Peroxisome proliferator-activated receptor-gamma-independent repression of collagenase gene expression by 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid and prostaglandin 15-deoxy-delta(12,14) J2: a role for Smad signaling.

Matrix metalloproteinases (MMPs) degrade extracellular matrix components, and overexpression of these enzymes contributes to tissue destruction in arthritis. Of particular importance are the collagenases, MMP-1 and MMP-13, which have high activity against the interstitial collagens in cartilage. In this study, we address the mechanisms of two inhibitors of collagenase gene expression, the synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid (CDDO) and 15-deoxy-delta(12,14)-prostaglandin J2 (15-dPGJ2). Although both inhibitors are ligands for the nuclear hormone receptor peroxisome proliferator-activated receptor-gamma (PPAR-gamma), a connection between PPAR-gamma and collagenase gene expression has yet to be established. Here, we test the hypothesis that CDDO and 15-dPGJ2 use PPAR-gamma to repress MMP gene expression. Our findings with the PPAR-gamma antagonist 2-[4-[2-[3-(2,4-difluorophenyl)-1-heptylureido]ethyl]rsqb]-phenylsulfanyl]-2-methylpropionic acid (GW9662) and mouse embryonic fibroblasts lacking PPAR-gamma demonstrate that CDDO and 15-dPGJ2 use PPAR-gamma-independent mechanisms to inhibit collagenase gene expression. To address a potential PPAR-gamma-independent mechanism leading to the repression of MMPs by CDDO, we tested the effect of CDDO on the transforming growth factor-beta (TGF-beta) signaling pathway. We found that CDDO requires Smads (transcription factors activated by TGF-beta) for the repression of MMP-1. Specifically, MMP-1 is inhibited neither by CDDO in the absence of TGF-beta receptor-activated Smad3 nor when a negative regulator, Smad7, attenuates TGF-beta signaling. We conclude that CDDO represses MMP gene expression through a novel PPAR-gamma-independent mechanism that requires Smad signaling.