EXPRESSION OF TOPOISOMERASE-II-ALPHA AND TOPOISOMERASE-II-BETA IN AN ADENOCARCINOMA CELL-LINE CARRYING AMPLIFIED TOPOISOMERASE-II-ALPHA ANDRETINOIC ACID RECEPTOR-ALPHA GENES

Human topoisomerase II enzymes are targets for a number of widely used anticancer agents. We have analysed a lung adenocarcinoma cell line C ALU3, which has co-amplified topoisomerase IIalpha and ERBB2 sequences , for the structure of the amplicon and for expression of both topoiso merase IIalpha and beta. The region of chromosome 17q amplified in CAL U3 also includes the retinoic acid receptor alpha locus and is therefo re similar to the amplicon observed in breast cancers carrying amplifi ed topoisomerase IIalpha and retinoic acid receptor sequences. The use of fluorescence in situ hybridisation localises the amplified topoiso merase IIalpha sequences to a cluster on one chromosome with single co pies localised to others. CALU3 expresses high levels of topoisomerase IIalpha as determined by Western blot, immunofluorescence and enzyme activity. The enzyme activity extracted from CALU3 is sensitive to inh ibition by the topoisomerase II poison etoposide. Topoisomerase IIbeta expression was observed in three lung cancer cell lines including CAL U3 and was confined to the nucleoli. Thus, the CALU3 cell line is an i deal model to study the amplification and expression of topoisomerase IIalpha in adenocarcinomas.