Role of Ape1 and base excision repair in the radioresponse and heat-radiosensitization of HeLa Cells.
BACKGROUND
The mechanism by which heat sensitizes mammalian cells to ionizing radiation remains to be elucidated. We determined whether base excision repair (BER) is involved in heat-radiosensitization and report novel findings that provide insight regarding the role of BER in the radiation response of HeLa cells.


METHODS
An siRNA approach was utilized to suppress expression of AP endonuclease (Ape1), a critical enzyme of BER. Clonogenic survival curves were obtained for HeLa cells expressing normal or reduced Ape1 content and which had been irradiated, and these were compared to survival curves from cells that were irradiated prior to hyperthermia treatment.


RESULTS
The amount of heat-radiosensitization observed in Ape1-suppressed cells was similar to or slightly greater than that observed in cells expressing near-normal levels of Ape1. Interestingly, we also found that for unheated HeLa cells, suppressed expression of Ape1 resulted in enhanced resistance to X-rays.


CONCLUSIONS
The data suggest that Ape1, and therefore BER, is not involved in heat-radiosensitization. However, the observation that suppressed expression of Ape1 results in enhanced radioresistance supports the notion that BER may be detrimental to the survival of irradiated cells.
Indiana University, Department of Radiation Oncology, Indianapolis, Indiana 46202, USA.
Christopher N
CN
Batuello
Mark R
MR
Kelley
Joseph R
JR
Dynlacht
D015153:Blotting, Western; D004260:DNA Repair / Q000528:radiation effects*; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006358:Hot Temperature; D006801:Humans; D034741:RNA, Small Interfering / Q000494:pharmacology; D011836:Radiation Tolerance; D014965:X-Rays
D034741:RNA, Small Interfering; C085108:APEX1 protein, human; D043603:DNA-(Apurinic or Apyrimidinic Site) Lyase