Carcinogenesis Advance Access originally published online on May 23, 2007
Carcinogenesis 2007 28(10):2089-2095; doi:10.1093/carcin/bgm125
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Adenomatous polyposis coli-mediated hypersensitivity of mouse embryonic fibroblast cell lines to methylmethane sulfonate treatment: implication of base excision repair pathways
Department of Anatomy and Cell Biology and UF Shands Cancer Center, University of Florida, Gainesville, FL 32610, USA
* To whom correspondence should be addressed. Tel: +1 352 273 8163; Fax: +1 352 273 8285; Email: snarayan{at}ufl.edu
The role of adenomatous polyposis coli (APC) has been implicated in various cellular functions including cell migration, cell–cell adhesion, cell cycle control, chromosomal segregation and apoptosis. Recently, we discovered a novel role of APC in DNA base excision repair (BER) and showed that APC interacts with DNA polymerase ß (Pol-ß) and flap endonuclease 1 and interferes long-patch base excision repair (LP-BER) by blocking strand displacement synthesis. Many times, the chemotherapeutic drugs induce DNA alkylation damage, which is primarily repaired by the BER pathway. Thus, the efficacy of such drugs can be increased by APC resulting in the blockage of LP-BER. In the present study, we tested this hypothesis by using isogenic wild-type and Pol-ß-knockout mouse embryonic fibroblast (MEF) cell lines in which the Apc gene was knocked down by the small interfering RNA technique and treated with methylmethane sulfonate (MMS). The MEF-Apc(WT)/Polß–/– cells were hypersensitive to MMS treatment compared with the MEF-Apc(WT)/Polß+/+ cells. However, once the Apc gene was knocked down, these cells became more resistant to MMS treatment, suggesting that the MMS-induced hypersensitivity was associated with Apc. We then determined whether the hypersensitivity of MEF-Apc(WT)/Polß–/– and MEF-Apc(WT)/Polß+/+ cell lines were due to decreased Pol-ß-independent and Pol-ß-dependent LP-BER pathways, respectively. The results of in vivo and in vitro LP-BER assays supported our findings. Furthermore, Apc-mediated hypersensitivity to MMS treatment was correlated with increased apoptosis of MEF-Apc(WT)/Polß–/– and MEF-Apc(WT)/Polß+/+ as compared with MEF-Apc(KD)/Polß–/– and MEF-Apc(KD)/Polß+/+ cells. These results suggest that an increased level of Apc can increase the efficacy of DNA-alkylating drugs used as a curative therapy.
Abbreviations: AP, apurinic/apyrimidinic; Apc, adenomatous polyposis coli; APE, apurinic/apyrimidinic endonuclease; BER, base excision repair; dRP, deoxyribose phosphate; Fen-1, flap endonuclease 1; LP-BER, long-patch base excision repair; MEF, mouse embryonic fibroblast; MMS, methylmethane sulfonate; Pol-ß, DNA polymerase ß; SP-BER, short-patch base excision repair
Received January 26, 2007; revised May 8, 2007; accepted May 10, 2007.
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