Hedgehog signaling drives glial cell plasticity and oncogenic reprogramming in gastroenteropancreatic neuroendocrine neoplasms

Disruption of the Men1 locus in epithelial and endocrine tissues fails to generate the full spectrum of gastroenteropancreatic neuroendocrine tumors (GEP-NETs), raising the possibility of a potential stromal source for these cancers. Neural crest-derived glial cells were previously implicated in neuroendocrine tumors arising in the pituitary and pancreas, yet these studies lacked a clear mechanism for these events. Here, we investigated the hypothesis that Men1 -driven Hedgehog (HH) signaling redirects the glial cell fate to give rise to neuroendocrine tumors in the gastrointestinal tract. Using archived patient specimens and The Cancer Genome Atlas, we demonstrated that GEP-NETs overexpress HH pathway components, including SHH and its cognate receptor PTCH1. We showed that patient-derived pancreatic NET tumoroids proliferate in response to SHH pathway agonists. In contrast, pharmacologic inhibition of GLI1/2, but not inhibition of SMO alone, attenuated tumoroid growth. Using two genetic mouse models, we showed that loss of Men1 in GFAP ⁺ and SOX10 ⁺ glial cells causes the development of pancreatic and small intestinal NETs that overexpress HH proteins. Further use of tdTomato ⁺ mice demonstrated the involvement of GFAP ⁺ and SOX10 ⁺ glial cells in these tumors. Tumoroid cultures of mouse pancreatic and small intestinal NETs recapitulated the drug response shown by patient-derived tumoroids. Lastly, Men1 -deficient enteric glial cultures showed a glial-to-neuroendocrine transition that was alleviated upon HH inhibition, and these events were reproduced in genetic mice harboring GFAP ⁺ cells with impaired primary cilia. Our study implicates the HH signaling pathway in GEP-NET development and underscores a glial cell of origin for these tumors.