Hedgehog Signaling Drives Cellular Survival in Human Colon Carcinoma Cells

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 PDGFRa, 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 PDGFRa 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. Cancer Res; 71(3); 1092-102. Ó2010 AACR.

Intermedin is overexpressed in hepatocellular carcinoma and regulates cell proliferation and survival

“…(26,27) As shown in Figure 3(D), phosphorylated Erk was increased after addition of IMD active peptide to SKHep-1 cells. This Erk activation by IMD was completely blocked when cells were pre-incubated with U0126 (Fig.…”

“…Consequently, it is likely that IMD increases HCC cell growth by preventing tumor cells from undergoing apoptotic pathways through regulation of the Hedgehog pathway, which transcriptionally controls Bcl2 expression. (26) Our finding regarding inhibition of IMDinduced apoptosis is particularly important because the progression of HCC is marked by its ability to escape programmed cell death. (30) We summarize our results in Figure 5, proposing that IMD not only regulates HCC proliferation but also influences cell survival through Gli1 and Bcl2.…”

“…(29) Galmiche et al (2010) report that Bcl2 family member BAD is a key regulator of apoptosis in HCC (30) Bcl2 expression is regulated by the glioma-associated oncogene 1 (Gli1) transcription factor, which plays an important role in HCC invasion and metastasis by inducing not only Bcl2 but also E-cadherin. (26,28) Gli1 was found to be upregulated in HCC tissues and closely correlated with clinicopathological characteristics. (28) It has been shown that blocking Gli1 inhibits heptoblastoma growth.…”

The Utility of Hedgehog Signaling Pathway Inhibition for Cancer

“…The use of this agent resulted in significant cell death across five different human colon carcinoma cell lines and was found to be more potent than cyclopamine [83]. Significant anti-tumor activity of GANT61 has been also noted in prostate cancer human xenografts [84].…”

GPCRs and cancer

“…Recently, a number of Hh pathway antagonists targeting Smo mutants [72] as well as inhibitors able to block both wild-type and Smo mutants have been identified [73] . In addition to Smo antagonists, other inhibitors were used to block Hh signaling like the small molecule inhibitor of GLI1 and GLI2 transcription factors, GANT61, which induced colon carcinoma cell death in a higher extent respect to the conventional Smo inhibitor cyclopamin [74] . The treatment with GANT61 reduced also the expression of the target gene Patched and decreased the viability of chronic lymphocytic leukemia cells [75] .…”