CLK4 and esophageal squamous cell carcinoma: Moreover, WT‐CLK4 but not CLK4‐K189R mutant in ESCC cells inhibited GSH, oxidative PPP flux, NADPH/NADP+ ratio and ribulose‐5‐phosphate (Ru‐5‐P) but enhanced lipid peroxidation (Figure 3F,G).