TRAF6 is upregulated in colon cancer and promotes proliferation of colon cancer cells

Narciclasine induces colon carcinoma cell apoptosis by inhibiting the IL-17A/Act1/TRAF6/NF-κB signaling pathway

IL-17 A is a promoter of colorectal cancer initiation and progression. Narciclasine is a polyhydroxy alkaloid compound isolated from Narcissus plants, which has potent anti-inflammatory and antitumor actions. The effects of narciclasine on colorectal tumors were evaluated, with a focus on IL-17 A. Narciclasine reduced the growth of HCT-116 and SW-480 colon cancer cells in vitro and in vivo in murine xenografts. The results of flow cytometry on JC-1 and Annexin V/PI revealed that narciclasine significantly reduced the mitochondrial membrane potential and induced apoptosis, findings confirmed by western blotting results of reduced Bcl-2 and enhanced Bax expression, as well as accumulation of cleaved Caspase-3, Caspase-8, Caspase-9, and cytoplasmic Cytochrome-c. After narciclasine incubation, IL-17 A, Act1, and TRAF6 were down-regulated, while p-P65 (Ser536) accumulated in the cytoplasm, a finding confirmed by laser scanning confocal microscopy. IL17A substitution could partly reverse these narciclasine effects while they were elevated by IL17A silencing. Moreover, IL-17 A, Act1, and TRAF6 were significantly expressed to greater extents in human colorectal cancer compared to normal adjacent tissue specimens and were closely linked with a poor prognosis. This study provided evidence that narciclasine may be a useful therapeutic drug for colorectal cancer treatment through its actions in down-regulating the L-17A/Act1/TRAF6/NF-κB anti-apoptotic signaling pathway.

A deep learning model predicts the presence of diverse cancer types using circulating tumor cells

Circulating tumor cells (CTCs) are cancer cells that detach from the primary tumor and intravasate into the bloodstream. Thus, non-invasive liquid biopsies are being used to analyze CTC-expressed genes to identify potential cancer biomarkers. In this regard, several studies have used gene expression changes in blood to predict the presence of CTC and, consequently, cancer. However, the CTC mRNA data has not been used to develop a generic approach that indicates the presence of multiple cancer types. In this study, we developed such a generic approach. Briefly, we designed two computational workflows, one using the raw mRNA data and deep learning (DL) and the other exploiting five hub gene ranking algorithms (Degree, Maximum Neighborhood Component, Betweenness Centrality, Closeness Centrality, and Stress Centrality) with machine learning (ML). Both workflows aim to determine the top genes that best distinguish cancer types based on the CTC mRNA data. We demonstrate that our automated, robust DL framework (DNNraw) more accurately indicates the presence of multiple cancer types using the CTC gene expression data than multiple ML approaches. The DL approach achieved average precision of 0.9652, recall of 0.9640, f1-score of 0.9638 and overall accuracy of 0.9640. Furthermore, since we designed multiple approaches, we also provide a bioinformatics analysis of the gene commonly identified as top-ranked by the different methods. To our knowledge, this is the first study wherein a generic approach has been developed to predict the presence of multiple cancer types using raw CTC mRNA data, as opposed to other models that require a feature selection step.

TRAF6 promotes chemoresistance to paclitaxel of triple negative breast cancer via regulating PKM2-mediated glycolysis

Ample evidence reveals that glycolysis is crucial to tumor progression; however, the underlying mechanism of its drug resistance is still worth being further explored. TRAF6, an E3 ubiquitin ligase, is well recognized to overexpress in various types of cancer, which predicts a poor prognosis. In our study, we discovered that TRAF6 was expressed more significantly in the case of triple-negative breast cancer (TNBC) than in other of breast cancers, promoting chemoresistance to paclitaxel; that inhibited TRAF6 expression in the chemoresistant TNBC (TNBC-CR) cells enhanced the sensitivity by decreasing glucose uptake and lactate production; that TRAF6 regulated glycolysis and facilitated chemoresistance via binding directly to PKM2; and that overexpressing PKM2 in the TNBC-CR cells with TRAF6 knocked down regained significantly TRAF6-dependent drug resistance and glycolysis. Additionally, we verified that TRAF6 could facilitate PKM2-mediated glycolysis and chemoresistance in animal models and clinical tumor tissues. Thus, we identified the novel function of TRAF6 to promote glycolysis and drug resistance in TNBC with the regulation of PKM2, which could provide a potential molecular target for TNBC treatment.

TRAF6 regulates the abundance of RIPK1 and inhibits the RIPK1/RIPK3/MLKL necroptosis signaling pathway and affects the progression of colorectal cancer

Colorectal cancer cannot be completely cured at present, and it is still an important clinical medical problem. TRAF6 is highly expressed in many malignant tumors. However, the role of TRAF6 in colorectal cancer is still controversial, mainly because the specific regulatory mechanism of colorectal cancer is still unclear, and the death mode of colorectal cancer cells has not been elucidated. The recent study found that TRAF6 inhibits necroptosis in colorectal cancer cells via the RIPK1/RIPK3/MLKL signaling pathway. The RIPK1 inhibitor Necrostain-1 inhibits colorectal cancer cell necroptosis via the RIPK1/RIPK3/MLKL signaling pathway. TRAF6 directly interacts with RIPK1 through the polyubiquitination of Lys48-linked RIPK1 and reduces the levels of RIPK1 protein in colorectal cancer cells, leading to necroptosis, thus promoting the proliferation of colorectal cancer cells. The recent study demonstrated that TRAF6 promotes colorectal cell progression by inhibiting the RIPK1/RIPK3/MLKL necroptosis signaling pathway, which may provide a new therapeutic target for colorectal cancer.

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.

CCL3 Promotes Proliferation of Colorectal Cancer Related with TRAF6/NF-κB Molecular Pathway

Chemokine C-C motif chemokine ligand 3 (CCL3) plays an important role in the invasion and metastasis of malignant tumors. For developing new therapeutic targets and antitumor drugs, the effect of chemokine CCL3 and the related cytokine network on colorectal cancer should be investigated. This study used cell, tissue, and animal experiments to prove that CCL3 is highly expressed in colorectal cancer and confirmed that CCL3 can promote the proliferation of cancer cells, and its expression is closely related to TRAF6/NF-κB molecular pathway. In addition, protein chip technology was used to examine colorectal cancer tissue samples and identify the key factors of chemokine CCL3 and the toll-like receptors/nuclear factor-κB (TLR/NF-κB) pathway in cancer and metastatic lymph nodes. Furthermore, the lentiviral vector technology was employed for transfection to construct interference and overexpression cell lines. The experimental results reveal the mechanism of CCL3 and TNF receptor-associated factor 6 (TRAF6)/NF-κB pathway-related factors and their effects on the proliferation of colon cancer cells. Finally, the expression and significance of CCL3 in colorectal cancer tissues and its correlation with clinical pathology were studied by immunohistochemistry. Also, the results confirmed that CCL3 and C-C motif chemokine receptor 5 (CCR5) were expressed in adjacent tissues, colorectal cancer tissues, and metastatic cancer. The expression level was correlated with the clinical stage and nerve invasion. The expression of chemokine CCL3 and receptor CCR5 was positively correlated with the expression of TRAF6 and NF-κB and could promote the proliferation, invasion, and migration of colorectal cancer cells through TRAF6 and NF-κB.

TRAF6 regulates the signaling pathway influencing colorectal cancer function by ubiquitination mechanisms

Tumor necrosis factor receptor‐associated factor‐6 (TRAF6) is a ubiquitin E3 ligase. TRAF6 plays an important role in tumor invasion and metastasis. However, the specific mechanism by which TRAF6 promotes colorectal cancer (CRC) metastasis is incompletely understood. This study aimed to determine whether TRAF6 affects the LPS‐NF‐κB‐VEGF‐C signaling pathway through ubiquitination, which plays a role in colorectal cancer metastasis. Here, our results showed that TRAF6 affected lymphangiogenesis through the LPS‐NF‐κB‐VEGF‐C signaling pathway. Using ubiquitination experiments, we found that TRAF6 was mainly ubiquitinated with the K63‐linked chains, and LPS promoted ubiquitination of TRAF6 and K63‐linked chains. More importantly, TRAF6 124mut is the main ubiquitination site of TRAF6 interacting with K63‐linked chains. TRAF6 affected the migration, invasion, and lymphatic metastasis of colorectal cancer through its ubiquitination. In subcutaneous xenograft models, TRAF6 124mut inhibited tumor growth. In conclusion, our results provide new insight for studying the mechanism of lymphangiogenesis in colorectal cancer to promote cancer metastasis, which may provide new ideas for tumor immunotherapy.

Survival of HT29 Cancer Cells Is Affected by IGF1R Inhibition via Modulation of Self-DNA-Triggered TLR9 Signaling and the Autophagy Response

Purpose: In HT29 colon cancer cells, a close interplay between self-DNA-induced TLR9 signaling and autophagy response was found, with remarkable effects on cell survival and differentiation. IGF1R activation drives the development and malignant progression of colorectal cancer. IGF1R inhibition displays a controversial effect on autophagy. The interrelated roles of IGF1R inhibition and TLR9/autophagy signaling in HT29 cancer cells have not yet been clarified. In our study, we aimed to investigate the complex interplay of IGF1R inhibition and TLR9/autophagy signaling in HT29 cells. Methods: HT29 cells were incubated with tumor-originated self-DNA with or without inhibitors of IGF1R (picropodophyllin), autophagy (chloroquine), and TLR9 (ODN2088), respectively. Cell proliferation and metabolic activity measurements, direct cell counting, NanoString and Taqman gene expression analyses, immunocytochemistry, WES Simple Western blot, and transmission electron microscopy investigations were performed. Results: The concomitant use of tumor-derived self-DNA and IGF1R inhibitors displays anti-proliferative potential, which can be reversed by parallel TLR9 signaling inhibition. The distinct effects of picropodophyllin, ODN2088, and chloroquine per se or in combination on HT29 cell proliferation and autophagy suggest that either the IGF1R-associated or non-associated autophagy machinery is "Janus-faced" regarding its actions on cell proliferation. Autophagy, induced by different combinations of self-DNA and inhibitors is not sufficient to rescue HT29 cells from death but results in the survival of some CD133-positive stem-like HT29 cells. Conclusion: The creation of new types of combined IGF1R, autophagy, and/or TLR9 signaling inhibitors would play a significant role in the development of more personalized anti-tumor therapies for colorectal cancer.

Survival of HT29 cancer cells is influenced by hepatocyte growth factor receptor inhibition through modulation of self-DNA-triggered TLR9-dependent autophagy response

HGFR activation drives the malignant progression of colorectal cancer, and its inhibition displays anti-autophagic activity. The interrelated role of HGFR inhibition and TLR9/autophagy signaling in HT29 cancer cells subjected to modified self-DNA treatments has not been clarified. We analyzed this complex interplay with cell metabolism and proliferation measurements, TLR9, HGFR and autophagy inhibitory assays and WES Simple Western blot-based autophagy flux measurements, gene expression analyses, immunocytochemistry, and transmission electron microscopy. The overexpression of MyD88 and caspase-3 was associated with enhanced HT29 cell proliferation, suggesting that incubation with self-DNAs could suppress the apoptosis-induced compensatory cell proliferation. HGFR inhibition blocked the proliferation-reducing effect of genomic and hypermethylated, but not that of fragmented DNA. Lowest cell proliferation was achieved with the concomitant use of genomic DNA, HGFR inhibitor, and chloroquine, when the proliferation stimulating effect of STAT3 overexpression could be outweighed by the inhibitory effect of LC3B, indicating the putative involvement of HGFR-mTOR-ULK1 molecular cascade in HGFR inhibitor-mediated autophagy. The most intense cell proliferation was caused by the co-administration of hypermethylated DNA, TLR9 and HGFR inhibitors, when decreased expression of both canonical and non-canonical HGFR signaling pathways and autophagy-related genes was present. The observed ultrastructural changes also support the context-dependent role of HGFR inhibition and autophagy on cell survival and proliferation. Further investigation of the influence of the studied signaling pathways and cellular processes can provide a basis for novel, individualized anti-cancer therapies.

Circ_0114427 promotes LPS-induced septic acute kidney injury by modulating miR-495-3p/TRAF6 through the NF-κB pathway

BACKGROUNDS

Septic acute kidney injury (AKI) is a severe illness in clinics. Enriching researches investigated the regulatory network of AKI during the past decades, evidences showed that circular RNAs (circRNAs) were involved in the molecular mechanism of human AKI. However, the special responses remain largely elusive. Thus, the study aims to investigate the function of circ_0114427 in the progression of AKI.

METHODS

The levels of circ_0114427, miR-495-3p and Tumour Necrosis Factor Receptor-Associated Factor 6 (TRAF6) were both assessed by quantitative real-time polymerase chain reaction (qRT-PCR). In addition, lipopolysaccharide (LPS) was applied to establish AKI cell model, and 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay was carried out to determine the viability of LPS-induced HK-2 cells. The expression of TRAF6, B-cell lymphoma-2 (Bcl-2), Bcl2-associated X (Bax), cleave-caspase 3, caspase 3, total IκBα (t-IκBα), phospho-IκBα (p-IκBα), total p65 (t-p65) and phospho-p65 (p-p65) were all detected via western blot. The levels of IL-1β and TNF-α were identified by western blot and ELISA. What's more, cell apoptosis was measured by flow cytometry. Lastly, dual-luciferase reporter, RNA Immunoprecipitation (RIP) and RNA pull-down assays were employed to verify the relationships between miR-495-3p and circ_0114427 or TRAF6 in vitro.

RESULTS

The level of miR-495-3p was remarkably restrained while circ_0114427 and TRAF6 levels were specially reinforced in AKI patient serum samples and LPS-induced HK-2 cells. Moreover, IL-1β and TNF-α were highly expressed in LPS-induced AKI cells. Functionally, circ_0114427 was a sponge of miR-495-3p, and circ_0114427 silence-mediated effects in LPS-induced HK-2 cells were partly ameliorated by the addition of miR-495-3p inhibitor. Moreover, TRAF6 was a target gene of miR-495-3p, and the inhibiting effect of miR-495-3p on cell apoptosis and inflammatory response was mitigated by TRAF6 overexpression. Mechanistically, the circ_0114427/miR-495-3p/TRAF6 axis modulated cell apoptosis and inflammatory response via NF-κB/p65 signalling pathway in AKI.

CONCLUSION

Circ_0114427 regulated cell apoptosis and inflammatory response through miR-495-3p/TRAF6 axis via NF-κB/p65 signalling pathway, providing a novel mechanism in clinical treatment of AKI patients.HighlightsCirc_0114427 is upregulated in serum specimens from septic AKI patients and LPS-induced HK-2 cells.LPS treatment suppresses cell viability and promotes apoptosis and inflammation in HK-2 cells.Circ_0114427 knockdown ameliorates the effects of LPS on cell viability, apoptosis and inflammation in HK-2 cells.Circ_0114427 regulates LPS-induced HK-2 cell injury by regulating miR-495-3p/TRAF6/NF-κB/p65 axis.

The Structure and Ubiquitin Binding Properties of TRAF RING Heterodimers

Tumour necrosis factor (TNF) receptor associated factor (TRAF) family members share a common domain architecture, but play non-redundant physiological roles in cell signalling. At the N terminus, most TRAFs have a RING domain, followed by a series of Zinc finger (ZF) domains. The RING domain of TRAF6 dimerizes, and the RING homodimer together with the first ZF assembles ubiquitin chains that form a platform which facilitates activation of downstream kinases. The RING dimer interface is conserved amongst TRAF proteins, suggesting that functional heterodimers could be possible. Here we report the structure of the TRAF5-TRAF6 RING heterodimer, which accounts for the stability of the heterodimer as well as its ability to assemble ubiquitin chains. We also show that the RING domain of TRAF6 heterodimerizes with TRAF3 and TRAF2, and demonstrate that the linker helix and first ZF of TRAF2 can cooperate with TRAF6 to promote chain assembly. Collectively our results suggest that TRAF RING homo- and hetero-dimers have the potential to bridge interaction of nearby TRAF trimers and modulate TRAF-mediated signalling.

Proteomics and molecular network analyses reveal that the interaction between the TAT-DCF1 peptide and TAF6 induces an antitumor effect in glioma cells

Glioblastoma is the most lethal brain cancer in adults. Despite advances in surgical techniques, radiotherapy, and chemotherapy, their therapeutic effect is far from significant, since the detailed underlying pathological mechanism of this cancer is unclear. The establishment of molecular interaction networks has laid the foundation for the exploration of these mechanisms with a view to improving therapy for glioblastoma. In the present study, to further explore the cellular role of DCF1 (dendritic cell-derived factor 1), the proteins bound to TAT-DCF1 (transactivator of transcription-dendritic cell-derived factor 1) were identified, and biosystem analysis was employed. Functional enrichment analyses indicate that TAT-DCF1 induced important biological changes in U251 cells. Furthermore, the established molecular interaction networks indicated that TAT-DCF1 directly interacted with TAF6 in glioma cells and with UBC in HEK293T (human embryonic kidney 293T) cells. In addition, further biological experiments demonstrate that TAT-DCF1 induced the activation of the RPS27A/TOP2A/HMGB2/BCL-2 signaling pathway via interaction with TAF6 in U251 cells. Taken together, these findings suggest that the TAT-DCF1 peptide possesses great potential for the development of glioblastoma therapy through the interaction with TAF6-related pathways and provides further theoretic evidence for the mechanisms underlying the antitumor effects of TAT-DCF1.

The relationship between TRAF6 and tumors

Tumor necrosis factor receptor (TNFR)-related factors (TRAFs) are important linker molecules in the tumor necrosis factor superfamily (TNFSF) and the Toll-like/interleukin-1 receptor (TLR/ILR) superfamily. There are seven members: TRAF1-TRAF7, among those members, tumor necrosis factor receptor-associated factor 6 (TRAF6) is upregulated in various tumors, which has been related to tumorigenesis and development. With the in-depth study of the relationship between TRAF6 and different types of tumors, TRAF6 has oncogenic characteristics involved in tumorigenesis, tumor development, invasion, and metastasis through various signaling pathways, therefore, targeting TRAF6 has provided a novel strategy for tumor treatment. This review summarizes and analyzes the role of TRAF6 in tumorigenesis and tumor development in combination with the current research on TRAF6 and tumors.

Molecular and Cellular Complexity of Glioma. Focus on Tumour Microenvironment and the Use of Molecular and Imaging Biomarkers to Overcome Treatment Resistance

This review highlights the importance and the complexity of tumour biology and microenvironment in the progression and therapy resistance of glioma. Specific gene mutations, the possible functions of several non-coding microRNAs and the intra-tumour and inter-tumour heterogeneity of cell types contribute to limit the efficacy of the actual therapeutic options. In this scenario, identification of molecular biomarkers of response and the use of multimodal in vivo imaging and in particular the Positron Emission Tomography (PET) based molecular approach, can help identifying glioma features and the modifications occurring during therapy at a regional level. Indeed, a better understanding of tumor heterogeneity and the development of diagnostic procedures can favor the identification of a cluster of patients for personalized medicine in order to improve the survival and their quality of life.

TRAF6-Mediated Inflammatory Cytokines Secretion in LPS-induced Colorectal Cancer Cells Is Regulated by miR-140

BACKGROUND/AIM

Colorectal cancer (CRC) cells secrete inflammatory cytokines that affect CRC progression. The aim of the present study was to determine if micro-RNA-140(miR-140) regulates inflammatory cytokine secretion induced by lipopolysaccharide (LPS) in colorectal cancer cells by targeting tumor necrosis factor receptor (TNFR)-associated factor 6 (TRAF6).

MATERIALS AND METHODS

Fifty fresh colon-cancer specimens and normal colorectal tissues were collected from patients with CRC and tested for the expression miR-140. Human CRC cell lines SW480 and HCT116 were treated with various concentrations and times with LPS. miR-140 and mRNA expression of potentially related genes were analyzed by qPCR. Protein expression was analyzed using western blot or ELISA. Overexpression plasmids with pcDNA3.1-TRAF6, pGL4.10-wtTRAF6 and pGL4.10-mutTRAF6 were constructed. miRNA target gene prediction and a dual luciferase assay were used to analyze miR-140-targeted TRAF6.

RESULTS

miR-140 expression was up-regulated in CRC tissues. In CRC cells, LPS could increase miR-140 expression in a time- and concentration-dependent manner. LPS increased inflammatory cytokine mRNA expression levels in SW480 and HCT116 human colon-cancer cells. miRNA-140 suppressed TRAF6 expression via targeting the 3'UTR. TRAF6 affected miR-140-mediated inflammatory cytokine expression of SW480 and HCT116 cells under LPS treatment.

CONCLUSION

miR-140 regulates inflammatory cytokine secretion of LPS-induced colorectal cancer cells by targeting TRAF6.

HIF-1β Positively Regulates NF-κB Activity via Direct Control of TRAF6

NF-κB signalling is crucial for cellular responses to inflammation but is also associated with the hypoxia response. NF-κB and hypoxia inducible factor (HIF) transcription factors possess an intense molecular crosstalk. Although it is known that HIF-1α modulates NF-κB transcriptional response, very little is understood regarding how HIF-1β contributes to NF-κB signalling. Here, we demonstrate that HIF-1β is required for full NF-κB activation in cells following canonical and non-canonical stimuli. We found that HIF-1β specifically controls TRAF6 expression in human cells but also in Drosophila melanogaster. HIF-1β binds to the TRAF6 gene and controls its expression independently of HIF-1α. Furthermore, exogenous TRAF6 expression is able to rescue all of the cellular phenotypes observed in the absence of HIF-1β. These results indicate that HIF-1β is an important regulator of NF-κB with consequences for homeostasis and human disease.

Long noncoding RNA LINC01234 promoted cell proliferation and invasion via miR-1284/TRAF6 axis in colorectal cancer

Colorectal cancer is one of the most common and leading malignancies globally. Long noncoding RNAs (lncRNAs) function as potentially critical regulator in colorectal cancer. LINC01234, a novel lncRNA in tumor biology, regulates the progression of various tumors. However, the tumorigenic mechanism of LINC01234 in colorectal cancer is still unclear. This study was performed with the aim to prospectively investigate clinical significance, effect, and mechanism of lncRNA LINC01234 in colorectal cancer. First, we found that LINC01234, localized in the cytoplasm, was increased in both colorectal cancer cell lines and tissues. Subsequent functional assays suggested LINC01234 knockdown suppressed cell proliferation, migration, and invasion of colorectal cancer cells, while blocked cell cycle and induced cell apoptosis. Moreover, we identified that miR-1284 was target of LINC01234, we further demonstrated a negative correlation with LINC01234 in colorectal cancer tissues and cells. Furthermore, miR-1284 targeted and suppressed tumor necrosis factor receptor-associated factor 6 (TRAF6). Loss-of-function assay revealed that LINC01234 silencing suppressed colorectal cancer progression through inhibition of miR-1284. In vivo subcutaneous xenotransplanted tumor model indicated LINC01234 knockdown inhibited in vivo tumorigenic ability of colorectal cancer via downregulation of TRAF6. Collectively, this study clarified the biological significance of LINC01234/miR-1284/TRAF6 axis in colorectal cancer progression, providing insights into LINC01234 as novel potential therapeutic target for colorectal cancer therapeutic from bench to clinic.

TRAF6 mediates human DNA2 polyubiquitination and nuclear localization to maintain nuclear genome integrity

The multifunctional human DNA2 (hDNA2) nuclease/helicase is required to process DNA ends for homology-directed recombination repair (HDR) and to counteract replication stress. To participate in these processes, hDNA2 must localize to the nucleus and be recruited to the replication or repair sites. However, because hDNA2 lacks the nuclear localization signal that is found in its yeast homolog, it is unclear how its migration into the nucleus is regulated during replication or in response to DNA damage. Here, we report that the E3 ligase TRAF6 binds to and mediates the K63-linked polyubiquitination of hDNA2, increasing the stability of hDNA2 and promoting its nuclear localization. Inhibiting TRAF6-mediated polyubiquitination abolishes the nuclear localization of hDNA2, consequently impairing DNA end resection and HDR. Thus, the current study reveals a mechanism for the regulation of hDNA2 localization and establishes that TRAF6-mediated hDNA2 ubiquitination activates DNA repair pathways to maintain nuclear genome integrity.

Modified Genomic Self-DNA Influences In Vitro Survival of HT29 Tumor Cells via TLR9- and Autophagy Signaling

In relation of immunobiology, the consequence of the crosstalk between TLR9-signaling and autophagy is poorly documented in HT29 cancer cells. To assess the TLR9-mediated biologic effects of modified self-DNA sequences on cell kinetics and autophagy response HT29 cells were incubated separately with intact genomic (g), hypermethylated (m), fragmented (f), and hypermethylated/fragmented (m/f) self-DNAs. Cell viability, apoptosis, cell proliferation, colonosphere-formation were determined. Moreover, the relation of TLR9-signaling to autophagy response was assayed by real-time RT-PCR, immunocytochemistry and transmission electron microscopy (TEM). After incubation with g-, m-, and m/f-DNAs cell viability and proliferation decreased, while apoptosis increased. F-DNA treatment resulted in an increase of cell survival. Methylation of self-DNA resulted in decrease of TLR9 expression, while it did not influence the positive effect of DNA fragmentation on MyD88 and TRAF6 overexpression, and TNFα downregulation. Fragmentation of DNA abrogated the positive effect of methylation on IRAK2, NFκB and IL-8 mRNA upregulations. In case of the autophagy genes and proteins, g- and f-DNAs caused significant upregulation of Beclin1, Atg16L1, and LC3B. According to TEM analyses, autophagy was present in each group of tumor cells, but to a varying degree. Incubation with m-DNA suppressed tumor cell survival by inducing features of apoptotic cell death, and activated mitophagy. F-DNA treatment enhanced cell survival, and activated macroautophagy and lipophagy. Colonospheres were only present after m-DNA incubation. Our data provided evidence for a close existing interplay between TLR9-signaling and the autophagy response with remarkable influences on cell survival in HT29 cells subjected to modified self-DNA treatments.

Structure based virtual screening of natural products to disrupt the structural integrity of TRAF6 C-terminal domain homotrimer

Tumor necrosis factor receptor-associated factor 6 (TRAF6) is an E3 ligase which takes part in different cellular pathways. TRAF6 is seen to be highly expressed in various cancers and most importantly is known to drive cancer metastasis. This makes TRAF6 a potential therapeutic target. In our previous studies, we observed that the C-terminal domain of TRAF6 forms a mushroom shaped trimer structure. Lys340 and Glu345 were identified to be the most critical residues in the trimer interface. In this current work, we screened for more than 14000 small molecules derived from various natural sources and they were screened against TRAF6 C-terminal trimer interaction interface to prevent the formation of the interface. All the obtained molecules were tested for their drug-likeliness properties. The ligands which qualified the filter were considered for protein-ligand docking or structure based virtual screening in GOLD 5.2. Pose selection was carried out on the basis of GoldScore and ChemScore function of GOLD 5.2. Top 20 molecules binding the TRAF6 trimeric interface were tested for their ADME properties. From the top 20 molecules, top 3 ligands were chosen based on their abilities to pass the maximum numbers of ADME filters.

TRAF6 function as a novel co-regulator of Wnt3a target genes in prostate cancer

Background

Tumour necrosis factor receptor associated factor 6 (TRAF6) promotes inflammation in response to various cytokines. Aberrant Wnt3a signals promotes cancer progression through accumulation of β-Catenin. Here we investigated a potential role for TRAF6 in Wnt signaling.

Methods

TRAF6 expression was silenced by siRNA in human prostate cancer (PC3U) and human colorectal SW480 cells and by CRISPR/Cas9 in zebrafish. Several biochemical methods and analyses of mutant phenotype in zebrafish were used to analyse the function of TRAF6 in Wnt signaling.

Findings

Wnt3a-treatment promoted binding of TRAF6 to the Wnt co-receptors LRP5/LRP6 in PC3U and LNCaP cells in vitro. TRAF6 positively regulated mRNA expression of β-Catenin and subsequent activation of Wnt target genes in PC3U cells. Wnt3a-induced invasion of PC3U and SW480 cells were significantly reduced when TRAF6 was silenced by siRNA. Database analysis revealed a correlation between TRAF6 mRNA and Wnt target genes in patients with prostate cancer, and high expression of LRP5, TRAF6 and c-Myc correlated with poor prognosis. By using CRISPR/Cas9 to silence TRAF6 in zebrafish, we confirm TRAF6 as a key molecule in Wnt3a signaling for expression of Wnt target genes.

Interpretation

We identify TRAF6 as an important component in Wnt3a signaling to promote activation of Wnt target genes, a finding important for understanding mechanisms driving prostate cancer progression.

Fund

KAW 2012.0090, CAN 2017/544, Swedish Medical Research Council (2016-02513), Prostatacancerförbundet, Konung Gustaf V:s Frimurarestiftelse and Cancerforskningsfonden Norrland. The funders did not play a role in manuscript design, data collection, data analysis, interpretation nor writing of the manuscript.

•

TRAF6 positively regulated mRNA expression of b-Catenin and subsequent activation of Wnt target genes in prostate cancer cells in vitro.

•

High expression of LRP5, TRAF6 and c-Myc correlated with poor prognosis for patients with prostate cancer.

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.

Tumor necrosis factor receptor-associated factor 6 contributes to malignant behavior of human cancers through promoting AKT ubiquitination and phosphorylation

Tumor necrosis factor receptor-associated factor 6 (TRAF6) has been found to be involved in carcinogenesis in multiple cancers. However, the precise role of TRAF6 in cancer has not been extensively investigated and remains largely unknown. In this study, we aimed to investigate the biological function of TRAF6 and its underlying molecular mechanisms in cancer. A positive correlation between poor tumor differentiation and TRAF6 expression status was observed in both oral cancer and breast cancer. Overexpression of TRAF6 promoted proliferation, migration, and G₀ /G₁ to S phase transition in tumor cells. Tumor necrosis factor receptor-associated factor 6-mediated AKT ubiquitination and subsequent phosphorylation played an essential role in the control of tumor cell malignant behavior. In vivo treatment with TRAF6, but not the E3 ligase deficient TRAF6 mutant, facilitated tumor growth. Our findings indicate that TRAF6 contributes to malignant behavior of human cancers through promoting AKT ubiquitination and phosphorylation. Therefore, TRAF6 could serve as a therapeutic target in cancers.

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.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

TRAF6 regulates EGF-induced cell transformation and cSCC malignant phenotype through CD147/EGFR

TRAF6, a well-known adapter molecule, plays pivotal role in TLR/IL-1R associated signaling pathway. Although TRAF6 has been shown to have oncogenic activity in various malignant tumors, the details remain unclear. In this study, we demonstrated that TRAF6 facilitates Ras (G12V) and EGF-induced cellular transformation through EGFR. Silencing of TRAF6 expression significantly downregulated AP-1 activity, as well as MMP-2,9 expression after EGF stimulation. Furthermore, we found that TRAF6 plays an essential role in cutaneous squamous cell carcinoma (cSCC) malignant phenotypes, affecting cell growth and migration. CD147/Basigin, a transmembrane glycoprotein belonging to the immunoglobulin superfamily, is over-expressed in tumors and induces tumorigenesis. Our results showed that CD147 formed complex with EGFR and TRAF6. Knockdown of TRAF6 disrupted the CD147-EGFR complex, thereby inducing EGFR endocytosis. Therefore, TRAF6 might be a novel molecular target for cSCC prevention or therapy.

Genetic Alterations of TRAF Proteins in Human Cancers

The tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of cytoplasmic adaptor proteins regulate the signal transduction pathways of a variety of receptors, including the TNF-R superfamily, Toll-like receptors (TLRs), NOD-like receptors (NLRs), RIG-I-like receptors (RLRs), and cytokine receptors. TRAF-dependent signaling pathways participate in a diverse array of important cellular processes, including the survival, proliferation, differentiation, and activation of different cell types. Many of these TRAF-dependent signaling pathways have been implicated in cancer pathogenesis. Here we analyze the current evidence of genetic alterations of TRAF molecules available from The Cancer Genome Atlas (TCGA) and the Catalog of Somatic Mutations in Cancer (COSMIC) as well as the published literature, including copy number variations and mutation landscape of TRAFs in various human cancers. Such analyses reveal that both gain- and loss-of-function genetic alterations of different TRAF proteins are commonly present in a number of human cancers. These include pancreatic cancer, meningioma, breast cancer, prostate cancer, lung cancer, liver cancer, head and neck cancer, stomach cancer, colon cancer, bladder cancer, uterine cancer, melanoma, sarcoma, and B cell malignancies, among others. Furthermore, we summarize the key in vivo and in vitro evidence that demonstrates the causal roles of genetic alterations of TRAF proteins in tumorigenesis within different cell types and organs. Taken together, the information presented in this review provides a rationale for the development of therapeutic strategies to manipulate TRAF proteins or TRAF-dependent signaling pathways in different human cancers by precision medicine.

Structural Characterization of the Trimerization of TRAF6 Protein Through Molecular Dynamics Simulations

The tumour necrosis factor (TNF) receptor-associated factor (TRAF) family of proteins having E3 ligase activity are the key molecules involved in cellular immune response pathways. TRAF6 is a unique member of the TRAF superfamily differing from other members of the family, owing to its specific interactions with molecules outside the TNF receptor superfamily. The C-terminal domain of TRAF proteins contains the catalytic residues and are known to be involved in self-oligomerization forming a mushroom-shaped trimeric structure, which is the functional form of the protein. However, the monomeric crystal structure of TRAF6 C-terminal domain has been already determined, but the trimeric structure of the same is still not available. We here applied computational structural modelling and molecular dynamics simulations studies to get insights into the molecular interactions involved in determining the trimeric structure of the TRAF6 C-terminal domain. The non-availability of the trimeric structure of the TRAF6 C-terminal domain prevented the elucidation of the molecular mechanism of many different biological processes. Our results suggest that the trimer complex is transient in nature. The amino acid residues Lys340 and Glu345 in the coiled coil domain in the C-terminus of TRAF6 play a critical role in trimer structure formation. This structural modelling study may therefore be utilized to obtain the experimentally validated trimeric structure of this important protein.

Suppression of endothelial cell migration by tumor associated macrophage-derived exosomes is reversed by epithelial ovarian cancer exosomal lncRNA

Objective

To study the mechanism by which epithelial ovarian cancer (EOC)-derived exosomes restore the migration of endothelial cells that is suppressed by TAM-derived exosomes.

Methods

Exosomes were isolated from TAMs in the ascites of patients with EOC. The effect of exosomes on the expression of endothelial cell miRNA was monitored by PCR. The miRNA mimics were transfected to explore their effects. Microarray data and literature searches were used to predict target genes and the impact of target gene pathways, and small interfering RNA was used to target these genes. We used migration assays to determine whether ovarian cancer cell-derived exosomes participate in the regulation of TAMs and endothelial cells. We used microarray data to identify the target lncRNA, and we constructed target lncRNA expression plasmids to validate targets by Western blotting.

Results

We separated TAMs from the ascites of patients with EOC and isolated exosomes from TAM supernatants. After co-culture with HUVECs, these exosomes were efficiently incorporated into HUVECs. The migration of HUVECs was suppressed significantly in the exosome group compared with blank controls (P < 0.05).The miRNA mimic transfection and target gene prediction found that TAM-derived exosomes targeted the miR-146b-5p/TRAF6/NF-κB/MMP2 pathway to suppress endothelial cell migration; this result was supported by PCR and Western blotting analyses. The expression of exosomal miR-146b-5p isolated from serum in the EOC group was significantly increased compared to healthy individuals. Finally, TAM-derived exosomes and EOC SKOV3-derived exosomes in combination stimulated HUVEC cells and overcame the inhibition of endothelial cell migration caused by TAM-derived exosomes. Two lncRNAs that were carried by SKOV3-derived exosomes were identified as NF-κB pathway-associated genes by Western blotting.

Conclusion

TAM-derived exosomes can inhibit the migration of endothelial cells by targeting the miR-146b-5p/TRAF6/NF-kB/MMP2 pathway. However, EOC-derived exosomes can transfer lncRNAs to remotely reverse this effect of TAMs on endothelial cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-017-0430-x) contains supplementary material, which is available to authorized users.

The Emerging Role of TRAF7 in Tumor Development

The seven members of the tumor necrosis factor receptor (TNF-R)-associated factor (TRAF) family of intracellular proteins were originally discovered and characterized as signaling adaptor molecules coupled to the cytoplasmic regions of receptors of the TNF-R superfamily. Functionally, TRAFs act both as a scaffold and/or enzymatic proteins to regulate activation of mitogen-activated protein kinases (MAPKs) and transcription factors of nuclear factor-κB family (NF-κB). Given the wide variety of stimuli intracellularly conveyed by TRAF proteins, they are physiologically involved in multiple biological processes, including embryonic development, tissue homeostasis, and regulation of innate and adaptive immune responses. In the last few years, it has become increasingly evident the involvement of TRAF7, the last member of the TRAF family to be discovered, in the genesis and progression of several human cancers, placing TRAF7 in the spotlight as a novel tumor suppressor protein. In this paper, we review and discuss the literature recently produced on this subject. J. Cell. Physiol. 232: 1233-1238, 2017. © 2016 The Authors. Journal of Cellular Physiology Published by Wiley Periodicals, Inc.

Cinchonine induces apoptosis of HeLa and A549 cells through targeting TRAF6

BACKGROUND

Cancer cells are known to over-express TRAF6 that is critical for both AKT and TAK1 activations. The Really Interesting New Gene (RING) domain of TRAF6 is believed to be responsible for the E3 ligase activity, ZINC fingers of TRAF6 provide critical support for the activity of the RING domain which is critical for both AKT and TAK1 activations.

METHODS

We employed computational docking program to identify small molecules that could effectively and competitively bind with the RING domain of TRAF6, which is believed to be responsible for its E3 ligase activity. MTT assay and flow cytometry were employed to analyze apoptosis of cancer cells. Signaling pathways were detected using immunoprecipitation and western blotting, and immunofluorescence was pursued to assess the nature of binding of cinchonine to TRAF6. We also performed animal experiments to test effect of cinchonine in vivo.

RESULTS

Cinchonine, a naturally occurring Cinchona alkaloid identified from the docking study, could bind to TRAF6 in HeLa and A549 cells and induce apoptosis of these cancer cells. We found that AKT ubiquitination and phosphorylation as well as phosphorylation of TAK1 were decreased. These activities would lead to subsequent suppression anti-apoptotic protein Bcl-2, while elevating pro-apoptotic protein Bax. Immunofluorescence staining unambiguously demonstrated the binding of cinchonine specifically at the RING domain of TRAF6 in cells, thereby validating the computational modeling. Animal experiments showed that cinchonine could suppress tumor growth in mice without showing significant acute toxicity.

CONCLUSION

These investigations suggest that through competitive binding with the RING domain of TRAF6, cinchonine could induce apoptosis via inhibiting AKT and TAK1 signaling pathways.

The Emerging Role of Non-traditional Ubiquitination in Oncogenic Pathways

The addition of ubiquitin to a target protein has long been implicated in the process of degradation and is the primary mediator of protein turnover in the cell. Recently, however, many non-proteolytic functions of ubiquitination have emerged as key regulators of cellular homeostasis. In this review, we will describe the various non-traditional functions of ubiquitination, with particular focus on how they can be used as signaling entities in cancer formation and progression. Elaboration of this topic can lead to a better understanding of oncogenic mechanisms, as well as the discovery of novel druggable proteins within the ubiquitin pathway.

TRAF6 regulates melanoma invasion and metastasis through ubiquitination of Basigin

TRAF6 plays a crucial role in the regulation of the innate and adaptive immune responses. Although studies have shown that TRAF6 has oncogenic activity, the role of TRAF6 in melanoma is unclear. Here, we report that TRAF6 is overexpressed in primary as well as metastatic melanoma tumors and melanoma cell lines. Knockdown of TRAF6 with shRNA significantly suppressed malignant phenotypes including cell proliferation, anchorage-independent cell growth and metastasis in vitro and in vivo. Notably, we demonstrated that Basigin (BSG)/CD147, a critical molecule for cancer cell invasion and metastasis, is a novel interacting partner of TRAF6. Furthermore, depletion of TRAF6 by shRNA reduced the recruitment of BSG to the plasma membrane and K63-linked ubiquitination, in turn, which impaired BSG-dependent MMP9 induction. Taken together, our findings indicate that TRAF6 is involved in regulating melanoma invasion and metastasis, suggesting that TRAF6 may be a potential target for therapy or chemo-prevention in melanoma.

Relationship between TRAF6 and deterioration of HCC: an immunohistochemical and in vitro study

Objective

To explore the relationship between tumor necrosis factor receptor-associated factor 6 (TRAF6) and the clinicopathological features in HCC as well as its biological function.

Methods

Totally, 412 liver tissues were collected, including 171 hepatocellular carcinoma (HCC) and their corresponding non-tumor tissues, 37 cirrhosis and 33 normal liver tissues. The expression of TRAF6 was assessed by immunohistochemistry. Then, analysis of the correlations between TRAF6 expression and clinicopathological parameters in HCC was conducted. Furtherer, in vitro experiments on HepG2 and Hep3B cells were performed to validate the biological function of TRAF6 on HCC cells. TRAF6 siRNA was transfected into HepG2 and Hep3B cell lines and TRAF6 expression was evaluated with RT-qPCR and western blot. The assays of cell viability, proliferation, apoptosis and caspase-3/7 activity were carried out to investigate the effects of TRAF6 on HCC cells with RNA interference. Cell viability was assessed with Cell Titer-Blue kit. Cell proliferation was tested with MTS kit. Cell apoptosis was checked through morphologic detection with fluorescence microscope, as well as caspase-3/7 activity was measured with fluorogenic substrate detection.

Results

The positive expression rate of TRAF6 protein was 49.7 % in HCC, significantly higher than that of normal liver (12.1 %), cirrhosis (21.6 %) and adjacent non-cancerous tissues (36.3 %, all P < 0.05). Upregulated TRAF6 was detected in groups with metastasis (Z = −2.058, P = 0.04) and with low micro-vessel density (MVD) expression (Z = −2.813, P = 0.005). Spearman correlation analysis further showed that the expression of TRAF6 was positively correlated with distant metastasis (r = 0.158, P = 0.039) and negatively associated with MVD (r = −0.249, P = 0.004). Besides, knock-down of TRAF6 mRNA in HCC cell lines HepG2 and Hep3B both resulted in cell viability and proliferation inhibition, also cell apoptosis induction and caspase-3/7 activity activation.

Conclusions

TRAF6 may contribute to metastasis and deterioration of the HCC via influencing cell growth and apoptosis. Thus, TRAF6 might become a predictive and therapeutic biomarker for HCC.

[Effect of TRAF6 Downregulation on Malignant Biological Behavior of Lung Cancer Cell Lines]

背景与目的

已有的研究提示肿瘤坏死因子受体相关因子6(tumor necrosis factor receptor-associated factor 6, TRAF6)在肺癌中常常扩增，可能扮演癌基因角色，但TRAF6的确切作用尚未充分阐明。本研究探索TRAF6表达对肺癌细胞株的增殖、凋亡、细胞周期、迁移及侵袭能力的影响以及可能作用机制。

方法

选用A549、H1650、SPC-A-1以及Calu-3等四种肺癌细胞株，应用蛋白印迹、qRT-PCR检测其TRAF6蛋白及mRNA表达。SPC-A-1、Calu-3细胞转染TRAF6 siRNA，以EMSA方法检测不同处理组核因子-κB的DNA结合活性，MTS法检测细胞增殖，流式细胞仪PI染色检测细胞凋亡，流式细胞仪进行细胞周期测定，划痕实验及Transwell小室法检测细胞迁移及侵袭能力，并应用蛋白印迹检测泛素化抗体、p65、CD24、CXCR4等蛋白表达。SPC-A-1细胞提取DNA后，应用二代测序法进行全基因组测序。

结果

在四种细胞株中，SPC-A-1和Calu-3细胞TRAF6相对高表达，TRAF6发生自身K63-泛素化，但仅在SPC-A-1细胞中观察到核因子-κB组成性活化。转染TRAF6 siRNA后，SPC-A-1、Calu-3细胞TRAF6表达明显下调，与空白组及对照组相比，下调TRAF6表达可抑制SPC-A-1细胞核因子-κB活性、降低迁移及侵袭能力以及促进细胞凋亡，CD24和CXCR4的表达也明显下调，但对细胞增殖及细胞周期无明显影响。下调TRAF6表达对Calu-3细胞株的核因子-κB活性、细胞增殖、凋亡、细胞周期、迁移及侵袭能力等均无明显影响。未发现SPC-A-1细胞株TRAF6基因突变或拷贝数改变。

结论

下调TRAF6表达可抑制SPC-A-1细胞迁移及侵袭能力，促进细胞凋亡，并且TRAF6可能是通过调控核因子-κB-CD24/CXCR4信号通路参与调控肺癌侵袭、细胞凋亡。

siRNA-induced TRAF6 knockdown promotes the apoptosis and inhibits the invasion of human lung cancer SPC-A1 cells

Tumor necrosis factor receptor-associated factor 6 (TRAF6) has been found to be involved in multiple cancers. However, the effect of small interfering RNA (siRNA)-induced knockdown of TRAF6 on the biological behaviors of cancer cells remains unknown. Thus, the present study aimed to investigate the effect of siRNA-induced knockdown of TRAF6 on the biological behaviors of human lung cancer SPC-A1 cells. The expression of TRAF6 was determined in human lung adenocarcinoma A549, non-small cell lung cancer H1650, human airway epithelial Calu-3 and human lung cancer SPC-A1 cell lines using quantitative RT-PCR (qRT-PCR) and western blotting at the transcriptional and translational levels. TRAF6 expression was knocked down in the SPC-A1 cells using an siRNA technique, and the effects of TRAF6 knockdown on NF-κB activity, cell proliferation, apoptosis, cell cycle, invasion and migration of the SPC-A1 cells were determined using electrophoretic mobility shift assay (EMSA), cell proliferation assay, flow cytometry, Transwell invasion assay and scratch wound assay. In addition, the protein expression of CD24, CXCR4, MMP1, MMP2, MMP9, TWIST, TIMP-2 and Slug was quantified using western blotting assay. Western blotting and qRT-PCR assays showed upregulation of TRAF6 at both the translational and transcriptional levels in the Calu-3 and SPC-A1 cells, and K63-linked ubiquitination of TRAF6 and constitutive NF-κB activation were detected in the SPC-A1 cells. Knockdown of TRAF6 inhibited the migration and invasion and promoted the apoptosis of the SPC-A1 cells, but had little effect on cell proliferation and the cell cycle. In addition, siRNA-induced TRAF6 knockdown caused a marked reduction in the protein expression of CD24 and CXCR4, but had little effect on MMP-1, MMP-2, MMP-9, Twist, TIMP-2 or Slug expression. The present study demonstrated that TRAF6 is upregulated in human lung cancer cells, and siRNA-induced TRAF6 knockdown inhibits the invasion of lung cancer cells and promotes apoptosis. It is suggested that TRAF6 may be a promising target for the therapy of lung cancer.

Elucidation, functional clustering and structural characterization of βTrCP1 substrates through a molecular dynamics study

Structural knowledge of substrate recognition by SKP1–CUL1–βTrCP1 complex for targeted cancer therapeutic strategy.

TRAF6 promotes the invasion and metastasis and predicts a poor prognosis in gastric cancer

PURPOSE

This study investigated the relationships of TRAF6 expression with clinical pathologic parameters and the prognosis of patients with gastric cancer. This study also explored the roles of TRAF6 in cell apoptosis and invasiveness, as well as underlying molecular mechanism of gastric cancer cell line in vitro.

METHODS

A total of 90 cases of tissue microarrays were immunohistochemically analyzed for TRAF6 expression. Cell proliferation was measured by MTT assay. Flow cytometry was used for analyzing cell apoptosis and cell invasion ability was detected by a Transwell invasion assay. Protein expression was assessed by Western blotting.

RESULTS

TRAF6 was expressed in 53 of 90 (58.9%) cases of gastric cancer. TRAF6 expression was significantly positively correlated with advanced N stage, pathological stage and a poor prognosis, but not an independent predictor of a poor prognosis in gastric cancer (p=0.083). The knockdown of TRAF6 increased cell apoptosis and reduced invasive ability of BGC-823 cell. Moreover, TRAF6 down-regulation decreased protein levels of phosphor-Akt, Bcl-2 and MMP9 and up-regulation of Bax in BGC-823 cell. Inversely, overexpression of TRAF6 in SGC-7901 cells increased protein levels of phosphor-Akt, Bcl-2 and MMP9 and down-regulation of Bax.

CONCLUSIONS

The expression of TRAF6 was positively correlated with an advanced N stage and acted as a predictor of a poor prognosis in patients with gastric cancer. Moreover, TRAF6 regulating cell apoptosis and invasive ability of gastric cancer cells might be associated with Akt activation and alterations of protein expression of Bcl2, Bax and MMP9.