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Survival of the Replication Checkpoint Deficient Cells Requires MUS81-RAD52 Function
Journal article   Open access   Peer reviewed

Survival of the Replication Checkpoint Deficient Cells Requires MUS81-RAD52 Function

Ivana Murfuni, Giorgia Basile, Shyamal Subramanyam, Eva Malacaria, Margherita Bignami, Maria Spies, Annapaola Franchitto and Pietro Pichierri
PLoS genetics, Vol.9(10), pp.e1003910-e1003910
10/2013
DOI: 10.1371/journal.pgen.1003910
PMCID: PMC3814295
PMID: 24204313
url
https://doi.org/10.1371/journal.pgen.1003910View
Published (Version of record) Open Access

Abstract

In checkpoint-deficient cells, DNA double-strand breaks (DSBs) are produced during replication by the structure-specific endonuclease MUS81. The mechanism underlying MUS81-dependent cleavage, and the effect on chromosome integrity and viability of checkpoint deficient cells is only partly understood, especially in human cells. Here, we show that MUS81-induced DSBs are specifically triggered by CHK1 inhibition in a manner that is unrelated to the loss of RAD51, and does not involve formation of a RAD51 substrate. Indeed, CHK1 deficiency results in the formation of a RAD52-dependent structure that is cleaved by MUS81. Moreover, in CHK1-deficient cells depletion of RAD52, but not of MUS81, rescues chromosome instability observed after replication fork stalling. However, when RAD52 is down-regulated, recovery from replication stress requires MUS81, and loss of both these proteins results in massive cell death that can be suppressed by RAD51 depletion. Our findings reveal a novel RAD52/MUS81-dependent mechanism that promotes cell viability and genome integrity in checkpoint-deficient cells, and disclose the involvement of MUS81 to multiple processes after replication stress. The replication checkpoint ensures a smooth duplication of the genome. It counteracts the replication stress, which can cause chromosome rearrangements as found in most tumours. Given the importance of dealing with perturbed replication, and since in tumours secondary mutations or epigenetic changes may hamper efficiency of the replication checkpoint, it is crucial to determine the mechanisms responding to replication perturbation upon checkpoint inactivation. Furthermore, it is highly relevant to understand how failure of these mechanisms correlates with chromosomal damage after replication perturbation. Here, we investigated pathways that, in checkpoint-deficient human cells, are involved in the handling of perturbed DNA replication forks, and we uncovered a previously unappreciated function of RAD52 and MUS81 in ensuring viability of cells, but at the expense of genome instability. We also demonstrated that checkpoint deficiency can trigger different mechanisms of recovery from replication arrest depending on the presence of RAD52 or MUS81, resulting in a poor survival and reduced genome instability or increased survival and chromosomal damage. Our work provides new clues about how human cells deal with replication stress, and how genome instability may arise in cancer cells.

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