DNA topoisomerases cause single (type-1) or double (type-2) strand DNA breaks, leading to DNA relaxation. They control DNA replication, transcription, recombination and chromatin remodeling. TOP1 (DNA topoisomerase 1) binding to the promoter areas induces nucleosome disassembly, histone acetylation and gene expression. Camptothecin is a non-competitive TOP1 inhibitor. TOP1 also controls alternative splicing through phosphorylation of serine/arginine-rich proteins. It is up-regulated in non-small cell lung cancer (NSCLC).
