MOLECULAR-CLONING OF THE GENES SUPPRESSED IN RVC LYMPHOMA-CELLS BY TOPOISOMERASE INHIBITORS

Etoposide is a topoisomerase II inhibitor that induces DNA cleavable c omplex and has been used as an antitumor drug. We isolated two genes t hat were transcriptionally suppressed at an early stage of incubation in etoposide-treated RVC lymphoma cells, using modified PCR-based subt ractive hybridization. Sequencing revealed that one of these genes, wh ich was approximately 1.7 kb and which encoded a protein of 320 amino acids, was identical to hnRNP A1. The other was a novel gene of about 2.2 kb encoding a protein of 469 amino acids. These genes were also do wn-regulated in the cells incubated with camptothecin, a topoisomerase I inhibitor that induces DNA single strand breaks, but not in those e xposed to ICRF-154, a topoisomerase Il inhibitor that does not induce DNA cleavable complex formation. These results suggest that the early down-regulation of these genes contributes to the cytotoxicity of the topoisomerase inhibitors that induce DNA cleavage. (C) 1996 Academic P ress, Inc.