Up-regulation of O-GlcNAc Transferase with Glucose Deprivation in HepG2 Cells Is Mediated by Decreased Hexosamine Pathway Flux
Up-regulation of O-GlcNAc Transferase with Glucose Deprivation in HepG2 Cells Is Mediated by Decreased Hexosamine Pathway Flux
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DOI：
10.1074/jbc.m803198200
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发表时间：
2009-02-06
影响因子：
4.8
通讯作者：
McClain, Donald A.
中科院分区：
文献类型：
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作者：
Taylor, Rodrick P.;Geisler, Taylor S.;McClain, Donald A.
O-连接N-乙酰氨基葡萄糖(O-GlcNAc)是一种蛋白质的翻译后修饰，具有营养感知机制。我们先前已经证明，在缺糖条件下，O-GlcNAc修饰具有显著的诱导性。O-GlcNAc修饰的增加是由核质型O-连接N-乙酰氨基葡萄糖基转移酶(NcOGT)的mRNA增加所介导的。我们研究了缺糖诱导ncOGT的机制。这一信号似乎不是一般的能量耗竭，因为在葡萄糖剥夺和正常葡萄糖处理的细胞之间，没有观察到AMP依赖的激酶蛋白水平或磷酸化的差异。然而，小剂量(1 MM)的氨基葡萄糖可阻断ncOGT mRNA的诱导和随后O-GlcNAc蛋白修饰的增加，提示氨基己糖通量的降低是ncOGT上调的信号。与此一致的是，用O-GlcNAcase抑制剂((O-(2-acetamido-2-deoxy-D-glucopyranosylidene)氨基N-苯基氨基甲酸酯)处理缺糖细胞完全阻止了随后ncOGT的上调。氨基葡萄糖治疗还使糖原合成酶活性下调的40%得到挽救，这种下调通常出现在葡萄糖剥夺后。我们的结论是，在缺糖的最初几个小时内，蛋白质的脱糖基化促进了ncOGT的诱导。这些发现提示了OGT和O-GlcNAc调控的一个新的负反馈调控环。
O-Linked N-acetylglucosamine (O-GlcNAc) is a post-translational modification of proteins that functions as a nutrient sensing mechanism. We have previously shown a significant induction of O-GlcNAc modification under conditions of glucose deprivation. Increased O-GlcNAc modification was mediated by increased mRNA for nucleocytoplasmic O-linked N-acetylglucosaminyltransferase (ncOGT). We have investigated the mechanism mediating ncOGT induction with glucose deprivation. The signal does not appear to be general energy depletion because no differences in AMP-dependent kinase protein levels or phosphorylation were observed between glucose-deprived and normal glucose-treated cells. However, treatment of glucose-deprived cells with a small dose (1 mM) of glucosamine blocked the induction of ncOGT mRNA and subsequent increase in O-GlcNAc protein modification, suggesting that decreased hexosamine flux is the signal for ncOGT up-regulation. Consistent with this, treatment of glucose-deprived cells with an inhibitor of O-GlcNAcase (O-(2-acetamido-2-deoxy-D-glucopyranosylidene) amino N-phenyl carbamat) completely prevented the subsequent up-regulation of ncOGT. Glucosamine treatment also resulted in a 40% rescue of the down-regulation of glycogen synthase activity normally seen after glucose deprivation. We conclude that deglycosylation of proteins within the first few hours of glucose deprivation promotes ncOGT induction. These findings suggest a novel negative feedback regulatory loop for OGT and O-GlcNAc regulation.