The interleukin-1β gene is transcribed from a poised promoter architecture in monocytes

Cytokine transcription is usually regulated by transcription factor binding and chromatin remodeling following an inducing signal. By contrast, these data showed the interleukin (IL)-1β promoter assembles into a "poised" structure, as evidenced by nuclease accessibility and loss of core histones immediately surrounding the transcription start site. Strikingly, these properties do not change upon transcriptional activation by lipopolysaccharide. Furthermore, association of two key transcriptional activators, PU.1 and C/EBPβ, is robust pre- and post-stimulation indicating the IL-1β promoter is packaged into a nontranscribed but poised promoter architecture in cells capable of rapidly inducing IL-1β. Monocyte stimulation causes recruitment of a third factor, IRF-4, to the IL-1β enhancer. PU.1 phosphorylation at a CK2 kinase consensus element is required for this recruitment. We showed that CK2 phosphorylates PU.1, CK2 inhibitors abrogate IL-1β induction, and CK2 inducibly associates with the IL-1β enhancer. Taken together, these data indicate a novel two-step mechanism for IL-1β transcription: 1) formation of a poised chromatin architecture, and 2) phosphorylation of an enhancer-bound factor that recruits other activators. We propose that this poised structure may generally characterize rapidly activated genes.