Nucleotide sequence homologies among mouse mammary tumor viruses

Quantitative Comparison of Milk-released C3H and RIII Mammary Tumor Viruses in Infected BALB/c Hosts

The C3H and RIII mammary tumor viruses (MTV) carried by BALB/cfC3H and BALB/cfRIII breeding females have been quantified and compared in milk samples, after partial purification with a sucrose density gradient. The samples were collected at identical times during the first 3 lactation periods from individual mice (6 per strain), standardized for age at delivery and size of litter. Milk samples from 6 MTV negative BALB/c controls have also been analyzed. Data for comparison are expressed in optical density units (ODU) and refer to the protein content of the whole milk using MTV-negative BALB/c milk as blank. The results have shown 1) an increase of MTV released through milk in each MTV-carrying female from the first (average ODU, 0.542) to the second (1.351) and third (2.105) lactation, 2) individual variations, and 3) a significant difference in release between C3H and RIIl MTV, the latter being more than double (average ODU, 1.801) in respect to the former (0.847). The apparent discrepancy between these results and the bioactivity in BALB/c mice of C3H and RIII MTV, significantly lower for the latter, is discussed.

Evolution of animal models in cancer vaccine development

Advances in cancer vaccine development are facilitated by animal models reflecting key features of human cancer and its interface with host immunity. Several series of transplantable preneoplastic and neoplastic mouse mammary lesions have been used to delineate mechanisms of anti-tumor immunity. Mimicking immune tolerance to tumor-associated antigens (TAA) such as HER2/neu, transgenic mice developing spontaneous mammary tumors are strong model systems for pre-clinical vaccine testing. In these models, HER2 DNA vaccines are easily administered, well-tolerated, and induce both humoral and cellular immunity. Although engineered mouse strains have advanced cancer immunotherapy, basic shortcomings remain. For example, multiple mouse strains have to be tested to recapitulate genetic regulation of immune tolerance in humans. Outbred domestic felines more closely parallel humans in the natural development of HER2 positive breast cancer and their varying genetic background. Electrovaccination with heterologous HER2 DNA induces robust adaptive immune responses in cats. Importantly, homologous feline HER2 DNA with a single amino acid substitution elicits unique antibodies to feline mammary tumor cells, unlocking a new vaccine principle. As an alternative approach to targeted vaccination, non-surgical tumor ablation such as cryoablation induces anti-tumor immunity via in situ immunization, particularly when combined with toll-like receptor (TLR) agonist. As strategies for vaccination advance, non-invasive monitoring of host response becomes imperative. As an example, magnetic resonance imaging (MRI) and positron emission tomography (PET) scanning following administration of tryptophan metabolism tracer [11C]-alpha-methyl-tryptophan (AMT) provides non-invasive imaging of both tumor growth and metabolic activities. Because AMT is a substrate of indoleamine-pyrrole 2,3-dioxygenase (IDO), an enzyme that produces the immune regulatory molecule kynurenine, AMT imaging can provide novel insight of host response. In conclusion, new feline models improve the predictive power of cancer immunotherapy and real-time PET imaging enables mechanistic monitoring of host immunity. Strategic utilization of these new tools will expedite cancer vaccine development.

The chick embryo as an expanding experimental model for cancer and cardiovascular research

A long and productive history in biomedical research defines the chick as a model for human biology. Fundamental discoveries, including the description of directional circulation propelled by the heart and the link between oncogenes and the formation of cancer, indicate its utility in cardiac biology and cancer. Despite the more recent arrival of several vertebrate and invertebrate animal models during the last century, the chick embryo remains a commonly used model for vertebrate biology and provides a tractable biological template. With new molecular and genetic tools applied to the avian genome, the chick embryo is accelerating the discovery of normal development and elusive disease processes. Moreover, progress in imaging and chick culture technologies is advancing real-time visualization of dynamic biological events, such as tissue morphogenesis, angiogenesis, and cancer metastasis. A rich background of information, coupled with new technologies and relative ease of maintenance, suggest an expanding utility for the chick embryo in cardiac biology and cancer research.

Mouse mammary tumor virus and mammary tumorigenesis in wild mice

The current knowledge of the distribution of the mouse mammary tumor virus (MMTV) proviral genomes and the mechanism of mammary tumorigenesis by MMTV in mice, with the main emphasis on Asian feral mice, is reviewed. The relevant earlier discoveries on the mode of MMTV transmission are summarized to provide an outline of the biology of MMTV. Finally, the viral etiology of human breast cancer will be discussed.

Induction of cytotoxic T lymphocytes to murine mammary tumor cells with a Kd-restricted immunogenic peptide

A synthetic peptide E474 SFAVATTAL, derived from the sequence of mouse mammary tumor virus envelope protein, was previously shown to bind class I MHC Kd. Immunization of BALB/c mice with E474 in 50% incomplete Freund's adjuvant (IFA) followed by in vitro stimulation of immune cells with E474-coated antigen-presenting cells resulted in peptide-specific cytotoxic T lymphocytes (CTL). Furthermore, anti-E474 CTL lysed mammary tumor cell lines D2F2 and D2A1, derived from a spontaneous tumor that arose in BALB/c pre-neoplastic hyperplastic alveolar nodule (HAN) D2 line. Expression of Kd by D2A1 and D2F2 cells was verified by flow cytometry, and lysis of D2 tumor cells was blocked by monoclonal antibody 31-34-S, which interacted with the peptide-binding region of Kd, supporting the recognition of E474 in Kd by anti-E474 CTL. Immunization of BALB/c mice with E474 before D2F2 tumor challenge resulted in reduced tumor growth. Therefore, E474 is naturally processed and presented by these tumor cells and can induce anti-tumor immunity.

Restriction endonuclease mapping of the proviral DNA of the exogenous RIII murine mammary tumor virus

Cellular DNA containing integrated murine mammary tumor virus (MuMTV) was isolated from FeI/C6 feline kidney cells and CCL64 mink lung cells infected with milkborne RIII MuMTV. By using restriction enzyme HpaI, intact RIII MuMTV provirus (length, 8.7 kilobases [kb]) was excised from the cellular DNA. Subsequent restriction endonuclease analysis of this HpaI fragment with KpnI, HindIII, EcoRI, BamHI, BglII, PstI, SstI, SalI, and XhoI enabled us to construct a map of the RIII virus genome. A comparison of this map with the maps of the GR and C3H MuMTV's revealed that there are greater sequence differences between the RIII virus and the GR and C3H MuMTV proviruses than there are between the GR and C3H proviruses. The following are features of the restriction map unique to the RIII provirus: the presence of three BamHI and two EcoRI cleavage sites, a HpaI cleavage site in the terminal 3'-5' repeat unit of the provirus, and the absence of an XhoI cleavage site. Another distinguishing feature of the RIII provirus is that the sizes of some of the restriction fragments produced by cleavage of the RIII provirus with PstI are different from the sizes of the fragments obtained by PstI cleavage of the GR and C3H proviruses. Like the GR proviral DNA, the RIII proviral DNA has three SstI (SacI) cleavage sites, whereas the C3H provirus has only two SstI sites. HpaI digestion of MuMTV-infected mink lung cell DNA revealed only one class of provirus (an 8.7-kb fragment); however, we observed several minor classes of RIII proviral DNA in addition to the major class of provirus DNA in infected cat kidney cells. PstI digestion of the HpaI 8.7-kb fragments from both feline and mink cells generated a 3.7-kb DNA fragment identical in size to a PstI-generated fragment that has been found in GR and C3H milkborne virus-infected cells. Although a fragment similar in size to the milkborne 3.7-kb PstI fragment has been found as an endogenous component in many C3H and GR mouse tissues, we did not observe such an endogenous fragment in the RIII mouse strain. Therefore, the 3.7-kb fragment may be useful as a marker for the milkborne RIII MuMTV provirus in RIII mice.

Sequence determination of the 3' end of mouse mammary tumor virus RNA

70S RNA has been prepared from mouse mammary tumor virus (MMTV) produced by the GR tumor cell line. After denaturation for 3 min at 60 degrees C the RNA was applied to a sucrose gradient and molecules sedimenting between 10-16S were selected and passed over an oligo-dT cellulose column. The poly A containing RNA fraction was used as a template for the synthesis of complementary DNA with reverse transcriptase in the presence of dideoxynucleoside triphosphates. Oligo-nucleotides p(dT)7rG, p(dT)7rA and (p(dT)7rC were tested for their primer activity. Two of the three primers gave readable sequences. This suggests a heterogeneity in the 3' end of the viral RNA, a phenomenon also observed with avian retroviruses. Nucleotides 37-45 from the 3' end are made up of only A's and T's and resemble a Hogness box. This finding could have biological consequences for the transcription of proviral DNA in the unintegrated and integrated state. Instead of the usual AAUAAA sequence present in mRNA's close and in front of the site of polyadenylation we find a sequence AGUAAA.

Number and location of mouse mammary tumor virus proviral DNA in mouse DNA of normal tissue and of mammary tumors

The Southern DNA filter transfer technique was used to characterize the genomic location of the mouse mammary tumor proviral DNA in different inbred strains of mice. Two of the strains (C3H and CBA) arose from a cross of a Bagg albino (BALB/c) mouse and a DBA mouse. The mouse mammary tumor virus-containing restriction enzyme DNA fragments of these strains had similar patterns, suggesting that the proviruses of these mice are in similar genomic locations. Conversely, the pattern arising from the DNA of the GR mouse, a strain genetically unrelated to the others, appeared different, suggesting that its mouse mammary tumor proviruses are located in different genomic sites. The structure of another gene, that coding for beta-globin, was also compared. The mice strains which we studied can be categorized into two classes, expressing either one or two beta-globin proteins. The macroenvironment of the beta-globin gene appeared similar among the mice strains belonging to one genetic class. Female mice of the C3H strain exogenously transmit mouse mammary tumor virus via the milk, and their offspring have a high incidence of mammary tumor occurrence. DNA isolated from individual mammary tumors taken from C3H mice or from BALB/c mice foster nursed on C3H mothers was analyzed by the DNA filter transfer technique. Additional mouse mammary tumor virus-containing fragments were found in the DNA isolated from each mammary tumor. These proviral sequences were integrated into different genomic sites in each tumor.

Integration of the DNA of mouse mammary tumor virus in virus-infected normal and neoplastic tissue of the mouse

We have used restriction endonucleases which cleave the DNA of mouse mammary tumor virus (MMTV) at one site (Eco RI) and several sites (Pst I, Sac I and Bam HI) to study infection and mammary tumorigenesis in mice. Proviruses acquired during infection of BALB/c mice foster-nursed by virus-producing C3H females can be distinguished from the MMTV proviruses endogenous to uninfected BALB/c mice by the nature of the fragments generated with Pst I and Bam HI. Using this assay, we show that lactating mammary glands as well as mammary tumors from BALB/cfC3H mice have acquired MMTV DNA, and that a minimum of approximately 10% of normal glandular cells can be infected. The new proviruses appear to be linked to cellular DNA of mammary tumors and infected lactating mammary glands within a limited region (0.2 x 10(6) daltons) of the viral DNA; the location of this region, based upon mapping studies with unintegrated MMTV DNA, suggests that the orientation of these proviruses is colinear with linear DNA synthesized in infected cells and thus approximately colinear with the viral RNA. Comparisons of many mammary tumors and studies of lactating mammary glands with a high proportion of independently infected cells indicate that a large number of sites in the cellular genome can accommodate a new provirus; the acquired proviruses are rarely, if ever, found in tandem with each other or with endogenous proviruses. We cannot, however, distinguish between random integration and integration into a large number of preferred sites in the host genome. Since Eco RI and Bam HI cleavage of DNA from each mammary tumor generates a unique set of viral-specific fragments, we propose that the tumors are composed principally of cells derived from a subset of the many infected cells in a mammary gland; this proposal is supported by our finding that Eco RI digestion of DNA from several transplants of a primary tumor yields the pattern characteristic of the primary tumor.

Regulation of mouse mammary tumor virus gene expression by glucocorticoid hormones

Several laboratories have documented that glucocorticoid hormones markedly stimulate the expression of mouse mammary tumor virus genes in a variety of mouse mammary tumor cells and in infected heterologous cells. The effect of the hormone appears to be a rapid and specific augmentation of the synthesis of viral RNA, mediated by interaction with glucocorticoid receptor proteins. The availability of virus-specific reagents and recent developments in the molecular biology of RNA tumor viruses now permit a highly refined analysis of hormonal regulation in this experimental system.