KLF11 mediates a critical mechanism in TGF-beta signaling that is inactivated by Erk-MAPK in pancreatic cancer cells.
OBJECTIVE
Smad-regulated transcription plays a central role in transforming growth factor (TGF)-beta-induced cell growth inhibition and tumor suppression. Like the Smads, KLF11 is an early response transcription factor that mediates TGF-beta-induced growth inhibition in untransformed epithelial cells. Here, we investigated the functional implications of KLF11 in TGF-beta signaling and transcription in normal epithelial as well as pancreatic cancer cells.


METHODS
The effects of KLF11 on TGF-beta signaling and transcription were examined on the levels of reporter transactivation, Smad2 phosphorylation, and expression of endogenous TGF-beta-regulated genes. Promoter analysis, real-time polymerase chain reaction, and coimmunoprecipitation studies were performed to study KLF11-induced and mSin3A corepressor-mediated repression of Smad7. Erk-induced KLF11 phosphorylation was examined in vitro and in vivo, and its impact on KLF11-mSin3A-mediated Smad7 repression was verified in pancreatic cancer cells using site-directed mutagenesis.


RESULTS
KLF11 potentiates TGF-beta signaling by terminating the inhibitory Smad7 loop. Mechanistically, KLF11 represses TGF-beta-induced transcription from the Smad7 promoter by recruiting mSin3a via GC-rich sites. This function is inhibited in pancreatic cancer cells with oncogenic Ras mutations, in which Erk/mitogen-activated protein kinase phosphorylates KLF11, leading to disruption of KLF11-mSin3a interaction. Expression of an Erk-insensitive KLF11 mutant restores both mSin3a binding and Smad7 repression and results in enhanced TGF-beta signaling in pancreatic cancer cells.


CONCLUSIONS
These results define a novel mechanism in TGF-beta-regulated gene expression. KLF11 potentiates Smad-signaling activity in normal epithelial cells through termination of the negative feedback loop imposed by Smad7. The fact that this function of KLF11 is inhibited by oncogenic Erk/mitogen-activated protein kinase in pancreatic cancer cells emphasizes the importance of this mechanism for oncogenesis.
Ellenrieder
Volker
V
Department of Internal Medicine, University of Ulm, Germany. volker.ellenrieder@medizin.uni-ulm.de
Buck
Anita
A
Harth
Ana
A
Jungert
Kerstin
K
Buchholz
Malte
M
Adler
Guido
G
Urrutia
Raul
R
Gress
Thomas M
TM
D000818:Animals; D051017:Apoptosis Regulatory Proteins; D016466:CHO Cells; D019556:COS Cells; D021441:Carcinoma, Pancreatic Ductal / Q000378:metabolism* / Q000503:physiopathology; D018797:Cell Cycle Proteins; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology; D020862:GC Rich Sequence; D015972:Gene Expression Regulation, Neoplastic; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism* / Q000494:pharmacology; D010190:Pancreatic Neoplasms / Q000378:metabolism* / Q000503:physiopathology; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000378:metabolism; D056264:Sin3 Histone Deacetylase and Corepressor Complex; D051899:Smad2 Protein; D051906:Smad7 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism* / Q000494:pharmacology; D014158:Transcription, Genetic / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000378:metabolism* / Q000494:pharmacology; D018631:ras Proteins / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C115117:KLF11 protein, human; D009687:Nuclear Proteins; D012097:Repressor Proteins; C099683:SIN3A transcription factor; D051899:Smad2 Protein; D051906:Smad7 Protein; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D020928:Mitogen-Activated Protein Kinases; D056264:Sin3 Histone Deacetylase and Corepressor Complex; D018631:ras Proteins