Enhanced cellular radiosensitivity induced by cofilin-1 over-expression is associated with reduced DNA repair capacity.
OBJECTIVE
A previous report has indicated that over-expression of cofilin-1 (CFL-1), a member of the actin depolymerizing factor (ADF)/cofilin protein family, enhances cellular radiosensitivity. This study explores the involvement of various DNA damage responses and repair systems in the enhanced cellular radiosensitivity as well as assessing the role of CFL-1 phosphorylation in radiosensitivity.


METHODS
Human non-small lung cancer H1299 cells harboring a tet-on gene expression system were used to induce exogenous expression of wild-type CFL-1. Colony formation assays were used to determine cell survival after γ-ray exposure. DNA damage levels were determined by Comet assay. DNA repair capacity was assessed by fluorescence-based DNA repair analysis and antibody detection of various repair proteins. The effects of CFL-1 phosphorylation on radiation responses were explored using two mutant CFL-1 proteins, S3D and S3A. Finally, endogenous CFL-1 phosphorylation levels were investigated using latrunculin A (LA), cytochalasin B (CB) and Y27632.


RESULTS
When phosphorylatable CFL-1 was expressed, radiosensitivity was enhanced after exposure to γ-rays and this was accompanied by DNA damage. Phosphorylated histone H2AX (γ-H2AX) and p53-binding protein-1 (53BP1) foci, as well as Chk1/2 phosphorylation, were apparently suppressed, although ataxia telangiectasia mutated (ATM) kinase activation was apparently unaffected. In addition, two radiation-induced double-strand break (DSB) repair systems, namely homologous recombination repair (HRR) and non-homologous end joining (NHEJ), were suppressed. Moreover, over-expression of CFL-1 S3D and CFL-1 S3A both enhanced radiosensitivity. However, enhanced radiosensitivity and reduced γ-H2AX expression were only detected in cells treated with LA which increased endogenous phospho-CFL-1, and not in cells treated with Y27632, which dephosphorylates CFL-1.


CONCLUSIONS
CFL-1 over-expression enhances radiosensitivity and this is associated with reduced DNA repair capacity. Although phosphorylated CFL-1 seems to be involved in radiosensitivity, further studies are required to address the importance of CFL-1 activity to the regulation of radiosensitivity.
Division of Radiation Oncology, Taipei City Hospital RenAi Branch , Taipei.
Jyh-Der
JD
Leu
Yu-Wen
YW
Chiu
Chia-Chien
CC
Lo
Pei-Hsun
PH
Chiang
Shu-Jun
SJ
Chiu
Cheng-Han
CH
Tsai
Jeng-Jong
JJ
Hwang
Ran-Chou
RC
Chen
Vera
V
Gorbunova
Yi-Jang
YJ
Lee
D002289:Carcinoma, Non-Small-Cell Lung / Q000503:physiopathology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D051338:Cofilin 1 / Q000378:metabolism*; D004249:DNA Damage / Q000502:physiology*; D004260:DNA Repair / Q000502:physiology*; D004273:DNA, Neoplasm / Q000235:genetics* / Q000528:radiation effects*; D005720:Gamma Rays; D006801:Humans; D011829:Radiation Dosage; D011836:Radiation Tolerance / Q000235:genetics*; D015854:Up-Regulation
D051338:Cofilin 1; D004273:DNA, Neoplasm