THE PLASMINOGEN RECEPTOR S100A10: STRUCTURE AND FUNCTION STUDIES

Abstract

The critical role of the fibrinolytic system is the maintenance of vascular patency. Dysregulation ultimately leads to death; an inappropriate activation that causes excessive bleeding, or an inability to clear blood clots, leading to thrombosis, ischemia and death. Plasminogen receptors (PgR) are found on the surface of many cells, notably endothelial cells and lymphocytes. PgR bind plasminogen to the cell surface, promote directed proteolytic plasmin activity and protect bound plasmin from inhibition. This process is important for vessel patency, wound healing and inflammation. In addition to homeo- and hemostatic roles, PgR can be hi-jacked by cancerous cells for more nefarious roles. Oncogenic cells utilize focussed proteolytic activity of cell-bound plasmin to escape from primary tumours. Understanding how the PgR, plasminogen and activators interact may lead to targeted therapies for clot dissolution or cancer, among other diseases. Plasminogen contains kringle domains that bind to C-terminal lysine residues of fibrin and PgR. Studies were undertaken to explore how alterations in the C-terminal region of S100A10, a PgR, impact its ability to accelerate plasmin generation. S100A10 has 4 lysine residues in its C-terminal region, two at the C-terminus. Deletion of both C-terminal lysine residues results in the loss of up to 90% of the rate of plasmin generation. Substitution of the C-terminal lysines with isoleucine resulted in minimal activity loss. This led to the possibility that another lysine residue is a secondary binding site for kringles. Mutating internal sequence lysine residues to arginine resulted in little change in plasmin generation ability, however, changing a lysine to arginine at position 56 in addition to the substitution of C-terminal lysines to isoleucine resulted in a significant loss of plasmin generating ability. Additionally, a study was initiated to explore a potential role of S100A10 in the demyelination of multiple sclerosis and other diseases whose hallmark is myelin loss. S100A10-null mice, 7 days post-demyelination event (lysophosphatidylcholine injection), had significantly larger lesion volumes than wild type mice injected concurrently. S100A10-null lesions had lower concentrations of microglia/macrophages within the borders of the lesion, indicating that the larger lesion possibly stemmed from a reduced ability to phagocytose degraded myelin.