Possible endocrine control by hepatocyte growth factor of liver regeneration after partial hepatectomy

Scatter factor from human embryonic lung fibroblasts is probably identical to hepatocyte growth factor

Human embryonic lung fibroblasts (MRC5) produced scatter factor which enhanced motility of Madin-Darby canine kidney (MDCK) epithelial cells and a factor which stimulates DNA synthesis of adult rat hepatocytes in primary culture. These activities were both completely neutralized by antibody against human hepatocyte growth factor (HGF). Human recombinant HGF induced a marked scattering of MDCK cells. Moreover, MRC5 cells highly expressed 6kb mRNA which hybridized with HGF cDNA probe and scatter factor cDNA cloned from the MRC5 cDNA library had the same sequence as that of HGF cDNA from human leukocytes. These results indicate that HGF possesses scatter factor activity and the scatter factor derived from the MRC5 cells is probably identical to HGF.

Hepatocyte growth factor has potent anti-proliferative activity in various tumor cell lines

Hepatocyte growth factor (HGF) has potent mitogenic activity for mature hepatocytes and various normal epithelial cells. We now have evidence that HGF at 1-10 ng/ml, strongly inhibits the growth of HepG2 hepatocellular carcinoma cells, B6/F1 melanoma cells and KB squamous carcinoma cells. These tumor cells express high affinity receptors for HGF with a Kd of 25-28 pM, similar to findings with hepatocytes. HGF at 1-100 ng/ml had no significant cytolytic effect on tumor cells. Therefore, the anti-proliferative effect of HGF on tumor cells seems to be cytostatic, not cytolytic. As HGF apparently has bidirectional effects on cell growth, the possibility that it can serve as an anti-tumor agent merits attention.

Growth factors in liver development, regeneration and carcinogenesis

Liver growth during regeneration is controlled by several growth factors which may be involved in the triggering, progression and termination of hepatocyte replication. It is likely that liver regeneration involves both circulating factors and those produced in hepatic tissue during the growth response. TGF alpha is an autocrine stimulator of hepatocyte proliferation which increases transiently in replicating hepatocytes both in vivo and in vitro. Constitutive TGF alpha overexpression in young transgenic mice causes liver hypertrophy and enhanced proliferation that progress to hepatic tumor development in the great majority of animals after 12 months of age. In contrast, HGF is present in normal blood in humans and animals and plasma concentrations increase after partial hepatectomy, liver injury and fulminant hepatic failure. In liver tissue, levels of HGF and its mRNA correlate better with the extent of injury than with the degree of proliferative activity. The factor is produced by nonparenchymal cells and presumably acts on hepatocytes through paracrine or endocrine mechanisms. A transient increase of TGF beta 1 in regenerating liver may promote the formation of extracellular matrix components and signal the end of hepatocyte proliferation. Prolonged overexpression of the factor in nonparenchymal cells causes liver fibrosis both in humans and experimental animals. The liver contains TGF beta 1,2 and 3, all of which inhibit hepatocyte DNA synthesis. Their mRNAs increase in the regenerating liver but with very different kinetics. Despite the enormous progress achieved in understanding the mechanisms that regulate liver regeneration, it is not known whether HGF, TGF alpha and TGF beta interact with each other or with other factors or hormones during the growth process. Further, it remains to be established how the effect of these factors may relate to the sequential changes in proto-oncogene expression that occur after partial hepatectomy.