Glucose-dependent glucose transporter 1 expression and its impact on viability of thyroid cancer cells

Cancer cells exhibit an altered metabolism characterized by enhanced glycolysis and glucose consumption. In glucose-addicted cancer cells upregulation of glucose transport across the plasma membrane is mediated by a family of facilitated glucose transporter proteins, particularly glucose transporter 1 (GLUT1). The aim of the present study was to investigate the impact of GLUT1 expression on glucose uptake and viability of FTC-133 and 8305c thyroid cancer cells growing in hypoglycemic, normoglycemic and hyperglycemic conditions. The results showed that the total expression of GLUT1 was higher in the two cell types growing in low glucose compared to cells growing in normoglycemia or hyperglycemia and this was correlated with AKT Ser473 phosphorylation but not with the expression of hypoxia inducible factor alpha (HIF1 alpha). However, the membrane expression of GLUT1 was correlated with HIF1 alpha expression. HIF1 alpha expression was positively correlated with the glucose concentration in FTC-133 cells, whereas this expression was inversely correlated in 8305c cells. Glucose uptake was dependent on the membrane level of GLUT1 but not total GLUT! expression. Downregulation of GLUT1 expression by RNAi in FTC-133 cells caused a reduction in glucose uptake but did not significantly affect cell viability. In the case of 8305c cells showing low endogenous GLUT1 expression and lack of HIF1 alpha expression in normoxic conditions GLUT1 RNAi impacted cell viability. These data suggested that GLUT1 may be part of an AKT1-dependent mechanism allowing cells to survive in low levels of glucose. Glucose concentration inversely affected HIF1 alpha expression and the level of GLUT1 in membrane as well as glucose uptake in FTC-133 and 8305c cells. The extent of GLUT1 impact on cell viability was also cell-type-dependent.