Modification of the ionizing radiation response in living cells by an scFv against the DNA-dependent protein kinase

Shuyi Li, Yoshihiko Takeda, Stéphanie Wragg, John Barrett, Andrew Phillips, William S. Dynan

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


The non-homologous end joining pathway uses pre-existing proteins to repair DNA double-strand breaks induced by ionizing radiation. Here we describe manipulation of this pathway in living cells using a newly developed tool. We generated a single chain antibody variable fragment (scFv) that binds to the DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a key enzyme in the pathway. In contrast to existing pharmacologic inhibitors, the scFv binds a newly defined regulatory site outside the kinase catalytic domain. Although the scFv inhibits kinase activity only modestly, it completely blocks DNA end joining in a cell-free system. Microinjection of the scFv sensitizes human cells to radiation, as measured by a reduction in efficiency of colony formation and induction of apoptosis at an otherwise sublethal dose of 1.5 Gy. The scFv blocks non-homologous end joining in situ at a step subsequent to histone γ-H2AX focus formation but preceding γ-H2AX dephosphorylation. Blockage occurs in cells exposed to as little as 0.1 Gy, indicating that DNA-PKcs is essential for double-strand break repair even at low radiation doses. The ability to modify the radiation response in situ in living cells provides a link between biochemical, genetic and cytologic approaches to the study of doublestrand break repair intermediates.

Original languageEnglish (US)
Pages (from-to)5848-5857
Number of pages10
JournalNucleic Acids Research
Issue number20
StatePublished - Oct 15 2003

ASJC Scopus subject areas

  • Genetics


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