The effect of
wortmannin posttreatment was studied in cells derived from different species (hamster, mouse, chicken, and human) with normal and defective
DNA-dependent protein kinase (
DNA-PK) activity, cells with and without the
ataxia telangiectasia (ATM) gene, and cells lacking other regulatory
proteins involved in the
DNA double-strand break (
DSB) repair pathways. Clonogenic assays were used to obtain all results.
Wortmannin radiosensitization was observed in Chinese hamster cells (V79-B310H , CHO-K1), mouse mammary
carcinoma cells (SR-1), transformed human fibroblast (N2KYSV), chicken B lymphocyte wild-type cells (DT40), and chicken Rad54 knockout cells (Rad54-/-). However, mouse mammary
carcinoma cells (SX9) with defects in the
DNA-PK and chicken
DNA-PK catalytic subunit (
DNA-
PKcs) knockout cells (
DNA-
PKcs-/-/-) failed to exhibit
wortmannin radiosensitization. On the other hand, SCID mouse cells (SC3VA2) exposed to
wortmannin exhibited significant increases in radiosensitivity, possibly because of some residual function of
DNA-
PKcs. Moreover, the transformed human cells derived from AT patients (AT2KYSV) and chicken ATM knockout cells (ATM-/-) showed pronounced
wortmannin radiosensitization. These studies demonstrate confirm that the mechanism underlying
wortmannin radiosensitization is the inhibition of
DNA-PK, but not of ATM, thereby resulting in the inhibition of
DSB repair via nonhomologous endjoining (NHEJ).