Avila-Flores Antonia, Santos Teresa, Rincón Esther, Mérida Isabel
Department of Immunology and Oncology, National Centre for Biotechnology, Consejo Superior de Investigaciones Científicas, Campus Cantoblanco, E-28049 Madrid, Spain.
J Biol Chem. 2005 Mar 18;280(11):10091-9. doi: 10.1074/jbc.M412296200. Epub 2005 Jan 4.
The protein known as mammalian target of rapamycin (mTOR) regulates cell growth by integrating different stimuli, such as available nutrients and mitogenic factors. The lipid messenger phosphatidic acid (PA) binds and positively regulates the mitogenic response of mTOR. PA generator enzymes are consequently potential regulators of mTOR. Here we explored the contribution to this pathway of the enzyme diacylglycerol kinase (DGK), which produces PA through phosphorylation of diacylglycerol. We found that overexpression of the DGKzeta, but not of the alpha isoform, in serum-deprived HEK293 cells induced mTOR-dependent phosphorylation of p70S6 kinase (p70S6K). After serum addition, p70S6K phosphorylation was higher and more resistant to rapamycin treatment in cells overexpressing DGKzeta. The effect of this DGK isoform on p70S6K hyperphosphorylation required the mTOR PA binding region. Down-regulation of endogenous DGKzeta by small interfering RNA in HEK293 cells diminished serum-induced p70S6K phosphorylation, highlighting the role of this isoform in the mTOR pathway. Our results confirm a role for PA in mTOR regulation and describe a novel pathway in which DGKzeta-derived PA acts as a mediator of mTOR signaling.
被称为雷帕霉素哺乳动物靶点（mTOR）的蛋白质通过整合不同刺激（如可用营养物质和促有丝分裂因子）来调节细胞生长。脂质信使磷脂酸（PA）结合并正向调节mTOR的促有丝分裂反应。因此，PA生成酶是mTOR的潜在调节因子。在这里，我们探讨了二酰基甘油激酶（DGK）对该途径的贡献，该酶通过二酰基甘油的磷酸化产生PA。我们发现，在血清饥饿的HEK293细胞中过表达DGKzeta而非α亚型会诱导p70S6激酶（p70S6K）的mTOR依赖性磷酸化。添加血清后，过表达DGKzeta的细胞中p70S6K磷酸化水平更高，且对雷帕霉素治疗更具抗性。这种DGK亚型对p70S6K过度磷酸化的作用需要mTOR的PA结合区域。在HEK293细胞中，通过小干扰RNA下调内源性DGKzeta会减少血清诱导的p70S6K磷酸化，突出了该亚型在mTOR途径中的作用。我们的结果证实了PA在mTOR调节中的作用，并描述了一种新的途径，其中DGKzeta衍生的PA作为mTOR信号传导的介质。
