Critical role of C/EBP delta and C/EBP beta factors in the stimulation of the cyclooxygenase-2 gene transcription by interleukin-1 beta in articular chondrocytes

The activity of the [-831; +103] promoter of the human cyclooxygenase-2 gen e in cultured rabbit chondrocytes is stimulated 2.9 +/- 0.3-fold by interle ukin-1 beta and this stimulation depends on [-132; -124] C/EBP binding-and [-223; -214] NF-kappaB binding-sites. The C/EBP beta and C/EBP delta factor s bind to the [-132; -124] sequence. The [-61; -53] sequence is also recogn ized by C/EBP beta and C/EBP delta as well as USF. Mutation of the whole [- 61; -53] sequence abolished the stimulation of transcription but single mut ations of the C/EBP or USF site did not alter the activity of the promoter, suggesting that the factors bound to the proximal [-61; -53] sequence inte ract with different members of the general transcription machinery. The [-2 23; -214] site binds only the p50/p50 homodimer and a non-rel-related prote in, but not the transcriptionally active heterodimer p50/p65. The p50/p50 h omodimer could interact with the C/EBP family members bound to the [-132; - 124] sequence for full stimulation of the COX-2 transcription by interleuki n-1 beta in chondrocytes. By contrast, the [-448; -449] sequence binds with a low affinity both the p50/p50 homodimeric and p50/p65 heterodimeric form s of NF-kappaB but has no role in the regulation of the human COX-2 promote r in chondrocytes.