David M. Waisman

Plasmin is a fundamentally important enzyme involved in physiological processes such as blood clot lysis and pathological processes such as tumor growth and metastasis. Recent work from our laboratory has shown that the multifunctional Ca2+-binding protein, annexin II heterotetramer (AIIt) regulates the production and activity of plasmin. We are utilizing biochemical, cellular and molecular biological approaches to study the mechanism by which AIIt regulates plasmin and contributes to the metastatic potential of cancerous cells. We are also examining the potential role of AIIt in tumor cell activated fibrin turnover and fibrin blood clot dissolution using antisense and knock-out strategies.

In addition to its extracellular function, AIIt is also present at the intracellular surface of the plasma membrane where it has been proposed to form a link between the cortical actin cytoskeleton and the plasma membrane. We have therefore begun an extensive series of site-directed mutagenesis studies aimed at identification of the F-actin, phospholipid and heparin-binding regions of the molecule. The role of these domains in the intracellular functions of the protein is being examined by cellular transfection experiments utilizing mutant AIIt cDNA.

We have also initiated studies aimed at identification of the mechanism by which the plasmin fragment, angiostatin, blocks the recruitment of blood vessels to primary and metastatic tumors. These studies will establish the structural regions of angiostatin that are involved in the tumor-killing activity of the protein.