OTA decreases the expressions of the proteasome subunits both at mRNA and protein levels. HK-2 cells were treated with OTA (10 µM) for 1, 3, 6, 12, and 24 h or vehicle (0.1% v/v Et-OH) for 24 h. Changes on the mRNA levels of (a) PSMB5, PSMB6, and PSMB7 forming proteasome β subunit and (b) PSMA5 and PSMA7 forming proteasome α subunit were analyzed with RT-qPCR with the primer sets given in Table S1. mRNA levels were shown relative to β-ACTIN and vehicle (VHC) control (2−ΔΔCt method). For the statistical analysis one-way ANOVA and Bonferroni (as post-hoc) tests were used. (c) HK-2 cells were treated with OTA (10 µM) for 1, 3, 6, 12, and 24 h or vehicle (VHC) (0.1% v/v Et-OH) for 24 h. Changes on the protein levels of the 26S proteasome subunits were detected with Western blot analysis. β subunit of 26S proteasome was analyzed with antibodies specific to PSMB5, PSMB6, and PSMB7 proteins, α subunit was analyzed with PSMA5 and PSMA7 specific antibodies. β-ACTIN antibody was used as loading control. Blots are representative of three independent experiments. The images were obtained from the same or parallel blots of identical samples (ns: Nonsignificant, * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001).