Cell surface-dependent generation of angiostatin4.5.

Area of Science:

• Biochemistry
• Molecular Biology
• Cancer Research

Background:

• Angiostatin4.5 (AS4.5) is a human angiostatin isoform derived from plasminogen.
• Previous studies showed plasminogen converts to AS4.5 via plasmin activation and autoproteolysis.
• This conversion typically requires specific chemical inducers like sulfhydryl donors or alkaline pH.

Purpose of the Study:

• To investigate the role of cell membranes in the conversion of plasminogen to AS4.5.
• To identify specific cell surface receptors involved in this conversion process.
• To explore the potential of surface beta-actin as a biomarker for tumor behavior.

Main Methods:

• Demonstrated plasminogen conversion to AS4.5 in a cell membrane-dependent reaction.
• Investigated the presence and function of beta-actin on the extracellular membranes of cancer cell lines (PC-3, HT1080, MDA-MB231).
• Utilized antibodies to actin to quantify the reduction in membrane-dependent AS4.5 generation and employed a cell-free system with purified actin.

Main Results:

• Beta-actin is present on the extracellular membranes of tested cancer cells and mediates plasmin binding and autoproteolysis to AS4.5.
• The presence of beta-actin facilitates AS4.5 generation without the need for small molecule-free sulfhydryl donors.
• Antibodies targeting actin reduced AS4.5 generation by 70%, and purified actin stoichiometrically converted plasmin to AS4.5 in a cell-free system.

Conclusions:

• Membrane-associated beta-actin acts as a key cell membrane receptor for converting plasmin to AS4.5.
• This beta-actin-mediated conversion is important for regulating tumor angiogenesis, invasion, and metastasis.
• Surface beta-actin may serve as a prognostic marker for predicting tumor behavior.