Cell Death Research Laboratory, Department of Biology, Faculty of Sciences, University of Haifa, Mount Carmel, Haifa, Israel.
PLoS One. 2012;7(7):e38837. doi: 10.1371/journal.pone.0038837. Epub 2012 Jul 9.
Parkinson's disease (PD) is associated with excessive cell death causing selective loss of dopaminergic neurons. Dysfunction of the Ubiquitin Proteasome System (UPS) is associated with the pathophysiology of PD. Mutations in Parkin which impair its E3-ligase activity play a major role in the pathogenesis of inherited PD. ARTS (Sept4_i2) is a mitochondrial protein, which initiates caspase activation upstream of cytochrome c release in the mitochondrial apoptotic pathway. Here we show that Parkin serves as an E3-ubiquitin ligase to restrict the levels of ARTS through UPS-mediated degradation. Though Parkin binds equally to ARTS and Sept4_i1 (H5/PNUTL2), the non-apoptotic splice variant of Sept4, Parkin ubiquitinates and degrades only ARTS. Thus, the effect of Parkin on ARTS is specific and probably related to its pro-apoptotic function. High levels of ARTS are sufficient to promote apoptosis in cultured neuronal cells, and rat brains treated with 6-OHDA reveal high levels of ARTS. However, over-expression of Parkin can protect cells from ARTS-induced apoptosis. Furthermore, Parkin loss-of-function experiments reveal that reduction of Parkin causes increased levels of ARTS and apoptosis. We propose that in brain cells in which the E3-ligase activity of Parkin is compromised, ARTS levels increase and facilitate apoptosis. Thus, ARTS is a novel substrate of Parkin. These observations link Parkin directly to a pro-apoptotic protein and reveal a novel connection between Parkin, apoptosis, and PD.
帕金森病（PD）与过量的细胞死亡有关，导致多巴胺能神经元的选择性丧失。泛素蛋白酶体系统（UPS）的功能障碍与 PD 的病理生理学有关。Parkin 的突变使其 E3-连接酶活性受损，在遗传性 PD 的发病机制中起主要作用。ARTS（Sept4_i2）是一种线粒体蛋白，它在线粒体凋亡途径中细胞色素 c 释放的上游引发半胱天冬酶的激活。在这里，我们表明 Parkin 作为一种 E3-泛素连接酶，通过 UPS 介导的降解来限制 ARTS 的水平。尽管 Parkin 与 ARTS 和 Sept4_i1（H5/PNUTL2），即 Sept4 的非凋亡剪接变异体，结合相等，但 Parkin 仅泛素化和降解 ARTS。因此，Parkin 对 ARTS 的影响是特异性的，可能与其促凋亡功能有关。高水平的 ARTS 足以促进培养神经元细胞的凋亡，并且用 6-OHDA 处理的大鼠大脑显示高水平的 ARTS。然而，Parkin 的过表达可以保护细胞免受 ARTS 诱导的凋亡。此外，Parkin 功能丧失实验表明，Parkin 的减少导致 ARTS 水平增加和凋亡增加。我们提出，在 Parkin 的 E3-连接酶活性受损的脑细胞中，ARTS 水平增加并促进凋亡。因此，ARTS 是 Parkin 的一种新底物。这些观察结果将 Parkin 直接与一种促凋亡蛋白联系起来，并揭示了 Parkin、细胞凋亡和 PD 之间的新联系。
