The tumor suppressor KLF11 mediates a novel mechanism in transforming growth factor beta-induced growth inhibition that is inactivated in pancreatic cancer.
c-myc promoter silencing is a key step in epithelial cell growth inhibition by transforming growth factor beta (TGFbeta). During carcinogenesis, however, epithelial cells escape from c-myc repression and consequently become refractory to TGFbeta-mediated antiproliferation. Here, we assessed the role of the repressor, KLF11, in TGFbeta-induced growth inhibition in normal epithelial as well as pancreatic carcinoma cells. Endogenous KLF11 was stably down-regulated by RNA interference technology, and the functional consequences were studied by proliferation assays, reporter assays, DNA binding studies, and expression analyses. Coimmunoprecipitation and glutathione S-transferase pulldown assays were conducted to define KLF11-Smad3 interaction and U0126 was administered to examine the effects of the extracellular signal-regulated kinase (ERK)-mitogen-activated protein kinase on complex formation and c-myc promoter binding of KLF11 and Smad3 in pancreatic cancer cells. In TGFbeta-stimulated normal epithelial cells, nuclear KLF11, in concert with Smad3, binds to and represses transcription from the core region of the TGFbeta-inhibitory element (TIE) of the c-myc promoter. Disruption of KLF11-Smad3 interaction or small interfering RNA-mediated knockdown of endogenous KLF11 strongly diminishes Smad3-TIE promoter binding and repression, and consequently impairs TGFbeta-mediated growth inhibition. In pancreatic cancer cells with oncogenic Ras mutations, hyperactive ERK counteracts TGFbeta-induced c-myc repression and growth inhibition through at least two mechanisms, i.e., via disruption of KLF11-Smad3 complex formation and through inhibition of KLF11-Smad3 binding to the TIE element. Together, these results suggest a central role for KLF11 in TGFbeta-induced c-myc repression and antiproliferation and identifies a novel mechanism through which ERK signaling antagonizes the tumor suppressor activities of TGFbeta in pancreatic cancer cells with oncogenic Ras mutations.
Buck
Anita
A
Department of Internal Medicine I, University of Ulm, Germany.
Buchholz
Malte
M
Wagner
Martin
M
Adler
Guido
G
Gress
Thomas
T
Ellenrieder
Volker
V
D051017:Apoptosis Regulatory Proteins; D001483:Base Sequence; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D049109:Cell Proliferation; D015536:Down-Regulation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D010190:Pancreatic Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics*; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D020218:Response Elements; D051900:Smad3 Protein / Q000378:metabolism; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*
D051017:Apoptosis Regulatory Proteins; D018797:Cell Cycle Proteins; C115117:KLF11 protein, human; C489427:MYC protein, human; D016271:Proto-Oncogene Proteins c-myc; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; D025521:Tumor Suppressor Proteins; D048049:Extracellular Signal-Regulated MAP Kinases