Syk Inhibitor Improves The Glucocorticoid Resistance Of Human Airway Epithelial Cells

Objective: To explore the role of R406,a small-molecule inhibitor of spleen tyrosine kinase(Syk),in improving the glucocorticoid resistance of human airway epithelial cells and elucidate the possible mechanisms involved.Methods: Human bronchial epithelial cell line BEAS-2B cells were pretreated with Syk inhibitor R406,following stimulation with dexamethasone and/or TNF-α.The expression of proinflammatory cytokine IL-8 in cell culture supernatant was detected by enzyme-linked immunosorbent assay(ELISA).The m RNA expression of IL-8,glucocorticoid induced leucine zipper proteins(GILZ)and glucocorticoid induced transcription 1(GLCCI1)were evaluated by real-time PCR.The phosphorylation level of extracellular signal regulating kinase(ERK1/2),jun kinase(JNK),Ser226 residue of glucocorticoid receptor(GR-Ser226)and nuclear factor-κB(NF-κB)were detected by Western blot.The expression and nuclear translocation of glucocorticoid receptor GRα was detected by immunefluorescence.Results: TNF-α-induced IL-8 production in BEAS-2B cells could not completely inhibit by dexamethasone,while Syk inhibitor R406 promoted the anti-inflammatory effect of dexamethasone significantly.Phosphorylation of ERK1/2 and JNK induced by TNF-α increased the phosphorylation of GR-Ser226,while R406 reduced the phosphorylation of GR-Ser226 through repressing phosphorylation of ERK1/2 and JNK.Moreover,R406 also restored impaired expression and nuclear translocation of GRα induced by TNF-α.Syk inhibitor R406 not only promoted the inhibitory effect of dexamethasone on NF-κB in the presence of TNF-α,but also increased the expression of GILZ and GLCCI1.Conclusion: Syk inhibitor R406 could improve the anti-inflammatory sensitivity of dexamethasone in human bronchial epithelial cells by inhibiting MAPKs pathway and then GR-Ser226 phosphorylation,restoring impaired GRα nuclear translocation induced by TNF-α,and regulating Dex-induced transrepression and transactivation.This study provides reference for the future development of drugs for the treatment of steroid-resistant asthma.