Oncostatin M Stimulates c-Fos to Bind a Transcriptionally Responsive AP-1 Element within the Tissue Inhibitor of Metalloproteinase-1 Promoter
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Tissue inhibitor of metalloproteinases-1 (TIMP-1) can be regulated by gp130 cytokines such as IL-6 and oncostatin M (OSM). Polymerase chain reaction deletion analysis of the murine TIMP-1 proximal promoter in chloramphenicol acetyltransferase reporter gene constructs identified an AP-1 element (-59/-53) that allows maximal responsiveness to OSM in HepG2 cells. Fos and Jun nuclear factors bound constitutively to this site as identified by supershift analysis in electrophoretic mobility shift assays, and oncostatin M (but not IL-6) induced an additional "complex 2" that contained c-Fos and JunD. OSM stimulated a rapid and transient increase in c-Fos mRNA and nuclear protein that coincided with complex 2 formation. Phorbol 13-myristate 12-acetate could also induce c-Fos but could not regulate the TIMP-1 reporter gene constructs. Transfection studies also showed that 3'-deletion of sequences downstream of the transcriptional start site (+1/+47) markedly reduced OSM -fold induction. Nuclear factors bound to SP1 and Ets sequences were detected, but were not altered upon OSM stimulation. Although OSM and IL-6 induced STAT (signal transducers and activators of transcription) factors to bind a high affinity Sis-inducible element DNA probe, binding to homologous TIMP-1 promoter sequences was not detected. Thus, OSM (but not IL-6) stimulates c-Fos, which participates in maximal activation of TIMP-1 transcription, likely in cooperation with other factors such as SP1 or as yet unidentified mechanisms involving the +1 to +47 region of the promoter.
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