title: Down-regulation of apoptosis-related bcl-2 but not bcl-xL or bax proteins in multidrug-resistant MCF-7/Adr human breast cancer cells.
abstract: Recent studies have shown that high levels of the apoptosis-related proteins bcl-2 and bcl-xL increase, while over-expression of bcl-xs or bax decreases, resistance to drugs that induce apoptosis in some human cancer cells. In the present report, we investigated whether expression of these apoptosis-related proteins correlates with changes in the degree of resistance to apoptosis induced by doxorubucin, taxol, vincristine and VP-16 and contributes to the development of acquired resistance in multidrug-resistant MCF-7/Adr breast cancer cells. In this study, high levels of bcl-xL and bax proteins are detected in both MCF-7 and MCF-7/Adr cells. In contrast, bcl-2 protein is down-regulated about 10-fold in MCF-7/Adr cells compared with MCF-7 cells. RT-PCR analysis showed that MCF-7/Adr cells express approximately 2-fold less bcl-2 mRNA than MCF-7 cells. Moreover, 4-24 hr cycloheximide treatment of MCF-7 and MCF-7/Adr cells did not affect the expression of bcl-2 protein, indicating that this protein is very stable in both cell lines. Our results suggest that bcl-2 expression is modulated partly by transcriptional, but mainly by post-transcriptional, mechanisms. Despite the down-regulation of bcl-2 in MCF-7/Adr cells and equal levels of bcl-x, and bax proteins in both cell lines, cytoplasmic DNA-histone complexes induced by doxorubucin, taxol, vincristine and VP-16 indicate that MCF-7/Adr cells are highly resistant to apoptosis. Moreover, treatments of MCF-7/Adr cells with P-glycoprotein (P-gp) modulators, cyclosporin A and verapamil increased doxorubicin and vincristine-induced DNA fragmentation about 1.4- and 2.5-fold, indicating that P-gp is involved in the development of resistance to chemotherapy-induced apoptosis in this cell line.
authors.affiliation: Department of Medicine, The University of Chicago, IL 60637, USA.
authors.forename: B
authors.initials: B
authors.lastname: Ogretmen
authors.forename: A R
authors.initials: AR
authors.lastname: Safa
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D001483:Base Sequence; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D016572:Cyclosporine / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D005047:Etoposide / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008969:Molecular Sequence Data; D017239:Paclitaxel / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014700:Verapamil / Q000494:pharmacology; D014750:Vincristine / Q000494:pharmacology; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: D000970:Antineoplastic Agents; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D014750:Vincristine; D005047:Etoposide; D004317:Doxorubicin; D016572:Cyclosporine; D014700:Verapamil; D017239:Paclitaxel