Binding and Degradation of Tissue-Type Plasminogen Activator by the Human Hepatoma Cell Line Hep G2

Summary

In this study, binding and degradation of tissue-type plasminogen activator (t-PA) by the human hepatoma cell line Hep G2 was investigated. Binding at 4° C was time-dependent and reached a maximum after ca. 2 hours. Scatchard analysis of saturation experiments showed about 170,000 high affinity binding sites for t-PA per cell with an apparent Kd of 90 nM. These binding sites were calcium-dependent. Part of the binding to the hepatoma cells was non-saturable, owing to a large amount of low affinity binding sites which are at least partially located on the extracellular matrix of the cells. Competition with mannose- and galactose-terminated glycoproteins had no effect on total binding of ¹²⁵I-t-PA. Degradation products of ¹²⁵I-t-PA were found in the supernatant after a short lag phase and then increased linearly for at least 5 hours at 37° C. Degradation could be inhibited by chloroquine, NH₄Cl and NaN₃. We conclude that the human hepatoma cell line Hep G2 has a specific binding mechanism for t-PA which is not mediated by known carbohydrate receptor systems. Binding is followed by cellular uptake and degradation in the lysosomes.

Keywords

Plasminogen activator - Tissue-type plasminogen activator - Catabolism - Receptor binding - Hep G2

• References

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