Rat hepatoproliferin revealed the status of a complete hepatomitogen in human hepatoma cells

Hepatoproliferin (HPF), a liver regeneration factor isolated from rat hepatocytes, was assessed for its mitogenic status in the human hepatoma cell line PLC/PRF-5. HPF was able to enhance hepatoma cell growth on its own without the aid of the established complete mitogens EGF and TGF-α or the hepato-priming factor TNF-α. HPF therefore acted as a complete hepatomitogen and had no co-mitogenic properties since it did not augment proliferation when combined with EGF or TGF-α but showed only an additive effect in the presence of TGF-α. Rat HPF was phylogenetically unrestricted, because it was found active in human cells. When each of the established growth factors (GFs) was used alone, the hepatoma cells responded with the same kind of response profile, namely a bi-phasic bell-shaped dose-dependent response due to stimulation at low levels and inhibition at higher levels. However, hepatocyte growth factor (HGF) was an exception since it did not induce a growth response in hepatoma cells. On the contrary HPF, on its own, showed a progressive enhanced linear dose response at the levels used for the GFs (ie 1.0–15 ng/5 × 10 5 cells). The comparative potency (CP) (dpm × 10 3/μg DNA/ng GF) of HPF (CP = 13) was in the same range as for the complete hepatomitogens EGF (CP = 12) and TGF-α (CP = 14), revealing that HPF has indeed the status of a complete mitogen.