Nur77, an immediate-early response gene, participates in a wide range of biological functions. Its human homologue, NUR77, is known by several names and has the HGNC-approved gene symbol NR4A1. However, the role of Nur77 in inflammatory bowel disease (IBD) and its underlying mechanisms remain elusive. Here, using public data from the International Inflammatory Bowel Disease Genetics Consortium (IIBDGC) on the most recent genome-wide association studies (GWAS) for ulcerative colitis (UC) and Crohn's disease (CD), we found that genetic variants of the NUR77 gene are associated with increased risk for both UC and CD. Accordingly, Nur77 expression was significantly reduced in colon tissues from patients with UC or CD and mice treated with DSS. Nur77 deficiency increased the susceptibility of mice to DSS-induced experimental colitis and prevented intestinal recovery, whereas treatment with cytosporone B (Csn-B), an agonist for Nur77, significantly attenuated excessive inflammatory response in the DSS-induced colitis mouse model. Mechanistically, NUR77 acts as a negative regulator of TLR-IL-1R signalling by interacting with TRAF6. This interaction prevented auto-ubiquitination and oligomerization of TRAF6 and subsequently inhibited NF-κB activation and pro-inflammatory cytokine production. Taken together, our GWAS-based analysis and in vitro and in vivo studies have demonstrated that Nur77 is an important regulator of TRAF6/TLR-IL-1R-initiated inflammatory signalling, and loss of Nur77 may contribute to the development of IBD, suggesting Nur77 as a potential target for the prevention and treatment of IBD.

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.

Nur77, an orphan member of the nuclear receptor superfamily, has been implicated in tumorigenesis. However, its contributions to colorectal cancer (CRC) invasion and metastasis are largely under characterized. Here, we present the first evidence that the invasion and metastasis of CRC is regulated by Nur77. High expression of Nur77 was observed in clinical CRC tissues, and this elevated expression was significantly associated with advanced tumor, lymph nodes, distant metastasis stage (P = 0.003), lymph node metastasis (P = 0.001) and poor survival (P = 0.03). Overexpression of Nur77 in CRC cells enhanced cell invasion in vitro, whereas knockdown of Nur77 diminished cell invasion and metastasis both in vitro and in vivo. In studying the possible mechanism by which overexpression of Nur77 contributes to CRC invasion and metastasis, we observed that the nuclear protein Nur77 promoted the expression of matrix metalloproteinase (MMP)-9, a novel downstream target of Nur77, and subsequently decreased the expression of E-cadherin. Examination of clinical samples further showed that Nur77 expression is positively correlated with MMP-9, whereas negatively correlated with E-cadherin. Interestingly, Nur77-mediated CRC invasion via MMP-9 and E-cadherin could be mimicked by some metastasis-inducible factors including hypoxia and prostaglandin E2. Collectively, our study demonstrated that Nur77 could promote the invasion and metastasis of CRC cells through regulation of MMP-9/E-cadherin signaling. These observations provide a possible new strategy for potentially treating or preventing the metastasis of CRC through targeting of Nur77.

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.