7471

WNT1

Accumulating evidence indicates that hyperactive Wnt signalling occurs in association with the development and progression of human breast cancer. As a consequence of engaging the canonical Wnt pathway, a beta-catenin-T-cell factor (TCF) transcriptional complex is generated, which has been postulated to trigger the epithelial-mesenchymal transition (EMT) that characterizes the tissue-invasive phenotype. However, the molecular mechanisms by which the beta-catenin-TCF complex induces EMT-like programmes remain undefined. Here, we demonstrate that canonical Wnt signalling engages tumour cell dedifferentiation and tissue-invasive activity through an Axin2-dependent pathway that stabilizes the Snail1 zinc-transcription factor, a key regulator of normal and neoplastic EMT programmes. Axin2 regulates EMT by acting as a nucleocytoplasmic chaperone for GSK3beta, the dominant kinase responsible for controlling Snail1 protein turnover and activity. As dysregulated Wnt signalling marks a diverse array of cancerous tissue types, the identification of a beta-catenin-TCF-regulated Axin2-GSK3beta-Snail1 axis provides new mechanistic insights into cancer-associated EMT programmes.

Perturbations in the adipocytokine profile, especially higher levels of leptin, are a major cause of breast tumor progression and metastasis; the underlying mechanisms, however, are not well understood. In particular, it remains elusive whether leptin is involved in epithelial-mesenchymal transition (EMT). Here, we provide molecular evidence that leptin induces breast cancer cells to undergo a transition from epithelial to spindle-like mesenchymal morphology. Investigating the downstream mediator(s) that may direct leptin-induced EMT, we found functional interactions between leptin, metastasis-associated protein 1 (MTA1), and Wnt1 signaling components. Leptin increases accumulation and nuclear translocation of beta-catenin leading to increased promoter recruitment. Silencing of beta-catenin or treatment with the small molecule inhibitor, ICG-001, inhibits leptin-induced EMT, invasion, and tumorsphere formation. Mechanistically, leptin stimulates phosphorylation of glycogen synthase kinase 3beta (GSK3beta) via Akt activation resulting in a substantial decrease in the formation of the GSK3beta-LKB1-Axin complex that leads to increased accumulation of beta-catenin. Leptin treatment also increases Wnt1 expression that contributes to GSK3beta phosphorylation. Inhibition of Wnt1 abrogates leptin-stimulated GSK3beta phosphorylation. We also discovered that leptin increases the expression of an important modifier of Wnt1 signaling, MTA1, which is integral to leptin-mediated regulation of the Wnt/beta-catenin pathway as silencing of MTA1 inhibits leptin-induced Wnt1 expression, GSK3beta phosphorylation, and beta-catenin activation. Furthermore, analysis of leptin-treated breast tumors shows increased expression of Wnt1, pGSK3beta, and vimentin along with higher nuclear accumulation of beta-catenin and reduced E-cadherin expression providing in vivo evidence for a previously unrecognized cross-talk between leptin and MTA1/Wnt signaling in epithelial-mesenchymal transition of breast cancer cells.

The Wnt beta-catenin pathway controls numerous cellular processes including cell differentiation and cell-fate decisions. Wnt ligands engage Frizzled receptors and the low-density-lipoprotein-related protein 5/6 (LRP5/6) receptor complex leading to the recruitment of Dishevelled (Dvl) and Axin1 to the plasma membrane. Axin1 has a regulator of G-protein signaling (RGS) domain that binds adenomatous polyposis coli and Galpha subunits, thereby providing a mechanism by which Galpha subunits can affect beta-catenin levels. Here we show that Wnt signaling enhances the expression of another RGS domain-containing protein, PDZ-RGS3. Reducing PDZ-RGS3 levels impaired Wnt3a-induced activation of the canonical pathway. PDZ-RGS3 bound GSK3beta and decreased its catalytic activity toward beta-catenin. PDZ-RGS3 overexpression enhanced Snail1 and led to morphological and biochemical changes reminiscent of epithelial mesenchymal transition (EMT). These results indicate that PDZ-RGS3 can enhance signals generated by the Wnt canonical pathway and that plays a pivotal role in EMT.

Retinoic acid receptor beta (RARbeta) has been proposed to act as a tumor suppressor in breast cancer. In contrast, recent data have shown that RARbeta promotes ERBB2-induced mammary gland tumorigenesis through remodeling of the stromal compartment and activation of cancer-associated fibroblasts. However, it is currently unknown whether RARbeta oncogenic activity is specific to ERBB2-induced tumors, or whether it influences the initiation and progression of other breast cancer subtypes. Accordingly, we set out to investigate the involvement of RARbeta in basal-like breast cancer using mouse mammary tumor virus (MMTV)-wingless-related integration site 1 (Wnt1)-induced mammary gland tumorigenesis as a model system. We found that compared with wild type mice, inactivation of Rarb resulted in a lengthy delay in Wnt1-induced mammary gland tumorigenesis and in a significantly slower tumor growth rate. Ablation of Rarb altered the composition of the stroma, repressed the activation of cancer-associated fibroblasts, and reduced the recruitment of inflammatory cells and angiogenesis. Reduced expression of IGF-1 and activity of its downstream signaling pathway contribute to attenuate EMT in the Rarb-null tumors. Our results show that, in the absence of retinoid signaling via RARbeta, reduced IGF-1 signaling results in suppression of epithelial-mesenchymal transition and delays tumorigenesis induced by the Wnt1 oncogene. Accordingly, our work reinforces the concept that antagonizing RARbeta-dependent retinoid signaling could provide a therapeutic avenue to treat poor outcome breast cancers.

BACKGROUND: EphA2 is a crucial oncogene in gastric cancer (GC) development and metastasis, this study aims to identify microRNAs that target it and serve as key regulators of gastric carcinogenesis. METHODS: We identified several potential microRNAs targeting EphA2 by bioinformatics websites and then analyzed the role of miR-302b in modulating EphA2 in vitro and in vivo of GC, and it's mechanism. RESULTS: Our analysis identified miR-302b, a novel regulator of EphA2, as one of the most significantly downregulated microRNA (miRNA) in GC tissues. Overexpression of miR-302b impaired GC cell migratory and invasive properties robustly and suppressed cell proliferation by arresting cells at G0-G1 phase in vitro. miR-302b exhibited anti-tumor activity by reversing EphA2 regulation, which relayed a signaling transduction cascade that attenuated the functions of N-cadherin, beta-catenin, and Snail (markers of Wnt/beta-catenin and epithelial-mesenchymal transition, EMT). This modulation of EphA2 also had distinct effects on cell proliferation and migration in GC in vivo. CONCLUSIONS: miR-302b serves as a critical suppressor of GC cell tumorigenesis and metastasis by targeting the EphA2/Wnt/beta-catenin/EMT pathway.