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Abstract

Oxygen dependent Erythropoietin (EPO) production is regulated by hypoxia inducible factor-1 (HIF-1) which consists of the O2-labile α- and the constitutive β-subunit. In human hepatoma cells (HepG2) HNF-4α enhances hypoxia-induced EPO expression. Herein, we investigated EPO gene regulation in human neuroblastoma (NB) cell lines. Methods: EPO production in SH-SY5Y, Kelly and HepG2 cells was measured by real time PCR and EPO elisa. Intracellular distribution of HIF-1α, HIF-1β and HNF-4α was studied by Western blot and immunohistochemistry. Cells were transiently transfected with HIF-1-driven luciferase and a dominant negative (dn) HNF-4 plasmid. Results: Hypoxia induced EPO gene expression in NB cells was maximal at <0.1% O2. HIF-1α protein accumulated and translocated to the nucleus at an oxygen threshold of 7% O2 in HepG2 cells but at 3% O2 in NB. Differences were also seen in HIF-1α protein degradation upon reoxygenation. Very little HNF-4α was expressed in NB, but did not colocalize with HIF-1α under hypoxic conditions. Transfection with dnHNF-4 did not affect hypoxic induction of EPO in NB cells. Conclusions: HIF-1, but not HNF-4α is involved in EPO gene regulation in human NB cell lines. (This abstract is as it is in the printed issue of the journal).