Suppression of REV7 enhances cisplatin sensitivity in ovarian clear cell carcinoma cells

Predictive tissue markers in testicular germ cell tumors: Immunohistochemical expression of MLH1 and REV-7 proteins

PURPOSE

Testicular Germ Cell Tumors (TGCTs) are the most frequent solid malignancies in young adult men. Regardless of differences in their cell of origin, all TGCTs are considered highly curable malignancies. However, approximately 3-5% of all TGCTs do not respond to platinum-based chemotherapies. The purpose of our paper is to investigate whether immunohistochemical expression of MLH1 and REV-7 can be used as predictive tissue markers for TGCTs.

MATERIAL AND METHODS

The main demographic and clinicopathological characteristics of 64 male patients with TGCTs who underwent orchiectomy from 2007 to 2022 were retrospectively obtained from two large Oncology Clinics in Greece. Both patients with chemosensitive and chemoresistant disease were included. Immunohistochemical staining for MLH1 and REV-7 proteins was applied in specimens of these patients.

RESULTS

31 seminomas and 33 non-seminomas were included. 48 patients had chemosensitive disease, while 16 had chemoresistant disease. 53 specimens showed preserved MLH1 expression, while 11 specimens had lost MLH1 expression. Expression of MLH1 was only significantly associated with patients' age. 16 specimens showed positive REV-7 expression, while 48 specimens were REV-7 negative. Interestingly, 50% of patients with chemoresistant disease and 16,7% of patients with chemosensitive disease were REV-7 positive. This difference was statistically significant. Moreover, REV-7 positivity was significantly associated with chemoresistance, various clinicopathological parameters and patients' prognosis and survival.

CONCLUSION

Loss of MLH1 expression was only found to be significantly associated with lower patients' age. Positive immunohistochemical REV-7 expression was significantly associated with various clinicopathological parameters, while it was also associated with significantly lower survival and greater hazard. REV-7 positive percentages were significantly higher in patients with chemoresistant disease. Our findings imply that immunohistochemical staining for REV-7 could potentially be used as a predictive tissue marker for TGCT tumors. Moreover, targeting of REV-7 protein, could represent a potential therapeutic strategy for chemoresistant TGCT cases. The implementation of well-designed studies on a larger scale is of utmost importance, in order to draw safer conclusions. Additional studies are needed so as to draw safer conclusions.

REV7 is involved in outcomes of platinum-based chemotherapy in pancreatic cancer by controlling the DNA damage response

REV7 is a multifunctional protein implicated in various biological processes, including DNA damage response. REV7 expression in human cancer cells affects their sensitivity to DNA-damaging agents. In the present study, we investigated the significance of REV7 in pancreatic ductal adenocarcinoma (PDAC). REV7 expression was immunohistochemically examined in 92 resected PDAC specimens and 60 endoscopic ultrasound-guided fine-needle aspiration biopsy (EUS-FNAB) specimens of unresectable PDAC treated with platinum-based chemotherapy, and its association with clinicopathologic features was analyzed. Although REV7 expression was not significantly associated with the progression of primary tumors (T-factor and Stage) in either resected or unresectable PDAC, decreased levels of REV7 expression in EUS-FNAB specimens of unresectable PDAC were significantly associated with better outcomes of platinum-based chemotherapy and a favorable prognosis. REV7-deficient PDAC cell lines showed suppressed cell growth and enhanced sensitivity to cisplatin in vitro. Tumor-bearing mice generated using REV7-deficient PDAC cell lines also showed enhanced sensitivity to cisplatin in vivo. RNA sequencing analysis using WT and REV7-deficient PDAC cell lines revealed that REV7 inactivation promoted the downregulation of genes involved in the DNA repair and the upregulation of genes involved in apoptosis. Our results indicate that decreased expression of REV7 is associated with better outcomes of platinum-based chemotherapy in PDAC by suppressing the DNA damage response. It is also suggested that REV7 is a useful biomarker for predicting the outcome of platinum-based chemotherapy and the prognosis of unresectable PDAC and is a potential target for PDAC treatment.

MAD2L2, a key regulator in ovarian cancer and promoting tumor progression

Ovarian cancer (OVCA), a prevalent gynecological malignancy, ranks as the fourth most common cancer among women. Mitotic Arrest Deficient 2 Like 2 (MAD2L2), a chromatin-binding protein and a component of DNA polymerase ζ, has been previously identified as an inhibitor of tumor growth in colorectal cancer. However, the roles of MAD2L2 in OVCA, including its expression, impact, and prognostic significance, remain unclear. We employed bioinformatics tools, Cox Regression analysis, and in vitro cell experiments to investigate its biological functions. Our findings reveal that MAD2L2 typically undergoes genomic alterations, such as amplifications and deep deletions. Moreover, we observed an overexpression of MAD2L2 mRNA in OVCA patients, correlating with reduced survival rates, particularly in those with Grade IV tumors. Furthermore, analysis of mRNA biofunctions indicated that MAD2L2 is predominantly localized in the organellar ribosome, engaging mainly in NADH dehydrogenase activity. This was deduced from the results of gene ontology enrichment analysis, which also identified its role as a structural constituent in mitochondrial translation elongation. These findings were corroborated by KEGG pathway analysis, further revealing MAD2L2's involvement in tumor metabolism and the cell death process. Notably, MAD2L2 protein expression showed significant associations with various immune cells, including CD4+T cells, CD8+T cells, B cells, natural killer cells, and Myeloid dendritic cells. Additionally, elevated levels of MAD2L2 were found to enhance cell proliferation and migration in OVCA cells. The upregulation of MAD2L2 also appears to inhibit the ferroptosis process, coinciding with increased mTOR signaling activity in these cells. Our study identifies MAD2L2 as a novel regulator in ovarian tumor progression and offers new insights for treating OVCA.

The Immunohistochemical Expression of REV-7 in Various Human Cancer Pathology Specimens: A Systematic Review

The purpose of this systematic review is to summarize all existing evidence, regarding the immunohistochemical expression of REV-7 in different human cancer pathology specimens. Moreover, the association of REV-7 expression with disease severity (clinical course), patients' survival, prognosis, and response to various treatments, such as chemotherapy and irradiation, was investigated. Three databases (PubMed, Scopus, and Cochrane) were systematically screened, from inception to September 2, 2023, as suggested by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Only studies using immunohistochemical staining for REV-7 in paraffin-embedded cancer tissues were included. Nine studies met the inclusion criteria and were included in the final qualitative synthesis. All nine studies were retrospective and non-comparative ones. Selected studies reported immunohistochemical expression of REV-7 in different types of cancer, including testicular cancer, ovarian cancer, esophagus squamous cell carcinoma, prostate cancer, colorectal cancer, diffuse large B-cell lymphoma, breast cancer, lung cancer, and skin cancer. High REV-7 expression was associated with faster disease progression, resistance to available treatment options, and worse prognosis in the majority of included studies. These results indicate that immunohistochemical staining of REV-7 protein could potentially be used as a predictive tissue marker in certain cases. Promising results, arising from REV-7 inactivation experiments, render REV-7 targeting a potential therapeutic strategy for future cancer management, especially in the cases of chemoresistant or radioresistant disease.

The promoting effect and mechanism of MAD2L2 on stemness maintenance and malignant progression in glioma

BACKGROUND

Glioblastoma, the most common primary malignant tumor of the brain, is associated with poor prognosis. Glioblastoma cells exhibit high proliferative and invasive properties, and glioblastoma stem cells (GSCs) have been shown to play a crucial role in the malignant behavior of glioblastoma cells. This study aims to investigate the molecular mechanisms involved in GSCs maintenance and malignant progression.

METHODS

Bioinformatics analysis was performed based on data from public databases to explore the expression profile of Mitotic arrest deficient 2 like 2 (MAD2L2) and its potential function in glioma. The impact of MAD2L2 on glioblastoma cell behaviors was assessed through cell viability assays (CCK8), colony formation assays, 5-Ethynyl-2'-deoxyuridine (EDU) incorporation assays, scratch assays, and transwell migration/invasion assays. The findings from in vitro experiments were further validated in vivo using xenograft tumor model. GSCs were isolated from the U87 and LN229 cell lines through flow cytometry and the stemness characteristics were verified by immunofluorescence staining. The sphere-forming ability of GSCs was examined using the stem cell sphere formation assay. Bioinformatics methods were conducted to identified the potential downstream target genes of MAD2L2, followed by in vitro experimental validation. Furthermore, potential upstream transcription factors that regulate MAD2L2 expression were confirmed through chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assays.

RESULTS

The MAD2L2 exhibited high expression in glioblastoma samples and showed significant correlation with patient prognosis. In vitro and in vivo experiments confirmed that silencing of MAD2L2 led to decreased proliferation, invasion, and migration capabilities of glioblastoma cells, while decreasing stemness characteristics of glioblastoma stem cells. Conversely, overexpression of MAD2L2 enhanced these malignant behaviors. Further investigation revealed that MYC proto-oncogene (c-MYC) mediated the functional role of MAD2L2 in glioblastoma, which was further validated through a rescue experiment. Moreover, using dual-luciferase reporter gene assays and ChIP assays determined that the upstream transcription factor E2F-1 regulated the expression of MAD2L2.

CONCLUSION

Our study elucidated the role of MAD2L2 in maintaining glioblastoma stemness and promoting malignant behaviors through the regulation of c-MYC, suggesting its potential as a therapeutic target.

Identification of the promoter region regulating the transcription of the REV7 gene

REV7 is involved in various biological processes including DNA repair and mutagenesis, cell cycle regulation, gene transcription, and carcinogenesis. REV7 is highly expressed in adult testicular germ cells as well as several malignant tumors. REV7 expression levels are associated with prognosis in several human cancers, however, the mechanism of REV7 transcriptional regulation has not been elucidated. In this study, we characterized the promoter region of the REV7 gene. A luciferase reporter assay using the human germ cell tumor cell line NEC8 was utilized to examine the upstream genomic region of REV7 for transcriptional activity, and two transcriptional activation regions were identified. We determined a small genomic region important for transcriptional activation using site-directed mutagenesis; this region is shared by several putative binding motifs for transcription factors, including the cAMP-responsive element modulator (CREM), cAMP-response element binding protein (CREB), and B-lymphocyte-induced maturation protein-1 (BLIMP-1). Exogenous CREM and CREB expression had no effect on the transcriptional activity in NEC8 cells or the human embryonic kidney cell line HEK293T. In contrast, exogenous BLIMP-1 expression increased luciferase reporter activity in HEK293T cells but unexpectedly decreased activity in NEC8 cells. Chromatin immunoprecipitation analysis demonstrated that BLIMP-1 binds to the genomic region near the binding motif in the REV7 promoter. Additionally, BLIMP-1 overexpression promoted endogenous REV7 expression in HEK293T cells. These findings suggest that BLIMP-1 may be a putative transcriptional regulator of REV7 in mammalian cells.

REV7 in Cancer Biology and Management

DNA repair and cell cycle regulation are potential biological fields to develop molecular targeting therapies for cancer. Human REV7 was originally discovered as a homologous molecule to yeast Rev7, which is involved in DNA damage response and mutagenesis, and as the second homolog of yeast Mad2, involved in the spindle assembly checkpoint. Although REV7 principally functions in the fields of DNA repair and cell cycle regulation, many binding partners of REV7 have been identified using comprehensive analyses in the past decade, and the significance of REV7 is expanding in various other biological fields, such as gene transcription, epigenetics, primordial germ cell survival, neurogenesis, intracellular signaling, and microbial infection. In addition, the clinical significance of REV7 has been demonstrated in studies using human cancer tissues, and investigations in cancer cell lines and animal models have revealed the greater impacts of REV7 in cancer biology, which makes it an attractive target molecule for cancer management. This review focuses on the functions of REV7 in human cancer and discusses the utility of REV7 for cancer management with a summary of the recent development of inhibitors targeting REV7.

Leveraging the replication stress response to optimize cancer therapy

High-fidelity DNA replication is critical for the faithful transmission of genetic information to daughter cells. Following genotoxic stress, specialized DNA damage tolerance pathways are activated to ensure replication fork progression. These pathways include translesion DNA synthesis, template switching and repriming. In this Review, we describe how DNA damage tolerance pathways impact genome stability, their connection with tumorigenesis and their effects on cancer therapy response. We discuss recent findings that single-strand DNA gap accumulation impacts chemoresponse and explore a growing body of evidence that suggests that different DNA damage tolerance factors, including translesion synthesis polymerases, template switching proteins and enzymes affecting single-stranded DNA gaps, represent useful cancer targets. We further outline how the consequences of DNA damage tolerance mechanisms could inform the discovery of new biomarkers to refine cancer therapies.

Mechanisms used by cancer cells to tolerate drug-induced replication stress

Activation of oncogenes in cancer cells forces cell proliferation, leading to DNA replication stress (RS). As a consequence, cancer cells heavily rely on the intra S-phase checkpoint for survival. This fundamental principle formed the basis for the development of inhibitors against key players of the intra S-phase checkpoint, ATR and CHK1. These drugs are often combined with chemotherapeutic drugs that interfere with DNA replication to exacerbate RS and exhaust the intra S-phase checkpoint in cancer cells. However, drug resistance impedes efficient clinical use, suggesting that some cancer cells tolerate severe RS. In this review, we describe how an increased nucleotide pool, boosted stabilization and repair of stalled forks and firing of dormant origins fortify the RS response in cancer cells. Notably, the vast majority of the genes that confer RS tolerance are regulated by the E2F and NRF2 transcription factors. These transcriptional programs are frequently activated in cancer cells, allowing simultaneous activation of multiple tolerance avenues. We propose that the E2F and NRF2 transcriptional programs can be used as biomarker to select patients for treatment with RS-inducing drugs and as novel targets to kill RS-tolerant cancer cells. Together, this review aims to provide a framework to maximally exploit RS as an Achilles' heel of cancer cells.

Cell Cycle Checkpoints and Beyond: Exploiting the ATR/CHK1/WEE1 Pathway for the Treatment of PARP Inhibitor–Resistant Cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPis) have become a mainstay of therapy in ovarian cancer and other malignancies, including BRCA-mutant breast, prostate, and pancreatic cancers. However, a growing number of patients develop resistance to PARPis, highlighting the need to further understand the mechanisms of PARPi resistance and develop effective treatment strategies. Targeting cell cycle checkpoint protein kinases, e.g., ATR, CHK1, and WEE1, which are upregulated in response to replication stress, represents one such therapeutic approach for PARPi-resistant cancers. Mechanistically, activated cell cycle checkpoints promote cell cycle arrest, replication fork stabilization, and DNA repair, demonstrating the interplay of DNA repair proteins with replication stress in the development of PARPi resistance. Inhibitors of these cell cycle checkpoints are under investigation in PARPi-resistant ovarian and other cancers. In this review, we discuss the cell cycle checkpoints and their roles beyond mere cell cycle regulation as part of the arsenal to overcome PARPi-resistant cancers. We also address the current status and recent advancements as well as limitations of cell cycle checkpoint inhibitors in clinical trials.

Disrupting the MAD2L2-Rev1 Complex Enhances Cell Death upon DNA Damage

DNA-damaging chemotherapy agents such as cisplatin have been the first line of treatment for cancer for decades. While chemotherapy can be very effective, its long-term success is often reduced by intrinsic and acquired drug resistance, accompanied by chemotherapy-resistant secondary malignancies. Although the mechanisms causing drug resistance are quite distinct, they are directly connected to mutagenic translesion synthesis (TLS). The TLS pathway promotes DNA damage tolerance by supporting both replication opposite to a lesion and inaccurate single-strand gap filling. Interestingly, inhibiting TLS reduces both cisplatin resistance and secondary tumor formation. Therefore, TLS targeting is a promising strategy for improving chemotherapy. MAD2L2 (i.e., Rev7) is a central protein in TLS. It is an essential component of the TLS polymerase zeta (ζ), and it forms a regulatory complex with Rev1 polymerase. Here we present the discovery of two small molecules, c#2 and c#3, that directly bind both in vitro and in vivo to MAD2L2 and influence its activity. Both molecules sensitize lung cancer cell lines to cisplatin, disrupt the formation of the MAD2L2-Rev1 complex and increase DNA damage, hence underlining their potential as lead compounds for developing novel TLS inhibitors for improving chemotherapy treatments.

Evolutionary Dynamics and Molecular Mechanisms of HORMA Domain Protein Signaling

Controlled assembly and disassembly of multi-protein complexes is central to cellular signaling. Proteins of the widespread and functionally diverse HORMA family nucleate assembly of signaling complexes by binding short peptide motifs through a distinctive safety-belt mechanism. HORMA proteins are now understood as key signaling proteins across kingdoms, serving as infection sensors in a bacterial immune system and playing central roles in eukaryotic cell cycle, genome stability, sexual reproduction, and cellular homeostasis pathways. Here, we describe how HORMA proteins' unique ability to adopt multiple conformational states underlies their functions in these diverse contexts. We also outline how a dedicated AAA+ ATPase regulator, Pch2/TRIP13, manipulates HORMA proteins' conformational states to activate or inactivate signaling in different cellular contexts. The emergence of Pch2/TRIP13 as a lynchpin for HORMA protein action in multiple genome-maintenance pathways accounts for its frequent misregulation in human cancers and highlights TRIP13 as a novel therapeutic target. Expected final online publication date for the Annual Review of Biochemistry, Volume 91 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Upregulation of REV7 correlates with progression of malignant melanoma

REV7 is a multifunctional protein implicated in DNA damage tolerance, cell cycle control, and gene expression, and is involved in the carcinogenesis of various human tumors. It has been reported that REV7 expression is associated with ultraviolet-induced mutagenesis; however, the role of REV7 expression in skin cancers, including malignant melanomas, remains unclear. In the present study, we investigated the clinical and biological significance of REV7 in malignant melanoma. Levels of REV7 expression in human skin cancers were evaluated immunohistochemically. Positive expression of REV7 was frequently observed in malignant melanomas, as well as in squamous cell carcinomas and basal cell carcinomas. Enhanced immunoreactivity to REV7 was closely linked with cell proliferation assessed by Ki-67 labeling indexes in the three skin cancers, and was related with tumor thickness in malignant melanomas. REV7 depletion in malignant melanoma cells MEWO and G361 suppressed cell proliferation, migration, and invasion abilities. REV7 depletion also affected the expression of intracellular signaling molecules AKT and ERK in MEWO cells, resulting in downregulation of ERK signal activation. In addition, REV7 depletion facilitated sensitivity to cisplatin, but not to dacarbazine, in MEWO cells. Our results suggest that REV7 expression correlates with disease progression of malignant melanoma.

Inhibition of MAD2B alleviates venous neointimal formation by suppressing VSMCs proliferation and migration

The proliferation and migration of vascular smooth muscle cells (VSMCs) are essential events in venous neointimal hyperplasia (VNH), a culprit of arteriovenous fistula (AVF) malfunction. Mitotic arrest-deficient protein 2B (MAD2B) is a critical regulator of cell proliferation and differentiation in many scenarios. To address the role of MAD2B in VSMCs proliferation and migration during VNH, AVFs from patients with end-stage renal disease (ESRD) and chronic kidney disease (CKD) mice were used to evaluate MAD2B expression. In cultured VSMCs treated with platelet-derived growth factor-BB (PDGF-BB), the effect of MAD2B on VSMCs proliferation and migration was detected by cell counting kit-8 (CCK8) assay, immunofluorescence, wound-healing scratch and transwell assays. Besides, we exploited different small interfering RNAs (siRNAs) to explore the potential mechanisms in the issue. Furthermore, rapamycin was applied to reveal whether MAD2B-associated pathways were involved in its inhibitory effect on VSMCs proliferation and migration. Accordingly, we found that MAD2B expression was enhanced in AVFs from patients with ESRD, CKD mice and VSMCs stimulated by PDGF-BB. Meanwhile, inhibition of MAD2B alleviated VSMCs proliferation and migration while the number of ski-related novel gene (SnoN)-positive VSMCs was also increased in vivo and in vitro. Moreover, gene deletion of MAD2B decreased the level of SnoN protein in PDGF-BB-stimulated VSMCs. Furthermore, rapamycin suppressed the increased expressions of MAD2B and SnoN induced by PDGF-BB. Thus, our study demonstrates that inhibition of MAD2B suppresses the proliferation and migration of VSMCs during VNH via reducing SnoN expression. Moreover, rapamycin exerts an inhibitory effect on intimal hyperplasia, possibly via the MAD2B-SnoN axis.

Implications of inhibition of Rev1 interaction with Y family DNA polymerases for cisplatin chemotherapy

Chemotherapy with cisplatin becomes limiting due to toxicity and secondary malignancies. In principle, therapeutics could be improved by targeting translesion synthesis (TLS) polymerases (Pols) that promote replication through intrastrand cross-links, the major cisplatin-induced DNA adduct. However, to specifically target malignancies with minimal adverse effects on normal cells, a good understanding of TLS mechanisms in normal versus cancer cells is paramount. We show that in normal cells, TLS through cisplatin intrastrand cross-links is promoted by Polη- or Polι-dependent pathways, both of which require Rev1 as a scaffolding component. In contrast, cancer cells require Rev1-Polζ. Our findings that a recently identified Rev1 inhibitor, JH-RE-06, purported to specifically disrupt Rev1 interaction with Polζ to block TLS through cisplatin adducts in cancer cells, abrogates Rev1's ability to function with Y family Pols as well, implying that by inactivating Rev1-dependent TLS in normal cells, this inhibitor will exacerbate the toxicity and tumorigenicity of chemotherapeutics with cisplatin.

The Fanconi anemia pathway and Breast Cancer: A comprehensive review of clinical data

The development of breast cancer depends on several risk factors, including environmental, lifestyle and genetic factors. Despite the evolution of DNA sequencing techniques and biomarker detection, the epidemiology and mechanisms of various breast cancer susceptibility genes have not been elucidated yet. Dysregulation of the DNA damage response causes genomic instability and increases the rate of mutagenesis and the risk of carcinogenesis. The Fanconi Anemia (FA) pathway is an important component of the DNA damage response and plays a critical role in the repair of DNA interstrand crosslinks and genomic stability. The FA pathway involves 22 recognized genes and specific mutations have been identified as the underlying defect in the majority of FA patients. A thorough understanding of the function and epidemiology of these genes in breast cancer is critical for the development and implementation of individualized therapies that target unique tumor profiles. Targeted therapies (PARP inhibitors) exploiting the FA pathway gene defects have been developed and have shown promising results. This narrative review summarizes the current literature on the involvement of FA genes in sporadic and familial breast cancer with a focus on clinical data derived from large cohorts.

Neurodevelopmental phenotypes in individuals with pathogenic variants in CHAMP1

De novo pathogenic variants in CHAMP1 (chromosome alignment maintaining phosphoprotein 1), which encodes kinetochore-microtubule associated protein on 13q34, cause a rare neurodevelopmental disorder. We enrolled 14 individuals with pathogenic variants in CHAMP1 that were documented by exome sequencing or gene panel sequencing. Medical history interviews, seizure surveys, Vineland Adapted Behavior Scales Second Edition, and other behavioral surveys were completed by primary caregivers of available participants in Simons Searchlight. Clinicians extracted clinical data from the medical record for two participants. We report on clinical features of 14 individuals (ages 2-26) with de novo predicted loss-of-function variants in CHAMP1 and compare them with previously reported cases (total n = 32). At least two individuals have the same de novo variant: p.(Ser181Cysfs*5), p.(Trp348*), p.(Arg398*), p.(Arg497*), or p.(Tyr709*). Common phenotypes include intellectual disability/developmental delay, language impairment, congenital and acquired microcephaly, behavioral problems including autism spectrum disorder, seizures, hypotonia, gastrointestinal issues of reflux and constipation, and ophthalmologic issues. Other rarely observed phenotypes include leukemia, failure to thrive, and high pain tolerance. Pathogenic variants in CHAMP1 are associated with a variable clinical phenotype of developmental delay/intellectual disability and seizures.

REV7: Jack of many trades

The HORMA domain protein REV7, also known as MAD2L2, interacts with a variety of proteins and thereby contributes to the establishment of different complexes. With doing so, REV7 impacts a diverse range of cellular processes and gained increasing interest as more of its activities became uncovered. REV7 has important roles in translesion synthesis and mitotic progression, and acts as a central component in the recently discovered shieldin complex that operates in DNA double-strand break repair. Here we discuss the roles of REV7 in its various complexes, focusing on its activity in genome integrity maintenance. Moreover, we will describe current insights on REV7 structural features that allow it to be such a versatile protein.

Core 2 β1,6-N-acetylglucosaminyltransferases accelerate the escape of choriocarcinoma from natural killer cell immunity

Hyperglycosylated human chorionic gonadotropin (H-hCG) is secreted from choriocarcinoma and contains a core2 O-glycan formed by core2 β1,6-N-acetylglucosaminyl transferase (C2GnT). Choriocarcinoma is considered immunogenic as it is gestational and contains paternal chromosomal components. Here we examined the function of C2GnT in the evasion of choriocarcinoma cells from natural killer (NK) cell-mediating killing. We determined that C2GnT is highly expressed in malignant gestational trophoblastic neoplasms. C2GnT KO downregulates core2 O-glycan expression in choriocarcinoma cells, which are more efficiently killed by NK cells than control cells. C2GnT KO cell containing tumor necrosis factor-related apoptosis inducing ligand have lower viability than control cells. Additionally, poly-N-acetyllactosamine in core2 branched oligosaccharides on MHC class I-related chain A (MICA) and mucin1 (MUC1) is significantly reduced in C2GnT KO cells. Meanwhile, the cumulative survival rate of nude mice inoculated with C2GnT KO tumors was higher than that of the control group. These findings suggest that choriocarcinoma cells may escape NK cell-mediated killing via glycosylation of MICA and MUC1.

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C2GnT knockout reduces core2 O-glycan expression in choriocarcinoma cells

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C2GnT KO cells are more readily killed by NK cells

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C2GnT KO cells containing TRAIL have lower viability than controls

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MHC class I-related chain A and MUC1 glycosylation is reduced in C2GnT KO cells

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Survival rate of nude mice inoculated with C2GnT KO tumors is higher than controls

Clinical impact of EZH2 and its antagonist SMARCA4 in ovarian cancer

SMARCA4 and EZH2 are two functional key players of their respective antagonizing chromatin remodeling complexes SWI/SNF and PRC2. EZH2 inhibitory drugs may abrogate pro-oncogenic features of PRC2 and turn the balance to cell differentiation via SWI/SNF activity in cancers. SMARCA4 and EZH2 expression was assessed by RT-PCR in 238 epithelial ovarian cancers (OCs) and put in relation to clinico-pathological parameters and patients' outcome. Optimal thresholds for high and low expression of both variables were calculated by the Youden's index based on receiver operating characteristic (ROC) curves. High SMARCA4 mRNA expression was independently associated with favorable progression-free survival (PFS) (P = 0.03) and overall survival (OS) (P = 0.018). As Youden's threshold determination for EZH2 yielded a S-shaped ROC-curve, two cut-off points (29th and 94th percentile) predicting opposite features were defined. Whereas EZH2 mRNA levels beyond the 29th percentile independently predicted poor PFS (P = 0.034), Cox-regression in EZH2 transcripts above the 94th percentile revealed a conversion from unfavorable to favorable PFS and OS (P = 0.009 and P = 0.032, respectively). High SMARCA4 expression associates with improved survival, whereas moderate/high EZH2 expression predicts poor outcome, which converts to favorable survival in ultra-high expressing OCs. This small OC subgroup could be characterized by REV7-abrogated platinum hypersensitivity but concomitant PARP-inhibitor resistance.

Increased expression of REV7 in small cell lung carcinomas and its association with tumor cell survival and proliferation

REV7 is involved in multiple biological processes including DNA damage tolerance, cell cycle regulation and gene expression, and is an accessory subunit of the mutation-prone DNA polymerase ζ. It has been reported that REV7 expression is associated with poor prognosis in several human cancers. The aim of this study is to investigate the significance of REV7 in lung carcinogenesis. Immunohistochemical analyses of surgically resected lung cancer specimens revealed that REV7 shows an increased expression in small cell lung carcinomas (SCLCs) when compared with other histological types of lung carcinoma. Association between REV7 expression levels and clinicopathological factors was investigated using SCLC cases with or without surgical resection. Our analyses revealed that high REV7 expression significantly correlated with tumor cell proliferation, assessed by Ki-67 labeling indices, and was negatively associated with distant metastasis and extensive-stage disease. No significant association was detected between REV7 expression and other factors, including prognosis or response to chemoradiotherapy in SCLC. Increase in REV7 expression in SCLC was confirmed using SCLC cell lines. In addition, siRNA-mediated depletion of REV7 activated the apoptotic pathway and suppressed cell growth in SCLC cells. These results suggest that REV7 plays an important role in tumor cell survival and proliferation in SCLC.

Structure and mechanism of B-family DNA polymerase ζ specialized for translesion DNA synthesis

DNA polymerase ζ (Polζ) belongs to the same B-family as high-fidelity replicative polymerases, yet is specialized for the extension reaction in translesion DNA synthesis (TLS). Despite its importance in TLS, the structure of Polζ is unknown. We present cryo-EM structures of the Saccharomyces cerevisiae Polζ holoenzyme in the act of DNA synthesis (3.1 Å) and without DNA (4.1 Å). Polζ displays a pentameric ring-like architecture, with catalytic Rev3, accessory Pol31' Pol32 and two Rev7 subunits forming an uninterrupted daisy chain of protein-protein interactions. We also uncover the features that impose high fidelity during the nucleotide-incorporation step and those that accommodate mismatches and lesions during the extension reaction. Collectively, we decrypt the molecular underpinnings of Polζ's role in TLS and provide a framework for new cancer therapeutics.

MAD2B contributes to parietal epithelial cell activation and crescentic glomerulonephritis via Skp2

Mitotic spindle assembly checkpoint protein 2 (MAD2B), a well-known anaphase-promoting complex/cyclosome (APC/C) inhibitor and a small subunit of DNA polymerase-ζ, is critical for mitotic control and DNA repair. Previously, we detected a strong increase of MAD2B in the glomeruli from patients with crescentic glomerulonephritis and anti-glomerular basement membrane (anti-GBM) rats, which predominantly originated from activated parietal epithelial cells (PECs). Consistently, in vitro MAD2B was increased in TNF-α-treated PECs, along with cell activation and proliferation, as well as extracellular matrix accumulation, which could be reversed by MAD2B genetic depletion. Furthermore, we found that expression of S phase kinase-associated protein 2 (Skp2), an APC/C^CDH1 substrate, was increased in the glomeruli of anti-GBM rats, and TNF-α-stimulated PECs and could be suppressed by MAD2B depletion. Additionally, genetic deletion of Skp2 inhibited TNF-α-induced PEC activation and dysfunction. Finally, TNF-α blockade or glucocorticoid therapy administered to anti-GBM rats could ameliorate MAD2B and Skp2 accumulation as well as weaken PEC activation. Collectively, our data suggest that MAD2B has a pivotal role in the pathogenesis of glomerular PEC activation and crescent formation through induction of Skp2 expression.

Biomarker-Guided Development of DNA Repair Inhibitors

Anti-cancer drugs targeting the DNA damage response (DDR) exploit genetic or functional defects in this pathway through synthetic lethal mechanisms. For example, defects in homologous recombination (HR) repair arise in cancer cells through inherited or acquired mutations in BRCA1, BRCA2, or other genes in the Fanconi anemia/BRCA pathway, and these tumors have been shown to be particularly sensitive to inhibitors of the base excision repair (BER) protein poly (ADP-ribose) polymerase (PARP). Recent work has identified additional genomic and functional assays of DNA repair that provide new predictive and pharmacodynamic biomarkers for these targeted therapies. Here, we examine the development of selective agents targeting DNA repair, including PARP inhibitors; inhibitors of the DNA damage kinases ataxia-telangiectasia and Rad3 related (ATR), CHK1, WEE1, and ataxia-telangiectasia mutated (ATM); and inhibitors of classical non-homologous end joining (cNHEJ) and alternative end joining (Alt EJ). We also review the biomarkers that guide the use of these agents and current clinical trials with these therapies.

Inactivation of REV7 enhances chemosensitivity and overcomes acquired chemoresistance in testicular germ cell tumors

REV7 is a multitasking protein involved in replication past DNA lesions, cell cycle regulation, and gene expression. REV7 is highly expressed in the adult testis and plays an essential role in primordial germ cell maintenance in mice. In this study, we analyzed whether REV7 can be a molecular target for the treatment of testicular germ cell tumors (TGCTs), in which acquired chemoresistance is a major cause of treatment failure. Strong expression of REV7 was detected in human TGCT tissues by immunohistochemistry. REV7 depletion in the TGCT cell lines suppressed cell proliferation and increased sensitivity to cisplatin and doxorubicin. cDNA microarray analysis revealed that REV7 depletion downregulated genes in the DNA repair gene set and upregulated genes in the apoptosis gene set. REV7 depletion-provoked chemosensitivity was associated with DNA double-strand break accumulation and apoptosis activation. In addition, inactivation of REV7 in cisplatin-resistant TGCT cells recovered chemosensitivity at almost equal levels as parental cells in vitro and in vivo. Our results indicate that inactivation of REV7 enhances chemosensitivity and overcomes chemoresistance in TGCT cells, suggesting REV7 as a potential therapeutic target in chemoresistant TGCTs.

Inhibitors of the Fanconi anaemia pathway as potential antitumour agents for ovarian cancer

The Fanconi anaemia (FA) pathway is an important mechanism for cellular DNA damage repair, which functions to remove toxic DNA interstrand crosslinks. This is particularly relevant in the context of ovarian and other cancers which rely extensively on interstrand cross-link generating platinum chemotherapy as standard of care treatment. These cancers often respond well to initial treatment, but reoccur with resistant disease and upregulation of DNA damage repair pathways. The FA pathway is therefore of great interest as a target for therapies that aim to improve the efficacy of platinum chemotherapies, and reverse tumour resistance to these. In this review, we discuss recent advances in understanding the mechanism of interstrand cross-link repair by the FA pathway, and the potential of the component parts as targets for therapeutic agents. We then focus on the current state of play of inhibitor development, covering both the characterisation of broad spectrum inhibitors and high throughput screening approaches to identify novel small molecule inhibitors. We also consider synthetic lethality between the FA pathway and other DNA damage repair pathways as a therapeutic approach.

DNA damage response and repair in ovarian cancer: Potential targets for therapeutic strategies

Ovarian cancer is among the most lethal gynecologic malignancies with a poor survival prognosis. The current therapeutic strategies involve surgery and chemotherapy. Research is now focused on novel agents especially those targeting DNA damage response (DDR) pathways. Understanding the DDR process in ovarian cancer necessitates having a detailed knowledge on a series of signaling mediators at the cellular and molecular levels. The complexity of the DDR process in ovarian cancer and how this process works in metastatic conditions is comprehensively reviewed. For evaluating the efficacy of therapeutic agents targeting DNA damage in ovarian cancer, we will discuss the components of this system including DDR sensors, DDR transducers, DDR mediators, and DDR effectors. The constituent pathways include DNA repair machinery, cell cycle checkpoints, and apoptotic pathways. We also will assess the potential of active mediators involved in the DDR process such as therapeutic and prognostic candidates that may facilitate future studies.

Post-replication repair: Rad5/HLTF regulation, activity on undamaged templates, and relationship to cancer

The eukaryotic post-replication repair (PRR) pathway allows completion of DNA replication when replication forks encounter lesions on the DNA template and are mediated by post-translational ubiquitination of the DNA sliding clamp proliferating cell nuclear antigen (PCNA). Monoubiquitinated PCNA recruits translesion synthesis (TLS) polymerases to replicate past DNA lesions in an error-prone manner while addition of K63-linked polyubiquitin chains signals for error-free template switching to the sister chromatid. Central to both branches is the E3 ubiquitin ligase and DNA helicase Rad5/helicase-like transcription factor (HLTF). Mutations in PRR pathway components lead to genomic rearrangements, cancer predisposition, and cancer progression. Recent studies have challenged the notion that the PRR pathway is involved only in DNA lesion tolerance and have shed new light on its roles in cancer progression. Molecular details of Rad5/HLTF recruitment and function at replication forks have emerged. Mounting evidence indicates that PRR is required during lesion-less replication stress, leading to TLS polymerase activity on undamaged templates. Analysis of PRR mutation status in human cancers and PRR function in cancer models indicates that down regulation of PRR activity is a viable strategy to inhibit cancer cell growth and reduce chemoresistance. Here, we review these findings, discuss how they change our views of current PRR models, and look forward to targeting the PRR pathway in the clinic.

Investigation into the Molecular Mechanisms underlying the Anti-proliferative and Anti-tumorigenesis activities of Diosmetin against HCT-116 Human Colorectal Cancer

Diosmetin (Dis) is a bioflavonoid with cytotoxicity properties against variety of cancer cells including hepatocarcinoma, breast and colorectal (CRC) cancer. The exact mechanism by which Dis acts against CRC however, still remains unclear, hence in this study, we investigated the possible molecular mechanisms of Dis in CRC cell line, HCT-116. Here, we monitored the viability of HCT-116 cells in the presence of Dis and investigated the underlying mechanism of Dis against HCT-116 cells at the gene and protein levels using NanoString and proteome profiler array technologies. Findings demonstrated that Dis exhibits greater cytotoxic effects towards HCT-116 CRC cells (IC50 = 3.58 ± 0.58 µg/ml) as compared to the normal colon CCD-841 cells (IC50 = 51.95 ± 0.11 µg/ml). Arrests of the cells in G2/M phase confirms the occurrence of mitotic disruption via Dis. Activation of apoptosis factors such as Fas and Bax at the gene and protein levels along with the release of Cytochrome C from mitochondria and cleavage of Caspase cascades indicate the presence of turbulence as a result of apoptosis induction in Dis-treated cells. Moreover, NF-ƙB translocation was inhibited in Dis-treated cells. Our results indicate that Dis can target HCT-116 cells through the mitotic disruption and apoptosis induction.

REV7 confers radioresistance of esophagus squamous cell carcinoma by recruiting PRDX2

Radiotherapy has been widely used for the clinical management of esophageal squamous cell carcinoma. However, radioresistance remains a serious concern that prevents the efficacy of esophageal squamous cell carcinoma (ESCC) radiotherapy. REV7, the structural subunit of eukaryotic DNA polymerase ζ, has multiple functions in bypassing DNA damage and modulating mitotic arrest in human cell lines. However, the expression and molecular function of REV7 in ESCC progression remains unclear. In this study, we first examined the expression of REV7 in clinical ESCC samples, and we found higher expression of REV7 in ESCC tissues compared to matched adjacent or normal tissues. Knockdown of REV7 resulted in decreased colony formation and increased apoptosis in irradiated Eca‐109 and TE‐1 cells coupled with decreased tumor weight in a xenograft nude mouse model postirradiation. Conversely, overexpression of REV7 resulted in radioresistance in vitro and in vivo. Moreover, silencing of REV7 induced increased reactive oxygen species levels postirradiation. Proteomic analysis of REV7‐interacting proteins revealed that REV7 interacted with peroxiredoxin 2 (PRDX2), a well‐known antioxidant protein. Existence of REV7‐PRDX2 complex and its augmentation postirradiation were further validated by immunoprecipitation and immunofluorescence assays. REV7 knockdown significantly disrupted the presence of nuclear PRDX2 postirradiation, which resulted in oxidative stress. REV7‐PRDX2 complex also assembled onto DNA double‐strand breaks, whereas REV7 knockdown evidently increased double‐strand breaks that were unmerged by PRDX2. Taken together, the present study sheds light on REV7‐modulated radiosensitivity through interacting with PRDX2, which provides a novel target for ESCC radiotherapy.

Clinical analysis of chemo-resistance risk factors in endometriosis associated ovarian cancer

BACKGROUND

To analyze the clinical characteristics and chemo-resistance related factors of patients with resistant and non-resistant endometriosis-associated ovarian cancer (ovarian clear cell carcinoma and endometrioid carcinoma) by reviewing the data of epithelial ovarian cancer patients who received initial treatment in our hospital over a 12-year period.

RESULTS

Among the 304 patients, 17.1% were seen with platinum-based drug resistance. The ROC curve of continuous variables was drawn according to resistance situation, then they were grouped by age (< 48 or ≥ 48 years), tumor size (< 7 cm or ≥ 7 cm) and Ca125 (< 90 and ≥ 90 U/ml). In univariate analysis, age ≥ 48 years, initial symptom of abdominal distension or weight loss, abnormal preoperative serum Ca125, Ca125 < 90 U/ml, advanced FIGO stage, absence of endometriosis, bilateral tumors, lack of lymphadenectomy, positive lymph nodes, unsatisfactory initial cytoreduction surgery and history of breast cancer were all related to drug resistance in ovarian cancer. In multivariate analysis, advanced stage, lack of lymphadenectomy, positive lymph nodes and history of breast cancer were independent risk factors related to platinum-based drug resistance (P < 0.05).

CONCLUSION

For patients of endometriosis-related ovarian cancer, platinum-based drug resistance were associated with advanced FIGO stage, lack of lymphadenectomy, positive lymph nodes and history of breast cancer.

MAD2L2 inhibits colorectal cancer growth by promoting NCOA3 ubiquitination and degradation

Nuclear receptor coactivator 3 (NCOA3) is a transcriptional coactivator that has elevated expression in multiple tumor types, including colorectal cancer (CRC). However, the molecular mechanisms that regulate the tumorigenic functions of NCOA3 in CRC remain largely unknown. In this study, we aimed to discover and identify the novel regulatory proteins of NCOA3 and explore their mechanisms of action. Immunoprecipitation (IP) coupled with mass spectrometry (IP-MS) analysis was used to detect, identify, and verify the proteins that interacted with NCOA3 in CRC cells. The biological functions of the candidate proteins and the underlying molecular mechanism were investigated in CRC cells and mouse model in vitro and in vivo. The clinical significance of NCOA3 and its interaction partner protein in CRC patients was also studied. We identified mitotic arrest deficient 2-like protein 2 (MAD2L2, also known as MAD2B or REV7), with two signal peptide sequences of LIPLK and EVYPVGIFQK, to be an interaction partner of NCOA3. Overexpression of MAD2L2 suppressed the proliferation, migration, and clonogenicity of CRC cells by inducing the degradation of NCOA3. The mechanism study showed that increased MAD2L2 expression in CRC cells activated p38, which was required for the phosphorylation of NCOA3 that led to its ubiquitination and degradation by the proteasome. Moreover, we found that MAD2L2 predicted favorable prognosis in CRC patients. We have discovered a novel role of MAD2L2 in the regulation of NCOA3 degradation and proposed that MAD2L2 serves as a tumor suppressor in CRC.

Mitotic Arrest-Deficient Protein 2B Overexpressed in Lung Cancer Promotes Proliferation, EMT, and Metastasis

As the noncatalytic subunit of mammalian DNA polymerase, mitotic arrest-deficient protein 2B (MAD2B) has been reported to play a role in cell cycle regulation, DNA damage tolerance, gene expression, and carcinogenesis. Although its expression is known to be associated with poor prognosis in several types of human cancers, the significance of MAD2B expression in lung malignancies is still unclear. Our study showed that MAD2B expression significantly increased in lung cancer, especially in the metastatic tissues. We also found that knockdown of MAD2B inhibited the migration, invasion, and epithelial–mesenchymal transition of lung cancer cells in vitro and the metastasis in vivo, while overexpression of MAD2B had the opposite effect. Microarray and Western blotting data indicated that slug might be its downstream target since knockdown of MAD2B inhibited, while overexpression increased, the expression of slug. Moreover, the expression of MAD2B was found to be positively correlated with slug in lung cancer tissues as well. Collectively, these findings indicate an oncogenic role of MAD2B in lung cancer, and slug might be involved in the process.

Involvement of AMPK in regulating the degradation of MAD2B under high glucose in neuronal cells

Although our recent study has demonstrated that mitotic spindle assembly checkpoint protein (MAD2B) mediates high glucose‐induced neuronal apoptosis, the mechanisms for MAD2B degradation under hyperglycaemia have not yet been elucidated. In this study, we first found that the activation of adenosine 5′‐monophosphate (AMP)‐activated protein kinase (AMPK) was decreased in neurons, accompanied with the increased expression of MAD2B. Mechanistically, we demonstrated that activation of AMPK with its activators such as AICAR and metformin decreased the expression of MAD2B, indicating a role of AMPK in regulating the expression of MAD2B. Moreover, activation of AMPK prevented neuronal cells from high glucose‐induced injury as demonstrated by the reduced expression of cyclin B1 and percentage of apoptosis as detected by TUNEL. We further found that when total protein synthesis was suppressed by chlorhexidine, the degradation of MAD2B was slower in high glucose‐treated neurons and was mainly dependent on the ubiquitin–proteasome system. Finally, it was indicated that high glucose inhibited the ubiquitination of MAD2B, which could be reversed by activation of AMPK. Collectively, this study demonstrates that AMPK acts as a key regulator of MAD2B expression, suggesting that activation of AMPK signalling might be crucial for the treatment of high glucose‐induced neuronal injury.

MAD2B promotes tubular epithelial-to-mesenchymal transition and renal tubulointerstitial fibrosis via Skp2

The mitotic arrest deficient protein MAD2B is a well-defined anaphase-promoting complex/cyclosome (APC/C) inhibitor and a small subunit of DNA polymerase zeta. It is critical for mitotic control and DNA repair. However, the pathological role of MAD2B in kidney diseases has not been fully elucidated. In the present study, we aim to explore the role of MAD2B in the pathogenesis of renal tubulointerstitial fibrosis (TIF) and the underlying mechanism. By immunofluorescence and immunohistochemistry, we found an obvious MAD2B enhancement in tubular area of TIF patients and unilateral ureteral obstruction (UUO) mice. In vitro, transforming growth factor-β1 (TGF-β1) induced a time-dependent MAD2B accumulation prior to tubular epithelial-to-mesenchymal transition (EMT) in a rat proximal tubular epithelial cell line, NRK-52E. Knocking down MAD2B using siRNA dramatically inhibited TGF-β1-induced tubular EMT process and subsequent extracellular matrix (ECM) production. We also found that Skp2, a confirmed APC/C-CDH1 substrate and E-cadherin destroyer, was increased in TGF-β1-treated proximal tubular epithelial cells, which could be blocked by MAD2B depletion. In addition, Skp2 expression was also found to be increased in the renal tubular area of UUO mice. Locally knocking down MAD2B expression in the renal cortex using lentiviral transfection inhibited Skp2 expression, tubular EMT, and subsequent ECM accumulation. Taken together, our data suggests a pro-fibrotic role of MAD2B in the pathogenesis of tubular EMT and TIF by inducing Skp2 expression. MAD2B might be a potential target of promising interventions for renal TIF.

KEY MESSAGES

Renal fibrosis activates MAD2B expression in renal tubules of human and mouse. TGF-β1 contributes to MAD2B enhancement in rat tubular epithelial cells. MAD2B depletion alleviates renal tubulointerstitial fibrosis in vivo and in vitro. MAD2B promotes EMT transition in rat tubular epithelial cells by inducing Skp2.

Identification of the first small-molecule inhibitor of the REV7 DNA repair protein interaction

DNA interstrand crosslink (ICL) repair (ICLR) has been implicated in the resistance of cancer cells to ICL-inducing chemotherapeutic agents. Despite the clinical significance of ICL-inducing chemotherapy, few studies have focused on developing small-molecule inhibitors for ICLR. The mammalian DNA polymerase ζ, which comprises the catalytic subunit REV3L and the non-catalytic subunit REV7, is essential for ICLR. To identify small-molecule compounds that are mechanistically capable of inhibiting ICLR by targeting REV7, high-throughput screening and structure-activity relationship (SAR) analysis were performed. Compound 1 was identified as an inhibitor of the interaction of REV7 with the REV7-binding sequence of REV3L. Compound 7 (an optimized analog of compound 1) bound directly to REV7 in nuclear magnetic resonance analyses, and inhibited the reactivation of a reporter plasmid containing an ICL in between the promoter and reporter regions. The normalized clonogenic survival of HeLa cells treated with cisplatin and compound 7 was lower than that for cells treated with cisplatin only. These findings indicate that a small-molecule inhibitor of the REV7/REV3L interaction can chemosensitize cells by inhibiting ICLR.

MAD2B-mediated SnoN downregulation is implicated in fibroblast activation and tubulointerstitial fibrosis

MAD2B, an anaphase-promoting complex/cyclosome (APC/C) inhibitor and a small subunit of DNA polymerase ζ, is indispensible for mitotic checkpoint control and DNA repair. Previously, we established that MAD2B is expressed in glomerular and tubulointerstitial compartments and participates in high glucose-induced podocyte injury. However, its role in other renal diseases remains elusive. In the present study, we aim to illustrate the potential role of MAD2B in the pathogenesis of renal fibrosis. By immunofluorescence and Western blotting, we found MAD2B expression is obviously increased in tubulointerstitial fibrosis (TIF) patients and unilateral ureteral obstruction (UUO) mice. It is widely accepted that resident fibroblasts are the major source of collagen-producing myofibroblasts during TIF. Therefore, we evaluated the level of MAD2B in fibroblasts (NRK-49F) exposed to transforming growth factor (TGF)-β1 by immunoblotting and revealed that MAD2B is upregulated in a time-dependent manner. Intriguingly, SnoN, a transcriptional repressor of the TGF-β1/Smad signaling pathway, is decreased in TGF-β1-treated fibroblasts as well as the kidney cortex from TIF patients and UUO mice. Either in vitro or in vivo, local genetic depletion of MAD2B by lentiviral transfection could preserve SnoN abundance and suppress Smad3 phosphorylation, which finally dampens fibroblast activation, ECM accumulation, and alleviates the severity of TIF. However, the ubiquitin ligase APC/C is not involved in the MAD2B-mediated SnoN decline, although this process is ubiquitination dependent. In conclusion, our observation proposes that besides cell cycle management, MAD2B has a profibrotic role during fibroblast activation and TIF by suppressing SnoN expression. Targeting the MAD2B-SnoN pathway is a promising intervention for TIF.

Crosstalk between translesion synthesis, Fanconi anemia network, and homologous recombination repair pathways in interstrand DNA crosslink repair and development of chemoresistance

Bifunctional alkylating and platinum based drugs are chemotherapeutic agents used to treat cancer. These agents induce DNA adducts via formation of intrastrand or interstrand (ICL) DNA crosslinks, and DNA lesions of the ICL type are particularly toxic as they block DNA replication and/or DNA transcription. However, the therapeutic efficacies of these drugs are frequently limited due to the cancer cell's enhanced ability to repair and tolerate these toxic DNA lesions. This ability to tolerate and survive the DNA damage is accomplished by a set of specialized low fidelity DNA polymerases called translesion synthesis (TLS) polymerases since high fidelity DNA polymerases are unable to replicate the damaged DNA template. TLS is a crucial initial step in ICL repair as it synthesizes DNA across the lesion thus preparing the damaged DNA template for repair by the homologous recombination (HR) pathway and Fanconi anemia (FA) network, processes critical for ICL repair. Here we review the molecular features and functional roles of TLS polymerases, discuss the collaborative interactions and cross-regulation of the TLS DNA damage tolerance pathway, the FA network and the BRCA-dependent HRR pathway, and the impact of TLS hyperactivation on development of chemoresistance. Finally, since TLS hyperactivation results from overexpression of Rad6/Rad18 ubiquitinating enzymes (fundamental components of the TLS pathway), increased PCNA ubiquitination, and/or increased recruitment of TLS polymerases, the potential benefits of selectively targeting critical components of the TLS pathway for enhancing anti-cancer therapeutic efficacy and curtailing chemotherapy-induced mutagenesis are also discussed.