beta(3)A-integrin downregulates the urokinase-type plasminogen activator receptor (u-PAR) through a PEA3/ets transcriptional silencing element in theu-PAR promoter

Migration of cells requires interactions with the extracellular matrix medi ated, in part, by integrins, proteases, and their receptors. Previous studi es have shown that beta (3)-integrin interacts with the urokinase-type plas minogen activator receptor (u-PAR) at the cell surface. Since integrins med iate signaling into the cell, the current study,vas undertaken to determine if in addition beta (3)-integrin regulates u PAR expression. Overexpressio n of beta (3)-integrin in CHO cells, which are avid expressers of the recep tor, downregulated u-PAR protein and mRNA expression. The u-PAR promoter (- 1,469 bp) that is normally constitutively active in CHO cells was downregul ated by induced beta (3)-integrin expression. A region between -398 and -19 7 bp of the u-PAR promoter was critical for beta (3)-integrin-induced downr egulation of u-PAR promoter activity. Deletion of the PEA3/ets motif at -24 8 bp substantially impaired the ability of beta (3)-integrin to downregulat e the u-PAR promoter, suggesting that the PEA3/ets site acts as a silencing element. An expression vector encoding the transcription factor PEA3 cause d 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 bi nding mas enhanced when beta (3)-integrin was overexpressed. A PEA3 antibod y inhibited DNA-protein complex formation, indicating the presence of PEA3. Downregulation of the u-PAR promoter mas achieved by the beta (3)-integrin isoform but not by other beta (3)-integrin isoforms and required the cytop lasmic membrane NITY759 motif. Moreover, overexpression of the short but no t the long isoform of the beta (3)-integrin adapter protein beta (3)-endone xin blocked u-PAR promoter activity through the PEA3/els binding site. Thus , besides the physical interaction of beta (3)-integrin and u-PAR at the ce ll surface, beta (3) signaling is implicated in the regulation of u-PAR gen e transcription, suggesting a mutual regulation of adhesion and prateolysis receptors.