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

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.

Research progress on the fanconi anemia signaling pathway in non-obstructive azoospermia

Non-obstructive azoospermia (NOA) is a disease characterized by spermatogenesis failure and comprises phenotypes such as hypospermatogenesis, mature arrest, and Sertoli cell-only syndrome. Studies have shown that FA cross-linked anemia (FA) pathway is closely related to the occurrence of NOA. There are FA gene mutations in male NOA patients, which cause significant damage to male germ cells. The FA pathway is activated in the presence of DNA interstrand cross-links; the key step in activating this pathway is the mono-ubiquitination of the FANCD2-FANCI complex, and the activation of the FA pathway can repair DNA damage such as DNA double-strand breaks. Therefore, we believe that the FA pathway affects germ cells during DNA damage repair, resulting in minimal or even disappearance of mature sperm in males. This review summarizes the regulatory mechanisms of FA-related genes in male azoospermia, with the aim of providing a theoretical reference for clinical research and exploration of related genes.

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.

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.

Implications of Translesion DNA Synthesis Polymerases on Genomic Stability and Human Health

Replication fork arrest-induced DNA double strand breaks (DSBs) caused by lesions are effectively suppressed in cells due to the presence of a specialized mechanism, commonly referred to as DNA damage tolerance (DDT). In eukaryotic cells, DDT is facilitated through translesion DNA synthesis (TLS) carried out by a set of DNA polymerases known as TLS polymerases. Another parallel mechanism, referred to as homology-directed DDT, is error-free and involves either template switching or fork reversal. The significance of the DDT pathway is well established. Several diseases have been attributed to defects in the TLS pathway, caused either by mutations in the TLS polymerase genes or dysregulation. In the event of a replication fork encountering a DNA lesion, cells switch from high-fidelity replicative polymerases to low-fidelity TLS polymerases, which are associated with genomic instability linked with several human diseases including, cancer. The role of TLS polymerases in chemoresistance has been recognized in recent years. In addition to their roles in the DDT pathway, understanding noncanonical functions of TLS polymerases is also a key to unraveling their importance in maintaining genomic stability. Here we summarize the current understanding of TLS pathway in DDT and its implication for human health.

Breaking the Mold: Epigenetics and Genomics Approaches Addressing Novel Treatments and Chemoresponse in TGCT Patients

Testicular germ-cell tumors (TGCT) have been widely recognized for their outstanding survival rates, commonly attributed to their high sensitivity to cisplatin-based therapies. Despite this, a subset of patients develops cisplatin resistance, for whom additional therapeutic options are unsuccessful, and ~20% of them will die from disease progression at an early age. Several efforts have been made trying to find the molecular bases of cisplatin resistance. However, this phenomenon is still not fully understood, which has limited the development of efficient biomarkers and precision medicine approaches as an alternative that could improve the clinical outcomes of these patients. With the aim of providing an integrative landscape, we review the most recent genomic and epigenomic features attributed to chemoresponse in TGCT patients, highlighting how we can seek to combat cisplatin resistance through the same mechanisms by which TGCTs are particularly hypersensitive to therapy. In this regard, we explore ongoing treatment directions for resistant TGCT and novel targets to guide future clinical trials. Through our exploration of recent findings, we conclude that epidrugs are promising treatments that could help to restore cisplatin sensitivity in resistant tumors, shedding light on potential avenues for better prognosis for the benefit of the patients.

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.

Response of the Urothelial Carcinoma Cell Lines to Cisplatin

Cisplatin (CDDP)-based chemotherapy is the standard of care in patients with muscle-invasive bladder cancer. However, in a large number of cases, the disease becomes resistant or does not respond to CDDP, and thus progresses and disseminates. In such cases, prognosis of patients is very poor. CDDP manifests its cytotoxic effects mainly through DNA damage induction. Hence, response to CDDP is mainly dependent on DNA damage repair and tolerance mechanisms. Herein, we have examined CDDP response in a panel of the urothelial carcinoma cell (UCC) lines. We characterized these cell lines with regard to viability after CDDP treatment, as well as kinetics of induction and repair of CDDP-induced DNA damage. We demonstrate that repair of CDDP-induced DNA lesions correlates, at least to some extent, with CDDP sensitivity. Furthermore, we monitored expression of the key genes involved in selected DNA repair and tolerance mechanisms, nucleotide excision repair, homologous recombination and translesion DNA synthesis, and show that it differs in the UCC lines and positively correlates with CDDP resistance. Our data indicate that CDDP response in the UCC lines is dependent on DNA damage repair and tolerance factors, which may, therefore, represent valuable therapeutic targets in this malignancy.

Translesion DNA synthesis mediates acquired resistance to olaparib plus temozolomide in small cell lung cancer

In small cell lung cancer (SCLC), acquired resistance to DNA-damaging therapy is challenging to study because rebiopsy is rarely performed. We used patient-derived xenograft models, established before therapy and after progression, to dissect acquired resistance to olaparib plus temozolomide (OT), a promising experimental therapy for relapsed SCLC. These pairs of serial models reveal alterations in both cell cycle kinetics and DNA replication and demonstrate both inter- and intratumoral heterogeneity in mechanisms of resistance. In one model pair, up-regulation of translesion DNA synthesis (TLS) enabled tolerance of OT-induced damage during DNA replication. TLS inhibitors restored sensitivity to OT both in vitro and in vivo, and similar synergistic effects were seen in additional SCLC cell lines. This represents the first described mechanism of acquired resistance to DNA damage in a patient with SCLC and highlights the potential of the serial model approach to investigate and overcome resistance to therapy in SCLC.

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.

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.

Between a Rock and a Hard Place: An Epigenetic-Centric View of Testicular Germ Cell Tumors

Simple Summary

This minireview focuses on the role of epigenetics in testicular cancer. A working model is developed that postulates that epigenetic features that drive testicular cancer malignancy also enable these tumors to be cured at a high rate with chemotherapy. Chemoresistance may occur by epigenetic uncoupling of malignancy and chemosensitivity, a scenario that may be amenable to epigenetic-based therapies.

Abstract

Compared to many common solid tumors, the main genetic drivers of most testicular germ cell tumors (TGCTs) are unknown. Decades of focus on genomic alterations in TGCTs including awareness of a near universal increase in copies of chromosome 12p have failed to uncover exceptional driver genes, especially in genes that can be targeted therapeutically. Thus far, TGCT patients have missed out on the benefits of targeted therapies available to treat most other malignancies. In the past decade there has been a greater appreciation that epigenetics may play an especially prominent role in TGCT etiology, progression, and hypersensitivity to conventional chemotherapy. While genetics undoubtedly plays a role in TGCT biology, this mini-review will focus on the epigenetic “states” or features of testicular cancer, with an emphasis on DNA methylation, histone modifications, and miRNAs associated with TGCT susceptibility, initiation, progression, and response to chemotherapy. In addition, we comment on the current status of epigenetic-based therapy and epigenetic biomarker development for TGCTs. Finally, we suggest a unifying “rock and a hard place” or “differentiate or die” model where the tumorigenicity and curability of TGCTs are both dependent on common but still ill-defined epigenetic states.

Translesion synthesis inhibitors as a new class of cancer chemotherapeutics

Introduction: Translesion synthesis (TLS) is a DNA damage tolerance mechanism that replaces the replicative DNA polymerase with a specialized, low-fidelity TLS DNA polymerase that can copy past DNA lesions during active replication. Recent studies have demonstrated a primary role for TLS in replicating past DNA lesions induced by first-line genotoxic agents, resulting in decreased efficacy and acquired chemoresistance. With this in mind, targeting TLS as a combination strategy with first-line genotoxic agents has emerged as a promising approach to develop a new class of anti-cancer adjuvant agents. Areas covered: In this review, we provide a brief background on TLS and its role in cancer. We also discuss the identification and development of inhibitors that target various TLS DNA polymerases or key protein-protein interactions (PPIs) in the TLS machinery. Expert opinion: TLS inhibitors have demonstrated initial promise; however, their continued study is essential to more fully understand the clinical potential of this emerging class of anti-cancer chemotherapeutics. It will be important to determine whether a specific protein involved in TLS is an optimal target. In addition, an expanded understanding of what current genotoxic chemotherapies synergize with TLS inhibitors will guide the clinical strategies for devising combination therapies.

Targeting translesion synthesis (TLS) to expose replication gaps, a unique cancer vulnerability

Introduction: Translesion synthesis (TLS) is a DNA damage tolerance (DDT) mechanism that employs error-prone polymerases to bypass replication blocking DNA lesions, contributing to a gain in mutagenesis and chemo-resistance. However, recent findings illustrate an emerging role for TLS in replication gap suppression (RGS), distinct from its role in post-replication gap filling. Here, TLS protects cells from replication stress (RS)-induced toxic single-stranded DNA (ssDNA) gaps that accumulate in the wake of active replication. Intriguingly, TLS-mediated RGS is specifically observed in several cancer cell lines and contributes to their survival. Thus, targeting TLS has the potential to uniquely eradicate tumors without harming non-cancer tissues. Areas Covered: This review provides an innovative perspective on the role of TLS beyond its canonical function of lesion bypass or post-replicative gap filling. We provide a comprehensive analysis that underscores the emerging role of TLS as a cancer adaptation necessary to overcome the replication stress response (RSR), an anti-cancer barrier. Expert Opinion: TLS RGS is critical for tumorigenesis and is a new hallmark of cancer. Although the exact mechanism and extent of TLS dependency in cancer is still emerging, TLS inhibitors have shown promise as an anti-cancer therapy in selectively targeting this unique cancer vulnerability.

PRDM14 mediates chemosensitivity and glycolysis in drug‑resistant A549/cisplatin cells and their progenitor A549 human lung adenocarcinoma cells

Recent studies have reported that aberrant PR domain zinc finger protein 14 (PRDM14) expression is associated with the therapeutic sensitivity of cancer cells to drugs. However, its role in lung adenocarcinoma (LUAD) remains unclear. The present study aimed to determine the functions of knockdown or overexpression of PRDM14 in the chemosensitivity and glycolysis of LUAD cells. PRDM14 expression was analyzed in lung cancer tissues from patients resistant and sensitive to cisplatin (DDP), as well as in LUAD cell lines A549 and DDP-resistant A549 (A549/DDP) using reverse transcription quantitative-PCR and western blotting. Additionally, apoptosis was analyzed by flow cytometry, and flow cytometry and biochemical analysis was used to analyze glycolysis, indicated by glucose uptake and lactate release. The results of the present study demonstrated that PRDM14 expression was upregulated in patients with DDP-resistant LUAD and DDP-resistant cell lines. Overexpression of PRDM14 suppressed the sensitivity of A549 cells to DDP and silencing of PRDM14 using shRNA targeting PRDM14 promoted the sensitivity of A549/DDP cells to DDP, compared with that in the respective control groups. In mice with xenograft tumors, knockdown of PRDM14 using shRNA targeting PRDM14 inhibited the A549/DDP cell-derived tumor growth compared with scramble shRNA. The results of the glycolysis assays demonstrated that PRDM14 silencing inhibited glucose uptake, lactate release and glucose transporter 1 expression in A549/DDP cells compared with those in the control cells. PRDM14 overexpression relieved the inhibitory effects of 3-bromopyruvate, a potent glycolytic inhibitor for glycolysis, on glucose uptake and lactate release in A549 cells compared with those in the control cells. Therefore, the results of the present study suggested that PRDM14 may inhibit the chemosensitivity and promote glycolysis in human LUAD cells.

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.