Carcinogenesis Advance Access originally published online on December 13, 2006
Carcinogenesis 2007 28(6):1356-1363; doi:10.1093/carcin/bgl239
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Mammary carcinogenesis in transgenic mice expressing a dominant-negative mutant of DNA polymerase ß in their mammary glands
Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA
1 Present address: Department of Biotechnology, Haldia Institute of Technology, Pin 721657, West Bengal, India
* To whom correspondence should be addressed. Tel: +1 216 444 0631; Fax: +1 216 445 6269; Email: banerjs{at}ccf.org
DNA polymerase ß (polß) is a major contributor to mammalian DNA damage repair through its gap-filling DNA synthesis and 5'-deoxyribose phosphate lyase activities. In this way, polß plays pivotal roles in the repair of oxidative DNA damage, replication, embryonic survival, neuronal development, meiosis, apoptosis and telomere function. A 36 kDa truncated polß
protein is expressed in human colorectal, breast, lung and renal carcinomas, but not in normal matched tissues. Interestingly, a binary protein–protein complex of polß and X-ray cross-complementing group 1 acts as dominant-negative mutant. In this study, the potential tumorigenic activity of polß was examined in nude and transgenic mouse models. Mouse embryonic fibroblasts (MEFs) expressing polß in the absence of endogenous polß exhibited increased susceptibility to N-methyl-N-nitrosourea (MNU)-induced morphological transformation as compared with cells expressing wild-type (WT) polß. This was accompanied by reduced gap-filling DNA synthesis activity. Anchorage-independent transformed cells derived from polß-expressing MEFs induced 100% tumor occurrence in nude mice. To support these data, we established transgenic mice expressing polß specifically in the mammary glands from a whey acidic protein promoter-driven transgene. This is the first report of transgenic mice with tissue-specific expression of polß. MNU-induced tumor formation was analyzed in transgenic mice expressing polß together with endogenous WT polß in their mammary glands and in normal control mice expressing only WT polß. The latent period of tumor appearance was markedly shorter and tumor incidence was significantly higher in transgenic animals than in control animals treated under the same conditions. These results indicate that cells expressing the mutant polß display an enhanced sensitivity to MNU that probably underlies an increased susceptibility to tumorigenesis.
Abbreviations: BER, base excision repair; MEF, mouse embryonic fibroblast; MNU, N-methyl-N-nitrosourea; PBS, phosphate-buffered saline; PCR, polymerase chain reaction; polß, polymerase ß; WAP, whey acidic protein; WT, wild type; XRCC1, X-ray cross-complementing group 1
These authors contribute equally to this work. Received April 26, 2006; revised November 10, 2006; accepted November 25, 2006.