RING-finger protein 6 enhances c-Myc-mediated Warburg effect by promoting MAD1 degradation to facilitate pancreatic cancer metastasis.

Aerobic glycolysis (the Warburg effect) promotes tumor metastasis; hence, drugs targeting its regulators are being developed. c-Myc, a critical transcription factor that regulates the Warburg effect, is involved in the tumorigenesis of many cancers, including pancreatic cancer (PC). However, the upstream regulating mechanisms of c-Myc in PC are unclear. Herein, we reported that E3 ubiquitin ligase RING-finger protein 6 (RNF6) was upregulated in PC tissues, and an elevated RNF6 level was closely associated with metastasis and poor prognosis in patients with PC. In functional experiments, RNF6 over-expression accelerated the metastatic ability of PC cells, whereas RNF6 knockdown impaired PC cell motility and invasiveness along with metastasis in an orthotopic mouse model. Furthermore, we found that RNF6 promoted PC cell metastasis by enhancing c-Myc-mediated aerobic glycolysis. Mechanistically, RNF6 increased the expression level of c-Myc by catalyzing the ubiquitination of Max-dimerization protein-1 (MAD1), a cellular antagonist of c-Myc. Lastly, RNF6 promoted the degradation of MAD1 via the ubiquitin-proteasome pathway, and this reduction in the MAD1 levels enabled c-Myc to promote the Warburg effect in PC. Our results demonstrate that RNF6 may be a novel biomarker in PC carcinogenesis, thereby indicating that targeting the RNF6/MAD1/c-Myc axis is a potential strategy for PC therapy.

E3 ubiquitin ligase UBR5 promotes pancreatic cancer growth and aerobic glycolysis by downregulating FBP1 via destabilization of C/EBPα.

Pancreatic cancer is one of the most fatal cancers in humans. While it thrives in a state of malnutrition, the mechanism by which pancreatic cancer cells adapt to metabolic stress through metabolic reprogramming remains unclear. Here, we showed that UBR5, an E3 ubiquitin ligase, was significantly upregulated in pancreatic cancer patient samples compared to the levels in adjacent normal tissues. Levels of UBR5 were closely related to a malignant phenotype and shorter survival among pancreatic cancer patients. Multivariate analyses also revealed that UBR5 overexpression was an independent predictor of poor outcomes among patients with pancreatic cancer. Functional assays revealed that UBR5 contributes to the growth of pancreatic cancer cells by inducing aerobic glycolysis. Furthermore, we demonstrated that UBR5 knockdown increased levels of fructose-1,6-bisphosphatase (FBP1), an important negative regulator in the process of aerobic glycolysis in many cancers. We found a significant negative correlation between levels of UBR5 and FBP1, further demonstrating that UBR5-induced aerobic glycolysis is dependent on FBP1 in pancreatic cancer cells. Mechanistically, UBR5 regulates FBP1 expression by modulating C/EBPα, directly binding to C/EBPα, and promoting its ubiquitination and degradation. Together, these results identify a mechanism used by pancreatic cancer cells to survive the nutrient-poor tumour microenvironment and also provide insight regarding the role of UBR5 in pancreatic cancer cell adaptation to metabolic stresses.

ROCK2 disturbs MKP1 expression to promote invasion and metastasis in hepatocellular carcinoma.

Dual-specificity phosphatase-1 (DUSP1/MKP1) plays a key role in controlling various physiological and pathological phenomena, including tumor metastasis and invasion. However, the role of MKP1 in tumorigenesis is controversial. We showed that the expression of MKP1 in hepatocellular carcinoma (HCC) is significantly downregulated, and MKP1 is an independent predictor of poor prognosis. In in vitro and in vivo studies, we showed that MKP1 significantly inhibits the invasion and metastasis of HCC cells. Additionally, we found that low MKP1 expression is associated with the expression of ROCK2, which plays an important role in HCC. Our data suggest that MKP1 is crucial for ROCK2-mediated metastasis and invasion. Interestingly, we demonstrated that ROCK2 has opposite effects on protein and mRNA levels of MKP1, as it decreases the expression at the protein level and increases the expression at the mRNA level. We also identified the mechanism responsible for this incongruency; ROCK2 activates ERK1/2-ATF2 signaling, which leads to the increased mRNA expression of MKP1. At the same time, ROCK2 promotes the ubiquitin-mediated degradation of MKP1 by activating ERK1/2, therefore promoting the metastasis of HCC. In conclusion, our data provide new evidence for the biological and clinical significance of MKP1 as a potential biomarker. We demonstrate that ROCK2 disturbs the protein and mRNA expression of MKP1 in human HCC progression.

The Ubiquitin-like Protein FAT10 Stabilizes eEF1A1 Expression to Promote Tumor Proliferation in a Complex Manner.

Human HLA-F adjacent transcript 10 (FAT10) is the only ubiquitin-like protein that can directly target substrates for degradation by proteasomes, but it can also stabilize the expression of certain substrates by antagonizing ubiquitination, through mechanisms as yet uncharacterized. In this study, we show how FAT10 stabilizes the translation elongation factor eEF1A1, which contributes to cancer cell proliferation. FAT10 overexpression increased expression of eEF1A1, which was sufficient to promote proliferation of cancer cells. Mechanistic investigations revealed that FAT10 competed with ubiquitin (Ub) for binding to the same lysines on eEF1A1 to form either FAT10-eEF1A1 or Ub-eEF1A1 complexes, respectively, such that FAT10 overexpression decreased Ub-eEF1A1 levels and increased FAT10-eEF1A1 levels. Overall, our work establishes a novel mechanism through which FAT10 stabilizes its substrates, advancing understanding of the biological function of FAT10 and its role in cancer. Cancer Res; 76(16); 4897-907. ©2016 AACR.

Rock2 promotes the invasion and metastasis of hepatocellular carcinoma by modifying MMP2 ubiquitination and degradation.

Rho-associated coiled-coil-containing protein kinase 2 (Rock2) is a downstream effector of Rho that plays an important role in the tumorigenesis and progression of hepatocellular carcinoma (HCC). Matrix metalloproteinase 2 (MMP2) is a master regulator of tumor metastasis. In this study, we investigated the collections of Rock2 and MMP2 in HCCs and determined the potential role and molecular mechanism of Rock2 in MMP2-mediated invasiveness and metastasis. We found that Rock2 and MMP2 were markedly overexpressed in HCCs compared with the corresponding adjacent tissues, where a positive correlation in their expression was found. The knockdown of Rock2 significantly decreased MMP2 expression and inhibited the invasion and metastasis of HCC in vitro and in vivo. Additionally, the upregulation of MMP2 rescued the decreased migration and invasion induced by the knockdown of Rock2, whereas the knockdown of MMP2 decreased Rock2-enhanced HCC migration and invasion. Mechanistically, Rock2 stabilized MMP2 by preventing its ubiquitination and degradation. Together, our results link two drivers of invasion and metastasis in HCC and identify a novel pathway for MMP2 control.