Guo Yuhong, Yang Meng-Chun W, Weissler Jonathan C, Yang Yih-Sheng
Department of Internal Medicine, Pulmonary and Critical Care Medicine, UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-8558, USA.
Biochem Biophys Res Commun. 2008 Sep 26;374(3):570-5. doi: 10.1016/j.bbrc.2008.07.064. Epub 2008 Jul 23.
Pleomorphic adenoma gene like-2 (PLAGL2), a developmentally regulated and stress inducible zinc finger protein can be post-translationally modified by small ubiquitin-like modifier peptide (SUMO-1); and SUMOylation attenuates PLAGL2 activity on the interactive promoter. Since PLAGL2 was a transactivator of the surfactant protein-C (SP-C) promoter, we hypothesized that SUMOylation down-regulated PLAGL2-activated SP-C promoter activity. Unexpectedly, the SUMO-conjugating enzyme Ubc9 enhanced, rather than reduced, PLAGL2 activated promoter activity but did not affect TTF-1 activation of the promoter. Ubc9 mutant (Ubc9-C93S) defective in SUMO-conjugating activity also enhanced PLAGL2-driven promoter activity suggesting that the stimulatory effect of Ubc9 on SP-C promoter activation was independent of its enzymatic function. PLAGL2 mutants without the K250 and/or K269 SUMOylation sites did not further improve PLAGL2 programmed transcription nor did they abolish Ubc9 enhanced promoter activity supporting the SUMOylation-independent mechanism. Chromatin immunoprecipitation (ChIP) assay demonstrated the association of PLAGL2 and Ubc9 with the SP-C promoter in vivo. Taken together, our data suggests that Ubc9 can function as a co-factor of PLAGL2, uncoupling from its enzymatic activity, to mediate PLAGL2 interactive SP-C promoter activity.
多形性腺瘤样基因-2（PLAGL2）是一种受发育调控且可被应激诱导的锌指蛋白，可通过小泛素样修饰肽（SUMO-1）进行翻译后修饰；SUMO化作用会减弱PLAGL2在相互作用启动子上的活性。由于PLAGL2是表面活性蛋白C（SP-C）启动子的反式激活因子，我们推测SUMO化作用下调了PLAGL2激活的SP-C启动子活性。出乎意料的是，SUMO结合酶Ubc9增强而非降低了PLAGL2激活的启动子活性，但不影响该启动子的TTF-1激活。SUMO结合活性有缺陷的Ubc9突变体（Ubc9-C93S）也增强了PLAGL2驱动的启动子活性，这表明Ubc9对SP-C启动子激活的刺激作用与其酶功能无关。没有K250和/或K269 SUMO化位点的PLAGL2突变体既没有进一步改善PLAGL2编程转录，也没有消除Ubc9增强的启动子活性，这支持了不依赖SUMO化的机制。染色质免疫沉淀（ChIP）分析证明了PLAGL2和Ubc9在体内与SP-C启动子的结合。综上所述，我们的数据表明，Ubc9可以作为PLAGL2的辅因子，与其酶活性解偶联，以介导PLAGL2相互作用的SP-C启动子活性。
