title: Differences between drug-sensitive and -resistant human leukemic CEM cells in c-jun expression, AP-1 DNA-binding activity, and formation of Jun/Fos family dimers, and their association with internucleosomal DNA ladders after treatment with VM-26.
abstract: Although the DNA topoisomerases are critical intracellular targets of a number of clinically important anticancer drugs, the mechanism(s) by which inhibition of these enzymes causes cell death are poorly understood. We found that treatment of human leukemic lymphoblasts (CCRF-CEM) with teniposide (VM-26), under conditions that stabilize DNA-topoisomerase II complexes, caused the formation of internucleosomal DNA ladders. However, it appeared unlikely that the VM-26-stabilized DNA-topoisomerase II-cleavable complexes directly produce these internucleosomal DNA ladders, since similar nucleosomal DNA ladders were observed following either continuous or a short (1 h) exposure of cells to VM-26. Under continuous exposure to VM-26, the internucleosomal DNA ladders were associated with the transient induction of c-jun mRNA in a dose-dependent fashion, reaching maximum expression at 6 h after treatment with VM-26 and being down-regulated to basal levels by 12 h. The induction of c-jun mRNA by VM-26 apparently preceded DNA ladder formation. However, in CEM sublines selected for resistance to VM-26 (CEM/VM-1 and CEM/VM-1-5; approximately 50- and 140-fold resistant, respectively) and which display the phenotype of multidrug resistance associated with altered DNA topoisomerase II (at-MDR), we found that the induction of c-jun mRNA by VM-26 and subsequent DNA ladder formation were progressively attenuated in proportion to the resistance of the cells, apparently due in part to decreased stabilization of DNA-topoisomerase II-cleavable complexes. Further, the attenuated induction of c-jun in the at-MDR cells was found to be associated with a decreased rate of c-jun transcription and an increase in the instability of its mRNA following VM-26 treatment. The attenuation of c-jun mRNA induction was also reflected in decreased production of c-Jun protein in the at-MDR cells. Of interest was the fact that no significant induction of c-fos mRNA by VM-26 was observed in either CEM or at-MDR cells. Furthermore, the induction of c-jun was related to the activation of AP-1 DNA-binding activity in a time- and dose-dependent manner in CEM cells, whereas the activation of AP-1 binding was attenuated in at-MDR cells in proportion to their resistance to VM-26. Using Jun and Fos family member antibody inhibition experiments in gel-mobility shift assays, we found that AP-1-binding activity appeared to be preferentially mediated by c-Jun/Fra-1 heterodimers in both CEM and at-MDR cells.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Department of Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38101.
authors.forename: R
authors.initials: R
authors.lastname: Kim
authors.forename: W T
authors.initials: WT
authors.lastname: Beck
mesh_terms: D001483:Base Sequence; D004250:DNA Topoisomerases, Type II / Q000187:drug effects / Q000378:metabolism*; D004273:DNA, Neoplasm / Q000187:drug effects* / Q000378:metabolism; D003609:Dactinomycin / Q000494:pharmacology; D004351:Drug Resistance / Q000235:genetics; D016758:Genes, jun / Q000187:drug effects*; D006801:Humans; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D013713:Teniposide / Q000494:pharmacology*; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: D004273:DNA, Neoplasm; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D003609:Dactinomycin; D013713:Teniposide; D004250:DNA Topoisomerases, Type II