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Although the expression of Mex3 RNA-binding family member B (MEX3B) is upregulated in human nasal epithelial cells (HNECs) predominately in the eosinophilic chronic rhinosinusitis (CRS) with nasal polyps (CRSwNP) subtype, its functions as an RNA binding protein in airway epithelial cells remain unknown. Here, we revealed the role of MEX3B based on different subtypes of CRS and demonstrated that MEX3B decreased the TGF-β receptor III (TGFBR3) mRNA level by binding to its 3′ UTR and reducing its stability in HNECs. TGF-βR3 was found to be a TGF-β2–specific coreceptor in HNECs. Knocking down or overexpressing MEX3B promoted or inhibited TGF-β2–induced phosphorylation of SMAD2 in HNECs, respectively. TGF-βR3 and phosphorylated SMAD2 levels were downregulated in CRSwNP compared with controls and CRS without nasal polyps with a more prominent downregulation in the eosinophilic CRSwNP. TGF-β2 promoted collagen production in HNECs. Collagen abundance decreased and edema scores increased in CRSwNP compared with control, again more prominently in the eosinophilic type. Collagen expression in eosinophilic CRSwNP was negatively correlated with MEX3B but positively correlated with TGF-βR3. These results suggest that MEX3B inhibits tissue fibrosis in eosinophilic CRSwNP by downregulating epithelial cell TGFBR3 expression; consequently, MEX3B might be a valuable therapeutic target against eosinophilic CRSwNP.

Abstract Background The role of endoplasmic reticulum (ER) stress in the pathogenesis of allergic rhinitis (AR) remains elusive. Methods Real‐time polymerase chain reaction (RT‐PCR), immunohistochemistry, and western blotting analyses were performed to detect the expression of ER stress and unfolded protein response markers: 78‐kDa glucose‐regulated protein (GRP78), C/EBP homologous protein (CHOP), activating transcription factor 6 (ATF6α), spliced X‐box binding protein 1 (sXBP‐1), and phosphorylated eukaryotic initiation factor 2α (p‐eIF2α), in inferior turbinate tissue samples from patients with AR and non‐AR controls. Nasal tissues from patients with AR were cultured ex vivo and treated with 4‐phenylbutyric acid (4‐PBA), an ER stress inhibitor. Results Compared to those in non‐AR controls, the mRNA and protein levels of GRP78, CHOP, ATF6α, sXBP‐1, and p‐eIF2α were significantly increased in nasal tissues from patients with AR. GRP78 and CHOP were mainly expressed in CD138+ plasma cells in nasal tissues from patients with AR. The frequency of IgE+CD138+ plasma cells was significantly higher in nasal tissues from patients with AR than that in non‐AR controls. IgE levels in nasal secretions and tissues were positively correlated with GRP78 and CHOP mRNA levels in the nasal tissues. After 4‐PBA treatment, the protein expression of GRP78, CHOP, ATF6α, sXBP‐1, and p‐eIF2α was significantly reduced in cultured AR‐derived nasal tissues, and IgE levels were simultaneously decreased in cultured supernatants. Conclusions ER stress may be involved in the regulation of local IgE production in patients with AR. Inhibition of ER stress potentially provides a therapeutic avenue in AR by reducing local IgE production. Level of Evidence NA