DIFFERENTIAL EXPRESSION OF DNA TOPOISOMERASE II-ALPHA AND II-BETA GENES BETWEEN SMALL-CELL AND NONSMALL CELL LUNG-CANCER

DNA topoisomerase II (Topo II) inhibitors are widely used in lung canc er chemotherapy, but small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) show different sensitivity to them. In this study, we examined the gene expression levels of both isoforms of Topo II (I I alpha and II beta) in lung cancer specimens to investigate the diffe rential expression between SCLC and NSCLC, The expression levels of th e Topo II alpha and Topo II beta genes were assessed in 80 autopsy sam ples (40 primary tumors and 40 corresponding normal lung tissues) by u sing the reverse transcription polymerase chain reaction. We found tha t the expression levels of the Topo II alpha gene in tumors were signi ficantly higher than those in normal lung tissues, and that those in S CLC were significantly higher than those in NSCLC, There were no signi ficant differences in Topo II beta gene expression between tumors and normal lung tissues and between SCLC and NSCLC, Furthermore, correlati on analysis revealed that Topo II alpha expression was correlated with Topo II beta expression in both tumors and normal lung tissues. These results indicate that a difference exists in the regulation of the To po II gene between lung tumors and normal lung tissues. Our finding of differential expression of Topo II alpha between SCLC and NSCLC also suggests that the Topo II alpha expression level is associated with se nsitivity to Topo II inhibitors.