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Human O6-methylguanine-DNA methyltransferase containing C145A does not prevent hepatocellular carcinoma in C3HeB/FeJ transgenic mice

Authors

  • Maryanne C.S. Herzig,

    1. Department of Cellular & Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas
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  • Kim Hildreth,

    1. Department of Cellular & Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas
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  • Jessica Huamani,

    1. Department of Radiology, Children's Healthcare of Atlanta, Atlanta, Georgia
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  • Marissa Perez,

    1. Department of Cellular & Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas
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  • Beth A. Goins,

    1. Department of Radiology, University of Texas Health Science Center at San Antonio, San Antonio, Texas
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  • C. Alex McMahan,

    1. Department of Pathology, University of Texas Health Science Center at San Antonio, San Antonio, Texas
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  • Robert L. Reddick,

    1. Department of Pathology, University of Texas Health Science Center at San Antonio, San Antonio, Texas
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  • Christi A. Walter

    Corresponding author
    1. Department of Cellular & Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, Texas
    2. South Texas Veteran's Health Care System, San Antonio, Texas
    3. Barshop Institute for Longevity and Aging Studies, San Antonio, Texas
    4. Cancer Therapy and Research Institute, San Antonio, Texas
    • Department of Cellular & Structural Biology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr., San Antonio, TX, 78229.
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Abstract

The prevalence of hepatocellular carcinoma (HCC) was diminished from 60% to 18% at 15 months of age in C3HeB/FeJ male transgenic mice expressing hMGMT in our previous studies. To directly test if the methyltransferase activity is required for diminished tumor prevalence, two separate lines of transgenic mice bearing an enzymatically inactive form of hMGMT were used. In these lines, cysteine 145 was substituted with alanine (C145A). Expression of the hMGMT C145A transgene in liver was demonstrated by Northern blots and Western blots. Immunohistochemistry revealed predominantly nuclear localization of the hMGMT C145A protein. hMGMT C145A transgenic mice were crossed with lacI transgenic mice to assess mutant frequencies in the presence of the mutant protein. Mutant frequencies were similar among livers of lacI × hMGMT C145A bi-transgenic mice and lacI × wild-type (WT) mice. DNA sequence analysis of recovered lacI mutants revealed similar mutation spectra for hMGMT C145A and WT mice. The prevalence of HCC was also similar for the two tested lines of hMGMT C145A mice, 45% and 48% prevalence with median tumor sizes of 11 and 8 mm, and WT mice, 40% prevalence and median tumor size of 10 mm. These results provide evidence that residue C145 in hMGMT is required to reduce the prevalence of HCC in C3HeB/FeJ mice transgenic for hMGMT. © 2011 Wiley Periodicals, Inc.

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