Wnt signalling pathways have been shown to play key roles in both normal development and tumorigenesis. Progression of many human cancers is associated with defined mutations in Wnt pathway components that result in dysregulated β-catenin-mediated gene transcription. Although Wnt pathway mutations are rare in epithelial ovarian cancer (with the exception of the endometrioid histotype), accumulating evidence supports a role for Wnt signalling in ovarian tumorigenesis in the absence of genetic mutations. The present review summarizes evidence in support of activated Wnt signalling in ovarian tumours and discusses alternative mechanisms for Wnt pathway activation in the ovarian tumour microenvironment.

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Reversible modulation of integrin-regulated cell-matrix adhesion and epithelial (E)-cadherin-mediated cell-cell adhesion plays a critical role in the establishment of ovarian cancer metastases. In contrast to most epithelial cell-derived tumors that down-regulate E-cadherin expression during progression, acquisition of E-cadherin expression accompanies malignant transformation of the ovarian surface epithelium and is maintained in peritoneal metastases. Metastatic epithelial ovarian cancer cells are disseminated intraperitoneally and preferentially adhere via integrins to interstitial collagens in the peritoneal cavity. This study was undertaken to determine whether integrin engagement influences E-cadherin and ␤-catenin localization and function. The data demonstrate that multivalent integrin engagement results in increased internalization of E-cadherin, inhibition of GSK-3␤, elevated levels of nuclear ␤-catenin, increased ␤-catenin-regulated promoter activation, and transcriptional activation of Wnt/␤-catenin target genes. Blocking ␤-catenin transcriptional control with inhibitor of ␤-catenin and Tcf-4 reduces cellular invasion, suggesting a key role for ␤-catenin nuclear signaling in EOC invasion and metastasis. These studies support a model wherein cell-matrix engagement regulates the functional integrity of cell-cell contacts, leading to increased ␤-catenin nuclear signaling and enhanced cellular invasive activity. Furthermore, these results provide a mechanism for activation of Wnt/␤-catenin signaling in the absence of activating mutations in this pathway.Epithelial (E) 3 -cadherin is a single-span transmembrane glycoprotein that mediates calcium-dependent cell-cell adhesion via interaction with the extracellular domains of cadherins on the surface of neighboring cells (1, 2). Key functions of E-cadherin include the regulation of cell polarity and the maintenance of epithelial organization (3). Although most normal epithelia express high levels of E-cadherin, this cadherin is absent in the mesenchymally derived normal ovarian surface epithelium, which expresses neural (N)-cadherin. In most carcinomas, E-cadherin expression is down-regulated or lost, facilitating cellular dispersal, invasion, and metastasis (4). However, a unique feature of EOC is that E-cadherin becomes more abundant in primary differentiated carcinomas, with all histotypes displaying strong immunoreactivity (reviewed in Refs. 5, 6). There is less clarity regarding relative E-cadherin levels during ovarian tumor progression and metastasis. Although complete loss of E-cadherin is uncommon, reduced staining is often detected in late stage tumors and in ascites-derived tumor cells (7-9), and negative E-cadherin is predictive of poor overall survival (10, 11).␤-Catenin is found predominantly in association with the E-cadherin cytoplasmic domain at cell-cell junctions (12). In the absence of cell-cell contact and Wnt signaling, cytosolic ␤-catenin forms a complex with adenomatous poliosis coli, Axin/conductin, casein kinases 1␣ and 1⑀, and glyc...

Background: Aberrant activation of Wnt/␤-catenin signaling is found in ovarian cancer, even when mutations are absent. Results: The bioactive lipid lysophosphatidic acid induces ␤1-integrin clustering, nuclear ␤-catenin translocation, and activation of Tcf/Lef-regulated gene expression. Conclusion: Microenvironmental lipids modulate ␤-catenin signaling. Significance: Understanding the mechanisms of Wnt/␤-catenin activation provides a basis for therapeutic targeting of the pathway in ovarian cancer.