Ski promotes tumor growth through abrogation of transforming growth factor-beta signaling in pancreatic cancer.
OBJECTIVE
We hypothesized that human pancreatic cancer resists TGF-beta signaling and cell death through increased Ski expression.


BACKGROUND
Ski is an oncogenic protein that acts as a TGF-beta repressor and prevents related gene transcription. Previous work suggests that Ski acts as an oncoprotein in melanoma and esophageal cancer. Ski expression and function have not been determined in human pancreatic cancer.


METHODS
Immunohistochemistry and immunoblots assessed Ski expression in human pancreatic cancer. Panc-1 cells were treated with or without Ski siRNA, and Ski and Smad protein expression, transcriptional reporter activation, and growth assays were determined. Panc-1 cells were inoculated in the flank of nude mice and tumor volume and histology assessed after administration of Ski siRNA or control vector.


RESULTS
Ski was abundantly expressed in human pancreatic cancer specimens assessed by immunohistochemistry (91%) and immunoblot analysis (67%). Panc-1 cells exhibited nascent Ski expression that was maximally inhibited 48 hours after transfection with Ski siRNA. TGF-beta transcriptional activity was increased 2.5-fold in Ski siRNA-treated cells compared with control (P < 0.05). Ski siRNA increased TGF-beta-induced Smad2 phosphorylation and p21 expression. Panc-1 growth in culture was decreased 2-fold at 72 hours. A Ski siRNA expression vector injected into nude mice resulted in a 5-fold decrease in growth.


CONCLUSIONS
Inhibition of Ski through RNA interference restored TGF-beta signaling and growth inhibition in vitro, and decreased tumor growth in vivo.
Heider
T Ryan
TR
Department of Surgery, Division of Gastrointestinal Surgery, University of North Carolina, Chapel Hill, NC, USA.
Lyman
Suzanne
S
Schoonhoven
Robert
R
Behrns
Kevin E
KE
D000230:Adenocarcinoma / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D000818:Animals; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D018450:Disease Progression; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008819:Mice, Nude; D010190:Pancreatic Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D011379:Prognosis; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics*; D015398:Signal Transduction / Q000235:genetics*; D051785:Smad Proteins / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D016211:Transforming Growth Factor alpha / Q000235:genetics* / Q000378:metabolism
D014408:Biomarkers, Tumor; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; D034741:RNA, Small Interfering; D051785:Smad Proteins; D016211:Transforming Growth Factor alpha; C060614:SKI protein, human