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Cryptic urokinase binding sites on human foreskin fibroblasts
Biochemical and Biophysical Research Communications
|December 17, 1985
Summary
Human foreskin cells have specific binding sites for urokinase, a key enzyme in cell surface interactions. These sites, initially occupied by endogenous activators, can be unmasked for further study.
Area of Science:
- Cell Biology
- Biochemistry
- Enzymology
Background:
- Urokinase is a serine protease involved in extracellular matrix degradation.
- Cell surface receptors play crucial roles in regulating enzyme activity and localization.
Purpose of the Study:
- To characterize the binding sites for urokinase on human foreskin cells.
- To investigate the nature and regulation of these cell surface binding sites.
Main Methods:
- Radioligand binding assays using iodinated urokinase.
- Treatment with low pH buffer to unmask cryptic binding sites.
- Enzymatic accessibility assays (trypsin).
Main Results:
- Human foreskin cells specifically bind the 2-chain, active form of urokinase, but not the single-chain form.
- Approximately 40,000 urokinase binding sites per cell were identified.
- Low pH treatment revealed 2-6 fold more binding sites and extracted cell-surface plasminogen activator.
- Bound urokinase is not internalized and dissociates slowly.
Conclusions:
- Human foreskin cells possess specific, high-affinity binding sites for active urokinase.
- Cryptic urokinase binding sites likely represent sites occupied by endogenous plasminogen activators.
- These findings contribute to understanding urokinase regulation at the cell surface.