The role of the plasminogen activator system in the cellular physiology of MDA‐MB‐231 breast cancer cells

Abstract

The purpose of this study is to examine the contribution of urokinase plasminogen activator (uPA) and plasminogen activator inhibitor type 1 (PAI‐1) to invasion, proliferation, and survival of MDA‐MB‐231 breast cancer cells and how their expression is controlled. Inhibition of uPA activity inhibited invasion 30%, while inhibition of PAI‐1 increased invasion 50%. Inhibition of uPA, PAI‐1, and their cell surface receptors (urokinase receptor and low density lipoprotein‐related protein 1) inhibited proliferation and survival in response to tumor necrosis factor. Growth of cells in three dimensional matrices appeared to be inhibited by the presence of a PAI‐1 blocking antibody. Immunoblot and PCR indicate inhibition of either uPA or PAI‐1 activity led to decreased uPA expression and increased PAI‐1 expression. Inhibition of either uPA or PAI‐1 activity led to decreased phosphatidyl inositol‐3 kinase (PI3K) activity whereas incubation with pre‐formed uPA‐PAI‐1 complexes led to increased PI3K activity. Inhibition of PI3K led to decreased uPA protein expression with concomitant increased PAI‐1 expression. These results indicate uPA and PAI‐1 contribute to MDA‐MB‐231 invasiveness and activity of both proteins promotes cell proliferation and survival. Furthermore, PI3K positively regulates uPA, negatively regulates PAI‐1, and PI3K may be activated by recognition of uPA‐PAI‐1 complexes at the cell surface.