A sequence-selective single-strand DNA-binding protein regulates basal transcription of the murine tissue inhibitor of metalloproteinases-1 (Timp-1) gene.

Tissue inhibitor of metalloproteinases-1 (TIMP-1) is important in maintaining the extracellular proteolytic balance during tissue remodeling processes. To allow homeostatic tissue turnover, the murine Timp-1 gene is expressed by most cells at a low basal level, and during acute remodeling its transcription is activated by a variety of stimuli. A non-consensus AP-1-binding site (5'-TGAGTAA-3') that is conserved in mammalian timp-1 genes is a critical element in basal and serum-stimulated transcription. We show here that each strand of this unusual AP-1 site binds a distinct single-stranded DNA-binding protein, although neither strand from a perfect consensus AP-1 site from the human collagenase gene shows similar binding. One of the single-strand binding factors, which we term ssT1, binds to a second upstream Timp-1 region between nucleotides -115 and -100. Deletion analysis demonstrated that this region is important in basal but not serum-inducible transcription. The ssT1 factor was 52-54 kDa by UV cross-linking of electrophoretic mobility shift assays and Southwestern blot analysis. Its binding to DNA shows sequence selectivity rather than specificity, with 5'-CT/ATTN((4-6))ATC-3' as a favored motif. Multiple ssT1-like activities were found in nuclear extracts from mouse fibroblasts and rat liver and testis, suggesting that these factors may regulate basal Timp-1 transcription in a tissue-specific fashion.