Spontaneous overexpression of the long form of the Bcl-X protein in a highly resistant P388 leukaemia.
A novel resistant variant of murine P388 leukaemia, P388/SPR, was identified by de novo resistance to doxorubicin (DOX) in vivo. This mutant displayed a similar level of cross-resistance to etoposide (VP-16) and other topoisomerase II (topo II) inhibitors. Further analysis of the phenotype revealed a broad cross-resistance to vinca alkaloids, alkylating agents, antimetabolites, aphidicolin and UV light. Low-level expression of mdr1 and P-glycoprotein (P-gp), as well as a modest impairment of cellular drug accumulation and partial reversion of resistance to DOX and VP-16 by cyclosporine, confirmed a moderate role of P-gp in conferring drug resistance in P388/SPR cells. Consistent changes in neither topo II expression or activity nor glutathione metabolism could be detected. Induction of apoptosis was significantly reduced in P388/SPR cells, as indicated by minimal DNA fragmentation. Analysis of oncogenes regulating apoptotic cell death revealed a marked decrease of bcl-2 in combination with a moderate reduction of bax protein, but a striking overexpression of the long form of the bcl-X protein. Transfection of human bcl-X-L into P388 cells conferred drug resistance similar to that of P388/SPR cells. The data suggest that overexpression of bcl-X-L results in an unusual phenotype with broad cross-resistance to non-MDR-related cytotoxins in vitro, and provide an interesting example of spontaneous overexpression of another member of the bcl-2 gene family in cancer.
Kühl
J S
JS
Department of Medicine, Stanford University School of Medicine, CA 94305-5306, USA.
Krajewski
S
S
Durán
G E
GE
Reed
J C
JC
Sikic
B I
BI
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D017398:Alternative Splicing; D000818:Animals; D017209:Apoptosis; D053938:DNA Fragmentation; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D018432:Drug Resistance, Multiple; D015972:Gene Expression Regulation, Neoplastic; D019450:Genes, MDR; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D007941:Leukemia P388 / Q000188:drug therapy / Q000235:genetics / Q000473:pathology*; D051379:Mice; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger / Q000235:genetics; D014162:Transfection; D051020:bcl-X Protein
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; C494812:Bcl2l1 protein, mouse; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051020:bcl-X Protein; D005982:Glutathione Transferase; D004250:DNA Topoisomerases, Type II; D005978:Glutathione