Lopez-Contreras group maps the protein landscape of CFSs and identifies ATRX as a crucial new player in CFS stability

In a new study, the Lopez-Contreras group harness the sensitivity of mass spectrometry (MS) in combination with the power classical biochemical approaches to map the proteins that bind challenged Common Fragile Sites (CFSs). In this collaborative effort with Jesper V. Olsen from the NNF Center for Protein Research, and the Liu group from the CCS, they revealed a new role for the tumor suppressor gene ATRX in maintaining genomic stability at a subset of CFSs.

CFSs are conserved genomic regions prone to break under conditions of replication stress (RS) and are hotspots of chromosomal alterations in cancer. In this article, published at Nucleic Acid Research, the authors optimized a quantitative MS-based approach to evaluate changes in the abundance of protein at CFSs in conditions that provoke these to break. By performing chromatin immunoprecipitation of FANCD2 in G2/M synchronized cells, the authors acquired the proteome of these genomic regions, successfully identifying proteins with previously known functions in their maintenance. Furthermore, a data set of proteins with unknown functions in CFS stability, remain to be explored, rendering the data a valuable resource to investigate CFS regulation.

Among the novel proteins found at CFSs, the authors identified the tumor suppressor ATRX and characterized its implication in regulating CFS stability. Loss of ATRX is the underlying cause of a rare neurodevelopmental syndrome (alpha thalassemia mental retardation X-linked) and previous studies showed that ATRX is important for telomere maintenance and DNA-RNA hybrid resolution. Here, Pladevall-Morera et al. showed that ATRX is recruited to a subset of CFSs, particularly under conditions of RS. Furthermore, loss of ATRX resulted in hallmarks of CFS instability, such as increased chromosome fragility, micronuclei and 53BP1 nuclear bodies in G1 cells. The authors showed that this novel function of ATRX requires its known interactor DAXX, in a mechanism that is downstream of FANCD2. Further investigations will be required to understand the relevance of CFS instability in tumors harboring ATRX mutations.