Li Ran, Tian Jin-Ze, Wang Mo-Ran, Zhu Li-Na, Sun Jin-Sheng
Tianjin Key Laboratory of Animal and Plant Resistance, College of Life Science, Tianjin Normal University, Tianjin 300387, People's Republic of China.
Tianjin Key Laboratory of Aqua-ecology and Aquaculture, Department of Fisheries Science, Tianjin Agricultural University, Tianjin 300384, People's Republic of China.
Biol Open. 2017 Sep 15;6(9):1279-1289. doi: 10.1242/bio.027532.
Glucose is an essential energy source for both vertebrates and invertebrates. In mammals, glucose uptake is mediated primarily by glucose transporters (GLUTs), members of the major facilitator superfamily (MFS) of passive transporters. Among the GLUTs, GLUT4 is the main glucose transporter in muscles and adipocytes. In skeletal muscle cells, GLUT4 interacts with the lipid raft protein flotillin to transport glucose upon stimulation by insulin. Although several studies have examined GLUT4 function in mammals, few have been performed in crustaceans, which also use glucose as their main energy source. Crustacean hyperglycemic hormone (CHH) is a multifunctional neurohormone found only in arthropods, and one of its roles is to regulate glucose homeostasis. However, the molecular mechanism that underlies CHH regulation and whether GLUT4 is involved in its regulation in crustaceans remain unclear. In the present study, we identified a full-length GLUT4 cDNA sequence (defined herein as EsGLUT4) from the Chinese mitten crab and analyzed its tissue distribution and cellular localization. By the ForteBio Octet system, two large hydrophilic regions within EsGLUT4 were found to interact with the CHH binding protein (CHHBP), an flotillin-like protein. Interestingly, live-cell imaging indicated that EsGLUT4 and CHHBP responded simultaneously upon stimulation by CHH, resulting in glucose release. In contrast to insulin-dependent GLUT4, however, EsGLUT4 and CHHBP were present within cytoplasmic vesicles, both translocating to the plasma membrane upon CHH stimulation. In conclusion, our results provide new evidence for the involvement of EsGLUT4 and CHHBP in the regulation of glucose homeostasis in crustacean carbohydrate metabolism.
葡萄糖是脊椎动物和无脊椎动物的重要能量来源。在哺乳动物中，葡萄糖摄取主要由葡萄糖转运蛋白（GLUTs）介导，GLUTs是被动转运蛋白的主要易化子超家族（MFS）的成员。在GLUTs中，GLUT4是肌肉和脂肪细胞中的主要葡萄糖转运蛋白。在骨骼肌细胞中，GLUT4与脂筏蛋白小窝蛋白相互作用，在胰岛素刺激下转运葡萄糖。尽管已有多项研究检测了GLUT4在哺乳动物中的功能，但在同样以葡萄糖为主要能量来源的甲壳类动物中开展的研究却很少。甲壳类高血糖激素（CHH）是一种仅在节肢动物中发现的多功能神经激素，其作用之一是调节葡萄糖稳态。然而，CHH调节的分子机制以及GLUT4是否参与其在甲壳类动物中的调节尚不清楚。在本研究中，我们从中华绒螯蟹中鉴定出一个全长GLUT4 cDNA序列（在此定义为EsGLUT4），并分析了其组织分布和细胞定位。通过ForteBio Octet系统，发现EsGLUT4内的两个大亲水区域与一种类似小窝蛋白的CHH结合蛋白（CHHBP）相互作用。有趣的是，活细胞成像表明，EsGLUT4和CHHBP在CHH刺激下同时做出反应，导致葡萄糖释放。然而，与胰岛素依赖的GLUT4不同，EsGLUT4和CHHBP存在于细胞质囊泡中，在CHH刺激下两者都转位到质膜。总之，我们的结果为EsGLUT4和CHHBP参与甲壳类动物碳水化合物代谢中葡萄糖稳态的调节提供了新证据。
