CLONING OF THE TIS GENE SUPPRESSED BY TOPOISOMERASE INHIBITORS

We recently cloned the cDNA TIS (topoisomerase inhibitor-suppressed) i n RVC lymphoma cells exposed to the topoisomerase inhibitors. To eluci date the suppression mechanism of the TIS mRNA by camptothecin, we cha racterized the structures of the TIS gene. The gene spanned about 21 k b including 11 exons and was present as a single copy. The putative tr anscription site was present 192 bp upstream from the ATG codon. The t ypical TATA sequence and CCAAT promoter element were located at positi ons -21 and -81, respectively. The unidirectional deletion analysis of the 5'-flanking region revealed that [-132/+160] is the promoter regi on, which participates in the responsiveness to camptothecin. A Northe rn blot analysis showed that the TIS was expressed in most mouse tissu es; at the highest level in the liver and to less extent in the heart and skeletal muscle. The present study showed that the expression of t he TIS is suppressed at the transcriptional level by camptothecin. Con sidering that topoisomerase I is an essential enzyme in mammalian cell s, the TIS protein may have an important role in camptothecin toxicity . (C) 1998 Elsevier Science B.V. All rights reserved.