Southgate Robert J, Neill Bronwyn, Prelovsek Oja, El-Osta Assam, Kamei Yasutomi, Miura Shinji, Ezaki Osamu, McLoughlin Thomas J, Zhang Wenwei, Unterman Terry G, Febbraio Mark A
Cellular & Molecular Metabolism Laboratory, The Baker Heart Research Institute, Commercial Road, Melbourne 3004, Victoria, Australia.
J Biol Chem. 2007 Jul 20;282(29):21176-86. doi: 10.1074/jbc.M702039200. Epub 2007 May 17.
The mammalian target of rapamycin (mTOR) is regulated by growth factors to promote protein synthesis. In mammalian skeletal muscle, the Forkhead-O1 transcription factor (FOXO1) promotes catabolism by activating ubiquitin-protein ligases. Using C2C12 mouse myoblasts that stably express inducible FOXO1-ER fusion proteins and transgenic mice that specifically overexpress constitutively active FOXO1 in skeletal muscle (FOXO(++/+)), we show that FOXO1 inhibits mTOR signaling and protein synthesis. Activation of constitutively active FOXO1 induced the expression of eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) mRNA via binding to the promoter. This resulted in an increased total 4E-BP1 abundance and a reduced 4E-BP1 (Thr-37/46) phosphorylation. The reduction in 4E-BP1 phosphorylation was associated with a reduction in the abundance of Raptor and mTOR proteins, Raptor-associated mTOR, reduced phosphorylation of the downstream protein p70S6 kinase, and attenuated incorporation of [(14)C]phenylalanine into protein. The FOXO(++/+) mice, characterized by severe skeletal muscle atrophy, displayed similar patterns of mRNA expression and protein abundance to those observed in the constitutively active FOXO1 C2C12 myotubes. These data suggest that FOXO1 may be an important therapeutic target for human diseases where anabolism is impaired.
雷帕霉素的哺乳动物靶点（mTOR）受生长因子调控以促进蛋白质合成。在哺乳动物骨骼肌中，叉头框O1转录因子（FOXO1）通过激活泛素 - 蛋白连接酶促进分解代谢。利用稳定表达可诱导型FOXO1 - ER融合蛋白的C2C12小鼠成肌细胞以及在骨骼肌中特异性过表达组成型活性FOXO1的转基因小鼠（FOXO(++/+)），我们发现FOXO1抑制mTOR信号传导和蛋白质合成。组成型活性FOXO1的激活通过与启动子结合诱导真核起始因子4E结合蛋白1（4E - BP1）mRNA的表达。这导致4E - BP1的总丰度增加以及4E - BP1（苏氨酸 - 37/46）磷酸化减少。4E - BP1磷酸化的减少与Raptor和mTOR蛋白丰度的降低、Raptor相关的mTOR减少、下游蛋白p70S6激酶磷酸化减少以及[(14)C]苯丙氨酸掺入蛋白质的减弱有关。以严重骨骼肌萎缩为特征的FOXO(++/+)小鼠，其mRNA表达和蛋白质丰度模式与在组成型活性FOXO1的C2C12肌管中观察到的相似。这些数据表明，FOXO1可能是合成代谢受损的人类疾病的重要治疗靶点。
