Nucleotide Excision Repair Genes Research Articles

Transcriptomic Evidence of Base and Nucleotide Excision Repair Mechanisms in Response to UV-B Radiation in an Arctic Fungus Pseudogymnoascus australis Strain HNDR4

Polar micro-fungi are known to have developed protective mechanisms and responses against the harmful effects of UV radiation. In this study, physiological, cellular, and transcriptomic responses of an Arctic fungal strain of Pseudogymnoascus australis towards UV-B radiation were examined. Fungal isolate was cultured on 0.45μm nylon membranes overlayed on Czapex-Dox agar (CDA) at 15ºC for 10 d in dark condition to reach the mid-log phase. To assess DNA damage and recovery, the isolates were exposed to UV-B radiation (UV dosage of 6.1 kj m-2 d-1) for 130 min, followed by 0, 2 and 6 hr incubation under light condition. Differential gene expression in DNA repair after UV-B treatment at these time points was analysed based on RNA-Seq data output of 40 million reads per sample from an Illumina NovaSeq 6000 system platform. The results revealed that radiation-repair (RAD) genes were upregulated and the photoreactivation (PHR1) gene was downregulated after UV-B exposure in light condition. Downregulation of oxidoreductase activity was observed from the GO enrichment analysis. The KEGG pathway enrichment analysis exhibited upregulation of base excision repair (BER) genes and nucleotide excision repair (NER) genes upon UV-B exposure. This is the fi rst RNASeq transcriptomic study on the DNA repair mechanisms employed by a polar fungus to mitigate UV-induced DNA damage.

ERCC1 abundance is an indicator of DNA repair-apoptosis decision upon DNA damage

DNA repair is essential for successful propagation of genetic material and fidelity of transcription. Nucleotide excision repair (NER) is one of the earliest DNA repair mechanisms, functionally conserved from bacteria to human. The fact that number of NER genes vary significantly between prokaryotes and metazoans gives the insight that NER proteins have evolved to acquire additional functions to combat challenges associated with a diploid genome, including being involved in the decision between DNA repair and apoptosis. However, no direct association between apoptosis and NER proteins has been shown to date. In this study, we induced apoptosis with a variety of agents, including oxaliplatin, doxorubicin and TRAIL, and observed changes in the abundance and molecular weight of NER complex proteins. Our results showed that XPA, XPC and ERCC1 protein levels change during DNA damage-induced apoptosis. Among these, ERCC1 decrease was observed as a pre-mitochondria depolarisation event which marks the “point of no return” in apoptosis signalling. ERCC1 decrease was due to proteasomal degradation upon lethal doses of oxaliplatin exposure. When ERCC1 protein was stabilised using proteasome inhibitors, the pro-apoptotic activity of oxaliplatin was attenuated. These results explain why clinical trials using proteasome inhibitors and platinum derivatives showed limited efficacy in carcinoma treatment and also the importance of how deep understanding of DNA repair mechanisms can improve cancer therapy.

XPA tumor variant leads to defects in NER that sensitize cells to cisplatin.

Nucleotide excision repair (NER) reduces efficacy of treatment with platinum (Pt)-based chemotherapy by removing Pt lesions from DNA. Previous study has identified that missense mutation or loss of the NER genes Excision Repair Cross Complementation Group 1 and 2 (ERCC1 and ERCC2) leads to improved patient outcomes after treatment with Pt-based chemotherapies. Although most NER gene alterations found in patient tumors are missense mutations, the impact of mutations in the remaining nearly 20 NER genes is unknown. Towards this goal, we previously developed a machine learning strategy to predict genetic variants in an essential NER protein, Xeroderma Pigmentosum Complementation Group A (XPA), that disrupt repair. In this study, we report in-depth analyses of a subset of the predicted variants, including in vitro analyses of purified recombinant protein and cell-based assays to test Pt agent sensitivity in cells and determine mechanisms of NER dysfunction. The most NER deficient variant Y148D had reduced protein stability, weaker DNA binding, disrupted recruitment to damage, and degradation. Our findings demonstrate that tumor mutations in XPA impact cell survival after cisplatin treatment and provide valuable mechanistic insights to improve variant effect prediction. Broadly, these findings suggest XPA tumor variants should be considered when predicting chemotherapy response.

Abstract B012: Pedigree and multi-omics analyses implicate nucleotide excision repair genes, XPA, ERCC6, and ERCC8, in susceptibility to breast cancer

Abstract Background: The majority of low- and moderate-risk [odds ratios (OR) ≤ 3] susceptibility genes for peri- and post-menopausal breast cancer (≥50 years of age), particularly those with minor allele frequency (MAF) of <30%, have not yet been identified and/or validated. We used a hypothesis-driven integrative approach to identify breast cancer susceptibility genes by analyzing pedigree and multi-omics (genomics, transcriptomics, mutation landscape) data. Methods: We conducted pedigree analysis in 31 families with DNA repair disorders, xeroderma pigmentosum (XP), trichothiodystrophy (TTD), Cockayne syndrome (CS), XP/TTD and XP/CS. These disorders can be caused by mutations in genes involved in the nucleotide excision repair (NER) pathway such as XPA-XPG, ERCC6 and ERCC8. We estimated the frequency of hereditary breast cancer, defined as the presence of at least two cases of premenopausal breast cancer (diagnosed <50 years of age) or one case of premenopausal breast cancer and one case of ovarian cancer in one side of the family, in our study. Furthermore, we conducted individual analysis of four genome-wide association studies (GWAS) datasets (totaling 2961 cases and 4335 controls), individual and meta-analysis of two gene expression microarray datasets (98 cases and 163 controls), and targeted analysis of The Cancer Genome Atlas (TCGA) (522 breast cancers). All analyses involved invasive ductal breast carcinoma in women diagnosed at ≥50 years of age. Results: In an XP family with causative mutations in XPA, there were four cases of premenopausal breast cancer (including heterozygote mutation carriers), one case of ovarian cancer, and one case of prostate cancer. Comprehensive sequencing failed to identify a BRCA1 or BRCA2 mutation in this family. Overall, 7 of 31 (22.6%) families with DNA repair disorders had a family history that was compatible with hereditary breast cancer. Hence, we selected a panel of NER genes as candidates for association studies with breast cancer. Our candidate-gene association analysis of GWAS datasets suggested an increased risk of breast cancer with ERCC6 (main effect:1.29 ≤ OR ≤ 2.91, 0.005 ≤ p ≤ 0.04, 11.8 ≤ MAF ≤ 29.7%) and implicated its interaction with ERCC8 (joint effect:3.03 ≤ OR ≤ 5.31, 0.01 ≤ pinteraction ≤ 0.03). Our transcriptomics analysis identified significant upregulation of ERCC6 (p=7.95 × 10–6) and ERCC8 (p=4.67 × 10–6) in breast cancer. Our analysis of TCGA breast tumor data showed similar mutation frequency of ERCC6 (1.8%) and ERCC8 (0.3%) as known breast cancer susceptibility genes such as BLM (1.9%) and LSP1 (0.3%). Conclusion: Our integrative analyses suggest that ERCC6 may be a previously unreported low- to moderate-risk breast cancer susceptibility gene, which may also interact with ERCC8. ERCC6 and ERCC8 code for the main components of the transcription-coupled (TC) repair sub-pathway of the NER. TC-NER protects against genotoxic agents, such as free radicals and reactive oxygen species. Our results provide a deeper biologic insight and leads for prevention of common breast cancer. Citation Format: Roxana Moslehi, Amiran Dzutsev. Pedigree and multi-omics analyses implicate nucleotide excision repair genes, XPA, ERCC6, and ERCC8, in susceptibility to breast cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: DNA Damage Repair: From Basic Science to Future Clinical Application; 2024 Jan 9-11; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2024;84(1 Suppl):Abstract nr B012.

Genetic Polymorphisms of XPC, XPD, XPG Genes and their Association with Radiotherapy Induced Toxicity among Head and Neck Cancer Patients: A Hospital Based Study from Maharashtra.

The present study was planned to investigate possible association of single nucleotide polymorphisms (SNPs) of nucleotide excision repair (NER) genes such as XPC, XPD, XPG with acute radiation induced toxicities such as skin reactions and oral mucositis in normal tissue from head and neck cancer (HNC) patients receiving radiotherapy. Methods: Two hundred and fifty HNC patients receiving radiotherapy were enrolled in this study and the acute toxicity reactions and radiation response were recorded. Association of SNPs rs2228001 of XPC, rs238406, rs13181 of XPD and rs17655 of XPG gene with normal tissue reactions in the form of dermatitis and mucositis were studied by PCR-RFLP and direct DNA sequencing. The results of univariate analysis of SNPs of XPC, XPD and XPG showed that XPC polymorphism at codon 939 of exon 15 (A>C) was not associated with dermatitis (OR=0.30, 95% CI: 0.06-1.39; p=0.125), or oral mucositis (OR=1.14, 95% CI: 0.41-3.20; p=0.793). The XPD codon 156 of exon 6 (C>A) and codon 751 of exon-23 A>C) polymorphism showed no association with radiosensitivity in HNC patients (OR=1.50, 95% CI: 0.60-3.71; p=0.080) for dermatitis, (OR=1.54, 95% CI: 0.66-3.61; p=0.312) for oral mucositis. The 1104 Asp variant genotype or allele of XPG (OR=1.35 95% CI: 0.50-3.64; p=0.541) showed no association with degree of radiotherapy associated dermatitis or mucositis (OR=0.80, 95% CI: 0.32-2.03; p=0.648) in HNC patients. The variant C allele of 2920 A/C genotype of XPC gene at codon 939 of exon 15, found protective with developing skin reactions with grade >1 (OR=0.60, 95% CI: 0.36-0.97; p=0.039) in HNC patients treated with radiotherapy. The results obtained in this study concluded that the SNPs rs2228001of XPC, rs238406, rs13181 SNPs of XPD and rs17655 SNP of XPG are not associated with normal tissue toxicity in HNC patients treated with radiotherapy. Radiotherapy with high radiation dose was significantly associated with oral mucositis in response to radiotherapy.

Melphalan-Induced Multiple Myeloma Cells Exhibit a Senescent-like Dormant Phenotype

Multiple myeloma (MM) is an incurable plasma cell malignancy. Despite therapeutic advances that have vastly improved survival, all patients are expected to relapse. One mechanism that may contribute to MM relapse is tumor dormancy. Dormant MM cells may persist in the bone marrow, where they exhibit reduced proliferative capacity and resistance to treatment. These cells may then exit dormancy following treatment to drive disease relapse. Dormancy shares many features with cellular senescence, a state of stable growth arrest induced by cell stress. Chemotherapies that produce genotoxic stress have been associated with therapy-induced senescence (TIS). One such genotoxic agent, melphalan (Mel), is routinely administered to MM patients for myeloablation prior to autologous bone marrow transplant. We hypothesized that High Dose Mel (HDM) induces a senescent-like dormant phenotype in surviving MM cells. To test our hypothesis, we developed an in vitro model for HDM. We identified 10µM Mel as a concentration to induce >90% cell toxicity (HDM) in 5TGM1 mouse MM cells over 10 days. 5TGM1-GFP MM cells were cultured with HDM or vehicle (Veh) for 6 hours; cells were then cultured in normal growth medium in the presence of primary mouse (C57BL/6) bone marrow stromal cells (BMSCs). Co-cultures were imaged by fluorescent microscopy every other day to quantify cumulative population doublings (CPD) and cell morphology over the following 10 days. The effect of HDM on CPDs was also evaluated in the human RPMI-8226 MM cell line. 5TGM1-GFP cells were isolated by FACS on day 10 for evaluation of senescence histological characteristics and gene expression. All studies represent n=3 independent experiments unless otherwise indicated. HDM-5TGM1 cells exhibited a significant reduction in mean CPDs over 10 days compared to Veh (HDM 0.32±0.31, Veh 6.72±0.69, p<0.0001), indicating stable growth arrest in HDM treated cells consistent with senescence. HDM-5TGM1 cells were also significantly larger versus Veh (median size in pixels units: HDM 413.2±99.98, Veh 207±8.88, p<0.05), consistent with classical enlarged morphology in senescent cells. Preliminary assessment (n=1) of HDM-RPMI-8226 cells showed similar growth arrest (mean cumulative doublings: HDM 0.058±0.101, Veh 4.185±0.358) and enlargement (mean size in pixel units: HDM 804.1±6.048, Veh 526.9±2.115), suggesting a translatable mechanism in humans. FACS-sorted 5TGM1-GFP cells were stained for telomere associated foci (TAF), a marker of persistent DNA damage characteristic of senescent cells. HDM-5TGM1 cells showed a higher percentage of TAF+ cells (Percent TAF+ cells: HDM 39.7%±9.1%, Veh 10.6%±0.8%, n=2). Sorted HDM-5TGM1 cells also exhibited significant increases over Veh (p<0.001) in senescence markers ( Cdkn1a, Cdkn1c, Glb1), senescence cell anti-apoptosis pathway genes (SCAPs, Bcl2l1), and senescence associated secretory phenotype (SASP) genes ( Ccl5, Icam1, Mmp13). In addition, HDM-5TGM1 cells showed significant increases in myeloid markers that have previously been shown to be increased in dormant 5TGM1 ( Axl, Fcer1g, Mpeg1). Single cell RNA-sequencing was used to further evaluate senescence gene expression changes in growth arrested HDM-5TGM1 cells. Gene set enrichment analysis (GSEA) of genes differentially expressed in HDM-5TGM1 versus Veh cells was performed for custom senescence phenotyping gene sets (Senescence Up, SenUp; Senescence Growth Arrest, SenGA; Inflammatory SASP, iSASP; SCAPs; and Plasma Cell Senescence; PCSen) as well as mouse ortholog versions of a published senescence and biological aging gene set (SenMayo) and KEGG curated gene sets. GSEA of HDM-5TGM1 versus Veh cells confirmed significant (FDR<0.25) upregulation of iSASP, MayoSen, PCSen, SenUp, SCAPs, and SenGA gene sets. Concurrently, GSEA revealed significant downregulation of KEGG DNA replication, cell cycle, and nucleotide excision repair gene sets, supporting our observations of proliferative arrest and persistent DNA damage TAF. Our findings demonstrate that HDM-MM cells exhibit multiple features of senescence, suggesting a potential mechanistic role for TIS in MM dormancy and highlight a novel therapeutic target that may be present in patients post-HDM. Thus, targeting senescence may be a novel approach to eliminate dormant MM cells and prevent relapse.

AHR-mediated DNA damage contributes to BaP-induced cardiac malformations in zebrafish

Benzo[a]pyrene (BaP) is a representative polycyclic aromatic hydrocarbon widely present in the environment. We previously reported that the aryl hydrocarbon receptor (AHR) mediates BaP-induced apoptosis and cardiac malformations in zebrafish embryos, but the underlying molecular mechanisms were unclear. Since BaP is a mutagenetic compound, we hypothesize that BaP induces apoptosis and heart defects via AHR-mediated DNA damage. In this study, zebrafish embryos were exposed to BaP at a concentration of 0.1 μM from 2 to 72 h post fertilization, either with or without inhibitors/agonists. AHR activity and levels of reactive oxygen species (ROS) were examined under a fluorescence microscope. mRNA expression levels were quantified by qPCR. DNA damage and apoptosis were detected by immunofluorescence. Our findings revealed that BaP exposure significantly increased BPDE-DNA adducts, mitochondrial damage, apoptosis and heart defects in zebrafish embryos. These effects were counteracted by inhibiting AHR/cyp1a1 using pharmaceutical inhibitors or genetic knockdown. Furthermore, we observed that spironolactone, an antagonist of nucleotide excision repair (NER), significantly enhanced BaP-induced BPDE-DNA adducts, mitochondrial damage, apoptosis and heart malformation rates. Conversely, SRT1720, a SIRT1 agonist, reduced the adverse effects of BaP. Supplementation with spironolactone also enhanced γ-H2AX signals in the heart of zebrafish embryos exposed to BaP. Additional experiments demonstrated that BaP suppressed the expression of SIRT1. We further established that AHR, when activated by BaP, directly inhibited SIRT1 transcription, leading to downregulation of XPC and XPA, which are essential NER genes involved in the recognition and verification steps of the NER process. Taken together, our results indicate that AHR mediates BaP-induced DNA damage in the heart of zebrafish embryos by inducing BPDE-DNA adduct formation via the AHR/Cyp1a1 signalling pathway, as well as suppressing NER via AHR-mediated inhibition of SIRT1.

Involvement of Nucleotide Excision Repair and Rec-Dependent Pathway Genes for UV Radiation Resistance in Deinococcus irradiatisoli 17bor-2.

Strain Deinococcus irradiatisoli 17bor-2 was isolated from a soil sample exposed to γ radiation at Seoul Women's University, Republic of Korea. The genus Deinococcus is a Gram-negative, coccus-shaped, and extremophilic bacterium, well renowned as being a radiation-resistant bacterium. Therefore, the mechanism behind the resistance to radiation and the gene responsible for the resistance could be helpful for detailed experimental studies with biotechnological applications. To study the involvement of genes in UV radiation resistance in strain 17bor-2, the genomic DNA of the strain was sequenced and constructed using the Pacific Biosciences RS II system. In addition, the complete genome sequence of strain 17bor-2 was annotated and interpreted using the Genomes-Expert Review (IMG-ER) system, along with Prodigal and JGI GenePRIMP analysis. The genome analysis of strain 17bor-2 revealed evidence of excinuclease UvrABC genes, which are key enzymes in the nucleotide excision repair (NER) mechanism, as well as genes from the recA-dependent and recQ pathways. The genome of strain Deinococcus irradiatisoli 17bor-2 was a circular chromosome comprising 3,052,043 bp with a GC content of 67.0%, including 2911 coding sequences (CDs), 49 tRNA genes, and 9 rRNA genes. In addition, their complete genome sequence annotation features provided evidence that radiation resistance genes play a central part in adaptation against extreme environmental conditions. In recent decades, excision repair genes have been indicated in considerable detail for both prokaryote and eukaryote resistance against UV-C radiation.

Codelivery of ERCC2 small interfering RNA and cisplatin with macrophage-derived mimetic nanovesicles for enhanced bladder cancer treatment.

Cisplatin-based chemotherapy plays a vital role in the management of muscle-invasive bladder cancer (MIBC); however, off-tumor toxicity and resistance often lead to cancer recurrence and eventual treatment failure. The loss of function of the nucleotide excision repair gene excision repair cross-complementing rodent repair deficiency gene 2 ( ERCC2 ) in cancer cells correlates with sensitivity to cisplatin, while its overexpression causes cisplatin resistance. Small interfering RNA (siRNA) knockdown of ERCC2 combined with cisplatin treatment may improve therapeutic outcomes in patients with bladder cancer. Here, we aimed to develop macrophage-derived mimetic nanovesicles (MNVs) as a nanoplatform for the simultaneous delivery of cisplatin and ERCC2 siRNA for enhancing the efficacy of bladder cancer chemotherapy. The cellular uptake, gene down-regulation, tumor inhibition effects, and biosafety of the synthesized nanodrugs (MNV-Co) as a synergistic therapeutic strategy for MIBC were evaluated in vitro and in vivo . The results indicated high efficacy of MNV-Co against MIBC and low off-tumor toxicity. Furthermore, by down-regulating ERCC2 mRNA and protein levels, MNV-Co improved chemosensitivity, promoted cancer cell apoptosis, and effectively suppressed tumor growth. This study presents a potential approach for delivering cisplatin and ERCC2 siRNA concurrently to treat bladder cancer using a biomimetic nanosystem.

Molecular and immune profiling of TP53-mutated ovarian cancers with non-BRCA1/2 homologous recombination gene alterations.

5579 Background: Molecular alterations in homologous recombination (HR) pathway genes lead to HR deficiency (HRD) in ~50% of high grade serous ovarian carcinomas (HGSOC). The immune microenvironment of BRCA1/2-mutated HGSOC has been extensively characterized, in contrast to tumors with mutations in other HR genes. We evaluated a cohort of epithelial ovarian cancers (EOC) enriched for HGSOC and compared molecular and immune signatures of tumors with BRCA1/2 mutations ( BRCAm) to those with non-BRCA1/2 HR gene mutations (NBHRD). Methods: We characterized 173 EOC by comprehensive genomic and immune profiling (CGIP) using panel-based next-generation DNA (523 genes) and RNA sequencing (384 genes), respectively. We enriched for HGSOC by selecting for TP53 mutations and excluding tumors with non-serous histology or any mutation in POLE, MLH1, PMS2, MSH2, MSH6, or nucleotide excision repair genes. Tumors lacking BRCA1/2-mutations were classified as NBHRD if a reportable mutation was present in canonical HR genes. Mutational burden (TMB, mut/Mb) was estimated from detected SNV/indels. We calculated immune-related expression signatures, including tumor immunogenicity score (TIGS), cellular proliferation (CP), and cancer testis antigen burden (CTAB). PD-L1 expression was assessed by tumor proportion score (TPS) following 22C3 immunohistochemistry. Differences in TMB, TIGS, CP, CTAB, PD-L1 and gene expression rank were tested for using Wilcoxon rank-sum test. Results: Of 173 EOC, 84 cases had complete CGIP, including 11 (13%) BRCAm, 7 (8%) NBHRD (Table), and 66 (79%) lacking HR gene alterations. On average, NBHRD tumors harbored lower TMB (4.1±2.3 vs. 6.6±2.3 vs. p=0.03) and elevated TIGS (59.1±16.2 vs. 41.7±16.2 p=0.044) compared to BRCAm tumors. We found no difference in PD-L1 (p=0.21), CP (p=0.26), or CTAB (p=0.48). Expression changes were identified in 32 immune genes, of which 31 (97%) were substantially up-regulated (1.3-3.3 fold) in NBHRD compared to BRCAm tumors. Conclusions: Our findings showed our cohort of NBHRD tumors were more immunogenic but less mutagenic than BRCAm tumors, implying enhanced immunogenicity unrelated to neoantigen load. Given that immune checkpoint inhibitors have shown limited efficacy in ovarian cancer, our data suggest NBHRD tumors may have stronger and possibly distinct immune escape mechanisms compared to BRCAm tumors. [Table: see text]

Dysregulation of DNA repair genes in Fuchs endothelial corneal dystrophy

Fuchs Endothelial Corneal Dystrophy (FECD), a late-onset oxidative stress disorder, is the most common cause of corneal endothelial degeneration and is genetically associated with CTG repeat expansion in Transcription Factor 4 (TCF4). We previously reported accumulation of nuclear (nDNA) and mitochondrial (mtDNA) damage in FECD. Specifically, mtDNA damage was a prominent finding in development of disease in the ultraviolet-A (UVA) induced FECD mouse model. We hypothesize that an aberrant DNA repair may contribute to the increased DNA damage seen in FECD. We analyzed differential expression profiles of 84 DNA repair genes by real-time PCR arrays using Human DNA Repair RT-Profiler plates using cDNA extracted from Descemet's membrane-corneal endothelium (DM-CE) obtained from FECD patients with expanded (>40) or non-expanded (<40) intronic CTG repeats in TCF4 gene and from age-matched normal donors. Change in mRNA expression of <0.5- or >2.0-fold in FECD relative to normal was set as cutoff for down- or upregulation. Downregulated mitochondrial genes were further validated using the UVA-based mouse model of FECD. FECD specimens exhibited downregulation of 9 genes and upregulation of 8 genes belonging to the four major DNA repair pathways, namely, base excision repair (BER), nucleotide excision repair (NER), mismatch repair (MMR), and double strand break (DSB) repair, compared to normal donors. MMR gene MSH2 and BER gene POLB were preferentially upregulated in expanded FECD. BER genes LIG3 and NEIL2, DSB repair genes PARP3 and TOP3A, NER gene XPC, and unclassified pathway gene TREX1, were downregulated in both expanded and non-expanded FECD. MtDNA repair genes, Lig3, Neil2, and Top3a, were also downregulated in the UVA-based mouse model of FECD. Our findings identify impaired DNA repair pathways that may play an important role in DNA damage due to oxidative stress as well as genetic predisposition noted in FECD.

Immune checkpoint VISTA regulates DNA sensing and repair pathways that contribute to type I interferon (IFN-I) production in the skin

Abstract Skin sterile injury by ultraviolet (UV) light stimulates production of type I interferons. While in healthy skin IFN-I response to UV returns to baseline over time, the IFN-I signature persists in photosensitive diseases like lupus. The pathways that downregulate IFN-I production in healthy skin, and fail to do so in lupus skin, are unknown. Previous studies showing that activating VISTA suppresses the IFN-I signature in monocytes suggest a role for this immune checkpoint in the regulation of the IFN-I response. Indeed, we showed that the skin IFN-I signature is elevated in mice globally deficient in VISTA (Vsir−/−), as well as in mice with a conditional deletion of VISTA in keratinocytes. Having confirmed its expression in keratinocytes, we tested if VISTA regulates UV-triggered IFN-I production in the skin. Expression analysis of IFN-I stimulated genes in skin biopsies collected prior to and 3h after a single dose of UVB, revealed ~10-fold higher IFN-I score in Vsir−/− vs. B6 skin after UV. RNAseq studies showed DNA sensors, ZBP1, cGAS, and IFI204 were upregulated, while nucleotide excision repair genes, Polɛ and DNA Ligase1, were suppressed in Vsir−/− skin, both at baseline and 3h after UV. Moreover, Polɛ protein levels were lower in Vsir−/− skin by immunoblot. Relevant to its role in keratinocytes, IFN-k protein levels were higher in VISTA-deficient epidermal keratinocytes ex vivo, accompanied by elevated mRNA levels of ZBP1 and IFI204 before and after UV. Together, this study identifies VISTA as a novel regulator of IFN-I production, by modulating DNA damage repair and sensing. The keratinocyte-intrinsic role of VISTA is therapeutically relevant as lupus keratinocytes express high IFN-k and are direct targets of UV-induced DNA damage. 1R21AR079661 – 01, Hitchcock Foundation, DOD lupus award

Correlation of ERCC5 polymorphisms and linkage disequilibrium associated with overall survival and clinical outcome to chemotherapy in breast cancer.

ERCC5 is a DNA endonuclease and nucleotide excision repair gene; its mutations lead to a lack of activity by this enzyme, causing oxidative DNA damage. This study aimed to assess the role of four selected single nucleotide polymorphisms (SNPs) in ERCC5 and their linkage disequilibrium associated with survival analysis and clinical outcomes in breast cancer. Four SNPs (rs751402, rs17655, rs2094258, and rs873601) of the ERCC5 gene were analyzed using the PCR-RFLP technique, followed by sequencing in 430 breast cancer (BC) cases and 430 cancer-free individuals. Statistical analysis was performed using MedCalc 17 and SPSS version 24, while bioinformatic analysis of linkage disequilibrium was performed using Haploview software 4.2. Multivariate analysis showed that the rs751402 and rs2094258 polymorphisms were significantly associated with an elevated risk of BC (P < 0.001), while the other two SNPs, rs17655 and rs873601, did not show any association (P > 0.001). Survival analysis revealed that rs751402 and rs2094258 had longer overall survival periods (P <0.001) than rs17655 and rs873601. Moreover, rs751402 and rs2094258 also had significantly longer overall survival (log-rank test, P < 0.005) for all three survival functions (positive family history, ER+PR status, and use of contraceptives), while rs17655 and rs873601 did not show any significant association. Only rs873601 showed a strong negative correlation with all the chemotherapeutic groups. The current results suggest that variations in ERCC5 may contribute to BC development and that their genetic anomalies may be associated with cancer risk and may be used as a biomarker of clinical outcome.

A Homozygous Nonsense Variant in UVSSA Causes UV-sensitive Syndrome from Very Large Kindred: The First Report from Iran.

Recessive disruptive mutations in nucleotide excision repair genes are responsible for a wide range of cutaneous photosensitivity and, in some cases, are associated with multi-system involvement. The heterogeneous nature of these conditions makes next-generation sequencing the method of choice to detect disease-causing variants. A patient from a large multiplex inbred Iranian kindred with several individuals suffering from skin sun-sensitive manifestations underwent complete clinical and molecular evaluations. Whole exome sequencing (WES) was performed on the genomic sample of the proband, followed by bioinformatics analysis. Subsequently, co-segregation of the candidate variant with the condition was performed by Sanger sequencing. A rare homozygous nonsense variant, c.1040G>A (p. Trp347*), was identified in the UVSSA gene, resulting in UV-sensitive syndrome (UVSS) complementation group A. The global minor allele frequency of the variant is < 0.001 in population databases. Tryptophan 347 residue is conserved among mammalians and vertebrates, and the null variant is believed to lead to a truncated protein with cellular mislocalization. Here, we report the first genetic diagnosis of UVSS-A in Iran via the successful application of Next-generation sequencing, which expands our understanding of the molecular pathogenesis of this condition.

Single-nucleotide polymorphisms of nucleotide excision repair genes and their association with overall survival in North Indian lung cancer patients treated with platinum-based doublet chemotherapy.

The aim of the study is to understand the association of Nucleotide excision repair (NER) inter-genetic polymorphic combinations with overall survival (OS) in lung cancer as well as its histological subtypes in the North Indian population. Genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism. For survival analysis, the univariate Kaplan-Meier and multivariate Cox regression model were applied. Recursive partitioning method, survival analysis tree was applied to study unfavorable genotypic combinations in NER single-nucleotide polymorphisms. Combinatorial studies suggested no association between polymorphic combinations of NER genes and OS in lung cancer patients. When stratified as per lung cancer histological subtypes, adenocarcinomas patients with XPG 670 and XPC 499 polymorphism a significant increase in OS in combined heterozygous and mutant genotype with a lower hazardous ratio (Hazard Ratio1 (HR) = 0.20; P = 0.004). Small-cell lung carcinoma (SCLC) patients with XPF 11985A>G and XPD Arg156Arg polymorphism showed a 4-fold hazard ratio among heterozygous genotype (HR1 = 4.84; P = 0.007) where no significant results are obtained in patients suffering from squamous cell carcinoma histological subtypes. STREE showed XPG Asp1104His (W), XPD Lys751Gln (H + M), XPF Arg415Gln (H + M) genotype was associated with a lower hazard ratio (P = 0.0007) showing survival of 11.6 months when compared with the reference (median survival time = 3.52). It can be concluded that SCLC patients with polymorphic combinations of the NER pathway were associated with a higher risk of mortality. STREE depicted the association of NER polymorphic combinations with a lower hazard ratio predicting them to be a good prognostic factor for lung cancer.

Abstract B033: LP-184, a tumor site activated small molecule therapeutic, is synthetically lethal in pancreatic cancers with DNA damage repair defects

Abstract Biomarker-based therapeutic strategies associated with increased efficacy, manageable toxicity and extended disease-free survival are urgently needed in pancreatic cancer (PaCa). 15-20% of PaCa carry mutations in DNA repair pathways (BRCA1/BRCA2/PALB2/RAD51/ATR/ATM/FANCD2). Additionally, mutations in nucleotide excision repair (NER) genes (ERCC2/3/4/5/6) have been reported in ~5% of PaCa. LP-184 is an acylfulvene analog that is converted to an active alkylating agent in the strict dependency on the oxidoreductase, prostaglandin reductase 1 (PTGR1). LP-184 induced tumor cell kill is enhanced in the presence of DNA damage repair (DDR) defects. Mutation or expression driven TC-NER and/or HR deficiency is expected to predispose PaCa cells to increased sensitivity to LP-184. To test the idea of LP-184 activity in DNA repair-deficient tumors, we evaluated the anti-tumor effects of LP-184 in mouse subcutaneous PDX models harboring pathogenic frameshift mutations in ATR (CTG-1522 model) or BRCA1 (CTG-1643 model) representing HR deficiency in PaCa. Two cycles of LP-184 treatment in CTG-1522 resulted in 140% tumor growth inhibition (TGI), relative to 80% TGI with gemcitabine in this FOLFIRONOX non-responder. Similarly, complete and durable tumor regression with 112% TGI was observed in CTG-1643 with single agent LP-184. There was &amp;lt;5% body weight loss and no significant hematological toxicity in both these models during or after LP-184 treatment. In selected PaCa models, we determined LP-184 efficacy to be synergistic in combination with multiple treatment modalities including standard of care agent gemcitabine, and ERCC3 degrader spironolactone in vitro, and with radiation therapy (RT) in vivo. Overall Bliss synergy scores (score &amp;gt; 10 indicates synergy) of 12.37 for LP-184 + gemcitabine in Capan-1, and 14.08, 16.47 and 15.52 for LP-184 + spironolactone in Capan-1 (BRCA2 loss), Hs766t (ATR mutant) and Panc03.27 cell lines respectively were achieved. Taking advantage of the transcriptional regulation underlying the NRF2 mediated anti-oxidant response pathway, we reasoned that induction of PTGR1 expression, a downstream NRF2 target gene, in irradiated PaCa tumors would thereafter poise them for LP-184 treatment. Indeed, we found that Panc03.27 xenograft tumors treated with 3 mg/kg i.p. LP-184 + 4 Gy RT once weekly for 3 weeks were significantly smaller than those receiving LP-184 alone or RT alone, thus capitalizing on the opportunity to increase PTGR1 expression (and linked LP-184 anti-tumor cytotoxicity) selectively in irradiated tumors. Increased PTGR1 expression has emerged as a promising biomarker for LP-184 cytotoxicity. Moreover, LP-184 can become synthetically lethal in multiple contexts when combined with genetic or pharmacologic DDR pathway aberrations, or with RT. Based on these properties, we anticipate that LP-184 will extend therapeutic opportunities to a large subset of PaCa patients. Citation Format: Aditya Kulkarni, Diana Restifo, Troy Dos Santos, Dusica Cvetkovic, Joseph McDermott, Kishor Bhatia, Panna Sharma, Charlie Ma, Igor Astsaturov. LP-184, a tumor site activated small molecule therapeutic, is synthetically lethal in pancreatic cancers with DNA damage repair defects [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B033.

Association of nonsynonymous SNPs of nucleotide excision repair genes ERCC4 rs1800067 (G/A) and ERCC5 rs17655 (G/C) as predisposing risk factors for gallbladder cancer.

Deregulation of DNA repair mechanisms have been frequently demonstrated in the pathology of cancers including gallbladder cancer. We aimed to investigate the association of ERCC4 rs1800067 (G/A) and ERCC5 rs17655 (G/C) with the predisposition in gallbladder cancer and its prognosis. We have also investigated the prognostic and diagnostic values of expression profiles of ERCC4 and ERCC5 in GBC. Polymorphisms of rs1800067 and rs17655 were genotyped by PCR-RFLP. The expression of these genes was analyzed by semi-quantitative PCR. Overall survival was analyzed using Kaplan-Meier plot and cox-regression analysis. Patients with risk group genotypes of rs17655 have shorter overall survival in patients with presence of gallstone, T1+T2 tumor invasion, absence of lymph node involvement and early stages of tumor. Homozygous wild genotype (GG) of rs1800067 and homozygous mutant genotype (CC) of rs17655 together increases two-fold risk of the disease. The variant genotypes (GC/CC) of rs17655 show significantly higher level of ERCC5 expression. Major allele of ERCC4 rs1800067 and minor allele of ERCC5 rs17655 are significantly associated with increased risk of GBC. Upregulation of ERCC4 and ERCC5 is an early event of development of GBC.

Combining Phenotypes of Nucleotide Excision Repair Pathway to Predict the Risk of Head and Neck Squamous Cell Carcinomas in a Chinese Population

Background Nucleotide excision repair (NER) is pivotal in the development of smoking-related malignancies. Nine core genes (XPA, XPB, XPC, XPD, XPF, XPG, ERCC1, DDB1, and DDB2) are highly involved in the NER process. We combined two phenotypes of NER pathway (NER protein and NER gene mRNA expression) and evaluated their associations with the risks of the head and neck squamous cell carcinomas (HNSCCs) in a Chinese population. Methods We conducted a case-control study of 337 HNSCC patients and 285 cancer-free controls by measuring the expression levels of nine core NER proteins and NER gene mRNA in cultured peripheral lymphocytes. Results Compared with the controls, cases had statistically significantly lower protein expression levels of XPA (P < 0.001) and lower mRNA expression levels of XPA and XPB (P = 0.005 and 0.001, respectively). After dividing the subjects by controls' medians of expression levels, we found an association between increased risks of HNSCCs and low XPA protein level (Ptrend = 0.031), as well as low mRNA levels of XPA and XPB (Ptrend = 0.024 and 0.001, respectively). Subsequently, we correlated the two phenotypes and found associations between the NER mRNA and protein levels. Finally, the sensitivity of the expanded model with protein and mRNA expression levels, in addition to demographic variables, on HNSCCs risk was significantly improved. Conclusions Combining two phenotypes of NER pathway may be more effective than the model only including one single phenotype for the assessment of risks of HNSCCs.

Cockayne syndrome in an Iranian pedigree with a homozygous missense variant in the ERCC6 gene

Cockayne syndrome (CS), a rare autosomal recessive multisystem disorder, is characterized by mental retardation, progressive growth failure, neurodegeneration, microcephaly, retinal degeneration, sensorineural deafness, cutaneous photosensitivity and premature aging. This genetic disorder is a member of the nucleotide excision repair (NER) disorder family. Excision repair cross-complementing, group 6 (ERCC6) and excision repair cross-complementing, group 8 (ERCC8) gene mutations underlie most CS cases. Furthermore, a small number of CS cases are caused by mutations in other NER genes. Furthermore, a small number of Cockayne syndrome cases are caused by certain mutations in the XP genes. This article describes the symptoms of Cockayne syndrome in an 8-year-old Iranian child. Using whole exome sequencing, we discovered a homozygous missense mutation in the ERCC6 gene, c.2551 T > A; p Trp851Arg.

The Effect of RAD7 Gene’s Null Mutation on Single-Cell Aging

Background: Although different theories and hypotheses were postulated for aging, molecular mechanisms of its regulations are still vastly unknown. In time, a post-mitotic cell ages with the aggregation of mutations within its genome and reach senescence. The DNA repair system that protects its genome also malfunctions with time. This study aims to discover whether manipulating a DNA repair gene can regulate the cellular life span, especially the chronological life span using the single-cell model (Saccharomyces cerevisiae) in the field of aging. Methods: In this study, yeast mutant that lacks nucleotide excision repair (NER) gene RAD7 along with the diploid wild type (DP-WT) yeast strain (BY4743) as control were used. RAD7 encodes a protein that acts in the NER of UV-damaged DNA. To characterize the mutant cell, experiments i.e. chronological lifespan assay, growth-proliferation, respiration status, mtDNA distribution patterns, and interaction analysis using bioinformatics were conducted. MIPS functional classification using FunSpec software was used to determine RAD7’s interaction with diverse genes.Results: In the chronological lifespan assay, it was found that the RAD7 gene’s null mutation (Δrad7) had a prolonged stationary phase compared to the wild-type strain. The mutant displayed respiration potency by growing well on a glycerol-based medium. Fluorescence microscopic observations disclosed that the mutants had a lower abundance of mtDNA compared to the control. Furthermore, RAD7 gene interaction analysis demonstrated how it interacts with other genes in the organism. Mutation of this repair gene affects mtDNA distribution and mtDNA abundance, yet cells could survive in the chronological phase. MtDNA depletion is a sign of altered mitochondrial morphology and function that may activate a retrograde response from mitochondria to the nucleus. Conclusion: From this study, it is suggested that the RAD7 gene can regulate yeast cells’ life span. However, the retrograde response was not investigated in this current study and thus further efforts are also required to draw a fine conclusion.