Fig 8. Effects of proteasome inhibitors MG132, epoxomicin and carfilzomib on OATP1B3-mediated transport and total ubiquitin-conjugated proteins in HEK293 stable cell lines.

HEK293-OATP1B3 cells were seeded at a density of 1.2 x 10⁵ cells/well in 24-well plates and cultured to confluence. (A) Model-estimated fold change and associated SE in [³H]CCK-8 accumulation (1 μM, 3 min) in HEK293-OATP1B3 cells pretreated with MG132 (10 μM), epoxomicin (50 nM) and carfilzomib (200 nM) for 2 h vs. vehicle control (CTL) pretreatment. Fold changes and SE were estimated by linear mixed effects models, as described in the “Data Analysis” section (n = 3 in triplicate). To account for multiple comparisons, p-values were adjusted based on the Bonferroni method. * indicates a statistically significant difference (adjusted p<0.05) vs. CTL. (B) Immunoblot of ubiquitin was conducted in whole cell lysates of HEK293-OATP1B3 cells pretreated with MG132 (10 μM), epoxomicin (50 nM) and carfilzomib (200 nM) or vehicle control for two hours. β-actin served as the loading control for the whole cell lysates.