Defective recognition of LC3B by mutant SQSTM1/p62 implicates impairment of autophagy as a pathogenic mechanism in ALS-FTLD.
Defective recognition of LC3B by mutant SQSTM1/p62 implicates impairment of autophagy as a pathogenic mechanism in ALS-FTLD.
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DOI：
10.1080/15548627.2016.1170257
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发表时间：
2016-07-02
期刊：
影响因子：
13.3
通讯作者：
Layfield R
中科院分区：
文献类型：
--
作者：
Goode A;Butler K;Long J;Cavey J;Scott D;Shaw B;Sollenberger J;Gell C;Johansen T;Oldham NJ;Searle MS;Layfield R
越来越多的证据表明自噬损伤是神经退行性疾病谱中的候选致病机制，包括肌萎缩性侧索硬化和额颞叶变性（ALS-FTLD）。编码自噬受体SQSTM 1/p62的SQSTM 1与ALS-FTLD遗传相关，尽管迄今为止尚未描述疾病相关变体中的自噬相关功能缺陷。自噬中的关键蛋白质-蛋白质相互作用是SQSTM 1识别吞噬细胞膜内的脂质锚定形式的LC 3（LC 3-II），通过其LC 3相互作用区（LIR）介导，值得注意的是一些ALS-FTLD突变映射到该区域。在这里，我们表明，尽管代表保守取代并且预测是良性的，但SQSTM 1的ALS相关L341 V突变在LC 3B的识别方面存在缺陷。我们将我们的观察结果建立在一个坚实的定量基础上，通过显示L341 V突变体LIR与LC 3B结合亲和力降低103倍相关，并使用蛋白质NMR，我们合理化了这种效应的结构基础。这种功能缺陷在运动神经元样细胞中实现，L341 V突变体EGFP-mCherry-SQSTM 1比野生型更不容易掺入酸性自噬囊泡中。我们的数据支持一种模型，其中L341 V突变限制了SQSTM 1招募到吞噬细胞的关键步骤。SQSTM 1的寡聚体性质（其对噬菌体的模板生长呈现多个LIR）可能引起亲合力效应，其放大任何单一突变对LC 3B结合的相对适度的影响。在神经元的一生中，受损的自噬可能会暴露出一个脆弱性，最终将细胞存活的平衡推向细胞死亡。
Growing evidence implicates impairment of autophagy as a candidate pathogenic mechanism in the spectrum of neurodegenerative disorders which includes amyotrophic lateral sclerosis and frontotemporal lobar degeneration (ALS-FTLD). SQSTM1, which encodes the autophagy receptor SQSTM1/p62, is genetically associated with ALS-FTLD, although to date autophagy-relevant functional defects in disease-associated variants have not been described. A key protein-protein interaction in autophagy is the recognition of a lipid-anchored form of LC3 (LC3-II) within the phagophore membrane by SQSTM1, mediated through its LC3-interacting region (LIR), and notably some ALS-FTLD mutations map to this region. Here we show that although representing a conservative substitution and predicted to be benign, the ALS-associated L341V mutation of SQSTM1 is defective in recognition of LC3B. We place our observations on a firm quantitative footing by showing the L341V-mutant LIR is associated with a ∼3-fold reduction in LC3B binding affinity and using protein NMR we rationalize the structural basis for the effect. This functional deficit is realized in motor neuron-like cells, with the L341V mutant EGFP-mCherry-SQSTM1 less readily incorporated into acidic autophagic vesicles than the wild type. Our data supports a model in which the L341V mutation limits the critical step of SQSTM1 recruitment to the phagophore. The oligomeric nature of SQSTM1, which presents multiple LIRs to template growth of the phagophore, potentially gives rise to avidity effects which amplify the relatively modest impact of any single mutation on LC3B binding. Over the lifetime of a neuron, impaired autophagy could expose a vulnerability, which ultimately tips the balance from cell survival toward cell death.