The development of an altered stromal microenvironment is a common feature of many tumours including squamous cell carcinoma (SCC), and there is increasing evidence that these changes in the stroma, which include increased expression of proteases and cytokines, may actually promote tumour progression. A common finding is that stromal fibroblasts become ‘activated’ myofibroblasts, expressing smooth muscle actin and secreting cytokines, proteases and matrix proteins. We show that myofibroblasts are commonly found in the stroma of oral SCC and are often concentrated at the invasive margin of the tumour. Using oral SCC cells and primary oral fibroblasts, we demonstrate that tumour cells directly induce a myofibroblastic phenotype, and that this transdifferentiation is dependent on SCC-derived TGF-?1. In turn, myofibroblasts secrete significantly higher levels of hepatocyte growth factor/scatter factor compared with fibroblast controls, and this cytokine promotes SCC invasion through Matrigel, a mixture of basement membrane proteins. This is the first time that this double paracrine mechanism has been demonstrated between squamous carcinoma cells and fibroblasts, and emphasises that cancer invasion can be promoted indirectly by the release of tumour-induced host factors from stroma
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