Das Rahul, Sebo Zachary, Pence Laramie, Dobens Leonard L
Division of Molecular Biology and Biochemistry, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, Missouri, United States of America.
PLoS One. 2014 Oct 15;9(10):e109530. doi: 10.1371/journal.pone.0109530. eCollection 2014.
Drosophila Tribbles (Trbl) is the founding member of the Trib family of kinase-like docking proteins that modulate cell signaling during proliferation, migration and growth. In a wing misexpression screen for Trbl interacting proteins, we identified the Ser/Thr protein kinase Akt1. Given the central role of Akt1 in insulin signaling, we tested the function of Trbl in larval fat body, a tissue where rapid increases in size are exquisitely sensitive to insulin/insulin-like growth factor levels. Consistent with a role in antagonizing insulin-mediated growth, trbl RNAi knockdown in the fat body increased cell size, advanced the timing of pupation and increased levels of circulating triglyceride. Complementarily, overexpression of Trbl reduced fat body cell size, decreased overall larval size, delayed maturation and lowered levels of triglycerides, while circulating glucose levels increased. The conserved Trbl kinase domain is required for function in vivo and for interaction with Akt in a yeast two-hybrid assay. Consistent with direct regulation of Akt, overexpression of Trbl in the fat body decreased levels of activated Akt (pSer505-Akt) while misexpression of trbl RNAi increased phospho-Akt levels, and neither treatment affected total Akt levels. Trbl misexpression effectively suppressed Akt-mediated wing and muscle cell size increases and reduced phosphorylation of the Akt target FoxO (pSer256-FoxO). Taken together, these data show that Drosophila Trbl has a conserved role to bind Akt and block Akt-mediated insulin signaling, and implicate Trib proteins as novel sites of signaling pathway integration that link nutrient availability with cell growth and proliferation.
果蝇 Tribbles（Trbl）是激酶样对接蛋白 Trib 家族的创始成员，该家族在细胞增殖、迁移和生长过程中调节细胞信号传导。在一项针对 Trbl 相互作用蛋白的翅膀异位表达筛选中，我们鉴定出了丝氨酸/苏氨酸蛋白激酶 Akt1。鉴于 Akt1 在胰岛素信号传导中的核心作用，我们测试了 Trbl 在幼虫脂肪体中的功能，脂肪体是一种其大小快速增加对胰岛素/胰岛素样生长因子水平极为敏感的组织。与拮抗胰岛素介导的生长作用一致，脂肪体中 trbl RNAi 敲低增加了细胞大小，提前了化蛹时间，并提高了循环甘油三酯水平。互补地，Trbl 的过表达减小了脂肪体细胞大小，降低了幼虫整体大小，延迟了成熟并降低了甘油三酯水平，而循环葡萄糖水平升高。保守的 Trbl 激酶结构域在体内发挥功能以及在酵母双杂交实验中与 Akt 相互作用是必需的。与对 Akt 的直接调节一致，脂肪体中 Trbl 的过表达降低了活化 Akt（pSer505-Akt）的水平，而 trbl RNAi 的异位表达增加了磷酸化 Akt 水平，并且两种处理均未影响总 Akt 水平。Trbl 的异位表达有效地抑制了 Akt 介导的翅膀和肌肉细胞大小增加，并降低了 Akt 靶标 FoxO（pSer256-FoxO）的磷酸化水平。综上所述，这些数据表明果蝇 Trbl 具有结合 Akt 并阻断 Akt 介导的胰岛素信号传导的保守作用，并暗示 Trib 蛋白是将营养物质可用性与细胞生长和增殖联系起来的信号通路整合的新位点。
