Decreased topoisomerase II (Topo II) activity results in resistance to antineoplastic agents targeting this enzyme. Dox1V derived from human multiple myeloma RPMI 8226 demonstrated a 4-fold resistance to doxorubicin in the absence of MDR1 overexpression or topo II mutations. Consistent with its drug resistant phenotype, a 2- to 3-fold decrease in topo II expression was identified. To investigate the molecular basis for decreased topo II expression in Dox1V, a semi-quantitative analysis of Topo II activity, protein level and mRNA transcript were performed. The results demonstrated that reduced Topo II activity is due to a decreased mRNA level. Southern blot and sequencing experiments revealed wild-type sequence of the topo II promoter in the drug resistant cells. Transient gene expression assays demonstrated that topo II is transcriptionally down-regulated in Dox1V independent of the promoter sequence of the endogenous alleles. Instead, the activity of a ubiquitous transcription factor CP-1 (NF-Y) interacting with the topo II promoter is decreased. The decrease in CP-1/NF-Y activity in Dox1V is correlated well with the decrease in topo II transcriptional activity, transcript level, Topo II protein and enzyme activity. Therefore, transcriptional down-regulation resulted from a reduced CP-1/NF-Y activity is responsible for decreased topo II expression in Dox1V cells.
|Original language||English (US)|
|Number of pages||8|
|Journal||Biochemical and Biophysical Research Communications|
|State||Published - Aug 18 1997|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology