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Ubiquitin specific protease 4 (USP4) is a deubiquitinating enzyme with key roles in the regulation of p53 and TGFb signaling, suggesting its importance in tumorigenesis. However, the mechanisms and regulatory roles of USP4 in cancer, including colorectal cancer, remain largely elusive. Here, we present the first evidence that USP4 regulates the growth, invasion, and metastasis of colorectal cancer. USP4 expression was significantly elevated in colorectal cancer tissues and was significantly associated with tumor size, differentiation, distant metastasis, and poor survival. Knockdown of USP4 diminished colorectal cancer cell growth, colony formation, migration, and invasion in vitro and metastasis in vivo. Importantly, we found that phosphatase of regenerating liver-3 (PRL-3) is indispensable for USP4-mediated oncogenic activity in colorectal cancer.Mechanistically, we observed that USP4 interacted with and stabilized PRL-3 via deubiquitination. This resulted in activation of Akt and reduction of E-cadherin, critical regulators of cancer cell growth and metastasis. Examination of clinical samples confirmed that USP4 expression positively correlates with PRL-3 protein expression, but not mRNA transcript levels. Taken together, our results demonstrate that aberrant expression of USP4 contributes to the development and progression of colorectal cancer and reveal a critical mechanism underlying USP4-mediated oncogenic activity. These observations suggest that the potential of harnessing proteolytic degradation processes for therapeutic manipulation may offer a much-needed new approach for improving colorectal cancer treatment strategies. Cancer Res; 76(1); 83-95. Ó2015 AACR.

Aberrant CTNNB1 signaling is one of the fundamental processes in cancers, especially colorectal cancer (CRC). Here, we reported that TRAF6, an E3 ubiquitin ligase important for inflammatory signaling, inhibited epithelial-mesenchymal transition (EMT) and CRC metastasis through driving a selective autophagic CTNNB1 degradation machinery. Mechanistically, TRAF6 interacted with MAP1LC3B/LC3B through its LC3-interacting region 'YxxL' and catalyzed K63-linked polyubiquitination of LC3B. The K63linked ubiquitination of LC3B promoted the formation of the LC3B-ATG7 complex and was critical to the subsequent recognition of CTNNB1 by LC3B for the selective autophagic degradation. However, TRAF6 was phosphorylated at Thr266 by GSK3B in most clinical CRC, which triggered K48-linked polyubiquitination and degradation of TRAF6 and thereby attenuated its inhibitory activity towards the autophagydependent CTNNB1 signaling. Clinically, decreased expression of TRAF6 was associated with elevated GSK3B protein levels and activity and reduced overall survival in CRC patients. Pharmacological inhibition of GSK3B activity stabilized the TRAF6 protein, promoted CTNNB1 degradation, and effectively suppressed EMT and CRC metastasis. Thus, targeting TRAF6 and its pathway may be meaningful for treating advanced CRC.

The Hippo-Yap pathway conveys oncogenic signals, but its regulation during cancer development is not well understood. Here, we identify the nuclear receptor RARg as a regulator of the Hippo-Yap pathway in colorectal tumorigenesis and metastasis. RARg is downregulated in human colorectal cancer tissues, where its expression correlates inversely with tumor size, TNM stage, and distant metastasis. Functional studies established that silencing of RARg drove colorectal cancer cell growth, invasion, and metastatic properties both in vitro and in vivo. Mechanistically, RARg controlled Hippo-Yap signaling to inhibit colorectal cancer development, acting to promote phosphorylation and binding of Lats1 to its transcriptional coactivator Yap and thereby inactivating Yap target gene expression. In clinical specimens, RARg expression correlated with overall survival outcomes and expression of critical Hippo-Yap pathway effector molecules in colorectal cancer patients. Collectively, our results defined RARg as tumor suppressor in colorectal cancer that acts by restricting oncogenic signaling by the Hippo-Yap pathway, with potential implications for new approaches to colorectal cancer therapy.Cancer Res; 76(13); 3813-25. Ó2016 AACR.

BackgroundUbiquitination is a basic post-translational modification for cellular homeostasis, and members of the conjugating enzyme (E2) family are the key components of the ubiquitin–proteasome system. However, the role of E2 family in colorectal cancer (CRC) is largely unknown. Our study aimed to investigate the role of Ube2v1, one of the ubiquitin-conjugating E2 enzyme variant proteins (Ube2v) but without the conserved cysteine residue required for the catalytic activity of E2s, in CRC.MethodsImmunohistochemistry and real-time RT-PCR were used to study the expressions of Ube2v1 at protein and mRNA levels in CRC, respectively. Western blotting and immunofluorescence, transmission electron microscopy, and in vivo rescue experiments were used to study the functional effects of Ube2v1 on autophagy and EMT program. Quantitative mass spectrometry, immunoprecipitation, ubiquitination assay, western blotting, and real-time RT-PCR were used to analyze the effects of Ube2v1 on histone H4 lysine 16 acetylation, interaction with Sirt1, ubiquitination of Sirt1, and autophagy-related gene expression.ResultsUbe2v1 was elevated in CRC samples, and its increased expression was correlated with poorer survival of CRC patients. Ube2v1 promoted migration and invasion of CRC cells in vitro and tumor growth and metastasis of CRC cells in vivo. Interestingly, Ube2v1suppressed autophagy program and promoted epithelial mesenchymal transition (EMT) and metastasis of CRC cells in an autophagy-dependent pattern in vitro and in vivo. Moreover, both rapamycin and trehalose attenuated the enhanced Ube2v1-mediated lung metastasis by inducing the autophagy pathway in an orthotropic mouse xenograft model of lung metastasis. Mechanistically, Ube2v1 promoted Ubc13-mediated ubiquitination and degradation of Sirt1 and inhibited histone H4 lysine 16 acetylation, and finally epigenetically suppressed autophagy gene expression in CRC.ConclusionsOur study functionally links Ube2v1, an E2 member in the ubiquitin–proteasome system, to autophagy program, thereby shedding light on developing Ube2v1 targeted therapy for CRC patients.Electronic supplementary materialThe online version of this article (10.1186/s13045-018-0638-9) contains supplementary material, which is available to authorized users.

Background Nur77, an orphan member of the nuclear receptor superfamily, has been implicated in the regulation of inflammation. However, the in vivo function of Nur77 remains largely unexplored. In the current study, we investigated the role of Nur77 in inflammation and immunity in mice.FindingsWe found that elderly 8-month-old Nur77-deficient mice (Nur77−/−) developed systemic inflammation. Compared to wild-type (WT) mice (Nur77+/+), Nur77−/− mice showed splenomegaly, severe infiltration of inflammatory cells in several organs including liver, lung, spleen and kidney, increased hyperplasia of fibrous tissue in the lung and enlargement of kidney glomeruli. Additionally, Nur77−/− mice had increased production of pro-inflammatory cytokines and immunoglobulin, and elicited pro-inflammatory M1-like polarization in macrophages as revealed by increased expression of CXCL11 and INDO, and decreased expression of MRC1.ConclusionsThese in vivo observations provide evidence for a pivotal role for Nur77 in the regulation of systemic inflammation and emphasize the pathogenic significance of Nur77 in vivo.Electronic supplementary materialThe online version of this article (doi:10.1186/s12950-015-0085-0) contains supplementary material, which is available to authorized users.

Malignant melanoma is the most aggressive form of skin cancer. Although various antimelanoma approaches have been used in the clinics to treat the disease over the last three decades, none of the drugs significantly prolonged the survival of metastatic melanoma patients; hence, effective drugs against metastatic melanoma are highly desired. In this study, we explored an antimetastatic melanoma agent derived from traditional Chinese medicinal herbs and found that jatrorrhizine hydrochloride (JH), an active component of the traditional Chinese medicinal herb Coptis chinensis, inhibited the proliferation and neovascularization of C8161 human metastatic melanoma cells. JH suppressed C8161 cell proliferation in a dose-dependent manner, with a half-maximal inhibitory concentration of 47.4±1.6 μmol/l; however, it did not induce significant cellular apoptosis at doses up to 320 μmol/l. Mechanistic studies showed that JH-induced C8161 cell cycle arrest at the G0/G1 transition, which was accompanied by overexpression of the cell cycle-suppressive genes p21 and p27 at higher doses. Moreover, JH reduced C8161 cell-mediated neovascularization in vitro and in vivo and impeded the expression of the gene for VE-cadherin, a key protein in tumor vasculogenic mimicry and angiogenesis. Taken together, the effective inhibitory effects of JH on metastatic melanoma cell proliferation and neovascularization with low toxicity suggest that JH is a potential new antimelanoma drug candidate.

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