The hypoxia inducible factor 1 (HIF-1) is a central transcription factor involved in the cellular and molecular adaptation to hypoxia and low glucose supply. The level of HIF-1 is to a large degree regulated by the HIF prolyl hydroxylase enzymes (HPHs) belonging to the Fe(II) and 2-oxoglutarate-dependent dioxygenase superfamily. In the present study, we compared competitive and noncompetitive HPH-inhibitor compounds in two different cell types (SH-SY5Y and PC12). Although the competitive HPH-inhibitor compounds were found to be pharmacologically more potent than the non-competitive compounds at inhibiting HPH2 and HPH1, this was not translated into the cellular effects of the compounds, where the non-competitive inhibitors were actually more potent than the competitive in stabilizing and translocatingHIF1αto the nucleus (quantified with Cellomics ArrayScan technology). This could be explained by the high cellular concentrations of the cofactor 2-oxoglutarate (2-OG) as the competitive inhibitors act by binding to the 2-OG site of the HPH enzymes. Both competitive and non-competitive HPH inhibitors protected the cells against 6-OHDA induced oxidative stress. In addition, the protective effect of a specific HPH inhibitor was partially preserved when the cells were serum starved and exposed to 2-deoxyglucose, an inhibitor of glycolysis, indicating that other processes than restoring energy supply could be important for the HIF-mediated cytoprotection. 1. Introduction HIF-1 belongs to the family of hypoxia-inducible transcription factors (HIFs) involved in the regulation of cellular and molecular adaptation to hypoxia [1]. The three isoforms (HIF-1, HIF-2, and HIF-3) are all heterodimers consisting of a constitutively expressed, stable -subunit and an inducible -subunit. The cellular level of the -subunit is regulated at the protein level where high cellular oxygen concentration results in hydroxylation and subsequent proteasomal degradation, whereas low cellular oxygen concentration results in repression of this degradation [2]. When the -subunit is not degraded, it interacts with the -subunit, and the whole complex is translocated to the nucleus and acts as a transcription factor. The hydroxylation and thereby stabilization of the HIF- subunit are regulated by the HIF prolyl and asparagine hydroxylase enzymes, of which the prolyl hydroxylases, HPHs, are the focus of this work. The activity of the HPHs is, in addition to oxygen, dependent on iron and 2-oxoglutarate. The activity of the HPHs can thus be inhibited with small molecules either indirectly
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