Divisions of Metabolic Diseases, National Institutes of Health, Eunpyeong-gu, Seoul 122-701, Korea.
J Biol Chem. 2010 Nov 26;285(48):37251-62. doi: 10.1074/jbc.M110.142315. Epub 2010 Sep 20.
Chronic ethanol consumption is known as an independent risk factor for type 2 diabetes, which is characterized by impaired glucose homeostasis and insulin resistance; however, there is a great deal of controversy concerning the relationships between alcohol consumption and the development of type 2 diabetes. We investigated the effects of chronic ethanol consumption on pancreatic β-cell dysfunction and whether generated peroxynitrite participates in the impaired glucose homeostasis. Here we show that chronic ethanol feeding decreases the ability of pancreatic β-cells to mediate insulin secretion and ATP production in coordination with the decrease of glucokinase, Glut2, and insulin expression. Specific blockade of ATF3 using siRNA or C-terminally deleted ATF3(ΔC) attenuated ethanol-induced pancreatic β-cell apoptosis or dysfunction and restored the down-regulation of glucokinase (GCK), insulin, and pancreatic duodenal homeobox-1 induced by ethanol. GCK inactivation and down-regulation were predominantly mediated by ethanol metabolism-generated peroxynitrite, which were suppressed by the peroxynitrite scavengers N(γ)-monomethyl-L-arginine, uric acid, and deferoxamine but not by the S-nitrosylation inhibitor DTT, indicating that tyrosine nitration is the predominant modification associated with GCK down-regulation and inactivation rather than S-nitrosylation of cysteine. Tyrosine nitration of GCK prevented its association with pBad, and GCK translocation into the mitochondria results in subsequent proteasomal degradation of GCK following ubiquitination. This study identified a novel and efficient pathway by which chronic ethanol consumption may induce GCK down-regulation and inactivation by inducing tyrosine nitration of GCK, resulting in pancreatic β-cell apoptosis and dysfunction. Peroxynitrite-induced ATF3 may also serve as a potent upstream regulator of GCK down-regulation and β-cell apoptosis.
慢性乙醇摄入是 2 型糖尿病的一个独立危险因素，其特征为葡萄糖稳态受损和胰岛素抵抗；然而，关于饮酒与 2 型糖尿病发展之间的关系，存在着大量的争议。我们研究了慢性乙醇摄入对胰腺β细胞功能障碍的影响，以及是否生成过氧亚硝酸盐参与葡萄糖稳态受损。在这里，我们表明慢性乙醇喂养会降低胰腺β细胞协调葡萄糖激酶、Glut2 和胰岛素表达来介导胰岛素分泌和 ATP 生成的能力。使用 siRNA 特异性阻断 ATF3 或 C 端缺失的 ATF3（ΔC）可减轻乙醇诱导的胰腺β细胞凋亡或功能障碍，并恢复乙醇诱导的葡萄糖激酶（GCK）、胰岛素和胰腺十二指肠同源盒-1 的下调。GCK 的失活和下调主要是由乙醇代谢生成的过氧亚硝酸盐介导的，而过氧亚硝酸盐清除剂 N（γ）-单甲基-L-精氨酸、尿酸和去铁胺可抑制其介导作用，但 S-亚硝基化抑制剂 DTT 则不能，表明酪氨酸硝化是与 GCK 下调和失活相关的主要修饰方式，而非半胱氨酸的 S-亚硝基化。GCK 的酪氨酸硝化阻止了其与 pBad 的结合，GCK 向线粒体的易位导致随后 GCK 的泛素化和蛋白酶体降解。这项研究确定了一条新的有效途径，即慢性乙醇摄入可能通过诱导 GCK 的酪氨酸硝化来诱导 GCK 的下调和失活，导致胰腺β细胞凋亡和功能障碍。过氧亚硝酸盐诱导的 ATF3 也可能作为 GCK 下调和β细胞凋亡的一个强有力的上游调控因子。
