Transcription factor C/EBP delta in fetal lung: Developmental regulation and effects of cyclic adenosine 3',5'-monophosphate and glucocorticoids
Transcription factor C/EBP delta in fetal lung: Developmental regulation and effects of cyclic adenosine 3',5'-monophosphate and glucocorticoids
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DOI：
10.1210/en.138.12.5527
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发表时间：
1997-12-01
期刊：
影响因子：
4.8
通讯作者：
Mendelson, CR
中科院分区：
文献类型：
--
作者：
Breed, DR;Margraf, LR;Mendelson, CR
肺表面活性物质是一种发育和激素调节的脂蛋白，仅在 II 型肺泡细胞中合成。糖皮质激素和 cAMP 刺激培养的人胎肺中表面活性蛋白-a (SP-A) 基因的转录； cAMP 还可以提高 II 型细胞的分化率。转录因子的 CCAAT/增强子结合蛋白 (C/EBP) 家族在能量代谢、脂质生物合成和细胞分化相关基因的调节中发挥着重要作用。编码 C/EBP δ 的基因在脂肪细胞分化的早期阶段由糖皮质激素诱导，与其他组织相比，在肺中的表达水平相对较高。在本研究中，我们分析了胎兔肺中 C/EBP δ 信使 RNA 水平的发育变化，以及器官培养分化过程中以及用 cAMP 和糖皮质激素治疗后人胎肺中免疫反应性 C/EBP δ 水平的变化。我们观察到，在妊娠第 19 天，胎儿兔肺中可检测到 C/EBP δ 信使 RNA，并在妊娠第 28 天（SP-A 基因转录增加到最大水平的时间）增加了 3.7 倍，达到最高水平。培养前对妊娠中期人胎肺中 C/EBP δ 的免疫组织化学分析显示上皮细胞和偶尔的基质细胞中存在微量核染色。在无血清培养基中进行器官培养 12 小时后，人胎儿肺组织前肺泡管内壁上皮细胞的 C/EBP δ 核染色显着增加。通过免疫印迹分析，发现在对照培养基中的器官培养过程中，C/EBP δ 水平迅速诱导，并且通过地塞米松和 (Bt)(2)cAMP 处理进一步增加。 C/EBP delta 水平在培养的前 24 小时内诱导最大，此后下降；在对照或含 cAMP 的培养基中孵育 72 小时后，C/EBP δ 显着降低。相比之下，在含有地塞米松或地塞米松加 (Bt)(2)cAMP 的培养基中孵育的胎儿肺组织中，C/EBP δ 的下降幅度较小，因此在整个 96 小时培养期间其水平保持升高。我们的研究结果表明，C/EBP δ 主要定位于肺泡上皮细胞，在培养物中的人胎肺分化过程中迅速诱导，并通过 cAMP 和糖皮质激素增加，这表明 C/EBP δ 可能在 II 型细胞分化的调节以及表面活性剂磷脂和蛋白质的合成中发挥作用。
Pulmonary surfactant is a developmentally and hormonally regulated lipoprotein synthesized exclusively in alveolar type II cells. Surfactant protein-a (SP-A) gene transcription in human fetal lung in culture is stimulated by glucocorticoids and cAMP; cAMP also enhances the rate of type II cell differentiation. The CCAAT/enhancer-binding protein (C/EBP) family of transcription factors serves an important role in the regulation of genes involved in energy metabolism, lipid biosynthesis, and cellular differentiation. The gene encoding C/EBP delta, which is induced by glucocorticoids during the early phases of adipocyte differentiation, is expressed at relatively high levels in lung compared with other tissues. In the present study we have analyzed developmental changes in C/EBP delta messenger RNA levels in fetal rabbit lung as well as changes in the levels of immunoreactive C/EBP delta in human fetal lung during differentiation in organ culture and after treatment with cAMP and glucocorticoids. We observed that C/EBP delta messenger RNA is detectable in fetal rabbit lung on day 19 of gestation and is increased similar to 3.7-fold to maximum levels on day 28 of gestation, the time when SP-A gene transcription increases to maximum levels. Immunohistochemical analysis of C/EBP delta in midgestation human fetal lung before culture revealed trace nuclear staining in epithelial and occasional stromal cells. After 12 h of organ culture in serum-free medium, nuclear staining of C/EBP delta was markedly increased in epithelial cells lining the prealveolar ducts of the human fetal lung tissue. By immunoblot analysis, it was found that C/EBP delta levels were induced rapidly during organ culture in control medium and were increased further by treatment with dexamethasone and (Bt)(2)cAMP. C/EBP delta levels were maximally induced during the first 24 h of culture and declined thereafter; after 72 h of incubation in control or cAMP-containing medium, C/EBP delta was reduced markedly. By contrast, in fetal lung tissues incubated in medium containing dexamethasone or dexamethasone plus (Bt)(2)cAMP, the decline in C/EBP delta was more modest, so that levels remained elevated throughout the 96-h culture period. Our findings that C/EBP delta is localized primarily to alveolar epithelial cells, rapidly induced during differentiation of human fetal lung in culture, and increased by cAMP and glucocorticoids suggest a possible role in the regulation of type II cell differentiation and in the synthesis of surfactant phospholipids and proteins.