Halbach Melanie Vanessa, Stehning Tanja, Damrath Ewa, Jendrach Marina, Şen Nesli Ece, Başak A Nazlı, Auburger Georg
Experimental Neurology, Dept. of Neurology, Goethe University Medical School, Theodor Stern Kai 7, 60590 Frankfurt am Main, Germany.
Neurodegeneration Research Laboratory (NDAL), Molecular Biology and Genetics Department, Boğaziçi University, 34470 Istanbul, Turkey.
PLoS One. 2015 Mar 19;10(3):e0121089. doi: 10.1371/journal.pone.0121089. eCollection 2015.
The involvement of the ubiquitin-proteasome system (UPS) in the course of various age-associated neurodegenerative diseases is well established. The single RING finger type E3 ubiquitin-protein ligase PARK2 is mutated in a Parkinson's disease (PD) variant and was found to interact with ATXN2, a protein where polyglutamine expansions cause Spinocerebellar ataxia type 2 (SCA2) or increase the risk for Levodopa-responsive PD and for the motor neuron disease Amyotrophic lateral sclerosis (ALS). We previously reported evidence for a transcriptional induction of the multi-subunit RING finger Skp1/Cul/F-box (SCF) type E3 ubiquitin-protein ligase complex component FBXW8 in global microarray profiling of ATXN2-expansion mouse cerebellum and demonstrated its role for ATXN2 degradation in vitro. Now, we documented co-localization in vitro and co-immunoprecipitations both in vitro and in vivo, which indicate associations of FBXW8 with ATXN2 and PARK2. Both FBXW8 and PARK2 proteins are driven into insolubility by expanded ATXN2. Whereas the FBXW8 transcript upregulation by ATXN2- expansion was confirmed also in qPCR of skin fibroblasts and blood samples of SCA2 patients, a FBXW8 expression dysregulation was not observed in ATXN2-deficient mice, nor was a PARK2 transcript dysregulation observed in any samples. Jointly, all available data suggest that the degradation of wildtype and mutant ATXN2 is dependent on FBXW8, and that ATXN2 accumulation selectively modulates FBXW8 levels, while PARK2 might act indirectly through FBXW8. The effects of ATXN2-expansions on FBXW8 expression in peripheral tissues like blood may become useful for clinical diagnostics.
泛素-蛋白酶体系统（UPS）参与各种与年龄相关的神经退行性疾病的过程已得到充分证实。单指环型E3泛素蛋白连接酶PARK2在帕金森病（PD）变体中发生突变，并被发现与ATXN2相互作用，ATXN2蛋白的多聚谷氨酰胺扩增会导致2型脊髓小脑共济失调（SCA2），或增加左旋多巴反应性PD和运动神经元疾病肌萎缩侧索硬化（ALS）的风险。我们之前在ATXN2扩增小鼠小脑的全基因组微阵列分析中报告了多亚基指环型Skp1/Cul/F-box（SCF）型E3泛素蛋白连接酶复合物成分FBXW8转录诱导的证据，并证明了其在体外对ATXN2降解的作用。现在，我们记录了体外共定位以及体外和体内的共免疫沉淀，这表明FBXW8与ATXN2和PARK2有关联。FBXW8和PARK2蛋白都因ATXN2扩增而变得不溶。虽然在SCA2患者的皮肤成纤维细胞和血液样本的qPCR中也证实了ATXN2扩增导致FBXW8转录上调，但在ATXN2缺陷小鼠中未观察到FBXW8表达失调，在任何样本中也未观察到PARK2转录失调。综合来看，所有现有数据表明野生型和突变型ATXN2的降解依赖于FBXW8，并且ATXN2积累选择性地调节FBXW8水平，而PARK2可能通过FBXW8间接发挥作用。ATXN2扩增对血液等外周组织中FBXW8表达的影响可能对临床诊断有用。
