Plasminogen activator inhibitor-1 (PAI-1) regulates the proteolytic activity of urokinase-type plasminogen activator (uPA) and there is increasing evidence for a PAI-1 role in regulating cell migration/invasion by other mechanisms like vitronectin (VN) binding and lipoprotein-receptor related protein (LRP) binding. We examined the role of PAI-1 to interact with uPA, VN, and LRP in MDA-MB-435 breast cancer and SKOV-3 ovarian cancer cells in a wound-induced cell migration assay. By different experimental conditions with PAI-1, expressed either by stable transfection or by adenoviral infection (wild-type PAI-1 and an inactive reactive site P14 mutant, T333R) or by addition of recombinant PAI-1 and various mutants (stable wild-type, P14 T333R, reactive center P1 R346A, reduced VN-binding Q123K, and reduced LRP-binding R76E), we found that the PAI-1-VN interaction was foremost in suppressing wound-induced cell migration. Likewise, a VN-antibody that blocks cell adhesion to VN mimicked the effect of PAI-1 to reduce wound-induced SKOV-3 cell migration. However, manipulation of the endogenous plasminogen activator system (using blocking antibodies to PAI-1 and to uPA) in wound-induced SKOV-3 cell migration demonstrated an important role for uPA inhibition by PAI-1 that was dependent on plasminogen. By contrast, smooth muscle cell wound-induced migration was promoted by exogenously added PAI-1, but this enhancement was dependent on PAI-1 binding to LRP, not binding to VN. These findings contribute to the overall complexity of the role of PAI-1 in regulating cell migration; especially since both VN binding and uPA inhibition are involved in suppressing wound-induced breast and ovarian cancer cell migration.

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