Zebrafish Dapper1 and Dapper2 play distinct roles in Wnt-mediated developmental processes

Wnt signaling pathways in vertebrates use the phosphoprotein Dishevelled (Dvl). The cellular responses to Wnt signaling may in part be modulated by Dvl-associated proteins, including Dapper (Dpr). We have cloned and characterized the zebrafish Dpr paralogs Dpr1 and Dpr2. Loss-of-function studies reveal that endogenous Dpr1 but not Dpr2 is required to enhance Wnt/beta-catenin activity in zebrafish embryos that are hypomorphic for Wnt8. Conversely, Dpr2 but not Dpr1 is required for normal convergence extension movements in embryos that are hypomorphic for Stbm or Wnt11, supporting a functional interaction of Dpr2 with Wnt/Ca2+-PCP signaling. In gain-of-function experiments, Dpr1 but not Dpr2 induces Wnt/beta-catenin target genes. Dpr1 synergizes with zebrafish Dvl2, and with the Dvl-interacting kinases CK1epsilon, Par1 and CK2, in activating target genes. We conclude that two Dvl-associated paralogs, Dpr1 and Dpr2, participate in distinct Wnt-dependent developmental processes.     

Glucose induces an autocrine activation of the Wnt/beta-catenin pathway in macrophage cell lines

The canonical Wnt signalling pathway acts by slowing the rate of ubiquitin-mediated beta-catenin degradation. This results in the accumulation and subsequent nuclear translocation of beta-catenin, which induces the expression of a number of genes involved in growth, differentiation and metabolism. The mechanisms regulating the Wnt signalling pathway in the physiological context is still not fully understood. In the present study we provide evidence that changes in glucose levels within the physiological range can acutely regulate the levels of beta-catenin in two macrophage cell lines (J774.2 and RAW264.7 cells). In particular we find that glucose induces these effects by promoting an autocrine activation of Wnt signalling that is mediated by the hexosamine pathway and changes in N-linked glycosylation of proteins. These studies reveal that the Wnt/beta-catenin system is a glucose-responsive signalling system and as such is likely to play a role in pathways involved in sensing changes in metabolic status.     

Activated macrophages promote Wnt signalling through tumour necrosis factor-alpha in gastric tumour cells

The activation of Wnt/beta-catenin signalling has an important function in gastrointestinal tumorigenesis. It has been suggested that the promotion of Wnt/beta-catenin activity beyond the threshold is important for carcinogenesis. We herein investigated the role of macrophages in the promotion of Wnt/beta-catenin activity in gastric tumorigenesis. We found beta-catenin nuclear accumulation in macrophage-infiltrated dysplastic mucosa of the K19-Wnt1 mouse stomach. Moreover, macrophage depletion in Apc(Delta716) mice resulted in the suppression of intestinal tumorigenesis. These results suggested the role of macrophages in the activation of Wnt/beta-catenin signalling, which thus leads to tumour development. Importantly, the conditioned medium of activated macrophages promoted Wnt/beta-catenin signalling in gastric cancer cells, which was suppressed by the inhibition of tumour necrosis factor (TNF)-alpha. Furthermore, treatment with TNF-alpha induced glycogen synthase kinase 3beta (GSK3beta) phosphorylation, which resulted in the stabilization of beta-catenin. We also found that Helicobacter infection in the K19-Wnt1 mouse stomach caused mucosal macrophage infiltration and nuclear beta-catenin accumulation. These results suggest that macrophage-derived TNF-alpha promotes Wnt/beta-catenin signalling through inhibition of GSK3beta, which may contribute to tumour development in the gastric mucosa.     

Beta-catenin regulates Cripto- and Wnt3-dependent gene expression programs in mouse axis and mesoderm formation

Gene expression profiling of beta-catenin, Cripto and Wnt3 mutant mouse embryos has been used to characterise the genetic networks that regulate early embryonic development. We have defined genes whose expression is regulated by beta-catenin during formation of the anteroposterior axis and the mesoderm, and have identified Cripto, which encodes a Nodal co-receptor, as a primary target of beta-catenin signals both in embryogenesis as well as in colon carcinoma cell lines and tissues. We have also defined groups of genes regulated by Wnt3/beta-catenin signalling during primitive streak and mesoderm formation. Our data assign a key role to beta-catenin upstream of two distinct gene expression programs during anteroposterior axis and mesoderm formation.     

TM4SF1, a binding protein of DVL2 in hepatocellular carcinoma,positively regulates beta-catenin/TCF signalling

The interaction between Axin and DVL2 is critical for the breaking down of the beta-catenin destruction complex and the activation of the Wnt/beta-catenin cascade. However, this biological process remains poorly understood. In the present study, TM4SF1 was identified as the interacting partner of DVL2 and positively regulated as Wnt/beta-catenin signalling by strengthening the DVL2-Axin interaction. The expression levels of TM4SF1 were elevated in hepatocellular carcinoma (HCC) and were induced by Kras signalling. The overexpression of TM4SF1 promoted the growth and motility of HCC cells, and up-regulated the target genes (Axin2 and cyclin D1). The down-regulation of TM4SF1 impaired the capability of HCC cells for growth, migration and metastasis. In addition, the down-regulation of TM4SF1 promoted the ubiquitination of beta-catenin. In summary, these results reveal the oncogenic functions of TM4SF1 in HCC progression and suggest that TM4SF1 might be a target for treatment.