Article ID Journal Published Year Pages File Type
8320329 DNA Repair 2018 13 Pages PDF
Abstract
Polynucleotide kinase/phosphatase (PNKP) has been implicated in non-homologous end joining (NHEJ) of DNA double-strand breaks (DSBs). To assess the consequences of PNKP deficiency for NHEJ of 3′-phosphate-ended DSBs, PNKP-deficient derivatives of HCT116 and of HeLa cells were generated using CRISPR/CAS9. For both cell lines, PNKP deficiency conferred sensitivity to ionizing radiation as well as to neocarzinostatin (NCS), which specifically induces DSBs bearing protruding 3′-phosphate termini. Moreover, NCS-induced DSBs, detected as 53BP1 foci, were more persistent in PNKP −/− HCT116 cells compared to their wild-type (WT) counterparts. Surprisingly, PNKP-deficient whole-cell and nuclear extracts were biochemically competent in removing both protruding and recessed 3′-phosphates from synthetic DSB substrates, albeit much less efficiently than WT extracts, suggesting an alternative 3′-phosphatase. Measurements by ligation-mediated PCR showed that PNKP-deficient HeLa cells contained significantly more 3′-phosphate-terminated and fewer 3′-hydroxyl-terminated DSBs than parental cells 5-15 min after NCS treatment, but this difference disappeared by 1 h. These results suggest that, despite presence of an alternative 3′-phosphatase, loss of PNKP significantly sensitizes cells to 3′-phosphate-terminated DSBs, due to a 3′-dephosphorylation defect.
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Life Sciences Biochemistry, Genetics and Molecular Biology Biochemistry
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