Inducible expression of hypoxia-inducible factor 1alpha (HIF-1alpha) as a tool for studying HIF-1alpha-dependent gene regulation during normoxia in vitro.

The hypoxia-inducible factor 1alpha (HIF-1alpha), a member of the PAS superfamily, is a global regulator of cellular and systemic O(2) homeostasis as well as embryonic development. As the activity of HIF-1alpha is increased by a lowered oxygen tension in vivo and in vitro, we established a cell line producing high amounts of HIF-1alpha under normoxic conditions. As this overexpression was inducible by doxycycline, we can now provide a system to study HIF-1alpha-dependent gene regulation under normoxic as well as hypoxic conditions. We were able to show that the doxycycline-induced induction of the target gene HIF-1alpha--followed by the message of its target genes erythropoietin and vascular endothelial growth factor--is a dose- and time-dependent process. As the inducible overexpression of HIF-1alpha did not increase the rate of apoptosis, it provides a helpful new tool in drug discovery and tumor research to differentiate between hypoxia-dependent and hypoxia-independent pathways during HIF-1alpha-dependent gene regulation and HIF-1alpha-dependent effects on apoptosis.