Indian hedgehog signaling pathway: Expression and regulation in pancreatic cancer

Pancreatic cancer is an aggressive malignancy that exhibits a number of genetic and epigenetic alterations. Indian hedgehog (Ihh) and its 2 signaling receptors, patched (Ptc) and smoothened (Smo), are involved in pancreatic development and regulation of β-cell function as well as in certain human tumors. In the current study, we analyzed the expression, distribution and function of Ihh and its receptors in pancreatic cancer. Quantitative RT-PCR and immunohistochemistry were utilized to analyze the expression, localization and transcriptional regulation of Ihh, Ptc and Smo. The effects of inhibition and stimulation of the hedgehog signaling pathway on pancreatic cancer cell growth were examined by the MTT cell growth assay. By quantitative RT-PCR, Ihh, Ptc and Smo mRNA levels were increased 35-, 1.2- and 1.6-fold, respectively, in pancreatic cancer tissues in comparison to normal pancreatic tissues. By immunohistochemistry, Ihh, Ptc and Smo were expressed in the islet cells of normal and cancerous tissues and in pancreatic cancer cells. The growth of pancreatic cancer cells was dose-dependently inhibited by the hedgehog antagonist cyclopamine through G₀/G₁ arrest. In contrast, Ihh agonists exhibited no significant effect on pancreatic cancer cell growth. TGF-β1 repressed Ihh transcription in a TGF-β1-responsive pancreatic cancer cell line, but had no effect on the other tested cell lines. In conclusion, Ihh and its receptors Ptc and Smo are expressed in pancreatic cancer, and blockage of hedgehog signaling results in inhibition of pancreatic cancer cell growth, suggesting that aberrant activation of the Ihh signaling pathway contributes to tumor development in this malignancy.