Ebner Petra, Poetsch Isabella, Deszcz Luiza, Hoffmann Thomas, Zuber Johannes, Ikeda Fumiyo
Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), 1030, Vienna, Austria.
Research Institute of Molecular Pathology (IMP), Vienna BioCenter (VBC), 1030, Vienna, Austria.
Nat Commun. 2018 Feb 9;9(1):599. doi: 10.1038/s41467-018-02823-x.
Autophagy has an important role in cellular homeostasis by degrading and recycling cytotoxic components. Ubiquitination is known to target cargoes for autophagy; however, key components of this pathway remain elusive. Here we performed an RNAi screen to uncover ubiquitin modifiers that are required for starvation-induced macroautophagy in mammalian cells. Our screen uncovered BRUCE/Apollon/Birc6, an IAP protein, as a new autophagy regulator. Depletion of BRUCE leads to defective fusion of autophagosomes and lysosomes. Mechanistically, BRUCE selectively interacts with two ATG8 members GABARAP and GABARAPL1, as well as with Syntaxin 17, which are all critical regulators of autophagosome-lysosome fusion. In addition, BRUCE colocalizes with LAMP2. Interestingly, a non-catalytic N-terminal BRUCE fragment that is sufficient to bind GABARAP/GABARAPL1 and Syntaxin 17, and to colocalize with LAMP2, rescues autolysosome formation in Bruce cells. Thus, BRUCE promotes autolysosome formation independently of its ubiquitin-conjugating activity and is a regulator of both macroautophagy and apoptosis.
自噬通过降解和循环利用细胞毒性成分在细胞内稳态中发挥重要作用。已知泛素化作用可将货物靶向自噬；然而，该途径的关键成分仍不清楚。在这里，我们进行了一项RNA干扰筛选，以发现哺乳动物细胞中饥饿诱导的巨自噬所需的泛素修饰因子。我们的筛选发现IAP蛋白BRUCE/Apollon/Birc6是一种新的自噬调节因子。BRUCE的缺失导致自噬体与溶酶体融合缺陷。从机制上讲，BRUCE选择性地与两个ATG8成员GABARAP和GABARAPL1以及Syntaxin 17相互作用，而这些都是自噬体 - 溶酶体融合的关键调节因子。此外，BRUCE与LAMP2共定位。有趣的是，一个足以结合GABARAP/GABARAPL1和Syntaxin 17并与LAMP2共定位的非催化性N端BRUCE片段可挽救Bruce细胞中的自溶酶体形成。因此，BRUCE独立于其泛素结合活性促进自溶酶体形成，并且是巨自噬和细胞凋亡的调节因子。
