Ubiquitin ligase UBE3C promotes melanoma progression by increasing epithelial-mesenchymal transition in melanoma cells

Emerging roles of the HECT E3 ubiquitin ligases in gastric cancer

Gastric cancer (GC) is one of the most pernicious gastrointestinal tumors with extraordinarily high incidence and mortality. Ubiquitination modification of cellular signaling proteins has been shown to play important roles in GC tumorigenesis, progression, and prognosis. The E3 ubiquitin ligase is the crucial enzyme in the ubiquitination reaction and determines the specificity of ubiquitination substrates, and thus, the cellular effects. The HECT E3 ligases are the second largest E3 ubiquitin ligase family characterized by containing a HECT domain that has E3 ubiquitin ligase activity. The HECT E3 ubiquitin ligases have been found to engage in GC progression. However, whether HECT E3 ligases function as tumor promoters or tumor suppressors in GC remains controversial. In this review, we will focus on recent discoveries about the role of the HECT E3 ubiquitin ligases, especially members of the NEDD4 and other HECT E3 ligase subfamilies, in GC.

IL13Rα1 prevents a castration resistant phenotype of prostate cancer by targeting hexokinase 2 for ubiquitin-mediated degradation

OBJECTIVE

Androgen deprivation therapy (ADT) is still the principal treatment option for prostate cancer (PCa). In addition to reactivation of androgen receptor signaling, the resistance of PCa to apoptosis during ADT also contributes to castration resistant PCa (CRPC). A previous study reported that gene transfer of IL-13Rα2 into PCa cells sensitized the cells to the IL-13R-targeted cytotoxin IL13Rα1, leading to apoptosis. Compared with IL-13Rα2, IL13Rα1 is more constitutively expressed in PCa cells, but its function in PCa remains to be established.

METHODS

We determined the role and expression of IL13Rα1 in PCa cancer cells using western blotting, flow cytometry, and cell proliferation assays. Co-immunoprecipitation and mass spectrometry were used to identify the proteins that interacted with IL13Rα1, to elucidate its function.

RESULTS

In this study, we showed that IL13Rα1 was selectively suppressed in androgen-deprived PCa cells and that its suppression tended to be associated with poor prognoses of PCa patients. IL13Rα1 overexpression promoted apoptosis and inhibited tumor growth under androgen-deprived or castrated conditions (P < 0.01). Mechanistically, IL13Rα1 recruited and facilitated ubiquitin protein ligase E3C-mediated ubiquitination and degradation of hexokinase 2 (HK2), resulting in glycolytic inhibition and eventually leading to PCa cell apoptosis. Furthermore, our data revealed that mutated ataxia-telangiectasia kinase phosphorylated and facilitated the selective ubiquitin proteasome-mediated degradation of HK2. Notably, IL13Rα1-overexpressing PCa cells were more susceptible to apoptosis and exhibited reduced tumor growth after exposure to the HK2 inhibitor, 2-deoxy-D-glucose (P < 0.01).

CONCLUSIONS

Our data identified a tumor suppressor role for IL13Rα1 in preventing the resistance of PCa cells to apoptosis during androgen deprivation by inhibiting glycolysis. IL13Rα1-mediated signaling involving HK2 may therefore provide a novel treatment target and strategy for CRPC.

Oncogenic UBE3C promotes breast cancer progression by activating Wnt/β-catenin signaling

Background

Breast cancer (BrCa) is the most common female malignancy worldwide and has the highest morbidity among all cancers in females. Unfortunately, the mechanisms of BrCa growth and metastasis, which lead to a poor prognosis in BrCa patients, have not been well characterized.

Methods

Immunohistochemistry (IHC) was performed on a BrCa tissue microarray (TMA) containing 80 samples to evaluate ubiquitin protein ligase E3C (UBE3C) expression. In addition, a series of cellular experiments were conducted to reveal the role of UBE3C in BrCa.

Results

In this research, we identified UBE3C as an oncogenic factor in BrCa growth and metastasis for the first time. UBE3C expression was upregulated in BrCa tissues compared with adjacent breast tissues. BrCa patients with high nuclear UBE3C expression in tumors showed remarkably worse overall survival (OS) than those with low nuclear expression. Knockdown of UBE3C expression in MCF-7 and MDA-MB-453 BrCa cells inhibited cell proliferation, migration and invasion in vitro, while overexpression of UBE3C in these cells exerted the opposite effects. Moreover, UBE3C promoted β-catenin nuclear accumulation, leading to the activation of the Wnt/β-catenin signaling pathway in BrCa cells.

Conclusion

Collectively, these results imply that UBE3C plays crucial roles in BrCa development and progression and that UBE3C may be a novel target for the prevention and treatment of BrCa.

Molecular Evolution, Neurodevelopmental Roles and Clinical Significance of HECT-Type UBE3 E3 Ubiquitin Ligases

Protein ubiquitination belongs to the best characterized pathways of protein degradation in the cell; however, our current knowledge on its physiological consequences is just the tip of an iceberg. The divergence of enzymatic executors of ubiquitination led to some 600–700 E3 ubiquitin ligases embedded in the human genome. Notably, mutations in around 13% of these genes are causative of severe neurological diseases. Despite this, molecular and cellular context of ubiquitination remains poorly characterized, especially in the developing brain. In this review article, we summarize recent findings on brain-expressed HECT-type E3 UBE3 ligases and their murine orthologues, comprising Angelman syndrome UBE3A, Kaufman oculocerebrofacial syndrome UBE3B and autism spectrum disorder-associated UBE3C. We summarize evolutionary emergence of three UBE3 genes, the biochemistry of UBE3 enzymes, their biology and clinical relevance in brain disorders. Particularly, we highlight that uninterrupted action of UBE3 ligases is a sine qua non for cortical circuit assembly and higher cognitive functions of the neocortex.

LINC00355 induces gastric cancer proliferation and invasion through promoting ubiquitination of P53

Long noncoding RNAs (LncRNAs) have been reported to play critical roles in gastric cancer, but true biomarkers remain unknown. In this study, we found a new lncRNA LINC00355 that was involved in malignant progression of gastric cancer (GC) and further revealed its role and mechanism. Differentially expressed lncRNAs were identified through bioinformatics, and qRT-PCR was used to validate the expression of LINC00355 in gastric cancer tissues and cells. The biological role of LINC00355 in GC was detected by gene overexpression and knockdown experiments. Subcellular fractionation, qRT-PCR, and FISH were performed to detect the subcellular localization. Co-IP and western blotting were used to study the ubiquitination-mediated regulation of P53 and the expression of the E3 ligases RAD18 and UBE3C. The results showed that LINC00355 was significantly increased in gastric cancer cell lines and patient tissues and closely correlated with late stages, distant metastasis, and poor prognosis of patients. High expression of LINC00355 promoted the proliferation and invasion of gastric cancer cells in vivo and in vitro. Mechanistic studies found that LINC00355 that mainly located in the nucleus, acting as a transcriptional activator, promoted transcription of RAD18 and UBE3C, which both bind to P53 and mediate the ubiquitination and degradation of P53. Furthermore, LINC00355 overexpression enhanced the ubiquitination process, and LINC00355 knockdown alleviated it. These results indicated that LINC00355 induces gastric cancer cell proliferation and invasion by promoting transcription of RAD18 and UBE3C, which mediates ubiquitination of P53 and thereby plays a critical role in survival and tumorigenicity of gastric cancer cells. LINC00355 may represent a new mechanism for GC progression and provide a potential marker for GC diagnosis and treatment.

MDA-19 Suppresses Progression of Melanoma Via Inhibiting the PI3K/Akt Pathway

Objective

To investigate the effect of MDA-19 on progression of melanoma, and explore the relevant mechanism.

Methods

The melanoma cell lines, M14 and UACC257, were treated with different concentrations of MDA-19, then CCK8, clone formation assay, Transwell and flow cytometry assays were performed to examine cell proliferation, migration, invasion and apoptosis, respectively. The expression of apoptosis-related proteins (Bcl-2, Bax and caspase 3 P17), EMT and signaling pathway-related proteins were also detected by Western blot.

Results

MDA-19 inhibited melanoma cells in a dose-dependent manner. Compared to the NC group, MDA-19 significantly inhibited cell growth capacity, migration and invasion of M14 and UACC257 cells, and accelerated cell apoptosis in a mitochondrial pathway through regulating Bcl-2/Bax and Caspase 3 in M14 and UACC257 cells. Moreover, MDA-19 was observed to up-regulate the expression of E-cad and down-regulate the expression of N-cad, Vimentin and Slug in melanoma cells in vitro. Furthermore, MDA-19 could inhibit the PI3K/Akt pathway by blocking Akt phosphorylation (p-Akt) and downstream proteins, P70 and Cyclin D1 in M14 and UACC257 cells.

Conclusion

Our data demonstrate that MDA-19 could inhibit progression of melanoma by suppressing the PI3K/Akt pathway, suggesting that MDA-19 is a potential anti-cancer agent for therapy of melanoma.

Ubiquitin-protein ligase E3C maintains non-small-cell lung cancer stemness by targeting AHNAK-p53 complex

Cancer stem-like cells (CSCs) are regarded as sources of tumorigenesis, metastasis, and drug resistance, which limits current cancer therapies. Elucidating the molecular modes governing CSC properties is necessary to optimize therapeutic approaches. In this study, we discovered that ubiquitin-protein ligase E3C (UBE3C)-mediated ubiquitination is a key posttranslational mechanism involved in maintaining CSC properties of non-small-cell lung cancer (NSCLC). UBE3C was overexpressed in stem-like NSCLC cells and acted as a stemness enhancer. Knockdown of UBE3C reduced NSCLC stemness and tumorigenesis both in vivo and in vitro. We further identified AHNAK as a novel UBE3C substrate, finding that UBE3C maintained stemness by ubiquitinating and promoting AHNAK degradation. AHNAK functioned as a cofactor assisting p53 binding to stemness-related gene promoters to inhibit transcription. Subsequent downregulation of AHNAK by UBE3C overexpression removed p53-mediated inhibition of gene expression, resulting in enhanced stemness. Clinical significance was investigated in 208 NSCLC patients and confirmed that attenuated UBE3C activity and elevated AHNAK protein levels correlated with extended survival time. Collectively, findings reveal the first global characterization of UBE3C-mediated ubiquitination as a key regulator of CSCs, with results suggesting involvement of the AHNAK-p53 complex.

The role of ubiquitination and deubiquitination in the regulation of cell junctions

Maintenance of cell junctions plays a crucial role in the regulation of cellular functions including cell proliferation, permeability, and cell death. Disruption of cell junctions is implicated in a variety of human disorders, such as inflammatory diseases and cancers. Understanding molecular regulation of cell junctions is important for development of therapeutic strategies for intervention of human diseases. Ubiquitination is an important type of post-translational modification that primarily regulates endogenous protein stability, receptor internalization, enzyme activity, and protein-protein interactions. Ubiquitination is tightly regulated by ubiquitin E3 ligases and can be reversed by deubiquitinating enzymes. Recent studies have been focusing on investigating the effect of protein stability in the regulation of cell-cell junctions. Ubiquitination and degradation of cadherins, claudins, and their interacting proteins are implicated in epithelial and endothelial barrier disruption. Recent studies have revealed that ubiquitination is involved in regulation of Rho GTPases’ biological activities. Taken together these studies, ubiquitination plays a critical role in modulating cell junctions and motility. In this review, we will discuss the effects of ubiquitination and deubiquitination on protein stability and expression of key proteins in the cell-cell junctions, including junction proteins, their interacting proteins, and small Rho GTPases. We provide an overview of protein stability in modulation of epithelial and endothelial barrier integrity and introduce potential future search directions to better understand the effects of ubiquitination on human disorders caused by dysfunction of cell junctions.

MiR-542-3p inhibits metastasis and epithelial-mesenchymal transition of hepatocellular carcinoma by targeting UBE3C

Accumulating evidence demonstrates that aberrant miRNAs contribute to hepatocellular carcinoma (HCC) development and progression. However, the roles of various miRNAs in HCC remain to be determined. In present research, we confirmed that a reduced miR-542-3p expression was present in HCC tissues and cell lines. Our clinical analysis revealed that the down-regulated miR-542-3p expression was significantly correlated with poor prognostic features including advanced TNM stage and venous infiltration. Moreover, we confirmed that miR-542-3p was a novel independent prognostic marker for predicting 5-year survival of HCC patients. The ectopic overexpression of miR-542-3p inhibited cell migration, invasion and EMT progress, while down-regulated miR-542-3p reversed the effect. In addition, miR-542-3p could regulate UBE3C by directly binding to its 3'-UTR. In clinical samples of HCC, miR-542-3p inversely correlated with UBE3C, which was upregulated in HCC. Alternation of UBE3C expression at least partially abolished the migration, invasion and EMT progress effects of miR-542-3p on HCC cells. In conclusion, our results indicated that miR-542-3p functioned as a tumor suppressor gene in regulating the EMT and metastasis of HCC via targeting UBE3C, and may represent a novel potential therapeutic target and prognostic marker for HCC.

Surgery combined with local 5-aminolevulinic acid-photodynamic therapy on skin cancer and its effect on the expression of cyclophilin A, cyclophilin B and CD147

The study evaluated an approach to treat skin cancer using surgery combined with local 5-aminolevulinic acid-photodynamic therapy (ALA-PDT). Seventy-six patients with skin cancer who were admitted to the Liaocheng People's Hospital from May 2014 to April 2015 were randomly divided into a control and an observation group (38 cases in each). The patients in the control group were treated with ALA-PDT alone. Those in the observation group were first subjected to surgical treatment, and then treated with ALA-PDT. The treatment efficacies of the two groups were compared. The expression of cancer markers CyPA, CyPB and CD147 were detected by immunohistochemical methods before and after the treatment. Our results showed the average healing time of the wounds of patients in the observation group was shorter, the number of treatments needed was less, the efficacy rate and the lesion appearance satisfaction were significantly higher, and the recurrence rate at 12 months after treatment and the incidence of adverse reactions were both significantly lower. Additionally, the levels of CyPA, CyPB and CD147 were reduced to a significantly higher degree after treatment in the observation group. No difference was found in the recurrence rate between the two groups at 6 months after treatment. We conclude that surgery combined with ALA-PDT is a safe and reliable treatment method, which can increase the survival rate while improving the recovery rate and appearance satisfaction in patients with skin cancer.

Future of circulating tumor cells in the melanoma clinical and research laboratory settings

Circulating tumor cells (CTC) have become a field of interest for oncologists based on the premise that they constitute the underpinning for metastatic dissemination. The lethal nature of cancer is no longer attributed to solid tumor formation, but rather to the process of metastasis; shifting the focus of current studies towards the isolation and identification of metastatic progenitors, such as CTCs. CTCs originate from primary tumor masses that undergo morphologic and genetic alterations, which involve the release of mesenchymal-like cancer cells into the bloodstream, capable of invading nearby tissues for secondary tumor development. Cancerous cells contained in the primary tumor mass acquire the motile mesenchymal phenotype as a result of the Epithelial-to-Mesenchymal Transition, where substantial variations in protein expression and signaling pathways take place. CTCs that migrate from the primary tumor, intravasate into the systemic vasculature, are transported through the bloodstream, and invade tissues and organs suitable for secondary tumor development. While only a limited number of CTCs are viable in the bloodstream, their ability to elude the immune system, evade apoptosis and successfully metastasize at secondary tumor sites, makes CTCs promising candidates for unraveling the triggers that initiates the metastatic process. In this article, these subjects are explored in greater depth to elucidate the potential use of CTCs in the detection, disease staging and management of metastatic melanoma.