Boban Mirta, Pantazopoulou Marina, Schick Anna, Ljungdahl Per O, Foisner Roland
Max F. Perutz Laboratories, Department of Medical Biochemistry, Medical University of Vienna, Dr. Bohr-Gasse 9, A-1030 Vienna, Austria.
Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, SE-106 91 Stockholm, Sweden.
J Cell Sci. 2014 Aug 15;127(Pt 16):3603-13. doi: 10.1242/jcs.153163. Epub 2014 Jun 13.
The nuclear envelope consists of inner and outer nuclear membranes. Whereas the outer membrane is an extension of the endoplasmic reticulum, the inner nuclear membrane (INM) represents a unique membranous environment containing specific proteins. The mechanisms of integral INM protein degradation are unknown. Here, we investigated the turnover of Asi2, an integral INM protein in Saccharomyces cerevisiae. We report that Asi2 is degraded by the proteasome independently of the vacuole and that it exhibited a half-life of ∼45 min. Asi2 exhibits enhanced stability in mutants lacking the E2 ubiquitin conjugating enzymes Ubc6 or Ubc7, or the E3 ubiquitin ligase Doa10. Consistent with these data, Asi2 is post-translationally modified by poly-ubiquitylation in a Ubc7- and Doa10-dependent manner. Importantly Asi2 degradation is significantly reduced in a sts1-2 mutant that fails to accumulate proteasomes in the nucleus, indicating that Asi2 is degraded in the nucleus. Our results reveal a molecular pathway that affects the stability of integral proteins of the inner nuclear membrane and indicate that Asi2 is subject to protein quality control in the nucleus.
核膜由内核膜和外核膜组成。外核膜是内质网的延伸，而内核膜（INM）则代表了一个包含特定蛋白质的独特膜环境。内核膜整合蛋白的降解机制尚不清楚。在这里，我们研究了酿酒酵母中一种内核膜整合蛋白Asi2的周转情况。我们报告称，Asi2由蛋白酶体独立于液泡进行降解，其半衰期约为45分钟。在缺乏E2泛素结合酶Ubc6或Ubc7，或E3泛素连接酶Doa10的突变体中，Asi2表现出增强的稳定性。与这些数据一致，Asi2在翻译后以Ubc7和Doa10依赖的方式被多聚泛素化修饰。重要的是，在未能在细胞核中积累蛋白酶体的sts1-2突变体中，Asi2的降解显著减少，这表明Asi2在细胞核中被降解。我们的结果揭示了一条影响内核膜整合蛋白稳定性的分子途径，并表明Asi2在细胞核中受到蛋白质质量控制。
