ABSTRACT
Migration of cells requires interactions with the extracellular matrix mediated, in part, by integrins, proteases, and their receptors. Previous studies have shown that β3-integrin interacts with the urokinase-type plasminogen activator receptor (u-PAR) at the cell surface. Since integrins mediate signaling into the cell, the current study was undertaken to determine if in addition β3-integrin regulates u-PAR expression. Overexpression of β3-integrin in CHO cells, which are avid expressers of the receptor, downregulated u-PAR protein and mRNA expression. The u-PAR promoter (−1,469 bp) that is normally constitutively active in CHO cells was downregulated by induced β3-integrin expression. A region between −398 and −197 bp of the u-PAR promoter was critical for β3-integrin-induced downregulation of u-PAR promoter activity. Deletion of the PEA3/ets motif at −248 bp substantially impaired the ability of β3-integrin to downregulate the u-PAR promoter, suggesting that thePEA3/ets site acts as a silencing element. An expression vector encoding the transcription factor PEA3 caused inhibition of the wild-type but not the PEA3/ets-deleted u-PAR promoter. The PEA3/ets site bound nuclear factors from CHO cells specifically, but binding was enhanced when β3-integrin was overexpressed. A PEA3 antibody inhibited DNA-protein complex formation, indicating the presence of PEA3. Downregulation of the u-PAR promoter was achieved by the β3A-integrin isoform but not by other β3-integrin isoforms and required the cytoplasmic membrane NITY759 motif. Moreover, overexpression of the short but not the long isoform of the β3-integrin adapter protein β3-endonexin blocked u-PAR promoter activity through the PEA3/etsbinding site. Thus, besides the physical interaction of β3-integrin and u-PAR at the cell surface, β3 signaling is implicated in the regulation of u-PAR gene transcription, suggesting a mutual regulation of adhesion and proteolysis receptors.
Urokinase-Type Plasminogen Activator/Type-2 Plasminogen-Activator Inhibitor Complexes are not Internalized Upon Binding to the Urokinase-Type-Plasminogen-Activator Receptor in THP-1 Cells. Interaction of Urokinase-Type Plasminogen Activator/Type-2 Plasminogen-Activator Inhibitor Complexes with the Cell Surface
