controls ( P < .0001). Further, our in vitro study revealed that OGG1 and APE1 expression is much greater in maternal cells (decidua) than in fetal cells (cytotrophoblasts) of placental tissue subjected to oxidative stress ( P < .0001). Our results suggest that OGG1 and APE1 likely protect decidual cells from oxidative base damage.

Novel protective mechanism of reducing renal cell damage in diabetes: Activation AMPK by AICAR increased NRF2/OGG1 proteins and reduced oxidative DNA damage.

Exposure of renal cells to high glucose (HG) during diabetes has been recently proposed to be involved in renal injury. In the present study, we investigated a potential mechanism by which AICAR treatment regulates the DNA repair enzyme, 8-oxoG-DNA glycosylase (OGG1) in renal proximal tubular mouse cells exposed to HG and in kidney of db/db mice. Cells treated with HG for 2 days show inhibition in OGG1 promoter activity as well as OGG1 and Nrf2 protein expression. In addition, activation of AMPK by AICAR resulted in an increase raptor phosphorylation at Ser792 and leads to increase the promoter activity of OGG1 through upregulation of Nrf2. Downregulation of AMPK by DN-AMPK and raptor and Nrf2 by siRNA resulted in significant decease in promoter activity and protein expression of OGG1. On the other hand, downregulation of Akt by DN-Akt and rictor by siRNA resulted in significant increase in promoter activity and protein expression of Nrf2 and OGG1. Moreover, gel shift analysis shows reduction of Nrf2 binding to OGG1 promoter in cells treated with HG while cells treated with AICAR reversed the effect of HG. Furthermore, db/db mice treated with AICAR show significant increased in AMPK and raptor phosphroylation as well as OGG1 and Nrf2 protein expression that associated with significant decrease in oxidative DNA damage (8-oxodG) compared to non-treated mice. In summary, our data provide a novel protective mechanism by which AICAR prevents renal cell damage in diabetes and the consequence complications of hyperglycemia with a specific focus on nephropathy.

Gut Microbiota Imbalance and Base Excision Repair Dynamics in Colon Cancer.

Gut microbiota are required for host nutrition, energy balance, and regulating immune homeostasis, however, in some cases, this mutually beneficial relationship becomes twisted (dysbiosis), and the gut flora can incite pathological disorders including colon cancer. Microbial dysbiosis promotes the release of bacterial genotoxins, metabolites, and causes chronic inflammation, which promote oxidative DNA damage. Oxidized DNA base lesions are removed by base excision repair (BER), however, the role of this altered function of BER, as well as microbiota-mediated genomic instability and colon cancer development, is still poorly understood. In this review article, we will discuss how dysbiotic microbiota induce DNA damage, its impact on base excision repair capacity, the potential link of host BER gene polymorphism, and the risk of dysbiotic microbiota mediated genomic instability and colon cancer.

Gastric cancer associated variant of DNA polymerase beta (Leu22Pro) promotes DNA replication associated double strand breaks.

DNA polymerase beta (Pol ß) is a key enzyme for the protection against oxidative DNA lesions via its role in base excision repair (BER). Approximately 1/3 of tumors studied to date express Pol ß variant proteins, and several tumors overexpress Pol ß. Pol ß possesses DNA polymerase and dRP lyase activities, both of which are known to be important for efficient BER. The dRP lyase activity resides within the 8kDa amino terminal domain of Pol ß, is responsible for removal of the 5' phosphate group (5'-dRP). The DNA polymerase subsequently fills the gaps. Previously, we demonstrated that the human gastric cancer-associated variant of Pol ß (Leu22Pro (L22P)) lacks dRP lyase function in vitro. Here, we report that L22P-expressing cells harbor significantly increased replication associated DNA double strand breaks (DSBs) and defective maintenance of the nascent DNA strand (NDS) during replication stress. Moreover, L22P-expressing cells are sensitive to PARP1 inhibitors, which suggests trapped PARP1 binds to the 5'-dRP group and blocks replications forks, resulting in fork collapse and DSBs. Our data suggest that the normal function of the dRP lyase is critical to maintain replication fork integrity and prevent replication fork collapse to DSBs and cellular transformation.

In vivo and in vitro evidence for placental DNA damage in preeclampsia.

Preeclampsia (PE) is an idiopathic multisystem disease affecting 5-7% of pregnant women. Placental oxidative stress is a characteristic feature of PE and occurs when the production of reactive oxygen species (ROS) within the placenta overwhelms the intrinsic anti-oxidant defenses. We hypothesize that excessive oxidative DNA damage at the fetal-maternal interface coupled with a defective DNA damage/repair response is causally related to PE. Here we demonstrate that γH2AX (a sensitive marker of DNA damage) is expressed in the maternal decidua but not trophoblast of normal placentas, and that expression is significantly higher in PE placental tissues in vivo. Using primary in vitro cultures of maternal decidual stromal cells (DSCs) and fetal cytotrophoblast cells (CTs), we show an increase in γH2AX foci in DSCs cultured with vs without H2O2 (70.6% vs 11.6%; P<0.0001) or under hypoxia-reperfusion vs normoxia (20- vs 3-fold; P = 0.01); no foci were seen in CTs. We further demonstrate that Base Excision Repair (BER) intermediates are significantly increased in DSCs (not CTs) under these same conditions. Our data show that DNA damage is significantly more common in PE placentas, and that this DNA damage is localized to the maternal and not fetal side of the placenta. CTs may be selectively resistant to DNA damage in an effort to protect the fetus.