Mesenchymal Stem Cells Exhibit Regulated Exocytosis in Response to Chemerin and IGF.

Mesenchymal stem cells (MSCs) play important roles in tissue repair and cancer progression. Our recent work suggests that some mesenchymal cells, notably myofibroblasts exhibit regulated exocytosis resembling that seen in neuroendocrine cells. We now report that MSCs also exhibit regulated exocytosis. Both a G-protein coupled receptor agonist, chemerin, and a receptor tyrosine kinase stimulant, IGF-II, evoked rapid increases in secretion of a marker protein, TGFßig-h3. The calcium ionophore, ionomycin, also rapidly increased secretion of TGFßig-h3 while inhibitors of translation (cycloheximide) or secretory protein transport (brefeldin A) had no effect, indicating secretion from preformed secretory vesicles. Inhibitors of the chemerin and IGF receptors specifically reduced the secretory response. Confocal microscopy of MSCs loaded with Fluo-4 revealed chemerin and IGF-II triggered intracellular Ca2+ oscillations requiring extracellular calcium. Immunocytochemistry showed co-localisation of TGFßig-h3 and MMP-2 to secretory vesicles, and transmission electron-microscopy showed dense-core secretory vesicles in proximity to the Golgi apparatus. Proteomic studies on the MSC secretome identified 64 proteins including TGFßig-h3 and MMP-2 that exhibited increased secretion in response to IGF-II treatment for 30min and western blot of selected proteins confirmed these data. Gene ontology analysis of proteins exhibiting regulated secretion indicated functions primarily associated with cell adhesion and in bioassays chemerin increased adhesion of MSCs and adhesion, proliferation and migration of myofibroblasts. Thus, MSCs exhibit regulated exocytosis that is compatible with an early role in tissue remodelling.

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

Stromal cells influence cancer progression. Myofibroblasts are an important stromal cell type, which influence the tumour 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 insulin-like growth factor (IGF) stimulation and, using functional genomic approaches, we identify proteins influencing the secretory response. IGF rapidly increased myofibroblast secretion of an ECM protein, TGFßig-h3. The secretory response was not blocked by inhibition of protein synthesis and was partially mediated by increased intracellular calcium (Ca(2+)). 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 characterized by Ca(2+)-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.