Patients with COPD have a progressive reduction in total HDAC activity that reflects the severity of the disease.

We have investigated the ability of dexamethasone to regulate interleukin-1␤ (IL-1␤)-induced gene expression, histone acetyltransferase (HAT) and histone deacetylase (HDAC) activity. Low concentrations of dexamethasone (10 ؊10 M) repress IL-1␤-stimulated granulocyte-macrophage colony-stimulating factor (GM-CSF) expression and fail to stimulate secretory leukocyte proteinase inhibitor expression. Dexamethasone (10 ؊7 M) and IL-1␤ (1 ng/ml) both stimulated HAT activity but showed a different pattern of histone H4 acetylation. Dexamethasone targeted lysines K5 and K16, whereas IL-1␤ targeted K8 and K12. Low concentrations of dexamethasone (10 ؊10 M), which do not transactivate, repressed IL-1␤-stimulated K8 and K12 acetylation. Using chromatin immunoprecipitation assays, we show that dexamethasone inhibits IL-1␤-enhanced acetylated K8-associated GM-CSF promoter enrichment in a concentration-dependent manner. Neither IL-1␤ nor dexamethasone elicited any GM-CSF promoter association at acetylated K5 residues. Furthermore, we show that GR acts both as a direct inhibitor of CREB binding protein (CBP)-associated HAT activity and also by recruiting HDAC2 to the p65-CBP HAT complex. This action does not involve de novo synthesis of HDAC protein or altered expression of CBP or p300/CBP-associated factor. This mechanism for glucocorticoid repression is novel and establishes that inhibition of histone acetylation is an additional level of control of inflammatory gene expression. This further suggests that pharmacological manipulation of of specific histone acetylation status is a potentially useful approach for the treatment of inflammatory diseases.

Glucocorticoids are the most effective antiinflammatory agents for the treatment of chronic inflammatory diseases even though some diseases, such as chronic obstructive pulmonary disease (COPD), are relatively glucocorticoid insensitive. However, the molecular mechanism of this glucocorticoid insensitivity remains uncertain. We show that a defect of glucocorticoid receptor (GR) deacetylation caused by impaired histone deacetylase (HDAC) 2 induces glucocorticoid insensitivity toward nuclear factor (NF)-κB–mediated gene expression. Specific knockdown of HDAC2 by RNA interference resulted in reduced sensitivity to dexamethasone suppression of interleukin 1β–induced granulocyte/macrophage colony-stimulating factor production. Loss of HDAC2 did not reduce GR nuclear translocation, GR binding to glucocorticoid response element (GRE) on DNA, or GR-induced DNA or gene induction but inhibited the association between GR and NF-κB. GR becomes acetylated after ligand binding, and HDAC2-mediated GR deacetylation enables GR binding to the NF-κB complex. Site-directed mutagenesis of K494 and K495 reduced GR acetylation, and the ability to repress NF-κB–dependent gene expression becomes insensitive to histone deacetylase inhibition. In conclusion, we show that overexpression of HDAC2 in glucocorticoid-insensitive alveolar macrophages from patients with COPD is able to restore glucocorticoid sensitivity. Thus, reduction of HDAC2 plays a critical role in glucocorticoid insensitivity in repressing NF-κB–mediated, but not GRE-mediated, gene expression.

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