The phenotypic changes of increased motility and invasiveness of cancer cells are reminiscent of the epithelial-mesenchymal transition (EMT) that occurs during embryonic development. Snail, a zinc-finger transcription factor, triggers this process by repressing E-cadherin expression; however, the mechanisms that regulate Snail remain elusive. Here we find that Snail is highly unstable, with a short half-life about 25 min. We show that GSK-3beta binds to and phosphorylates Snail at two consensus motifs to dually regulate the function of this protein. Phosphorylation of the first motif regulates its beta-Trcp-mediated ubiquitination, whereas phosphorylation of the second motif controls its subcellular localization. A variant of Snail (Snail-6SA), which abolishes these phosphorylations, is much more stable and resides exclusively in the nucleus to induce EMT. Furthermore, inhibition of GSK-3beta results in the upregulation of Snail and downregulation of E-cadherin in vivo. Thus, Snail and GSK-3beta together function as a molecular switch for many signalling pathways that lead to EMT.

SUMMARY The increased motility and invasiveness of tumor cells are reminiscent of epithelial-mesenchymal transition (EMT) that occurs during embryonic development, wound healing, and metastasis. In this study, we found that Snail is stabilized by the inflammatory cytokine TNFα through the activation of the NF-κB pathway. We demonstrated that NF-κB is required for the induction of COP9 signalosome 2 (CSN2) which, in turn, blocks the ubiquitination and degradation of Snail. Furthermore, we showed that the expression of Snail correlated with the activation of NF-κB in cancer cell lines and metastatic tumor samples. Knockdown of Snail expression inhibited cell migration and invasion induced by inflammatory cytokines and suppressed inflammation-mediated breast cancer metastasis. Our study provides a plausible mechanism for inflammation-induced metastasis.

Summary Twist is a key transcription activator of epithelial-mesenchymal transition (EMT). It remains unclear how Twist induces gene expression. Here we reported a mechanism by which Twist recruits BRD4 to direct WNT5A expression in basal-like breast cancer (BLBC). Twist contains a “histone H4 mimic” GK-X-GK motif that is di-acetylated by Tip60. The di-acetylated Twist binds the second bromodomain of BRD4, whose first bromodomain interacts with acetylated H4, thereby constructs an activated Twist/BRD4/P-TEFb/RNA-PolII complex at the WNT5A promoter and enhancer. Pharmacologic inhibition of the Twist-BRD4 association reduced WNT5A expression and suppressed invasion, cancer stem cell (CSC)-like properties, and tumorigenicity of BLBC cells. Our study indicates that the interaction with BRD4 is critical for the oncogenic function of Twist in BLBC.

beta-catenin plays an important role in development and homeostasis. Deregulated beta-catenin is involved in oncogenesis. In this study, we found that beta-catenin can physically complex with NF-kappa B, resulting in a reduction of NF-kappa B DNA binding, transactivation activity, and target gene expression. Repressed NF-kappa B activity is found in human colon cancer cells in which beta-catenin is activated. Importantly, activated beta-catenin was found to inhibit the expression of NF-kappa B target genes, including Fas and TRAF1. Furthermore, a strong inverse correlation was identified between the expression levels of beta-catenin and Fas in colon and breast tumor tissues, suggesting that beta-catenin regulates NF-kappa B and its targets in vivo. Thus, beta-catenin may play an important role in oncogenesis through the crossregulation of NF-kappa B.