Retinoid X receptor and peroxisome proliferator-activated receptor-gamma agonists cooperate to inhibit matrix metalloproteinase gene expression

INTRODUCTION: We recently described the ability of retinoid X receptor (RXR) ligand LG100268 (LG268) to inhibit interleukin-1-beta (IL-1-β)-driven matrix metalloproteinase-1 (MMP-1) and MMP-13 gene expression in SW-1353 chondrosarcoma cells. Other investigators have demonstrated similar effects in chondrocytes treated with rosiglitazone, a ligand for peroxisome proliferator-activated receptor-gamma (PPARγ), for which RXR is an obligate dimerization partner. The goals of this study were to evaluate the inhibition of IL-1-β-induced expression of MMP-1 and MMP-13 by combinatorial treatment with RXR and PPARγ ligands and to investigate the molecular mechanisms of this inhibition. METHODS: We used real-time reverse transcription-polymerase chain reaction to measure LG268- and rosiglitazone-mediated inhibition of MMP gene transcription in IL-1-β-treated SW-1353 chondrosarcoma cells. An in vitro collagen destruction assay was a functional readout of MMP collagenolytic activity. Luciferase reporter assays tested the function of a putative regulatory element in the promoters of MMP-1 and MMP-13, and chromatin immunoprecipitation (ChIP) assays detected PPARγ and changes in histone acetylation at this site. Post-translational modification of RXR and PPARγ by small ubiquitin-like modifier (SUMO) was assayed with immunoprecipitation and Western blot. RESULTS: Rosiglitazone inhibited MMP-1 and MMP-13 expression in IL-1-β-treated SW-1353 cells at the mRNA and heterogeneous nuclear RNA levels and blunted IL-1-β-induced collagen destruction in vitro. Combining LG268 and rosiglitazone had an additive inhibitory effect on MMP-1 and MMP-13 transcription and collagenolysis. IL-1-β inhibited luciferase expression in the MMP reporter assay, but rosiglitazone and LG268 had no effect. ChIP indicated that treatment with IL-1-β, but not LG268 and rosiglitazone, increased PPARγ at the proximal promoters of both MMPs. Finally, rosiglitazone or LG268 induced 'cross-SUMOylation' of both the target receptor and its binding partner, and IL-1-β-alone had no effect on SUMOylation of RXR and PPARγ but antagonized the ligand-induced SUMOylation of both receptors. CONCLUSIONS: The PPARγ and RXR ligands rosiglitazone and LG268 may act through similar mechanisms, inhibiting MMP-1 and MMP-13 transcription. Combinatorial treatment activates each partner of the RXR:PPARγ heterodimer and inhibits IL-1-β-induced expression of MMP-1 and MMP-13 more effectively than either compound alone. We conclude that the efficacy of combined treatment with lower doses of each drug may minimize potential side effects of treatment with these compounds.