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Developmental and cancer models show Wnt/β-catenin signaling mediates diverse phenotypic outcomes in the pancreas dictated by its temporospatial context and relative levels of activation. While Wnt/β-catenin signaling is generally thought to promote tumorigenesis, it is still unclear how and to what extent the Wnt pathway is deregulated in pancreatic adenocarcinoma (PDAC) or whether its deregulation appreciably alters PDAC phenotype or patient outcome. To begin to address these important questions, Wnt/β-catenin signaling was examined in numerous PDAC cell lines by dual luciferase reporter assays and endogenous target gene expression. Two patterns of Wnt/β-catenin activity were observed across PDAC cell lines: (1) those with high constitutive Wnt/β-catenin activity and (2) those with low constitutive Wnt/β-catenin activity and variable responsiveness to Wnt ligand stimulation. Gene expression microarray analysis revealed cell lines with high constitutive Wnt activity consistently had elevated expression of WNT7B. Addressing this mechanistically, WNT7B gene knockdown studies verified Wnt/β-catenin signaling was heavily dependent upon WNT7B expression in cell lines with high levels of activity. Phenotypically, WNT7B knockdown had no appreciable effect on PDAC cell line anchorage-dependent cell growth or survival, but did significantly decreased PDAC cell line anchorage-independent cell growth and survival, as well as clonogenicity and sphere-forming capacity. Similar dual luciferase reporter and phenotypic results were obtained when cell lines were treated with IWP-2, a drug that blocks the palmitoylation and secretion of Wnt ligands. The impact of elevated Wnt/β-catenin signaling was further addressed in patient tumors by (1) examining the immunohistochemical expression of nuclear β-catenin (a widely used surrogate of Wnt/β-catenin activation) on a large tissue microarray of PDAC tumors and (2) measuring levels of an experimentally determined WNT7B gene signature on a series of gene expression arrays performed on PDAC patient tumors. In both instances, elevated Wnt/β-catenin signaling was significantly associated with improved patient survival in Kaplan-Meier and univariate analyses. This unexpected but not unprecedented finding has been shown for other tumor types such as hepatocellular carcinoma and melanoma where Wnt/β-catenin signaling also correlates with better survival. In conclusion, our findings demonstrate WNT7B and possibly other Wnt ligands are essential mediators of autocrine-mediated, Wnt/β-catenin signaling in PDAC and may be the primary determinant of differential Wnt activation seen across the spectrum of PDAC tumors. Hypothetically, Wnt ligand driven signaling may prove more amenable to Wnt-directed therapy than those instances where hyperconstitutive Wnt pathway activation is driven by genetic mutations in APC, CTNNB1 or AXIN. In this regard, future work exploring the utility of Wnt-targeted therapy in PDAC will also need to focus on the development and optimization of predictive clinical markers that are able to stratify tumors more likely to respond to such therapy. This research study received initial support from a 2008 Pancreatic Cancer Action Network-AACR Career Development Award for Pancreatic Cancer Research in memory of Seena Magowitz. This critical financial support and career development opportunities provided by the Pancreatic Cancer Action Network have been invaluable to the success of my pancreatic cancer research program and have also led to significant extramural funding from the American Cancer Society in further support of the work presented here. Citation Format: Michael D. Arensman, Anne N. Kovochich, Anna R. Lay, Rima M. Kulikauskas, Andy J. Chien, David W. Dawson. Wnt7B mediates high levels of autocrine Wnt/β-catenin signaling in pancreatic adenocarcinoma. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Progress and Challenges; Jun 18-21, 2012; Lake Tahoe, NV. Philadelphia (PA): AACR; Cancer Res 2012;72(12 Suppl):Abstract nr B72. |
