Mouse mammary tumor virus (MMTV)-like DNA sequences in the breast tumors of father, mother, and daughter

<p>Abstract</p> <p>Background</p> <p>The diagnosis of late onset breast cancer in a father, mother, and daughter living in the same house for decades suggested the possibility of an environmental agent as a common etiological factor. Both molecular and epidemiological data have indicated a possible role for the mouse mammary tumor virus (MMTV), the etiological agent of breast cancer in mice, in a certain percentage of human breast tumors. The aim of this study was to determine if MMTV might be involved in the breast cancer of this cluster of three family members.</p> <p>Results</p> <p>MMTV-like envelope (<it>env</it>) and long terminal repeat (<it>LTR</it>) sequences containing the MMTV superantigen gene (<it>sag</it>) were detected in the malignant tissues of all three family members. The amplified <it>env </it>gene sequences were 98.0%–99.6% homologous to the MMTV <it>env </it>sequences found in the GR, C3H, and BR6 mouse strains. The amplified <it>LTR </it>sequences containing <it>sag </it>sequences segregated to specific branches of the MMTV phylogenetic tree and did not form a distinct branch of their own.</p> <p>Conclusion</p> <p>The presence of MMTV-like DNA sequences in the malignant tissues of all three family members suggests the possibility of MMTV as an etiological agent. Phylogenetic data suggest that the MMTV-like DNA sequences are mouse and not human derived and that the ultimate reservoir of MMTV is most likely the mouse. Although the route by which these family members came to be infected with MMTV is unknown, the possibility exists that such infection may have resulted from a shared exposure to mice.</p

Integration of New Endogenous Mouse Mammary Tumor Virus Proviral DNA at Common Sites in the DNA of Mammary Tumors of C3Hf Mice and Hypomethylation of the Endogenous Mouse Mammary Tumor Virus Proviral DNA in C3Hf Mammary Tumors and Spleens

To understand the molecular mechanisms by which the endogenous murine mammary tumor virus (MuMTV) proviruses are expressed and produce late-occurring mammary tumors in C3Hf mice, we analyzed, by the use of restriction enzymes and the Southern transfer procedure, genomic DNA from normal organs of mammary tumor-bearing and tumor-free mice and from 12 late-occurring C3Hf mammary tumors. We found, by using the restriction enzymes EcoRI and HindIII, that in addition to the preexisting endogenous MuMTV proviruses, new MuMTV-specific proviral DNA was integrated into new sites in the host genome in all 12 of the tumors that we examined. PstI digests of C3Hf tumor DNA revealed that the new proviral DNA found in C3Hf tumors was of endogenous origin. Moreover, the respective sizes of at least one of the new DNA fragments generated by EcoRI or HindIII digestion were the same in at least 50% of the C3Hf tumors analyzed, suggesting that the integration site of this new proviral DNA could be at the same location in the host genome of these tumors. Our results may imply that mammary tumorigenesis in C3Hf mice results from activation of cellular oncogenes by an MuMTV proviral DNA promoter. Specific hypomethylation of MuMTV proviral DNA was detected in the mammary tumors and spleens of C3Hf tumor-bearing mice. Our results indicated that most, if not all, of the hypomethylated MuMTV proviral DNA sequences were derived from the endogenous MuMTV provirus located at the MTV-1 locus, a locus responsible for the production of MuMTV antigens and increased incidence of mammary carcinoma in C3Hf mice. In spleens of non-tumor-bearing mice of ages 3, 6, 9, and 12 months, there was progressive hypomethylation of proviral DNA with increasing age, suggesting a possible correlation between demethylation of MuMTV proviral DNA in the spleens of C3Hf mice and the expression of endogenous MuMTV

A, Ethidium bromide stained 1% agarose gel electrophoresis of amplified MMTV-like sequences; B, Southern blot 13 hybridization of A using 5' Pend-labeled 23-mer probe

Lanes 2, 3 and 4 represent the amplified DNA from the daughter, mother and father respectively. C, Ethidium bromide stained 1.8 % agarose gel electrophoresis of amplified MMTV-like sequences; D, Southern blot [13] hybridization of C using 5' Pend-labeled 20 mer probe. Lanes 2, 3, and 4 represent amplified DNA from mother, daughter and father respectively. In Panels A-D, Lane 1 containing no template DNA and lanes 5, 6, and 7 containing normal breast tissue DNA from three separate individuals represent negative controls for sample contamination. M is the molecular weight marker ΦX174 RF DNA cut with the restriction enzyme .<p><b>Copyright information:</b></p><p>Taken from "Mouse mammary tumor virus (MMTV)-like DNA sequences in the breast tumors of father, mother, and daughter"</p><p>http://www.infectagentscancer.com/content/3/1/2</p><p>Infectious Agents and Cancer 2008;3():2-2.</p><p>Published online 28 Feb 2008</p><p>PMCID:PMC2277433.</p><p></p

The numbers 1, 2 and 3 indicate the three locations where the BR6 strain differs from the GR and C3H strains in this region of the MMTV gene 17,18,19

The and ↓ indicate the location at which the identical single base change described in the text occurs. The numbers 7656 and 7905 indicate the location of the MMTV 250 bp gene sequence within the MMTV genome [17]. Clones are designated as M (mother), D (daughter), and F (father) followed by a number (1–4) denoting the order in which they were cloned. - denotes the same nucleotide.<p><b>Copyright information:</b></p><p>Taken from "Mouse mammary tumor virus (MMTV)-like DNA sequences in the breast tumors of father, mother, and daughter"</p><p>http://www.infectagentscancer.com/content/3/1/2</p><p>Infectious Agents and Cancer 2008;3():2-2.</p><p>Published online 28 Feb 2008</p><p>PMCID:PMC2277433.</p><p></p

Clones are named as M (mother), D (daughter), and F (father) followed by a dash and the letter s for and numbers (1–4) identifying the order in which they were cloned

- denotes the same nucleotide.<p><b>Copyright information:</b></p><p>Taken from "Mouse mammary tumor virus (MMTV)-like DNA sequences in the breast tumors of father, mother, and daughter"</p><p>http://www.infectagentscancer.com/content/3/1/2</p><p>Infectious Agents and Cancer 2008;3():2-2.</p><p>Published online 28 Feb 2008</p><p>PMCID:PMC2277433.</p><p></p

The 12 human MMTV-like sequences from the three family members as well as the human sequences previously isolated from human breast tumors, non-Hodgkin's lymphomas, and primary biliary cirrhosis tissue, clustered with their murine counterparts

Boxes denote sequences from mother (M-S1-4), daughter (D-S1-4), and father (F-S1-4). Previously published human isolates AF346815, AY325271, AF243039, AY652977, AY652968, AY652964, AY652975, AY652974, AY652967, AY652969, AY652973, from human breast tumors [6,16,27], AY652970, AY652976, AY652978, AY652965, AY652971, AY652966, AY652972 from human non-Hodgkin's lymphomas [6], and AF513913, AF513923, from human primary biliary cirrhosis patients [26,27]. The mouse sequences, JYG, FM, and SW21 from Asian mice that were used to root the tree, the endogenous MMTV proviral sequences Mtv-8, Mtv-1, and Mtv-6, and the exogenous MMTV sequences BR6, HEJ, and C3H are bolded. Numbers on branches indicate percent frequencies of assortment in an individual branch after the bootstrap procedure (45) and indicate the robustness of branch assignments. Branch lengths are indicative of the number of nucleotide changes to individual branch points (see scale bar).<p><b>Copyright information:</b></p><p>Taken from "Mouse mammary tumor virus (MMTV)-like DNA sequences in the breast tumors of father, mother, and daughter"</p><p>http://www.infectagentscancer.com/content/3/1/2</p><p>Infectious Agents and Cancer 2008;3():2-2.</p><p>Published online 28 Feb 2008</p><p>PMCID:PMC2277433.</p><p></p