DNA topoisomerase IIalpha and -beta expression in human ovarian cancer

Abstract

To study DNA topoisomerase IIalpha (Topo-IIalpha) and -beta expression and regulation in human ovarian cancer, 15 ovarian tumour samples were investigated. To compare different levels of expression, the samples were screened for topo IIalpha and -beta mRNA with Northern blotting and a quantitative reverse transcriptase polymerase chain reaction (RT-PCR) assay for Topo-IIalpha mRNA. Additionally, protein levels were determined with Western blotting and topoisomerase II activity levels with the decatenation assay. The results obtained were compared with each other and with the tumour volume index of the samples. In tumours with a tumour volume index > or = 50%, the mRNA levels (as determined by Northern blotting) and protein levels for each isozyme were in accordance. Additionally, correlations were found between Topo-IIalpha RT-PCR data and Topo-IIalpha Northern blot results, and between Topo-IIalpha RT-PCR data and Topo-IIalpha protein levels. Interestingly, Topo-IIbeta protein levels correlated better with Topo-II activity than Topo-IIalpha protein levels. In eight ovarian cystadenoma samples, no Topo-IIalpha protein could be found. In only three out of eight of these cystadenomas, Topo-IIbeta protein could be detected. These findings suggest that Topo-IIalpha and Topo-IIbeta protein levels are up-regulated in ovarian cancer and may indicate that Topo-IIbeta is an interesting target for chemotherapy in ovarian tumours.