Hepatocyte growth factor prevents acute renal failure and accelerates renal regeneration in mice

Hepatocyte growth factor releases epithelial and endothelial cells from growth arrest induced by transforming growth factor-beta1

Human lung fibroblasts and Mv1Lu mink lung epithelial cells were used as a model to study the role of extracellular matrix in epithelial-mesenchymal interactions. Extracellular matrices of fibroblasts were found to contain growth promoting activity that reduced the sensitivity of Mv1Lu cells to the growth inhibitory effects of transforming growth factor-beta (TGF-beta). The majority of the activity was identified as hepatocyte growth factor/scatter factor (HGF) by inhibition with specific antibodies and by reconstitution of the effect by recombinant HGF. HGF induced cell proliferation when contact-inhibited Mv1Lu cells were trypsinized and plated in the presence of TGF-beta1. The effect was valid also in assays where Madin-Darby canine kidney epithelial cells or bovine capillary endothelial cells were used. The multiplication of chronically TGF-beta1 inhibited Mv1Lu cells was also induced by HGF. In addition, HGF induced anchorage independent growth of Mv1Lu cells that was refractory to TGF-beta1 growth inhibition. Immunoprecipitation analysis indicated that HGF prevented the suppression of Cdk4 and Cdk2, but not the induction of p21, by TGF-beta1. Since both TGF-beta1 and HGF require proteolysis for activation, the results imply that proteolytic activity of epithelial and endothelial cells directs their responses to signals from mesenchymal-type extracellular matrices, and that during development, matrix-bound growth and invasion promoting and suppressing factors are activated in a coordinated manner.

Loss of MDCK cell alpha 2 beta 1 integrin expression results in reduced cyst formation, failure of hepatocyte growth factor/scatter factor-induced branching morphogenesis, and increased apoptosis

Cellular interactions with collagen in a model of kidney tubulogenesis were investigated using Madin-Darby canine kidney (MDCK) cells in an in vitro morphogenetic system. MDCK cells adhered to collagen types I and IV in a Mg(2+)-dependent manner, typical of the alpha 2 beta 1 integrin. Collagen-Sepharose affinity chromatography and immunoblotting demonstrated the presence and collagen binding activity of the alpha 2 beta 1 integrin on MDCK cells. To assess the function of alpha 2 beta 1 integrin, MDCK cells were transfected with a plasmid pRSV alpha 2′ which allowed the expression of alpha 2-integrin subunit antisense RNA. Three G418-resistant clones showing reduced adhesion to collagen, stable genomic integration of the antisense construct, decreased alpha 2-integrin subunit mRNA and decreased alpha 2-integrin subunit protein expression were selected for analysis in morphogenetic experiments. MDCK cells and plasmid-only control transfectants, cultured in three-dimensional collagen type I gels, showed normal cyst formation, whereas the antisense RNA transfectants showed increased apoptosis and formed small rudimentary cysts. Stimulation with hepatocyte growth factor/scatter factor-containing 3T3 fibroblast-conditioned medium or recombinant hepatocyte growth factor/scatter factor resulted in extensive branching of the preformed control cysts whereas the surviving small cysts formed by antisense expressing cells increased in size but failed to elongate and branch upon stimulation. We conclude that alpha 2 beta 1 integrin collagen interactions play a crucial role in the hepatocyte growth factor/scatter factor-induced tubulogenesis and branching morphogenesis of MDCK cells in collagen gels as well as an important role in cell survival.

Hepatocyte growth factor--pleiotropic cytokine produced by human leukemia cells

Hepatocyte growth factor (HGF) was identified, purified and molecularly cloned as a potent mitogen for mature rat hepatocytes in primary culture. It is one of the largest cytokines and is composed of disulfide-linked subunits of approximately 60 (heavy chain) and 35 kilodaltons (light chain). Recent observations revealed that HGF is mitogenic to various epithelial cells other than hepatocytes and to endothelial cells, and that it also acts as a motogen, morphogen and tumor-suppressor as well as a mitogen. These various biological activities of HGF are presumably transduced through the same receptor, c-Met, which is a member of the tyrosine kinase receptor family. Although it shows multiple biological activities on cells in culture, HGF is most likely the physiological hepatotrophic factor which triggers liver regeneration. It may also function as a renotrophic and pulmotrophic factor after tissue injury. HGF production in the liver, kidney and lung increases after injury to these organs. An elevated HGF level may act as an inducer of compensatory DNA synthesis. The regulation of HGF production is, therefore, important for the control of organ regeneration. HGF is produced mainly by mesenchymal cells such as fibroblasts and vascular smooth muscle cells. Various types of human leukemia cells also secrete HGF both in vitro and in vivo. Some biological activities of HGF on hematopoietic cells, including co-mitogenic activity on myeloid leukemia cell lines, were recently demonstrated. HGF gene expression and the protein production in leukemia and fibroblast cells are modulated by various cytokines and hormones. Those modulators may indirectly affect organ regeneration and other biological processes by controlling HGF production.

Scatter factor and the c-met receptor: a paradigm for mesenchymal/epithelial interaction

Epithelia and mesenchyme interact during various physiologic and pathologic processes. Scatter factor is a mesenchyme-derived cytokine that stimulates motility, proliferation, and morphogenesis of epithelia. Recent studies suggest that scatter factor and its receptor (c-met) mediate mesenchyme/epithelia signalling and even interconversion. In this mini-review, we will discuss how scatter factor and c-met may mediate interactions between mesenchyme and epithelia during embryogenesis, organ repair, and neoplasia.