Formoterol restores oxidative stress-induced corticosteroid insensitivity via activation of protein phosphatase PP2A

Introduction: Oxidative stress induces corticosteroid (CS) insensitivity via the activation of phosphoinositide-3-kinase (PI3K) and reduced HDAC2 activity. We have demonstrated that the long-acting β 2 -adrenoceptor agonist formoterol (FORM) restores CS sensitivity via PI3Kδ-Akt signalling inhibition (BJP 2012). However, the mechanism for this effect has not yet been elucidated. Here, we investigated whether FORM (10 -9 M) inhibited PI3K signalling through a serine/threonine phosphatase PP2A. Methods: CS sensitivity was determined by IC 50 of dexamethasone on TNFα-induced IL-8 in U937 cells exposed to H 2 O 2 or by budesonide ability of inhibition of LPS-induced TNFα in PBMCs transfected with PP2A. HDAC2 and PP2A were measured by fluorescence-based activity assays. Phosphorylation of Akt was used as a marker of PI3K activation determined by Western blotting and okadaic acid (OA) was used to inhibit PP2A. Results: Dexamethasone potency, reduced 3-fold by H 2 O 2 , was restored by FORM in U937 cells. FORM also counteracted H 2 O 2 -induced increase of Akt phosphorylation, decrease of HDAC2 activation and PP2A activity. Pretreatment with OA abrogated the effects of FORM. In PBMCs from COPD patients, PP2A activity was significantly reduced by 50% vs. healthy volunteers but was restored by FORM ex vivo treatment. Furthermore, PP2A overexpression increased responsiveness to budesonide in PBMCs from COPD patients. Conclusions: Activation of PP2A by FORM inhibits PI3K activation, thereby restoring HDAC2 activity and CS sensitivity after oxidative stress. PP2A appears to be a negative regulator of PI3K signalling and impaired PP2A in COPD may be a potential therapeutic target.