Fig. 4

Serine starvation inhibits NADPH synthesis and induces DNA oxidative damage. A The NADPH/NADP⁺ ratio in ESCC cells cultured in Com or -Ser medium for 24 h. B The GSH/GSSG ratio in ESCC cells cultured in Com or -Ser medium for 24 and 48 h. C The proline level in KYSE150 cells cultured in Com or -Ser medium for 24 and 48 h was detected by HPLC. D The GSH/GSSG ratio of ESCC cells cultured in Com or -Ser medium with or without 1 mM FA for 24 h. E The mortality of ESCC cells cultured in Com or -Ser medium with or without H₂O₂ for 24 h was detected by using trypan blue staining. F, G The total and mitochondrial ROS levels of ESCC cells cultured in Com or -Ser medium for 48 h were measured by using 2′7'-DCFH-DA (F) and MitoSOX Red (G), respectively. H Representative images of ESCC cells cultured in Com or -Ser medium with the supplementation of 1 mM FA and/or 2 mM H₂O₂ for 24 h. Scale bar represents 200 μm. I The total ROS levels of ESCC cells cultured in Com or -Ser medium with or without 1 mM FA for 24 h. J, K Representative images of immunofluorescence assay of 8-OxoG in ESCC cells cultured in Com or -Ser medium with or without 1 mM FA for 48 h. DAPI was used to stain the nucleus. Scale bar represents 100 μm. Data are presented as mean ± SD. Unpaired two-sided Student’s t test (A, B, C, F and G), and one-way ANOVA with Tukey’s post hoc test (D, E and I). ns: no significance, *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001