Overexpression of P-glycoprotein in heat- and/or drug-resistant hepatoma variants.
We have earlier isolated a glucocorticoid-resistant, dedifferentiated rat hepatoma variant, the clone 2, which exhibited deficient stress activation of the major stress-inducible heat-shock protein hsp68. Multidrug-resistant variants were isolated from clone 2 cells using increasing concentrations of colchicine. The induction deficiency of hsp68 was maintained in the colchicine-resistant clone 2 cells grown for several months in the presence of 1 microgram/ml colchicine (termed as highly multidrug-resistant variant) indicating that this heat-shock protein is not involved in the multidrug resistance. No alteration of the protein synthesis pattern was observed except the strong increase of the P-glycoprotein, which correlated with high level of corresponding mRNA. Stable heat-resistant variants of clone 2 were also isolated, which showed increased drug resistance to several drugs, i.e. they became moderately multidrug-resistant. This moderate multidrug resistance of the heat-resistant variants was further increased by stepwise selection with colchicine (highly multidrug-resistant heat-resistant variants). The levels of P-glycoprotein mRNA and protein were elevated both in the heat-resistant, non drug selected, moderately drug-resistant and in heat-resistant, colchicine selected, highly drug-resistant variants. Decreased retention of antitumor drugs was observed in all multidrug-resistant variants indicating that P-glycoprotein was functional. Verapamil increased doxorubicin retention and cytotoxicity significantly. Our results showing that severely stressed hepatoma cells overexpressed the multidrug resistance gene(s) raise the possibility that the P-glycoprotein may participate in protection against environmental stress such as heat.
Pirity
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Institute of Genetics, Biological Research Center, Hungarian Academy of Sciences, Szeged, Hungary.
Hevér-Szabó
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Venetianer
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D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D000818:Animals; D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology*; D002999:Clone Cells / Q000187:drug effects / Q000378:metabolism; D003078:Colchicine / Q000378:metabolism / Q000494:pharmacology; D003609:Dactinomycin / Q000378:metabolism / Q000494:pharmacology; D004317:Doxorubicin / Q000378:metabolism / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D018840:HSP70 Heat-Shock Proteins / Q000096:biosynthesis* / Q000235:genetics; D006358:Hot Temperature; D008114:Liver Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D011691:Puromycin / Q000378:metabolism / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D012334:RNA, Neoplasm / Q000096:biosynthesis; D051381:Rats; D012641:Selection, Genetic; D013312:Stress, Physiological / Q000378:metabolism*; D014407:Tumor Cells, Cultured / Q000187:drug effects; D014700:Verapamil / Q000494:pharmacology; D014747:Vinblastine / Q000378:metabolism / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000970:Antineoplastic Agents; D018840:HSP70 Heat-Shock Proteins; C097210:Hspa1a protein, rat; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D003609:Dactinomycin; D011691:Puromycin; D014747:Vinblastine; D004317:Doxorubicin; D014700:Verapamil; D003078:Colchicine