β2-Adrenoceptor Agonists, Like Glucocorticoids, Repress Eotaxin Gene Transcription by Selective Inhibition of Histone H4 Acetylation

Abstract

Eotaxin is a potent eosinophil chemoattractant implicated in various allergic inflammatory conditions including asthma, but relatively little is known about its regulation. Human airway smooth muscle cells are an important source of eotaxin in the airway. We have previously demonstrated that β2-adrenoceptor agonists (β2-agonists) and glucocorticoids additively inhibit eotaxin production in human airway smooth muscle cells, but the underlying mechanisms are unclear. Here, we studied the molecular mechanisms of their actions and interactions on eotaxin gene transcription. TNF-α-induced eotaxin gene transcription was mediated mainly by the transcription factor NF-κB (p65/p50) as analyzed by luciferase reporter gene assay, Western blotting, EMSA, and electrophoretic mobility supershift assay. Chromatin immunoprecipitation assay demonstrated that TNF-α also induced selective histone H4 acetylation on lysines 5 and 12 at the eotaxin promoter site and p65 binding to the eotaxin promoter, resulting in eotaxin gene transcription. The inhibition of eotaxin production by β2-agonists and glucocorticoids was transcriptional and not due to altered NF-κB nuclear translocation or in vitro promoter binding capability, but due to their inhibition of TNF-α-induced histone H4 acetylation and p65 in vivo binding to the promoter. Additive inhibition was achieved when the two groups of drugs were combined. Our findings reveal a novel mechanism by which β2-agonists, like glucocorticoids, regulate NF-κB-mediated inflammatory gene expression through inhibition of histone acetylation. This provides one explanation for the benefits that result when these agents are combined to treat asthma, and may have important implications in a wide range of inflammatory diseases.