Balabanova, Silviya (2012) The neuroendocrine-like phenotype of gastric myofibroblasts and its significance in cancer. Doctoral thesis, University of Liverpool.
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Cell-cell communication, and specifically epithelial-mesenchymal signalling, is a key factor determining normal tissue development and organisation in hollow organs such as gastrointestinal tract. Mechanisms governing normal epithelial-mesenchymal communication have been studied for many years, but the changes occurring during tissue damage, infection and inflammation, and in cancer, remain unclear. Myofibroblasts are recognised as key mesenchymal cells involved in this communication in health and in disease. Myofibroblasts produce and secrete many proteins responsible for the assembly of extracellular matrix (ECM), tissue organisation and morphogenesis. Initial studies from this laboratory suggested that myofibroblasts might exhibit regulated secretion. The aim of this project was to determine the secretory mechanisms of myofibroblasts from the upper gut of normal and cancer tissues, and to address their significance in cancer. Gastric myofibroblasts were shown to exhibit calcium-dependent secretion of the small ECM protein, Transforming growth factor-β inducible protein or TGFβig-h3, in response to acute stimulation (30 min) with insulin-like growth factor (IGF)s. Inhibitors of protein synthesis (actinomycin D and cycloheximide) and of protein transport from endoplasmic reticulum (ER) to Golgi (brefeldin A) inhibited basal, but not IGF-stimulated secretion, as seen from Western blot analyses of media. These observations support the idea that evoked secretion occurs from a pre-formed pool of vesicles. Myofibroblasts from the upper gut showed differences in their secretory phenotype; specifically normal myofibroblasts from stomach exhibited regulated secretion, but their counterparts from oesophagus did not. Moreover, gastric cancer-associated myofibroblasts (CAMs) from patients with poor survival tend not to exhibit regulated secretion. These findings suggest a role for the tissue microenvironment in determining the secretory phenotype of myofibroblasts. Secretome-wide analysis of myofibroblasts media collected after IGF stimulation revealed that about 85% of the secretome exhibits evoked release. The relevant proteins belonged to different classes including ECM proteins, ligands, binding proteins, carbohydrate-binding proteins, proteases and protease inhibitors. These data indicate that myofibroblasts may contribute to tissue organisation by rapid release of substances involved in re-modelling the tissue microenvironment. The regulated secretory phenotype of myofibroblasts was associated with the expression of the chromogranin-like protein, secretogranin II. Knock-down of secretogranin II inhibited regulated secretion, whereas over-expression in myofibroblasts that lacked regulated released - induced it. Expression of secretogranin II by myofibroblasts coincided with the expression of dense core secretory vesicles that were similar to those found in neuroendocrine cells. This work indicates that there is a neuroendocrine-like secretory phenotype in myofibroblasts, as illustrated by the expression of neuroendocrine cell protein secretogranin II and the presence of regulated secretion. However, not all normal myofibroblasts exhibit the regulated phenotype, and in gastric cancer the phenotype correlates with early stage of disease. These findings may be exploitable both in the development of novel therapies and in understanding cancer progression.
|Item Type:||Thesis (Doctoral)|
|Uncontrolled Keywords:||myofibroblasts, tumour microenvironment, regulated secretion|
|Departments, Research Centres and Related Units:||Academic Faculties, Institutes and Research Centres > Faculty of Medicine > School of Biomedical Sciences|
|Deposited On:||06 Aug 2012 10:38|
|Last Modified:||06 Aug 2012 10:38|
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