Wortmannin inhibits repair of DNA double-strand breaks in irradiated normal human cells

Ryuichi Okayasu, Katsutoshi Suetomi, Robert L. Ullrich

Research output: Contribution to journalArticle

70 Citations (Scopus)

Abstract

Wortmannin, a specific inhibitor of PI-3 kinase, was recently found to be an effective radiosensitizer in cells of various human and murine cell lines. Another study indicated that wortmannin inhibited repair of DNA double-strand breaks (DSBs) in irradiated Chinese hamster ovary cells using the neutral elution assay. To further clarify the mechanism behind radiosensitization by wortmannin, we have studied DSB repair in γ-irradiated normal human fibroblasts using pulsed-field gel electrophoresis. The rejoining of DSBs in irradiated cells was significantly inhibited when 20 μM or more of wortmannin was added to the cells. The colony formation assay in cultures treated with wortmannin showed that the radiosensitization occurred in a manner that was dependent on the drug concentration. However, significant sensitization was observed only with a concentration of wortmannin of 20 μM or higher, reflecting the results of DSB rejoining studies. No marked reduction in plating efficiencies was observed for cells treated with wortmannin alone. The studies of the levels of expression of DNA-dependent protein kinase (DNA-PK) indicated that, while there were no significant changes in expression of Ku protein, the expression of the DNA- PK catalytic sub-unit (DNA-PKcs) was reduced markedly in cultures treated with wortmannin using an antibody against the C-terminus region of DNA-PKcs. In addition, no reduction in the levels of expression of DNA-PKcs was observed in cells treated with wortmannin using an antibody which recognizes a mid-region of this large protein. These results together with those of related studies suggest that wortmannin radiosensitizes normal human cells by inhibiting DSB repair and that this inhibition is a consequence of an inactivation of kinase activity and/or a structural change caused by binding of wortmannin to the C-terminus region of DNA-PKcs.

Original languageEnglish (US)
Pages (from-to)440-445
Number of pages6
JournalRadiation Research
Volume149
Issue number5
DOIs
StatePublished - May 1998

Fingerprint

Double-Stranded DNA Breaks
DNA repair
strands
deoxyribonucleic acid
Catalytic DNA
DNA
cells
proteins
antibodies
ovaries
elution
hamsters
fibroblasts
electrophoresis
plating
cultured cells
phosphatidylinositol 3-kinase
deactivation
Chinese hamsters
inhibitors

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Radiology Nuclear Medicine and imaging
  • Biophysics
  • Radiation

Cite this

Wortmannin inhibits repair of DNA double-strand breaks in irradiated normal human cells. / Okayasu, Ryuichi; Suetomi, Katsutoshi; Ullrich, Robert L.

In: Radiation Research, Vol. 149, No. 5, 05.1998, p. 440-445.

Research output: Contribution to journalArticle

Okayasu, Ryuichi ; Suetomi, Katsutoshi ; Ullrich, Robert L. / Wortmannin inhibits repair of DNA double-strand breaks in irradiated normal human cells. In: Radiation Research. 1998 ; Vol. 149, No. 5. pp. 440-445.
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