Snail and Sonic Hedgehog activation in neuroendocrine tumors of the ileum

The transcription factor Snail represses E-cadherin and induces epithelial-mesenchymal transition, a process also exploited by invasive cancer cells. Aberrant Hedgehog (Hh) signaling was recently observed in a variety of epithelial cancers and it has been shown that the Hh target gene Gli1 induces expression of Snail. In this study, we examined whether Snail and Sonic Hedgehog (SHH) are expressed in neuroendocrine tumors (NETs) of the ileum. Using immunohistochemistry, we found expression of Snail in 22 out of 37 (59%) of evaluated NET samples, but not in adjacent normal tissues. Snail expression was mostly restricted to the invasive front of the tumors. Six of seven liver metastases analyzed were positive for Snail. Intratumoral expression of SHH was detected in 27 out of 37 (73%) tumors. As opposed to Snail, cells expressing SHH were found to be distributed more randomly throughout the tumors. Out of 30 primary NETs, 16 (53%) showed both Snail and SHH expression. Furthermore, we found downregulation of E-cadherin in Snail-expressing cells by immunofluorescence. Real-time RT-PCR revealed conservation of the Hh target genes Gli1, Gli2, and Ptch in the pancreatic carcinoid cell line BON-1, which were downregulated upon Hh inhibition with cyclopamine. Moreover, Hh inhibition attenuated in vitro cell growth in a dose-dependent manner. In conclusion, we describe for the first time that Snail and SHH are overexpressed in a large subset of NETs of the ileum. Aberrant activation of these pathways might be involved in invasion and metastatic spread in NETs.