RUNX3 inhibits cell proliferation and induces apoptosis by reinstating transforming growth factor beta responsiveness in esophageal adenocarcinoma cells.
BACKGROUND
SEG-1, a Barrett's-derived esophageal adenocarcinoma cell line, is not responsive to transforming growth factor beta (TGF-beta) growth effects. We hypothesize that SEG-1 cells lack the tumor-suppressor gene Runt domain transcription factor 3 (RUNX3) and that its reinstatement can restore the antiproliferative and apoptotic effects of TGF-beta.


METHODS
RUNX3 expression was assessed by immunoblotting. SEG-1 cells were transfected with RUNX3 and treated with TGF-beta. The effects of RUNX3 transfection on cell proliferation and apoptosis were determined. Smad-mediated TGF-beta transcriptional activity was evaluated with the use of dual-luciferase assay.


RESULTS
SEG-1 cells are not responsive to TGF-beta. SEG-1 cells lack RUNX3 protein expression, while RUNX3 is highly expressed in normal human gastric and esophageal epithelium. Although the Smad-2 signaling is activated by TGF-beta, SEG-1 cells lack Smad-mediated TGF-beta transcriptional activity. In cells transfected with RUNX3, TGF-beta acquired an antiproliferative effect and induced apoptosis (P = .001). RUNX3 transfection, in the absence of TGF-beta, had no effect on proliferation and apoptosis of SEG-1 cells. RUNX3 expression dramatically increases SMAD-mediated TGF-beta-induced transcriptional activity when compared with controls (P = .0001).


CONCLUSIONS
RUNX3 is not expressed in SEG-1 cells, while it is present in normal esophageal mucosa. RUNX3 is essential for the antiproliferative and apoptotic effects of TGF-beta in SEG-1 cells and for the Smad-mediated transcriptional activity of TGF-beta.
Torquati
Alfonso
A
Department of Surgery, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
O'rear
Lynda
L
Longobardi
Lara
L
Spagnoli
Anna
A
Richards
William O
WO
Daniel Beauchamp
R
R
D000230:Adenocarcinoma / Q000473:pathology* / Q000628:therapy; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D019556:COS Cells; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D050677:Core Binding Factor Alpha 3 Subunit; D004268:DNA-Binding Proteins / Q000032:analysis / Q000502:physiology*; D004938:Esophageal Neoplasms / Q000473:pathology* / Q000628:therapy; D006801:Humans; D014157:Transcription Factors / Q000032:analysis / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D050677:Core Binding Factor Alpha 3 Subunit; D004268:DNA-Binding Proteins; C493729:Runx3 protein, human; D014157:Transcription Factors; D016212:Transforming Growth Factor beta