Metabolic-scale gene activation screens identify SLCO2B1 as a heme transporter that enhances cellular iron availability

Iron is the most abundant transition metal essential for numerous cellular processes. Although most mammalian cells acquire iron through transferrin receptors, molecular players of iron utilization under iron restriction are incompletely understood. To address this, we performed metabolism-focused CRISPRa gain-of-function screens, which revealed metabolic limitations under stress conditions. Iron restriction screens identified not only expected members of iron utilization pathways but also SLCO2B1, a poorly characterized membrane carrier. SLCO2B1 expression is sufficient to increase intracellular iron, bypass the essentiality of the transferrin receptor, and enable proliferation under iron restriction. Mechanistically, SLCO2B1 mediates heme analog import in cellular assays. Heme uptake by SLCO2B1 provides sufficient iron for proliferation through heme oxygenases. Notably, SLCO2B1 is predominantly expressed in microglia in the brain, and primary Slco2b1−/− mouse microglia exhibit strong defects in heme analog import. Altogether, our work identifies SLCO2B1 as a microglia-enriched plasma membrane heme importer and provides a genetic platform to identify metabolic limitations under stress conditions. [Display omitted] •CRISPRa screens identify metabolic limitations for growth under stress conditions•Expression of SLCO2B1 confers resistance to iron limitation•SLCO2B1-mediated heme uptake increases iron availability via heme oxygenase•SLCO2B1 is required for heme analog import in primary microglia Unlu et al. perform metabolic-scale CRISPRa screens to reveal metabolic limitations under stress conditions. Focusing on iron restriction, they identify SLCO2B1 as a plasma membrane heme carrier that increases cellular iron availability independently of TFRC. SLCO2B1 is enriched in microglia in the brain and required for heme analog import.