Prostaglandin D2 induces MUC5B gene expression through the DP1 receptor and the ERK MAPK/RSK1/CREB signaling in human airway epithelial cells

Abstract

Up-regulated expression of the secreted gel-forming mucin gene MUC5B is a major factor in various inflammatory diseases of the airway. Mucin gene expression is affected by inflammatory mediators such as prostaglandin (PG) D2, which is synthesized from arachidonic acid via enzymatic conversion by both cyclooxygenase and a hematopoietic form of prostaglandin D synthase (H-PGDS). PGD2 is known to act through two cell-membrane receptors, D-prostanoid receptor (DP1) and chemoattractant receptor homologous molecule expressed on T-helper type 2 (Th2) cells (CRTH2/DP2), but the mechanisms whereby DP1 and CRTH2 receptors are involved in PGD2-induced MUC5B gene expression in the airway remain unclear. The goal of this study was to determine the mechanisms by which PGD2 induces MUC5B gene expression in airway epithelial cells. Western blot analysis indicated that H-PGDS was highly expressed in nasal polyp tissues of patients, but no differences were detected between the allergic and non-allergic group. Similar results were obtained for the level of PGD2 in nasal polyp tissues. In addition, we could clearly detect H-PGDS in human nasal epithelial cells. The DP1 receptor was expressed at significant levels in human primary nasal epithelial cells, whereas CRTH2 expression was undetectable. We demonstrated that PGD2 induced MUC5B gene expression in a dose-dependent and a time-dependent manner in both normal human nasal epithelial cells (NHNE) and NCI-H292 cells. DP1 specific antagonist S5751 inhibited both PGD2-induced extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinase (MAPK) activation and MUC5B gene expression. However, CRTH2 antagonist (OC0459) did not have an inhibitory effect. Finally, we demonstrate that PGD2 induced MUC5B expression through DP1 receptor in airway epithelial cells. Pretreatment with ERK1/2 inhibitor (PD98059) blocked both PGD2-induced ERK1/2 MAPK activation and MUC5B gene expression. PGD2 induced the activation of p90 ribosomal S6 protein kinase 1 (RSK1) and cAMP response element-binding protein (CREB) in NCI-H292 cells, but it did not induce an increase in intracellular calcium concentration [Ca2+]. Two cAMP-response element (CRE) sites (-921/-914 and -900/-893) in the MUC5B promoter were found to be essential for PGD2-induced MUC5B gene expression, and CRE responsive signaling cascades through ERK1/2 MAPK are critical aspects of the intracellular mechanisms that mediate MUC5B gene expression.In summary, our data provide new insights into the molecular mechanisms by which PGD2 induces MUC5B gene expression in airway epithelial cells.