Department of Structural and Functional Biology, Institute of Biology, University of Campinas, UNICAMP, CP 6109, 13083862, Campinas, São Paulo, Brazil.
Faculty of Medical Science and Health, Pontifical Catholic University of São Paulo, 13030-095 - Sorocaba, São Paulo, Brazil.
BMC Cancer. 2019 Apr 11;19(1):349. doi: 10.1186/s12885-019-5448-0.
The exact signalling mechanism of the mTOR complex remains a subject of constant debate, even with some evidence that amino acids participate in the same pathway as used for insulin signalling during protein synthesis. Therefore, this work conducted further study of the actions of amino acids, especially leucine, in vivo, in an experimental model of cachexia. We analysed the effects of a leucine-rich diet on the signalling pathway of protein synthesis in muscle during a tumour growth time-course.
Wistar rats were distributed into groups based on Walker-256 tumour implant and subjected to a leucine-rich diet and euthanised at three different time points following tumour development (the 7th, 14th and 21st day). We assessed the mTOR pathway key-proteins in gastrocnemius muscle, such as RAG-A-GTPase, ERK/MAP4K3, PKB/Akt, mTOR, p70S6K1, Jnk, IRS-1, STAT3, and STAT6 comparing among the experimental groups. Serum WF (proteolysis-induced factor like from Walker-256 tumour) and muscle protein synthesis and degradation were assessed.
The tumour-bearing group had increased serum WF content, and the skeletal-muscle showed a reduction in IRS-1 and RAG activation, increased PKB/Akt and Erk/MAP4K3 on the 21st day, and maintenance of p70S6K1, associated with increases in muscle STAT-3 and STAT-6 levels in these tumour-bearing rats.
Meanwhile, the leucine-rich diet modulated key steps of the mTOR pathway by triggering the increased activation of RAG and mTOR and maintaining JNK, STAT-3 and STAT-6 levels in muscle, leading to an increased muscle protein synthesis, reducing the degradation during tumour evolution in a host, minimising the cancer-induced damages in the cachectic state.
尽管有证据表明氨基酸在蛋白质合成过程中与胰岛素信号通路相同，但 mTOR 复合物的确切信号机制仍然存在争议。因此，这项工作在恶病质的实验模型中进一步研究了氨基酸，特别是亮氨酸的体内作用。我们分析了富含亮氨酸的饮食对肿瘤生长过程中肌肉蛋白质合成信号通路的影响。
Wistar 大鼠根据 Walker-256 肿瘤植入物进行分组，并接受富含亮氨酸的饮食，在肿瘤发展后的三个不同时间点（第 7、14 和 21 天）进行安乐死。我们评估了腓肠肌中 mTOR 通路的关键蛋白，如 RAG-A-GTPase、ERK/MAP4K3、PKB/Akt、mTOR、p70S6K1、Jnk、IRS-1、STAT3 和 STAT6，并在实验组之间进行了比较。评估了血清 WF（来自 Walker-256 肿瘤的蛋白水解诱导因子）和肌肉蛋白质合成和降解。
荷瘤组血清 WF 含量增加，IRS-1 和 RAG 激活减少，第 21 天 PKB/Akt 和 Erk/MAP4K3 增加，p70S6K1 维持，与这些荷瘤大鼠肌肉中 STAT-3 和 STAT-6 水平的增加相关。
同时，富含亮氨酸的饮食通过触发 RAG 和 mTOR 的激活增加，维持 JNK、STAT-3 和 STAT-6 水平，从而调节 mTOR 通路的关键步骤，导致肌肉蛋白质合成增加，在宿主中减少肿瘤演变过程中的降解，最大限度地减少恶病质状态下的癌症损伤。
