Abstract 2438: BAMBI Is overexpressed in metastatic pancreatic cancers with genetically Intact TGF-β pathways: A potential mechanism to escape TGF-β signaling during metastasis formation

Abstract

Abstract Introduction: Pancreatic cancer remains a largely fatal disease, with an estimated 95% of patients succumbing within five years of initial diagnosis, many by metastatic spread. We have previously shown that genetic inactivation of DPC4, a central mediator of TGF-β signaling, is strongly associated with widespread metastasis in pancreatic cancer patients at autopsy. However, because some patients with metastatic pancreatic cancer do not have genetic inactivation of DPC4 or other TGF-β members, we investigated the role of alternative mechanisms of TGF-β pathway inactivation in promoting pancreatic cancer metastasis. Methods: Eighteen cell lines that underwent whole exome sequencing in association with the pancreatic cancer genome project or directed sequencing of all members of the TGF-β pathway were used. TGF-β signaling levels were analyzed in each cell line using a luciferase reporter system under the control of a Smad Binding Element (SBE). Quantitative real-time PCR was performed using cDNA from representative cell lines to assess expression levels of nine known TGF-β pathway antagonists; data were analyzed using the ΔΔCt method with normalization to β-actin. Immunohistochemistry was performed on pancreatic cancer tissue microarrays that included 27 matched pairs of primary and metastatic cancer. Staining intensity and protein localization were analyzed in relation to DPC4 status as well as clinicopathologic data. Results: Functional TGF-β signaling was completely abolished in cell lines with known DPC4 inactivation compared to normal controls, and was also decreased in cell lines with an intact TGF-β pathway, to a lesser extent. Quantitative RT-PCR of known TGF-β antagonists in cell lines with genetically intact TGF-β pathways revealed 50-fold overexpression of BMP and Activin Membrane-Bound Inhibitor (BAMBI) in two of seven cell lines (29%). Immunolabeling for BAMBI in human pancreatic cancer tissues indicated that it is highly expressed in a subset (26%) of pancreatic cancers, consistent with the cell line data. BAMBI overexpression was not associated with clinicopathologic features at diagnosis, nor was there a difference in BAMBI expression among DPC4 wild type versus DPC4 inactive carcinomas. However, specifically, BAMBI overexpression was significantly more frequent in metastases from patients with wild type DPC4 compared to those with inactivated DPC4 (p=0.01). Conclusion: Overexpression of BAMBI occurs at an appreciable level in pancreatic cancer cell lines and tissues, and may promote metastasis in the presence of a genetically intact TGF-β pathway. Mechanistic studies are ongoing to clarify the role of BAMBI in pancreatic cancer metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2438. doi:10.1158/1538-7445.AM2011-2438