Relationship between the radiosensitizing effect of wortmannin, DNA double-strand break rejoining, and p21WAF1 induction in human normal and tumor-derived cells
✍ Scribed by Razmik Mirzayans; Scott Pollock; April Scott; Louise Enns; Bonnie Andrais; David Murray
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 219 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0899-1987
- DOI
- 10.1002/mc.20005
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
Wortmannin (WM) is a potent inhibitor of the catalytic sub‐unit of DNA‐PK, which is involved in one pathway of DNA double‐strand break (DSB) rejoining, and of ATM, which functions upstream in the p53 signaling pathway. WM is known to be an efficient radiosensitizer in a variety of mammalian cell types, to inhibit DSB rejoining following exposure to supralethal doses (≥30 Gy) of ionizing radiation, and to abrogate the induction of p53 at early times after radiation exposure. We report here that WM is a more effective radiosensitizer in A549 human lung carcinoma cells than in normal human fibroblasts (NHFs). In addition, WM strongly inhibits DSB rejoining in A549 cells exposed to relatively low doses (e.g., 10 Gy) of ionizing radiation, without having any detectable effect in NHFs. We further demonstrate that WM significantly potentiates the induction of p21^WAF1^, a p53‐regulated gene that encodes for a key mediator of cell‐cycle/growth arrest, when determined at late times (e.g., 24 h) after irradiation. This late WM‐dependent potentiation of p21^WAF1^ induction following radiation exposure is observed in NHFs and in the p53 wild‐type tumor cell lines A549, A172, and SKNSH, but not in the p53‐deficient tumor cell lines DLD‐1, HeLa, and SKNSH‐E6. We conclude that: (i) inhibition of DSB rejoining by WM may be an important contributor to its radiosensitizing effect in A549 cells but not in NHFs; and (ii) radiosensitization of p53‐proficient human cells by WM may in part be associated with the delayed induction of p21^WAF1^, which can lead to a sustained growth‐arrested phenotype resembling senescence. © 2004 Wiley‐Liss, Inc.