Carcinogenesis Advance Access published online on May 23, 2007
Carcinogenesis, 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
* Correspondence to – Satya Narayan, UF Shands Cancer Center, Cancer and Genetics Research Complex, Room 255, PO Box 103633, 1376 Mowry Road, University of Florida, Gainesville, FL 32610; Tel: 352-273-8163; FAX: 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 (Fen-1) and interferes long-patch (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 cell lines in which the Apc gene was knocked down by the SiRNA technique and treated with methylmethane sulfonate (MMS). The MEF-Apc(WT)/Polß–/– cells were hypersensitive to MMS treatment compared to 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 to 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.
Key Words: Adenomatous polyposis coli • apoptosis • base excision repair • cell cycle control • DNA polymerase ß • flap endonuclease 1 • MMS • mouse embryonic fibroblast cell line • SiRNA
Received January 26, 2007; revised May 8, 2007; accepted May 10, 2007.
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