Genomewide Analysis of Inherited Variation Associated with Phosphorylation of PI3K/AKT/mTOR Signaling Proteins

While there exists a wealth of information about genetic influences on gene expression, less is known about how inherited variation influences the expression and post-translational modifications of proteins, especially those involved in intracellular signaling. The PI3K/AKT/mTOR signaling pathway contains several such proteins that have been implicated in a number of diseases, including a variety of cancers and some psychiatric disorders. To assess whether the activation of this pathway is influenced by genetic factors, we measured phosphorylated and total levels of three key proteins in the pathway (AKT1, p70S6K, 4E-BP1) by ELISA in 122 lymphoblastoid cell lines from 14 families. Interestingly, the phenotypes with the highest proportion of genetic influence were the ratios of phosphorylated to total protein for two of the pathway members: AKT1 and p70S6K. Genomewide linkage analysis suggested several loci of interest for these phenotypes, including a linkage peak for the AKT1 phenotype that contained the AKT1 gene on chromosome 14. Linkage peaks for the phosphorylated:total protein ratios of AKT1 and p70S6K also overlapped on chromosome 3. We selected and genotyped candidate genes from under the linkage peaks, and several statistically significant associations were found. One polymorphism in HSP90AA1 was associated with the ratio of phosphorylated to total AKT1, and polymorphisms in RAF1 and GRM7 were associated with the ratio of phosphorylated to total p70S6K. These findings, representing the first genomewide search for variants influencing human protein phosphorylation, provide useful information about the PI3K/AKT/mTOR pathway and serve as a valuable proof of concept for studies integrating human genomics and proteomics.尽管目前已有大量关于遗传因素对基因表达影响的研究，但对于遗传变异如何调控蛋白质的表达及翻译后修饰，尤其是参与细胞内信号转导的蛋白质，相关认知仍较为匮乏。PI3K/AKT/mTOR信号通路中便存在数类此类蛋白质，它们已被证实与多种癌症及部分精神疾病存在关联。为探究该通路的激活是否受遗传因素调控，本研究从14个家系中获取122株淋巴母细胞系（lymphoblastoid cell lines），采用酶联免疫吸附试验（ELISA）检测了该通路中3种关键蛋白质（AKT1、p70S6K、4E-BP1）的磷酸化水平与总蛋白水平。值得注意的是，受遗传影响占比最高的表型为该通路中两种蛋白的磷酸化蛋白与总蛋白比值：即AKT1与p70S6K。针对上述表型的全基因组连锁分析（Genomewide linkage analysis）揭示了数个潜在关联基因座，其中针对AKT1表型的连锁峰包含了14号染色体上的AKT1基因。AKT1与p70S6K的磷酸化/总蛋白比值对应的连锁峰在3号染色体上存在重叠。我们对连锁峰区域内的候选基因进行了筛选与基因分型，并发现了数个具有统计学意义的关联信号。HSP90AA1基因的一处多态性位点与AKT1的磷酸化/总蛋白比值相关，而RAF1与GRM7基因的多态性位点则与p70S6K的磷酸化/总蛋白比值相关。本研究作为首个针对影响人类蛋白质磷酸化的遗传变异开展的全基因组筛查，其研究结果不仅为PI3K/AKT/mTOR信号通路的相关研究提供了重要参考，同时也为整合人类基因组学与蛋白质组学（proteomics）的交叉研究提供了极具价值的概念验证。