Chronic ethanol intake impairs insulin signaling in rats by disrupting akt association with the cell membrane - Role of TRB3 in inhibition of Akt/protein kinase B activation
Chronic ethanol intake impairs insulin signaling in rats by disrupting akt association with the cell membrane - Role of TRB3 in inhibition of Akt/protein kinase B activation
复制标题
DOI：
10.1074/jbc.m510724200
复制
发表时间：
2006-04-21
影响因子：
4.8
通讯作者：
Badger, TM
中科院分区：
文献类型：
--
作者：
He, L;Simmen, FA;Badger, TM
长期过量饮酒是导致2型糖尿病的一个重要且可改变的危险因素。我们之前曾报道，乙醇喂养的大鼠肝脏1类酒精脱氢酶(ADH)表达增加，与成熟的核类固醇调节元件结合蛋白-1(SREBP-1)水平降低相对应，SREBP-1是胰岛素诱导的ADH基因转录抑制因子。在本报告中，我们研究了胰岛素和乙醇对高分化大鼠肝癌细胞系(FGC-4)ADH基因表达的影响，以及长期摄入含乙醇饮食对肝脏胰岛素信号转导的影响。胰岛素抑制ADH基因的表达，这种抑制作用可被LY294002(一种磷脂酰肌醇3-激酶抑制剂)和SREBP-1的小干扰RNA敲除而取消。慢性酒精摄入导致蛋白激酶B(Akt)在Thr(308)位的磷酸化降低，在Ser473位(Ser)的Akt的磷酸化增加，并且降低了Akt的下游效应因子-糖原合成酶-3β的磷酸化。饲喂含乙醇饲料的大鼠肝细胞膜相关Akt含量降低，胞浆Akt含量升高。因此，乙醇对胰岛素信号转导的干扰作用是通过受损的Akt在Thr(308)的磷酸化来实现的。在酒精喂养的大鼠肝脏中诱导了Akt的负调控因子TRB3。在乙醇处理的FGC-4细胞中，TRB3的小干扰RNA敲除增加了膜相关Akt和Thr(308)Akt的磷酸化。我们的结果表明，乙醇诱导TRB3，TRB3通过与Akt的pleckstrin同源结构域结合，阻止其质膜结合，Akt-Thr(308)磷酸化，以及随后的Akt介导的信号转导。乙醇抑制胰岛素信号转导可减少SREBP的核积聚，并导致抑制1类ADH转录。
Chronic and excessive alcohol consumption is an important and modifiable risk factor for type 2 diabetes. We previously reported elevations in hepatic Class 1 alcohol dehydrogenase (ADH) expression in ethanol-fed rats correspondent with reduced levels of mature, nuclear sterol-regulatory element-binding protein-1 (SREBP-1), an insulin-induced transcriptional repressor of the ADH gene. In this report, we have studied the effects of insulin and ethanol on ADH gene expression in a highly differentiated rat hepatoma cell line (FGC-4), as well as the in vivo effects of chronic intake of an ethanol-containing diet on hepatic insulin signaling. Insulin inhibited ADH gene expression, and this was abolished by LY294002 ( a phosphatidylinositol 3-kinase inhibitor) and small interfering RNA knockdown of SREBP-1. Chronic ethanol intake led to decreased phosphorylation of Akt ( protein kinase B) at Thr(308), increased phosphorylation of Akt at Ser(473), and decreased phosphorylation of glycogen synthase kinase-3 beta ( a downstream effector of Akt). Hepatic membrane-associated Akt content was decreased and cytosolic Akt content was increased in rats fed an ethanol-containing diet. Thus, disruptive effects of ethanol on insulin signaling occurred via impaired phosphorylation of Akt at Thr(308). TRB3, a negative regulator of Akt, was induced in liver of ethanol-fed rats. In ethanol-treated FGC-4 cells, small interfering RNA knockdown of TRB3 increased membrane-associated Akt and the phosphorylation of Akt at Thr(308). Our results suggest that ethanol induces TRB3, which, through binding to the pleckstrin homology domain of Akt, prevents its plasma membrane association, Akt-Thr(308) phosphorylation, and subsequent Akt-mediated signaling. Ethanol inhibition of insulin signaling reduces nuclear SREBP accumulation and results in disinhibition of Class 1 ADH transcription.