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Pim-1 kinase protects P-glycoprotein from degradation and enables its glycosylation and cell surface expression

Yingqiu Xie1, Mehmet Burcu, Douglas E Linn

  • 1University of Maryland Greenebaum Cancer Center, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.

Molecular Pharmacology
|May 13, 2010
PubMed

Insights

The kinase Pim-1 directly phosphorylates P-glycoprotein (Pgp), promoting its stability and cell surface expression. Inhibiting Pim-1 reduces Pgp levels, sensitizing cancer cells to chemotherapy drugs.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cancer Research

Background:

  • The oncogenic kinase Pim-1 activates the ABCG2 transporter.
  • P-glycoprotein (Pgp; ABCB1), an ABC transporter, has a Pim-1 phosphorylation site, suggesting potential regulation.
  • Pgp undergoes complex processing including glycosylation, translocation, and degradation pathways.

Purpose of the Study:

  • To investigate whether Pim-1 regulates P-glycoprotein (Pgp).
  • To elucidate the mechanism by which Pim-1 might affect Pgp expression and function.
  • To assess the therapeutic potential of targeting Pim-1 in Pgp-overexpressing cells.

Main Methods:

  • GST pull-down and in vitro kinase assays to study Pim-1 and Pgp interaction.
  • Immunoblotting and flow cytometry to assess Pgp expression and stability.
  • Cycloheximide treatment to evaluate Pgp degradation.
  • Use of glycosylation inhibitor 2-deoxy-d-glucose.

Main Results:

  • Pim-1 directly interacts with and phosphorylates Pgp in cells and in vitro.
  • Pim-1 knockdown or inhibition decreased cell surface Pgp levels.
  • Pim-1 inhibition led to increased Pgp degradation via proteolysis and ubiquitination.
  • Pim-1 inhibition reduced Pgp expression in the presence of a glycosylation inhibitor.
  • Pim-1 inhibition sensitized Pgp-overexpressing cells to doxorubicin.

Conclusions:

  • Pim-1 regulates Pgp expression by preventing its degradation and promoting its maturation and cell surface transport.
  • Pim-1 plays a critical role in Pgp-mediated drug efflux.
  • Pim-1 inhibitors represent a potential strategy to overcome drug resistance in cancer therapy.

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