M. A. Alvarez1, S. M. Husain1, P. V. Dickson1,2, J. L. Deneve1,2, D. Shibata1,2, K. W. Freeman1, E. S. Glazer1,2 1University of Tennessee Health Science Center,General Surgery,Memphis, TN, USA 2UT West Cancer Center,Memphis, TN, USA
Introduction: The loss of the tumor suppressor gene ARID1a is correlated with worse oncologic outcomes in a variety of malignancies. In pancreatic ductal adenocarcinoma (PDAC), decreased ARID1a expression has been associated with increased tumor size and worse cellular differentiation. TGF-β has paradoxical functions and can be either tumor promotive or suppressive depending on disease stage. There is little data, however, on the interaction of TGF-β and ARID1a in PDAC. We hypothesize that loss of ARID1a expression in PDAC is modulated by TGF- β and is associated with decreased survival.
Methods: The Cancer Genome Atlas (TCGA) data set was used to investigate 165 unique patients with PDAC and greater than 1-day follow-up. Patients were divided into top, median and bottom quartiles based on the level of ARID1a gene expression. Survival trends were analyzed between the three groups using Wilcoxon test. In order to investigate the effects of TGF- β on ARID1a expression, Panc-1 cells (derived from primary PDAC), gemcitabine-resistant Panc-1 cells (selected by gemcitabine exposure), or Capan-1 cells (derived from metastatic PDAC) were treated with recombinant TGF- β (10 ng/mL) vs. PBS control. Cells were treated twice over 1 week with pre- and post-treatment assessments of ARID1a protein expression by Western Blot analysis.
Results: In our TCGA analysis, patients with low ARID1a expression had the shortest median survival (MS;15.8 months), whereas those with high expression had the longest MS (23.2 months), and patients with median expression demonstrated an intermediate MS (20 months, p=0.01). In our in vitro studies, ARID1a protein expression was lowest in Capan-1 cells, highest in the Panc-1 cells, and intermediate in the gemcitabine-resistant Panc-1 cells. TGF-β treatment resulted in reduced expression of ARID1a in gemcitabine-resistant Panc-1 cells and Capan-1 cells, but not in normal Panc-1 cells.
Conclusion: High expression of ARID1a, a known tumor suppressor gene was associated with a survival advantage in PDAC patients. We have demonstrated that TGF-β downregulates ARID1a in metastatic and gemcitabine-resistant PDAC cells, but not in untreated Panc-1 cells. Our data suggest that regulation of ARID1a may contribute to the oncogenic effects of TGF-β in drug resistant and metastatic PDAC. Further work will investigate the mechanistic connection between TGF-β and ARID1a to identify potential future therapeutic targets.
