Differential BET protein recruitment to IL6 and IL8 promoters and suppression of inflammatory and cell cycle genes by BET inhibitor in keratinocytes.

Bromodomain containing BET proteins are druggable proteins which bind acetylated chromatin and are implicated in dysregulated gene expression in chronic inflammatory disorders. We set out to test whether BET proteins regulate inflammatory responses in keratinocytes, which are key effector cells in cutaneous inflammation. Primary human keratinocytes were stimulated with TNF/IL-17 and treated with BET inhibitor (I-BET151). TNF/IL-17 induced histone hyperacetylation, recruitment of BET proteins (BRD2/3/4) to the promoter regions of IL-6/-8 and activation of PolII (S2P) which correlated with increased gene expression. These effects were blocked by I-BET151. Notably a greater enrichment of BRD4/p65 was observed at the IL-6 compared to the IL-8 promoter. Transcriptomics analysis showed I-BET151 treatment modulated gene expression involved in cell cycle, apoptosis, cell proliferation and innate immune responses, which overlapped with psoriasis-associated genes. These results demonstrate disease-relevant stimuli induced dynamic histone modifications and recruitment of BET proteins at inflammatory gene loci in human keratinocytes. New evidence for BRD4/p65 enrichment at the IL-6 promoter indicated BRD4 may be a critical factor in integrating inflammatory stimuli via NF-κB in cutaneous inflammation. Inhibition of these responses by I-BET151 highlighted BET proteins as regulators of keratinocyte innate immune responses and potential therapeutic targets in inflammatory skin disease.