Differential modulation of P-glycoprotein transport by protein kinase inhibition

• Published in: Biochemistry (Easton) 1993-09, Vol.32 (35), p.9156-9164
• Main Authors: Bates, Susan E, Lee, Jong Seok, Dickstein, Bruce, Spolyar, Mary, Fojo, Antonio T
• Format: Article
• Language: English
• Subjects: Affinity Labels - pharmacology; Alkaloids - pharmacology; ATP Binding Cassette Transporter, Subfamily B, Member 1; 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
• ISSN: 0006-2960; 1520-4995
• 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.