Prostaglandin ei inhibits collagenase gene expression in rabbit synoviocytes and human fibroblasts

Cartilage breakdown, as seen in inflammatory and degenerative joint diseases, can be mediated by proteolytic enzymes, such as the metalloproteinase collagenase, the only enzyme able to digest collagen at neutral pH. In vitro collagenase gene expression can be stimulated by the phorbol ester tumor promoter 12-0-tetradecanoyl-phorbol-13-ace- tate. We have investigated the effect of prostaglandin E₁ (PGEi) on 12-0-tetradecanoyl-phorbol-13-acetate-stimulated collagenase mRNA levels in the rabbit synoviocyte cell line HIG-82. PGE₁, but not PGE₂ or PGF_2α was able to selectively reduce collagenase mRNA levels in a dose-dependent fashion. PGE₁ markedly increased intracellular levels of cAMP, while PGE₂ and PGF_2α, had little or no effect on cAMP production in the HIG-82 synoviocytes. Agents known to increase intracellular cAMP levels, such as the adenyl cyclase activator forskolin and the phosphodiesterase inhibitor 3-isobutyl-l-methylxanthine (IBMX), mimicked the effect of PGEi on collagenase mRNA levels. PGE1; forskolin, and IBMX also decreased collagenase mRNA levels in human skin fibroblasts, demonstrating that this observation was not unique to the HIG-82 cell line. Transient transfection experiments carried out in HIG-82 cells using a 1.2-kilobase portion of the 5'-flanking region of the human collagenase gene linked to the reporter gene luciferase demonstrated that PGE₁, forskolin, and IBMX exert their inhibitory effect on the promoter region of the collagenase gene.