Transcriptional Roles of CCAAT/Enhancer Binding Protein-β, Nuclear Factor-κB, and C-promoter Binding Factor 1 in Interleukin (IL)-1β-induced IL-6 Synthesis by Human Rheumatoid Fibroblast-like Synoviocytes

The involvement of interleukin (IL)-6 in the pathogenesis of rheumatoid arthritis (RA) has been recently demonstrated. IL-1beta stimulated rheumatoid fibroblast-like synoviocytes (FLSs) to produce IL-6 in a concentration- and time-dependent manner. In the present study we investigated how the IL-6 promoter is transcriptionally regulated in rheumatoid FLSs in response to a physiologically relevant mediator of inflammation, IL-1beta. Deletion analysis showed that the IL-6 promoter is regulated by two positive elements (located at -159 to -142 base pairs (bp) and -77 to -59 bp). Electrophoretic mobility shift assays revealed that CCAAT/enhancer binding protein-beta (C/EBPbeta) binding to nucleotides -159 to -142 bp was constitutively present. The probe corresponding to nucleotides -77 to -59 bp gave three positive bands. The two slower migrating bands were induced by IL-1beta and comprised an nuclear factor (NF)-kappaB p50/p65 heterodimer and a p65/p65 homodimer. The faster migrating band was constitutively expressed and identified as Epstein-Barr virus C-promoter binding factor 1, CBF1. Site-specific mutagenesis analysis demonstrated that the NF-kappaB and CBF1 binding elements regulated inducible activity of the IL-6 promoter in response to IL-1beta stimulation, whereas the C/EBPbeta binding element mainly regulated basal activity. We also provide the first evidence that CBF1 functions as a positive regulator of human IL-6 gene transcription.