The role of AP-1 in matrix metalloproteinase gene expression

In an effort to understand the mechanism of matrix metalloproteinase (MMP) induction, lapine synoviocytes were isolated and incubated with phorbol myristate acetate (PMA) and autocrine "cell-activating factors" (CAF), agents which significantly increase MMP mRNA abundance. AP-1 complexes, formed by c-fos and c-jun which bind to 5′ residues of the MMP genes, seem causally related to MMP gene expression in response to PMA. However, although AP-1 DNA binding activity is strongly induced following exposure of synoviocytes to CAF, MMP gene expression in response to CAF does not correlate well with AP-1 activity and is not inhibited by antisense DNA to fos and jun. We hypothesize that there is a CAF-response factor involved in MMP gene expression and that this factor competes with the binding of the AP-1 complex to its target response element.