Autophagy mediates resistance of pancreatic cancer cells to chemotherapy through a novel E2F1-P300-VMP1 pathway

VACCARO, M. I.; ALEJANDRO JAVIER ROPOLO; GIOVENCO, M.; CATRINACIO, C.; RENNA, F.; GRASSO, D.; BOGGIO, V.

Waashington, DC

Congreso; Digestive Disease Week; 2015

American Gastroenterological Association

Autophagy is an evolutionarily preserved degradation process of cytoplasmic cellular constituents, which participates in cell response to disease. We characterized VMP1 (Vacuole Membrane Protein 1) as an essential autophagy related-protein that mediates autophagy in pancreatic diseases. VMP1 is induced by activated K-Ras and gemcitabine treatment in human pancreatic tumor cells. Moreover, VMP1 is over-expressed in poorly differentiated human pancreatic cancer. Here we characterize a new molecular pathway, mediated by VMP1, by which gemcitabine is able to trigger autophagy in human pancreatic tumor cells. We demonstrated that gemcitabine requires VMP1 expression to induce autophagy in highly resistant pancreatic cancer cells PANC-1 carrying activated K-Ras, but not in BxPC-3 cells that do not carry K-Ras mutation. Analysis of the mechanisms identified E2F1, a transcription factor that is regulated by the retinoblastoma pathway, as an effector of gemcitabine-induced autophagy. E2F1 regulates the expression and promoter activity of VMP1. Chromatin immunoprecipitation assays demonstrated that E2F1 binds to the VMP1 promoter in PANC-1 cells. We also identified the histone acetyltransferase p300 as a modulator of this promoter activity. Our data show that the E2F1-p300 activator/co-activator complex is part of the regulatory pathway controlling the expression and promoter activity of VMP1 triggered by gemcitabine in PANC 1 cells. Finally, downregulation of VMP1 expression and pharmacological modulation of autophagy sensitize PANC-1 cells to apoptosis and diminish clonogenicity under gemcitabine treatment. Together, these data provide evidence of a transcriptional regulation mechanism of autophagy that integrates this cellular process into the complex network of events involved in PDAC chemoresistance.