Cleavage of cell surface proteins by thrombin

Area of Science:

• Cell Biology
• Biochemistry
• Proteomics

Background:

• Thrombin's mitogenic effect on fibroblasts involves cell surface interaction without internalization.
• Proteolytic activity of thrombin is essential for stimulating cell division.
• Previous findings suggest cell surface protein cleavage is key to thrombin's mitogenic action.

Purpose of the Study:

• To identify specific cell surface proteins cleaved by thrombin.
• To investigate the role of these cleavages in thrombin-stimulated cell division.
• To analyze thrombin's proteolytic activity on cell surface glycoproteins.

Main Methods:

• Utilized 2-dimensional gel electrophoresis for analyzing labeled cell surface proteins.
• Employed three distinct labeling procedures: 125I-iodination, 3H-NaBH4 reduction of oxidized glycoproteins, and 3H-fucose metabolic labeling.
• Identified thrombin-sensitive proteins, including fibronectin, using immunoprecipitation.

Main Results:

• Identified approximately five thrombin-sensitive cell surface proteins, indicating high protease specificity.
• Fibronectin was identified as a thrombin-sensitive cell surface glycoprotein.
• Observed thrombin-sensitive proteins of 140K and 55K daltons, and an increase in 45K and 130-150K dalton proteins.

Conclusions:

• Thrombin specifically cleaves certain cell surface proteins, including fibronectin.
• These cleavages are potential mediators of thrombin's mitogenic effects on cell division.
• Further studies on cloned cell lines will elucidate the necessity of these proteolytic events for cell proliferation.