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Oncogenic Raf1 induces epithelial cell transformation by activating Slug and suppressing Occludin promoter activity
Author(s) -
Wang Zili,
Mrsny Randall,
Wade Paul,
Nusrat Asma
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a201
Subject(s) - occludin , slug , microbiology and biotechnology , gene knockdown , transcription factor , epithelial–mesenchymal transition , downregulation and upregulation , tight junction , transfection , transactivation , biology , cell culture , cancer research , chemistry , gene , biochemistry , genetics
The apical junctional complex (AJC) is important in regulating epithelial intercellular adhesion. Disruption of the AJC with the loss of concomitant junctional protein expression is a hallmark of cancer cell invasion. Activation of the Ras‐Raf signaling pathway has been implicated in some epithelial cancers. Thus, our studies examined mechanisms by which Raf‐1 induces epithelial mesenchymal transition (EMT) and oncogenic transformation. Using a rat salivary gland epithelial cell line (Pa4), we have previously demonstrated that constitutive expression of the Raf‐1 oncogene in Pa4 cells disrupts functional AJC and induces oncogenic transformation by downregulating occludin expression. To better characterize the mechanism by which Raf‐1 influences occludin expression and EMT, we analyzed the influence of Raf‐1 on occludin promoter activity. A 1853 bp fragement of the occludin promoter was isolated and a series of deletion constructs were generated. Transfection of these constructs into Raf‐1 transformed cells revealed that the minimal Occludin promoter segment (−50/+240) was repressed by Raf‐1. Oncogenic Raf‐1 induced upregulation of the transcription repressor Slug with subsequent down regulation of occludin. These events correlated with epithelial cell transformation. Interestingly, in contrast to other studies analyzing EMT, E‐cadherin expression remained unchanged. Knockdown of Slug in Raf‐1 transformed cells induced occludin expression and transition to an epithelial phenotype. These findings support a role of Slug in mediating Raf‐1 induced suppression of occludin and subsequent EMT.