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Ubiquitinated Fancd2 recruits Fan1 to stalled replication forks to prevent genome instability

Science  19 Feb 2016:
Vol. 351, Issue 6275, pp. 846-849
DOI: 10.1126/science.aad5634

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A key player in cancer prevention

Obstacles that block DNA replication can lead to chromosomal abnormalities and ultimately cancer. Fanconi anemia, for example, is caused by defects in the repair of DNA interstrand cross-links. The Fan1 nuclease was originally identified as a protein essential for this cross-link repair. Lachaud et al. now show that it does much more. It is recruited to stalled replication forks by ubiquitinated Fancd2 enabling the processing of these structures, thereby preventing chromosomal abnormalities and acting more broadly in cancer prevention.

Science, this issue p. 846

Abstract

Mono-ubiquitination of Fancd2 is essential for repairing DNA interstrand cross-links (ICLs), but the underlying mechanisms are unclear. The Fan1 nuclease, also required for ICL repair, is recruited to ICLs by ubiquitinated (Ub) Fancd2. This could in principle explain how Ub-Fancd2 promotes ICL repair, but we show that recruitment of Fan1 by Ub-Fancd2 is dispensable for ICL repair. Instead, Fan1 recruitment—and activity—restrains DNA replication fork progression and prevents chromosome abnormalities from occurring when DNA replication forks stall, even in the absence of ICLs. Accordingly, Fan1 nuclease-defective knockin mice are cancer-prone. Moreover, we show that a Fan1 variant in high-risk pancreatic cancers abolishes recruitment by Ub-Fancd2 and causes genetic instability without affecting ICL repair. Therefore, Fan1 recruitment enables processing of stalled forks that is essential for genome stability and health.

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