CD38 Expression Is Insensitive to Steroid Action in Cells Treated with Tumor Necrosis Factor-α and Interferon-γ by a Mechanism Involving the Up-Regulation of the Glucocorticoid Receptor β Isoform

Abstract

Evidence shows that the CD38 molecule, recently involved in the two main features of asthma, bronchial hyper-responsiveness and airway inflammation, could represent a new potential therapeutic target for asthma. In this study, we investigated whether glucocorticoid (GC), the most effective treatment for lung diseases, can affect CD38 expression in human airway smooth muscle (ASM) cells treated with different pro-inflammatory cytokines, such as tumor necrosis factor-α (TNFα) and interferons (IFNs). We found that CD38 expression induced by TNFα alone was completely abrogated by fluticasone (100 nM), dexamethasone (1 μM), or budesonide (100 nM). In contrast, the synergistic induction of CD38 by the combination of TNFα with IFNγ or IFNβ, but not with IL-1β or IL-13, was completely insensitive to the GC inhibitory effects. We also found that TNFα and IFNγ impaired GC responsiveness by inhibiting steroid induced both 1) GRα-DNA binding activity and 2) GC-responsive element-(GRE)-dependent gene transcription. Although levels of the GC receptor (GR) α isoform remained unchanged, expression of GRβ, the dominant-negative GR isoform, was synergistically increased by TNFα and IFNγ with a GRα/GRβ ratio of 1 to 3. More importantly, fluticasone failed to induce GRE-dependent gene transcription and to suppress TNFα-induced CD38 expression in ASM cells transfected with constitutively active GRβ. We conclude that, upon pro-inflammatory cytokine stimulation, CD38 expression becomes insensitive to GC action by a mechanism involving the up-regulation of GRβ isoform, thus providing a novel in vitro cellular model to dissect GC resistance in primary cells.