FIG 4.

Riboflavin mediates cell death induced by H₂O₂ but not by paraquat. SLC52A1, SLC52A2, and SLC52A3 are all riboflavin transporters, with SLC52A2 having the highest affinity for riboflavin. (A) Knockout SLC52A1, SLC52A2, and SLC52A3 monoclonal cells were grown in complete IMDM, treated with 350 μM H₂O₂, and assessed for cell survival using trypan blue after 3 days of treatment. Error bars represent SEM (n = 6 independent experiments). ***, P < 0.0005 (compared to WT cells). (B) WT HAP1 cells were grown in base DMEMgfp-2 supplemented with riboflavin (+RB) or in base DMEMgfp-2 depleted of riboflavin (−RB) and were treated with 350 μM H₂O₂ (left panel) or 375 μM paraquat (right panel). After 3 days, cell survival was determined using trypan blue. Error bars represent SEM (n = 6 independent experiments). **, P < 0.05 (compared to cells in riboflavin-containing medium [+RB]).