MUC4 impairs the anti-inflammatory effects of corticosteroids in patients with chronic rhinosinusitis with nasal polyps

Background: Current evidence suggests that membranete-thered mucins could mediate corticosteroid efficacy, interacting with glucocorticoid receptor (GR) in patients with chronic rhinosinusitis with nasal polyps (CRSwNP). Mucin 4 (MUC4)-tethered mucin is expressed in nasal polyp (NP) epithelial cells and upregulated under inflammatory conditions. Moreover, MUC4 beta has the capacity to interact with other intracellular proteins. We hypothesized that MUC4 modulates corticosteroid efficacy of patients with CRSwNP. Objective: We sought to analyze the role of MUC4 in corticosteroid effectiveness in different cohorts of patients with CRSwNP and elucidate the possible mechanisms involved. Methods: Eighty-one patients with CRSwNP took oral corticosteroids for 15 days. Corticosteroid resistance was evaluated by using nasal endoscopy. Expression of MUC4 and MUC4b was evaluated by means of real-time PCR, Western blotting, and immunohistochemistry. BEAS-2B knockdown with RNA interference for MUC4 (small interfering RNA [siRNA]MUC4) was used to analyze the role of MUC4 in the antiinflammatory effects of dexamethasone. Results: Twenty-two patients had NPs resistant to oral corticosteroids. MUC4(expression) was upregulated in these patients. In siRNA-MUC4 BEAS-2B airway epithelial cells dexamethasone produced higher anti-inflammatory effects, increased inhibition of phospho-extracellular signal-regulated kinase 1/2, increased mitogen-activated protein kinase phosphatase 1 expression, and increased glucocorticoid response element activation. Immunoprecipitation and immunofluorescence experiments revealed that MUC4 beta forms a complex with GR alpha in the nuclei of NP epithelial cells from corticosteroid- resistant patients. Conclusion: MUC4b participates in the corticosteroid resistance process, inhibiting normal GRa nuclear function. The high expression of MUC4 in patients with CRSwNP might participate in corticosteroid resistance.