Mammalian DNA topoisomerase I activity and poisoning by camptothecin are inhibited by simian virus 40 large T antigen.
DNA topoisomerase I (top1) is a ubiquitous enzyme that forms reversible DNA single-strand breaks (cleavage complexes) and plays a role in transcription, DNA replication, and repair. Top1 is the target of camptothecins which selectively trap top1 cleavage complexes and represent a novel class of anticancer drugs active against human solid tumors. The present study demonstrates that recombinant large T antigen (T-Ag), a virus encoded helicase with strong affinity for tumor suppressors and cell cycle- and replication-related proteins, suppresses top1 cleavage complexes and top1 catalytic activity. This top1 suppressive activity is probably not due to T-Ag binding to DNA, as a T-Ag truncation mutant containing only the first 246 amino acids and deficient in DNA binding also inhibited top1, and the inhibition was independent of ATP. T-Ag also antagonized and reversed the trapping of top1 cleavage complexes by camptothecin. These results demonstrate a functional interaction between T-Ag and top1: they also suggest the importance of top1-protein interactions for the regulation of DNA replication and modulation of camptothecin activity.
Pommier
Y
Y
Laboratory of Molecular Pharmacology, National Cancer Institute, Bethesda, Maryland 20892-4255, USA. pommier@nih.gov
Kohlhagen
G
G
Wu
C
C
Simmons
D T
DT
D000952:Antigens, Polyomavirus Transforming / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D002166:Camptothecin / Q000037:antagonists & inhibitors* / Q000633:toxicity*; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics; D004587:Electrophoresis, Agar Gel; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D008969:Molecular Sequence Data; D017384:Sequence Deletion; D013539:Simian virus 40 / Q000235:genetics* / Q000276:immunology; D059004:Topoisomerase I Inhibitors
D000952:Antigens, Polyomavirus Transforming; D004268:DNA-Binding Proteins; D059004:Topoisomerase I Inhibitors; D004264:DNA Topoisomerases, Type I; D004250:DNA Topoisomerases, Type II; D002166:Camptothecin