Activation of Hif1[alpha] by the Prolylhydroxylase Inhibitor Dimethyoxalyglycine Decreases Radiosensitivity

Hypoxia inducible factor 1[alpha] (Hif1[alpha]) is a stress responsive transcription factor, which regulates the expression of genes required for adaption to hypoxia. Hif1[alpha] is normally hydroxylated by an oxygen-dependent prolylhydroxylase, leading to degradation and clearance of Hif1[alpha] from the cell. Under hypoxic conditions, the activity of the prolylhydroxylase is reduced and Hif1[alpha] accumulates. Hif1[alpha] is also constitutively expressed in tumor cells, where it is associated with resistance to ionizing radiation. Activation of the Hif1[alpha] transcriptional regulatory pathway may therefore function to protect normal cells from DNA damage caused by ionizing radiation. Here, we utilized the prolylhydroxylase inhibitor dimethyloxalylglycine (DMOG) to elevate Hif1[alpha] levels in mouse embryonic fibroblasts (MEFs) to determine if DMOG could function as a radioprotector. The results demonstrate that DMOG increased Hif1[alpha] protein levels and decreased the sensitivity of MEFs to ionizing radiation. Further, the ability of DMOG to function as a radioprotector required Hif1[alpha], indicating a key role for Hif1[alpha]'s transcriptional activity. DMOG also induced the Hif1[alpha] -dependent accumulation of several DNA damage response proteins, including CHD4 and MTA3 (sub-units of the NuRD deacetylase complex) and the Suv39h1 histone H3 methyltransferase. Depletion of Suv39h1, but not CHD4 or MTA3, reduced the ability of DMOG to protect cells from radiation damage, implicating increased histone H3 methylation in the radioprotection of cells. Finally, treatment of mice with DMOG prior to total body irradiation resulted in significant radioprotection of the mice, demonstrating the utility of DMOG and related prolylhydroxylase inhibitors to protect whole organisms from ionizing radiation. Activation of Hif1[alpha] through prolylhydroxylase inhibition therefore identifies a new pathway for the development of novel radiation protectors.