Oxidative stress promotes post-translational down-regulation of MRP2 in Caco-2 cells: Involvement of proteasomal degradation and toxicological implications

The intestinal tract is highly susceptible to oxidative stress (OS), which impairs gut barrier function. Multidrug Resistance-Associated Protein 2 (MRP2) is a key efflux pump in the intestinal transcellular barrier, regulating toxicant and drug disposition. We here evaluated the effects of OS on MRP2 in Caco-2 cells treated with tert-butyl hydroperoxide (TBH). After 24 h, TBH 250 μM increased ROS production and lipid peroxidation while decreasing GSH content and SOD activity, confirming OS induction. Under these conditions, total MRP2 protein levels decreased, while P-gp levels remained unchanged. Correspondingly, MRP2 efflux activity decreased, impairing barrier function against ochratoxin A (OTA), a substrate of MRP2, and exacerbating OTA toxicity. Localization analysis revealed reduced apical MRP2 signal in TBH 250 group, with unchanged mRNA levels, indicating post-transcriptional regulation. Mechanistically, TBH induced rapid MRP2 internalization (30 min), mediated by cPKC and clathrin, without microtubule involvement, followed by proteasomal degradation at 24 h. Both processes were dependent on GSH depletion, as treatment with N-Acetyl-l-Cysteine (NAC) restored GSH levels, MRP2 localization, and activity. We provide here the first evidence that human intestinal MRP2 is post-translationally downregulated under specific OS conditions, highlighting its potential role in exacerbating xenobiotic absorption and toxicity in OS-related human diseases.