Differential modulation of P-glycoprotein transport by protein kinase inhibition

Biochemistry. 1993 Sep 7;32(35):9156-64. doi: 10.1021/bi00086a022.


Previous studies of P-glycoprotein have demonstrated that its function can be modulated by phosphorylation. In the present study, inhibition of protein kinase C with calphostin C or stauroporine or prolonged treatment with the phorbol ester TPA decreased phosphorylation of P-glycoprotein, and impaired transport of vinblastine. Calphostin C also inhibited transport of actinomycin D, vincristine, rhodamine, and azidopine in SW620 Ad300 multidrug-resistant human colon carcinoma cells. Photoaffinity labeling of P-glycoprotein with azidopine was decreased by calphostin C, suggesting that dephosphorylation alters the affinity of P-glycoprotein for its substrates. Impaired transport of rhodamine in normal T lymphocytes treated with staurosporine demonstrates that modulation of P-glycoprotein function is not limited to cells selected for drug resistance in vitro. Transport of P-glycoprotein antagonists in SW620 Ad300 cells was also affected by calphostin C. Cyclosporin A transport decreased, while verapamil transport increased. Cyclosporin A in calphostin C-treated cells resulted in additive P-glycoprotein antagonism, while no additive effect could be demonstrated with verapamil, suggesting that the increase in verapamil transport makes it a poorer P-glycoprotein antagonist. These studies suggest that transport by P-glycoprotein is a dynamic process which can be modulated by phosphorylation, and that antagonists may block P-glycoprotein differently in different phosphorylation states.

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • Affinity Labels / pharmacology
  • Alkaloids / pharmacology
  • Azides / pharmacology
  • Biological Transport / drug effects
  • Carrier Proteins / metabolism*
  • Cyclosporine / pharmacology
  • Dactinomycin / pharmacology
  • Dihydropyridines / pharmacology
  • Drug Resistance / physiology
  • Humans
  • Isoenzymes / metabolism
  • Membrane Glycoproteins / metabolism*
  • Naphthalenes*
  • Polycyclic Compounds / pharmacology
  • Protein Kinase C / antagonists & inhibitors*
  • Rhodamine 123
  • Rhodamines / pharmacology
  • Staurosporine
  • T-Lymphocytes / metabolism
  • Tetradecanoylphorbol Acetate / pharmacology
  • Tumor Cells, Cultured
  • Verapamil / pharmacology
  • Vinblastine / pharmacology
  • Vincristine / pharmacology


  • ATP Binding Cassette Transporter, Subfamily B, Member 1
  • Affinity Labels
  • Alkaloids
  • Azides
  • Carrier Proteins
  • Dihydropyridines
  • Isoenzymes
  • Membrane Glycoproteins
  • Naphthalenes
  • Polycyclic Compounds
  • Rhodamines
  • calphostin complex
  • Dactinomycin
  • Rhodamine 123
  • Vincristine
  • Vinblastine
  • azidopine
  • Cyclosporine
  • Verapamil
  • Protein Kinase C
  • Staurosporine
  • Tetradecanoylphorbol Acetate