Das Aparajita, Boggaram Vijayakumar
Department of Molecular Biology, The University of Texas Health Center at Tyler, 11937 US Highway 271, Tyler, TX 75708-3154, USA.
Am J Physiol Lung Cell Mol Physiol. 2007 Jan;292(1):L74-84. doi: 10.1152/ajplung.00103.2006. Epub 2006 Aug 11.
Surfactant proteins maintain lung function through their actions to reduce alveolar surface tension and control of innate immune responses in the lung. The ubiquitin proteasome pathway is responsible for the degradation of majority of intracellular proteins in eukaryotic cells, and proteasome dysfunction has been linked to the development of neurodegenerative, cardiac, and other diseases. Proteasome function is impaired in interstitial lung diseases associated with surfactant protein C (SP-C) mutation mapping to the BRICHOS domain located in the proSP-C protein. In this study we determined the effects of proteasome inhibition on surfactant protein expression in H441 and MLE-12 lung epithelial cells to understand the relationship between proteasome dysfunction and surfactant protein gene expression. Proteasome inhibitors lactacystin and MG132 reduced the levels of SP-A, SP-B, and SP-C mRNAs in a concentration-dependent manner in H441 and MLE-12 cells. In H441 cells, lactacystin and MG132 inhibition of SP-B mRNA was associated with similar decreases in SP-B protein, and the inhibition was due to inhibition of gene transcription. Proteasome inhibitors decreased thyroid transcription factor-1 (TTF-1)/Nkx2.1 DNA binding activity, and the reduced TTF-1 DNA binding activity was due to reduced expression levels of TTF-1 protein. These data indicated that the ubiquitin proteasome pathway is essential for the maintenance of surfactant protein gene expression and that disruption of this pathway inhibits surfactant protein gene expression via reduced expression of TTF-1 protein.
表面活性蛋白通过降低肺泡表面张力以及控制肺部固有免疫反应来维持肺功能。泛素蛋白酶体途径负责真核细胞中大多数细胞内蛋白质的降解，蛋白酶体功能障碍与神经退行性疾病、心脏疾病及其他疾病的发生有关。在与表面活性蛋白C（SP-C）突变相关的间质性肺疾病中，蛋白酶体功能受损，该突变定位在proSP-C蛋白的BRICHOS结构域。在本研究中，我们测定了蛋白酶体抑制对H441和MLE-12肺上皮细胞中表面活性蛋白表达的影响，以了解蛋白酶体功能障碍与表面活性蛋白基因表达之间的关系。蛋白酶体抑制剂乳胞素和MG132在H441和MLE-12细胞中以浓度依赖的方式降低了SP-A、SP-B和SP-C mRNA的水平。在H441细胞中，乳胞素和MG132对SP-B mRNA的抑制与SP-B蛋白的类似降低相关，且这种抑制是由于基因转录的抑制。蛋白酶体抑制剂降低了甲状腺转录因子-1（TTF-1）/Nkx2.1的DNA结合活性，而TTF-1 DNA结合活性的降低是由于TTF-1蛋白表达水平的降低。这些数据表明泛素蛋白酶体途径对于维持表面活性蛋白基因表达至关重要，并且该途径的破坏通过降低TTF-1蛋白的表达来抑制表面活性蛋白基因表达。
