Chromatin determinants impart camptothecin sensitivity

Puddu F. et al. (2017)  EMBO Rep. pii: e201643560. doi: 10.15252/ embr.201643560. [Epub ahead of print]

Synopsis from the paper

Camptothecin traps topoisomerase on DNA, which generates DNA damage and topological chromosomal stress in S phase. Synthetic viability screening reveals that Sir2 deacetylase activity drives topology‐mediated camptothecin sensitivity in yeast and human cells.

• Genetic suppressor screening and whole‐genome sequencing provide a rapid and effective approach to identify drug resistance mechanisms.
• Loss of chromatin factors Sir1, Sir2, Sir3 or Sir4 rescues camptothecin hypersensitivity of yeast tof1∆ cells and reduces camptothecin toxicity in wild‐type cells.
• Sirtinol‐mediated Sir2 inhibition suppresses camptothecin toxicity in cultured human epithelial cells.

Abstract from the paper

Camptothecin‐induced locking of topoisomerase 1 on DNA generates a physical barrier to replication fork progression and creates topological stress. By allowing replisome rotation, absence of the Tof1/Csm3 complex promotes the conversion of impending topological stress to DNA catenation and causes camptothecin hypersensitivity. Through synthetic viability screening, we discovered that histone H4 K16 deacetylation drives the sensitivity of yeast cells to camptothecin and that inactivation of this pathway by mutating H4 K16 or the genes SIR1‐4 suppresses much of the hypersensitivity of tof1∆ strains towards this agent. We show that disruption of rDNA or telomeric silencing does not mediate camptothecin resistance but that disruption of Sir1‐dependent chromatin domains is sufficient to suppress camptothecin sensitivity in wild‐type and tof1∆ cells. We suggest that topoisomerase 1 inhibition in proximity of these domains causes topological stress that leads to DNA hypercatenation, especially in the absence of the Tof1/Csm3 complex. Finally, we provide evidence of the evolutionarily conservation of this mechanism.

Synopsis, Abstract and Figure extract reproduced under the CC BY 4.0 license. 

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