Nemeth B A, Tsang S W, Geske R S, Haney P M
Department of Pediatrics, University of Wisconsin Children's Hospital, University of Wisconsin, Madison 53792, USA.
Pediatr Res. 2000 Apr;47(4 Pt 1):444-50. doi: 10.1203/00006450-200004000-00006.
Lactose, the major carbohydrate of human milk, is synthesized in the Golgi from glucose and UDP-galactose. The lactating mammary gland is unique in its requirement for the transport of glucose into Golgi. Glucose transporter-1 (GLUT1) is the only isoform of the glucose transporter family expressed in mammary gland. In most cells, GLUT1 is localized to the plasma membrane and is responsible for basal glucose uptake; in no other cell type is GLUT1 a Golgi resident. To test the hypothesis that GLUT1 is targeted to Golgi during lactation, the amount and subcellular distribution of GLUT1 were examined in mouse mammary gland at different developmental stages. Methods including immunohistochemistry, immunofluorescence, subcellular fractionation, density gradient centrifugation, and Western blotting yielded consistent results. In virgins, GLUT1 expression was limited to plasma membrane of epithelial cells. In late pregnant mice, GLUT1 expression was increased with targeting primarily to basolateral plasma membrane but also with some intracellular signal. During lactation, GLUT expression was further increased, and targeting to Golgi, demonstrated by colocalization with the 110-kD coatomer-associated protein beta-COP, predominated. Removal of pups 18 d after delivery resulted in retargeting of GLUT1 from Golgi to plasma membrane and a decline in total cellular GLUT1 within 3 h. In mice undergoing natural weaning, GLUT1 expression declined. Changes in the amount and targeting of GLUT1 during mammary gland development are consistent with a key role for GLUT1 in supplying substrate for lactose synthesis and milk production.
乳糖是母乳中的主要碳水化合物，在高尔基体中由葡萄糖和尿苷二磷酸半乳糖合成。泌乳期乳腺在将葡萄糖转运到高尔基体方面有独特需求。葡萄糖转运蛋白1（GLUT1）是在乳腺中表达的葡萄糖转运蛋白家族的唯一亚型。在大多数细胞中，GLUT1定位于质膜，负责基础葡萄糖摄取；在其他细胞类型中，GLUT1都不是高尔基体驻留蛋白。为了验证GLUT1在泌乳期靶向高尔基体的假说，研究人员检测了不同发育阶段小鼠乳腺中GLUT1的含量和亚细胞分布。免疫组织化学、免疫荧光、亚细胞分级分离、密度梯度离心和蛋白质免疫印迹等方法得出了一致的结果。在未生育的小鼠中，GLUT1的表达仅限于上皮细胞质膜。在妊娠后期的小鼠中，GLUT1表达增加，主要靶向基底外侧质膜，但也有一些细胞内信号。在泌乳期，GLUT的表达进一步增加，并且通过与110-kD包被蛋白相关蛋白β-COP共定位证明，靶向高尔基体占主导。分娩后18天摘除幼崽导致GLUT1从高尔基体重新靶向质膜，并且在3小时内细胞内GLUT1总量下降。在自然断奶的小鼠中，GLUT1表达下降。乳腺发育过程中GLUT1含量和靶向的变化与GLUT1在为乳糖合成和乳汁分泌提供底物方面的关键作用一致。
