Reynolds Paul R, Hoidal John R
Department of Internal Medicine, Pulmonary Division, University of Utah Health Sciences Center, Salt Lake City, 84132, USA.
J Biol Chem. 2005 Sep 16;280(37):32548-54. doi: 10.1074/jbc.M502231200. Epub 2005 Jul 20.
Nicotinic acetylcholine receptors are ligand-gated ion channels formed by five homologous subunits that are involved in processes including signal transduction, proliferation, and apoptosis. The developmental role of these receptors, however, is unclear. In the present investigation, alpha(7) nicotinic acetylcholine receptor expression was assessed by immunohistochemistry in mouse lungs from embryonic day (E)13.5 to postnatal day (PN)20. Transcriptional mechanisms that regulate alpha(7) were assessed by the transfection of murine bronchiolar cells with a reporter containing 1.1 kb of the mouse alpha(7) promoter, TTF-1, and Egr-1. alpha(7) was initially detected at E13.5 in pulmonary mesenchymal cells and in the epithelium of the primitive tubules at E15.5. From E18.5 to PN1, alpha(7) was expressed in conducting airway and saccule epithelial cells. By PN10, expression was observed in the peripheral epithelium and on luminal membranes of bronchiolar epithelial cells in the proximal lung, a pattern that continued through PN20. From E15.5 to PN20, type II alveolar cells expressed both prosurfactant protein C and alpha(7). From E18.5 to PN20, Clara cells in the bronchiolar epithelium co-expressed Clara cell secretory protein and alpha(7). TTF-1 dose-dependently activated alpha(7) transcription in vitro by binding specific TTF-1 regulatory elements in the mouse alpha(7) promoter. Furthermore, alpha(7) was not detected in TTF-1-null mice and markedly increased in TTF-1-overexpressing mice. Conversely, Egr-1 inhibited alpha(7) expression. Temporal-spatial alpha(7) expression supports the concept that these receptors function during normal pulmonary morphogenesis. A model is also supported whereby alpha(7) is induced by the essential pulmonary transcription factor TTF-1 and suppressed by Egr-1 during pulmonary development.
烟碱型乙酰胆碱受体是由五个同源亚基组成的配体门控离子通道，参与信号转导、增殖和凋亡等过程。然而，这些受体在发育过程中的作用尚不清楚。在本研究中，通过免疫组织化学方法评估了从胚胎第（E）13.5天到出生后第（PN）20天小鼠肺中α（7）烟碱型乙酰胆碱受体的表达。通过用含有1.1 kb小鼠α（7）启动子、TTF-1和Egr-1的报告基因转染小鼠细支气管细胞，评估了调节α（7）的转录机制。α（7）最初在E13.5时在肺间充质细胞中被检测到，在E15.5时在原始小管的上皮细胞中被检测到。从E18.5到PN1，α（7）在传导气道和囊泡上皮细胞中表达。到PN10时，在近端肺的外周上皮和细支气管上皮细胞的腔膜上观察到表达，这种模式一直持续到PN20。从E15.5到PN20，II型肺泡细胞同时表达前表面活性蛋白C和α（7）。从E18.5到PN20，细支气管上皮中的克拉拉细胞共表达克拉拉细胞分泌蛋白和α（7）。TTF-1通过结合小鼠α（7）启动子中的特定TTF-1调节元件在体外剂量依赖性地激活α（图7）转录。此外，在TTF-1基因敲除小鼠中未检测到α（7），而在TTF-1过表达小鼠中α（7）明显增加。相反，Egr-1抑制α（7）表达。α（7）的时空表达支持了这些受体在正常肺形态发生过程中发挥作用的概念。还支持一种模型，即在肺发育过程中，α（7）由必需的肺转录因子TTF-1诱导并被Egr-1抑制。
