TTF-1 regulates α5nicotinic acetylcholine receptor (nAChR) subunits in proximal and distal lung epithelium

Abstract

Background: Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels comprised of five similar subunits that influence signal transduction and cell turnover. α5is a structural subunit detected in many non-neuronal tissues; however, its function during pulmonary development is unknown.Results: α5was assessed by immunohistochemistry and RT-PCR in mouse lungs from embryonic day (E)13.5 to post-natal day (PN)20. From E13.5 to E18.5, α5expression was primarily observed in primitive airway epithelial cells while mesenchymal expression was faint and sporadic. α5expression was detected throughout the proximal lung at PN1 and extensively expressed in the peripheral lung at PN4, an early stage of murine alveologenesis. An interesting shift occurred wherein α5expression was almost undetectable in the proximal lung from PN4-PN10, but significant localization was again observed at PN20. Transcriptional control of α5was determined by assessing the activity of reporters containing 2.0-kb and 850-bp of the mouse α5promoter. Because perinatal expression of α5was abundant in bronchiolar and alveolar epithelium, we assessed transcriptional control of α5in Beas2B cells, a human bronchiolar epithelial cell line, and A-549 cells, an alveolar type II cell-like human epithelial cell line. Thyroid Transcription Factor-1 (TTF-1), a key transcription regulator of pulmonary morphogenesis, significantly increased α5transcription by acting on both the 2.0-kb and 850-bp α5promoters. Site-directed mutagenesis revealed that TTF-1 activated α5transcription by binding specific TTF-1 response elements. Exogenous TTF-1 also significantly induced α5transcription.Conclusions: These data demonstrate that α5is specifically controlled in a temporal and spatial manner during pulmonary morphogenesis. Ongoing research may demonstrate that precise regulation of α5is important during normal organogenesis and misexpression correlates with tobacco related lung disease. © 2010 Reynolds et al; licensee BioMed Central Ltd.