Expression and Clinical Significance of Tumor Necrosis Factor Receptor-Associated Factor 6 in Patients With Colon Cancer

Tumor Necrosis Factor Receptor-Associated Factor 6 and Human Cancer: A Systematic Review of Mechanistic Insights, Functional Roles, and Therapeutic Potential

Cancer imposes a substantial burden and its incidence is persistently increasing in recent years. Cancer treatment has been difficult due to its inherently complex nature. The tumor microenvironment (TME) includes a complex interplay of cellular and noncellular constituents surrounding neoplastic cells, intricately contributing to the tumor initiation and progression. This critical aspect of tumors involves a complex interplay among cancer, stromal, and inflammatory cells, forming an inflammatory TME that promotes tumorigenesis across all stages. Tumor necrosis factor receptor-associated factor 6 (TRAF6) is implicated in modulating various critical processes linked to tumor pathogenesis, including but not limited to the regulation of tumor cell proliferation, invasion, migration, and survival. Furthermore, TRAF6 prominently contributes to various immune and inflammatory pathways. The TRAF6-mediated activation of nuclear factor (NF)-κB in immune cells governs the production of proinflammatory cytokines. These cytokines sustain inflammation and stimulate tumor growth by activating NF-κB in tumor cells. In this review, we discuss various types of tumors, including gastrointestinal cancers, urogenital cancers, breast cancer, lung cancer, head and neck squamous cell carcinoma, uterine fibroids, and glioma. Employing a rigorous and systematic approach, we comprehensively evaluate the functional repertoire and potential roles of TRAF6 in various cancer types, thus highlighting TRAF6 as a compelling and emerging therapeutic target worthy of further investigation and development.

POU5F1 promotes the proliferation, migration, and invasion of gastric cancer cells by reducing the ubiquitination level of TRAF6

POU5F1 plays an important role in maintaining the cancer stem cell (CSC) -like properties of gastric cancer (GC) cells. The impact of POU5F1 on the proliferation and metastasis of GC was examined, along with the potential of ATRA as a specific therapeutic agent for GC. The dysregulation of POU5F1 expression in GC tissues was analyzed using public databases and bioinformatics techniques, and the disparity in POU5F1 expression between normal gastric tissues and GC tissues was further assessed through western blot, RT-qPCR, and immunohistochemistry. The present study aimed to investigate the impact of POU5F1 on the proliferation, migration, and invasion of GC cells through both in vivo and in vitro experiments. Additionally, the effects of ATRA on the proliferation, migration, and invasion of GC cells were examined using in vivo and in vitro approaches. Our findings revealed a significant upregulation of POU5F1 in GC tissues, which was found to be associated with a poorer prognosis in patients with GC. Moreover, POU5F1 was observed to enhance the proliferation, migration, and invasion of GC cells in vitro, as well as promote subcutaneous tumor growth and lung metastasis of GC cells in vivo. The overexpression of POU5F1 mechanistically triggers the process of Epithelial-mesenchymal transition (EMT) by down-regulating E-Cadherin and up-regulating N-Cadherin and VIM. POU5F1 hinders the ubiquitination of TRAF6 through negative regulation of TRIM59, thereby facilitating the activation of the NF-κB pathway. Furthermore, the administration of ATRA effectively impedes the proliferation, migration, and invasion of GC cells by suppressing the expression of POU5F1. The upregulation of POU5F1 elicits EMT, fosters the initiation of the NF-κB signaling pathway in GC cells, and stimulates the proliferation, invasion, and metastasis of GC cells. All-trans retinoic acid (ATRA) can impede these POU5F1-induced effects, thereby potentially serving as an adjunctive therapeutic approach for GC.

Associations of Gastrointestinal Tract Tumor Necrosis Factor Receptor-Associated Factor 6 Expression with Clinical Features and Prognosis of Eosinophilic Gastroenteritis

BACKGROUND

Few studies have been conducted to explore the expression of tumor necrosis factor receptor-associated factor 6 in eosinophilic gastroenteritis patients. Therefore, the expression profile of tumor necrosis factor receptor-associated factor 6 in the gastrointestinal tract of eosinophilic gastroenteritis patients and its associations with clinical features were explored in this study.

METHODS

Thirty-four eosinophilic gastroenteritis patients who presented in Ruijin Hospital from December 2012 to May 2019 and had accepted gastrointestinal endoscopic examinations were recruited. Medical records and endoscopic biopsies were collected, and the prognosis was followed up by telephone. Healthy persons were selected as the control group. Hematoxylin and eosin and immunohistochemical staining were performed in both eosinophilic gastroenteritis patients and healthy persons. The final results were analyzed by skilled pathologists, and mean optical density values of tumor necrosis factor receptor-associated factor 6 were calculated by Image J software. Final results were analyzed by Statistical Package for the Social Sciences software 22.0.

RESULTS

Thirty-four patients (mean age: 25.56 ± 21.14 years, 61.76% males) were recruited for this study. There was no significant difference in tumor necrosis factor receptor-associated factor 6 mean optical density values of gastric tissues in eosinophilic gastroenteritis patients and healthy people (0.22 ± 0.16 vs. 0.14 ± 0.05, P > .05). Eosinophilic gastroenteritis patients had a significantly lower level of intestinal tumor necrosis factor receptor-associated factor 6 mean optical density values than that of healthy people (0.16 ± 0.05 vs. 0.23 ± 0.06, P < .05). Intestinal tumor necrosis factor receptor-associated factor 6 mean optical density values negatively linearly correlated with serum interleukin-10 level (r = -0.618, P = .043 < .05). There were no differences between eosinophilic gastroenteritis patients with or without relapse regarding the expression level of intestinal tumor necrosis factor receptor-associated factor 6 (P = .227 > .05).

CONCLUSION

Patients with eosinophilic gastroenteritis might have a deficiency of intestinal tumor necrosis factor receptor-associated factor 6 compared to healthy controls.

The roles of E3 ubiquitin ligases in cancer progression and targeted therapy

Ubiquitination is one of the most important post-translational modifications which plays a significant role in conserving the homeostasis of cellular proteins. In the ubiquitination process, ubiquitin is conjugated to target protein substrates for degradation, translocation or activation, dysregulation of which is linked to several diseases including various types of cancers. E3 ubiquitin ligases are regarded as the most influential ubiquitin enzyme owing to their ability to select, bind and recruit target substrates for ubiquitination. In particular, E3 ligases are pivotal in the cancer hallmarks pathways where they serve as tumour promoters or suppressors. The specificity of E3 ligases coupled with their implication in cancer hallmarks engendered the development of compounds that specifically target E3 ligases for cancer therapy. In this review, we highlight the role of E3 ligases in cancer hallmarks such as sustained proliferation via cell cycle progression, immune evasion and tumour promoting inflammation, and in the evasion of apoptosis. In addition, we summarise the application and the role of small compounds that target E3 ligases for cancer treatment along with the significance of targeting E3 ligases as potential cancer therapy.

MCPIP1 Suppresses the NF-κB Signaling Pathway Through Negative Regulation of K63-Linked Ubiquitylation of TRAF6 in Colorectal Cancer

The abnormal activation of the nuclear factor-kappa B (NF-κB) signaling pathway is an important precipitating factor for the inception and development of colorectal cancer (CRC), one of the most common tumors worldwide. As a pro-apoptotic transcription factor, monocyte chemotactic protein-induced protein 1 (MCPIP1) has been closely associated with many tumor types. In the present study, the expression of MCPIP1 was firstly discovered reduced in CRC tissues and correlated with poor patient prognosis. The decreased expression was caused by promoter hypermethylation. Overexpressed MCPIP1 was found to inhibit the proliferative and migratory abilities of CRC cells, whereas knockdown of MCPIP1 produced the opposite result. The subsequent investigation demonstrated that MCPIP1 exerted its "anti-cancer" effect by suppression of the NF-κB signaling pathway through negative regulation of K63-linked ubiquitylation of TNF receptor associated factor 6 (TRAF6). Therefore, our results indicate a prognostic marker for CRC and a theoretical basis for MCPIP1 as a treatment.

miR‑146b‑5p promotes colorectal cancer progression by targeting TRAF6

Increasing evidence highlights the multiple roles of microRNAs (miRs) in the tumorigenesis of colorectal cancer (CRC); however, the molecular mechanism, particularly the target of miR-146b-5p in CRC has not been fully elucidated. The present study aimed to elucidate the influence of miR-146b-5p via regulating tumor necrosis factor receptor-associated factor 6 (TRAF6) in CRC. The expression levels of miR-146b-5p and TRAF6 in CRC tissue and cells were determined by reverse transcription quantitative PCR and western blotting. Binding between miR-146b-5p and TRAF6 was examined using a dual luciferase reporter gene assay. The impact of miR-146b-5p and TRAF6 on proliferation and migration of CRC cells was determined using Cell Counting Kit-8 and Transwell assays, respectively. An animal model of CRC was established to determine the carcinogenic effect of the miR-146b-5p-TRAF6 axis. The results demonstrated that miR-146b-5p was highly expressed in CRC tissue samples compared with in normal adjacent tissue samples and in CRC cells compared with in the normal NCM460 cell line, whereas TRAF6 was expressed at low levels. Overexpression of miR-146b-5p decreased TRAF6 expression in CRC HT29 and SW620 cells. miR-146b-5p targeted and inhibited TRAF6 expression in CRC cells. Furthermore, transfection with a miR-146b-5p mimic promoted the proliferation, migration and invasion of CRC cells and tumor growth; however, these effects were abolished by TRAF6 overexpression. Transfection with a miR-146b-5p inhibitor suppressed the proliferation of CRC cells. Taken together, the results from the present study demonstrated that miR-146b-5p could enhance the initiation and tumorigenesis of CRC by targeting TRAF6. These results will help elucidate the mechanisms underlying CRC development and will facilitate the development of targeted therapy for CRC.

TRAF6 Regulates the Immunosuppressive Effects of Myeloid-Derived Suppressor Cells in Tumor-Bearing Host

Myeloid-derived suppressor cells (MDSCs) are immature heterogeneous cells derived from the bone marrow and they are the major component of the tumor-induced immunosuppressive environment. Tumor necrosis factor receptor-associated factor 6 (TRAF6), an E3 ubiquitin ligase, catalyzes the polyubiquitination of target proteins. TRAF6 plays a critical role in modulating the immune system. However, whether TRAF6 is involved in the regulation of MDSCs has not been thoroughly elucidated to date. In this study, we found that the expression of TRAF6 in MDSCs derived from tumor tissue was significantly upregulated compared with that of MDSCs from spleen of tumor-bearing mice. Knockdown of TRAF6 remarkably attenuated the immunosuppressive effects of MDSCs. Mechanistically, TRAF6 might improve the immunosuppression of MDSCs by mediating K63-linked polyubiquitination and phosphorylation of signal transducer and activator of transcription 3 (STAT3). Additionally, it was discovered that the accumulation of MDSCs was abnormal in peripheral blood of lung cancer patients. TRAF6 and arginase 1 were highly expressed in MDSCs of patients with lung cancer. Taken together, our study demonstrated that TRAF6 participates in promoting the immunosuppressive function of MDSCs and provided a potential target for antitumor immunotherapy.

TRAF6 promotes the progression and growth of colorectal cancer through nuclear shuttle regulation NF-kB/c-jun signaling pathway

AIMS

TRAF6 is an intracellular signal adapter molecule plays a significant role in tumor development. However, the specific mechanism causes and promotes of colorectal cancer keep largely unknown. Therefore, we sought to investigate the roles and the molecular mechanisms of TRAF6 in regulation colorectal cancer.

MATERIAL AND METHODS

The immunohistochemistry analyzed the expression of TRAF6 in colorectal cancer samples and analyzed the effects of expression of TRAF6 on the prognosis in colorectal cancer. The roles of TRAF6 in regulating colorectal cancer cell proliferation, colony formation, cell migration, cell wound healing and cell invasion were evaluated in vitro. Animal studies were performed to investigate the effects of TRAF6 on tumor growth. mRNA abundance of key genes was analyzed via qPCR. Protein level of TRAF6 and NF-κB/AP-1 signaling pathways was examined by Western blot. Luciferase reporter and Immunofluorescence assays were used to identify the activities NF-κB/AP-1 signaling pathways.

KEY FINDINGS

TRAF6 high expression in colorectal cancer tissues. And colorectal cancer patients with high expression of TRAF6 had a poor survival rate. TRAF6 knockdown can inhibit proliferation, migration, and invasion of colorectal cancer cells in vitro and in vivo experiments. TRAF6 activates the TRAF6-NF-κB/AP-1 signaling pathway by entering the nucleus, causing biobehavioral changes in colorectal cancer cells.

SIGNIFICANCE

TRAF6 plays a vital role in the progression of colorectal cancer. What's more, research elucidating the biological mechanisms of TRAF6 can treated as potential therapeutic target for colorectal cancer.

The Role of Ubiquitination in Regulating Embryonic Stem Cell Maintenance and Cancer Development

Ubiquitination regulates nearly every aspect of cellular events in eukaryotes. It modifies intracellular proteins with 76-amino acid polypeptide ubiquitin (Ub) and destines them for proteolysis or activity alteration. Ubiquitination is generally achieved by a tri-enzyme machinery involving ubiquitin activating enzymes (E1), ubiquitin conjugating enzymes (E2) and ubiquitin ligases (E3). E1 activates Ub and transfers it to the active cysteine site of E2 via a transesterification reaction. E3 coordinates with E2 to mediate isopeptide bond formation between Ub and substrate protein. The E1-E2-E3 cascade can create diverse types of Ub modifications, hence effecting distinct outcomes on the substrate proteins. Dysregulation of ubiquitination results in severe consequences and human diseases. There include cancers, developmental defects and immune disorders. In this review, we provide an overview of the ubiquitination machinery and discuss the recent progresses in the ubiquitination-mediated regulation of embryonic stem cell maintenance and cancer biology.

MicroRNA-124 regulates TRAF6 expression and functions as an independent prognostic factor in colorectal cancer

An increasing number of studies have confirmed that miR-124 exhibits a suppressive role in glioblastoma, cervical cancer and breast cancer; however, the function of miR-124 in colorectal cancer (CRC) has not been completely elucidated. In the present study, miR-124 expression was confirmed by reverse transcription-quantitative PCR in 80 colorectal tissues and para-cancerous tissues. The influence of altered miR-124 expression was analyzed by statistical approaches including Cox multivariate regression analysis and the Kaplan-Meier method, and the target genes of miR-124 were confirmed by luciferase reporter assays. Immunohistochemical techniques were also performed in order to measure the expression levels of target proteins. miR-124 expression was observed to be decreased in colorectal tissue samples, and this phenomenon was correlated with adverse clinical indicators and poor patient survival time. Luciferase reporter assays indicated that miR-124 directly regulated TNF receptor associated factor 6 (TRAF6) 3′-untranslated region (UTR). Hence, it was proposed that miR-124 dysregulation may negatively influence the expression of TRAF6 and therefore serve as a biomarker of epithelial-mesenchymal transition in CRC tissues. In summary, the present study demonstrated that miR-124 regulates the expression of TRAF6, and may potentially function as an independent prognostic factor and therapeutic target in patients with CRC.

Oncogenic potential of truncated RXRα during colitis-associated colorectal tumorigenesis by promoting IL-6-STAT3 signaling

Retinoid X receptor-alpha (RXRα) is a potent regulator of inflammatory responses; however, its therapeutic potential for inflammatory cancer remains to be explored. We previously discovered that RXRα is abnormally cleaved in tumor cells and tissues, producing a truncated RXRα (tRXRα). Here, we show that transgenic expression of tRXRα in mice accelerates the development of colitis-associated colon cancer (CAC). The tumorigenic effect of tRXRα is primarily dependent on its expression in myeloid cells, which results in interleukin-6 (IL-6) induction and STAT3 activation. Mechanistic studies reveal an extensive interaction between tRXRα and TRAF6 in the cytoplasm of macrophages, leading to TRAF6 ubiquitination and subsequent activation of the NF-κB inflammatory pathway. K-80003, a tRXRα modulator derived from nonsteroidal anti-inflammatory drug (NSAID) sulindac, suppresses the growth of tRXRα-mediated colorectal tumor by inhibiting the NF-κB-IL-6-STAT3 signaling cascade. These results provide new insight into tRXRα action and identify a promising tRXRα ligand for treating CAC.

Emodin suppresses angiogenesis and metastasis in anaplastic thyroid cancer by affecting TRAF6‑mediated pathways in vivo and in vitro

Emodin has been recognized to be an anti‑cancer agent against a number of types of human cancer. It was demonstrated that TNF receptor‑associated factor 6 (TRAF6) was correlated with cancer angiogenesis and metastasis. The present study confirmed the association between TRAF6 and the angiogenesis/metastasis of anaplastic thyroid cancer (ATC). The anti‑angiogenesis and metastatic effects of emodin, in addition to its molecular mechanisms in ATC, were investigated. A total of two ATC cell lines, namely 8505c and SW1736, were studied. ATC cells were implanted into nude mice to form xenografts or to establish lung metastasis models. Emodin was used to incubate ATC cells or to treat animals orally. An MTT assay was used to assess cell proliferation. A wound healing assay was employed to evaluate cell migration. ELISA analysis was used to detect the vascular endothelial growth factor (VEGF) content. Western blotting was used to determine the protein expression levels. In the in vivo study, cancer angiogenesis was assessed by micro vascular density measurement. The lung metastatic rate was the criterion for cancer metastasis. The results of the present study demonstrated that the proliferation of ATC was inhibited by emodin. The activation of the TRAF6/hypoxia inducible factor (HIF)‑1α/VEGF and TRAF6/basigin (CD147)/matrix metalloproteinase‑9 (MMP9) pathways were associated with the angiogenesis and metastasis of ATC. In a concentration‑dependent manner, emodin inhibited the TRAF6/HIF‑1α/VEGF and TRAF6/CD147/MMP9 signaling pathways to suppress angiogenesis and metastasis. In conclusion, emodin exerted anti‑angiogenic and anti‑metastatic activities in ATC by affecting TRAF6‑mediated pathways.

Bortezomib enhances radiosensitivity in oral cancer through inducing autophagy-mediated TRAF6 oncoprotein degradation

Background

Oral squamous cell carcinoma (OSCC) is a malignant tumor that may occur anywhere within the oral cavity. The survival rate of OSCC patients has not improved over the past decades due to its heterogeneous etiology, genetic aberrations, and treatment outcomes. We investigated the role of tumor necrosis factor receptor-associated factor 6 (TRAF6) in OSCC cells treated with bortezomib (a proteasome inhibitor) combined with irradiation (IR) treatment.

Methods

The effects of combined treatment in OSCC cells were investigated using assays of cell viability, autophagy, apoptosis, western blotting, and immunofluorescence staining. The ubiquitination of proteins was analyzed by immunoprecipitation. Stable knockdown of TRAF6 in OSCC cells was constructed with lentivirus. The xenograft murine models were used to observe tumor growth.

Results

We found synergistic effects of bortezomib and IR on the viability of human oral cancer cells. The combination of bortezomib and IR treatment induced autophagic cell death. Furthermore, bortezomib inhibited IR-induced TRAF6 ubiquitination and inhibited TRAF6-mediated Akt activation. Bortezomib reduced TRAF6 protein expression through autophagy-mediated lysosomal degradation. TRAF6 played an oncogenic role in tumorigenesis of human oral cancer cells and oral tumor growth was suppressed by bortezomib and IR treatment. In addition, OSCC patients with expression of TRAF6 showed a trend towards poorer cancer-specific survival when compared with patients without TRAF6 expression.

Conclusions

A combination of a proteasome inhibitor, IR treatment and TRAF6 inhibition could be a novel therapeutic strategy in OSCC.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0760-0) contains supplementary material, which is available to authorized users.

TRAF6 regulates tumour metastasis through EMT and CSC phenotypes in head and neck squamous cell carcinoma

Epithelial–mesenchymal transition (EMT) is associated with metastasis formation, generation and maintenance of cancer stem cells (CSCs). However, the regulatory mechanisms of CSCs have not been clarified. This study aims to investigate the role of TNF receptor‐associated factor 6 (TRAF6) on EMT and CSC regulation in squamous cell carcinoma of head and neck (SCCHN). We found TRAF6 was overexpressed in human SCCHN tissues, and high TRAF6 expression was associated with lymphatic metastasis and resulted in poor prognosis in patients with SCCHN. In addition, elevated TRAF6 expression was observed in several HNSCC cell lines, and wound healing and transwell assay results showed that TRAF6 knockdown inhibited the migration and invasion ability of the SCCHN cells. Moreover, the expression of Vimentin, Slug and N‐cadherin was down‐regulated and that of E‐cadherin was elevated after TRAF6 knockdown but decreased by transforming growth factor beta 1 (TGF‐β1) and CAL27 similar to mesenchymal cells formed after TGF‐β1 induction. In addition, the expression levels of CD44, ALDH1, KLF4 and SOX2 were inhibited after TRAF6 knockdown, and the anchor‐dependent colony formation number and sphere number were remarkably reduced. Flow cytometry showed TRAF6 knockdown reduced ALDH1‐positive cancer stem cells. We also demonstrated that TRAF6 is closely associated with EMT process and cancer stem cells using a Tgfbr1/Pten 2cKO mice SCCHN model and human SCCHN tissue microarray. Our findings indicate that TRAF6 plays a role in EMT phenotypes, the generation and maintenance of CSCs in SCCHN, suggesting that TRAF6 is a potential therapeutic target for SCCHN.

Functional significance and therapeutic implication of ring-type E3 ligases in colorectal cancer

Accumulative studies revealed that E3 ubiquitin ligases have important roles in colorectal carcinogenesis. The pathogenic mechanisms of colorectal cancer (CRC) initiation and progression are complex and heterogeneous, involving somatic mutations, abnormal gene fusion, deletion or amplification and epigenetic alteration, which may cause aberrant expression or altered function of E3 ligases in CRC. Defects of E3 ligases have been reported to be involved in the molecular etiology and pathogenesis of CRC. The aberrant expressed E3 ligases can function as either oncogenes or tumor suppressors depending on ubiquiting target substrates in CRC. Recently, considerable progress has been made in our understanding of the potential roles of E3 ligase-mediated ubiquitylation in colorectal carcinogenesis. There are mainly two subtypes of E3 ubiquitin ligases in humans, as defined by the presence of either a HECT domain or a RING finger domain on the basis of structural similitude. Most cancer-associated E3 ligases participate in regulating the cell cycle, apoptosis, gene transcription, cell signaling and DNA repair, the critical parts of CRC tumorigenesis. In this review, we have provided a comprehensive summary of abnormally expressed E3 ligases and their related pivotal mechanistic effects in CRC. In particular, we have highlighted the function of RING-type E3 ubiquitin enzymes in modulating cancer signaling pathways, immunity and tumor microenvironment in CRC development and progression; their mechanism(s) of action in CRC involving both ubiquitylation-dependent and ubiquitylation-independent effects; and the potential of RING E3 ligases as molecular biomarkers for predicting patient prognosis and as therapeutic targets in CRC. A better understanding of E3 ligase-mediated substrates' ubiquitylation involved in the development of CRC will provide new insights into the pathophysiology mechanisms of CRC, and unravel novel prognostic markers and therapeutic strategies for CRC.