Department of Nutrition, Food Science and Physiology, University of Navarra, Pamplona, Spain.
Nutrition Research Centre, University of Navarra, Pamplona, Spain.
J Cell Physiol. 2019 Apr;234(4):4396-4408. doi: 10.1002/jcp.27231. Epub 2018 Oct 23.
GLUT12 was cloned from the mammary cancer cell line MCF-7, but its physiological role still needs to be elucidated. To gain more knowledge of GLUT12 function in the intestine, we investigated GLUT12 subcellular localization in the small intestine and its regulation by sugars, hormones, and intracellular mediators in Caco-2 cells and mice. Immunohistochemical methods were used to determine GLUT12 subcellular localization in human and murine small intestine. Brush border membrane vesicles were isolated for western blot analyses. Functional studies were performed in Caco-2 cells by measuring α-methyl-d-glucose (αMG) uptake in the absence of sodium. GLUT12 is located in the apical cytoplasm, below the brush border membrane, and in the perinuclear region of murine and human enterocytes. In Caco-2 cells, GLUT12 translocation to the apical membrane and α-methyl- d-glucose uptake by the transporter are stimulated by protons, glucose, insulin, tumor necrosis factor-α (TNF-α), protein kinase C, and AMP-activated protein kinase. In contrast, hypoxia decreases GLUT12 expression in the apical membrane. Upregulation of TNF-α and hypoxia-inducible factor-1α ( HIF-1α) genes is found in the jejunal mucosa of diet-induced obese mice. In these animals, GLUT12 expression in the brush border membrane is slightly decreased compared with lean animals. Moreover, an intraperitoneal injection of insulin does not induce GLUT12 translocation to the membrane, as it occurs in lean animals. GLUT12 rapid translocation to the enterocytes' apical membrane in response to glucose and insulin could be related to GLUT12 participation in sugar absorption during postprandial periods. In obesity, in which insulin sensitivity is reduced, the contribution of GLUT12 to sugar absorption is affected.
GLUT12 是从乳腺癌细胞系 MCF-7 中克隆出来的，但它的生理作用仍有待阐明。为了更深入地了解 GLUT12 在肠道中的功能，我们研究了 GLUT12 在 Caco-2 细胞和小鼠小肠中的亚细胞定位及其对糖、激素和细胞内介质的调节。我们采用免疫组织化学方法确定了人及鼠小肠中 GLUT12 的亚细胞定位。我们还通过分离刷状缘膜囊泡进行 Western blot 分析。我们在 Caco-2 细胞中进行了功能研究，即在无钠离子的情况下测量 α-甲基-d-葡萄糖（αMG）的摄取。GLUT12 位于鼠和人肠上皮细胞的顶细胞质、刷状缘膜下和核周区域。在 Caco-2 细胞中，质子、葡萄糖、胰岛素、肿瘤坏死因子-α（TNF-α）、蛋白激酶 C 和 AMP 激活的蛋白激酶刺激 GLUT12 向顶膜易位和转运体对 α-甲基-d-葡萄糖的摄取。相反，缺氧会降低顶膜上的 GLUT12 表达。在饮食诱导肥胖小鼠的空肠黏膜中发现 TNF-α 和缺氧诱导因子-1α（HIF-1α）基因的上调。在这些动物中，与瘦小动物相比，GLUT12 在刷状缘膜上的表达略有下降。此外，与瘦小动物一样，胰岛素的腹腔内注射不会诱导 GLUT12 向膜易位。GLUT12 对葡萄糖和胰岛素的快速易位到肠上皮细胞的顶膜可能与 GLUT12 在餐后吸收糖中的参与有关。在胰岛素敏感性降低的肥胖中，GLUT12 对糖吸收的贡献受到影响。
