RNF126 Quenches RNF168 Function in the DNA Damage Response

Histone ubiquitination: Role in genome integrity and chromatin organization

Maintenance of genome integrity is a precise but tedious and complex job for the cell. Several post-translational modifications (PTMs) play vital roles in maintaining the genome integrity. Although ubiquitination is one of the most crucial PTMs, which regulates the localization and stability of the nonhistone proteins in various cellular and developmental processes, ubiquitination of the histones is a pivotal epigenetic event critically regulating chromatin architecture. In addition to genome integrity, importance of ubiquitination of core histones (H2A, H2A, H3, and H4) and linker histone (H1) have been reported in several cellular processes. However, the complex interplay of histone ubiquitination and other PTMs, as well as the intricate chromatin architecture and dynamics, pose a significant challenge to unravel how histone ubiquitination safeguards genome stability. Therefore, further studies are needed to elucidate the interactions between histone ubiquitination and other PTMs, and their role in preserving genome integrity. Here, we review all types of histone ubiquitinations known till date in maintaining genomic integrity during transcription, replication, cell cycle, and DNA damage response processes. In addition, we have also discussed the role of histone ubiquitination in regulating other histone PTMs emphasizing methylation and acetylation as well as their potential implications in chromatin architecture. Further, we have also discussed the involvement of deubiquitination enzymes (DUBs) in controlling histone ubiquitination in modulating cellular processes.

An essential role of the E3 ubiquitin ligase RNF126 in ensuring meiosis I completion during spermatogenesis

INTRODUCTION

Homologous recombination repair during meiosis is essential for the exchange of genetic information between sister chromosomes, underpinning spermatogenesis and, consequently, fertility. The disruption of this process can lead to infertility, highlighting the importance of identifying the molecular actors involved.

OBJECTIVES

This study aims to elucidate the role of the E3 ubiquitin ligase Rnf126 in spermatogenesis and its impact on fertility, particularly through its involvement in meiotic homologous recombination repair.

METHODS

We used heterozygous and homozygous Rnf126 deletion models in mouse testes to examine the consequences on testicular health, sperm count, and the process of spermatogenesis. Additionally, we explored the association between RNF126 gene missense variants and nonobstructive male infertility in patients, with a focus on their functional impact on the protein's ubiquitin ligase activity.

RESULTS

Rnf126 deletion led to testicular atrophy, disrupted seminiferous tubule structure, reduced sperm count, and spermatogenesis arrest at meiotic prophase I. Furthermore, male mice exhibited impaired homologous recombination repair and increased apoptosis within the seminiferous tubules. We identified four missense variants of the RNF126 (V68M, R241H, E261A, D253N) associated with male infertility. Specifically, the E261A and D253N variants, located in the RING domain, directly compromised the E3 ubiquitin ligase activity of RNF126.

CONCLUSION

Our findings demonstrate the pivotal role of RNF126 in maintaining spermatogenesis and fertility, offering insights into the molecular mechanisms underlying male infertility. The identified RNF126 variants present novel targets for diagnostic and therapeutic strategies in treating nonobstructive male infertility.

ZNF263 cooperates with ZNF31 to promote the drug resistance and EMT of pancreatic cancer through transactivating RNF126

The poor prognosis of pancreatic ductal adenocarcinoma (PDAC) is attribute to the aggressive local invasion, distant metastasis and drug resistance of PDAC patients, which was strongly accelerated by epithelial-mesenchymal transition (EMT). In current study, we systematically investigate the role of ZNF263/RNF126 axis in the initiation of EMT in PDAC in vitro and vivo. ZNF263 is firstly identified as a novel transactivation factor of RNF126. Both ZNF263 and RNF126 were overexpressed in PDAC tissues, which were associated with multiple advanced clinical stages and poor prognosis of PDAC patients. ZNF263 overexpression promoted cell proliferation, drug resistance and EMT in vitro via activating RNF126 following by the upregulation of Cyclin D1, N-cad, and MMP9, and the downregulation of E-cad, p21, and p27. ZNF263 silencing contributed to the opposite phenotype. Mechanistically, ZNF263 transactivated RNF126 via binding to its promoter. Further investigations revealed that ZNF263 interacted with ZNF31 to coregulate the transcription of RNF126, which in turn promoted ubiquitination-mediated degradation of PTEN. The downregulation of PTEN activated AKT/Cyclin D1 and AKT/GSK-3β/β-catenin signaling, thereby promoting the malignant phenotype of PDAC. Finally, the coordination of ZNF263 and RNF126 promotes subcutaneous tumor size and distant liver metastasis in vivo. ZNF263, as an oncogene, promotes proliferation, drug resistance and EMT of PDAC through transactivating RNF126.

RNF126, 168 and CUL1: The Potential Utilization of Multi-Functional E3 Ubiquitin Ligases in Genome Maintenance for Cancer Therapy

Ubiquitination is a post-translational modification (PTM) that is involved in proteolysis, protein-protein interaction, and signal transduction. Accumulation of mutations and genomic instability are characteristic of cancer cells, and dysfunction of the ubiquitin pathway can contribute to abnormal cell physiology. Because mutations can be critical for cells, DNA damage repair, cell cycle regulation, and apoptosis are pathways that are in close communication to maintain genomic integrity. Uncontrolled cell proliferation due to abnormal processes is a hallmark of cancer, and mutations, changes in expression levels, and other alterations of ubiquitination factors are often involved. Here, three E3 ubiquitin ligases will be reviewed in detail. RNF126, RNF168 and CUL1 are involved in DNA damage response (DDR), DNA double-strand break (DSB) repair, cell cycle regulation, and ultimately, cancer cell proliferation control. Their involvement in multiple cellular pathways makes them an attractive candidate for cancer-targeting therapy. Functional studies of these E3 ligases have increased over the years, and their significance in cancer is well reported. There are continuous efforts to develop drugs targeting the ubiquitin pathway for anticancer therapy, which opens up the possibility for these E3 ligases to be evaluated for their potential as a target protein for anticancer therapy.

E3 ubiquitin ligases and deubiquitinases in bladder cancer tumorigenesis and implications for immunotherapies

With the rapidly increasing incidence of bladder cancer in China and worldwide, great efforts have been made to understand the detailed mechanism of bladder cancer tumorigenesis. Recently, the introduction of immune checkpoint inhibitor-based immunotherapy has changed the treatment strategy for bladder cancer, especially for advanced bladder cancer, and has improved the survival of patients. The ubiquitin-proteasome system, which affects many biological processes, plays an important role in bladder cancer. Several E3 ubiquitin ligases and deubiquitinases target immune checkpoints, either directly or indirectly. In this review, we summarize the recent progress in E3 ubiquitin ligases and deubiquitinases in bladder cancer tumorigenesis and further highlight the implications for bladder cancer immunotherapies.

Emerging Roles of RNF168 in Tumor Progression

RING finger protein 168 (RNF168) is an E3 ubiquitin ligase with the RING finger domain. It is an important protein contributing to the DNA double-strand damage repair pathway. Recent studies have found that RNF168 is significantly implicated in the occurrence and development of various cancers. Additionally, RNF168 contributes to the drug resistance of tumor cells by enhancing their DNA repair ability or regulating the degradation of target proteins. This paper summarizes and prospects the research progress of the structure and main functions of RNF168, especially its roles and the underlying mechanisms in tumorigenesis.

RNF126-Mediated MRE11 Ubiquitination Activates the DNA Damage Response and Confers Resistance of Triple-Negative Breast Cancer to Radiotherapy

Triple-negative breast cancer (TNBC) has higher molecular heterogeneity and metastatic potential and the poorest prognosis. Because of limited therapeutics against TNBC, irradiation (IR) therapy is still a common treatment option for patients with lymph nodes or brain metastasis. Thus, it is urgent to develop strategies to enhance the sensitivity of TNBC tumors to low-dose IR. Here, the authors report that E3 ubiquitin ligase Ring finger protein 126 (RNF126) is important for IR-induced ATR-CHK1 pathway activation to enhance DNA damage repair (DDR). Mechanistically, RNF126 physically associates with the MRE11-RAD50-NBS1 (MRN) complex and ubiquitinates MRE11 at K339 and K480 to increase its DNA exonuclease activity, subsequent RPA binding, and ATR phosphorylation, promoting sustained DDR in a homologous recombination repair-prone manner. Accordingly, depletion of RNF126 leads to increased genomic instability and radiation sensitivity in both TNBC cells and mice. Furthermore, it is found that RNF126 expression is induced by IR activating the HER2-AKT-NF-κB pathway and targeting RNF126 expression with dihydroartemisinin significantly improves the sensitivity of TNBC tumors in the brain to IR treatment in vivo. Together, these results reveal that RNF126-mediated MRE11 ubiquitination is a critical regulator of the DDR, which provides a promising target for improving the sensitivity of TNBC to radiotherapy.

Ring finger protein 126 promotes breast cancer metastasis and serves as a potential target to improve the therapeutic sensitivity of ATR inhibitors

BACKGROUND/AIMS

This study explores the relationship between the E3 ubiquitin ligase Ring finger protein 126 (RNF126) and early breast cancer metastasis and tests the hypothesis that RNF126 determines the efficacy of inhibitors targeting Ataxia telangiectasia mutated and Rad3-related kinase (ATR).

METHODS

Various metastasis-related genes were identified by univariable Cox proportional hazards regression analysis based on the GSE11121 dataset. The RNF126-related network modules were identified by WGCNA, whereas cell viability, invasion, and migration assays were performed to evaluate the biological characteristics of breast cancer cells with or without RNF126 knockdown. MTT, immunoblotting, immunofluorescence, and DNA fiber assays were conducted to determine the efficiency of ATR inhibitor in cells with or without RNF126 knockdown.

RESULTS

RNF126 was associated with early breast cancer metastasis. RNF126 promoted breast cancer cell proliferation, growth, migration, and invasion. ATR inhibitors were more effective at killing breast cancer cells with intact RNF126 due to replication stress compared with the corresponding cells with RNF126 knockdown. Cyclin-dependent kinase 2 (CDK2) was involved in regulating replication stress in breast cancer cells with intact RNF126.

CONCLUSION

A high level of expression of RNF126 in early breast cancer patients without lymph node metastases may indicate a high-risk type of metastatic disease, possibly due to RNF126, which may increase breast cancer cell proliferation and invasion. RNF126-expressing breast cancer cells exhibit CDK2-mediated replication stress that makes them potential targets for ATR inhibitors.

E3 ubiquitin ligase RNF126 affects bladder cancer progression through regulation of PTEN stability

E3 ubiquitin ligase RNF126 (ring finger protein 126) is highly expressed in various cancers and strongly associated with tumorigenesis. However, its specific function in bladder cancer (BCa) is still debatable. Here, we found that RNF126 was significantly upregulated in BCa tissue by TCGA database, and our studies indicated that downregulation of RNF126 significantly inhibited cell proliferation and metastasis through the EGFR/PI3K/AKT signaling pathway in BCa cells. Furthermore, we identified PTEN, an inhibitor of the PI3K/AKT signaling pathway, as a novel substrate for RNF126. By co-immunoprecipitation assays, we proved that RNF126 directly interacts with PTEN. Predominantly, PTEN binds to the C-terminal containing the RING domain of RNF126. The in vivo ubiquitination assay showed that RNF126 specifically regulates PTEN stability through poly-ubiquitination. Furthermore, PTEN knockdown restored cell proliferation, metastasis, and tumor formation of BCa cells inhibited by RNF126 silencing in vitro and in vivo. In conclusion, these results identified RNF126 as an oncogene that functions through ubiquitination and degradation of PTEN in BCa.

Regulation of chromatin structure and function: insights into the histone chaperone FACT

In eukaryotic cells, changes in chromatin accessibility are necessary for chromatin to maintain its highly dynamic nature at different times during the cell cycle. Histone chaperones interact with histones and regulate chromatin dynamics. Facilitates chromatin transcription (FACT) is an important histone chaperone that plays crucial roles during various cellular processes. Here, we analyze the structural characteristics of FACT, discuss how FACT regulates nucleosome/chromatin reorganization and summarize possible functions of FACT in transcription, replication, and DNA repair. The possible involvement of FACT in cell fate determination is also discussed.Abbreviations: FACT: facilitates chromatin transcription, Spt16: suppressor of Ty16, SSRP1: structure-specific recognition protein-1, NTD: N-terminal domain, DD: dimerization domain, MD: middle domain, CTD: C-terminus domain, IDD: internal intrinsically disordered domain, HMG: high mobility group, CID: C-terminal intrinsically disordered domain, Nhp6: non-histone chromosomal protein 6, RNAPII: RNA polymerase II, CK2: casein kinase 2, AID: acidic inner disorder, PIC: pre-initiation complex, IR: ionizing radiation, DDSB: DNA double-strand break, PARlation: poly ADP-ribosylation, BER: base-excision repair, UVSSA: UV-stimulated scaffold protein A, HR: homologous recombination, CAF-1: chromatin assembly factor 1, Asf1: anti-silencing factor 1, Rtt106: regulator of Ty1 transposition protein 106, H3K56ac: H3K56 acetylation, KD: knock down, SETD2: SET domain containing 2, H3K36me3: trimethylation of lysine36 in histone H3, H2Bub: H2B ubiquitination, iPSCs: induced pluripotent stem cells, ESC: embryonic stem cell, H3K4me3: trimethylation of lysine 4 on histone H3 protein subunit, CHD1: chromodomain protein.

Overexpression of RNF126 Promotes the Development of Colorectal Cancer via Enhancing p53 Ubiquitination and Degradation

Background

RING finger protein 126 (RNF126), as a novel E3 ubiquitin ligase, plays an oncogenic role in several solid cancers. But its potential role in colorectal cancer (CRC) that harbored 50% mutant p53, to our knowledge, is rarely reported.

Materials and Methods

We investigated the clinical significance and relationship of RNF126 and p53 in CRC tissues and cells. Meanwhile, WB, qRT-PCR, co-IP, MTT, and transwell were used to investigate the function and molecular mechanism of RNF126 in regulating malignant biology in vitro.

Results

RNF126 was overexpressed in human CRC specimens, which was tightly associated with tumor size (P=0.021), T stage (P=0.030), lymph node metastasis (P=0.006), TNM stage (P=0.001), and the poor survival (P=0.003) of CRC patients. RNF126 had no association with p53 mutation in CRC specimens, and in p53 mutant Colo-205 and SW620 cells. However, in p53 wildtype HCT116 and HCT-8 cells, RNF126 silencing upregulated p53 and p21 but inhibited Rb phosphorylation at Serine 780 (pRb), which was inhibited by p53siRNA. Conversely, RNF126 overexpression downregulated p53 and p21 but promoted pRb expression, which was reversed by a classic proteasome inhibitor, MG132. However, the mRNA levels of above target genes were unchanged, implying a ubiquitination dependent post-translational modification involving in above regulation. Meanwhile, RNF126 was co-immunoprecipitated with p53 and p21 to form a triple complex. RNF126 silencing and overexpression inhibited and promoted p53 ubiquitination and degradation in vitro, respectively. In addition, p53siRNA reversed RNF126 silencing-inhibited cell proliferation, drug resistance, and cell mobility in HCT116 cells. Conversely, MG132 inhibited RNF126 overexpression-promoted above cell biology in HCT-8 cells.

Conclusion

Overexpression of RNF126 was remarkably associated with multiple advanced clinical characters of CRC patients independent of mutant p53. RNF126 promotes cell proliferation, mobility, and drug resistance in CRC via enhancing p53 ubiquitination and degradation.

Role of RING-Type E3 Ubiquitin Ligases in Inflammatory Signalling and Inflammatory Bowel Disease

Ubiquitination is a three-step enzymatic cascade for posttranslational protein modification. It includes the ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2), and ubiquitin ligase (E3). RING-type E3 ubiquitin ligases catalyse the posttranslational proteolytic and nonproteolytic functions in various physiological and pathological processes, such as inflammation-associated signal transduction. Resulting from the diversity of substrates and functional mechanisms, RING-type ligases regulate microbe recognition and inflammation by being involved in multiple inflammatory signalling pathways. These processes also occur in autoimmune diseases, especially inflammatory bowel disease (IBD). To understand the importance of RING-type ligases in inflammation, we have discussed their functional mechanisms in multiple inflammation-associated pathways and correlation between RING-type ligases and IBD. Owing to the limited data on the biology of RING-type ligases, there is an urgent need to analyse their potential as biomarkers and therapeutic targets in IBD in the future.

Molecular Mechanisms of Arsenic-Induced Disruption of DNA Repair

Exposure to arsenic in contaminated drinking water is an emerging public health problem that impacts more than 200 million people worldwide. Accumulating lines of evidence from epidemiological studies revealed that chronic exposure to arsenic can result in various human diseases including cancer, type 2 diabetes, and neurodegenerative disorders. Arsenic is also classified as a Group I human carcinogen. In this review, we survey extensively different modes of action for arsenic-induced carcinogenesis, with focus being placed on arsenic-mediated impairment of DNA repair pathways. Inorganic arsenic can be bioactivated by methylation, and the ensuing products are highly genotoxic. Bioactivation of arsenicals also elicits the production of reactive oxygen and nitrogen species (ROS and RNS), which can directly damage DNA and modify cysteine residues in proteins. Results from recent studies suggest zinc finger proteins as crucial molecular targets for direct binding to As3+ or for modifications by arsenic-induced ROS/RNS, which may constitute a common mechanism underlying arsenic-induced perturbations of DNA repair.