Mutational analysis of P-glycoprotein: Suppression of caspase activation in the absence of ATP-dependent drug efflux

K. M. Tainton, M. J. Smyth, J. T. Jackson, J. E. Tanner, L. Cerruti, S. M. Jane, P. K. Darcy, R. W. Johnstone

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P-glycoprotein (P-gp) can induce multidrug resistance (MDR) through the ATP-dependent efflux of chemotherapeutic agents. We have previously shown that P-gp can inhibit nondrug apoptotic stimuli by suppressing the activation of caspases. To determine if this additional activity is functionally linked to ATP hydrolysis, we expressed wild-type and ATPase-mutant P-gp and showed that cells expressing mutant P-gp could not efflux chemotherapeutic drugs but remained relatively resistant to apoptosis. CEM lymphoma cells expressing mutant P-gp treated with vincristine showed a decrease in the fraction of cells with apoptotic morphology, cytochrome c release from the mitochondria and suppression of caspase activation, yet still accumulated in mitosis and showed a loss of clonogenic potential. The loss of clonogenicity in vincristine-treated cells expressing mutant P-gp was associated with accumulation of cells in mitosis and the presence of multinucleated cells consistent with mitotic catastrophe. The antiapoptotic effect of mutant P-gp was not affected by antibodies that inhibit the efflux function of the protein. These data are consistent with a dual activity model for P-gp-induced MDR involving both ATPase-dependent drug efflux and ATPase-independent inhibition of apoptosis. The structure-f unction analyses described herein provide novel insight into the mechanisms of action of P-gp in mediating MDR.

Original languageEnglish
Pages (from-to)1028-1037
Number of pages10
JournalCell Death and Differentiation
Issue number9
Publication statusPublished - 1 Sept 2004
Externally publishedYes


  • Apoptosis
  • Caspace
  • Drug resistance
  • P-glycoprotein

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