Abstract B88: Decreased expression of Disabled-2 correlates with epithelial-to-mesenchymal transition in pancreatic cancer.

Background: As the fourth leading cause of cancer deaths in the United States, pancreatic cancer is one of the most lethal forms of cancer diagnosed. Despite advances in understanding the underlying mechanisms driving disease progression, median survival time following diagnosis remains < 6 months, with a five-year survival rate of only 3-5%. Part of this is due to the rapid metastasis of pancreatic cancer to the lymphatic system, as well as other organs such as the liver and lungs. Metastatic tumor cells are characterized by acquisition of migratory and invasive properties; properties shared by cells which have undergone epithelial-to-mesenchymal transition, or EMT. Disabled-2 (Dab2) is a putative tumor suppressor whose expression has been shown to be downregulated in several cancer types; however, its role in pancreatic cancer progression is unknown. We have previously shown that loss of Dab2 expression promotes EMT in normal mammary epithelial cells. The present study investigates the hypothesis that loss of Dab2 expression correlates with EMT in pancreatic cancer. This was addressed by investigating the expression of Dab2 and EMT markers in human pancreatic cancer cell lines and tumor samples. Epigenetic regulation of Dab2 expression was also examined. Methods: Dab2 and EMT marker expression was determined by qRT-PCR analysis in human pancreatic cancer cell lines, normal pancreatic tissue and pancreatic cancer stage I, II, III, and metastatic tumors. Using shRNA-mediated technology, Dab2 expression was stably downregulated in two pancreatic cancer cell lines. These cells were characterized for expression of EMT markers by qRT-PCR and Western analysis. Methylation of Dab2 exon 1 was determined by methylation specific PCR in the pancreatic cancer cell lines and tumor samples. Results: In pancreatic cancer cell lines, decreased expression of Dab2 was associated with decreased expression of Ecadherin and increased expression of EMT-associated genes. Targeted downregulation of Dab2 expression in Colo357 and Hs766T cells led to the upregulation of EMT-associated genes. Decreased expression of Dab2 was observed in human pancreatic tumors in comparison to normal pancreatic tissue. This decrease was observed as early as stage I and maintained throughout progression to metastasis. We also observed decreased expression of Ecadherin in all stages of pancreatic cancer, with stage I exhibiting the lowest level of expression. Methylation of exon 1 of the Dab2 gene was observed in 60% of stage I tumors (3/5) while methylation in all other stages was infrequent (1/13). The pancreatic cancer cell line MiaPaCa2 exhibited Dab2 promoter methylation which could be reversed with 5-azacytidine treatment. Conclusion: Targeted downregulation of Dab2 in pancreatic cancer cell lines leads to increased expression of EMT-associated genes. In addition, decreased expression of Dab2, which occurs early in pancreatic cancer progression, is temporally correlated with loss of Ecadherin expression in human pancreatic tumor samples. Together, these results suggest that loss of Dab2 expression in the pancreas may facilitate EMT and therefore increase the propensity for metastasis. Citation Format: Barbara A. Hocevar. Decreased expression of Disabled-2 correlates with epithelial-to-mesenchymal transition in pancreatic cancer. [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 B88.