A Genome-Wide CRISPR/Cas9 Screen Reveals that Riboflavin Regulates Hydrogen Peroxide Entry into HAP1 Cells

Abstract

Extracellular hydrogen peroxide can induce oxidative stress, which can cause cell death if unresolved. However, the cellular mediators of H₂O₂-induced cell death are unknown. We determined that H₂O₂-induced cytotoxicity is an iron-dependent process in HAP1 cells and conducted a CRISPR/Cas9-based survival screen that identified four genes that mediate H₂O₂-induced cell death: POR (encoding cytochrome P450 oxidoreductase), RETSAT (retinol saturase), KEAP1 (Kelch-like ECH-associated protein-1), and SLC52A2 (riboflavin transporter). Among these genes, only POR also mediated methyl viologen dichloride hydrate (paraquat)-induced cell death. Because the identification of SLC52A2 as a mediator of H₂O₂ was both novel and unexpected, we performed additional experiments to characterize the specificity and mechanism of its effect. These experiments showed that paralogs of SLC52A2 with lower riboflavin affinities could not mediate H₂O₂-induced cell death and that riboflavin depletion protected HAP1 cells from H₂O₂ toxicity through a specific process that could not be rescued by other flavin compounds. Interestingly, riboflavin mediated cell death specifically by regulating H₂O₂ entry into HAP1 cells, likely through an aquaporin channel. Our study results reveal the general and specific effectors of iron-dependent H₂O₂-induced cell death and also show for the first time that a vitamin can regulate membrane transport.IMPORTANCE Using a genetic screen, we discovered that riboflavin controls the entry of hydrogen peroxide into a white blood cell line. To our knowledge, this is the first report of a vitamin playing a role in controlling transport of a small molecule across the cell membrane.

Keywords: KEAP1; P450 oxidoreductase; aquaporin; hydrogen peroxide; membrane transport; oxidative stress; retinol saturase; riboflavin; riboflavin transporter.