Sterol regulatory element-binding proteins are negatively regulated through SUMO-1 modification independent of the ubiquitin/26 S proteasome pathway
Sterol regulatory element-binding proteins are negatively regulated through SUMO-1 modification independent of the ubiquitin/26 S proteasome pathway
复制标题
DOI：
10.1074/jbc.m212448200
复制
发表时间：
2003-05-09
影响因子：
4.8
通讯作者：
Sato, R
中科院分区：
文献类型：
--
作者：
Hirano, Y;Murata, S;Sato, R
固醇调节元件结合蛋白（SREBP）是激活胆固醇和脂肪酸生物合成相关基因的主要转录因子。我们在这里报告的核形式的SREBP的小泛素相关的修饰剂（SUMO）-1修改。突变分析鉴定了SREBP-1a中的两个主要SUMO化位点（Lys（123）和Lys（418））和SREBP-2中的单个位点（Lys（464））。突变体SREBP缺乏一个或两个sumoylation位点表现出增加的反式激活能力的SREBP响应启动子。SUMO-1的过表达降低了SREBP反应基因的mRNA水平，而其显性负性形式增加了SREBP反应基因的mRNA水平。核SREBP与SUMO-1结合酶Ubc 9相互作用，并且Ubc 9的显性负性形式的过表达增加了SREBP响应基因的mRNA水平。脉冲追踪实验表明，SUMO化并不影响SREBPs通过泛素-蛋白酶体途径的降解。体外泛素化实验表明泛素和SUMO-1对同一赖氨酸没有竞争。综合考虑，我们的研究结果表明，SUMO-1修饰抑制核SREBPs的反式激活能力的方式不同的蛋白水解介导的负调控机制。
Sterol regulatory element-binding proteins (SREBPs) are major transcription factors that activate the genes involved in cholesterol and fatty acid biosynthesis. We here report that the nuclear forms of SREBPs are modified by the small ubiquitin-related modifier (SUMO)-1. Mutational analyses identified two major sumoylation sites (Lys(123) and Lys(418)) in SREBP-1a and a single site (Lys(464)) in SREBP-2. Mutant SREBPs lacking one or two sumoylation sites exhibited increased transactivation capacity on an SREBP-responsive promoter. Overexpression of SUMO-1 reduced whereas its dominant negative form increased mRNA levels of SREBP-responsive genes. Nuclear SREBPs interacted with the SUMO-1-conjugating enzyme Ubc9, and overexpression of a dominant negative form of Ubc9 increased the mRNA levels of SREBP-responsive genes. Pulse-chase experiments revealed that sumoylation did not affect the degradation of SREBPs through the ubiquitin-proteasome pathway. In vitro ubiquitylation assay showed no competition between ubiquitin and SUMO-1 for the same lysine. Considered together, our results indicate that SUMO-1 modification suppresses the transactivation capacity of nuclear SREBPs in a manner different from the negative regulatory mechanism mediated by proteolysis.