Characteristics of Insulin Receptor in Human Hepatoma

Abstract

The properties of the insulin receptors on plasma membranes isolated from human hepatoma were studied in comparison with those from normal liver. The plasma membranes from human hepatoma and normal liver bound specifically to insulin and had at least two classes of insulin receptor sites in respect of their affinity and capacity. 1251-insulin binding in the hepatoma was higher than that of the normal liver at either 4°, 22° or 37°C.
When analyzed from Scatchard plots, the affinity constant of the hepatoma was lower than that of the normal liver. The binding capacity of the hepatoma, however, was higher than that of the normal liver. The average total binding capacity (high affinity plus low affinity) was significantly higher than that in the normal liver (p<0.05)
As for the proteolytic activity of the membrane preparation, only 7% of both 125I-insulin and receptors was degraded on incubation at 4°C for 24hr, whereas 23% of insulin was degraded at 37°C for 5hr. Of the proteolytic inhibitors examined, phenylmethylsulfonyl fluoride strongly prevented the degradation of insulin in the hepatoma.
These results suggest that tumorigenesis may induce changes in the properties of insulin receptors on plasma membranes.