title: Antisense transcripts enhanced by camptothecin at divergent CpG-island promoters associated with bursts of topoisomerase I-DNA cleavage complex and R-loop formation.
abstract: DNA Topoisomerase I (Top1) is required to relax DNA supercoils generated by RNA polymerases (RNAPs). Top1 is inhibited with high specificity by camptothecin (CPT), an effective anticancer agent, and by oxidative base damage and ribonucleotides in DNA strands, resulting into Top1-DNA cleavage complexes (Top1ccs). To understand how Top1ccs affect genome stability, we have investigated the global transcriptional response to CPT-induced Top1ccs. Top1ccs trigger an accumulation of antisense RNAPII transcripts specifically at active divergent CpG-island promoters in a replication-independent and Top1-dependent manner. As CPT increases antisense transcript levels in the presence of 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole, a transcription inhibitor, Top1ccs likely impair antisense RNA degradation. Time-course data showed a burst of Top1ccs increased by CPT at promoter sites and along transcribed regions, causing a transient block of RNAPII at the promoter. Moreover, cell immunofluorescence analyses showed that Top1ccs induce a transient increase of R-loops specifically at highly transcribed regions such as nucleoli in a Top1-dependent manner. Thus, a specific and highly dynamic transcriptional response to Top1ccs occurs at divergent active CpG-island promoters, which may include a transient stabilization of R-loops. The results clarify molecular features of a response pathway leading to transcription-dependent genome instability and altered transcription regulation.
authors.affiliation: Department of Pharmacy and Biotechnology, University of Bologna, via Irnerio 48, 40126 Bologna, Italy and CASPUR, via dei Tizii 6, Rome 00185, Italy.
authors.forename: Jessica
authors.initials: J
authors.lastname: Marinello
authors.forename: Giovanni
authors.initials: G
authors.lastname: Chillemi
authors.forename: Susana
authors.initials: S
authors.lastname: Bueno
authors.forename: Stefano G
authors.initials: SG
authors.lastname: Manzo
authors.forename: Giovanni
authors.initials: G
authors.lastname: Capranico
mesh_terms: D002166:Camptothecin / Q000494:pharmacology*; D045744:Cell Line, Tumor; D018899:CpG Islands; D042863:Cyclin-Dependent Kinase 9 / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D053837:DNA Cleavage; D004261:DNA Replication; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D006801:Humans; D011401:Promoter Regions, Genetic; D012319:RNA Polymerase II / Q000378:metabolism; D016372:RNA, Antisense / Q000096:biosynthesis*; D059004:Topoisomerase I Inhibitors / Q000494:pharmacology*
chemical_list: D016372:RNA, Antisense; D059004:Topoisomerase I Inhibitors; D004247:DNA; D042863:Cyclin-Dependent Kinase 9; D012319:RNA Polymerase II; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin