Iron Drives Anabolic Metabolism Through Active Histone Demethylation and mTORC1

All living cells require a minimal iron threshold to sustain anabolic metabolism. However, the mechanisms by which cells sense iron to regulate anabolic processes are unclear. Here, we report a universal eukaryotic pathway for iron sensing in which molecular iron is required to sustain active histone demethylation and maintain the expression of critical components of the pro-anabolic mTORC1 pathway. Specifically, we identify the iron-binding histone-demethylase KDM3B as an intrinsic iron sensor that regulates mTORC1 activity by demethylating H3K9me2 at enhancers of genes encoding high-affinity leucine transporters and RAPTOR. By directly suppressing leucine availability and RAPTOR levels, iron deficiency (ID) supersedes other nutrient inputs into mTORC1. This process occurs in vivo, and is not an indirect effect by canonical iron-utilizing pathways. Elevated expression of KDM3B targets is associated with reduced survival in a subset of human cancers and ID represses mTORC1 in patient-derived tumor cells and sensitizes cancer cells to chemotherapy. These data demonstrate a novel mechanism of eukaryotic iron sensing through dynamic chromatin remodeling and repression of mTORC1 mediated anabolism. Due to ancestral eukaryotes sharing homologues of KDMs and mTORC1 core components, this pathway likely predated the emergence of the other kingdom-specific nutrient sensors for mTORC1 Overall design: 293T cells treated with Vehicle (H2O) or 150uM DFO for 12 hours Grant ID: NRSA 5F30DK109608-02 Name: Jason Solomon Shapiro Grant ID: NRSA T32-DK007169 Name: Jason Solomon Shapiro