Hypoxia-inducible factor (HIF) is a transcriptional complex that plays a central role in the regulation of gene expression by oxygen. In oxygenated and iron replete cells, HIF-α subunits are rapidly destroyed by a mechanism that involves ubiquitylation by the von Hippel–Lindau tumor suppressor (pVHL) E3 ligase complex. This process is suppressed by hypoxia and iron chelation, allowing transcriptional activation. Here we show that the interaction between human pVHL and a specific domain of the HIF-1α subunit is regulated through hydroxylation of a proline residue (HIF-1α P564) by an enzyme we have termed HIF-α prolyl-hydroxylase (HIF-PH). An absolute requirement for dioxygen as a cosubstrate and iron as cofactor suggests that HIF-PH functions directly as a cellular oxygen sensor.

Variants in theFTO(fat mass and obesity associated) gene are associated with increased body mass index in humans. Here, we show by bioinformatics analysis that FTO shares sequence motifs with Fe(II)- and 2-oxoglutarate–dependent oxygenases. We find that recombinant murine Fto catalyzes the Fe(II)- and 2OG-dependent demethylation of 3-methylthymine in single-stranded DNA, with concomitant production of succinate, formaldehyde, and carbon dioxide. Consistent with a potential role in nucleic acid demethylation, Fto localizes to the nucleus in transfected cells. Studies of wild-type mice indicate thatFtomessenger RNA (mRNA) is most abundant in the brain, particularly in hypothalamic nuclei governing energy balance, and thatFtomRNA levels in the arcuate nucleus are regulated by feeding and fasting. Studies can now be directed toward determining the physiologically relevant FTO substrate and how nucleic acid methylation status is linked to increased fat mass.

Mutations in isocitrate dehydrogenases (IDHs) have a gain‐of‐function effect leading to R (−)‐2‐hydroxyglutarate ( R‐ 2HG) accumulation. By using biochemical, structural and cellular assays, we show that either or both R ‐ and S ‐2HG inhibit 2‐oxoglutarate (2OG)‐dependent oxygenases with varying potencies. Half‐maximal inhibitory concentration (IC50) values for the R ‐form of 2HG varied from approximately 25 μM for the histone N ε‐lysine demethylase JMJD2A to more than 5 mM for the hypoxia‐inducible factor (HIF) prolyl hydroxylase. The results indicate that candidate oncogenic pathways in IDH‐associated malignancy should include those that are regulated by other 2OG oxygenases than HIF hydroxylases, in particular those involving the regulation of histone methylation.