Characterization of the human protease nexin-1 promoter and its regulation by Sp1 through a G/C-rich activation domain.

Protease nexin-1 (PN-1 ) is a potent inhibitor of serine proteases in the extracellular environment. It is abundantly expressed in the nervous system, where it is thought to participate in local injury and repair processes. Although some information has been obtained regarding PN-1 gene structure, relatively little is known about the cis- and trans-acting factors that regulate its expression. Elucidation of these factors should provide a better understanding of PN-1 function during development and wound repair. In this report we describe the characterization of the human PN-1 promoter and identify regulatory domains and a transactivator mediating its transcriptional activity. The promoter is highly G/C rich proximal to the transcriptional start site. It exhibits tissue specificity and is negatively regulated by a silencer element upstream of position -480. A positive regulatory element was mapped between -199 and -45, which contains multiple putative Sp1 consensus binding sites. Electrophoretic mobility shift analysis confirmed that Sp1 specifically binds this region of the PN-1 promoter. DNase I foot-printing revealed six potential Sp1 binding sites between -103 and -56 that were protected by recombinant Sp1. Cotransfection experiments into the Sp1-deficient Drosophila SL2 cell line also showed that Sp1 activates PN-1 promoter activity in a dose-dependent fashion. Thus, our analysis demonstrates that activation of PN-11 transcription is regulated by Sp1 through G/C-rich cis-acting elements in the 5'proximal promoter region.