Single-stranded DNA-binding protein hSSB1 is critical for genomic stability.
Single-strand DNA (ssDNA)-binding proteins (SSBs) are ubiquitous and essential for a wide variety of DNA metabolic processes, including DNA replication, recombination, DNA damage detection and repair. SSBs have multiple roles in binding and sequestering ssDNA, detecting DNA damage, stimulating nucleases, helicases and strand-exchange proteins, activating transcription and mediating protein-protein interactions. In eukaryotes, the major SSB, replication protein A (RPA), is a heterotrimer. Here we describe a second human SSB (hSSB1), with a domain organization closer to the archaeal SSB than to RPA. Ataxia telangiectasia mutated (ATM) kinase phosphorylates hSSB1 in response to DNA double-strand breaks (DSBs). This phosphorylation event is required for DNA damage-induced stabilization of hSSB1. Upon induction of DNA damage, hSSB1 accumulates in the nucleus and forms distinct foci independent of cell-cycle phase. These foci co-localize with other known repair proteins. In contrast to RPA, hSSB1 does not localize to replication foci in S-phase cells and hSSB1 deficiency does not influence S-phase progression. Depletion of hSSB1 abrogates the cellular response to DSBs, including activation of ATM and phosphorylation of ATM targets after ionizing radiation. Cells deficient in hSSB1 exhibit increased radiosensitivity, defective checkpoint activation and enhanced genomic instability coupled with a diminished capacity for DNA repair. These findings establish that hSSB1 influences diverse endpoints in the cellular DNA damage response.
Richard
Derek J
DJ
Signal Transduction Laboratory, Queensland Institute of Medical Research, Brisbane, Queensland 4029, Australia.
Bolderson
Emma
E
Cubeddu
Liza
L
Wadsworth
Ross I M
RI
Savage
Kienan
K
Sharma
Girdhar G
GG
Nicolette
Matthew L
ML
Tsvetanov
Sergie
S
McIlwraith
Michael J
MJ
Pandita
Raj K
RK
Takeda
Shunichi
S
Hay
Ronald T
RT
Gautier
Jean
J
West
Stephen C
SC
Paull
Tanya T
TT
Pandita
Tej K
TK
White
Malcolm F
MF
Khanna
Kum Kum
KK
D064007:Ataxia Telangiectasia Mutated Proteins; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D018797:Cell Cycle Proteins / Q000378:metabolism; D004260:DNA Repair / Q000528:radiation effects; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D042822:Genomic Instability / Q000528:radiation effects; D006367:HeLa Cells; D006801:Humans; D024101:Mitochondrial Proteins; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D021381:Protein Transport / Q000528:radiation effects; D011839:Radiation, Ionizing; D015398:Signal Transduction / Q000187:drug effects / Q000528:radiation effects; D025521:Tumor Suppressor Proteins / Q000378:metabolism
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D024101:Mitochondrial Proteins; C504091:NABP2 protein, human; D025521:Tumor Suppressor Proteins; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases