Extended Data Figure 8. Reactive oxygen species production by excess selenium, and implications in SEPHS2 KO toxicity.

(a) Selenoprotein immunoblots of MDAMB231 cells at 24hr recovery after 2 hr sodium selenite treatment or treated with 2-selenocysteine-containing peptide for 24hr. (b) ROS quantification of cells treated with indicated concentrations of sodium selenite or 2xselenocysteine containing peptide, 250 μM TBH, or 500μM H₂O₂ for 45 mins. (c) Viability of U251 cells overexpressing vector or CAT treated with vehicle or H₂O₂ for 48 hr. (d)Viability of U251, and MDAMB231 cells overexpressing blank vector or CAT and subjected to KO with guides against SEPHS2 for 9 days. (e) Immunoblots of CAT and SEPHS2 in U251 and MDAMB231 cells overexpressing blank vector or CAT and subjected to KO with guides against SEPHS2 for 9 days. For b, n=3 independent experiments; error bars are S.D. For c,d n=3 biological replicates; error bars are S.D. For all panels, the measure of center is mean. For all panels, *p<0.05 and **p<0.01 (student’s two-tailed t test).