Exo1 plays a major role in DNA end resection in humans and influences double-strand break repair and damage signaling decisions.
The resection of DNA double-strand breaks (DSBs) to generate ssDNA tails is a pivotal event in the cellular response to these breaks. In the two-step model of resection, primarily elucidated in yeast, initial resection by Mre11-CtIP is followed by extensive resection by two distinct pathways involving Exo1 or BLM/WRN-Dna2. However, resection pathways and their exact contributions in humans in vivo are not as clearly worked out as in yeast. Here, we examined the contribution of Exo1 to DNA end resection in humans in vivo in response to ionizing radiation (IR) and its relationship with other resection pathways (Mre11-CtIP or BLM/WRN). We find that Exo1 plays a predominant role in resection in human cells along with an alternate pathway dependent on WRN. While Mre11 and CtIP stimulate resection in human cells, they are not absolutely required for this process and Exo1 can function in resection even in the absence of Mre11-CtIP. Interestingly, the recruitment of Exo1 to DNA breaks appears to be inhibited by the NHEJ protein Ku80, and the higher level of resection that occurs upon siRNA-mediated depletion of Ku80 is dependent on Exo1. In addition, Exo1 may be regulated by 53BP1 and Brca1, and the restoration of resection in BRCA1-deficient cells upon depletion of 53BP1 is dependent on Exo1. Finally, we find that Exo1-mediated resection facilitates a transition from ATM- to ATR-mediated cell cycle checkpoint signaling. Our results identify Exo1 as a key mediator of DNA end resection and DSB repair and damage signaling decisions in human cells.
Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, USA.
Nozomi
N
Tomimatsu
Bipasha
B
Mukherjee
Katherine
K
Deland
Akihiro
A
Kurimasa
Emma
E
Bolderson
Kum Kum
KK
Khanna
Sandeep
S
Burma
D034961:Antigens, Nuclear / Q000378:metabolism; D064007:Ataxia Telangiectasia Mutated Proteins; D019313:BRCA1 Protein / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism; D002460:Cell Line; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects; D004260:DNA Repair / Q000528:radiation effects; D045643:DNA Repair Enzymes / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D005090:Exodeoxyribonucleases / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D000072200:Ku Autoantigen; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics* / Q000528:radiation effects; D025521:Tumor Suppressor Proteins / Q000378:metabolism; D000071857:Tumor Suppressor p53-Binding Protein 1
D034961:Antigens, Nuclear; D019313:BRCA1 Protein; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; C498301:TP53BP1 protein, human; D025521:Tumor Suppressor Proteins; D000071857:Tumor Suppressor p53-Binding Protein 1; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases; C114331:EXO1 protein, human; D005090:Exodeoxyribonucleases; C000606509:Xrcc6 protein, human; D000072200:Ku Autoantigen; D045643:DNA Repair Enzymes