From the Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Rutgers, The State University of New Jersey, Piscataway, New Jersey 08854 and.
Department of Medicine, Division of Endocrinology, Child Health Institute of New Jersey, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08901.
J Biol Chem. 2018 Oct 19;293(42):16464-16478. doi: 10.1074/jbc.RA118.003991. Epub 2018 Sep 10.
The mechanistic target of rapamycin (mTOR) controls metabolic pathways in response to nutrients. Recently, we have shown that mTOR complex 2 (mTORC2) modulates the hexosamine biosynthetic pathway (HBP) by promoting the expression of the key enzyme of the HBP, glutamine:fructose-6-phosphate aminotransferase 1 (GFAT1). Here, we found that GFAT1 Ser-243 phosphorylation is also modulated in an mTORC2-dependent manner. In response to glutamine limitation, active mTORC2 prolongs the duration of Ser-243 phosphorylation, albeit at lower amplitude. Blocking glycolysis using 2-deoxyglucose robustly enhances Ser-243 phosphorylation, correlating with heightened mTORC2 activation, increased AMPK activity, and -GlcNAcylation. However, when 2-deoxyglucose is combined with glutamine deprivation, GFAT1 Ser-243 phosphorylation and mTORC2 activation remain elevated, whereas AMPK activation and -GlcNAcylation diminish. Phosphorylation at Ser-243 promotes GFAT1 expression and production of GFAT1-generated metabolites including ample production of the HBP end-product, UDP-GlcNAc, despite nutrient starvation. Hence, we propose that the mTORC2-mediated increase in GFAT1 Ser-243 phosphorylation promotes flux through the HBP to maintain production of UDP-GlcNAc when nutrients are limiting. Our findings provide insights on how the HBP is reprogrammed via mTORC2 in nutrient-addicted cancer cells.
雷帕霉素的作用靶点（mTOR）控制代谢途径以响应营养物质。最近，我们发现 mTOR 复合物 2（mTORC2）通过促进己糖胺生物合成途径（HBP）的关键酶谷氨酰胺：果糖-6-磷酸氨基转移酶 1（GFAT1）的表达来调节 HBP。在这里，我们发现 GFAT1 Ser-243 磷酸化也受到 mTORC2 的调节。在谷氨酰胺限制的情况下，活性 mTORC2 延长 Ser-243 磷酸化的持续时间，尽管幅度较低。使用 2-脱氧葡萄糖阻断糖酵解会强烈增强 Ser-243 磷酸化，这与 mTORC2 激活增加、AMPK 活性增加和 -GlcNAc 化增加相关。然而，当 2-脱氧葡萄糖与谷氨酰胺缺乏结合使用时，GFAT1 Ser-243 磷酸化和 mTORC2 激活仍然升高，而 AMPK 激活和 -GlcNAc 化减少。Ser-243 磷酸化促进 GFAT1 的表达和 GFAT1 产生的代谢物的产生，包括 HBP 终产物 UDP-GlcNAc 的大量产生，尽管存在营养饥饿。因此，我们提出 mTORC2 介导的 GFAT1 Ser-243 磷酸化增加促进了 HBP 中的通量，以在营养有限时维持 UDP-GlcNAc 的产生。我们的研究结果提供了关于营养依赖性癌细胞中如何通过 mTORC2 重新编程 HBP 的见解。
