The Met-HGF/SF autocrine signaling mechanism is involved in sarcomagenesis

Hepatocyte growth factor/scatter factor (HGF/SF) can elicit a wide variety of effects upon cells expressing its receptor, the tyrosine kinase proto-oncogene product Met, including mitogenicity, motility, and morphogenesis. Normally, met expression is restricted to epithelial cells and is activated in a paracrine fashion by HGF/SF secreted from cells of mesenchymal origin. In this chapter, we review data showing that: (i) met over-expression in HGF/SF-expressing NIH/3T3 fibroblasts leads to sarcomagenesis and metastasis via an autocrine mechanism; (ii) Met-HGF/SF autocrine signalling occurs to a low level in normal fibroblasts and to a much greater extent in human sarcomas and sarcoma cell lines; (iii) met expression is enhanced as p53-deficient fibroblasts are passaged in vitro and (iv) met and HGF/SF over-expression are selected for during tumorigenesis of p53-deficient late-passage fibroblasts. Thus, loss of p53 predisposes a mesenchymal cell to over-express met and high level Met-HGF/SF autocrine signaling in mesenchymal cells promotes both sarcomagenesis and metastasis through inappropriate induction of the pleiotropic responses to Met-HGF/SF stimulation.