Chromosomal Integrity after UV Irradiation Requires FANCD2-Mediated Repair of Double Strand Breaks.

María Belén Federico,María Belén Vallerga,Marina Di Giorgio,José Luis Bocco,Vanesa Gottifredi,Gastón Soria,Analía Radl,Natalia Soledad Paviolo,Sue Jinks-Robertson

doi:10.1371/journal.pgen.1005792

Abstract

Fanconi Anemia (FA) is a rare autosomal recessive disorder characterized by hypersensitivity to inter-strand crosslinks (ICLs). FANCD2, a central factor of the FA pathway, is essential for the repair of double strand breaks (DSBs) generated during fork collapse at ICLs. While lesions different from ICLs can also trigger fork collapse, the contribution of FANCD2 to the resolution of replication-coupled DSBs generated independently from ICLs is unknown. Intriguingly, FANCD2 is readily activated after UV irradiation, a DNA-damaging agent that generates predominantly intra-strand crosslinks but not ICLs. Hence, UV irradiation is an ideal tool to explore the contribution of FANCD2 to the DNA damage response triggered by DNA lesions other than ICL repair. Here we show that, in contrast to ICL-causing agents, UV radiation compromises cell survival independently from FANCD2. In agreement, FANCD2 depletion does not increase the amount of DSBs generated during the replication of UV-damaged DNA and is dispensable for UV-induced checkpoint activation. Remarkably however, FANCD2 protects UV-dependent, replication-coupled DSBs from aberrant processing by non-homologous end joining, preventing the accumulation of micronuclei and chromatid aberrations including non-homologous chromatid exchanges. Hence, while dispensable for cell survival, FANCD2 selectively safeguards chromosomal stability after UV-triggered replication stress.

Highlights

Fanconi anemia (FA) is a rare recessive disorder characterized by increased spontaneous rearrangements of chromosomes, tumorigenesis and cell death [1,2]
The Fanconi Anemia protein FANCD2 is central to prevent the aberrant processing of UVtriggered double strand breaks (DSBs) and the generation of micronuclei and chromosome fusions but is dispensable to modulate cell death
We found that the UV irradiation of FANCD2-depleted cells with doses as low as 1.5 J/m2 cause a striking increase of genomic instability markers, such as aberrant chromatid exchanges and micronuclei (MN) formation

Summary

Introduction

Fanconi anemia (FA) is a rare recessive disorder characterized by increased spontaneous rearrangements of chromosomes, tumorigenesis and cell death [1,2]. Initial signs of FA include bone or skeleton defects, renal dysfunction, short stature and very frequently abnormal hyperand hypo-pigmentation of the skin and café_au_lait spots [3]. FA is characterized by bone marrow failure and high risk of developing myeloid leukemias and squamous cell carcinomas [4]. Cells derived from FA patients are strikingly sensitive to DNA interstrand crosslinks (ICLs), i.e. cross-links between two DNA strands. 17 genes with described mutations in patients were defined as components of the FA pathway that are all required for ICL repair [5]

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Discussion

Conclusion