IGF-1 induces hypoxia-inducible factor 1α-mediated GLUT3 expression through PI3K/Akt/mTOR dependent pathways in PC12 cells

Glucose metabolism is essential for most mammalian neurons, and the passage of glucose across cell membranes is mainly facilitated by glucose transporter 3 (GLUT3). In ischemia/reperfusion injured brains, increase of IGF-1 secretion and GLUT3 up-regulation, are regarded as protective processes. Recent works have shown that various growth factors and cytokines including IGF-1 can stimulate HIF-1α expression, thereby triggering transcription of numerous hypoxia-inducible genes by oxygen-independent mechanisms. So, we hypothesized that HIF-1α might play important role in the process of IGF-1 induced GLUT3. Using echinomycin, a HIF-1 inhibitor, and HIF-1α siRNA, we demonstrated IGF-1 induced GLUT3 expression through HIF-1α in neuronal PC12 cells. Moreover, IGF-1 stimulated HIF-1α and GLUT3 protein expression through phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR dependent pathways. Analysis of GLUT3 promoter deletion sequences indicated that a putative hypoxia-response element (HRE) was critical in GLUT3 promoter activity when PC12 cells were treatment with CoCl2 and IGF-1. In conclusion, we showed that the expression of GLUT3 in response to IGF-1 was dependent on PI-3-kinase and mTOR activity, and required the transcription factor HIF-1α.