Molecular mechanisms of the increased glucose transport in transformed FRTL-5 rat thyroid cells

We investigated the molecular mechanisms involved in the glucose carrier (Glut 1) regulation in FRTL-5 cells and two derived transformed clones (SRC and Ki-Mol cells). When compared to the wild-type strain, SRC and Ki-Mol cells showed an increase in both glucose consumption and uptake (about 60 fold), associated with 6-8 fold higher Glut 1 mRNA levels. Transcriptional studies revealed a 2- to 3 fold increased activation of the gene in the transformed cells, suggesting that transcription alone cannot fully account for the higher Glut 1 gene expression. Western blot studies showed an increase of the Glut 1 protein in SRC and Ki-Mol cells, associated with a different gel migration pattern and a disparate distribution rate between the plasma membrane and the microsomal fraction. These data indicate that the higher rate of glucose uptake observed in SRC and Ki-Mol cells is associated to an increase in Glut 1 gene expression, and that also changes in the subcellular distribution and probably in the structure of Glut 1 protein are present.