Park Joo-Man, Kim Tae-Hyun, Jo Seong-Ho, Kim Mi-Young, Ahn Yong-Ho
Department of Biochemistry and Molecular Biology, Yonsei University College of Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 120-752, Republic of Korea.
Brain Korea 21 PLUS Project for Medical Sciences, Yonsei University College of Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 120-752, Republic of Korea.
Sci Rep. 2015 Dec 1;5:17395. doi: 10.1038/srep17395.
Glucokinase (GK), mainly expressed in the liver and pancreatic β-cells, is critical for maintaining glucose homeostasis. GK expression and kinase activity, respectively, are both modulated at the transcriptional and post-translational levels. Post-translationally, GK is regulated by binding the glucokinase regulatory protein (GKRP), resulting in GK retention in the nucleus and its inability to participate in cytosolic glycolysis. Although hepatic GKRP is known to be regulated by allosteric mechanisms, the precise details of modulation of GKRP activity, by post-translational modification, are not well known. Here, we demonstrate that GKRP is acetylated at Lys5 by the acetyltransferase p300. Acetylated GKRP is resistant to degradation by the ubiquitin-dependent proteasome pathway, suggesting that acetylation increases GKRP stability and binding to GK, further inhibiting GK nuclear export. Deacetylation of GKRP is effected by the NAD(+)-dependent, class III histone deacetylase SIRT2, which is inhibited by nicotinamide. Moreover, the livers of db/db obese, diabetic mice also show elevated GKRP acetylation, suggesting a broader, critical role in regulating blood glucose. Given that acetylated GKRP may affiliate with type-2 diabetes mellitus (T2DM), understanding the mechanism of GKRP acetylation in the liver could reveal novel targets within the GK-GKRP pathway, for treating T2DM and other metabolic pathologies.
葡萄糖激酶(GK)主要在肝脏和胰腺β细胞中表达,对维持葡萄糖稳态至关重要。GK的表达和激酶活性分别在转录和翻译后水平受到调节。在翻译后水平,GK通过与葡萄糖激酶调节蛋白(GKRP)结合而受到调控,导致GK滞留在细胞核中,无法参与细胞质糖酵解。尽管已知肝脏GKRP受变构机制调节,但通过翻译后修饰调节GKRP活性的精确细节尚不清楚。在这里,我们证明GKRP在赖氨酸5位点被乙酰转移酶p300乙酰化。乙酰化的GKRP对泛素依赖性蛋白酶体途径的降解具有抗性,这表明乙酰化增加了GKRP的稳定性以及与GK的结合,进一步抑制了GK的核输出。GKRP的去乙酰化由NAD(+)依赖性的III类组蛋白去乙酰化酶SIRT2介导,而SIRT2受到烟酰胺的抑制。此外,db/db肥胖糖尿病小鼠的肝脏中也显示出GKRP乙酰化水平升高,这表明其在调节血糖方面具有更广泛的关键作用。鉴于乙酰化的GKRP可能与2型糖尿病(T2DM)相关,了解肝脏中GKRP乙酰化机制可能揭示GK-GKRP途径中的新靶点,用于治疗T2DM和其他代谢性疾病。