Inhibition of Hypoxia-Inducible Factor-1α (HIF-1α) Protein Synthesis by DNA Damage Inducing Agents

Hypoxia-inducible factor (HIF) is a heterodimeric transcription factor that is composed of a hypoxia-inducible alpha subunit (HIF-1 alpha and HIF-2 alpha) and a constitutively expressed beta subunit (HIF-1 beta). HIF mediates the adaptation of cells and tissues to low oxygen concentrations. It also plays an important role in tumorigenesis and constitutes an important therapeutic target in anti-tumor therapy. We have screened a number of reported HIF inhibitors for their effects on HIF-transcriptional activity and found that the DNA damage inducing agents camptothecin and mitomycin C produced the most robust effects. Camptothecin is a reported inhibitor of HIF-1 alpha translation, while mitomycin C has been reported to induce p53-dependent HIF-1 alpha degradation. In this study we demonstrate that the inhibitory effect of mitomycin C on HIF-1 alpha protein expression is not dependent on p53 and protein degradation, but also involves HIF-1 alpha translational regulation. Initiation of a DNA damage response with the small molecule p53 activator NSC-652287 (RITA) has been reported to inhibit HIF-1 alpha protein synthesis by increasing the phosphorylation of eIF2 alpha. However, we show here that even when eIF2 alpha phosphorylation is prevented, the DNA damage inducing drugs mitomycin C, camptothecin and NSC-652287 still inhibit HIF-1 alpha protein synthesis to the same extent. The inhibitory effects of camptothecin on HIF-1 alpha expression but not that of mitomycin C and NSC-652287 were dependent on cyclin-dependent kinase activity. In conclusion, specific types of DNA damage can bring about selective inhibition of HIF-1 alpha protein synthesis. Further characterization of the involved mechanisms may reveal important novel therapeutic targets.