TNFα Induces Multidrug Resistance-Associated Protein 4 Expression through p38-E2F1-Nrf2 Signaling in Obstructive...

Area of Science:

• Hepatology and Molecular Biology
• Biochemistry
• Cellular Signaling

Background:

• Cholestasis is a condition characterized by impaired bile flow.
• Multidrug resistance-associated protein 4 (MRP4) plays a role in bile acid transport and is often dysregulated in liver diseases.
• Understanding the molecular mechanisms behind MRP4 upregulation is crucial for developing targeted therapies.

Purpose of the Study:

• To elucidate the molecular mechanism responsible for the increased expression of multidrug resistance-associated protein 4 (MRP4) during cholestasis.
• To investigate the role of tumor necrosis factor α (TNFα) in regulating MRP4 expression in cholestatic conditions.

Main Methods:

• Quantitative real-time PCR and Western blot analysis of MRP4 in human cholestatic liver samples.
• Electrophoretic mobility shift assay (EMSA) to assess nuclear factor-E2-related factor (Nrf2) binding to the MRP4 promoter in HepG2 cells.
• Dual-luciferase reporter assays to evaluate TNFα's effect on E2F1 promoter activity.
• Establishment of bile duct ligation mouse models and siRNA-mediated knockdown experiments.

Main Results:

• MRP4 mRNA and protein levels were significantly elevated in cholestatic patients.
• TNFα treatment increased MRP4 and Nrf2 expression and enhanced Nrf2 binding to the MRP4 promoter.
• Knockdown of Nrf2 reduced MRP4 mRNA levels, while TNFα treatment activated the p38-E2F1 pathway.
• Inhibition of E2F1 or p38 signaling abrogated TNFα-induced MRP4 and Nrf2 expression in vitro and in vivo.

Conclusions:

• TNFα induces hepatic MRP4 expression in obstructive cholestasis.
• The p38-E2F1-Nrf2 signaling pathway is a key mediator of TNFα-induced MRP4 upregulation.
• This study reveals a novel molecular mechanism contributing to cholestasis pathophysiology.