MEX3B inhibits collagen production in eosinophilic nasal polyps by downregulating epithelial cell TGFBR3 mRNA stability
Jin-Xin Liu, Ao-Nan Chen, Qihong Yu, Ke-Tai Shi, Yi-Bo Liu, Cui-Lian Guo, Zhe-Zheng Wang, Yin Yao, Li Pan, Xiang Lu, Kai Xu, Heng Wang, Ming Zeng, Chaohong Liu, Robert P. Schleimer, Ning Wu, Bo Liao, Zheng Liu
Jin-Xin Liu, Ao-Nan Chen, Qihong Yu, Ke-Tai Shi, Yi-Bo Liu, Cui-Lian Guo, Zhe-Zheng Wang, Yin Yao, Li Pan, Xiang Lu, Kai Xu, Heng Wang, Ming Zeng, Chaohong Liu, Robert P. Schleimer, Ning Wu, Bo Liao, Zheng Liu
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Research Article Inflammation

MEX3B inhibits collagen production in eosinophilic nasal polyps by downregulating epithelial cell TGFBR3 mRNA stability

Abstract

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.

Authors

Jin-Xin Liu, Ao-Nan Chen, Qihong Yu, Ke-Tai Shi, Yi-Bo Liu, Cui-Lian Guo, Zhe-Zheng Wang, Yin Yao, Li Pan, Xiang Lu, Kai Xu, Heng Wang, Ming Zeng, Chaohong Liu, Robert P. Schleimer, Ning Wu, Bo Liao, Zheng Liu

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Figure 3

MEX3B binds to 3′ UTR of TGFBR3 mRNA and destabilizes it.

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MEX3B binds to 3′ UTR of TGFBR3 mRNA and destabilizes it. (A) Distributi...
(A) Distribution of MEX3B binding sites among coding exons (CDS), introns, intergenic, 5′ UTRs, and 3′ UTRs were calculated (right) based on 2 iRIP-Seq assays in BEAS-2B cells. The fold-changes of iRIP cluster distribution relative to genomic distribution were calculated. (B) The enrichment of MEX3B binding sites in TGFBR3 mRNA in HNECs studied by RIP assay followed by RT-PCR (n = 6). Data are presented as the mean ± SEM and were analyzed by the Mann-Whitney U 2-tailed test. (C) Sequences of MEX3B binding cluster motifs in 3′ UTRs were analyzed by HOMER to identify enriched binding motifs. The top 5 most-enriched motifs and their P values in the 2 iRIP-Seq assays are shown. (D) The DNA fragments from the human TGFBR3 3′ UTR were amplified and subcloned into a firefly luciferase reporter pGL3. HNECs were cotransfected with the indicated pGL3-TGFBR3 and pcMEX3B. Cell lysates were harvested for the luciferase assay (n = 6). (E) A schematic presentation of potential MEX3B binding sites in 3′ UTR TGFBR3 mRNA and the corresponding mutants are shown. HNECs were cotransfected with the indicated mutated pGL3-TGFBR3 and pcMEX3B. Cell lysates were harvested for the luciferase assay (n = 6). For D and E, data are presented as the mean ± SEM and were analyzed by unpaired Student’s t test. (F) TGFBR3 mRNA stability detected by means of RT-PCR in siMEX3B or pcMEX3B transfected ALI-cultured HNECs after treatment with actinomycin D (ActD) at 5 μg/mL (n = 6). Data are presented as the mean and were analyzed by the paired Student’s t test. *P < 0.05, **P < 0.01, and #P < 0.05 compared with their corresponding control group.