Treating GBM cells under hypoxia with MG132 (proteasome inhibitor) or IOX2 (PHD2-specific inhibitor), we found that MG132 or IOX2 increased the HIF1α protein level but had no noticeable effect on FIH1 (shown in Supplementary Fig. S3), suggesting that HIF1α was degraded in the PHD2-dependent ubiquitin–proteasome degradation pathway. This evidence concerns the gene EGLN1 and glioblastoma.