Background: Despite well-documented immunomodulation by interferon gamma (IFN-γ), its role and mechanism of regulation of matrix metalloproteinase-13 (MMP-13) gene expression in human chondrocytes is unknown.
Objective: To investigate the ability and mechanism of IFN-γ to suppress interleukin-1 (IL- 1)-induced MMP-13 expression in articular chondrocytes.
Methods: Human chondrocytes were treated with IFN- γ or IL-1β alone or in combination. MMP-13 mRNA was analyzed by semi-quantitative RT-PCR. MMP-13 protein, phospho-STAT1 and p44/42 MAPK levels were measured by Western blotting. MMP-13 promoter- luciferase, CMV-CBP/p300 plasmids and STAT1 siRNA were transfected by Calcium phosphate method. IFN-γ receptor was also neutralized. AP-1 activity was monitored by TransAM transcription factor kit. STAT1- CBP/p300 interaction was studied by immunoprecipitation.
Results: IFN-γ potently suppressed IL-1- induced expression of MMP-13 and promoter activity. Blockade with neutralizing IFN-γR1 antibody revealed that MMP-13 inhibition by IFN-γ was mediated by the IFN receptor. IFN-β-stimulated activation of STAT1 was directly correlated with MMP-13 suppression. Knockdown of STAT1 gene by specific siRNA or its inhibition with Fludarabine partially restored the IL-1 induction of MMP-13 expression and promoter activity. IFN-γ did not alter activator protein (AP-1) binding ability but promoted physical interaction of STAT1 and CBP/p300 co-activator. P300 overexpression reversed IFN-γ inhibition of endogenous MMP-13 mRNA expression and exogenous MMP-13 promoter activity.
Conclusion: IFN-γ through its receptor activates STAT1, which binds with CBP/p300 co-activator, sequesters it from the cell system and thus inhibits transcriptional induction of MMP-13 gene in chondrocytes. IFN-γ and its signaling pathways could be targeted therapeutically for diminishing IL-1- induced cartilage degradation by MMP-13 in patients with arthritis.
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