Characterization of sonic hedgehog as a novel NF‐κB target gene that promotes NF‐κB‐mediated apoptosis resistance and tumor growth in vivo

Abstract

To explore mechanisms controlling sonic hedgehog (Shh) expression in human cancers, we investigated regulation of Shh by the transcription factor NF-kappaB. We identify putative NF-kappaB binding sites in the human Shh promoter region that specifically bind NF-kappaB complexes. Further, NF-kappaB activation by tumor necrosis factor alpha (TNF-alpha) or p65 overexpression stimulates Shh promoter activity and p65 binds to Shh promoter in vivo. NF-kappaB-mediated transcriptional activation of Shh is mapped to a minimal NF-kappaB consensus site at position +139 of Shh promoter. NF-kappaB activation results in increased Shh mRNA and protein expression in vitro and, notably, also in vivo in a genetic mouse model of inducible NF-kappaB activity. Specific NF-kappaB inhibition by inhibitory NF-kappaBalpha (Ikappa-Balpha) superrepressor or p65 knockdown inhibits NF-kappaB-induced Shh promoter activation and Shh expression. NF-kappaB-mediated Shh expression promotes proliferation and confers resistance to TRAIL-induced apoptosis. Silencing of Shh prevents NF-kappaB-stimulated proliferation, while the addition of Shh rescues the proliferation defect imposed by NF-kappaB inhibition. Notably, NF-kappaB-stimulated tumor growth is significantly impaired by Shh knockdown in an in vivo model of pancreatic cancer. By demonstrating that NF-kappaB regulates Shh expression, which contributes to NF-kappaB-mediated proliferation and apoptosis resistance in vitro and in vivo, our findings have important implications to target aberrant Shh expression in human cancers.

Activation of the hedgehog-signaling pathway in human cancer and the clinical implications

“…In several cases, the regulation mechanism is known. Koga et al, 2008;Kasperczyk et al, 2009). Expression of Gli1 is reported to be regulated by TGFb, Ras, JUN, SCL/TAL1 and EWS-FLI1 oncoprotein (Ji et al, 2007;Kasai et al, 2008;Zwerner et al, 2008;Beauchamp et al, 2009;Laner-Plamberger et al, 2009;NolanStevaux et al, 2009).…”

Inhibition of smoothened decreases proliferation of synoviocytes in rheumatoid arthritis

“…Studies have shown that tumor-necrosis factor-alpha (TNF-a) and interleukin-6 (IL-6) can upregulate Shh expression and promote cell proliferation, contributing to tumor growth. 17,18 Suppression of Shh signaling by pharmacologically targeting the Smo receptor resulted in downregulation of TNF-a and IL1b mRNA expression in cholestatic rat liver. 19 Heller et al…”

Hedgehog signaling pathway as a therapeutic target in various types of cancer

“…Kasperczyk et al (41) demonstrated that the expression of transcription factors nuclear factorjB (NF-jB) and Shh was closely related and that Shh activated through NF-jB pathway activation contributed to the proliferation of pancreatic cancer and resistance to TNF related apoptosis inducing ligand (TRAIL)-induced apoptosis by analyzing Shh promoter activation. Hedgehog signaling activation in cancer tissue has also been demonstrated in breast cancer.…”

“…This result indicates that Hh signaling can suppress Wnt signaling and that Hh signaling might be implicated in colon cancer. Recently, many researchers have demonstrated crosstalk between the Hh signaling pathway and other pathways, including the NF-jB, (41) ERa, (43) KRAS, (57) PI3k-AKT, (58) EWS ⁄ FLI1, (59) PKC-delta (60) and p53 (61) pathways (Fig. 3).…”