Human MDR 1 Protein Overexpression Delays the Apoptotic Cascade in Chinese Hamster Ovary Fibroblasts

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• 作者：Laura J. Robinson ; Wendy K. Roberts ; Tao Tao Ling ; Dudley Lamming ; Stephen S. Sternberg ; and Paul D. Roepe
• 刊名：Biochemistry
• 出版年：1997
• 出版时间：September 16, 1997
• 年：1997
• 卷：36
• 期：37
• 页码：11169 - 11178
• 全文大小：220K
• 年卷期：v.36,no.37(September 16, 1997)
• ISSN：1520-4995

文摘

Several laboratories have reported that overexpression of themultidrug resistance (MDR) proteinis associated with intracellular alkalinization, and severalinvestigators have reported that cells induced toundergo programmed cell death (apoptosis) acidify quite significantly.Because it is difficult to fullyexplain the resistance to apoptosis-inducing chemotherapeutic drugsthat is exhibited by MDR tumorcells solely via altered drug transport alone [Hoffman etal. (1996) J. Gen. Physiol. 108,295-313], wehave investigated whether overexpression of the hu MDR 1 protein altersprogression of the apoptoticcascade. LR73 fibroblasts induced to undergo apoptosis either viatreatment with the chemotherapeuticdrug colchicine or by serum withdrawal exhibit cellular volume changes,intracellular acidification, nuclearcondensation, and chromosomal digestion ("ladder formation"),characteristic of apoptosis, in a temporallywell-defined pattern. However, multidrug resistant LR73/20E orLR73/27 hu MDR 1 transfectants recentlycreated in our laboratory without selection on chemotherapeutic drugare significantly delayed in theonset of apoptosis as defined by the above criteria, regardless ofwhether apoptosis is induced by colchicinetreatment or by serum withdrawal. Thus, the delay cannot simply bedue to the well-known ability ofMDR protein overexpression to lower chemotherapeutic drug accumulationin MDR cells. LR73/27V500"selectants", exhibiting similar levels of MDR proteinoverexpression but higher multidrug resistancedue to selection with the chemotherapeutic drug vincristine, exhibit aslightly longer delay in the progressionof apoptosis. Normal apoptotic cascade kinetics are partiallyrestored by pre-treatment of the MDR cellswith the MDR protein inhibitor verapamil. Untransfected LR73 cellsnot expressing MDR protein butelevated in pH_i via manipulation ofCO₂/HCO₃^- as described [Hoffmanet al. (1996) J. Gen. Physiol.108, 295-313] are inhibited in DNA ladder formation, similar toLR73/hu MDR 1 transfectants. Theseresults uncover an additional mechanism whereby MDR proteinoverexpression may promote the survivalof tumor cells and further support the notion that in some systemsintracellular acidification may be eithercausal or permissive for proper progression of the apoptoticcascade.