Article

Hedgehog signaling drives cellular survival in human colon carcinoma cells.

Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195, USA.
Cancer Research (impact factor: 7.86). 02/2011; 71(3):1092-102. DOI:10.1158/0008-5472.CAN-10-2315 pp.1092-102
Source: PubMed

ABSTRACT Aberrant activation of Hedgehog (HH) signaling is implicated in many human cancers. Classical HH signaling is characterized by Smoothened (Smo)-dependent activation of Gli1 and Gli2, which transcriptionally regulate target genes. A small molecule inhibitor of Gli1 and Gli2, GANT61, was used to block HH signaling in human colon carcinoma cell lines that express HH signaling components. GANT61 administration induced robust cytotoxicity in 5 of 6 cell lines and moderate cytotoxicity in the remaining 1 cell line. In comparison, the classical Smo inhibitor, cyclopamine, induced modest cytotoxicity. Further, GANT61 treatment abolished the clonogenicity of all six human colon carcinoma cell lines. Analysis of the molecular mechanisms of GANT61-induced cytotoxicity in HT29 cells showed increased Fas expression and decreased expression of PDGFRα, which also regulates Fas. Furthermore, DR5 expression was increased whereas Bcl-2 (direct target of Gli2) was downregulated following GANT61 treatment. Suppression of Gli1 by shRNA mimicked the changes in gene expression observed in GANT61-treated cells. Overexpression of dominant-negative FADD (to abrogate Fas/DR5-mediated death receptor signaling) and/or Bcl-2 (to block mitochondria-mediated apoptosis) partially rescued GANT61-induced cytotoxicity in HT29 cells. Thus, activated GLI genes repress DR5 and Fas expressions while upregulating Bcl-2 and PDGFRα expressions to inhibit Fas and facilitate cell survival. Collectively, these results highlight the importance of Gli activation downstream of Smo as a therapeutic target in models of human colon carcinoma.

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Keywords

6 cell lines
 
block HH signaling
 
block mitochondria-mediated apoptosis
 
Classical HH signaling
 
classical Smo inhibitor
 
express HH signaling components
 
GANT61 administration induced robust cytotoxicity
 
GANT61-induced cytotoxicity
 
GANT61-treated cells
 
Gli activation downstream
 
HT29 cells
 
human cancers
 
human colon carcinoma
 
human colon carcinoma cell lines
 
induced modest cytotoxicity
 
moderate cytotoxicity
 
remaining 1 cell line
 
shRNA mimicked
 
small molecule inhibitor
 
target genes