The endothelial cell tissue plasminogen activator receptor. Specific interaction with plasminogen

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Medicine

Background:

• Human endothelial cells (EC) express surface proteins that facilitate plasmin generation.
• A previously identified EC membrane protein (Mr ~40,000) specifically binds tissue plasminogen activator (t-PA).

Purpose of the Study:

• To purify and characterize the t-PA receptor protein (t-PA-R).
• To investigate the binding properties and functional significance of t-PA-R in plasmin generation.

Main Methods:

• Purification of t-PA-R using affinity chromatography and preparative gel electrophoresis.
• Solid-phase binding assays to assess interactions with 125I-t-PA and 125I-Lys-plasminogen (PLG).
• Functional assays measuring plasmin generation mediated by t-PA-R.

Main Results:

• Purified t-PA-R specifically bound both 125I-t-PA and 125I-Lys-PLG in a reversible, noncompetitive manner.
• Binding of Lys-PLG, but not t-PA, was inhibited by lipoprotein(a) and epsilon-aminocaproic acid.
• Anti-t-PA-R antibody significantly inhibited t-PA and Lys-PLG binding to EC monolayers.
• t-PA bound to immobilized t-PA-R generated significantly more plasmin compared to fluid-phase t-PA.

Conclusions:

• t-PA-R binds both t-PA and Lys-PLG, mimicking EC surface interactions.
• This receptor protein likely plays a crucial role in modulating cell surface plasmin generation.