FIGURE 6.

Fumarate and succinate regulate HIF target gene expression via TETs. FH and SDH mutations with impaired enzyme activity are found in various cancers, where they cause the accumulation of fumarate or succinate, respectively. Fumarate inhibits the TETs and HIF-P4Hs, leading to a reduction in global 5-hmC levels and HIF-1α/HIF-2α stabilization, respectively. Expression of the glycolysis-associated HIF1 target genes PGK1, HK2, and ENO1 was reduced in cells treated with fumarate, suggesting that the TETs and 5-hmC have a crucial role in the regulation of these genes. The expression of VEGFA and BNIP3 mRNAs was nevertheless, increased in cells treated with fumarate, suggesting that these genes are more driven by HIF-1α/HIF-2α stabilization than by the reduction in 5-hmC levels. *, cells treated with succinate showed reductions in VEGFA, PGK1, and HK2 mRNA expression, suggesting that the TETs and 5-hmC can regulate their expression when HIF-1α is not stabilized. HIF target genes are thus regulated in a multilayered manner in which 5-hmC acts as an additional layer of regulation. Not all HIF target genes are regulated equally by 5-hmC, suggesting that there could be promoter-specific gains and reductions in 5-hmC via TETs.