Mutagenesis Advance Access originally published online on March 9, 2007
Mutagenesis 2007 22(3):235-243; doi:10.1093/mutage/gem008
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Reduced host cell reactivation of oxidative DNA damage in human cells deficient in the mismatch repair gene hMSH2
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1 1Present address: GeneNews Corporation, 800 Petrolia Road, Unit 15, Toronto, Ontario, Canada M3J 3K4
Germ line mutations in the mismatch repair (MMR) genes hMSH2 and hMLH1 account for 
98% of hereditary non-polyposis colorectal cancers. In addition, there is increasing evidence for an involvement of MMR gene expression in the response of cells to UV-induced skin cancer. The link between MMR and skin cancer suggests an involvement of MMR gene expression in the response of skin cells to UV-induced DNA damage. In this report, we have used two reporter gene assays to examine the role of hMSH2 and hMLH1 in the repair of oxidative DNA damage induced by UVA light and DNA damage caused by methylene blue plus visible light (MB+VL). UVA and MB+VL produce 8-hydroxyguanines in DNA that are repaired by base excision repair (BER). AdHCMVlacZ is a replication-deficient recombinant adenovirus that expresses the ß-galactosidase (ß-gal) reporter gene under the control of the human cytomegalovirus (CMV) immediate-early promoter. We show a reduced host cell reactivation for ß-gal expression of UVA-treated and MB+VL-treated AdHCMVlacZ in hMSH2-deficient LoVo human colon adenocarcinoma cells compared to their hMSH2-proficient counterpart SW480 cells, but not in hMLH1-deficient HCT116 human colon adenocarcinoma cells compared to hMLH1-proficient HCT116-chr3 cells. We have also reported previously that enhanced expression of the undamaged AdHCMVlacZ reporter gene is induced by the pre-treatment of cells with lower levels of the DNA-damaging agent and to higher expression levels in transcription-coupled repair (TCR)-deficient compared to TCR-proficient cells. Here we show that pre-treatment of cells with UVA or MB+VL enhanced expression of the undamaged reporter gene to a higher level in LoVo compared to SW480 cells but there was little or no difference in HCT116 compared to HCT116-chr3 cells. These results suggest a substantial involvement of hMSH2 but little or no involvement of hMLH1 in the repair of UVA- and MB+VL-induced oxidative DNA damage by BER.
* To whom correspondence should be addressed. Tel: 1 905 525 9140; Fax: 1 905 522 6066; Email: rainbow{at}mcmaster.ca
Received on November 3, 2006; revised on January 19, 2007; accepted on January 31, 2007.
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  S. N. Kassam and A. J. Rainbow UV-inducible base excision repair of oxidative damaged DNA in human cells Mutagenesis, January 1, 2009; 24(1): 75 - 83. [Abstract] [Full Text] [PDF]
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