Hypoxia Inducible Factor 1 (HIF-1) Activation in U87 Glioma Cells Involves a Decrease in Reactive Oxygen Species Production and Protein Kinase C Activity

摘要

Hypoxia regulates physiological functions including erythropoeisis, ventilatory drive, angiogenesis, vascular tone, and glycolytic function all which are essential for systemic and cellular adaptation to lowered oxygen tension. This is mediated in part through induction of a hypoxia-inducible transcription factor (HIF-1) which is instrumental in the regulation of genes such as vascular endothelial growth factor (VEGF) and erythropoietin (EPO). The purpose of the following work was to identify specific elements of the hypoxic signaling pathways involved in HIF-1 activation in a glial derived cell line (U87 glioma) using gel shift analysis. Since lowering of available oxygen effectively lowers the production of reactive oxygen species (ROS), this shift in ROS production could be the hypoxic signal which mediated HIF-1 induction. Exogenously added H202 prevented HIF-1 activation by hypoxia, and catalase, an enzyme which depletes H202 , was found to activate HIF-1 DNA binding activity under normoxic conditions. Reduction of mitochondrial produced H202 , using thenoyltrifluoroacetone (TTFA), induced HIF-1 DNA binding activity under normoxia. These findings suggest that a decrease in the production of ROS such as H202 during hypoxia may serve as an upstream signal for hypoxic gene expression in gliorna cells.