Synergistic induction of matrix metalloproteinase 1 by interleukin-1 alphaand oncostatin M in human chondrocytes involves signal transducer and activator of transcription and activator protein 1 transcription factors via a novel mechanism

Objective. To investigate the mechanism of interleukin-1 alpha (IL-1 alpha) and oncostatin M (OSM) synergistic regulation of matrix metalloproteinase 1 (MMP-1) in human chondrocytes. Methods. Using an immortalized human chondrocyte cell line (T/C28a4), we in vestigated regulation of the MMP-1 gene. Northern blotting and flow cytomet ric analysis were used to assess changes in receptor, MMP-1, and c-fos expr ession. Transient transfections using MMP-1 promoter/luciferase constructs, electrophoretic mobility shift assay, and site-directed mutagenesis were u sed to investigate MMP-1 promoter activation. Results. We found no alteration in the expression of receptors used by thes e cytokines after stimulation with IL-1 alpha /OSM. Using MMP-1 promoter/lu ciferase reporter constructs, we found that the proximal (-517/+63) region of the MMP-1 promoter was sufficient to support a synergistic activation. A role for activated signal transducers and activators of transcription (STA T-3) was demonstrated, although no binding of STAT-3 to the MMP-1 promoter was found. However, constitutive binding of activator protein 1 (AP-1) was detected, and changes in c-fos expression could modulate promoter activity. Conclusion. Since no changes in receptor expression were observed, receptor modulation cannot account for the IL-1 alpha /OSM synergy observed. Instea d, the interplay of various intracellular signaling pathways is a more like ly explanation. STAT activation is required, but STAT proteins do not inter act directly with the MMP-1 promoter. We propose that activated STATs stimu late c-fos expression, and changes in expression of the AP-1 components reg ulate MMP-1 expression. We highlight a new mechanism for MMP-1 regulation i n human chondrocytes that could provide potential new therapeutic targets.