Jin Ling, Guo Tingting, Li Zhixin, Lei Zhen, Li Hui, Mao Yiqing, Wang Xi, Zhou Na, Zhang Yizhuang, Hu Ruobi, Zhang Xuehui, Niu Gang, Irwin David M, Tan Huanran
Department of Pharmacology, Peking University, Health Science Center, Beijing 100191, China.
Department of Integrated Traditional Chinese and Western Medicine, Peking University, Health Science Center, Beijing 100191, China.
Int J Mol Sci. 2015 Apr 2;16(4):7377-93. doi: 10.3390/ijms16047377.
Glucokinase (GCK) is the rate-limiting enzyme of liver glucose metabolism. Through protein-protein interactions, glucokinase regulatory protein (GCKR) post-transcriptionally regulates GCK function in the liver, and causes its nuclear localization. However the role of GCK in regulating GCKR localization is unknown. In the present study, using in vitro and in vivo models, we examined the levels of GCK and GCKR, and their subcellular localization. We found that total cellular levels of GCKR did not vary in the in vivo models, but its subcellular localization did. In animals with normal levels of GCK, GCKR is mainly localized to the nuclei of hepatocytes. In seven-day old rats and liver-specific Gck gene knockout mice (animals that lack or have reduced levels of GCK protein), GCKR was found primarily in the cytoplasm. The interaction of GCK with GCKR was further examined using in vitro models where we varied the levels of GCK and GCKR. Varying the level of GCK protein had no effect on total cellular GCKR protein levels. Taken together, our results indicate that GCK is important for the localization of GCKR to the nucleus and raises the possibility that GCKR may have functions in addition to those regulating GCK activity in the cytoplasm.
葡萄糖激酶（GCK）是肝脏葡萄糖代谢的限速酶。通过蛋白质-蛋白质相互作用，葡萄糖激酶调节蛋白（GCKR）在转录后调控肝脏中GCK的功能，并使其定位于细胞核。然而，GCK在调节GCKR定位中的作用尚不清楚。在本研究中，我们使用体外和体内模型，检测了GCK和GCKR的水平及其亚细胞定位。我们发现，在体内模型中，GCKR的总细胞水平没有变化，但其亚细胞定位发生了变化。在GCK水平正常的动物中，GCKR主要定位于肝细胞的细胞核。在7日龄大鼠和肝脏特异性Gck基因敲除小鼠（缺乏或GCK蛋白水平降低的动物）中，GCKR主要存在于细胞质中。我们使用体外模型进一步检测了GCK与GCKR的相互作用，在该模型中我们改变了GCK和GCKR的水平。改变GCK蛋白水平对总细胞GCKR蛋白水平没有影响。综上所述，我们的结果表明，GCK对GCKR定位于细胞核很重要，并增加了GCKR可能除了在细胞质中调节GCK活性之外还具有其他功能的可能性。
