hSSB1 phosphorylation is dynamically regulated by DNA-PK and PPP-family protein phosphatases

- hSSB1 S134 phosphorylation is enhanced following replication fork disruption.
- Phosphorylation of hSSB1 S134 is directly mediated by DNA-PK.
- DNA-PK phosphorylation of hSSB1 is opposed by PPP-family protein phosphatases.
- Cells expressing S134A hSSB1 are sensitive to replication fork disruption.

The maintenance of genomic stability is essential for cellular viability and the prevention of diseases such as cancer. Human single-stranded DNA-binding protein 1 (hSSB1) is a protein with roles in the stabilisation and restart of stalled DNA replication forks, as well as in the repair of oxidative DNA lesions and double-strand DNA breaks. In the latter process, phosphorylation of threonine 117 by the ATM kinase is required for hSSB1 stability and efficient DNA repair. The regulation of hSSB1 in other DNA repair pathways has however remained unclear. Here we report that hSSB1 is also directly phosphorylated by DNA-PK at serine residue 134. While this modification is largely suppressed in undamaged cells by PPP-family protein phosphatases, S134 phosphorylation is enhanced following the disruption of replication forks and promotes cellular survival. Together, these data thereby represent a novel mechanism for hSSB1 regulation following the inhibition of replication.