Basic fibroblast growth factor stimulates hepatocyte growth factor/scatter factor secretion by human mesenchymal cells.

Basic fibroblast growth factor (bFGF) together with other pleiotropic factors plays an important role in many complex physiological processes such as embryonic development, angiogenesis, and wound repair. Among these factors, hepatocyte growth factor/scatter factor (HGF/SF) which is secreted by cells of mesodermal origin exerts its mito- and motogenic activities on cells of epithelial and endothelial origin. Knowledge of the regulatory mechanisms of HGF/SF may contribute to the understanding of its role in physio-pathological processes. We observed that the secretion of HGF/SF by MRC-5 cells and by other fibroblast-derived cell cultures in conditioned media was enhanced by exposure to bFGF. HGF/SF was measured by the scatter assay, a bioassay for cell motility, and was further characterized by Western blot analysis with anti-HGF/SF antibodies. Exposure of MRC-5 cultures to 10 ng/ml of bFGF resulted already 6 h posttreatment in a threefold higher amount of scatter factor secreted into the medium as compared to untreated cultures. HGF/SF secretion was sustained after bFGF treatment for the following 72 h when increased amounts of HGF/SF were detected both in conditioned media as well as associated to the extracellular matrix. The secretion of HGF/SF in cell supernatants increased dose dependently upon treatment with bFGF starting from basal levels of 6 U/ml and reaching 27 U/ml at 30 ng/ml bFGF, plateauing thereafter. Upregulation of HGF/SF by IL-1, already described by others, was confirmed in this study. Based on our findings an articulated interaction can be speculated for bFGF, HGF/SF, and IL-1, e.g., in tissue regeneration during inflammatory processes or in wound healing.

Suramin modulates cellular levels of hepatocyte growth factor receptor by inducing shedding of a soluble form.

Several growth factor receptors undergo shedding from the cell surface as a result of limited proteolysis via mechanisms that are at present poorly understood. By Western blotting of the conditioned media and cell lysates of several cell lines expressing the hepatocyte growth factor receptor, we found that suramin, a pharmacological agent that inhibits the activity of many growth factors, was able to induce shedding of this receptor. Increased levels of soluble hepatocyte growth factor receptor were observed in the conditioned media of GTL-16, a cell line over-expressing the receptor, as early as ten minutes after initial exposure to the agent, and incubation of this line with 300 microM suramin caused a 50% reduction in cell-associated levels of receptor after 6 hours. Although protein kinase C activation by treatment of cells with phorbol esters has previously been found to stimulate shedding of the hepatocyte growth factor receptor, this hitherto undescribed activity of suramin was not affected by protein kinase C inhibitors. Since shedding represents a possible means of down-modulation of receptor activity, suramin may inhibit the hepatocyte growth factor ligand/receptor system, not only by abrogation of hepatocyte growth factor binding to intact receptor, but also by induction of receptor shedding.

Endothelin-1-selective binding sites are downregulated by transforming growth factor-beta and upregulated by basic fibroblast growth factor in a vascular smooth muscle-derived cell line.

Endothelins (ETs) elicit in vivo and in vitro a potent vasoconstrictor activity after binding to high-affinity receptors on vascular smooth muscle cells (VSMC). A617 cells, a VSM-derived cell line, were used as an in vitro model system to study selected growth factors and cytokines involved in proliferative and/or inflammatory diseases of the vessel wall as possible regulators of the high-affinity binding capacity of ET-1 to the cells. Radioligand studies characterized the binding of ET-1 to the isopeptide selective ETA receptor subtype on A617 cells as a time- and temperature-dependent saturable process (Kd = 0.13 +/- 0.04 nM, Bmax = 49 +/- 7 fmol/10(6) cells). Pretreatment of A617 cells with basic fibroblast growth factor (bFGF), a mitogenic agent for vascular cells, resulted in a time- and dose-dependent increase in ET-1 binding capacity, whereas preexposure to transforming growth factor-beta (TGF-beta) induced a reduction of the Bmax for ET-1. Platelet-derived growth factor (PDGF), interleukin-6 (IL-6), tumor necrosis factor-alpha, and fetal bovine serum (FBS) pretreatments did not affect consequent ET-1 binding to A617 cells.