E3泛素连接酶FBXW17降解PRMT6对COPD炎症基因的转录调控研究

慢性炎症在慢性阻塞性肺疾病（COPD）的发病机制中扮演着重要角色，但对该疾病中炎症基因转录调控机制仍知之甚少。蛋白精氨酸甲基转移酶6（PRMT6）通过对组蛋白H3R2非对称双甲基化抑制基因转录。我们前期研究显示COPD中PRMT6蛋白表达下降并直接参与调控炎症基因表达。吸烟所致泛素-蛋白酶体系统异常活化参与了COPD病程，我们已证实PRMT6半衰期短，蛋白酶体特异性抑制剂能抑制其降解，同时E3泛素连接酶FBXW17能特异性降解PRMT6蛋白。但COPD中是否存在FBXW17降解PRMT6增加，进而影响组蛋白甲基化并激活肺内炎症基因转录仍有待进一步求证。本研究拟从COPD患者、动物和细胞水平中观察FBXW17、PRMT6、组蛋白甲基化和炎症基因的表达，探讨PRMT6通过组蛋白甲基化调控COPD炎症基因转录的机制，并进一步研究FBXW17调控PRMT6降解的机制，为COPD治疗探索新的途径。

Chronic obstructive pulmonary disease (COPD) is a major cause of chronic morbidity and mortality throughout the world. Chronic inflammation plays the pivotal role in pathogenesis of COPD. The mechanism of the inflammatory gene expression in this disease is yet illusive. Epigenetic control of inflammatory gene expresion in COPD has been reported recently. A decreased deacetylase activity was observed in patients indicating that cross-talk among histone acetlylation, deacetlylation, and/or other modifications regulates gene expression in COPD. Albeit, the contribuition of histone methylation in inflammatory gene expression in COPD is largely unknown. Our preliminary study proved a decreased protein level of a histone methylation enzyme protein arginine methyltransferase (PRMT6) in COPD patient lung tissues. PRMT6 is an epigenetic code inhibiting gene expression by methylation of histone H3R2. We observed that PRMT6 directly involved in inflammatory gene expression. Proinflammatory gene expression was repressed by overexpression of PRMT6, while knockdown of PRMT6 unleashed proinflammatory gene expression in cultured lung epithelial cells. Of note, we found that PRMT6 is a short life protein with a half-life of approximately 4 h. We identified that PRMT6 is specifically degraded by ubiquitin-proteasomal machinery, proteasome inhibitor MG132 treatment stops PRMT6 degradation and results in PRMT6 accumulation. Furthermore, we discovered a novel E3 ubiquitin ligase FBXW17 that degrades PRMT6 in a dose dependent manner by screening the E3 ubiquitin ligase. Overexpression of FBXW17 accelerates PRMT6 degradation as compared to control E3 ubiquitin ligase FBXW14 that does not degrade PRMT6. Therefore, we hypothesis that histone methylation enzyme PRMT6 is ubiquitin-proteasomal degraded by FBXW17, PRMT6 degradation leads to inflammatory gene upregulation in COPD. To prove this hypothesis, we will 1) investigate the mRNA and protein levels of PRMT6 and FBXW17 in CSE treated lung epthelial cells, COPD model animal lung tissues and human COPD lung tissues, and their levels correlation to proinflammatory gene upregulations; 2) determine the molecular mechanism of ubiquitin-proteasomal degradation of PRMT6 by FBXW17; and 3) interfer inflammatory gene expression in the pathogenesis of COPD by change the protein level of PRMT6 and FboxL18. Thus, we have uncovered a new E3 ubiquitin ligase that epigenetically controls inflammatory gene expression by degradation of histone methylase PRMT6 in COPD. Execution of these studies will lay the groundwork for a potentially significant conceptual advance with regard to a novel E3 ubiquitin lagse involved in the pathogenesis of COPD and the epigenetic control of genes during inflammation in COPD. Completion of this study may represent a new therapeutic option in the prevention and treatment of COPD.