MAD2L2 dimerization and TRIP13 control shieldin activity in DNA repair

POGZ targeted by LINC01355/miR-27b-3p retards thyroid cancer progression via interplaying with MAD2L2

Despite the high morbidity of thyroid cancer (THCA), the underlying molecular pathology remains elusive. That autism-associated protein POGZ has recently been involved in tumorigenesis intrigues us exploring its relevant molecular regulatory network in THCA. Clinical characteristics and intermolecular relationships were dissected by bioinformatics. Interaction between POGZ and MAD2L2 was examined by Co-IP assay. Targeting relationships between miR-27b-3p and POGZ/LINC01355 was verified by sequence prediction and dual-luciferase reporter detection. Cellular effects of genes were assessed by CCK-8 assay, clone formation assay, and Transwell assay, and further confirmed by a tumor-bearing nude mice model. Our results demonstrated a decrease in POGZ expression in THCA tissues and cell lines, and an interaction between POGZ and MAD2L2 protein. POGZ inhibited both the proliferation and motility of THCA cells, with these effects being reversed upon MAD2L2 silencing. LINC01355 exhibited low expression level and a positive correlation with POGZ in THCA. Both miR-27b-3p and LINC01355 were identified as regulators of POGZ through targeting. Elevated miR-27b-3p suppressed POGZ expression. LINC01355 promoted POGZ and counteracted the inhibitory effects of miR-27b-3p. Furthermore, miR-27b-3p increased the proliferation and motility of THCA cells, an effect that was blocked by LINC01355. At the animal level, POGZ, LINC01355, and MAD2L2 all attenuated tumor growth in THCA. Collectively, POGZ restrains THCA growth by interacting with MAD2L2 protein, and POGZ modulation involves a complex interplay orchestrated by LINC01355-targeted miR-27b-3p. By reporting the first POGZ-focused ceRNA network involving noncoding RNA in THCA, our study paves the way for exploring POGZ-related pathways and developing new therapeutic strategies in cancer.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-025-04231-7.

TRIP13 protects pancreatic cancer cells against intrinsic and therapy-induced DNA replication stress

Oncogene activation in normal untransformed cells induces DNA replication stress and creates a dependency on DNA damage response (DDR) mechanisms for cell survival. Different oncogenic stimuli signal via distinct mechanisms in every cancer setting. The DDR is also pathologically reprogrammed and deployed in diverse ways in different cancers. Because mutant KRAS is the driver oncogene in 90% of pancreatic ductal adenocarcinomas (PDACs), here we have investigated DDR mechanisms by which KRAS-induced DNA replication stress is tolerated in normal human pancreatic epithelial cells [human pancreatic nestin-expressing (HPNE) cells]. Using a candidate screening approach, we identify TRIP13 as a KRASG12V-induced messenger RNA that is also expressed at high levels in PDAC relative to normal tissues. Using genetic and pharmacological tools, we show that TRIP13 is necessary to sustain ongoing DNA synthesis and viability specifically in KRASG12V-expressing cells. TRIP13 promotes survival of KRASG12V-expressing HPNE cells in a homologous recombination (HR)-dependent manner. KRASG12V-expressing HPNE cells lacking TRIP13 acquire hallmark HR deficiency phenotypes, including sensitivity to inhibitors of translesion synthesis and poly-ADP ribose polymerase. Established PDAC cell lines are also sensitized to intrinsic DNA damage and therapy-induced genotoxicity following TRIP13 depletion. Taken together, our results expose TRIP13 as an attractive new and therapeutically tractable vulnerability of KRAS-mutant PDAC.

TRIP13 protects pancreatic cancer cells against intrinsic and therapy-induced DNA replication stress

Oncogene activation in normal untransformed cells induces DNA replication stress and creates a dependency on DNA Damage Response (DDR) mechanisms for cell survival. Different oncogenic stimuli signal via distinct mechanisms in every cancer setting. The DDR is also pathologically re-programmed and deployed in diverse ways in different cancers. Because mutant KRAS is the driver oncogene in 90% of Pancreatic Ductal Adenocarcinomas (PDAC), here we have investigated DDR mechanisms by which KRAS-induced DNA replication stress is tolerated in normal human pancreatic epithelial cells (HPNE). Using a candidate screening approach, we identify TRIP13 as a KRASG12V-induced mRNA that is also expressed at high levels in PDAC relative to normal tissues. Using genetic and pharmacological tools, we show that TRIP13 is necessary to sustain ongoing DNA synthesis and viability specifically in KRASG12V-expressing cells. TRIP13 promotes survival of KRASG12V-expressing HPNE cells in a Homologous Recombination (HR)-dependent manner. KRASG12V-expressing HPNE cells lacking TRIP13 acquire hallmark HR-deficiency (HRD) phenotypes including sensitivity to inhibitors of Trans-Lesion Synthesis (TLS) and Poly-ADP Ribose Polymerase (PARP). Established PDAC cell lines are also sensitized to intrinsic DNA damage and therapy-induced genotoxicity following TRIP13-depletion. Taken together our results expose TRIP13 as an attractive new and therapeutically-tractable vulnerability of KRAS-mutant PDAC.

The RING Finger E3 Ligase RNF25 Protects DNA Replication Forks Independently of its Canonical Roles in Ubiquitin Signaling

The DNA damage response (DDR) mechanisms that allow cells to tolerate DNA replication stress are critically important for genome stability and cell viability. Using an unbiased genetic screen we identify a role for the RING finger E3 ubiquitin ligase RNF25 in promoting DNA replication stress tolerance. In response to DNA replication stress, RNF25-deficient cells generate aberrantly high levels of single-stranded DNA (ssDNA), accumulate in S-phase and show reduced mitotic entry. Using single-molecule DNA fiber analysis, we show that RNF25 protects reversed DNA replication forks generated by the fork remodeler HLTF from nucleolytic degradation by MRE11 and CtIP. Mechanistically, RNF25 interacts with the replication fork protection factor REV7 and recruits REV7 to nascent DNA after replication stress. The role of RNF25 in protecting replication forks is fully separable from its canonical functions in ubiquitin conjugation. This work reveals the RNF25-REV7 signaling axis as an important protective mechanism in cells experiencing replication stress.

REV7: a small but mighty regulator of genome maintenance and cancer development

REV7, also known as MAD2B, MAD2L2, and FANCV, is a HORMA-domain family protein crucial to multiple genome stability pathways. REV7's canonical role is as a member of polymerase ζ, a specialized translesion synthesis polymerase essential for DNA damage tolerance. REV7 also ensures accurate cell cycle progression and prevents premature mitotic progression by sequestering an anaphase-promoting complex/cyclosome activator. Additionally, REV7 supports genome integrity by directing double-strand break repair pathway choice as part of the recently characterized mammalian shieldin complex. Given that genome instability is a hallmark of cancer, it is unsurprising that REV7, with its numerous genome maintenance roles, is implicated in multiple malignancies, including ovarian cancer, glioma, breast cancer, malignant melanoma, and small-cell lung cancer. Moreover, high REV7 expression is associated with poor prognoses and treatment resistance in these and other cancers. Promisingly, early studies indicate that REV7 suppression enhances sensitivity to chemotherapeutics, including cisplatin. This review aims to provide a comprehensive overview of REV7's myriad roles in genome maintenance and other functions as well as offer an updated summary of its connections to cancer and treatment resistance.

Repeated ionizing radiation exposure induces TRIP13 expression, conferring radioresistance in lung cancer cells

Radiation therapy is a common treatment modality for lung cancer, and resistance to radiation can significantly affect treatment outcomes. We recently described that lung cancer cells that express more germ cell cancer genes (GC genes, genes that are usually restricted to the germ line) can repair DNA double-strand breaks more rapidly, show higher rates of proliferation and are more resistant to ionizing radiation than cells that express fewer GC genes. The gene encoding TRIP13 appeared to play a large role in this malignant phenotype. However, the molecular regulatory mechanism of TRIP13 in radiation resistance remained largely unknown. Here, we show that TRIP13 is a key contributor to non-small cell lung cancer (NSCLC) treatment resistance, particularly in patients following radiation treatment, for whom levels of TRIP13 expression are correlated with a poor prognosis. Repeated irradiation of led to an increase of basal TRIP13 levels and radioresistance. This effect of radioresistance could be enhanced or abrogated by overexpressing or knocking out TRIP13. Elevated TRIP13 is also correlated with enhanced repair of radiation-induced DNA damage. We further showed the proteins NBS1 and RAD51 (homologous recombination. HR) and XRCC5 (non-homologous end-joining, NHEJ) to act downstream of TRIP13, although inhibition of TRIP13 mostly reduced the HR associated proteins in response to induced resistance to irradiation. This study elucidates a novel mechanism of treatment resistance in NSCLC cells, in which TRIP13 promotes HR mediated DNA repair and resistance to ionizing radiation.

MAD2L1 supports MYC-driven liver carcinogenesis in mice and predicts poor prognosis in human hepatocarcinoma

Mitotic arrest-deficient 2 like 1 (MAD2L1) is a component of the mitotic spindle assembly checkpoint implicated in cancer cell proliferation and tumorigenesis. The functional role of MAD2L1 in hepatocellular carcinoma (HCC) has not been adequately investigated, especially in vivo. In the current manuscript, we sought to address the function of MAD2L1 in hepatocarcinogenesis. We found that MAD2L1 expression is upregulated in human HCCs, where its expression is associated with higher aggressive tumor grade, elevated proliferative activity, and poor prognosis. In human HCC cell lines, MAD2L1 knockdown led to decreased cell growth. Moreover, RNA-seq results demonstrated that MAD2L1 silencing induces the expression of genes associated with cell cycle, DNA replication, and various cancer-related pathways, supporting the critical role of MAD2L1 during HCC growth and differentiation. In a c-MYC-induced mouse HCC model, we revealed an increased expression of Mad2l1. Furthermore, Mad2l1 CRIPSR-mediated silencing prevented c-MYC-driven mouse liver development. Altogether, our study suggests that MAD2L1 plays a crucial role in hepatocarcinogenesis, and that its suppression could be a promising therapeutic strategy for treating human HCC. MAD2L1 plays a critical role in liver cancer development, silencing MAD2L1 reduced cell growth in vitro and inhibited c-MYC-driven liver cancer development in vivo. MAD2L1 suppression might be a promising therapeutic approach for treating human liver cancer.

Mosaic variegated aneuploidy in development, ageing and cancer

Mosaic variegated aneuploidy (MVA) is a rare condition in which abnormal chromosome counts (that is, aneuploidies), affecting different chromosomes in each cell (making it variegated) are found only in a certain number of cells (making it mosaic). MVA is characterized by various developmental defects and, despite its rarity, presents a unique clinical scenario to understand the consequences of chromosomal instability and copy number variation in humans. Research from patients with MVA, genetically engineered mouse models and functional cellular studies have found the genetic causes to be mutations in components of the spindle-assembly checkpoint as well as in related proteins involved in centrosome dynamics during mitosis. MVA is accompanied by tumour susceptibility (depending on the genetic basis) as well as cellular and systemic stress, including chronic immune response and the associated clinical implications.

MAD2L2 Dimerization Is Not Essential for Mitotic Regulation

MAD2L2 is a small HORMA domain protein that plays a crucial role in DNA repair and mitosis. In both TLS and shieldin, the dimerization of MAD2L2 via its HORMA domain is critical for the stability and function of these complexes. However, in mitosis, the dimerization state of MAD2L2 remains unknown. To assess the importance of MAD2L2's dimerization during mitosis, we utilized CRISPR/Cas9 to generate MAD2L2 knockout cells, which were subsequently complemented with MAD2L2 species carrying different dimer-disrupting point mutations. We assessed the ability of these MAD2L2 dimer-disrupting mutants to regulate mitosis by evaluating early mitotic events and mitotic fidelity. Our findings indicate that MAD2L2 can function in its monomeric form during mitosis, suggesting that MAD2L2 homodimerization is dispensable for early mitotic regulation. Furthermore, our results suggest that the binding of CDH1 to MAD2L2 is a key regulating factor in mitosis that may actively prevent the formation of MAD2L2 dimers, thereby shifting the cellular balance toward MAD2L2-CDH1 interaction. Thus, the equilibrium between the monomeric and dimeric forms of MAD2L2 is an important cellular factor regulating the MAD2L2-containing complexes.

OTUD5 promotes end-joining of deprotected telomeres by promoting ATM-dependent phosphorylation of KAP1S824

Appropriate repair of damaged DNA and the suppression of DNA damage responses at telomeres are essential to preserve genome stability. DNA damage response (DDR) signaling consists of cascades of kinase-driven phosphorylation events, fine-tuned by proteolytic and regulatory ubiquitination. It is not fully understood how crosstalk between these two major classes of post-translational modifications impact DNA repair at deprotected telomeres. Hence, we performed a functional genetic screen to search for ubiquitin system factors that promote KAP1S824 phosphorylation, a robust DDR marker at deprotected telomeres. We identified that the OTU family deubiquitinase (DUB) OTUD5 promotes KAP1S824 phosphorylation by facilitating ATM activation, through stabilization of the ubiquitin ligase UBR5 that is required for DNA damage-induced ATM activity. Loss of OTUD5 impairs KAP1S824 phosphorylation, which suppresses end-joining mediated DNA repair at deprotected telomeres and at DNA breaks in heterochromatin. Moreover, we identified an unexpected role for the heterochromatin factor KAP1 in suppressing DNA repair at telomeres. Altogether our work reveals an important role for OTUD5 and KAP1 in relaying DDR-dependent kinase signaling to the control of DNA repair at telomeres and heterochromatin.

PARP inhibitor resistance mechanisms and PARP inhibitor derived imaging probes

INTRODUCTION

Poly(ADP-ribose) polymerase 1 (PARP1) inhibition has become a major target in anticancer therapy. While PARP inhibitors (PARPi) are approved for homologous recombination (HR) deficient cancers, therapeutic resistance is a challenge and PARPi are now being investigated in cancers lacking HR deficiencies. This creates a need to develop molecular and imaging biomarkers of PARPi response to improve patient selection and circumvent therapeutic resistance.

AREAS COVERED

PubMed and clinicaltrials.gov were queried for studies on PARPi resistance and imaging. This review summarizes established and emerging resistance mechanisms to PARPi, and the current state of imaging and theragnostic probes for PARPi, including fluorescently labeled and radiolabeled probes.

EXPERT OPINION

While progress has been made in understanding PARPi therapeutic resistance, clinical evidence remains lacking and relatively little is known regarding PARPi response outside of HR deficiencies. Continued research will clarify the importance of known biomarkers and resistance mechanisms in patient cohorts and the broader utility of PARPi. Progress has also been made in PARPi imaging, particularly with radiolabeled probes, and both imaging and theragnostic probes have now reached clinical validation. Reducing abdominal background signal from probe clearance will broaden their applicability, and improvements to molecular synthesis and radiation delivery will increase their utility.

REV7-p53 interaction inhibits ATM-mediated DNA damage signaling

REV7 is an abundant, multifunctional protein that is a known factor in cell cycle regulation and in several key DNA repair pathways including Trans-Lesion Synthesis (TLS), the Fanconi Anemia (FA) pathway, and DNA Double-Strand Break (DSB) repair pathway choice. Thus far, no direct role has been studied for REV7 in the DNA damage response (DDR) signaling pathway. Here we describe a novel function for REV7 in DSB-induced p53 signaling. We show that REV7 binds directly to p53 to block ATM-dependent p53 Ser15 phosphorylation. We also report that REV7 is involved in the destabilization of p53. These findings affirm REV7's participation in fundamental cell cycle and DNA repair pathways. Furthermore, they highlight REV7 as a critical factor for the integration of multiple processes that determine viability and genome stability.

Germline specific genes increase DNA double-strand break repair and radioresistance in lung adenocarcinoma cells

In principle, germline cells possess the capability to transmit a nearly unaltered set of genetic material to infinite future generations, whereas somatic cells are limited by strict growth constraints necessary to assure an organism's physical structure and eventual mortality. As the potential to replicate indefinitely is a key feature of cancer, we hypothesized that the activation of a "germline program" in somatic cells can contribute to oncogenesis. Our group recently described over one thousand germline specific genes that can be ectopically expressed in cancer, yet how germline specific processes contribute to the malignant properties of cancer is poorly understood. We here show that the expression of germ cell/cancer (GC) genes correlates with malignancy in lung adenocarcinoma (LUAD). We found that LUAD cells expressing more GC genes can repair DNA double strand breaks more rapidly, show higher rates of proliferation and are more resistant to ionizing radiation, compared to LUAD cells that express fewer GC genes. In particular, we identified the HORMA domain protein regulator TRIP13 to be predominantly responsible for this malignant phenotype, and that TRIP13 inhibition or expression levels affect the response to ionizing radiation and subsequent DNA repair. Our results demonstrate that GC genes are viable targets in oncology, as they induce increased radiation resistance and increased propagation in cancer cells. Because their expression is normally restricted to germline cells, we anticipate that GC gene directed therapeutic options will effectively target cancer, with limited side effects besides (temporary) infertility.

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.

Weighted Gene Co-Expression Network Analysis Based on Stimulation by Lipopolysaccharides and Polyinosinic:polycytidylic Acid Provides a Core Set of Genes for Understanding Hemolymph Immune Response Mechanisms of Amphioctopus fangsiao

The primary influencer of aquaculture quality in Amphioctopus fangsiao is pathogen infection. Both lipopolysaccharides (LPS) and polyinosinic:polycytidylic acid (Poly I:C) are recognized by the pattern recognition receptor (PRR) within immune cells, a system that frequently serves to emulate pathogen invasion. Hemolymph, which functions as a transport mechanism for immune cells, offers vital transcriptome information when A. fangsiao is exposed to pathogens, thereby contributing to our comprehension of the species' immune biological mechanisms. In this study, we conducted analyses of transcript profiles under the influence of LPS and Poly I:C within a 24 h period. Concurrently, we developed a Weighted Gene Co-expression Network Analysis (WGCNA) to identify key modules and genes. Further, we carried out Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses to investigate the primary modular functions. Co-expression network analyses unveiled a series of immune response processes following pathogen stress, identifying several key modules and hub genes, including PKMYT1 and NAMPT. The invaluable genetic resources provided by our results aid our understanding of the immune response in A. fangsiao hemolymph and will further our exploration of the molecular mechanisms of pathogen infection in mollusks.

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.

REV7 Monomer Is Unable to Participate in Double Strand Break Repair and Translesion Synthesis but Suppresses Mitotic Errors

Rev7 is a regulatory protein with roles in translesion synthesis (TLS), double strand break (DSB) repair, replication fork protection, and cell cycle regulation. Rev7 forms a homodimer in vitro using its HORMA (Hop, Rev7, Mad2) domain; however, the functional importance of Rev7 dimerization has been incompletely understood. We analyzed the functional properties of cells expressing either wild-type mouse Rev7 or Rev7K44A/R124A/A135D, a mutant that cannot dimerize. The expression of wild-type Rev7, but not the mutant, rescued the sensitivity of Rev7-/- cells to X-rays and several alkylating agents and reversed the olaparib resistance phenotype of Rev7-/- cells. Using a novel fluorescent host-cell reactivation assay, we found that Rev7K44A/R124A/A135D is unable to promote gap-filling TLS opposite an abasic site analog. The Rev7 dimerization interface is also required for shieldin function, as both Rev7-/- cells and Rev7-/- cells expressing Rev7K44A/R124A/A135D exhibit decreased proficiency in rejoining some types of double strand breaks, as well as increased homologous recombination. Interestingly, Rev7K44A/R124A/A135D retains some function in cell cycle regulation, as it maintains an interaction with Ras-related nuclear protein (Ran) and partially rescues the formation of micronuclei. The mutant Rev7 also rescues the G2/M accumulation observed in Rev7-/- cells but does not affect progression through mitosis following nocodazole release. We conclude that while Rev7 dimerization is required for its roles in TLS, DSB repair, and regulation of the anaphase promoting complex, dimerization is at least partially dispensable for promoting mitotic spindle assembly through its interaction with Ran.

Shieldin complex assembly kinetics and DNA binding by SHLD3

The Shieldin complex represses end resection at DNA double-strand breaks (DSBs) and thereby serves as a pro-non homologous end joining (NHEJ) factor. The molecular details of the assembly of Shieldin and its recruitment to DSBs are unclear. Shieldin contains two REV7 molecules, which have the rare ability to slowly switch between multiple distinct native states and thereby could dynamically control the assembly of Shieldin. Here, we report the identification of a promiscuous DNA binding domain in SHLD3. At the N-terminus, SHLD3 interacts with a dimer of REV7 molecules. We show that the interaction between SHLD3 and the first REV7 is remarkably slow, while in contrast the interaction between SHLD3 and SHLD2 with a second REV7 molecule is fast and does not require structural remodeling. Overall, these results provide insights into the rate-limiting step of the molecular assembly of the Shieldin complex and its recruitment at DNA DSBs.

MAD2B Blunts Chronic Unpredictable Stress and Corticosterone Stimulation-Induced Depression-Like Behaviors in Mice

BACKGROUND

Depression is a prevalent and recurrent psychiatric disorder. Aberrant neural structure and activity play fundamental roles in the occurrence of depression. Mitotic arrest deficient protein (MAD2B) is highly expressed in neurons and may be implicated in synaptic plasticity in the central nervous system. However, the effect of MAD2B in depression, as well as the related molecular mechanism, is uncertain.

METHODS

Here, we employed mouse models of depression induced by chronic unpredictable stress exposure or corticosterone (CORT) stimulation. Depression-like behaviors in mice were evaluated by sucrose preference, forced swimming, and tail suspension tests. Hippocampal MAD2B overexpression was mediated by adeno-associated virus 8 containing enhanced green fluorescent protein. In vitro primary neuronal cells were obtained from the hippocampus of rat embryos and were treated with CORT, and MAD2B overexpression was performed using lentivirus. MAD2B and glutamate metabotropic receptor 4 (GRM4) levels were evaluated by western blots and quantitative PCR. Primary neuronal miR-29b-3p expression was detected by quantitative PCR.

RESULTS

MAD2B expression was reduced in the hippocampus in mice exhibiting depressive-like behaviors. However, hippocampal MAD2B overexpression protected mice from developing either chronic unpredictable stress- or CORT-induced depression-like behaviors, an effect associated with reduced expression of GRM4, a presynaptic receptor involved in depression. Moreover, MAD2B overexpression in primary neuronal cells also decreased GRM4 expression while enhancing the level of miR-29b-3p; this phenomenon was also observed under CORT stimulation.

CONCLUSIONS

Our results suggest an important role of neuronal MAD2B in the pathogenesis of depression via the miR-29b-3p/GRM4 signaling pathway. MAD2B could be a potential therapeutic target for depressive disorders.

TRIP13 Participates in Immediate-Early Sensing of DNA Strand Breaks and ATM Signaling Amplification through MRE11

Thyroid hormone receptor-interacting protein 13 (TRIP13) participates in various regulatory steps related to the cell cycle, such as the mitotic spindle assembly checkpoint and meiotic recombination, possibly by interacting with members of the HORMA domain protein family. Recently, it was reported that TRIP13 could regulate the choice of the DNA repair pathway, i.e., homologous recombination (HR) or nonhomologous end-joining (NHEJ). However, TRIP13 is recruited to DNA damage sites within a few seconds after damage and may therefore have another function in DNA repair other than regulation of the pathway choice. Furthermore, the depletion of TRIP13 inhibited both HR and NHEJ, suggesting that TRIP13 plays other roles besides regulation of choice between HR and NHEJ. To explore the unidentified functions of TRIP13 in the DNA damage response, we investigated its genome-wide interaction partners in the context of DNA damage using quantitative proteomics with proximity labeling. We identified MRE11 as a novel interacting partner of TRIP13. TRIP13 controlled the recruitment of MDC1 to DNA damage sites by regulating the interaction between MDC1 and the MRN complex. Consistently, TRIP13 was involved in ATM signaling amplification. Our study provides new insight into the function of TRIP13 in immediate-early DNA damage sensing and ATM signaling activation.

CCAR2 functions downstream of the Shieldin complex to promote double-strand break end-joining

The 53BP1-RIF1 pathway restricts the resection of DNA double-strand breaks (DSBs) and promotes blunt end-ligation by non-homologous end joining (NHEJ) repair. The Shieldin complex is a downstream effector of the 53BP1-RIF1 pathway. Here, we identify a component of this pathway, CCAR2/DBC1, which is also required for restriction of DNA end-resection. CCAR2 co-immunoprecipitates with the Shieldin complex, and knockout of CCAR2 in a BRCA1-deficient cell line results in elevated DSB end-resection, RAD51 loading, and PARP inhibitor (PARPi) resistance. Knockout of CCAR2 is epistatic with knockout of other Shieldin proteins. The S1-like RNA-binding domain of CCAR2 is required for its interaction with the Shieldin complex and for suppression of DSB end-resection. CCAR2 functions downstream of the Shieldin complex, and CCAR2 knockout cells have delayed resolution of Shieldin complex foci. Forkhead-associated (FHA)-dependent targeting of CCAR2 to DSB sites re-sensitized BRCA1-/-SHLD2-/- cells to PARPi. Taken together, CCAR2 is a functional component of the 53BP1-RIF1 pathway, promotes the refill of resected DSBs, and suppresses homologous recombination.

The Anaphase-Promoting Complex/Cyclosome Is a Cellular Ageing Regulator

The anaphase-promoting complex/cyclosome (APC/C) is a complicated cellular component that plays significant roles in regulating the cell cycle process of eukaryotic organisms. The spatiotemporal regulation mechanisms of APC/C in distinct cell cycle transitions are no longer mysterious, and the components of this protein complex are gradually identified and characterized. Given the close relationship between the cell cycle and lifespan, it is urgent to understand the roles of APC/C in lifespan regulation, but this field still seems to have not been systematically summarized. Furthermore, although several reviews have reported the roles of APC/C in cancer, there are still gaps in the summary of its roles in other age-related diseases. In this review, we propose that the APC/C is a novel cellular ageing regulator based on its indispensable role in the regulation of lifespan and its involvement in age-associated diseases. This work provides an extensive review of aspects related to the underlying mechanisms of APC/C in lifespan regulation and how it participates in age-associated diseases. More comprehensive recognition and understanding of the relationship between APC/C and ageing and age-related diseases will increase the development of targeted strategies for human health.

CHAMP1 binds to REV7/FANCV and promotes homologous recombination repair

A critical determinant of DNA repair pathway choice is REV7, an adaptor that binds to various DNA repair proteins through its C-terminal seatbelt domain. The REV7 seatbelt binds to either REV3, activating translesion synthesis, or to SHLD3, activating non-homologous end joining (NHEJ) repair. Recent studies have identified another REV7 seatbelt-binding protein, CHAMP1 (chromosome alignment-maintaining phosphoprotein 1), though its possible role in DNA repair is unknown. Here, we show that binding of CHAMP1 to REV7 activates homologous recombination (HR) repair. Mechanistically, CHAMP1 binds directly to REV7 and reduces the level of the Shieldin complex, causing an increase in double-strand break end resection. CHAMP1 also interacts with POGZ in a heterochromatin complex further promoting HR repair. Importantly, in human tumors, CHAMP1 overexpression promotes HR, confers poly (ADP-ribose) polymerase inhibitor resistance, and correlates with poor prognosis. Thus, by binding to either SHLD3 or CHAMP1 through its seatbelt, the REV7 protein can promote either NHEJ or HR repair, respectively.

Feng et al. demonstrate that CHAMP1 promotes homologous recombination by binding to REV7 and reducing the level of the Shieldin complex, causing an increase in double-strand break end resection. CHAMP1 and POGZ form a complex to further promote HR. Upregulation of CHAMP1 expression is a mechanism of acquired PARP inhibitor resistance.

Genetic Variants in Double-Strand Break Repair Pathway Genes to Predict Platinum-Based Chemotherapy Prognosis in Patients With Lung Cancer

Objective: The purpose of this study was to investigate the associations of genetic variants in double-strand break (DSB) repair pathway genes with prognosis in patients with lung cancer treated with platinum-based chemotherapy.

Methods: Three hundred ninety-nine patients with lung cancer who received platinum-based chemotherapy for at least two cycles were included in this study. A total of 35 single nucleotide polymorphisms (SNPs) in DSB repair, base excision repair (BER), and nucleotide excision repair (NER) repair pathway genes were genotyped, and were used to evaluate the overall survival (OS) and the progression-free survival (PFS) of patients who received platinum-based chemotherapy using Cox proportional hazard models.

Results: The PFS of patients who carried the MAD2L2 rs746218 GG genotype was shorter than that in patients with the AG or AA genotypes (recessive model: p = 0.039, OR = 5.31, 95% CI = 1.09–25.93). Patients with the TT or GT genotypes of TNFRSF1A rs4149570 had shorter OS times than those with the GG genotype (dominant model: p = 0.030, OR = 0.57, 95% CI = 0.34–0.95). We also investigated the influence of age, gender, histology, smoking, stage, and metastasis in association between SNPs and OS or PFS in patients with lung cancer. DNA repair gene SNPs were significantly associated with PFS and OS in the subgroup analyses.

Conclusion: Our study showed that variants in MAD2L2 rs746218 and TNFRSF1A rs4149570 were associated with shorter PFS or OS in patients with lung cancer who received platinum-based chemotherapy. These variants may be novel biomarkers for the prediction of prognosis of patients with lung cancer who receive platinum-based chemotherapy.

SHLD1 is dispensable for 53BP1-dependent V(D)J recombination but critical for productive class switch recombination

SHLD1 is part of the Shieldin (SHLD) complex, which acts downstream of 53BP1 to counteract DNA double-strand break (DSB) end resection and promote DNA repair via non-homologous end-joining (NHEJ). While 53BP1 is essential for immunoglobulin heavy chain class switch recombination (CSR), long-range V(D)J recombination and repair of RAG-induced DSBs in XLF-deficient cells, the function of SHLD during these processes remains elusive. Here we report that SHLD1 is dispensable for lymphocyte development and RAG-mediated V(D)J recombination, even in the absence of XLF. By contrast, SHLD1 is essential for restricting resection at AID-induced DSB ends in both NHEJ-proficient and NHEJ-deficient B cells, providing an end-protection mechanism that permits productive CSR by NHEJ and alternative end-joining. Finally, we show that this SHLD1 function is required for orientation-specific joining of AID-initiated DSBs. Our data thus suggest that 53BP1 promotes V(D)J recombination and CSR through two distinct mechanisms: SHLD-independent synapsis of V(D)J segments and switch regions within chromatin, and SHLD-dependent protection of AID-DSB ends against resection.

Checkpoint control in meiotic prophase: Idiosyncratic demands require unique characteristics

Chromosomal transactions such as replication, recombination and segregation are monitored by cell cycle checkpoint cascades. These checkpoints ensure the proper execution of processes that are needed for faithful genome inheritance from one cell to the next, and across generations. In meiotic prophase, a specialized checkpoint monitors defining events of meiosis: programmed DNA break formation, followed by dedicated repair through recombination based on interhomolog (IH) crossovers. This checkpoint shares molecular characteristics with canonical DNA damage checkpoints active during somatic cell cycles. However, idiosyncratic requirements of meiotic prophase have introduced unique features in this signaling cascade. In this review, we discuss the unique features of the meiotic prophase checkpoint. While being related to canonical DNA damage checkpoint cascades, the meiotic prophase checkpoint also shows similarities with the spindle assembly checkpoint (SAC) that guards chromosome segregation. We highlight these emerging similarities in the signaling logic of the checkpoints that govern meiotic prophase and chromosome segregation, and how thinking of these similarities can help us better understand meiotic prophase control. We also discuss work showing that, when aberrantly expressed, components of the meiotic prophase checkpoint might alter DNA repair fidelity and chromosome segregation in cancer cells. Considering checkpoint function in light of demands imposed by the special characteristics of meiotic prophase helps us understand checkpoint integration into the meiotic cell cycle machinery.

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.

DNA damage is overcome by TRIP13 overexpression during cisplatin nephrotoxicity

Cisplatin is a commonly used chemotherapeutic agent to treat a wide array of cancers that is frequently associated with toxic injury to the kidney due to oxidative DNA damage and perturbations in cell cycle progression leading to cell death. In this study, we investigated whether thyroid receptor interacting protein 13 (TRIP13) plays a central role in the protection of the tubular epithelia following cisplatin treatment by circumventing DNA damage. Following cisplatin treatment, double-stranded DNA repair pathways were inhibited using selective blockers to proteins involved in either homologous recombination or non-homologous end joining. This led to increased blood markers of acute kidney injury (AKI) (creatinine and neutrophil gelatinase–associated lipocalin), tubular damage, activation of DNA damage marker (γ-H2AX), elevated appearance of G2/M blockade (phosphorylated histone H3 Ser10 and cyclin B1), and apoptosis (cleaved caspase-3). Conditional proximal tubule–expressing Trip13 mice were observed to be virtually protected from the cisplatin nephrotoxicity by restoring most of the pathological phenotypes back toward normal conditions. Our findings suggest that TRIP13 could circumvent DNA damage in the proximal tubules during cisplatin injury and that TRIP13 may constitute a new therapeutic target in protecting the kidney from nephrotoxicants and reduce outcomes leading to AKI.