Stability of Characters of Mammary Tumors in Balb/cfRIII Mice

The biological and morphological characteristics of mammary tumors in BALB/c mice infected with RIII mammary tumor virus (MTV) by foster nursing have substantially kept stable and unchanged after 20 years, 53 inbred generations and transfer of the strain from Perugia to Pisa. This suggests that the causal MTV keeps unaltered in time its biological properties.

Solid tumors provide niche-specific conditions that lead to preferential growth of Salmonella

Therapeutic attenuated strains of Salmonella Typhimurium target and eradicate tumors in mouse models. However, the mechanism of S. Typhimurium for tumor targeting is still poorly understood. We performed a high-throughput screening of single-gene deletion mutants of S. Typhimurium in an orthotopic, syngeneic murine mammary model of breast cancer. The mutants under selection in this system were classified into functional categories to identify bacterial processes involved in Salmonella accumulation within tumors. Niche-specific genes involved in preferential tumor colonization were identified and exemplars were confirmed by competitive infection assays. Our results show that the chemotaxis gene cheY and the motility genes motAB confer an advantage for colonization of Salmonella within orthotopic syngeneic breast tumors. In addition, eutC, a gene belonging to the ethanolamine metabolic pathway, also confers an advantage for Salmonella within tumors, perhaps by exploiting either ethanolamine or an alternative nutrient in the inflamed tumor environment.

Attenuated Salmonella enterica Typhimurium reduces tumor burden in an autochthonous breast cancer model

BACKGROUND/AIM

Cancer treatment with attenuated Salmonella enterica Typhimurium (S. Typhimurium) has gained momentum in recent years. However, the effectiveness of this treatment has not been explored in autochthonous models. We report the efficacy of S. Typhimurium in mice with autochthonous mammary tumors.

MATERIALS AND METHODS

S. Typhimurium attenuated by deletion of cyclic adenosine monophosphate signaling, SalpNG.1, was injected into female BALB-neuT tumor-bearing mice. Mice were monitored for efficacy and sacrificed for mechanistic studies.

RESULTS

In treated mice, seven-week post-treatment tumor burden was reduced by 85% and median survival was increased by 88%. Efficacy was correlated with increased tumor-infiltrating CD8 and natural killer cells. In addition, SalpNG.1 treatment caused a systemic increase of monocytic myeloid-derived suppressor cells that accumulated to high numbers within tumor tissue. Bacteria were not detected in tumor tissue, suggesting that the observed efficacy was due to a systemic rather than a tumor-specific effect of the bacteria.

CONCLUSION

S. Typhimurium treatment reduces tumor burden and increases survival in an autochthonous breast cancer model.

The int genes in mouse mammary tumorigenesis and in normal development

In mice, the mouse mammary tumour virus causes tumours by insertional activation of host cell oncogenes. By the application of transposon tagging techniques, several cellular oncogenes, called int, have been discovered. The int-1 gene encodes a cysteine-rich protein with a signal peptide, suggesting that it may act as an extracellular growth or differentiation factor. Normally, the int-1 gene is expressed in early embryogenesis of the mouse, in particular in the developing nervous system. The essential role of int-1 in embryogenesis is underscored by its high degree of homology with the Drosophila segment polarity gene wingless, a gene involved in pattern formation in segments of the developing fly. In Drosophila, the int-1/wingless gene appears to encode a secreted factor, as concluded from antibody staining experiments. The int-4 gene is not yet fully characterized at the molecular level. From its expression pattern, however, we have concluded that int-4 may also act in the control of embryogenesis: the gene is expressed only during specific time intervals in mouse embryos and it is highly conserved in evolution.

Tumor-specific colonization, tissue distribution, and gene induction by probiotic Escherichia coli Nissle 1917 in live mice

Systemic administration of microorganisms into tumor-bearing mice revealed preferential accumulation in tumors in comparison to clearance in organs such as spleen and liver. Here we compared the efficiency of tumor-specific colonization of pathogenic Salmonella typhimurium strains 14028 and SL1344 to the enteroinvasive Escherichia coli 4608-58 strain and to the attenuated Salmonella flexneri 2a SC602 strain, as well as to the uropathogenic E. coli CFT073, the non-pathogenic E. coli Top10, and the probiotic E. coli Nissle 1917 strain. All strains colonized and replicated in tumors efficiently each resulting in more than 1 x 10(8) colony-forming units per gram tumor tissue. Colonization of spleen and liver were significantly lower when E. coli strains were used in comparison to S. typhimurium and the non-pathogenic strains did not colonize those organs at all. Further investigation of E. coli Nissle 1917 showed that no drastic differences in colonization and amplification were seen when immunocompetent and immunocompromised animals were used, and we were able to show that E. coli Nissle 1917 replicates at the border of live and necrotic tumor tissue. We also demonstrated exogenously applied L-arabinose-dependent gene activation in colonized tumors in live mice. These findings will prepare the way for bacterium-mediated controlled protein delivery to solid tumors.

Innate Immune Inflammatory Response against Enteric Bacteria Helicobacter hepaticus Induces Mammary Adenocarcinoma in Mice

Inflammation associated with bacterial infections is a risk factor for cancers in humans, yet its role in breast cancer remains poorly understood. We have previously shown that innate immune inflammatory response against intestinal bacteria is sufficient to induce colon cancer. Here we report that infecting Rag2-deficient C57BL/6 Apc(Min/+) mice with an intestinal bacterial pathogen, Helicobacter hepaticus, significantly promotes mammary carcinoma in females and enhances intestinal adenoma multiplicity by a tumor necrosis factor alpha (TNFalpha)-dependent mechanism. The mammary and intestinal tumor development as well as the increase in proinflammatory mediators is suppressed by adoptive transfer of interleukin 10-competent CD4+CD45RB(lo)CD25+ regulatory (T(R)) cells. Furthermore, prior exposure of donor mice to H. hepaticus significantly enhances antitumor potency of their T(R) cells. Interestingly, these microbially experienced T(R) cells suppress tumorigenesis more effectively in recipient mice irrespective of their tumor etiology. These data suggest that infections with enteric pathogens enhance T(R)-cell potency and protect against epithelial cancers later in life, potentially explaining paradoxical increases in cancer risk in developed countries having more stringent hygiene practices. The possibility that dysregulated gut microbial infections in humans may lead to cancer in anatomically distant organs, such as breast, highlights the need for novel immune-based strategies in cancer prevention and treatment.

Optimization of tumor-targeted gene delivery by engineered attenuated Salmonella typhimurium

BACKGROUND

Attenuated Salmonella typhimurium has been demonstrated as a potential gene delivery vector. Previous findings induce the necessity to optimize tumor selectivity and bacterial dosing in relation to tumor volume and intratumoral therapeutic gene expression.

MATERIALS AND METHODS

Attenuated Salmonella VNP20009 and VNP20047 (expressing cytosine deaminase) were systemically administered to tumor-bearing rats. The bacteria were quantified in tumor and normal organs. Conversion of 5-fluorocytosine to 5-fluorouracil was evaluated using thin layer chromatography.

RESULTS

Tumor colonization efficiency was dependent on Salmonella density, administration route and tumor volume. Colonization of normal tissues gradually decreased with time, while intratumoral proliferation of bacteria remained high during the follow-up period. The Optimal Therapeutic Dose (OTD) was found to be 5.10(7) cfu/rat. Intratumoral VNP20047-expressed CDase leading to the conversion of 5-FC to 5-FU was detected in vivo.

CONCLUSION

Our results indicate the need to define an OTD, probably for each species, when using genetically engineered Salmonella as a tumor- and species-selective vector in cancer therapy.

[Antitumor cross-resistance of trichinosis]

Our experiments were concerned with formation of antitumor cross-resistance by Trichinella spiralis infection in rats. Prophylactic infection was followed by an insignificant decrease in the number of 3,4-benzpyrene-induced malignant fibrous histiocytoma. It also inhibited mammary gland cancer induced by 7,12-dimethylbenzo(a)anthracene. No significant influence on the formation of fibroadenomas as a side effect was reported.

Coexpression of exogenous and endogenous mouse mammary tumor virus RNA in vivo results in viral recombination and broadens the virus host range

Mouse mammary tumor virus is a replication-competent B-type murine retrovirus responsible for mammary gland tumorigenesis in some strains of laboratory mice. Mouse mammary tumor virus is transmitted horizontally through the milk (exogenous or milk-borne virus) to susceptible offspring or vertically through the germ line (endogenous provirus). Exogenously acquired and some endogenous mouse mammary tumor viruses are expressed at high levels in lactating mammary glands. We show here that there is packaging of the endogenous Mtv-1 virus, which is expressed at high levels in the lactating mammary glands of C3H/HeN mice, by the virions of exogenous C3H mouse mammary tumor virus [MMTV(C3H)]. The mammary tumors induced in C3H/HeN mice infected with exogenous MMTV (C3H) virus contained integrated copies of recombinant virus containing a region of the env gene from an endogenous virus. This finding indicates that there was copackaging of the Mtv-1 and MMTV(C3H) RNAs in the same virions. Moreover, because Mtv-1 encodes a superantigen protein with a V beta specificity different from that encoded by the exogenous virus, the packaging of Mtv-1 results in an infectious virus with a broader host range than MMTV(C3H).

Dietary regulation of mammary tumorigenesis in RIII/Sa mice: investigation of a possible mechanism

The effects of caloric restriction on the incidence of mammary tumor development, the levels of the expression of mouse mammary tumor virus (MMTV)- and prolactin-RNA, as well as the levels of serum prolactin, were investigated in virgin RIII/Sa mice, a strain known to display a high incidence of spontaneous mammary tumor development. Of the 54 mice fed a low-calorie (LC; 10 kcal/day) diet containing low fat (LF; 5% corn oil) for a period of 72 weeks, only seven mice were found to develop mammary tumors, an incidence of 13%. By contrast, the cumulative tumor incidence in a similar sized group of mice, fed a high-calorie (HC; 16 kcal/day) low fat-containing diet was 73%. Estimation of the relative levels of MMTV-RNA, as determined by Northern and slot blot hybridizations, in the mammary glands of mice fed LCLF and HCLF diets for 8, 10, 16, 28, and 36 weeks revealed that the LCLF diet-fed mice expressed 4-15-fold less RNA than the HCLF diet-fed mice. Interestingly, however, the LCLF diet did not appear to exert any effect on the expression of prolactin RNA even though it reduced the levels of serum prolactin. We suggest that in RII/Sa mice the modulation of MMTV-induced mammary tumors by dietary calorie is linked to the secretion of serum prolactin which, in turn, affects the replication of MMTV required for mammary cell transformation.

Activation of natural killer cells by mouse mammary tumor virus C4 in BALB/c and T-cell receptor V beta 2-transgenic mice

Lymphocytic infiltrates of BALB/c C4 hyperplastic alveolar nodule (HAN) have elevated natural killer (NK) activity, which correlates positively with the progression of C4 HAN to tumor: C4 HAN produces an infectious mouse mammary tumor virus, MMTV(C4), which encodes a superantigen that activates and deletes T-cells with the V beta 2 segment in the T-cell receptor. In this report, NK activation by both MMTV(C4) and MMTV(C4) superantigen was tested. NK activity was measured in naive BALB/c mice, BALB/c mice depleted of V beta 2+ T-cell, or V beta 2-transgenic mice after they received injections of either purified MMTV(C4) or MMTV(C4)-infected splenocytes. Elevated NK activity was observed in BALB/c mice receiving MMTV(C4) or MMTV(C4)-infected splenocytes. Depletion of V beta 2+, but not V beta 8+, T-cells by specific anti-V beta hybridoma before injection of MMTV(C4)-infected cells reduced but did not eliminate NK activation. NK activation in V beta 2-transgenic mice occurred before massive CD4 T-cell deletion took place and was more pronounced than that in the nontransgenic littermates. These results indicate that MMTV activates NK cells through superantigen-dependent and -independent pathways and supports the role of MMTV(C4) in the augmented NK activity observed in C4 HAN infiltrates. The progression of C4 HAN to tumor represents a model system for the analysis of how tumorigenesis may be affected by lesion-associated viruses.

Mammary tumorigenesis and metastasis in transgenic mice

The transgenic mouse has emerged as an important model system to assess the transforming potential of oncogenes in the mammary epithelium. Mammary gland-specific expression of oncogenes in transgenic mice has resulted in the induction of a variety of phenotypes ranging from benign epithelial hyperplasias to metastatic mammary tumors. The induction of tumors in most of these transgenic models is a multi-step process where transgene expression, although required, is not sufficient for conversion of the primary mammary epithelial cell to the transformed phenotype. While the identity of many of these collaborating genetic events is obscure, several approaches have been applied with might shed light on their nature. In a few exceptional transgenic strains, tumor progression can occur very rapidly suggesting that, if additional genetic events are required, they occur very frequently. Recent genetic and biochemical characterization of these strains offers insight into the molecular mechanisms that may underlie the complex phenotypic features exhibited by these transgenic strains.

Pregnancy dependence of mammary tumours in DDD mice congenic for Mtv-2, DDD/1-Mtv-2/Mtv-2

Mammary tumours developed in 110 (95.7%) of 115 DDD/1-Mtv-2/Mtv-2 (DDD/1-Mtv-2) and 24 (47.1%) of 51 DDD/1fDDD/1-Mtv-2 (DDD/1fMtv-2) force-bred female mice during a one-year period. The mean tumour age +/- SE was 220 +/- 7 and 269 +/- 7 days, respectively. These tumours were examined for responsiveness to pregnancies by comparing their growth after transplantation between virgin and breeding recipients. Of 73 tumours from DDD/1-Mtv-2 mice, 9 (12%) were completely pregnancy-dependent (CPD), 3 (4%) pregnancy-dependent (PD), 9 (12%) pregnancy-responsive (PR), and 52 (71%) pregnancy-independent (PI), and of 25 tumours from DDD/1fMtv-2 mice, one (4%) was CPD, one (4%) PR, and 23 (92%) PI. Although most tumours were heterogeneous in morphology and there was no clear relation between morphology and PD properties, most CPD tumours were type P and considered to be connected with mammary plaques. When 9 CPD tumours from DDD/1-Mtv-2 mice were serially transplanted in breeders, 6, 2 and one progressed to lose pregnancy dependence within 3, 8 and 18 generations, respectively. DDD/1-Mtv-2 mice will provide a model for studies on progression of mammary tumours from hormone-dependent to autonomous states.

A new infectious mammary tumor virus in the milk of mice implanted with C4 hyperplastic alveolar nodules

We have previously characterized an infectious mouse mammary tumor virus [(MMTV(SW)] which induces a strong superantigen response in vivo. Here we describe the isolation and characterization of MMTV(C4) which was derived from milk of mice implanted with hyperplastic alveolar nodules. MMTV(C4) stimulates V beta 2 expressing T cells after local injection in vivo. Comparison with known open reading frame (orf) sequences revealed high homology to Mtv-6, an endogenous virus interacting with V beta 3-expressing T cells. The carboxyl-terminal amino acids were, however, altered. High homology including the carboxyl-terminal orf amino acids were found with MMTV(C3H-K). We show here that MMTV(C3H-K) has lost its superantigen function. Sequence comparisons permitted the characterization of few key amino acids which could be important for T cell receptor interaction and superantigen processing.

Lipids alter the level and distribution of mouse mammary tumor virus gp52 in vitro

Linoleic acid, cholesterol, dexamethasone and progesterone were tested by immunocytochemistry and immunoprecipitation for their single and combined effects in vitro on mouse mammary tumor virus (MMTV) gp52 distribution among three compartments: cell-associated antigen, extracellular virus particles and extracellular shed antigen unassociated with virus particles. Results indicated that all additives significantly increased total MMTV gp52 levels and altered the distribution. Linoleic acid and dexamethasone induced the greatest relative proportion of extracellular gp52, whereas cholesterol and progesterone induced the greatest proportion of cell-associated gp52. The implications of these findings for the immune response to mammary tumors is discussed.

Role of the gene on trisomic and pentasomic chromosome 13 in murine mammary tumorigenesis

To study a possible role(s) played by the trisomy and pentasomy of chromosome 13 in murine mammary tumors, we examined, in eight cloned established cell lines derived from a single BALB/c mammary tumor induced by MTV, a correlation between the presence of trisomy or pentasomy 13 and transformation parameters and in vivo tumorigenicity in syngeneic mice. We found that cell lines with a higher incidence of trisomy or pentasomy 13 in cells of diploid and tetraploid chromosome numbers, respectively, grew to a much higher cell density in flasks than did those with low incidence, and they formed tumors in syngeneic BALB/c mice, whereas those with a low incidence of trisomy or pentasomy 13 were poorly tumorigenic. The presence in the tumorigenic cells of trisomy or pentasomy 13 was not correlated with their growth in soft agar. Furthermore, other chromosomes manifested a wide range of copy numbers in the presence of trisomy or pentasomy 13, indicating that no chromosomes counteracted chromosome 13 to prevent the tumorigenicity. In light of the tumorigenic growth of the cells that maintain gene dosage of chromosome 13 at different ploidy levels, the possibility of the yeast G1 cyclin-like roles played by the gene(s) residing on chromosome 13 in murine mammary tumorigenesis is discussed.

Mouse mammary-tumor virus activates Fgf-3/Int-2 less frequently in tumors from virgin than from parous mice

Tumorigenesis by mouse mammary-tumor virus (MMTV) involves proviral disruption and transcriptional activation of a number of cellular oncogenes, generically termed Int. The frequencies with which different Int genes are activated in different mouse strains can be quite variable, and previous surveys have suggested that insertions at Int-2/Fgf-3 occur primarily in strains that develop pregnancy-dependent mammary tumors. To address this issue, we have determined the relative contributions of 5 known Int genes (Wnt-1, Wnt-3, Fgf-3, Fgf-4 and Int-3) in mammary tumors from virgin BR6 and multiparous BR6, BALB/cfBR6 and RIII mice. Whereas Fgf-3 was implicated in 66%, 80% and 92% of the tumors from the respective parous animals, only 20% of the tumors from virgin mice expressed Fgf-3. This reduced involvement of Fgf-3 was compensated by proviral insertions in Fgf-4, Int-3 and Wnt-3, but the frequency of Wnt-1 activation was relatively constant. These data strengthen the link between Fgf-3 and a pregnancy-dependent phenotype and suggest that, in the strains analyzed, the frequency of Int-gene activation was influenced more by the hormonal status than by the genetic background.

Superantigen-induced immune stimulation amplifies mouse mammary tumor virus infection and allows virus transmission

Endogenous and infectious mouse mammary tumor viruses (MMTVs) encode in their 3' long terminal repeat a protein that exerts superantigen activity; that is, it is able to interact with T cells via the variable domain of the T cell receptor (TCR) beta chain. We show here that transmission of an infectious MMTV is prevented when superantigen-reactive cells are absent through either clonal deletion due to the expression of an endogenous MTV with identical superantigen specificity or exclusion due to expression of a transgenic TCR beta chain that does not interact with the viral superantigen. A strict requirement for superantigen-reactive T cells is also seen for a local immune response following MMTV infection. This immune response locally amplifies the number of MMTV-infected B cells, most likely owing to their clonal expansion. Collectively, our data indicate that a superantigen-induced immune response is critical for the MMTV life cycle.

Hexadecylphosphocholine differs from conventional cytostatic agents

Alkylphosphocholines, and especially their main representative hexadecylphosphocholine (HPC), show high anticancer activity in methylnitrosourea (MNU)-induced autochthonous rat mammary carcinoma. The regression of MNU-induced rat mammary carcinoma during HPC treatment can be evaluated by computed tomography and sonography. This allows a noninvasive monitoring of therapy in vivo (tumor size, morphology, and blood supply). Both diagnostic modalities can show a rapid concentric decrease in tumor volume as well as the appearance of cystic, scarry, and necrotic areas in the tumor tissue as a result of HPC treatment. In addition, prior to, during and after therapy tumor perfusion can be assessed by color Doppler sonography in vivo. A more than 4-fold difference in HPC efficacy was observed when the colony growth of explanted MNU-induced mammary carcinoma cells was measured in the methylcellulose colony assay (IC50 = 180 mumol HPC/l) and the Hamburger Salmon colony assay (IC50 = 740 mumol HPC/l). In the latter assay, growth of concomitantly seeded untransformed cells, especially of fibroblasts, is much lower than in the methyl-cellulose colony assay. We therefore assume that the antitumor efficacy of HPC against MNU-induced mammary carcinoma is enhanced by neighboring cells such as fibroblasts. Cell culture experiments with the three MNU-induced rat mammary carcinoma cell clones 1-C-2, 1-C-30, and 1-C-32 revealed IC50 values in the range of 50-70 mumol HPC/l. The volume of 1-C-2 cells increased up to 4-fold after 72 h of permanent exposure to 100 mumol HPC/l, a concentration that completely inhibited proliferation of tumor cell numbers without being cytotoxic. Nucleotide triphosphate levels dropped significantly after 24 h and were slowly restored in spite of continued exposure. After 72 h, they nearly reached those levels observed in plateau-phase cells. This suggests that HPC-induced growth inhibition has similarities with physiologically occurring growth arrest. Finally, replication of RNA viruses and DNA viruses was suppressed 30-fold and 7-fold, respectively, at low concentrations of HPC (12 mumol/l), which caused no or negligible growth inhibition in the virus-harboring cells, thus demonstrating specific antiviral activity of HPC. From these observations we conclude that HPC differs in many important aspects from conventional cytostatic agents and is certainly worth following-up in further investigations.

Mouse mammary tumor virus infection accelerates mammary carcinogenesis in Wnt-1 transgenic mice by insertional activation of int-2/Fgf-3 and hst/Fgf-4

Transgenic mice carrying the Wnt-1 protooncogene modified for expression in mammary epithelial cells exhibit hyperplastic mammary glands and stochastically develop mammary carcinomas, suggesting that additional events are necessary for tumorigenesis. To induce such events and to identify the genes involved, we have infected Wnt-1 transgenic mice with mouse mammary tumor virus (MMTV), intending to insertionally activate, and thereby molecularly tag, cooperating protooncogenes. Infection of breeding female Wnt-1 transgenics decreased the average age at which tumors appeared from approximately 4 months to approximately 2.5 months and increased the average number of primary tumors per mouse from 1-2 to > 5. A smaller effect was observed in virgin females, and infection of transgenic males showed no significant effect on tumor latency. More than half of the tumors from the infected breeding group contained one or more newly acquired MMTV proviruses in a pattern suggesting that most cells in tumors arose from a single infected cell. Analyses of provirus-containing tumors for induced or altered expression of int-2/Fgf-3, hst/Fgf-4, int-3, and Wnt-3 showed activation of int-2 in 39% of tumors, hst in 3%, and both int-2 and hst in 3%. DNA analyses with probes for protooncogenes and MMTV confirmed that the activations resulted from proviral insertions. There was no evidence for proviral insertions at the int-3, Wnt-3, or Wnt-1 loci. These findings provide further evidence that fibroblast growth factors Int-2 and Hst can cooperate with Wnt-1, another secreted factor, in mammary tumorigenesis, and they illustrate the capacity of this system to identify cooperating oncogenes.

Characterization of mammary plaques in DDD mice congenic for Mtv-2 gene, DDD/1-Mtv-2/Mtv-2

DDD/1 mice free from exogenous mouse mammary tumor virus (MMTV) do not develop any neoplastic mammary lesions. In GR mice, the expression of Mtv-2, an endogenous proviral MMTV, leads to 100% incidence of mammary ductal hyperplasias and tumors. An Mtv-2 congenic line, DDD/1-Mtv-2/Mtv-2, was established by introducing Mtv-2 from GR into DDD/1 to elucidate its function. Development of mammary plaques (MPQ) characterized by ductal hyperplasias was investigated in 152 congenic females on day 17 to 19 of the first pregnancy. The incidence of MPQ was 48.0% and most MPQ-positive mice (75.3%) had only one MPQ. Generally, MPQ were small in size: the diameter was as small as < or = 3 mm in 77.6% of them. Of 84 MPQ implanted into intact fat pads, 43 (51.2%), 38 (45.2%) and 3 (3.6%) showed undetectable, pregnancy-dependent and autonomous growths; respectively when the hosts underwent pregnancy. Almost all MPQ produced normal-appearing ductal-alveolar outgrowths in mammary epithelium-divested or cleared fat pads of virgins. MPQ implanted into cleared fat pads were very similar to normal mammary glands in the responses to progesterone (P) and estradiol (E) alone or in combination except for association of ductal hyperplasias in 4 of 12 MPQ under E+P treatment. These findings revealed the preneoplastic nature of MPQ. Exogenous MMTV proviruses were demonstrated in all MPQ. The int-2 DNA rearrangement was found in 2 of 10 MPQ but in none of 9 mammary carcinomas and the int-1 DNA rearrangement in none of 10 MPQ but in 5 of 10 carcinomas. It is thus likely that the Mtv-2 gene participates in a very early stage of mammary tumorigenesis not directly but indirectly through insertion mutation of host genes, while the cellular oncogenes, int-2 and int-1, may contribute to preneoplastic transformation of mammary epithelium and progression from preneoplastic to more malignant states, respectively.

Requirement for the adenovirus type 9 E4 region in production of mammary tumors

Oncogenic viruses demonstrating a strict tropism for the mammary gland provide special opportunities to study the susceptibility of this tissue to neoplasia. In rats, human adenovirus type 9 (Ad9) elicits mammary fibroadenomas that are similar to common breast tumors in women, as well as phyllodes-like tumors and mammary sarcomas. By constructing recombinant adenoviruses between Ad9 and Ad26 (a related nontumorigenic virus), it was shown that the Ad9 E4 region was absolutely required to produce these mammary tumors. This indicates that an adenovirus gene located outside the classic transforming region (E1) can significantly influence the in vivo oncogenicity of an adenovirus. Consistent with a direct role in mammary gland oncogenesis, the Ad9 E4 region also exhibited transforming properties in vitro. Therefore, the Ad9 E4 region is a viral oncogene specifically involved in mammary gland tumorigenesis.

Interferon-alpha/beta in virus-induced mouse mammary carcinogenesis: effects on the spontaneous process and on the progression of transplanted pre-neoplastic lesions

Low levels of anti-viral activity, mainly interferon alpha/beta (IFN-alpha/beta), are regularly found in lymphoid tissues of BALB/c mice infected with the C3H strain of mammary tumor virus. At the time of tumor development, significant amounts of anti-viral activity were detected in homogenates of spleen and mammary tumors, but not in blood and normal mammary glands. This activity is pH2-resistant and neutralized by antibody to IFN/alpha-beta. The pathogenetic role of IFN in mammary carcinogenesis was investigated in 2 ways: (a) by treating virus-infected newborn mice with antibody to IFN-alpha/beta, and (b) by giving either the latter antibody or IFN-alpha/beta to virus-free animals transplanted with pre-neoplastic lesions. Mice were treated only for 2 months, starting either 1 week after birth or immediately after tumor transplant. In case (a), treatment with antibody to IFN-alpha/beta shortened the incubation period of mammary carcinomas and decreased the mean survival time. In case (b), anti-IFN antibody did not significantly affect the development of mammary tumors. However, exogenous IFN-alpha/beta markedly reduced both tumor incidence and mortality rate. These results indicate that endogenous IFN-alpha/beta plays a crucial role in the in vivo restriction of the early infectious phase of spontaneous carcinogenesis and that relatively high doses of IFN-alpha/beta may inhibit the progression of pre-neoplastic lesions.

Characterization of the mammary hyperplasia, dysplasia and neoplasia induced in athymic female adult mice by polyomavirus

We have characterized mammary oncogenesis induced after polyomavirus infection of adult female nude mice regarding histopathogenesis, viral replication and viral and cellular oncogene expression. A unique transient generalized epithelial hyperplasia was observed (starting at 2 weeks post infection), preceding the development of dysplasias (onset 6 weeks post infection) and multiple neoplasias (onset 6 weeks post infection) in all glands. The ductal epithelium was the target for neoplastic transformation, and the occurrence of numerous ductal dysplasias coincided with the appearance of frank tumors. Stromal abnormalities were also seen. Tumor growth was not dependent upon ovarian hormones, and new tumors continued to develop in ovariectomized mice. Viral replication, high although variable, preceded but did not correlate with oncogenesis. Most but not all tumors contained high levels of unintegrated viral DNA. Tumors produced very low levels of live virus. Viral gene expression was markedly increased in the tumors compared with the infected but morphologically normal glands. The expression of c-myc was moderately increased (fourfold); changes in c-int-2 and c-Ha-ras expression were slight and inconsistent, while expression of c-neu and c-int-1 was unchanged.

The diversity of retroviral diseases of the immune system

Retroviruses have been implicated as causative agents for a range of diseases including neoplasia, autoimmunity and immunosuppression. No two retroviruses carry the same complement of genes and for this reason it is not surprising that they induce a variety of different disease states. One common element in retroviral evolution has been the need to avoid immune recognition in order to persist within the host. A comparative approach, looking at various persistent retroviruses, has been used to pin-point the types of genetic adaptations adopted by retroviruses to remain hidden, often within the T cell compartment. Most of these retroviruses are T-cell-tropic and the diseases which they induce usually reflect the effect of the retrovirus on normal lymphocyte function.

Decreasing expression of NM23 gene in metastatic murine mammary tumors of viral etiology (MMTV)

Murine mammary tumors induced by the Murine Mammary Tumor Virus (MMTV) were chosen to study the expression of the NM23 gene during the metastatic process because of their viral etiology, different from that of the previously reported experimental tumor systems. NM23 mRNA levels are higher in non metastatic tumors than in metastatic ones. Moreover, the NM23 expression is higher in tumors induced by the C3H variant of the MMTV than in tumors induced by the RIII variant. These data are a further support to the hypothesis of a basic role of the NM23 gene in the down-regulation of tumor progression.

Augmentation of host resistance to Candida albicans infection in ascites tumor-bearing mice

We found that the number of peripheral blood polymorphonuclear leukocytes (PMN) dramatically increased in both sarcoma 180 (S-180) and MM-46 mammary carcinoma (MM-46) ascites tumor-bearing mice, and mice required a remarkable resistance to Candida albicans infection via intravenous route. When the resistance was determined by number of cells of C. albicans in the kidney, a significant decrease in the number of fungal cells was observed in the kidneys of infected ascites tumor-bearing mice. An increase of active oxygen levels of PMN from ascites tumor-bearing mice was observed, suggesting that this factor is important in developing of resistance in ascites tumor-bearing mice. Additionally, a culture supernatant of tumor cells co-cultivated with bone-marrow cells in vitro increased the number of granulocytes and macrophages differentiated from the bone-marrow cells.

Effects of amphetamine on the development of MTV-induced mammary tumors in female mice

Female C3H/He mice carrying the mammary tumor virus (MTV) were monitored for mammary tumor incidence and latent periods while submitted to a daily subcutaneous injection with amphetamine (0,4 mg/kg/day). Results show that amphetamine caused an increase in incidence and a decrease in latency of tumors compared with placebo. There was also appreciated a correlation with the lethality of mice.

Immunological elimination of infected cells as the candidate mechanism for tumor protection in polyomavirus-infected mice

The uniformly lethal development of mammary tumors in polyomavirus-infected adult female nude mice was prevented by adoptive cell transfer of polyomavirus-immune splenocytes or peritoneal cells. Transferred immune cells also lowered the growth rate of emerging tumors. The induction of other relatively less frequent tumors of the skin and bone was decreased as well. Using in situ hybridization of whole-body sections as well as hybridization of nucleic acids from the mammary glands, we show for the first time that transferred immune cells, but not normal cells, virtually eliminated virus signal in the whole mouse and in the mammary glands. Since infected and tumorous mammary glands produce very little infectious virus, it appears that a major mechanism mediating the prevention of polyomavirus oncogenesis involves the immunological elimination of nonproductively and persistently infected cells.

Tissue distribution of mouse mammary tumor virus (MMTV) antigens and new endogenous MMTV loci in Japanese laboratory mouse strains

The distribution of mouse mammary tumor virus (MMTV) antigens was studied by the immunoperoxidase method in the II-TES and I-TES mouse strains as well as their progenitors, CS and DBA/2 strains. In the II-TES, I-TES and CS strains, and BALB/c mice foster-nursed with these strains, MMTV antigens were found not only in epithelial cells of the mammary glands but also in those of other tissues including the seminal vesicle, vas deferens, epididymis, prostate, parotid, submandibular, lacrimal, sebaceous, and urethral glands. In DBA/2 and BALB/cfDBA/2 mice, however, the MMTV antigens were found only in the mammary glands. Electron microscopic examination showed MMTV particles in these organs. When we examined the presence of Mtv-1 and 2 proviruses, which are known to be responsible for MMTV expression, in the genomes of the II-TES, I-TES, CS and DBA/2 strains by Southern blotting, Mtv-2 was not found in any of the mice and Mtv-1 was found in the II-TES and DBA/2 mice but not in the I-TES and CS mice. Instead, four new endogenous MMTV loci, which have never previously been reported in laboratory mouse strains, were detected in the genomes of the II-TES, I-TES and CS strains. One (designated Mtv-42) was common in the three strains and the other three (designated Mtv-43, 44 and 45) were common in the II-TEX and I-TES strains or the II-TES and CS strains. These results thus suggest that new endogenous MMTV loci may be responsible for MMTV expression in a variety of tissues of these three strains.

The different activation of int genes in mammary carcinomas developed in three mouse strains harboring mouse mammary tumor viruses derived from DD/Tbr

RNA expressions of common integration site (int) genes and several oncogenes were investigated in mammary carcinomas spontaneously developed in different three strains of mice; DD/Tbr, NIH Swiss and BALB/c which harbor DD-MMTV derived from DD/Tbr mouse. Latter two strains of mice were designated NIH/Mtv+ and BALB/Mtv+, respectively. An increased expression of int-1 (wnt-1) and int-2 genes was observed in 56% (9/16) and 50% (8/16) of mammary carcinomas of DD/Tbr mice, respectively. Either int-1 or int-2 RNAs were expressed in 81% (13/16) of the carcinomas of DD/Tbr mice. IN NIH/Mtv+ mice, activation of int-1 and int-2 was observed in 41% (7/17) and 24% (4/17) of mammary carcinomas, respectively. Either int-1 or int-2 RNAs were expressed in 47% (8/17) of the carcinomas examined in this strain. In BALB/Mtv+ mice, on the other hand, either int-1 or int-2 gene were transcribed into RNAs at low frequency (33%: 3/9). These results suggest that the frequency of activation of int genes in mammary carcinomas induced by the same DD-MMTV in three strains of mice is genetically defined characteristics of these strains, and that the involvement of int-1 and int-2 genes in virus-induced mammary carcinogenesis may be influenced by genetic properties of animals. The activation of int-1 and int-2 genes did not clearly correlate with an increase in the expression of oncogenes examined; H-ras, K-ras, N-ras, myc, raf, fgr, fms, erB, mos, and src genes.

Host genetic background effect on the frequency of mouse mammary tumor virus-induced rearrangements of the int-1 and int-2 loci in mouse mammary tumors

The frequency with which int-1 and int-2 are rearranged in mouse mammary tumors by mouse mammary tumor virus (MMTV)-induced insertional mutagenesis is a consequence of the host genetic background. In 75% of C3H mammary tumors, int-1 is rearranged by MMTV insertion, whereas only 30% of BALB/cfC3H tumors contain a virus-induced rearrangement of int-1. This difference is significant (P less than 0.005) and could not be accounted for by the potentially additive effect of the genetically transmitted Mtv-1-encoded virus in C3H mice. Similarly, MMTV-induced rearrangement of the int-2 gene in mammary tumors of the R111 mouse strain (59%) occurred at a significantly (P less than 0.025) higher frequency than in BALB/cfR111 (25%) mammary tumors. Moreover, in BALB/cfR111 mammary tumors, there is evidence that rearrangement of int-1 and int-2 does not occur independently (P less than 0.025). These results suggest that the long history of inbreeding for high tumor incidence of C3H and R111 mouse strains has selected for the fixation of host mutations which either complement the action of the particular int gene or affect the sensitivity of specific subpopulations of mammary epithelium to infection by particular strains of MMTV.

The mouse biliary glycoprotein gene (Bgp): partial nucleotide sequence, expression, and chromosomal assignment

Transcripts related to the human carcinoembryonic antigen were found in mRNA isolated from both dimethylbenzanthracene-induced and mouse mammary tumor virus-induced mammary tumors. A cDNA library was prepared from a dimethylbenzanthracene-induced tumor, and a clone was isolated by hybridization with a human carcinoembryonic antigen cDNA probe. Its sequence, when compared to those of members of the human carcinoembryonic antigen gene family, was most homologous to the sequence of the human biliary glycoprotein (BGP) gene. Thus, this clone appears to encode a portion of the mouse biliary glycoprotein gene. Southern blot analysis of EcoRI-digested mouse cellular DNA with this probe detected four restriction fragments, all of which appear to be located on mouse chromosome 7, Northern blot analysis using the mouse probe demonstrated that related mRNA species were expressed in some normal adult mouse tissues.

Establishment and characterization of immortalized non-transplantable mouse mammary cell lines cloned from a MMTV-induced tumor cell line cultured for a long duration

During the culturing of a mouse mammary tumor cell line, MuMT73, maintained in vitro for more than a decade, we found morphological heterogeneity in its cells; some showed contact inhibition in their growth, some formed domes and some grew criss cross and piled up. In trying to clone the cell line to isolate cells showing contact inhibition or dome formation, we were able to establish six clonal cell lines. These six cell lines were categorically divided into three groups according to their phenotypical behavior, Groups A, B and C. Group A (clones 1, 5 and 7) cells had a property of contact inhibition. They induced no tumor when injected into the subcutaneous tissue of the back, nor even when injected into the mammary fat pads or under the kidney capsule of syngenic or nude mice, and therefore were thought to be non-malignant in nature. They were positively stained by anti-keratin antiserum and had mouse mammary tumor viruses (MMTVs). Group B (clone 6) cells grew in a crisscross pattern and piled up, and they induced tumors when injected into the subcutaneous tissue of the back of mice. Group C (clones 3 and 4) cells formed domes in their growth and induced some tumors in the mammary fat pads and under the kidney capsule of KSN nude mice. In Southern blots with MMTV-env probe, numerous exogenous MMTV proviruses were detected in these cell lines. The insertion patterns of these proviruses in cells of non-malignant clonal lines (Group A) resembled those of malignant lines (Group B), except one band (about 26 Kb), but were considerably different from those of intermediate lines (Group C). On the other hand, no difference was detected in Southern blots with int-1 or int-2 probes among the non-malignant, intermediate and malignant clonal cell lines.

Effects of energy restriction on mouse mammary tumor virus mRNA levels in mammary glands and uterus and on uterine endometrial hyperplasia and pituitary histology in C3H/SHN F1 mice

We investigated the effects of energy restriction on the pituitary-ovarian axis and on a hormone responsive gene, the mouse mammary tumor virus (MMTV). Female C3H/SHN F1-hybrid mice, known to display a high incidence of mammary tumors, ate an energy-restricted diet (48 kcal/wk) or a control diet (95 kcal/wk) beginning at the time of weaning. By 67 wk of age, 12 of 32 mice in the control group, but none of the 33 mice in the energy-restricted group, had developed mammary tumors. Six tumor-free mice from each group were studied in detail at 67 wk of age. All six tumor-free control mice, but none of the six energy-restricted mice, showed uterine endometrial hyperplasia at autopsy. Mice subjected to energy restriction did not display an estrous cycle. The average levels of MMTV mRNA in mammary glands and uteri were strongly reduced by energy restriction. MMTV mRNA levels in mammary glands from control mice were two orders of magnitude lower than those in mammary tumors. Energy restriction lowered the percentage of pituitary mammatropes and suppressed proliferation of mammatropes with advancing age. Energy restriction thus appeared to inhibit endometrial hyperplasia and to decrease MMTV production at the mRNA level in the mammary glands and in the uterus. These effects may be a consequence of hormonal changes originating at the pituitary-ovarian axis.

Wnt-3, a gene activated by proviral insertion in mouse mammary tumors, is homologous to int-1/Wnt-1 and is normally expressed in mouse embryos and adult brain

We have isolated a common insertion site, Wnt-3, for proviruses of the mouse mammary tumor virus (MMTV). Of mammary tumors induced by the GR variant of MMTV, 5% contains a provirus at Wnt-3, which is located on mouse chromosome 11. The gene is transcribed into a 3.8-kilobase (kb) mRNA in tumors with nearby proviral insertions but not in tumors with proviruses at other loci or in most adult tissues. Normal expression of Wnt-3 is detected in mouse embryos (with a peak around day 12 of gestation) and at low levels in adult brain. The transcriptional unit of the Wnt-3 gene spans approximately 55 kb, with a first intron of 36 kb. The deduced amino acid sequence of the Wnt-3 protein is 47% identical to the int-1/Wnt-1 gene product.

Differentiation-dependent expression of provirus-activated int-1 oncogene in clonal cell lines derived from a mouse mammary tumor

The int-1 mammary oncogene is frequently activated by proviral insertion in mouse mammary tumors. To characterize the target cell for the oncogenic action of int-1, we have isolated permanent cell lines with distinct morphologies and differentiation characteristics, starting from a tumor with a rearranged int-1 gene. Polygonal cells had retained many differentiation markers of epithelial cells and produced adenocarcinomas upon transplantation in syngenic mice. Sphere-forming-cuboidal cells are poorly differentiated and produced anaplastic tumors. Cuboidal and elongated cells were negative for epithelial markers. Cuboidal cells were poorly tumorigenic, but elongated cells produced highly malignant sarcoma-like tumors. In all lines, the int-1 gene was identically rearranged due to insertion of proviral DNA of the Mouse Mammary Tumor Virus, but the expression of int-1 varied with the state of differentiation of the cells. Polygonal cells contained relatively high levels of int-1 RNA, which were not influenced by steroid hormones. In the sphere-forming-cuboidal cells, expression of int-1 was low but inducible by dexamethasone. In the cuboidal and elongated cells no expression of int-1 was detectable, showing that the continued expression of int-1 was not required for progression to more malignant cells. By immunoprecipitation, two int-1 protein species, of 42 and 40 kD were identified in polygonal and in sphere-forming-cells but not in the culture media.

Suppression of mouse mammary tumor proviral DNA and protooncogene expression: association with nutritional regulation of mammary tumor development

Chronic energy intake restriction (CEIR) reduces mouse mammary tumor virus (MMTV)-induced mammary tumors in C3H/Ou mice. Fewer than 10% of C3H/Ou mice developed mammary tumors during 88 wk of study when subjected to CEIR regardless of calorie source (fat vs. carbohydrate). By contrast, 100% of mice fed ad libitum diets relatively high in fat or carbohydrate or a commercial diet developed tumors by 35-40 wk. MMTV proviral DNA transcription was shown to be activated in spleen, liver, lung, kidney, small intestine, and mammary gland of mice consuming these diets ad libitum. By contrast, these messages were suppressed by CEIR in all tissues analyzed except spleen. MMTV proviral messages in liver and mammary gland increased with age in full-fed mice and were suppressed by CEIR. These findings suggest that the nutritional regulation of MMTV proviral DNA expression is tissue-specific. In CEIR mice the suppressed MMTV proviral DNA transcripts in mammary gland and liver increased with time in association with the delayed onset of mammary tumors. Mammary tumorigenesis in C3H mice is associated with integration of MMTV proviral DNA, which appears to activate a putative mammary tumor protooncogene, int-1. CEIR apparently decreases the frequency of viral reintegration adjacent to the int-1 gene and thus inhibits expression of int-1 and probably an initiation step in mammary tumorigenesis. Expression of other putative protooncogenes, int-2 and ras, in liver tissue was also reduced by CEIR. These findings indicate that both initiation and promotion of mammary tumorigenesis are influenced by CEIR in C3H/Ou mice.

Estradiol dependence of the specific mammary tissue targeting of polyoma virus oncogenicity in nude mice

We have previously reported (Berebbi et al., 1988) that in athymic nude mice, Polyoma virus induces mammary adenocarcinomas (MAC) at high frequency and exclusively in females. In the present study we show that in nude mice: (1) Ovariectomy results in a reduced frequency of MAC and a longer latency period of induction. When testosterone is administered to ovariectomized females, tumor induction is drastically reduced. (2) When estradiol is administered continuously to ovariectomized females the incidence and kinetics of MAC induction are the same as in control females. (3) MAC are induced in castrated males administered with estradiol although only osteosarcomas are observed in control males. (4) The tumor cells are found to harbor functional estradiol and progesterone receptors. (5) MAC can be transplanted from females to males, indicating that tumor growth is estradiol independent. (6) Estradiol is required only between day 10 and day 20 following polyoma injection, whereas the first tumors are detected only around day 60. Our results indicate that MAC induction by Polyoma virus in nude mice is estradiol-dependent during a short initiation period and that tumor progression is estradiol-independent in spite of the fact tumor cells carry functional estradiol and progesterone receptors.

Insertion mutation of the int-1 and int-2 loci by mouse mammary tumor virus in premalignant and malignant neoplasms from the GR mouse strain

Mouse mammary tumor virus (MMTV)-induced mammary adenocarcinomas can develop from several different premalignant precursors common in GR mice. Insertion mutagenesis of the mammary protooncogenes int-1 and int-2 was studied in this multistep system by analyzing samples from various stages of neoplastic development for novel int-1 and int-2 restriction fragments generated by MMTV provirus integration. int-1 and int-2 insertion mutations were observed in both premalignant lesions and malignant tumors. Some of the tumors with insertion mutations were experimentally derived from insertion mutation-free premalignant precursors. Each class of neoplasm examined had a characteristic frequency of int-1 and int-2 insertion mutations; however, no correspondence was observed between neoplasm morphology and mutation of either gene. These results indicate that insertion mutation of the int-1 and int-2 loci by MMTV provirus can be involved in the earliest identifiable stages of neoplastic development as well as during progression of premalignant lesions to tumors. Insertion mutation of int-1 and int-2 is therefore not stage specific in this system.