The neuroendocrine phenotype of gastric myofibroblasts and its loss with cancer progression

Abstract

Stromal cells influence cancer progression. Myofibroblasts are an important stromal cell type that influence the tumor microenvironment by release of extracellular matrix (ECM) proteins, proteases, cytokines and chemokines. The mechanisms of secretion are poorly understood. Here we describe the secretion of marker proteins in gastric cancer and control myofibroblasts in response to IGF stimulation and using functional genomic approaches identify proteins influencing the secretory response. IGF rapidly increased myofibroblast secretion of an ECM protein, TGFβig-h3. The secretory response was not blocked by inhibition of protein synthesis and was partially mediated by increased intracellular calcium. The capacity for evoked secretion was associated with the presence of dense-core secretory vesicles, and was lost in cells from patients with advanced gastric cancer. In cells responding to IGF-II, the expression of neuroendocrine marker proteins, including secretogranin-II and proenkephalin, was identified by gene array and LC-MS/MS respectively, and verified experimentally. The expression of proenkephalin was decreased in cancers from patients with advanced disease. Inhibition of secretogranin-II expression decreased the secretory response to IGF, and its over-expression recovered the secretory response consistent with a role in secretory vesicle biogenesis. We conclude that normal and some gastric cancer myofibroblasts have a neuroendocrine-like phenotype characterised by calcium-dependent regulated secretion, dense-core secretory vesicles and expression of neuroendocrine marker proteins; loss of the phenotype is associated with advanced cancer. A failure to regulate myofibroblast protein secretion may contribute to cancer progression.