Cloning and functional analysis of goat glucose transporter 4

Glucose transporter (GLUT) 4 is a major mediator of blood glucose levels and a key regulator of whole-body glucose homeostasis. This study aimed at evaluating the function of goat GLUT4 on glucose absorption and the effect of GLUT4 on lactose synthesis in goat mammary gland epithelial (GMGE) cells. Currently, the cDNA of GLUT4, a putative facilitative GLUT, was cloned from goat. To investigate the function of goat GLUT4, we constructed the eukaryotic expression vector pcDNA3.1-GLUT4 and used it to transfect GMGE cells, and then GLUT4 transfected GMGE (G4T-GMGE) cells were generated. The deduced GLUT4 sequence comprised 509 amino acids, what meant that a putative protein with a molecular weight of approximately 55 kDa would be produced. Both glucose uptake and lactose synthesis increased in the G4T-GMGE cells compared with the GMGE cells. At the transcriptional level, GLUT4 expression increased by nearly 55-fold in the G4T-GMGE cells, and the expression of amino acid transporters (SLC1A5, SLC3A2 and SLC7A5) enhanced as well; in contrast, GLUT1 expression decreased by more than 50 % in the G4T-GMGE cells. These results suggest that goat GLUT4 functions in the transport of glucose and it may play a positive role in amino acid uptake in mammary glands.