Transcriptional activity of the human tissue inhibitor of metalloproteinases 1 (TIMP-1) gene in fibroblasts involves elements in the promoter, exon 1 and intron 1

Abstract

The active forms of all of the matrix metalloproteinases (MMPs) are inhibited by a family of specific inhibitors, the tissue inhibitors of metalloproteinases (TIMPs). Inhibition represents a major level of control of MMP activity. A detailed knowledge of the mechanisms controlling TIMP gene expression is therefore important. We have isolated a genomic clone of the human TIMP-1 gene. A 3 kbp XbaI fragment has been sequenced; this fragment contains 1718 bp 5′ flanking sequences, exon 1, a 929 bp intron 1 and part of exon 2. Computer analysis reveals 10 consensus sequences for Sp1, six for activating protein 1 (AP-1), six for polyoma enhancer A3 (PEA3), 12 for AP-2 and five CCAAT boxes. The region hybridizing with a murine TIMP-1 promoter fragment has been subcloned and analysed further. RNase protection identifies six transcription start points, making exon 1 up to 48 bp in length. Transient transfection of promoter–chloramphenicol O-acetyltransferase reporter constructs into primary human connective tissue fibroblasts shows that a 904 bp fragment that hybridizes to a murine TIMP-1 promoter fragment contains a functional promoter. Constructs of -738/+95 to -194/+21 are inducible with serum or phorbol ester to a similar extent to the endogenous TIMP-1 gene. These results and further mapping with 5′ deletion mutants from the -738/+95 region have demonstrated that an AP-1 site at -92/-86 is essential for basal expression of the gene. Point mutations within this region have further confirmed the role of this site, along with a more minor role for a neighbouring PEA3 site, in basal expression. Deletions from the 3′ end also implicate a region across the exon 1/intron 1 boundary and especially +21 to +58 in basal expression. The +21/+58 region contains a putative binding site for the transcription factor leader-binding protein 1 (LBP-1). Gel-shift analysis shows that protein binds specifically to this region, but competition studies suggest that it is unlikely to be LBP-1.