Knockdown of RAD18 inhibits glioblastoma development

Role of Rad18 in B cell activation and lymphomagenesis

Maintenance of genome integrity is instrumental in preventing cancer. In addition to DNA repair pathways that prevent damage to DNA, damage tolerance pathways allow for the survival of cells that encounter DNA damage during replication. The Rad6/18 pathway is instrumental in this process, mediating damage bypass by ubiquitination of proliferating cell nuclear antigen. Previous studies have shown different roles of Rad18 in vivo and in tumorigenesis. Here, we show that B cells induce Rad18 expression upon proliferation induction. We have therefore analysed the role of Rad18 in B cell activation as well as in B cell lymphomagenesis mediated by an Eµ-Myc transgene. We find no activation defects or survival differences between Rad18 WT mice and two different models of Rad18 deficient tumour mice. Also, tumour subtypes do not differ between the mouse models. Accordingly, functions of Rad18 in B cell activation and tumorigenesis may be compensated for by other pathways in B cells.

Modulation of the ubiquitin-proteasome system by phytochemicals: Therapeutic implications in malignancies with an emphasis on brain tumors

Regarding the multimechanistic nature of cancers, current chemo- or radiotherapies often fail to eradicate disease pathology, and frequent relapses or resistance to therapies occur. Brain malignancies, particularly glioblastomas, are difficult-to-treat cancers due to their highly malignant and multidimensional biology. Unfortunately, patients suffering from malignant tumors often experience poor prognoses and short survival periods. Thus far, significant efforts have been conducted to discover novel and more effective modalities. To that end, modulation of the ubiquitin-proteasome system (UPS) has attracted tremendous interest since it affects the homeostasis of proteins critically engaged in various cell functions, for example, cell metabolism, survival, proliferation, and differentiation. With their safe and multimodal actions, phytochemicals are among the promising therapeutic tools capable of turning the operation of various UPS elements. The present review, along with an updated outline of the role of UPS dysregulation in multiple cancers, provided a detailed discussion on the impact of phytochemicals on the UPS function in malignancies, especially brain tumors.

RAD18 confers radioresistance of esophagus squamous cell carcinoma through regulating p‐DNA‐PKcs

Background

Radiotherapy has recently become more common for the treatment of esophageal squamous cell carcinoma (ESCC). Radioresistance, on the other hand, continues to be a major issue because it interferes with the effectiveness of ESCC radiation. It has been demonstrated that RAD18, an E3 ubiquitin‐protein ligase that regulates translesion DNA synthesis (TLS), is implicated in the regulation of genomic integrity and DNA damage response.

Methods

In the present study, immunohistochemical staining and western blotting were utilized to determine RAD18 expression in ESCC tissues and cells. ESCC cell proliferation was determined using a colony formation assay. Immunofluorescence staining, comet assay, and homologous recombination (HR)/non‐homologous end‐joining (NHEJ) assays were conducted to examine the effect of RAD18 on the DNA damage response in ESCC cells.

Results

We found that high RAD18 expression was positively associated with a poorer prognosis in patients with ESCC who received radiotherapy. Downregulation of RAD18 expression significantly increased the sensitivity of ESCC cells to irradiation. Moreover, RAD18 knockdown prolonged the repair kinetics of γH2AX foci and resulted in longer comet tails. Furthermore, loss of RAD18 expression markedly decreased non‐homologous end‐joining (NHEJ) activity, but it did not affect homologous recombination (HR)‐mediated double‐strand break repair in ESCC cells. RAD18 upregulated p‐DNA‐dependent protein kinase complex (p‐DNA‐PKc) expression in vivo and in vitro.

Conclusions

These data indicated that RAD18 may regulate radioresistance by facilitating NHEJ via phosphorylation of DNA‐PKcs in ESCC cells, providing a novel radiotherapy target for ESCC.

Identification of Survival-Associated Hub Genes in Pancreatic Adenocarcinoma Based on WGCNA

Pancreatic adenocarcinoma is one of the leading causes of cancer-related death worldwide. Since little clinical symptoms were shown in the early period of pancreatic adenocarcinoma, most patients were found to carry metastases when diagnosis. The lack of effective diagnosis biomarkers and therapeutic targets makes pancreatic adenocarcinoma difficult to screen and cure. The fundamental problem is we know very little about the regulatory mechanisms during carcinogenesis. Here, we employed weighted gene co-expression network analysis (WGCNA) to build gene interaction network using expression profile of pancreatic adenocarcinoma from The Cancer Genome Atlas (TCGA). STRING was used for the construction and visualization of biological networks. A total of 22 modules were detected in the network, among which yellow and pink modules showed the most significant associations with pancreatic adenocarcinoma. Dozens of new genes including PKMYT1, WDHD1, ASF1B, and RAD18 were identified. Further survival analysis yielded their valuable effects on the diagnosis and treatment of pancreatic adenocarcinoma. Our study pioneered network-based algorithm in the application of tumor etiology and discovered several promising regulators for pancreatic adenocarcinoma detection and therapy.

Analysis of the Mechanism of RAD18 in Glioma

INTRODUCTION

This study aimed to evaluate the regulatory mechanism of RAD18 in glioma development.

METHODS

RAD18 expression was compared in glioma tumors and normal samples. Furthermore, we investigated the association between gene transcription and clinical factors in glioma samples, followed by functional enrichment analysis, screening for key Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, immune infiltration analysis of high and low RAD18 expression groups, and correlation analysis of quantified KEGG signaling pathways and immune cell types.

RESULTS

The expression of RAD18 was upregulated in gliomas. Moreover, RAD18 expression was significantly correlated with age, tumor grade, and histological subtype. Notably, patients with gliomas with high RAD18 expression levels had worse overall survival. Functional enrichment analysis showed that RAD18 was significantly related to biological processes, such as cell division, chemical synaptic transmission, and mitotic nuclear division, and KEGG pathways such as cell cycle, oxidative phosphorylation, and extracellular matrix (ECM)-receptor interaction. The infiltration of five immune cells (plasma B cells, naive B cells, resting CD4+ memory T cells, monocytes, and M1 macrophages) was significantly different between the high and low RAD18 expression groups, and this difference was significantly related to key KEGG pathways, such as neuroactive ligand-receptor interaction and ECM-receptor interaction.

CONCLUSION

RAD18 may serve as a target for glioma treatment and as a key regulator of glioma development.

Post-Translational Modifications of PCNA in Control of DNA Synthesis and DNA Damage Tolerance-the Implications in Carcinogenesis

The faithful DNA replication is a critical event for cell survival and inheritance. However, exogenous or endogenous sources of damage challenge the accurate synthesis of DNA, which causes DNA lesions. The DNA lesions are obstacles for replication fork progression. However, the prolonged replication fork stalling leads to replication fork collapse, which may cause DNA double-strand breaks (DSB). In order to maintain genomic stability, eukaryotic cells evolve translesion synthesis (TLS) and template switching (TS) to resolve the replication stalling. Proliferating cell nuclear antigen (PCNA) trimer acts as a slide clamp and encircles DNA to orchestrate DNA synthesis and DNA damage tolerance (DDT). The post-translational modifications (PTMs) of PCNA regulate these functions to ensure the appropriate initiation and termination of replication and DDT. The aberrant regulation of PCNA PTMs will result in DSB, which causes mutagenesis and poor response to chemotherapy. Here, we review the roles of the PCNA PTMs in DNA duplication and DDT. We propose that clarifying the regulation of PCNA PTMs may provide insights into understanding the development of cancers.

Targeting the Ubiquitin System in Glioblastoma

Glioblastoma is the most common primary brain tumor in adults with poor overall outcome and 5-year survival of less than 5%. Treatment has not changed much in the last decade or so, with surgical resection and radio/chemotherapy being the main options. Glioblastoma is highly heterogeneous and frequently becomes treatment-resistant due to the ability of glioblastoma cells to adopt stem cell states facilitating tumor recurrence. Therefore, there is an urgent need for novel therapeutic strategies. The ubiquitin system, in particular E3 ubiquitin ligases and deubiquitinating enzymes, have emerged as a promising source of novel drug targets. In addition to conventional small molecule drug discovery approaches aimed at modulating enzyme activity, several new and exciting strategies are also being explored. Among these, PROteolysis TArgeting Chimeras (PROTACs) aim to harness the endogenous protein turnover machinery to direct therapeutically relevant targets, including previously considered "undruggable" ones, for proteasomal degradation. PROTAC and other strategies targeting the ubiquitin proteasome system offer new therapeutic avenues which will expand the drug development toolboxes for glioblastoma. This review will provide a comprehensive overview of E3 ubiquitin ligases and deubiquitinating enzymes in the context of glioblastoma and their involvement in core signaling pathways including EGFR, TGF-β, p53 and stemness-related pathways. Finally, we offer new insights into how these ubiquitin-dependent mechanisms could be exploited therapeutically for glioblastoma.

Long non-coding RNA LINC00858 aggravates the oncogenic phenotypes of ovarian cancer cells through miR-134-5p/RAD18 signaling

PURPOSE

Ovarian cancer is a common gynecological cancer. Herein, we focused on the function and probable mechanisms of LINC00858 in ovarian cancer.

METHODS

Real-time quantitative polymerase chain reaction (RT-qPCR) was employed for detecting the expression of LINC00858, miR-134-5p and RAD18 E3 ubiquitin protein ligase (RAD18). Cell proliferation, migration, invasion, epithelial-mesenchymal transition (EMT) and apoptosis were detected by cell counting kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU), transwell, terminal deoxynucleotidyl transferase (TdT) dUTP Nick-End Labeling (TUNEL) and western bolt experiments, as appropriate. Interplays between LINC00858, miR-134-5p and RAD18 were detected by RNA immunoprecipitation (RIP), RNA pull down and luciferase reporter assays.

RESULTS

LINC00858 were up-regulated in ovarian cancer tissues and cells, and its expression was elevated in advanced samples compared to early ones. Knocking down LINC00858 inhibited cell proliferation, motility and EMT, but accelerated cell apoptosis in ovarian cancer. Moreover, could be sponged by LINC00858 sponged miR-134-5p to enhance RAD18 expression in ovarian cancer. Also, silenced RAD18 could also restrain oncogenic behaviors of ovarian cancer cells. Rescue experiments showed that overexpressing RAD18 reversed the effects caused by knocking down LINC00858 on cellular processes.

CONCLUSION

LINC00858 sequestered miR-134-5p to elevate RAD18 expression, resulting in aggravated development of ovarian cancer. This might provide promising targets for treating patients with ovarian cancer.

RAD18 promotes colorectal cancer metastasis by activating the epithelial‑mesenchymal transition pathway

RAD18 is an E3 ubiquitin-protein ligase that has a role in carcinogenesis and tumor progression owing to its involvement in error-prone replication. Despite its significance, the function of RAD18 has not been fully examined in colorectal cancer (CRC). In the present research, by collecting clinical samples and conducting immunohistochemical staining, we found that RAD18 expression was significantly increased in the CRC tissue compared with that noted in the adjacent non-cancerous normal tissues and that high expression of RAD18 was associated with lymph node metastasis and poor prognosis in CRC patients. In vitro, as determined by cell transfection, scratch, and Transwell experiments, it was also demonstrated that RAD18 increased the invasiveness and migration capacity of CRC cells (HCT116, DLD-1, SW480). The signaling pathway was analyzed by western blotting and the clinical data were analyzed by immunohistochemical staining and RT-PCR, indicating that the process of epithelial-mesenchymal transition (EMT) may be involved in RAD18-mediated migration and invasion of CRC cells. All of the above data indicate that RAD18 is a novel prognostic biomarker that may become a potential therapeutic target for CRC in the future.