Evidence for the involvement of DNA-dependent protein kinase in the phenomena of low dose hyper-radiosensitivity and increased radioresistance.
OBJECTIVE
To investigate the role of DNA-dependent protein kinase (DNA-PK) in the phenomena of low dose hyper-radiosensitivity (HRS) and increased radioresistance (IRR) using the genetically related M059 cell lines of disparate PRKDC status.


METHODS
Clonogenic survival was measured for the three cell lines following low doses of X-irradiation using a flowactivated cell sorting (FACS) plating technique. The presence of PRKDC, G22p1 and Xrcc5 proteins was determined by Western blotting and a kinase assay used to measure DNA-PK complex activity.


RESULTS
The survival responses for the three cell lines over the 0-0.3Gy dose range were comparable, but differences in radiosensitivity were evident at doses >0.4Gy. M059K and M059J/Fus1 cells (both PRKDC competent) exhibited marked HRS/IRR responses, albeit to different extents. M059J cells (PRKDC incompetent) were extremely radiosensitive exhibiting a linear survival curve with no evidence of IRR. The presence of IRR was coincident with the presence of PRKDC protein and functional DNA-PK activity.


CONCLUSIONS
HRS is a response that is independent of DNA-PK activity. In contrast, IRR showed a dependence on the presence of PRKDC protein and functional DNA-PK activity. These data support a role for DNA-PK activity in the IRR response.
Marples
B
B
Radiation Biology Group, Karmanos Cancer Institute, Wayne State University, Hudson Webber Building, Room 824 4100 John R, Detroit, MI 48201, USA. marplesb@kci.wayne.edu
Cann
N E
NE
Mitchell
C R
CR
Johnston
P J
PJ
Joiner
M C
MC
D015153:Blotting, Western; D002469:Cell Separation; D002470:Cell Survival; D004260:DNA Repair / Q000502:physiology / Q000528:radiation effects; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins; D004307:Dose-Response Relationship, Radiation; D005434:Flow Cytometry; D006801:Humans; D008962:Models, Theoretical; D009687:Nuclear Proteins; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011836:Radiation Tolerance / Q000502:physiology*; D012044:Regression Analysis; D014407:Tumor Cells, Cultured; D014965:X-Rays
D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D051747:DNA-Activated Protein Kinase; C497263:PRKDC protein, human; D017346:Protein Serine-Threonine Kinases