Camptothecin resistance is determined by the regulation of topoisomerase I degradation mediated by ubiquitin proteasome pathway.

Proteasomal degradation of topoisomerase I (topoI) is one of the most remarkable cellular phenomena observed in response to camptothecin (CPT). Importantly, the rate of topoI degradation is linked to CPT resistance. Formation of the topoI-DNA-CPT cleavable complex inhibits DNA re-ligation resulting in DNA-double strand break (DSB). The degradation of topoI marks the first step in the ubiquitin proteasome pathway (UPP) dependent DNA damage response (DDR). Here, we show that the Ku70/Ku80 heterodimer binds with topoI, and that the DNA-dependent protein kinase (DNA-PKcs) phosphorylates topoI on serine 10 (topoI-pS10), which is subsequently ubiquitinated by BRCA1. A higher basal level of topoI-pS10 ensures rapid topoI degradation leading to CPT resistance. Importantly, PTEN regulates DNA-PKcs kinase activity in this pathway and PTEN deletion ensures DNA-PKcs dependent higher topoI-pS10, rapid topoI degradation and CPT resistance.

Citation

Koji Ando, Ankur K Shah, Vibhu Sachdev, Benjamin P Kleinstiver, Julian Taylor-Parker, Moira M Welch, Yiheng Hu, Ravi Salgia, Forest M White, Jeffrey D Parvin, Al Ozonoff, Lucia E Rameh, J Keith Joung, Ajit K Bharti. Camptothecin resistance is determined by the regulation of topoisomerase I degradation mediated by ubiquitin proteasome pathway. Oncotarget. 2017 Jul 04;8(27):43733-43751

PMID: 28415827

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