The long-term goal of this project is to understand the fundamental molecular mechanism of tumor cell killing by topoisomerase I (Top I)-directed anticancer drugs. Top I has been firmly established as a highly effective new molecular target for camptothecins (CPTs) (e.g. irinotecan and topotecan). CPTs kill tumor cells by trapping a key covalent Top I-DNA reaction intermediate, the reversible cleavable complex. In addition to CPTs and other Top I-directed drugs, DNA structural modifications (e.g. benzo[a]pyrene-DNA adducts, UV adducts, oxidative modifications and AraC-substituted DNA) have also been shown to cause trapping of Top I cleavable complexes. Despite the importance of Top I cleavable complexes as a new type of cellular lesion , our current understanding of repair/processing of Top I cleavable complexes is still quite limited. Our preliminary studies have identified two novel molecular events downstream of the Top I cleavable complex, ubiquitin/26S proteasome-mediated degradation of Top I (Top I down-regulation) and SUMO-1 (small ubiquitin-related modifier) conjugation to Top I. Our studies have suggested that Top I down-regulation is triggered by arrest of the RNA polymerase elongation complex. In this application, we propose to determine the molecular mechanism through which transcriptional arrest triggers Top I down-regulation and p53-dependent apoptosis. The function of SUMO-1 conjugation to Top I cleavable complexes is still unclear, but has been suggested to modulate the lethal action of Top I cleavable complexes. In view of the potential importance of both of these novel responses in modulating tumor cell killing by Top I-directed anticancer drugs, we plan to elucidate their mechanism and function with the following specific aims: (1) to establish the role of transcription in the processing of CPT-induced Top I cleavable complexes, and (2) to characterize the SUMO-1-Top I conjugation reaction in response to CPT.
Showing the most recent 10 out of 97 publications
