Beers M F, Shuman H, Liley H G, Floros J, Gonzales L W, Yue N, Ballard P L
Institute for Environmental Medicine, University of Pennsylvania, Philadelphia, USA.
Pediatr Res. 1995 Nov;38(5):668-75. doi: 10.1203/00006450-199511000-00007.
Pulmonary surfactant protein B (SP-B) enhances phospholipid film formation in vitro and is essential for normal surfactant function in vivo. We examined human fetal lung before and during explant culture for content and cellular localization of SP-B mRNA and protein. SP-B mRNA was low in preculture specimens (18-20 wk) but hybridization signal increased over epithelial cells during culture and was enhanced by dexamethasone treatment (10 nM). SP-B immunofluorescence was very low in preculture specimens, increased during culture, and was uniformly intense in epithelial cells of dexamethasone-treated tissue. With a newly developed immunoassay, SP-B protein was undetectable in preculture lung (< 2% of adult), appeared during culture (26% of adult), and was further increased approximately 3-fold by dexamethasone treatment (86% of adult); lung tissue of two newborn infants contained 7-9-fold more SP-B than is found in the adult. Using Western blot with enhanced chemiluminescence, mature SP-B was undetectable in 16-wk specimens but was present in 19-24-wk preculture tissue at 0.2-2.9% of the adult level. By comparison, SP-B mRNA content is 14 and 50% of adult level in 19- and 24-wk lung tissue, respectively; levels increase 3-fold during culture and a further 3-fold with dexamethasone. Based on these observed differences between mRNA and protein content, we conclude that basal SP-B gene expression in epithelial cells of human fetal lung is regulated primarily at the level of translation or protein stability, whereas glucocorticoids act transcriptionally. We speculate that SP-B protein accumulates only as type II cells differentiate and acquire lamellar bodies for processing and storage of SP-B.
肺表面活性物质蛋白B（SP - B）在体外可增强磷脂膜的形成，且对体内正常的表面活性物质功能至关重要。我们检测了人胎儿肺在植块培养前后SP - B mRNA和蛋白的含量及细胞定位。培养前标本（18 - 20周）中SP - B mRNA水平较低，但培养过程中上皮细胞上的杂交信号增强，地塞米松处理（10 nM）可使其进一步增强。培养前标本中SP - B免疫荧光非常低，培养过程中增加，在地塞米松处理组织的上皮细胞中呈均匀强烈表达。采用新开发的免疫测定法，培养前肺中未检测到SP - B蛋白（<成人水平的2%），培养过程中出现（成人水平的26%），地塞米松处理使其进一步增加约3倍（成人水平的86%）；两名新生儿的肺组织中SP - B含量比成人高7 - 9倍。使用增强化学发光的蛋白质印迹法，16周标本中未检测到成熟的SP - B，但19 - 24周培养前组织中存在，为成人水平的0.2 - 2.9%。相比之下，19周和24周肺组织中SP - B mRNA含量分别为成人水平的14%和50%；培养过程中水平增加3倍，地塞米松处理后再增加3倍。基于这些观察到的mRNA和蛋白含量差异，我们得出结论，人胎儿肺上皮细胞中基础SP - B基因表达主要在翻译或蛋白质稳定性水平受到调控，而糖皮质激素则通过转录起作用。我们推测，只有当II型细胞分化并获得板层小体以加工和储存SP - B时，SP - B蛋白才会积累。
