Wnt Pathway Activation in Mesothelioma Evidence of Dishevelled Overexpression and Transcriptional Activity of β-Catenin

Thoracic Oncology Laboratory, Department of Medicine, University of California-San Francisco Cancer Center, San Francisco, CA 94115, USA.
Cancer Research (Impact Factor: 9.33). 08/2003; 63(15):4547-51.
Source: PubMed

ABSTRACT Malignant pleural mesothelioma is a relatively uncommon and yet incurable tumor. The pathogenesis of mesothelioma remains poorly understood. This study evaluated the role of Wnt signaling in mesothelioma. Western blot analysis was conducted to confirm the expression of Dishevelled (Dvl) and cytosolic β-catenin in matched autologous tissue samples (tumor and normal pleura), malignant pleural effusions, and in established mesothelioma cell lines LRK1A, REN and H513. Thirteen of 15 mesotheliomas examined showed consistent overexpression of Dvl and increased cytosolic β-catenin levels as compared with controls. To evaluate T-cell factor (Tcf)-dependent transcriptional activity of β-catenin, luciferase assays were conducted. Fresh mesothelioma cells (effusion derived), as well as LRK1A, REN, and H513 cell lines showed a significant fold increase (1.5-2.4-fold, P < 0.01) in Tcf-dependent transcriptional activity of β-catenin. To evaluate the biological significance of Dvl function in mesothelioma, a PDZ domain deletion mutant (ΔPDZ-Dvl) was created and stably transfected into LRK1A, REN, and H513. The effect of ΔPDZ-Dvl on mesothelioma growth was assayed in vitro (colony formation assay in soft agar) and in vivo (s.c. implantation in athymic mice NCRNU-M). In mesothelioma cells tested, ΔPDZ-Dvl-mediated inhibition of Dvl decreased cytosolic β-catenin levels, diminished Tcf-mediated transcription, and suppressed tumorigenesis of LRK1A and REN in vitro and in vivo. ΔPDZ-Dvl also down-regulated expression of c-myc in REN and COX-2 in H513. Our data suggest that in malignant pleural mesothelioma, Wnt signaling is activated through Dvl overexpression and downstream signaling through β-catenin. Inhibition of this signaling leads to significant antitumor effects. These results demonstrate Dvl overexpression in human cancer and, specifically, that Wnt signaling plays a role in mesothelioma pathogenesis. These data offer possible new avenues for therapeutic intervention.

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    • "Overexpression of Dvl proteins is frequently observed in many types of cancer, and a correlation between Dvl protein expression and b-catenin protein expression and histological tumor grade is reported for several cancers (Mizutani et al., 2005; Uematsu et al., 2003; Wei et al., 2008). Therefore, Dvl protein levels must be tightly controlled to fine-tune Wnt/b-catenin signaling without causing tumors. "
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    ABSTRACT: The phosphoprotein Dishevelled (Dvl) is a common essential component of Wnt/β-catenin and Wnt/planar cell polarity (PCP) signaling pathways. However, the regulation and significance of Dvl phosphorylation are not fully understood. Here, we show that homeodomain-interacting protein kinase 2 (Hipk2) facilitates protein phosphatase 1 catalytic subunit (PP1c)-mediated dephosphorylation of Dvl via its C-terminal domain and that this dephosphorylation blocks ubiquitination and consequent degradation mediated by the E3 ubiquitin ligase Itch, which targets the phosphorylated form of Dvl proteins. Inhibition of Hipk2 or PP1c function reduces Dvl protein levels and suppresses Wnt/β-catenin and Wnt/PCP pathway-dependent events in mammalian cells and zebrafish embryos, suggesting that Hipk2 and PP1c are essential for maintaining Dvl protein levels that are sufficient to activate Wnt signaling. We also show that Wnt-3a, a Wnt/β-catenin ligand, induces dissociation of the Dvl-Hipk2-PP1c complex and Dvl degradation under high-cell-density conditions. This regulation may be a negative feedback mechanism that fine-tunes Wnt/β-catenin signaling.
    Cell Reports 09/2014; 8(5). DOI:10.1016/j.celrep.2014.07.040 · 8.36 Impact Factor
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    • "However, these mechanistic studies employed β-catenin deficient MM cell lines. Current evidence indicates that MM tissue and cells are overwhelmingly β-catenin positive [173] [174] [181], suggesting that studies in β-catenin deficient cells may not be particularly relevant to the disease. "
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    ABSTRACT: The Wnt (wingless-type) signalling pathway plays an important role in embryonic development, tissue homeostasis, and tumour progression because of its effect on cell proliferation, migration, and differentiation. Secreted frizzled-related proteins (SFRPs) are extracellular inhibitors of Wnt signalling that act by binding directly to Wnt ligands or to Frizzled receptors. In recent years, aberrant expression of SFRPs has been reported to be associated with numerous cancers. As gene expression of SFRP members is often lost through promoter hypermethylation, inhibition of methylation through the use of epigenetic modifying agents could renew the expression of SFRP members and further antagonize deleterious Wnt signalling. Several reports have described epigenetic silencing of these Wnt signalling antagonists in various human cancers, suggesting their possible role as tumour suppressors. SFRP family members thus come across as potential tools in combating Wnt-driven tumourigenesis. However, little is known about SFRP family members and their role in different cancers. This review comprehensively covers all the available information on the role of SFRP molecules in various human cancers.
    Biochimica et Biophysica Acta (BBA) - Reviews on Cancer 01/2014; 1845(1):53-65. DOI:10.1016/j.bbcan.2013.11.004 · 7.85 Impact Factor
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    • "e l s e v i e r . c o m / l o c a t e / y b b r c biochemical consequences for cell proliferation and apoptosis [8] [10] [11]. Aberrant downregulation of the secreted frizzled-related protein (sFRP) family of Wnt regulators has been reported in MM [12] [13] and one member of this family, sFRP4, may suppress growth and induce apoptosis in mesothelioma cells [14]. "
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    ABSTRACT: Malignant mesothelioma (MM) is an uncommon and particularly aggressive cancer associated with asbestos exposure, which currently presents an intractable clinical challenge. Wnt signalling has been reported to play a role in the neoplastic properties of mesothelioma cells but has not been investigated in detail in this cancer. We surveyed expression of Wnts, their receptors, and other key molecules in this pathway in well established in vitro mesothelioma models in comparison with primary mesothelial cultures. We also tested the biological response of MM cell lines to exogenous Wnt and secreted regulators, as well as targeting β-catenin. We detected frequent expression of Wnt3 and Wnt5a, as well as Fzd 2, 4 and 6. The mRNA of Wnt4, Fzd3, sFRP4, APC and axin2 were downregulated in MM relative to mesothelial cells while LEF1 was overexpressed in MM. Functionally, we observed that Wnt3a stimulated MM proliferation while sFRP4 was inhibitory. Furthermore, directly targeting β-catenin expression could sensitise MM cells to cytotoxic drugs. These results provide evidence for altered expression of a number of Wnt/Fzd signalling molecules in MM. Modulation of Wnt signalling in MM may prove a means of targeting proliferation and drug resistance in this cancer.
    Biochemical and Biophysical Research Communications 09/2013; 440(1). DOI:10.1016/j.bbrc.2013.09.025 · 2.30 Impact Factor
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