Identification of a novel proliferation-dependent C-rich element that mediates inhibition of the rat GLUT1 promoter.

Abstract Expression of the glucose transporter GLUT1 is high in proliferating and tumour cells. Conditions in which the transcriptional activity of GLUT1 promoter are maximal are characterized by the operation of activators such as Sp1 and inhibitors as Sp3. Here, we have identified an element at −67/−60 (C8 box) in the rat GLUT1 promoter to which nuclear factors bind in a proliferation-dependent manner. Competition studies with a series of mutated oligonucleotides suggest that these nuclear factors are different in the proliferative state and after confluence. The C8 element does not bind any of the known factors defined in databases. Mutation of the C8 sequence enhanced transcriptional activity of the GLUT1 promoter in 10T1/2 fibroblasts and in L6E9 myoblasts but not in myotubes. Furthermore, the functional activity of the C8 box is maximal in the presence of serum. In summary, we have identified a novel inhibitory element, C8 box, in the rat GLUT1 promoter that operates in a proliferation-dependent manner. In keeping with this view, serum enhances the inhibitory activity of the C8 box, suggesting that this is regulated by growth factors.