Zhou Beiyun, Zhong Qian, Minoo Parviz, Li Changgong, Ann David K, Frenkel Baruch, Morrisey Edward E, Crandall Edward D, Borok Zea
Will Rogers Institute Pulmonary Research Center, Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Southern California, 2020 Zonal Avenue, Los Angeles, CA 90033, USA.
Am J Respir Cell Mol Biol. 2008 Jun;38(6):750-8. doi: 10.1165/rcmb.2007-0350OC. Epub 2008 Jan 31.
The transcription factor (TF) Foxp2 has been shown to partially repress surfactant protein C (SP-C) transcription, presumably through interaction of an independent repressor domain with a conserved Foxp2 consensus site in the SP-C promoter. We explored the role of interactions between Foxp2 and the homeodomain TF Nkx2.1 that may contribute to the marked reduction in SP-C expression accompanying phenotypic transition of alveolar epithelial type II (AT2) to type I (AT1) cells. Foxp2 dose-dependently inhibited Nkx2.1-mediated activation of SP-C in MLE-15 cells. While electrophoretic mobility shift assays and chromatin immunoprecipitations revealed an interaction between Foxp2 and the conserved consensus motif in the SP-C promoter, Nkx2.1-mediated activation of the 318-bp proximal SP-C promoter (which lacks a Foxp2 consensus) was attenuated by increasing amounts of Foxp2. Co-immunoprecipitation and mammalian two-hybrid assays confirmed a physical interaction between Nkx2.1 and Foxp2 mediated through the Nkx2.1 homeodomain. Formation of an Nkx2.1 complex with an SP-C oligonucleotide was inhibited dose-dependently by recombinant Foxp2. These findings demonstrate that direct interaction between Foxp2 and Nkx2.1 inhibits Nkx2.1 DNA-binding and transcriptional activity and suggest a mechanism for down-regulation of SP-C (and probably other AT2 cell genes) during transition of AT2 cells to an AT1 cell phenotype.
转录因子（TF）Foxp2已被证明可部分抑制表面活性蛋白C（SP-C）的转录，推测是通过一个独立的阻遏结构域与SP-C启动子中保守的Foxp2共有位点相互作用实现的。我们探究了Foxp2与同源结构域转录因子Nkx2.1之间相互作用的作用，这种相互作用可能导致肺泡II型上皮细胞（AT2）向I型上皮细胞（AT1）表型转变时SP-C表达显著降低。Foxp2在MLE-15细胞中呈剂量依赖性地抑制Nkx2.1介导的SP-C激活。虽然电泳迁移率变动分析和染色质免疫沉淀显示Foxp2与SP-C启动子中的保守共有基序存在相互作用，但随着Foxp2量的增加，Nkx2.1介导的318 bp近端SP-C启动子（缺乏Foxp2共有序列）的激活受到减弱。免疫共沉淀和哺乳动物双杂交分析证实了Nkx2.1与Foxp2之间通过Nkx2.1同源结构域介导的物理相互作用。重组Foxp2剂量依赖性地抑制了Nkx2.1与SP-C寡核苷酸形成复合物。这些发现表明，Foxp2与Nkx2.1之间的直接相互作用抑制了Nkx2.1的DNA结合和转录活性，并提示了AT2细胞向AT1细胞表型转变过程中SP-C（可能还有其他AT2细胞基因）下调的机制。
