Kang Jengmin, Chung Kwang Chul
Department of Systems Biology, College of Life Science and Biotechnology, Yonsei University, Yonsei-ro 50, Seodaemun-gu, Seoul, 120-749, Korea.
Cell Mol Life Sci. 2015 Jan;72(1):181-95. doi: 10.1007/s00018-014-1665-5. Epub 2014 Jun 20.
Parkinson's disease (PD) is characterized by progressive midbrain dopaminergic neuron degeneration and the formation of intracellular protein aggregates, referred to as Lewy bodies. F-box only protein 7 (FBXO7) gene mutations are closely associated with progression of the autosomal recessive form of familial PD. FBXO7 encodes a component of Skp1, cullin, F-box ubiquitin ligase complexes; however, its cellular targets, including substrates and regulators, are not yet clarified. To identify potential substrates of FBXO7, we performed a yeast two-hybrid screen of a human fetal brain library and identified neurotrophin receptor-interacting MAGE protein (NRAGE) as a novel FBXO7-binding partner. We found that FBXO7 interacts with NRAGE and mediates Lys-63-linked poly-ubiquitination of NRAGE in mammalian cells. FBXO7 overexpression accelerates formation of NRAGE-TAK1-TAB1 complexes, whereas FBXO7 knockdown correspondingly decreases complex formation. In addition, BMP4 stimulation enhances NRAGE ubiquitination through FBXO7 and facilitates endogenous NRAGE-TAK1-TAB1 complex formation. Furthermore, FBXO7 positively regulates formation of the BMP receptor-NRAGE-TAK1-TAB1 complex, and up-regulates NF-κB activity. Taken together, our results suggest that FBXO7 affects BMP4-mediated signaling through proteasome-independent ubiquitination of NRAGE and augments formation of downstream signaling components.
帕金森病（PD）的特征是中脑多巴胺能神经元进行性退化以及细胞内蛋白质聚集体（即路易小体）的形成。仅含F盒蛋白7（FBXO7）基因突变与常染色体隐性遗传型家族性PD的进展密切相关。FBXO7编码Skp1、cullin、F盒泛素连接酶复合物的一个组分；然而，其细胞靶点，包括底物和调节因子，尚未明确。为了鉴定FBXO7的潜在底物，我们对人类胎儿脑文库进行了酵母双杂交筛选，并鉴定出神经营养因子受体相互作用MAGE蛋白（NRAGE）作为一种新的FBXO7结合伴侣。我们发现FBXO7与NRAGE相互作用，并在哺乳动物细胞中介导NRAGE的K63连接的多聚泛素化。FBXO7过表达加速NRAGE-TAK1-TAB1复合物的形成，而FBXO7敲低相应地减少复合物的形成。此外，骨形态发生蛋白4（BMP4）刺激通过FBXO7增强NRAGE泛素化，并促进内源性NRAGE-TAK1-TAB1复合物的形成。此外，FBXO7正向调节BMP受体-NRAGE-TAK1-TAB1复合物的形成，并上调核因子κB（NF-κB）活性。综上所述，我们的结果表明，FBXO7通过NRAGE的蛋白酶体非依赖性泛素化影响BMP4介导的信号传导，并增强下游信号组分的形成。
