Yang Meng-Chun, Guo Yuhong, Liu Chia-Chi, Weissler Jonathan C, Yang Yih-Sheng
Department of Internal Medicine, Pulmonary and Critical Care Medicine, UT Southwestern Medical Center, Dallas, TX 75390-9034, USA.
Biochem Biophys Res Commun. 2006 Jun 2;344(2):484-90. doi: 10.1016/j.bbrc.2006.03.158. Epub 2006 Apr 4.
Surfactant protein-B (SP-B) and -C (SP-C) are small hydrophobic surfactant proteins that maintain surface tension in alveoli. Both SP-B and SP-C are regulated by a key factor, thyroid transcription factor-1 (TTF-1), in lung cells. Previously, we identified a 26-kDa, TTF-1-associated protein (TAP26) that was shown to interact with TTF-1 and enhance TTF-1-transactivated SP-B promoter activity. In this study, we hypothesized that TAP26 could also serve as a co-activator of the SP-C promoter. Using the chromatin immunoprecipitation assay (ChIP), we demonstrated that TAP26 was not only a component of the SP-B promoter, but was also a component of the SP-C promoter complex in lung cells. TAP26 could synergistically stimulate TTF-1-activated SP-B and SP-C promoter activities in H441 cells (a lung adenocarcinoma cell). However, in MLE12 cells (a murine lung type II cell), only SP-B, but not SP-C, promoter activity was improved by TAP26 in a concentration-dependent manner. This result indicated that the TTF-1/TAP26 complex-activated SP-C promoter activity was already optimized in MLE12 cells and that the response of the SP-C promoter to the complex was different from that of the SP-B promoter. Via promoter mutation analysis, adjacent TTF-1 binding sites within the proximal promoter region of SP-C were found to be essential for TTF-1/TAP26-enhanced SP-C promoter activity. Thus, a dimerized complex structure was needed for advanced promoter activity. This result also provided a molecular mechanism by which both the SP-B and SP-C promoters could be differentially regulated by the same complex.
表面活性蛋白B（SP-B）和表面活性蛋白C（SP-C）是维持肺泡表面张力的小疏水表面活性蛋白。SP-B和SP-C在肺细胞中均受关键因子甲状腺转录因子-1（TTF-1）调控。此前，我们鉴定出一种26 kDa的TTF-1相关蛋白（TAP26），它可与TTF-1相互作用并增强TTF-1反式激活的SP-B启动子活性。在本研究中，我们推测TAP26也可能作为SP-C启动子的共激活因子。通过染色质免疫沉淀分析（ChIP），我们证明TAP26不仅是SP-B启动子的组成部分，也是肺细胞中SP-C启动子复合物的组成部分。TAP26可协同刺激H441细胞（一种肺腺癌细胞）中TTF-1激活的SP-B和SP-C启动子活性。然而，在MLE12细胞（一种小鼠肺II型细胞）中，TAP26仅以浓度依赖的方式提高了SP-B而非SP-C的启动子活性。这一结果表明，在MLE12细胞中，TTF-1/TAP26复合物激活的SP-C启动子活性已经优化，且SP-C启动子对该复合物的反应不同于SP-B启动子。通过启动子突变分析，发现SP-C近端启动子区域内相邻的TTF-1结合位点对于TTF-1/TAP26增强的SP-C启动子活性至关重要。因此，高级启动子活性需要二聚化复合物结构。这一结果也提供了一种分子机制，通过该机制，相同的复合物可对SP-B和SP-C启动子进行差异调控。
