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A novel hepatoma-derived growth factor was purified from the conditioned medium of human hepatoma-derived cell line, HuH-7, by the assay of [3H]thymidine incorporation into Swiss 3T3 cells. Molecular cloning of a complementary DNA from the cDNA library of HuH-7 cells was done on the basis of the N-terminal amino acid sequence. This protein was acid- and heat-labile heparin-binding protein and inactivated by reducing condition. The cDNA is 2.4 kilobase pairs long, and the deduced amino acid sequence from cDNA contained 240 amino acids without a signal peptide-like N-terminal hydrophobic sequence. Heparin column-eluted fraction of the conditioned medium of Cos-7 cells transfected by the cDNA stimulated the DNA synthesis. Northern blot analysis revealed its ubiquitous expression in several tumor-derived cell lines, as well as in normal tissues. The primary sequence shares homology with the high mobility group (HMG)-1 protein (23.4% amino acid identity and 35.6% similarity). However, its hydrophobic profile was distinct from that of HMG-1 except for the C-terminal acidic region, and it contained no apparent HMG box motif. Immunofluorescence study showed that it is localized in the cytoplasma of hepatoma cells. These findings suggest that this factor is a novel heparin-binding protein, with mitogenic activity for fibroblasts.

Human plasma contains two actin-binding proteins, plasma gelsolin and vitamin D-binding protein. These proteins are considered to play an important role in the disposition of actin derived from injured tissue. To evaluate this actin-scavenger system, gelsolin concentrations were measured in serial plasma samples obtained from patients with acute liver injury using an enzyme-linked immunosorbent assay. Plasma gelsolin levels in 43 healthy persons were 226 +/- 52 micrograms/mL. They were markedly reduced to 80 +/- 40 micrograms/mL in 14 patients with an early stage of acute hepatitis and returned to normal levels of 232 +/- 38 micrograms/mL as the disease resolved. Moreover, they showed a significant negative correlation with serum aminotransferase and bilirubin levels. In 7 patients with hepatocellular carcinoma, plasma gelsolin levels rapidly decreased from 182 +/- 42 to 87 +/- 41 micrograms/mL after transcatheter arterial embolization therapy. Because plasma gelsolin is not a hepatic protein, the decreased levels are considered to depend exclusively on the extent of actin leakage from the injured liver.

A human hepatoma cell line, HuH-7, which was established from a hepatoma tissue removed at surgical operation from an adult Japanese male, grows autonomously in a serum-free chemically defined medium. A human hepatoma-derived growth factor with potent growth-promoting activity, was partially purified from the conditioned medium of HuH-7 cells, using ion-exchange, heparin affinity chromatography and gel filtration. The partially purified growth factor (HuHGF) is acid- and heat-labile, and sensitive to reduction and trypsin digestion. HuHGF, which is of relatively high molecular weight (about 64 kDa) examined by gel filtration, stimulates not only the DNA synthesis of Swiss mouse 3T3 fibroblasts, but also the growth of HuH-7 cells in serum-free chemically defined medium, suggesting that it is produced by and acts on HuH-7 cells as an autocrine growth factor. This putative growth factor may play an important role in the autonomous growth of hepatoma and may lead to useful diagnostic or therapeutic approaches to human hepatoma.