Induction of glucose transporter 1 expression through hypoxia-inducible factor 1α under hypoxic conditions in trophoblast-derived cells

Glucose transporter 1 (GLUT1) plays an important role in the transport of glucose in the placenta. During early pregnancy, placentation occurs in a relatively hypoxic environment that is essential for appropriate embryonic development, and GLUT1 expression is enhanced in response to oxygen deficiency in the placenta. Hypoxia-inducible factor-1 (HIF-1)alpha is involved in the induction of GLUT1 expression in other cells. The present study was designed to test whether HIF-1alpha is involved in hypoxia-induced activation of GLUT1 expression using trophoblast-derived human BeWo and rat Rcho-1 cells as models. GLUT1 mRNA and protein expression were elevated under 5% O-2 or in the presense of cobalt chloride, which has been shown to mimic hypoxia. Using rat GLUT1 (rGLUT1) promoter-luciferase constructs, we showed that this up-regulation was mediated at the transcriptional level. Deletion mutant analysis of the rGLUT1 promoter indicated that a 184 bp hypoxia-responsive element (HR-E) of the promoter was essential to increase GLUT1 reporter gene expression in response to low-oxygen conditions. BeWo and Rcho-1 cells cultured under 5% O-2 or with CoCl2 showed increased expression of HIF-1alpha protein compared with those cultured under 20% O-2. To test whether this factor is directly involved in hypoxia-induced GLUT1 promoter activation, BeWo and Rcho-1 cells were transiently transfected with an HIF-1alpha expression vector. Exogeneous HIF-1alpha markedly increased the GLUT1 promoter activity from constructs containing the HRE site, while the GLUT1 promoter constructs lacking the HRE site were not activated by exogenous HIF-1alpha. These data demonstrate that GLUT1 is up-regulated under 5% 02 or in the presence of CoCl2 in the placental cell lines through HIF-1alpha interaction with a consensus HRE site of the GLUT1 promoter.