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p38 MAPK α and β isoforms differentially regulate plasma membrane localization of MRP2

Christopher M Schonhoff1, Se Won Park1, Cynthia R L Webster2

  • 1Department of Biomedical Sciences, Cummings School of Veterinary Medicine at Tufts University, North Grafton, Massachusetts; and.

American Journal of Physiology. Gastrointestinal and Liver Physiology
|March 26, 2016
PubMed

Insights

Cyclic AMP (cAMP) and taurolithocholate (TLC) differentially regulate plasma membrane multidrug resistance-associated protein-2 (MRP2) via distinct p38 MAPK isoforms. p38α MAPK increases MRP2 with cAMP, while p38β MAPK decreases MRP2 with TLC.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Hepatocyte Signaling

Background:

  • Hepatocytes utilize cyclic AMP (cAMP) to increase plasma membrane multidrug resistance-associated protein-2 (PM-MRP2) via p38 mitogen-activated protein kinase (MAPK).
  • Paradoxically, taurolithocholate (TLC) activates p38 MAPK but decreases PM-MRP2, suggesting differential regulation by p38 MAPK isoforms (α and β).

Purpose of the Study:

  • To test the hypothesis that p38α MAPK and p38β MAPK mediate increases and decreases in PM-MRP2 by cAMP and TLC, respectively.
  • To elucidate the roles of upstream kinases MKK3 and MKK6 in these signaling pathways.

Main Methods:

  • Studies utilized hepatocytes from wild-type (WT) and MKK3-knockout (MKK3(-/-)) mice.
  • A hepatoma cell line (HuH-NTCP) overexpressing sodium-taurocholate cotransporting polypeptide (NTCP) was used.
  • Western blotting, small interfering RNA (siRNA) knockdown, and analysis of PM-MRP2 levels were performed.

Main Results:

  • cAMP activated MKK3, p38 MAPK, and p38α MAPK, increasing PM-MRP2 in WT hepatocytes, but not in MKK3(-/-) hepatocytes.
  • TLC activated p38 MAPK and decreased PM-MRP2 independently of MKK3, activating MKK6 in MKK3(-/-) hepatocytes.
  • siRNA knockdown of p38β MAPK abrogated TLC-mediated decreases in PM-MRP2, implicating p38β MAPK in TLC's effect.

Conclusions:

  • p38α MAPK facilitates cAMP-induced plasma membrane insertion of MRP2 in hepatocytes.
  • p38β MAPK mediates TLC-induced retrieval of PM-MRP2 from hepatocytes.
  • Differential activation of p38 MAPK isoforms by upstream kinases dictates MRP2 membrane localization.
Keywords:
MKK3 knockout micecAMPp38 MAPK isoformstaurolithocholate

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