Role of the intracellular localization of HIF-prolyl hydroxylases

Hypoxia-inducible factor-1 (HIF-1) is a major transcription factor regulating the response of tumor cells to hypoxia and is comprised of HIF-1alpha and Arnt (HIF-1beta). In mammalian cells, HIF-1 protein levels are regulated by three HIF-prolyl hydroxylases, termed PHD1, PHD2 and PHD3. To assess whether intracellular localization of PHD1 and PHD2 affects the hypoxic response via HIF-1, we investigated the localization signal of PHDs. PHD1 possessed at least one nuclear localization signal (NLS), and PHD2 contained a region as essential for nuclear export in their N-terminal region. Treatment of cells with leptomycin B revealed that PHD2 was able to shuttle between the cytoplasm and the nucleus. Reporter assay indicated that differences in the intracellular distribution of PHD1 did not influence on HIF-1alpha activity. However, a PHD2 mutant lacking the region for nuclear export exhibited significantly reduced effect to HIF-1alpha activity compared to wild-type PHD2, suggesting that the regulation of the intracellular distribution of PHD2 is an effective pathway for the control of the hypoxic response.