Young Hays W J, Williams Olatunji W, Chandra Divay, Bellinghausen Lindsey K, Pérez Guillermina, Suárez Alberto, Tuvim Michael J, Roy Michelle G, Alexander Samantha N, Moghaddam Seyed J, Adachi Roberto, Blackburn Michael R, Dickey Burton F, Evans Christopher M
Department of Pulmonary Medicine, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Am J Respir Cell Mol Biol. 2007 Sep;37(3):273-90. doi: 10.1165/rcmb.2005-0460OC. Epub 2007 Apr 26.
Mucus hypersecretion contributes to morbidity and mortality in many obstructive lung diseases. Gel-forming mucins are the chief glycoprotein components of airway mucus, and elevated expression of these during mucous metaplasia precedes the hypersecretory phenotype. Five orthologous genes (MUC2, MUC5AC, MUC5B, MUC6, and MUC19) encode the mammalian gel-forming mucin family, and several have been implicated in asthma, cystic fibrosis, and chronic obstructive pulmonary disease pathologies. However, in the absence of a comprehensive analysis, their relative contributions remain unclear. Here, we assess the expression of the entire gel-forming mucin gene family in allergic mouse airways and show that Muc5ac is the predominant gel-forming mucin induced. We previously showed that the induction of mucous metaplasia in ovalbumin-sensitized and -challenged mouse lungs occurs within bronchial Clara cells. The temporal induction and localization of Muc5ac transcripts correlate with the induced expression and localization of mucin glycoproteins in bronchial airways. To better understand the tight regulation of Muc5ac expression, we analyzed all available 5'-flanking sequences of mammalian MUC5AC orthologs and identified evolutionarily conserved regions within domains proximal to the mRNA coding region. Analysis of luciferase reporter gene activity in a mouse transformed Clara cell line demonstrates that this region possesses strong promoter activity and harbors multiple conserved transcription factor-binding motifs. In particular, SMAD4 and HIF-1alpha bind to the promoter, and mutation of their recognition motifs abolishes promoter function. In conclusion, Muc5ac expression is the central event in antigen-induced mucous metaplasia, and phylogenetically conserved 5' noncoding domains control its regulation.
黏液高分泌在许多阻塞性肺部疾病中会导致发病和死亡。凝胶形成黏蛋白是气道黏液的主要糖蛋白成分，在黏液化生过程中这些黏蛋白的表达升高先于高分泌表型出现。五个直系同源基因（MUC2、MUC5AC、MUC5B、MUC6和MUC19）编码哺乳动物凝胶形成黏蛋白家族，其中几个基因与哮喘、囊性纤维化和慢性阻塞性肺疾病的病理过程有关。然而，在缺乏全面分析的情况下，它们的相对作用仍不清楚。在此，我们评估了整个凝胶形成黏蛋白基因家族在变应性小鼠气道中的表达，结果表明Muc5ac是诱导产生的主要凝胶形成黏蛋白。我们之前表明，在卵清蛋白致敏和激发的小鼠肺中，黏液化生的诱导发生在支气管克拉拉细胞内。Muc5ac转录本的时间诱导和定位与支气管气道中黏蛋白糖蛋白的诱导表达和定位相关。为了更好地理解Muc5ac表达的严格调控，我们分析了哺乳动物MUC5AC直系同源基因所有可用的5'侧翼序列，并在mRNA编码区近端的结构域内鉴定出进化保守区域。对小鼠转化克拉拉细胞系中荧光素酶报告基因活性的分析表明，该区域具有强大的启动子活性，并含有多个保守的转录因子结合基序。特别是，SMAD4和HIF-1α与启动子结合，其识别基序的突变会消除启动子功能。总之，Muc5ac表达是抗原诱导黏液化生的核心事件，系统发育保守的5'非编码结构域控制其调控。
