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Nortriptyline reverses corticosteroid insensitivity by inhibition of phosphoinositide-3-kinase-?.

ABSTRACT: Corticosteroid insensitivity represents a major barrier to the treatment of chronic obstructive pulmonary disease (COPD) and severe asthma. It is caused by oxidative stress, leading to reduced histone deacetylase-2 (HDAC2) function through activation of phosphoinositide-3-kinase-? (PI3K?). The tricyclic antidepressant nortriptyline has been identified in high-throughput screens as an agent that increases corticosteroid responsiveness. The aim of this study was to identify the molecular mechanism whereby nortriptyline increases corticosteroid sensitivity. Phosphorylation of Akt, a footprint of PI3K activation, and HDAC activity were evaluated by Western blotting and fluorescent activity assay in U937 monocytic cells. Corticosteroid sensitivity was evaluated by the inhibition of tumor necrosis factor ? (TNF?)-induced interleukin 8 (IL-8) production by budesonide. Hydrogen peroxide (H(2)O(2)) or cigarette smoke extract (CSE) increased the level of phosphorylated Akt (pAkt) and reduced HDAC activity. Pretreatment with nortriptyline inhibited pAkt induced by CSE and H(2)O(2) as well as restored HDAC activity that had been decreased by H(2)O(2) and CSE. In addition, nortriptyline inhibited PI3K? activity, but had no effect on the PI3K? and PI3K? isoforms. Although CSE reduced the effects of budesonide on TNF?-induced IL-8 production in U937 cells, nortriptyline reversed CSE-induced corticosteroid insensitivity. Nortriptyline restores corticosteroid sensitivity induced by oxidative stress via direct inhibition of PI3K? and is a potential treatment for corticosteroid-insensitive diseases such as COPD and severe asthma.

SUBMITTER: Mercado N

PROVIDER: S-EPMC3083104 | biostudies-literature | 2011 May

REPOSITORIES: biostudies-literature

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Nortriptyline reverses corticosteroid insensitivity by inhibition of phosphoinositide-3-kinase-δ.

Mercado Nicolas N To Yasuo Y Ito Kazuhiro K Barnes Peter J PJ

The Journal of pharmacology and experimental therapeutics 20110207 2

Corticosteroid insensitivity represents a major barrier to the treatment of chronic obstructive pulmonary disease (COPD) and severe asthma. It is caused by oxidative stress, leading to reduced histone deacetylase-2 (HDAC2) function through activation of phosphoinositide-3-kinase-δ (PI3Kδ). The tricyclic antidepressant nortriptyline has been identified in high-throughput screens as an agent that increases corticosteroid responsiveness. The aim of this study was to identify the molecular mechanism ...[more]

PMID: 21300705

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Project description:BACKGROUND: Corticosteroid insensitivity is a major barrier of treatment for some chronic inflammatory diseases, such as severe asthma, but the molecular mechanism of the insensitivity has not been fully elucidated. The object of this study is to investigate the role of protein phosphate 2A (PP2A), a serine/threonine phosphatase, on corticosteroid sensitivity in severe asthma. METHODOLOGY/PRINCIPAL FINDINGS: Corticosteroid sensitivity was determined by the dexamethasone ability to inhibit TNF?-induced IL-8 or LPS-induced TNF? production. PP2A expression, glucocorticoid receptor (GR) nuclear translocation defined as the nuclear/cytoplasmic GR ratio and phosphorylation of GR-Ser²²?, c-Jun N-terminal kinase 1 (JNK1) and PP2A were analysed by Western-blotting. Phosphatase activity was measured by fluorescence-based assay. Okadaic acid (OA), a PP2A inhibitor, reduced corticosteroid sensitivity with reduced GR nuclear translocation and increased GR phosphorylation in U937 monocytic cells. PP2A knockdown by RNA interference showed similar effects. IL-2/IL-4 treatment to U937 reduced corticosteroid sensitivity, and PP2A expression/activity. In peripheral blood mononuclear cells (PBMCs) from severe asthma, the PP2A expression and activity were significantly reduced with concomitant enhancement of PP2A(C)-Tyr³?? phosphorylation compared with those in healthy volunteers. As the results, GR-Ser²²? and JNK1 phosphorylation were increased. The expression and activity of PP2A were negatively correlated with phosphorylation levels of GR-Ser²²?. Furthermore, co-immunoprecipitation assay in U937 cells revealed that PP2A associated with GR and JNK1 and IL-2/IL-4 exposure caused dissociation of each molecule. Lastly, PP2A overexpression increased corticosteroid sensitivity in U937 cells. CONCLUSIONS/SIGNIFICANCE: PP2A regulates GR nuclear translocation and corticosteroid sensitivity possibly by dephosphorylation of GR-Ser²²? via dephosphorylation of upstream JNK1. This novel mechanism will provide new insight for the development of new therapy for severe asthma.

Dataset Information

Nortriptyline reverses corticosteroid insensitivity by inhibition of phosphoinositide-3-kinase-?.

Publications

Nortriptyline reverses corticosteroid insensitivity by inhibition of phosphoinositide-3-kinase-δ.

Similar Datasets

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