Partial inhibition of multidrug resistance by safingol is independent of modulation of P-glycoprotein substrate activities and correlated with inhibition of protein kinase C

C. W. Sachs, Ahmad Safa, S. D. Harrison, R. L. Fine

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92 Citations (Scopus)

Abstract

Safingol is a lysosphingolipid protein kinase C (PKC) inhibitor that competitively interacts at the regulatory phorbol binding domain of PKC. We investigated the effects of safingol on antineoplastic drug sensitivity and PKC activity of MCF-7 tumor cell lines. Safingol treatment of 32P-labeled MCF-7 WT and MCF-7 DOX(R) cells inhibited phosphorylation of the myristoylated alanine-rich protein kinase C substrate in both cell lines, suggesting inhibition of cellular PKC. However, only in MCF-7 DOX(R) cells did safingol treatment increase accumulation of [3H]vinblastine and enhance toxicity of Vinca alkaloids and anthracyclines. Drug accumulation changes in MCF-7 DOX(R) cells treated with safingol were accompanied by inhibition of basal and phorbol 12,13-dibutyrate-stimulated phosphorylation of P- glycoprotein (P-gp). Expression of P-gp and levels of mdr1 message in MCF-7 DOX(R) cells were not altered by safingol treatment alone or in combination with vinblastine. Treatment of MCF-7 DOX(R) cell membranes with safingol did not inhibit [3H]vinblastine binding or [3H]azidopine photoaffinity labeling of P-gp. Furthermore, safingol did not stimulate P-gp ATPase activity in membranes prepared from MCF-7 DOX(R) cells. We conclude that enhanced drug accumulation and sensitivity in MCF-7 DOX(R) cells treated with safingol are correlated with inhibition of PKC rather than competitive interference with P-gp drug binding through direct interaction with P-glycoprotein.

Original languageEnglish (US)
Pages (from-to)26639-26648
Number of pages10
JournalJournal of Biological Chemistry
Volume270
Issue number44
DOIs
StatePublished - 1995
Externally publishedYes

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Multiple Drug Resistance
P-Glycoprotein
Protein Kinase C
Modulation
Substrates
Vinblastine
Phosphorylation
Cells
Pharmaceutical Preparations
Vinca Alkaloids
Phorbol 12,13-Dibutyrate
safingol
Sphingolipids
Protein C Inhibitor
Anthracyclines
MCF-7 Cells
Cell membranes
Protein Kinase Inhibitors
Tumor Cell Line
Alanine

ASJC Scopus subject areas

  • Biochemistry

Cite this

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title = "Partial inhibition of multidrug resistance by safingol is independent of modulation of P-glycoprotein substrate activities and correlated with inhibition of protein kinase C",
abstract = "Safingol is a lysosphingolipid protein kinase C (PKC) inhibitor that competitively interacts at the regulatory phorbol binding domain of PKC. We investigated the effects of safingol on antineoplastic drug sensitivity and PKC activity of MCF-7 tumor cell lines. Safingol treatment of 32P-labeled MCF-7 WT and MCF-7 DOX(R) cells inhibited phosphorylation of the myristoylated alanine-rich protein kinase C substrate in both cell lines, suggesting inhibition of cellular PKC. However, only in MCF-7 DOX(R) cells did safingol treatment increase accumulation of [3H]vinblastine and enhance toxicity of Vinca alkaloids and anthracyclines. Drug accumulation changes in MCF-7 DOX(R) cells treated with safingol were accompanied by inhibition of basal and phorbol 12,13-dibutyrate-stimulated phosphorylation of P- glycoprotein (P-gp). Expression of P-gp and levels of mdr1 message in MCF-7 DOX(R) cells were not altered by safingol treatment alone or in combination with vinblastine. Treatment of MCF-7 DOX(R) cell membranes with safingol did not inhibit [3H]vinblastine binding or [3H]azidopine photoaffinity labeling of P-gp. Furthermore, safingol did not stimulate P-gp ATPase activity in membranes prepared from MCF-7 DOX(R) cells. We conclude that enhanced drug accumulation and sensitivity in MCF-7 DOX(R) cells treated with safingol are correlated with inhibition of PKC rather than competitive interference with P-gp drug binding through direct interaction with P-glycoprotein.",
author = "Sachs, {C. W.} and Ahmad Safa and Harrison, {S. D.} and Fine, {R. L.}",
year = "1995",
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T1 - Partial inhibition of multidrug resistance by safingol is independent of modulation of P-glycoprotein substrate activities and correlated with inhibition of protein kinase C

AU - Sachs, C. W.

AU - Safa, Ahmad

AU - Harrison, S. D.

AU - Fine, R. L.

PY - 1995

Y1 - 1995

N2 - Safingol is a lysosphingolipid protein kinase C (PKC) inhibitor that competitively interacts at the regulatory phorbol binding domain of PKC. We investigated the effects of safingol on antineoplastic drug sensitivity and PKC activity of MCF-7 tumor cell lines. Safingol treatment of 32P-labeled MCF-7 WT and MCF-7 DOX(R) cells inhibited phosphorylation of the myristoylated alanine-rich protein kinase C substrate in both cell lines, suggesting inhibition of cellular PKC. However, only in MCF-7 DOX(R) cells did safingol treatment increase accumulation of [3H]vinblastine and enhance toxicity of Vinca alkaloids and anthracyclines. Drug accumulation changes in MCF-7 DOX(R) cells treated with safingol were accompanied by inhibition of basal and phorbol 12,13-dibutyrate-stimulated phosphorylation of P- glycoprotein (P-gp). Expression of P-gp and levels of mdr1 message in MCF-7 DOX(R) cells were not altered by safingol treatment alone or in combination with vinblastine. Treatment of MCF-7 DOX(R) cell membranes with safingol did not inhibit [3H]vinblastine binding or [3H]azidopine photoaffinity labeling of P-gp. Furthermore, safingol did not stimulate P-gp ATPase activity in membranes prepared from MCF-7 DOX(R) cells. We conclude that enhanced drug accumulation and sensitivity in MCF-7 DOX(R) cells treated with safingol are correlated with inhibition of PKC rather than competitive interference with P-gp drug binding through direct interaction with P-glycoprotein.

AB - Safingol is a lysosphingolipid protein kinase C (PKC) inhibitor that competitively interacts at the regulatory phorbol binding domain of PKC. We investigated the effects of safingol on antineoplastic drug sensitivity and PKC activity of MCF-7 tumor cell lines. Safingol treatment of 32P-labeled MCF-7 WT and MCF-7 DOX(R) cells inhibited phosphorylation of the myristoylated alanine-rich protein kinase C substrate in both cell lines, suggesting inhibition of cellular PKC. However, only in MCF-7 DOX(R) cells did safingol treatment increase accumulation of [3H]vinblastine and enhance toxicity of Vinca alkaloids and anthracyclines. Drug accumulation changes in MCF-7 DOX(R) cells treated with safingol were accompanied by inhibition of basal and phorbol 12,13-dibutyrate-stimulated phosphorylation of P- glycoprotein (P-gp). Expression of P-gp and levels of mdr1 message in MCF-7 DOX(R) cells were not altered by safingol treatment alone or in combination with vinblastine. Treatment of MCF-7 DOX(R) cell membranes with safingol did not inhibit [3H]vinblastine binding or [3H]azidopine photoaffinity labeling of P-gp. Furthermore, safingol did not stimulate P-gp ATPase activity in membranes prepared from MCF-7 DOX(R) cells. We conclude that enhanced drug accumulation and sensitivity in MCF-7 DOX(R) cells treated with safingol are correlated with inhibition of PKC rather than competitive interference with P-gp drug binding through direct interaction with P-glycoprotein.

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