INHIBITION OF RABBIT COLLAGENASE (MATRIX METALLOPROTEINASE-1 - MMP-1)TRANSCRIPTION BY RETINOID RECEPTORS - EVIDENCE FOR BINDING OF RARS RXRS TO THE -77 AP-1 SITE THROUGH INTERACTIONS WITH C-JUN/

Treatment of synovial fibroblasts with retinoic acid (RA) decreases th eir expression of collagenase (matrix metalloproteinase-1 or MMP-1), a n enzyme that degrades interstitial collagens and contributes to the p athology of rheumatoid arthritis. This inhibition results, at least in part, from RA-induced decreases in the mRNA for the transactivators F os and Jun (with concominant increases in RAR mRNA) and by sequestrati on of Fos/Jun by RARs/RXRs. Previously, we provided evidence that reti noid receptors are also present in complexes that bind to fragments of rabbit MMP-1 promoter DNA containing an AP-1 site at -77 (Pan et al., 1995, J. Cell. Biochem., 57:575-589). However, it was unclear whether RARs and retinoid X receptors (RXRs) were binding directly to the DNA or indirectly through another protein. We now use a sensitive MMP-1 p romoter/luciferase reporter construct to confirm the transcriptional r ole of the AP-1 site at -77. In addition, with electrophoretic mobilit y shift analyses (EMSAs), antibody ''supershifts'' and DNAase I footpr inting, we examine the interaction of retinoid receptors and AP-1 prot ein on the MMP-1 promoter. We demonstrate that RARs, RXRs, and c-Jun f orm a complex at the AP-1 site in which c-Jun binds directly to the DN A and apparently tethers the retinoid receptors to the complex. We con clude that retinoid receptors/AP-1 protein interactions at the DNA may provide an additional means of controlling collagenase gene transcrip tion by retinoids. (C) 1996 Wiley-Liss, Inc.