Kuo MeiShiue, Zilberfarb Vladimir, Gangneux Nicolas, Christeff Névéna, Issad Tarik
Institut Cochin, Université Paris Descartes, CNRS (UMR 8104), Paris, France.
Biochimie. 2008 May;90(5):679-85. doi: 10.1016/j.biochi.2008.03.005. Epub 2008 Mar 21.
O-GlcNAc glycosylations on serines or threonines are reversible post-translational modifications that control the localisation, the activity or the stability of cytosolic and nuclear proteins. These dynamic modifications are tightly dependent on the availability of glucose and on its flux through the hexosamine biosynthetic pathway. We recently showed that treatments that increase protein O-GlcNAc glycosylation (high-glucose concentrations, glucosamine) or inhibit their deglycosylation (PUGNAc), induced O-GlcNAc modification of FoxO1 in HEK293 cells. O-GlcNAc glycosylation of FoxO1 resulted in an increased of its activity towards a glucose 6-phosphatase promoter-luciferase reporter gene (G6Pase-luc). This effect appeared to be independent of FoxO1 sub-cellular re-localisation, since it was also observed with the constitutively nuclear FoxO1-AAA mutant. In liver-derived HepG2 cells, glucosamine and PUGNAc increased the expression of G6Pase mRNA, and synergistic effects were observed when both agents were present together. In addition, the expression of PGC1 alpha gene, which is known to be under the control of FoxO1, was also increased by glucosamine and PUGNAc. In HepG2 cells stably expressing the G6Pase-luc reporter gene, glucosamine and PUGNAc also increased the activity of the G6Pase promoter. The stimulation of the G6Pase reporter gene by these agents was abolished by two different FoxO1 siRNAs, thereby demonstrating the involvement of endogenous FoxO1 in the observed effects. Since G6Pase plays a key role in glucose production by the liver, increased in its expression through FoxO1 O-GlcNAc modification may be of considerable importance in the context of glucotoxicity associated with chronic hyperglycaemia. Moreover, since FoxO1 also plays important roles in several aspects of cell biology, including cell proliferation, survival and apoptosis, the regulation of FoxO1 activity by O-GlcNAc modification may have implications for other crucial biological processes.
丝氨酸或苏氨酸上的O-连接N-乙酰葡糖胺糖基化是可逆的翻译后修饰，可控制胞质和核蛋白的定位、活性或稳定性。这些动态修饰紧密依赖于葡萄糖的可用性及其通过己糖胺生物合成途径的通量。我们最近发现，增加蛋白质O-连接N-乙酰葡糖胺糖基化的处理（高葡萄糖浓度、氨基葡萄糖）或抑制其去糖基化的处理（PUGNAc），可诱导HEK293细胞中FoxO1的O-连接N-乙酰葡糖胺修饰。FoxO1的O-连接N-乙酰葡糖胺糖基化导致其对葡萄糖6-磷酸酶启动子-荧光素酶报告基因（G6Pase-luc）的活性增加。这种效应似乎与FoxO1亚细胞重新定位无关，因为在组成型核FoxO1-AAA突变体中也观察到了这种效应。在肝源性HepG2细胞中，氨基葡萄糖和PUGNAc增加了G6Pase mRNA的表达，当两种试剂同时存在时观察到协同效应。此外，已知受FoxO1控制的PGC1α基因的表达也因氨基葡萄糖和PUGNAc而增加。在稳定表达G6Pase-luc报告基因的HepG2细胞中，氨基葡萄糖和PUGNAc也增加了G6Pase启动子的活性。两种不同的FoxO1 siRNA消除了这些试剂对G6Pase报告基因的刺激，从而证明内源性FoxO1参与了观察到的效应。由于G6Pase在肝脏葡萄糖生成中起关键作用，通过FoxO1的O-连接N-乙酰葡糖胺修饰增加其表达在与慢性高血糖相关的糖毒性背景下可能具有相当重要的意义。此外，由于FoxO1在细胞生物学的几个方面也起着重要作用，包括细胞增殖、存活和凋亡，O-连接N-乙酰葡糖胺修饰对FoxO1活性的调节可能对其他关键生物学过程有影响。
