INHIBITION OF N-LINKED GLYCOSYLATION OF P-GLYCOPROTEIN BY TUNICAMYCINRESULTS IN A REDUCED MULTIDRUG-RESISTANCE PHENOTYPE

Characterisation of altered glycosylation of P-glycoprotein (P-gp) fou nd associated with the absence of a multidrug resistance (MDR) phenoty pe in cell lines prompted an investigation to assess the role of post- translational processing in establishing P-gp efflux pump functionalit y. The clone A cell line used in this study displays a strong MDR phen otype mediated by high constitutive levels of expression of P-gp. Incu bation of clone A cells with tunicamycin for different periods resulte d in a time-dependent increase in daunorubicin accumulation, reflectin g a reduction in P-gp function. Parallel experiments conducted with ve rapamil resulted in no loss of P-gp functionality in clone A cells. Re duction in surface-associated P-gp following exposure to tunicamycin w as established by FAGS analysis, Western blot analysis and immunopreci pitation of surface-iodinated P-gp. In addition, immunoprecipitation o f P-gp from P-32-orthophosphate-labelled cells demonstrated reduced ph osphorylation of P-gp associated with tunicamycin exposure. From these studies we conclude that glycosylation of P-gp is required to establi sh the cellular MDR phenotype.