Expression of Cathepsin B by tumour-associated oral fibroblasts
There is substantial evidence to suggest that the underlying stroma has a significant role to play in the local invasion of cancer cells and that the neoplastic state is associated with an activated stromal phenotype. Furthermore, it seems likely that proteases, such as cysteine proteases and matrix metalloproteinases (MMPs), secreted into the extracellular matrix aid invasion by breaking down extracellular matrix components. Objectives: The aim of this study was to investigate regulation of the expression of the cysteine protease, cathepsin B, by oral fibroblasts, and to investigate the roles of cathepsin B and MMPs in oral cancer invasion. Methods: Fibroblasts and TGF-β-induced myofibroblasts were treated with TGF-β, IL-1α and IL-1β and a fluorogenic assay employed to investigate cathepsin B expression levels. Detection of the isoforms of cathepsin B was performed by Western blotting. The roles of cathepsin B and MMPs in the invasion of oral cancer cells were determined using specific inhibitors in organotypic models of tumour invasion. Results: TGF-β induced a temporary myofibroblastic phenotype, indicative of tumour-associated stromal fibroblasts. All Cathepsin B activity in fibroblast cultures was detected in the cell layer, with no activity in the medium fraction. IL-1α significantly increased cathepsin B production by myofibroblasts. A novel cysteine protease (103kDa) was detected in fibroblast cultures. Inhibition of cysteine protease activity had no effect on tumour cell invasion in organotypic models, whereas inhibition of MMP activity resulted in the significant inhibition of invasion. Conclusion:The retention of cathepsin B proteolytic activity within fibroblast cells may explain the lack of effect of this protease on tumour cell invasion.