Fig. 4.

ATRA has little effect on Nrf2 expression in LLC-PK₁ cells. A: LLC-PK₁ cells were exposed to ATRA (25 μM) for a maximum of 24 h. B: LLC-PK₁ cells were pretreated with ATRA (25 μM, 24 h) and then treated with PAP (150 μM, 1 h). Sulforaphane (5 μM, 4 h) and MG132 (10 μM, 4 h) were used as positive controls. GAPDH was used as a loading control. LLC-PK₁ cells were pretreated with ATRA, sulforaphane (C), or MG132 (D), or a combination of ATRA and sulforaphane or MG132 for 24 h. ATRA (25 μM), sulforaphane (SF; 5 μM, 4 h), and MG132 (0.5 μM, 24 h). Cell viability was determined by the neutral red assay. Black bars: cells treated without PAP; open bars: cells treated with PAP. Statistical significance was determined from comparisons to vehicle-treated cells for Nrf2 induction and from cells treated with PAP alone for the cytoprotection experiments (*P < 0.05; **P < 0.01; ***P < 0.001; n ≥ 3).