Interleukin-1β and tumor necrosis factor-α stimulate DNA binding of hypoxia-inducible factor-1

The rate of transcription of several genes encoding proteins involved in O₂ and energy homeostasis is controlled by hypoxia-inducible factor-1 (HIF- 1), a heterodimeric DNA binding complex composed of α and β subunits. HIF-1 is considered the primary trans-acting factor for the erythropoietin (EPO) and vascular endothelial growth factor (VEGF) genes. Since EPO gene expression is inhibited by the proinflammatory cytokines interleukin-1β (IL- 1β) and tumor necrosis factor-α (TNF-α), while no such effect has been reported with respect to the VEGF gene, we investigated the effects of IL-1β and TNF-α on the activation of the HIF-1 DNA-binding complex and the amount of HIF-1β protein in human hepatoma cells in culture. Under normoxic conditions, both cytokines caused a moderate activation of HIF-1 DNA binding. In hypoxia, cytokines strongly increased HIF-1 activity compared with the effect of hypoxia alone. Only IL-1β increased HIF-1α protein levels. In transient transfection experiments, HIF-1-driven reporter gene expression was augmented by cytokines only under hypoxic conditions. In contrast to their effect on EPO synthesis, neither IL-1β nor TNF-α decreased VEGF production. The mRNA levels of HIF-1α and VEGF were unaffected. Thus, cytokine-induced inhibition of EPO production is not mediated by impairment of HIF-1 function. We propose that HIF-1 may be involved in modulating gene expression during inflammation.