Binding and degradation of tissue-type plasminogen activator by the human hepatoma cell line Hep G2.
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 degrees 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 degrees 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.
Otter
M
M
Gaubius Institute TNO, Leiden, The Netherlands.
Van Berkel
T J
TJ
Rijken
D C
DC
D001667:Binding, Competitive; D002118:Calcium / Q000502:physiology; D006801:Humans; D008099:Liver / Q000378:metabolism*; D011485:Protein Binding; D010959:Tissue Plasminogen Activator / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D010959:Tissue Plasminogen Activator; D002118:Calcium