Tumor cytotoxic activity of HGF-SF

IMR-90 human embryonic lung fibroblasts secrete a tumor cytotoxic factor. This factor, termed F-TCF, is moderately cytotoxic in human tumor cell lines (KB, MCF-7, BG-1) and is very cytotoxic in mouse tumor cell lines (Sarcoma 180, Meth A sarcoma, P388). The cytotoxicity depends on the initial target cell number and is due to cytostasis rather than cytolysis. F-TCF was purified from conditioned medium by a combination of UF-concentration, CM sephadex C-50, Con A sepharose, Mono S cation-exchange and heparin sepharose chromatography and exhibited a molecular mass (M(r)) of 76 to 80 kD on SDS-PAGE under non-reducing conditions. F-TCF is a heterodimer composed of a large alpha-subunit with M(r) 52 to 56 kD and a small beta-subunit with M(r) 30 to 34 kD. F-TCF is a heparin-binding, heat-labile, basic glycoprotein (pI 7.4-8.6). Its activity is stable over the pH range of 6.0 to 9.0, but is completely lost after reduction with 2-mercaptoethanol. Protein sequencing indicates that the alpha-subunit is blocked at the aminoterminus. The primary amino acid sequences deduced from hepatocyte growth factor (HGF) cDNAs cloned from human placenta and liver cDNA libraries indicate that F-TCF is identical to the placenta type HGF in the aminoterminal sequence of the beta-subunit, but differs at two sites from the liver type HGF. Two forms of F-TCF cDNA were found in an IMR-90 human fibroblast cDNA library. One form was identical to placenta type HGF cDNA and the other was a variant with a 15 base pair deletion in the coding region. In addition, mRNA corresponding to the deleted form of cDNA was present in total RNA prepared from IMR-90 cells. F-TCF was thus identified as placenta type HGFs including a variant. The deleted form of recombinant HGF (rHGF) expressed in CHO cells had slightly lower heparin-binding affinity than did the intact form. Both rHGFs had almost the same dose-response curves for cytotoxicity in Sarcoma 180 or Meth A sarcoma cells. Moreover, rHGF (the deleted form) was cytotoxic in hepatocellular carcinoma cells (HepG2, Hep3B, H35). Dose-response curves for the stimulation of DNA synthesis in rat hepatocytes by HGFs were very similar up to about 12.5 ng/ml, but differed significantly at higher concentrations. The deleted form gave maximal activity in a dose range of 12.5 to 100 ng/ml and had about 1.4- to 1.9-fold higher specific activity in that range than the intact form did.(ABSTRACT TRUNCATED AT 400 WORDS)