Inhibition of Histone Deacetylase 2 Expression by Elevated Glucocorticoid Receptor β in Steroid-resistant Asthma

Rationale: Cross-talk between glucocorticoid receptors and histone deacetylases (HDACs) under steroid-insensitive conditions has not been explored. Objectives: To evaluate expression and interaction of HDACs with glucocorticoid receptor isoforms in bronchoalveolar lavage and peripheral blood mononuclear cells from steroid-resistant versus steroid-sensitive patients with asthma. Methods: Expression of HDACs 1 through 11 was measured by real-time polymerase chain reaction in primary cells and in the DO11.10 cell line, designed to overexpress glucocorticoid receptor beta. Glucocorticoid receptor beta expression was inhibited in bronchoalveolar lavage cells by small interfering RNA. Human HDAC2 promoter fragments were cloned into a luciferase reporter vector, and transiently transfected with glucocorticoid receptor alpha- and beta-encoding plasmids into the cells. Luciferase activity was then assayed in response to glucocorticoids. Measurements and Main Results: Levels of HDAC2 mRNA, but not other histone deacetylases, were significantly decreased in bronchoalveolar lavage cells but not in peripheral blood mononuclear cells from steroid-resistant patients with asthma. Overexpression of glucocorticoid receptor beta in DO11.10 cells selectively reduced HDAC2 mRNA and protein levels. Silencing of glucocorticoid receptor beta in bronchoalveolar lavage cells from patients with asthma significantly increased HDAC2 mRNA. Luciferase activity assays with HDAC2 promoter reporter constructs identified two glucocorticoid-inducible regions in the HDAC2 promoter. Promoter activity was increased more than fourfold in dexamethasone-treated cells cotransfected with glucocorticoid receptor alpha. Cotransfection of glucocorticoid receptor beta abolished this effect in a dose-dependent manner. Conclusions: Glucocorticoid receptor beta controls expression of histone deacetylase 2 by inhibiting glucocorticoid response elements in its promoter. This highlights a novel mechanism by which glucocorticoid receptor beta promotes steroid insensitivity (Li et al.: J Allergy Clin Immunol 2009;123:S146; and Li et al.: I Allergy Clin Immunol 2010;125:AB104).