Cakir Zeynep, Funk Kathrin, Lauterwasser Joachim, Todt Franziska, Zerbes Ralf M, Oelgeklaus Aline, Tanaka Atsushi, van der Laan Martin, Edlich Frank
Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, University of Freiburg, 79104 Freiburg, Germany.
Faculty of Biology, University of Freiburg, 79104 Freiburg, Germany.
J Cell Sci. 2017 Sep 1;130(17):2903-2913. doi: 10.1242/jcs.200162. Epub 2017 Jul 31.
The pro-apoptotic BCL-2 protein BAX commits human cells to apoptosis by permeabilizing the outer mitochondrial membrane. BAX activation has been suggested to require the separation of helix α5 from α6 - the 'latch' from the 'core' domain - among other conformational changes. Here, we show that conformational changes in this region impair BAX translocation to the mitochondria and retrotranslocation back into the cytosol, and therefore BAX inhibition, but not activation. Redirecting misregulated BAX to the mitochondria revealed an alternative mechanism of BAX inhibition. The E3 ligase parkin, which is known to trigger mitochondria-specific autophagy, ubiquitylates BAX K128 and targets the pro-apoptotic BCL-2 protein for proteasomal degradation. Retrotranslocation-deficient BAX is completely degraded in a parkin-dependent manner. Although only a minor pool of endogenous BAX escapes retrotranslocation into the cytosol, parkin-dependent targeting of misregulated BAX on the mitochondria provides substantial protection against BAX apoptotic activity.
促凋亡的BCL-2蛋白BAX通过使线粒体外膜通透化，使人类细胞发生凋亡。有人提出，BAX激活需要螺旋α5与α6分离——即“闩锁”与“核心”结构域分离——以及其他构象变化。在此，我们表明该区域的构象变化会损害BAX向线粒体的转运以及逆向转运回细胞质，从而导致BAX受到抑制而非激活。将失调的BAX重新导向线粒体揭示了一种BAX抑制的替代机制。已知E3连接酶帕金可触发线粒体特异性自噬，它使BAX的K128位点泛素化，并将促凋亡的BCL-2蛋白靶向蛋白酶体降解。逆向转运缺陷型BAX以帕金依赖的方式被完全降解。尽管只有一小部分内源性BAX能逃脱逆向转运进入细胞质，但帕金对线粒体上失调的BAX的依赖性靶向作用能为抵御BAX的凋亡活性提供实质性保护。
