Ski overexpression impairs TGF-B signaling and results in loss of growth control in human pancreatic cancer

Abstract Introduction: Ski is an oncogenic protein that binds to and inhibits the TGF-B signaling proteins, Smad 2/3, and thereby prevents gene transcription. We hypothesized that human pancreatic cancer resists TGF-B signaling through Ski overexpression. Methods: Immunohistochemistry and western blots confirmed Ski overexpression in human pancreatic cancer. In vitro experiments assessed Ski function in Panc-1 cells by TGF-B-induced transcriptional reporter activation and growth assays in the presence of control or Ski short interfering RNAs (siRNA). Panc-1 cells were inoculated in the flank of nude mice and tumor volume measured after Ski siRNA vector or control administration. Results: Ski overexpression was detected in human pancreatic cancer specimens by immunohistochemistry (91%) and immmunoblot (67%), and in Panc-1 cells. In vitro, Ski siRNA maximally inhibited protein levels 48 hours after transfection, and TGF-B transcriptional activity was increased 2-fold compared to control siRNA treated cells (p Conclusions: Human pancreatic cancers overexpress Ski. Inhibition of Ski through RNA interference restored TGF-B signaling and growth inhibition in vitro and decreased tumor growth in vivo. These findings support a role for Ski as a suppressor of TGF-B signaling in pancreatic cancer.