The Activity of JmjC Histone Lysine Demethylase KDM4A is Highly Sensitive to Oxygen Concentrations

The JmjC histone lysine demethylases (ICDMs) are epigenetic regulators involved in the removal of methyl groups from: post-translationally modified lysyl residues within histone tails, modulating gene transcription. These enzymes require molecular oxygen for catalytic activity and, as 2-oxoglutarate (2OG)-dependent oxygenases, are related to the cellular oxygen sensing HIE hydroxylases PHD2 and FIH. Recent studies have indicated that the activity of some KDMs, including the pseudogene-encoded KDM4E, may be sensitive to changing oxygen concentrations. Here, we report detailed analysis the effect of oxygen availability on the activity of the KDM4 subfamily member KDM4A, importantly demonstrating a high level of O-2 sensitivity both with isolated protein and in cells Kinetic analysis of the recombinant enzyme revealed a high K-M(app)(O-2) of 173 +/- 23 mu M, indicating that the activity of the enzyme able to respond sensitively to a reduction in oxygen concentration. Furthermore, immunofluorescence experiments in U2OS tells conditionally overexpressing KDM4A showed that the cellular activity of KDM4 against its primary, substrate, H3K9me3, displayed 4 graded response to depleting oxygen concentrations in lino with the data obtained using isolated protein. These results suggest that KDM4 possesses the potential to act as an oxygen sensor in the context of chromatin Modifications, with possible implications for epigenetic regulation in hypoxic disease states. Importantly, this correlation between the oxygen sensitivity of the catalytic activity of KDM4A in biochemical and cellular assays demonstrates the utility of biochemical studies in understanding the factors contributing to the diverse biological functions and varied activity of the 2OG oxygenases.