Extracellular proteolytic cleavage by urokinase is required for activation of hepatocyte growth factor/scatter factor.

Abstract

The extracellular protease urokinase is known to be crucially involved in morphogenesis, tissue repair and tumor invasion by mediating matrix degradation and cell migration. Hepatocyte growth factor/scatter factor (HGF/SF) is a secretory product of stromal fibroblasts, sharing structural motifs with enzymes of the blood clotting cascade, including a zymogen cleavage site. HGF/SF promotes motility, invasion and growth of epithelial and endothelial cells. Here we show that HGF/SF is secreted as a single‐chain biologically inactive precursor (pro‐HGF/SF), mostly found in a matrix‐associated form. Maturation of the precursor into the active alpha beta heterodimer takes place in the extracellular environment and results from a serum‐dependent proteolytic cleavage. In vitro, pro‐HGF/SF was cleaved at a single site by nanomolar concentrations of pure urokinase, generating the active mature HGF/SF heterodimer. This cleavage was prevented by specific urokinase inhibitors, such as plasminogen activator inhibitor type‐1 and protease nexin‐1, and by antibodies directed against the urokinase catalytic domain. Addition of these inhibitors to HGF/SF responsive cells prevented activation of the HGF/SF precursor. These data show that urokinase acts as a pro‐HGF/SF convertase, and suggest that some of the growth and invasive cellular responses mediated by this enzyme may involve activation of HGF/SF.

Progression of familial adenomatous polyposis (FAP) colonic cells after transfer of the src or polyoma middle T oncogenes: cooperation between src and HGF/Met in invasion

“…The phosphorylation level of Met is representative of its tyrosine kinase activity (Naldini et al, 1992). The relative abundance of the Met protein was also analysed on Western blots using whole-cell extracts and quantified by scanning densitometry of the radiographic films.…”

Expression of HGF/SF in mesothelioma cell lines and its effects on cell motility, proliferation and morphology

“…It is synthesized as a single-chain inactive precursor peptide that is cleaved after secretion into an a,B heterodimer (Miyazawa et al, 1989;Nakamura et al, 1989). The cleavage step is required for biological activity and occurs outside two proteins are known that are capable of cleaving the precursor, a serine proteinase HGF/SF activator (Miyazawa et al, 1993) and urokinase-type plasminogen activator (Naldini et al, 1992). HGF/SF acts as a strong mitogenic, motogenic and morphogenic agent and has been shown both in vivo and in vitro to have the remarkable capacity to rupture cell-cell junctions of a wide variety of epithelial cell types (reviews, Gherardi et al, 1993;Rosen et al, 1994).…”

Overexpression and activation of hepatocyte growth factor/scatter factor in human non-small-cell lung carcinomas

“…However, only a small amount of HGF/SF is produced by either lung fibroblasts or bronchial cells, under the same conditions. In addition, HGF/SF is secreted as an inactive precursor (pro-HGF) that binds the extracellular matrix (Mizuno et al, 1992;Naka et al, 1992;Naldini et al, 1992;Masumoto et al, 1991). In the extracellular environment, pro-HGF is converted to the mature heterodimer and activated either by uPA secreted by the cells themselves or non-specifically by serum proteases, such as blood-coagulation factor XIIa and its homologous protein named HGF-activator (Miyazawa et al, 1993;Shimomura et al, 1995).…”