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Related Experiment Videos

P-glycoprotein-independent decrease in drug accumulation by phorbol ester treatment of tumor cells

P R Wielinga1, M Heijn, H J Broxterman

  • 1University Hospital Vrije Universiteit, Department of Medical Oncology, Amsterdam, The Netherlands.

Biochemical Pharmacology
|November 14, 1997
PubMed
Summary
This summary is machine-generated.

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Phosphorylation of P-glycoprotein (P-gp) by protein kinase C (PKC) did not alter its drug transport activity. However, PKC activation decreased cellular drug accumulation through a P-gp-independent mechanism.

Area of Science:

  • Pharmacology
  • Molecular Biology
  • Cell Biology

Background:

  • P-glycoprotein (P-gp) is a key efflux transporter involved in multidrug resistance (MDR).
  • The phosphorylation state of P-gp can potentially modulate its drug transport activity.
  • Protein kinase C (PKC) and protein phosphatase 1/2A (PP1/PP2A) are implicated in regulating protein function through phosphorylation and dephosphorylation.

Purpose of the Study:

  • To investigate the effect of altered P-gp phosphorylation on its drug transport activity.
  • To determine whether PKC and PP1/PP2A regulate P-gp-mediated drug efflux.

Main Methods:

  • Studied the cellular accumulation of P-gp substrates daunorubicin (DNR), etoposide (VP-16), and calcein acetoxymethyl ester (Cal-AM).
  • Utilized phorbol ester (PMA) to stimulate PKC, staurosporine (ST) as a kinase inhibitor, and okadaic acid (OA) to inhibit PP1/PP2A.

Related Experiment Videos

  • Compared drug accumulation in P-gp-overexpressing MDR cells and wild-type cells.

    • Main Results:

    • PMA-induced P-gp phosphorylation decreased DNR and VP-16 accumulation in both cell types, an effect reversed by ST.
    • PMA did not affect Cal-AM accumulation, but ST increased it in MDR cells.
    • PKC activation or PP1/PP2A inhibition did not alter Cal-AM accumulation, suggesting P-gp transport activity is not regulated by these enzymes.
    • ST directly inhibits P-gp, independent of PKC or PP1/PP2A activity.

    Conclusions:

    • PKC and PP1/PP2A activity do not directly regulate the drug transport function of P-gp.
    • PMA-induced PKC activity leads to decreased cellular drug accumulation via a P-gp-independent pathway.