Radiosensitization by a dominant negative to DNA polymerase beta is DNA polymerase beta-independent and XRCC1-dependent.
OBJECTIVE
DNA base damages and single strand breaks after ionizing radiation are repaired by base excision repair (BER) and single strand break repair (SSBR), with both DNA polymerase beta (polbeta) and XRCC1 playing key roles. We previously showed that a dominant negative to polbeta (polbetaDN) sensitized human tumor cells to ionizing radiation. However, polbeta-deficient cells, in contrast to XRCC1-deficient cells, are not more radiosensitive. The purpose of the present study was to further elucidate the mechanism of action of the polbetaDN to better understand the roles of BER and SSBR in determining radiosensitivity.


METHODS
Mouse embryonic fibroblasts, both polbeta wildtype and knockout, and hamster XRCC1-deficient EM9 cells together with its parental line, were transfected with the polbetaDN. Clones with equal polbetaDN expression levels were selected and used in clonogenic assays to determine radiosensitivity.


RESULTS
Radiosensitization of polbeta deficient cells by the polbetaDN is shown here, demonstrating inhibition of a polbeta-independent pathway. In addition, we observed radiosensitization of wildtype hamster cells but no radiosensitization of the XRCC1-deficient EM9 cells.


CONCLUSIONS
The polbetaDN acts independently of polbeta status and inhibits a pathway, which is dependent on XRCC1, consistent with inhibition of BER and/or SSBR. The data further indicate involvement of other polymerases, which are inhibited by polbetaDN. Finally, they demonstrate that inhibition of BER and SSBR can increase radiosensitivity, with potential clinical relevance.
Neijenhuis
Sari
S
Division of Experimental Therapy, The Netherlands Cancer Institute, Amsterdam, The Netherlands.
Begg
Adrian C
AC
Vens
Conchita
C
D000818:Animals; D016466:CHO Cells; D002999:Clone Cells; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage / Q000528:radiation effects; D019951:DNA Polymerase beta / Q000502:physiology*; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000502:physiology*; D005347:Fibroblasts / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D011836:Radiation Tolerance / Q000502:physiology*; D014162:Transfection; D000076105:X-ray Repair Cross Complementing Protein 1
D004268:DNA-Binding Proteins; D000076105:X-ray Repair Cross Complementing Protein 1; C000619371:XRCC1 protein, human; C000619352:Xrcc1 protein, mouse; D019951:DNA Polymerase beta