The ubiquitin-proteasome system regulates the stability and activity of the glucose sensor glucokinase in pancreatic β-cells
The ubiquitin-proteasome system regulates the stability and activity of the glucose sensor glucokinase in pancreatic β-cells
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DOI：
10.1042/bj20130262
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发表时间：
2013-12-01
影响因子：
4.1
通讯作者：
Baltrusch, Simone
中科院分区：
文献类型：
--
作者：
Hofmeister-Brix, Anke;Lenzen, Sigurd;Baltrusch, Simone
泛素蛋白酶体系统是维持胰腺SS细胞功能的重要途径。抑制蛋白酶体显著减少了葡萄糖诱导的胰岛素分泌。刺激/分泌级联反应的关键调节因子似乎受到蛋白质错误折叠的影响，如果蛋白酶体下调，就像最近在患有2型糖尿病的人类中所报道的那样。然而，目前尚不清楚葡萄糖感受器酶葡糖激酶是否参与了这一过程。在体内，FRET可以显示葡糖激酶和泛素之间的直接相互作用，这表明葡糖激酶受到蛋白酶体的调节。蛋白酶体抑制后，MIN6细胞的葡萄糖激酶活性显著降低，而蛋白质含量增加，表明蛋白质错误折叠。用环己胺提高伴侣的利用率可以诱导复性和恢复葡糖激活酶活性。在MIN6细胞、原代SS细胞和肝细胞中均可检测到MG132、Bortezomib、Epoxomicin或lactacystin阻断蛋白酶体所致的葡萄糖激酶聚集。葡萄糖激酶侵袭体的形成是在微管辅助下进行的，环己胺可以避免。因此，本研究的结果支持在胰腺SS细胞中泛素蛋白酶体系统的能力减弱的情况下葡糖激酶的错误折叠和聚集。在2型糖尿病的情况下，这可能有助于减少葡萄糖诱导的胰岛素分泌。
The ubiquitin proteasome system is important to maintain pancreatic ss-cell function. Inhibition of the proteasome significantly reduced glucose-induced insulin secretion. Key regulators of the stimulus/secretion cascade seem to be affected by protein misfolding if the proteasome is down-regulated as recently reported in humans with Type 2 diabetes. It remains unknown, however, whether the glucose sensor enzyme glucokinase is involved in this process. A direct interaction between glucokinase and ubiquitin could be shown in vivo by FRET, suggesting regulation of glucokinase by the proteasome. After proteasome inhibition glucokinase activity was significantly reduced in MIN6 cells, whereas the protein content was increased, indicating protein misfolding. Enhancing the availability of chaperones by cyclohexamide could induce refolding and restored glucokinase activity. Glucokinase aggregation due to proteasome blocking with MG132, bortezomib, epoxomicin or lactacystin could be detected in MIN6 cells, primary ss-cells and hepatocytes using fluorescence-based assays. Glucokinase aggresome formation proceeded microtubule-assisted and was avoided by cyclohexamide. Thus the results of the present study provide support for glucokinase misfolding and aggregation in case of a diminished capacity of the ubiquitin proteasome system in pancreatic ss-cells. In the Type 2 diabetic situation this could contribute to reduced glucose-induced insulin secretion.