Wnt/beta-catenin signaling inhibits death receptor-mediated apoptosis and promotes invasive growth of HNSCC

The Wnt/beta-catenin signaling pathway plays a critical role in cell proliferation and oncogenesis. It has been found to be chronically activated in a variety of human cancers, including head and neck squamous cell carcinoma (HNSCC). Previously, we have found that the activation of the Wnt/beta-catenin signaling pathway inhibits mitochondria-mediated apoptosis. In this study, we extended our studies to determine whether the Wnt/beta-catenin signaling pathway inhibited death receptor-mediated apoptosis in HNSCC cells. We found that Wnt/beta-catenin inhibited not only tumor necrosis factor (TNF)/c-Myc-mediated apoptosis, but also cell detachment-mediated apoptosis (anoikis) which is dependent on the death receptor signaling pathway. Interestingly, we also observed that the Wnt/beta-catenin signaling pathway induced HNSCC cell scattering and promoted cell invasion in the Matrigel, both of which are hallmarks for the invasive growth of HNSCC. Consistently, the over-expression of beta-catenin promoted HNSCC tumor growth in nude mice. Taken together, our results suggest that the Wnt/beta-catenin signaling pathway plays dual functions in HNSCC development: promoting both cell survival and invasive growth of HNSCC cells.     

Heparanase modulation by Wingless/INT (Wnt)

Heparanase is an endo-beta-glucuronidase, the only enzyme in mammals capable of cleaving heparan sulfate/heparin chains from proteoglycans. The oligosaccharides generated by heparanase present extensive biological functions since such oligosaccharides interact with adhesion molecules, growth factors, angiogenic factors and cytokines, modulating cell proliferation, migration, inflammation, and carcinogenesis. However, the regulation of heparanase activity is not fully understood. It is known that heparanase is synthesized as an inactive 65 kDa isoform and that post-translation processing forms an active 50 kDa enzyme. In the present study, we are interested in investigating whether heparanase is regulated by its own substrate as observed with many other enzymes. Wild-type Chinese hamster (Cricetulus griséus) ovary cells (CHO-K1) were treated with different doses of heparin. Heparanase expression was analyzed by Real-time PCR and flow cytometry. Also, heparanase activity was measured. The heparanase activity assay was performed using a coated plate with biotinylated heparan sulfate. In the present assay, a competitive heparin inhibition scenario was set aside. Exogenous heparin trigged a cell signaling pathway that increased heparanase mRNA and protein levels. The Wnt/beta-catenin pathway, judged by TCF-driven luciferase activity, seems to be involved to enhance heparanase profile during treatment with exogenous heparin. Lithium chloride treatment, an activator of the Wnt/beta-catenin pathway, confirmed such mechanism of transduction in vivo using zebrafish embryos and in vitro using CHO-K1 cells. Taken together the results suggest that heparin modulates heparanase expression by Wnt/beta-catenin.

     

The Wnt pathway is active in a small subset of pancreas cancer cell lines

Activation of the Wnt pathway plays an important role in the development of a wide variety of tumor types. Two genes involved in the activation of this pathway in tumors are Adenomatous Polyposis Coli (APC) and beta-catenin. Here, we analyze the activity of the Wnt pathway in cultured cells derived from ductal and acinar pancreatic adenocarcinomas using a reporter assay dependent on the activity of the beta-catenin/Tcf4 complex. We find that low-level Wnt activity can be detected in several pancreas cancer lines. High levels of reporter activity were detected exclusively in RWP-1 cells. These cells display nuclear beta-catenin and express a truncated APC protein resulting from a CAA>TAA mutation (Q1303X). Expression of a dominant negative Tcf4 protein inhibited proliferation of RWP-1 cells but not in other lines lacking beta-catenin-dependent reporter activity, supporting the functional relevance of this mutation. Our findings indicate that activation of the Wnt pathway may play a role in a small subset of ductal pancreatic cancers. Alternatively, RWP-1 cells may have been derived from a tumor arising in a structure adjacent to the pancreas such as the biliary tract or the Ampulla of Vater. Additional studies on the role of Wnt pathway components in the development/progression of tumors of the peripancreatic region merit consideration.     

Antagonistic regulation of convergent extension movements in Xenopus by Wnt/beta-catenin and Wnt/Ca2+ signaling

Convergent extension movements are the main driving force of Xenopus gastrulation. A fine-tuned regulation of cadherin-mediated cell-cell adhesion is thought to be required for this process. Members of the Wnt family of extracellular glycoproteins have been shown to modulate cadherin-mediated cell-cell adhesion, convergent extension movements, and cell differentiation. Here we show that endogenous Wnt/beta-catenin signaling activity is essential for convergent extension movements due to its effect on gene expression rather than on cadherins. Our data also suggest that XLEF-1 rather than XTCF-3 is required for convergent extension movements and that XLEF-1 functions in this context in the Wnt/beta-catenin pathway to regulate Xnr-3. In contrast, activation of the Wnt/Ca2+ pathway blocks convergent extension movements, with potential regulation of the Wnt/beta-catenin pathway at two different levels. PKC, activated by the Wnt/Ca2+ pathway, blocks the Wnt/beta-catenin pathway upstream of beta-catenin and phosphorylates Dishevelled. CamKII, also activated by the Wnt/Ca2+ pathway, inhibits the Wnt/beta-catenin signaling cascade downstream of beta-catenin. Thus, an opposing cross-talk of two distinct Wnt signaling cascades regulates convergent extension movements in Xenopus.     

Wnt control of stem cells and differentiation in the intestinal epithelium

The intestinal epithelium represents a very attractive experimental model for the study of integrated key cellular processes such as proliferation and differentiation. The tissue is subjected to a rapid and perpetual self-renewal along the crypt-villus axis. Renewal requires division of multipotent stem cells, still to be morphologically identified and isolated, followed by transit amplification, and differentiation of daughter cells into specialized absorptive and secretory cells. Our understanding of the crucial role played by the Wnt/beta-catenin signaling pathway in controlling the fine balance between cell proliferation and differentiation in the gut has been significantly enhanced in recent years. Mutations in some of its components irreversibly lead to carcinogenesis in humans and in mice. Here, we discuss recent advances related to the Wnt/beta-catenin signaling pathway in regulating intestinal stem cells, homeostasis, and cancer. We emphasize how Wnt signaling is able to maintain a stem cell/progenitor phenotype in normal intestinal crypts, and to impose a very similar phenotype onto colorectal adenomas.     

Essential roles of mesenchyme-derived beta-catenin in mouse Müllerian duct morphogenesis

Members of the Wnt family of genes such as Wnt4, Wnt5a, and Wnt7a have been implicated in the formation and morphogenesis of the Müllerian duct into various parts of the female reproductive tract. These WNT ligands elicit their action via either the canonical WNT/beta-catenin or the non-canonical WNT/calcium pathway and could possibly function redundantly in Müllerian duct differentiation. By using the Müllerian duct-specific anti-Müllerian hormone receptor 2 cre (Amhr2-cre) mouse line, we established a conditional knockout model that removed beta-catenin specifically in the mesenchyme of the Müllerian duct. At birth, loss of beta-catenin in the Müllerian duct mesenchyme disrupted the normal coiling of the oviduct in the knockout embryo, resembling the phenotype of the Wnt7a knockout. The overall development of the female reproductive tract was stunted at birth with a decrease in proliferation in the mesenchyme and epithelium. We also discovered that Wnt5a and Wnt7a expression remained normal, excluding the possibility that the phenotypes resulted from a loss of these WNT ligands. We examined the expression of Frizzled (Fzd), the receptors for WNT, and found that Fzd1 is one receptor present in the Müllerian duct mesenchyme and could be the putative receptor for beta-catenin activation in the Müllerian duct. In summary, our findings suggest that mesenchymal beta-catenin is a downstream effector of Wnt7a that mediates the patterning of the oviduct and proper differentiation of the uterus.