MIGRATING VASCULAR SMOOTH-MUSCLE CELLS POLARIZE CELL-SURFACE UROKINASE RECEPTORS AFTER INJURY IN-VITRO

The localization of proteases to cell surfaces via receptors may facil itate cell migration, invasion, and matrix degradation. Since vascular smooth muscle cell (SMC) migration may be an important event in ather osclerosis and in intimal thickening after vascular injury, we studied the cell surface expression of a receptor for urokinase-type plasmino gen activator (u-PAR) in cultured human vascular SMC. Using immunofluo rescence microscopy, we demonstrated several staining patterns of SMC u-PAR: at the periphery of the cell membrane, at the leading edge, and at cell-cell contact sites. When migration experiments were performed using a wound assay, one-third of the SMC at the wound edge demonstra ted polarization of cell surface u-PAR toward the leading edge of the cell membrane (32 +/- 2%, +/- SEM, n = 7). A similar pattern was seen with an antibody to caveolin, a transmembrane protein found in caveola e, but not with an antibody to 5'-nucleotidase, another cell surface g lycophosphatidylinositol-anchored protein, which was homogeneously exp ressed on the cell surface. Low-density lipoprotein receptor-related p rotein, which mediates internalization of u-PAR bound ligands, was dis tributed in a diffuse punctate pattern, not polarized to the leading e dge. Double immunofluorescent studies demonstrated codistribution of S MC u-PAR with vinculin and caveolin in migrating SMC at the leading ed ge in a wound assay. Polarization of cell surface u-PAR was not observ ed in either nonwounded or subconfluent cultures, despite random migra tory behavior. These studies suggest that in response to wounding, hum an vascular SMC polarize and concentrate cell surface u-PAR to their l eading edge, perhaps facilitating directional migration. (C) 1995 Acad emic Press, Inc.