TTF-1 regulates α(5 )nicotinic acetylcholine receptor (nAChR) subunits in proximal and distal lung epithelium

BACKGROUND: Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels comprised of five similar subunits that influence signal transduction and cell turnover. α(5 )is a structural subunit detected in many non-neuronal tissues; however, its function during pulmonary development is unknown. RESULTS: α(5 )was 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, α(5 )expression was primarily observed in primitive airway epithelial cells while mesenchymal expression was faint and sporadic. α(5 )expression 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 α(5 )expression was almost undetectable in the proximal lung from PN4-PN10, but significant localization was again observed at PN20. Transcriptional control of α(5 )was determined by assessing the activity of reporters containing 2.0-kb and 850-bp of the mouse α(5 )promoter. Because perinatal expression of α(5 )was abundant in bronchiolar and alveolar epithelium, we assessed transcriptional control of α(5 )in 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 α(5 )transcription by acting on both the 2.0-kb and 850-bp α(5 )promoters. Site-directed mutagenesis revealed that TTF-1 activated α(5 )transcription by binding specific TTF-1 response elements. Exogenous TTF-1 also significantly induced α(5 )transcription. CONCLUSIONS: These data demonstrate that α(5 )is specifically controlled in a temporal and spatial manner during pulmonary morphogenesis. Ongoing research may demonstrate that precise regulation of α(5 )is important during normal organogenesis and misexpression correlates with tobacco related lung disease.