A. A. Gaidarski1, N. Nagathihalli1, M. Van Saun1, N. Merchant1 1University Of Miami,Department Of Surgery,Miami, FL, USA
Introduction: Pancreatic ductal adenocarcinoma (PDAC) is extremely fatal due to its predilection for early metastasis. The hallmark of this tremendous metastatic potential is the epithelial-mesenchymal transition (EMT), signaled by loss of membranous E-cadherin expression. EMT thus represents a crucial target for PDAC therapy but remains elusive due to our poor understanding of its underlying biology. Recently, activation of the Src family of non-receptor tyrosine kinases has been implicated in tumor progression, invasion, and metastasis of PDAC. Moreover, Src has been shown to regulate E-cadherin-induced EMT. The purpose of this study was to examine the effect of Src kinase inhibition on the transcriptional regulation of E-cadherin in PDAC cells.
Methods: Drug-sensitive and -resistant PDAC cell lines were treated with dasatinib (BMS-354825) a novel, multi-targeted kinase inhibitor that targets Src family kinases. The effects of dasatinib on E-cadherin and β-catenin expression were measured by western blot and immunofluorescence for sub-cellular localization. Dasatinib-treated cells were further analyzed for mRNA expression of E-cadherin and its various transcriptional repressors. Finally, E-cadherin promoter activity was measured in both drug-sensitive and drug-resistant PDAC cell lines.
Results: Src kinase inhibition with dasatinib resulted in enhanced E-cadherin and β-catenin expression in the drug-sensitive PDAC cells (BxPC-3 and SW-1990), whereas no change was seen in the more resistant Panc-1 cells. The sensitive cell lines demonstrated an increased expression and membranous localization of E-cadherin and β-catenin upon dasatinib treatment, which was not observed in the resistant cell line. Dasatinib treatment also increased E-cadherin expression at the transcriptional level with a concomitant decrease in the expression of the EMT-associated transcription factor Slug but not LEF-1, ZEB or Snail. Repression of Slug further correlated with an increase in the E-cadherin promoter activity in the sensitive cell lines.
Conclusion: This study elucidates a novel pathway of epithelial-mesenchymal transition in PDAC. In certain populations, Src activation induces the transcription factor Slug, leading to the repression of E-cadherin, precipitating EMT. Dasatinib, a Src-inhibitor, reverses this process and reverts cells back to an epithelial phenotype. Hence, we identify Src as a potential therapeutic target in PDAC and distinguish resistant tumors as those that can upregulate Slug in the face of Src repression.