Transcriptional activation of the glucose transporter GLUT1 in ventricular cardiac myocytes by hypertrophic agonists.

Myocardial hypertrophy is associated with increased basal glucose metabolism. Basal glucose transport into cardiac myocytes is mediated by the GLUT1 isoform of glucose transporters, whereas the GLUT4 isoform is responsible for regulatable glucose transport. Treatment of neonatal cardiac myocytes with the hypertrophic agonist 12-O-tetradecanoylphorbol-13-acetate or phenylephrine increased expression of Glut1 mRNA relative to Glut4 mRNA. To study the transcriptional regulation of GLUT1 expression, myocytes were transfected with luciferase reporter constructs under the control of the Glut1 promoter. Stimulation of the cells with 12-O-tetradecanoylphorbol-13-acetate or phenylephrine induced transcription from the Glut1 promoter, which was inhibited by cotransfection with the mitogen-activated protein kinase phosphatases CL100 and MKP-3. Cotransfection of the myocytes with constitutively active versions of Ras and MEK1 or an estrogen-inducible version of Raf1 also stimulated transcription from the Glut1 promoter. Hypertrophic induction of the Glut1 promoter was also partially sensitive to inhibition of the phosphatidylinositol 3-kinase pathway and was strongly inhibited by cotransfection with dominant-negative Ras. Thus, Ras activation and pathways downstream of Ras mediate induction of the Glut1 promoter during myocardial hypertrophy.