| Co-Investigator(Kenkyū-buntansha) |
NAKATSURU Yoko University of Tokyo, Department of Pathology, Faculty of Medicine, Assistant, 医学部, 助手 (00237314)
ODA Hideaki University of Tokyo, Department of Pathology, Faculty of Medicine, Associate Pro, 医学部, 助教授 (40214142)
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| Research Abstract |
The E.coli ada gene encodes O^6-methylguanine DNA methyltransferase (MGMT) which repairs the methylation of guanine at the O^6 position in DNA.After recombination with a Chinese hamster metallothionein I gene promoter, the ada gene was micro injected into C3H/HeN mouse Zygotes. Eventually, transgenic mice containing the ada fusion DNA were generated. The integrated ada DNA complex was transmitted to the progeny in a mode conforming to tandem integration a single chromosome site, and homozygotes were also obtained from an inter-transgenic mouse cross. RNA transcripts of the chimeric ada gene were identified in the livers of these transgenic mice using Northern blot analysis. The ada gene product was detected in the liver from ada mice by immunoblot analysis. Because the ada gene was expressed under the control of the metallothionein promoter, the MGMT activity of the liver from transgenic homozygote showed approximately 3 times the control activity, a marked increase of up to about 8 times the non-transgenic control levels being observed 10 h after zinc treatment. Using ada mice and nontransgenic control mice, ada mouse was resistant to tumorigenesis when treated with liver carcinogens, dimethylnitrosamine or diethylnitrosamine. Transgenic mice expressing ada gene derived from C3H/HeN mouse, C3H mouse strain is generally known to develop spontaneous liver tumors at high incidence in later life. We further compared the incidence of spontaneous liver tumors between ada mice and nontransgenic control mice. In results, both groups developed liver tumors at the same incidence (48%). However, the histological examination showed the incidence of hepatocellular carcinoma in ada mouse was significantly lower than in nontransgenic mouse. These observations suggest that MGMT may also protect mice from tumor progression.
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