Regulation of GLUT3 and glucose uptake by the cAMP signalling pathway in the breast cancer cell line ZR-75

Increased glucose uptake as a principal energy source is a requirement for the continued survival of tumour cells. Facilitative glucose transporter-1 (GLUT 1) and -3(GLUTS) have been previously shown to be present and regulated in breast cancer cells and are associated with poor patient prognosis. In cancer cells, the cAMP secondary messenger pathway is known to potentiate described glucose transporter activators and regulate cell fate. However, no regulation of the glucose transporters in breast cancer cells by cAMP has previously been examined. Herein, we determined in the well-characterized breast cancer cell line ZR-75, if the cAMP analogue 8-br-cAMP was capable of regulating GLUT I and GLUTS expression and thus glucose uptake. We demonstrated that 8-br-cAMP transiently up-regulates GLUTS mRNA levels. The use of actinomycin-D and the cloning of 1,200 by upstream of the human GLUTS promoter demonstrated that this regulation was transcriptional. Immunocytochemistry and Western blotting confirmed that the increase in mRNA was reflected by an increase in protein levels. No notable regulation of GLUT I in the presence of 8-br-cAMP was detected. Finally, we determined using the non-metabolizable glucose analogue 2-DOG if this up-regulation in GLUTS increased glucose uptake. We observed the presence of two uptake components, one corresponding to the Km of GLUT 1/4 and the other to GLUTS. A doubling in the uptake velocity was observed only at the Km corresponding to GLUTS. In conclusion, we demonstrate and characterize for the first time, an upregulation of GLUTS mRNA, protein and glucose uptake by the cAMP pathway in breast cancer cells.