USP18 directly regulates Snail1 protein through ubiquitination pathway in colorectal cancer

The ISG15-Protease USP18 Is a Pleiotropic Enhancer of HIV-1 Replication

The innate immune response to viruses is formed in part by interferon (IFN)-induced restriction factors, including ISG15, p21, and SAMHD1. IFN production can be blocked by the ISG15-specific protease USP18. HIV-1 has evolved to circumvent host immune surveillance. This mechanism might involve USP18. In our recent studies, we demonstrate that HIV-1 infection induces USP18, which dramatically enhances HIV-1 replication by abrogating the antiviral function of p21. USP18 downregulates p21 by accumulating misfolded dominant negative p53, which inactivates wild-type p53 transactivation, leading to the upregulation of key enzymes involved in de novo dNTP biosynthesis pathways and inactivated SAMHD1. Despite the USP18-mediated increase in HIV-1 DNA in infected cells, it is intriguing to note that the cGAS-STING-mediated sensing of the viral DNA is abrogated. Indeed, the expression of USP18 or knockout of ISG15 inhibits the sensing of HIV-1. We demonstrate that STING is ISGylated at residues K224, K236, K289, K347, K338, and K370. The inhibition of STING K289-linked ISGylation suppresses its oligomerization and IFN induction. We propose that human USP18 is a novel factor that potentially contributes in multiple ways to HIV-1 replication.

Comprehensive analysis of the role of ubiquitin-specific peptidases in colorectal cancer: A systematic review

BACKGROUND

Colorectal cancer (CRC) is the third most frequent and the second most fatal cancer. The search for more effective drugs to treat this disease is ongoing. A better understanding of the mechanisms of CRC development and progression may reveal new therapeutic strategies. Ubiquitin-specific peptidases (USPs), the largest group of the deubiquitinase protein family, have long been implicated in various cancers. There have been numerous studies on the role of USPs in CRC; however, a comprehensive view of this role is lacking.

AIM

To provide a systematic review of the studies investigating the roles and functions of USPs in CRC.

METHODS

We systematically queried the MEDLINE (via PubMed), Scopus, and Web of Science databases.

RESULTS

Our study highlights the pivotal role of various USPs in several processes implicated in CRC: Regulation of the cell cycle, apoptosis, cancer stemness, epithelial-mesenchymal transition, metastasis, DNA repair, and drug resistance. The findings of this study suggest that USPs have great potential as drug targets and noninvasive biomarkers in CRC. The dysregulation of USPs in CRC contributes to drug resistance through multiple mechanisms.

CONCLUSION

Targeting specific USPs involved in drug resistance pathways could provide a novel therapeutic strategy for overcoming resistance to current treatment regimens in CRC.

ERK3 Increases Snail Protein Stability by Inhibiting FBXO11-Mediated Snail Ubiquitination

Snail is a key regulator of the epithelial-mesenchymal transition (EMT), the key step in the tumorigenesis and metastasis of tumors. Although induction of Snail transcription precedes the induction of EMT, the post-translational regulation of Snail is also important in determining Snail protein levels, stability, and its ability to induce EMT. Several kinases are known to enhance the stability of the Snail protein by preventing its ubiquitination; however, the precise molecular mechanisms by which these kinases prevent Snail ubiquitination remain unclear. Here, we identified ERK3 as a novel kinase that interacts with Snail and enhances its protein stability. Although ERK3 could not directly phosphorylate Snail, Erk3 increased Snail protein stability by inhibiting the binding of FBXO11, an E3 ubiquitin ligase that can induce Snail ubiquitination and degradation, to Snail. Importantly, functional studies and analysis of clinical samples indicated the crucial role of ERK3 in the regulation of Snail protein stability in pancreatic cancer. Therefore, we conclude that ERK3 is a key regulator for enhancing Snail protein stability in pancreatic cancer cells by inhibiting the interaction between Snail and FBXO11.

Tumor-promoting action of ubiquitin protease 43 in gastric cancer progression through deubiquitination and stabilization of stress-inducible phosphoprotein 1

Gastric cancer (GC) is the 5th most common cancer over the world. Ubiquitin protease 43 (UBP43) is a multifunctional protein with deubiquitinase activities. Abnormal expression of UBP43 has been reported in numerous types of malignancies. Bioinformatic analysis was performed to identify the differentially expressed genes (Fold change ≥2 or ≤ -2 and p < 0.01) in GC from the datasets downloaded from Gene Expression Omnibus and Gene Expression Profiling Interactive Analysis databases, which showed that UBP43 and stress-inducible phosphoprotein 1 (STIP1) were up-regulated in both datasets. Online databases displayed the binding of UBP43 to STIP1 and the positive correlation between the two proteins. This study aims to explore: the role of UBP43 in cell proliferation and apoptosis in GC; the relationship between UBP43 and STIP1; and whether UBP43 exerts its function via STIP1 in GC. Knockdown/overexpression stable GC cell lines were generated by transducing lentivirus carrying coding sequence/short hairpin RNA of UBP43 and puromycin selection. GC patients with higher expressions of UBP43 had poor prognosis. Loss-/gain-of-function experiments revealed that pro-proliferative and anti-apoptotic abilities of UBP43 in GC cells and xenografts. UBP43 could interact with STIP1, inhibit its ubiquitination, and promote its protein stability, thereby enhancing STIP1 expression. Moreover, STIP1 knockdown reversed the pro-proliferative ability of UBP43 in GC cells. Our study uncovers that the pro-proliferative role of UBP43 in GC development is STIP1-dependent and indicates that UBP43 may act as a potent therapeutic target in GC treatment.

USP18 enhances the resistance of BRAF-mutated melanoma cells to vemurafenib by stabilizing cGAS expression to induce cell autophagy

This study aims to discern the possible molecular mechanism of the effect of ubiquitin-specific peptidase 18 (USP18) on the resistance to BRAF inhibitor vemurafenib in BRAF V600E mutant melanoma by regulating cyclic GMP-AMP synthase (cGAS). The cancer tissues of BRAF V600E mutant melanoma patients before and after vemurafenib treatment were collected, in which the protein expression of USP18 and cGAS was determined. A BRAF V600E mutant human melanoma cell line (A2058R) resistant to vemurafenib was constructed with its viability, apoptosis, and autophagy detected following overexpression and depletion assays of USP18 and cGAS. Xenografted tumors were transplanted into nude mice for in vivo validation. Bioinformatics analysis showed that the expression of cGAS was positively correlated with USP18 in melanoma, and USP18 was highly expressed in melanoma. The expression of cGAS and USP18 was up-regulated in cancer tissues of vemurafenib-resistant patients with BRAF V600E mutant melanoma. Knockdown of cGAS inhibited the resistance to vemurafenib in A2058R cells and the protective autophagy induced by vemurafenib in vitro. USP18 could deubiquitinate cGAS to promote its protein stability. In vivo experimentations confirmed that USP18 promoted vemurafenib-induced protective autophagy by stabilizing cGAS protein, which promoted resistance to vemurafenib in BRAF V600E mutant melanoma cells. Collectively, USP18 stabilizes cGAS protein expression through deubiquitination and induces autophagy of melanoma cells, thereby promoting the resistance to vemurafenib in BRAF V600E mutant melanoma.

USP18 regulates the malignant phenotypes of glioblastoma stem cells

Glioblastoma (GBM) is the most malignant primary brain tumor. The 5-year survival rate of the patients is poor, and they are prone to relapse and the treatment is limited. Therefore, the search for biological targets is one of the key measures for the treatment and prognosis of GBM. Ubiquitin-specific peptidase 18 (USP18) plays a regulatory role in tumorigenesis. In this study, we found that USP18 was up-regulated in GBM, promoted the growth and proliferation of glioblastoma stem cells (GSCs), affected the epithelial-mesenchymal transition (EMT), and was associated with poor clinical prognosis of patients. Finally, our findings reveal a critical role for USP18 in GBM malignancy, targeting USP18 may open new avenues for GBM treatment.

UBP43 promotes epithelial ovarian carcinogenesis via activation of β-catenin signaling pathway

Dysregulation of the deubiquitinating protease, UBP43, has been implicated in many human diseases, including cancer. Here, we evaluated the functional significance and mechanism of action of UBP43 in epithelial ovarian cancer. We found that UBP43 was significantly upregulated in the tumor tissues of patients with epithelial ovarian cancer. Similar results were observed in OVCAR-3, Caov-3, TOV-112D, A2780, and SK-OV-3 cells. Furthermore, in vitro functional assays of A2780 and TOV-112D cells demonstrated that UBP43 overexpression promoted cell proliferation, migration, and invasion. Upregulation of UBP43 might result in epithelial-mesenchymal transition by inducing the nuclear transport of β-catenin, which was accompanied by enhanced N-cadherin but decreased E-cadherin expression. These malignant phenotypes were reversed by UBP43 silencing. Further investigation revealed that the knockdown of UBP43 inhibited cell proliferation by inducing a cell cycle arrest at the G2/M phase. The oncogenic characteristics of UBP43 were validated in a subcutaneous xenograft mouse model. In vivo, tumor growth was delayed in the UBP43-silenced group but accelerated after UBP43 overexpression. Finally, we demonstrated that β-catenin is a key protein in the UBP43-mediated malignant development of epithelial ovarian cancer. Specifically, overexpression of UBP43 decreased the ubiquitination degradation of β-catenin and enhanced its protein stability. Also, we observed that the downstream genes of beta-catenin such as cyclin D1, MMP2, and MMP9 were upregulated due to UBP43 overexpression. Thus, we concluded that UBP43 promoted epithelial ovarian cancer tumorigenesis and metastasis through activation of the β-catenin pathway, suggesting that UBP43 may be a potential therapeutic target for this intractable disease.

USP22 aggravated diabetic renal tubulointerstitial fibrosis progression through deubiquitinating and stabilizing Snail1

Renal tubulointerstitial fibrosis (TIF) is one of the main pathological changes induced by diabetic kidney disease (DKD), and epithelial-to-mesenchymal transition (EMT) induced by high glucose (HG) can promote TIF. Our previous study has shown that ubiquitin-specific protease 22 (USP22) could affect the process of DKD by deubiquitinating and stabilizing Sirt1 in glomerular mesangial cells. However, whether USP22 could regulate EMT occurrence in renal tubular epithelial cells and further aggravate the pathological process of TIF in DKD remains to be elucidated. In this study, we found that USP22 expression was upregulated in kidney tissues of db/db mice and HG-treated NRK-52E cells. In vitro, USP22 overexpression promoted the EMT process of NRK-52E cells stimulated by HG and further increased the levels of extracellular matrix (ECM) components such as fibronectin, Collagen I, and Collagen Ⅳ. Meanwhile, USP22 deficiency exhibited the opposite effects. Mechanism studies showed that USP22, depending on its deubiquitinase activity, deubiquitinated and stabilized the EMT transcriptional factor Snail1. In vivo experiment showed that interfering with USP22 could improve the renal pathological damages and renal function of the db/db spontaneous diabetic mice by decreasing Snail1 expression, which could inhibit EMT occurrence, and reduce the production of ECM components. These results suggested that USP22 could accelerate renal EMT and promote the pathological progression of diabetic TIF by deubiquitinating Snail1, providing an experimental basis for using USP22 as a potential target for DKD.

ARL9 is upregulated and serves as a biomarker for a poor prognosis in colon adenocarcinoma

BACKGROUND

ARL9 is a newly identified member of the ARF family, and the clinical significance of ARL9 in colon adenocarcinoma is unknown. In this study, we aimed to explore the expression of ARL9 mRNA in colon adenocarcinoma, and its effect on the prognosis of patients with colon adenocarcinoma.

METHODS

We investigated the differential expression of ARL9 between colon adenocarcinoma tissue and adjacent tissues through a bioinformatics analysis using The Cancer Genome Atlas (TCGA) database. The correlation between clinical characteristics and the mRNA expression level of ARL9 were analyzed. A survival analysis and a Cox regression analysis were used to determine the prognostic significance of ARL9. Finally, we conducted a gene set enrichment analysis (GSEA) to explore the ARL9 signaling pathways involved in the development of colon adenocarcinoma. The effect of the expression of ARL9 on the proliferation and migration of colon adenocarcinoma was analyzed by the CCK8 method and a cell scratch test, respectively.

RESULTS

The mRNA expression of ARL9 in colon adenocarcinoma tissues was higher in comparison to the level in normal adjacent tissues (P < 0.05). The mRNA expression of ARL9 was not related to sex, tumor stage, T stage, N stage, M stage, but to age. The 5-year survival rate of colon adenocarcinoma patients with high ARL9 mRNA expression levels was significantly lower than that of patients with low ARL9 mRNA expression levels (P < 0.05). Age and the high mRNA expression of ARL9 were independent risk factors for a poor prognosis in patients with colon adenocarcinoma. The GSEA suggested that ARL9 may be able to upregulate cell adhesion, extracellular matrix receptor interactions, tumor-associated pathways, and downregulate the citrate cycle and tricarboxylic acid cycle pathway, which are involved in the development of colon adenocarcinoma. After knocking down ARL9, the proliferation and migration abilities of colon adenocarcinoma cells were decreased (P < 0.01).

CONCLUSION

The mRNA expression of ARL9 is upregulated in colon adenocarcinoma, and higher mRNA expression levels are associated with a poor prognosis. Knocking down ARL9 can reduce the proliferation and migration of colon adenocarcinoma cells. ARL9 mRNA can be used as a prognostic biomarker in patients with colon adenocarcinoma.

Loss of ubiquitin-specific peptidase 18 destabilizes 14-3-3ζ protein and represses lung cancer metastasis

Cancer metastasis is a major cause of cancer-related mortality. Strategies to reduce metastases are needed especially in lung cancer, the most common cause of cancer mortality. We previously reported increased ubiquitin-specific peptidase 18 (USP18) expression in lung and other cancers. Engineered reduction of USP18 expression repressed lung cancer growth and promoted apoptosis. This deubiquitinase (DUB) stabilized targeted proteins by removing the complex interferon-stimulated gene 15 (ISG15). This study explores if the loss of USP18 reduced lung cancer metastasis. USP18 knock-down in lung cancer cells was independently achieved using small hairpin RNAs (shRNAs) and small interfering RNAs (siRNAs). USP18 knock-down reduced lung cancer growth, wound-healing, migration, and invasion versus controls (P < .001) and markedly decreased murine lung cancer metastases (P < .001). Reverse Phase Protein Arrays (RPPAs) in shRNA knock-down lung cancer cells showed that 14-3-3ζ protein was regulated by loss of USP18. ISG15 complexed with 14-3-3ζ protein reducing its stability. Survival in lung adenocarcinomas (P < .0015) and other cancers was linked to elevated 14-3-3ζ expression as assessed by The Cancer Genome Atlas (TCGA). The findings were confirmed and extended using 14-3-3ζ immunohistochemical assays of human lung cancer arrays and syngeneic murine lung cancer metastasis models. A direct 14-3-3ζ role in controlling lung cancer metastasis came from engineered 14-3-3ζ knock-down in lung cancer cell lines and 14-3-3ζ rescue experiments that reversed migration and invasion inhibition. Findings presented here revealed that USP18 controlled metastasis by regulating 14-3-3ζ expression. These data provide a strong rationale for developing a USP18 inhibitor to combat metastases.

RNF128 suppresses the malignancy of colorectal cancer cells via inhibition of Wnt/β-catenin signaling

PURPOSE

Colorectal cancer (CRC) is one of the most frequent tumors and causes of mortality worldwide. Ubiquitin ligase was reported to regulate multiple cellular processes, including tumorigenesis. As ubiquitin E3 ligases, RING-finger proteins play a key role in physiological and pathophysiological processes.

METHODS

We compared the expression levels of RNF128 in CRC tissues by western-blotting and qRT-PCR. Knockdown and overexpression of RNF128 were performed to examine its effect on proliferation and metastasis of CRC cells. Using western blot and co-immunoprecipitation assays, we explored the possible mechanisms underlying the effect of RNF128 in CRC cells.

RESULTS

We found that the expression level of RNF128 was correlated with the CRC tumorigenicity. Overexpression or knockdown of RNF128 suppressed or elevated CRC cell proliferation, migration and invasion, respectively. We further determined that RNF128 regulated β-catenin ubiquitination and thus inhibited Wnt/β-catenin signaling in CRC cells.

CONCLUSION

Our research demonstrated that RNF128 inhibited cell proliferation and metastasis of CRC cells via Wnt/β-catenin signaling-mediated deubiquitination.

USP18 promotes tumor metastasis in esophageal squamous cell carcinomas via deubiquitinating ZEB1

The dysregulation of deubiquitinating enzymes (DUBs), which regulate the stability of most cellular proteins, have been implicated in many human diseases, including cancers. Ubiquitin-specific protease 18 (USP18), a member of the DUBs family, functions as a potential tumour promoter in various cancers. However, the biological function and clinical significance of USP18 in esophageal squamous cell carcinomas (ESCC) are still unclear. Here, we found that ESCC tumors had higher USP18 expression compared with that of normal esophageal epithelial tissues, and high USP18 level was significantly correlated with malignant phenotype and shorter survival in patients with ESCC. In functional experiments, USP18 knockdown significantly inhibited ESCC invasion and metastasis in vitro. Consistently, a xenograft assay showed that knockdown of USP18 in ESCC cell suppressed their dissemination to lung tissue in vivo. Furthermore, we showed that USP18 promoted ESCC cell metastasis by inducing ZEB1 mediated epithelial-mesenchymal transition (EMT). Importantly, our results demonstrated that the oncogenic effect of USP18 in ESCC is partially dependent on ZEB1 enhancement. Mechanistic investigations revealed that USP18 directly bound ZEB1 and decreased its ubiquitination to enhance the protein stability of ZEB1 in ESCC cells. Overall, our data highlighted an essential role of USP18 in ESCC metastasis, suggesting that it could be a potential diagnostic and therapeutic target for ESCC.

HOTAIR regulates colorectal cancer stem cell properties and promotes tumorigenicity by sponging miR-211-5p and modulating FLT-1

We intended to investigate the underlying mechanism of action of long noncoding RNA (lncRNA) HOX transcript antisense RNA (HOTAIR) in colorectal cancer (CRC) progression, especially in tumor cell stemness. For that purpose, different assays were performed such as real-time PCR and western blotting to determine the expression of target genes. Cell stemness was determined by sphere formation assay, flow cytometry assay, and the analysis of stemness-related markers. The interplay among target genes was evaluated using bioinformatics analyses, luciferase reporter and biotin-labeled RNA pull down assays. We found that HOTAIR was highly expressed and predicted poor prognosis survival in CRC. Downregulation of HOTAIR repressed tumor malignant behaviors and cancer stemness. Mechanistically, HOTAIR facilitated the expression of the microRNA (miR)-211-5p target gene fms-like tyrosine kinase-1 (FLT-1), thereby modulating cancer stem cell (CSC) properties in CRC. We conclude that HOTAIR/miR-211-5p/FLT-1 axis contributes to CRC cancer stemness.

High expression of USP18 is associated with the growth of colorectal carcinoma

AIM

To investigate whether USP18 can be used as a predictive marker for the diagnosis and development of colorectal cancer.

METHODS

The Gene Expression Omnibus (GEO) Dataset and the Cancer Genome Atlas (TCGA) database were used to select differential proteins for the ubiquitin-specific peptidases (USPs). The extensive target prediction and network analysis methods were used to assess the association with the USP18 interacting proteins, as well as the statistical correlation between USP18 and the clinical pathology parameters. The effects of USP18 on the proliferation of colorectal cancer were examined using CCK8. The effects of USP18 on the migration of colorectal cancer were examined using wound healing assays. Immunohistochemistry (IHC) was performed on the tissue microarray.

RESULTS

The results showed that the expression of USP18 was related to age (P=0.014). The positive rates of the USP18 protein in T1, T2, T3, and T4 were 0.00%, 22.92%, 78.38%, and 95.35%, respectively (P<0.00). The positive rates of the USP18 protein in I, II, III, and IV were 47.43%, 83.12%, 66.67%, and 100.00%, respectively (P<0.00). The Western blot assay showed that the expression of USP18 in colorectal cancer tissues was significantly higher than that in matched paracancerous tissues (P<0.05). The CCK8 experiments suggested that USP18 promoted the migration of CRC cells. Wound healing assays suggested that USP18 promoted the proliferation of CRC cells.

CONCLUSION

This study showed that USP18 can promote the proliferation of colorectal cancer cells and might be a potential biomarker for the diagnosis of CRC.