Clonal isolation of different strains of mouse mammary tumor virus-like DNA sequences from both the breast tumors and non-Hodgkin's lymphomas of individual patients diagnosed with both malignancies

Exploring the link between viruses and cancer in companion animals: a comprehensive and comparative analysis

Currently, it is estimated that 15% of human neoplasms globally are caused by infectious agents, with new evidence emerging continuously. Multiple agents have been implicated in various forms of neoplasia, with viruses as the most frequent. In recent years, investigation on viral mechanisms underlying tumoral transformation in cancer development and progression are in the spotlight, both in human and veterinary oncology. Oncogenic viruses in veterinary medicine are of primary importance not only as original pathogens of pets, but also in the view of pets as models of human malignancies. Hence, this work will provide an overview of the main oncogenic viruses of companion animals, with brief notes of comparative medicine.

Life after Cleavage: The Story of a β-Retroviral (MMTV) Signal Peptide-From Murine Lymphoma to Human Breast Cancer

An increasing body of evidence in recent years supports an association of the betaretrovirus mouse mammary tumor virus (MMTV) with human breast cancer. This is an issue that still raises heated controversy. We have come to address this association using the signal peptide p14 of the MMTV envelope precursor protein as a key element of our strategy. In addition to its signal peptide function, p14 has some significant post endoplasmic reticulum (ER)-targeting characteristics: (1) it localizes to nucleoli where it binds key proteins (RPL5 and B23) involved (among other activities) in the regulation of nucleolar stress response, ribosome biogenesis and p53 stabilization; (2) p14 is a nuclear export factor; (3) it is expressed on the cell surface of infected cells, and as such, is amenable to, and successfully used, in preventive vaccination against experimental tumors that harbor MMTV; (4) the growth of such tumors is impaired in vivo using a combination of monoclonal anti-p14 antibodies or adoptive T-cell transfer treatments; (5) p14 is a phospho-protein endogenously phosphorylated by two different serine kinases. The phosphorylation status of the two sites determines whether p14 will function in an oncogenic or tumor-suppressing capacity; (6) transcriptional activation of genes (RPL5, ErbB4) correlates with the oncogenic potential of MMTV; (7) finally, polyclonal anti-p14 antibodies have been applied in immune histochemistry analyses of breast cancer cases using formalin fixed paraffin-embedded sections, supporting the associations of MMTV with the disease. Taken together, the above findings constitute a road map towards the diagnosis and possible prevention and treatment of MMTV-associated breast cancer.

The Viral Origin of Human Breast Cancer: From the Mouse Mammary Tumor Virus (MMTV) to the Human Betaretrovirus (HBRV)

A Human Betaretrovirus (HBRV) has been identified in humans, dating as far back as about 4500 years ago, with a high probability of it being acquired by our species around 10,000 years ago, following a species jump from mice to humans. HBRV is the human homolog of the MMTV (mouse mammary tumor virus), which is the etiological agent of murine mammary tumors. The hypothesis of a HMTV (human mammary tumor virus) was proposed about 50 years ago, and has acquired a solid scientific basis during the last 30 years, with the demonstration of a robust link with breast cancer and with PBC, primary biliary cholangitis. This article summarizes most of what is known about MMTV/HMTV/HBRV since the discovery of MMTV at the beginning of last century, to make evident both the quantity and the quality of the research supporting the existence of HBRV and its pathogenic role. Here, it is sufficient to mention that scientific evidence includes that viral sequences have been identified in breast-cancer samples in a worldwide distribution, that the complete proviral genome has been cloned from breast cancer and patients with PBC, and that saliva contains HBRV, as a possible route of inter-human infection. Controversies that have arisen concerning results obtained from human tissues, many of them outdated by new scientific evidence, are critically discussed and confuted.

Presence of a mouse mammary tumour virus-like in feline lymphomas: a preliminary study

The mouse mammary tumour virus (MMTV) is implicated in the aetiology of murine mammary carcinomas and a variant of it, the type B leukemogenic virus, can cause murine thymic lymphomas. Interestingly, a MMTV-like virus is suspected to be involved in human breast cancer and feline mammary carcinomas. However, to date, no cases of MMTV-like sequence amplifications have been described in lymphoid neoplasms in veterinary literature. The aim of this study was to investigate the presence of env nucleotide sequences and protein 14 (p14) of a MMTV-like virus in fifty-three feline lymphoma samples. Our results show that MMTV-like sequences were detected in 5/53 tumours (9.4%): three gastrointestinal lymphomas (one B-type diffuse large, one B-type small non-cleaved, and one T-type diffuse mixed lymphoma); and two nasal lymphomas (one B-type diffuse small cleaved lymphoma and one B-type diffuse mixed lymphoma). P14 expression was detected in the cytoplasm, and rarely in nuclei, exclusively of neoplastic cells from PCR-positive tumours. The correlation between the presence of the MMTV-env like sequences (MMTVels) and p14 antigen was statistically significant in nasal lymphomas. All cats with MMTVels-positive lymphoma had a history of contact with the outdoor environment and/or catteries, and two deceased subjects shared their environment with cats that also died of lymphoma. In conclusion, this study succeeds in demonstrating the presence of MMTVels and p14 in feline lymphomas. The characterization of the immunophenotype of MMTVels-positive lymphomas could contribute to the understanding of a possible role of a MMTV-like virus in feline tumour aetiology. The significant association between the presence of the viral sequences in lymphoid tumours and their nasal localization, together with the data collected through supplementary anamnesis, should be further analysed in order to understand the epidemiology of the virus.

Mouse Mammary Tumor Virus (MMTV) and MMTV-like Viruses: An In-depth Look at a Controversial Issue

Since its discovery as a milk factor, mouse mammary tumor virus (MMTV) has been shown to cause mammary carcinoma and lymphoma in mice. MMTV infection depends upon a viral superantigen (sag)-induced immune response and exploits the immune system to establish infection in mammary epithelial cells when they actively divide. Simultaneously, it avoids immune responses, causing tumors through insertional mutagenesis and clonal expansion. Early studies identified antigens and sequences belonging to a virus homologous to MMTV in human samples. Several pieces of evidence fulfill a criterion for a possible causal role for the MMTV-like virus in human breast cancer (BC), though the controversy about whether this virus was linked to BC has raged for over 40 years in the literature. In this review, the most important issues related to MMTV, from its discovery to the present days, are retraced to fully explore such a controversial issue. Furthermore, the hypothesis of an MMTV-like virus raised the question of a potential zoonotic mouse–man transmission. Several studies investigate the role of an MMTV-like virus in companion animals, suggesting their possible role as mediators. Finally, the possibility of an MMTV-like virus as a cause of human BC opens a new era for prevention and therapy.

Prevalence and characteristics of mouse mammary tumor virus-like virus associated breast cancer in China

BACKGROUND

Despite extensive molecular epidemiological studies, the prevalence and characteristics of Mouse Mammary Tumor Virus-Like Virus (MMTV-LV) in Chinese women breast cancer are still unclear. Besides, the prevalence of MMTV-LV in women breast cancer tissue varies in different countries and its dependent factors remain inconclusive.

METHODS

In the first part of the study, a case-control study was performed. 119 breast cancer samples (84 from Northern China and 35 from Southern China) and 50 breast fibroadenoma specimens were collected from Chinese women patients. MMTV-like env sequence and the homology to MMTV env gene were analysed by semi-nested polymerase chain reaction (PCR). We also explored the association of MMTV-LV prevalence with sample sources (Southern and Northern China) and patients' clinicopathological characteristics. To investigate the dependent factors of the prevalence of MMTV-LV in breast cancer worldwide, a meta-analysis was conducted in the second part of the study.

RESULTS

We found that the prevalence of MMTV-LV was much higher in breast cancer tissues (17.65%) than that in breast fibroadenoma specimens (4.00%) (P < 0.05). MMTV-LV prevalence in Chinese women breast cancer tissues was significantly different between Southern China (5.71%) and Northern China (22.62%) (P < 0.05). The prevalence of MMTV-LV also associates significantly with expression of HER2, but shows no significant correlation with other parameters. In the meta-analysis, we found that MMTV-LV prevalence in breast cancer tissue was dependent on the distribution of M. domesticus mouse (M. d), M. musculus mouse (M.m) and M.castaneus mouse (M.c) worldwide (P < 0.05).

CONCLUSION

The distribution of house mice may be a crucial environmental factor that explains the geographic differences in human breast cancer incidence. Our findings may provide a potential avenue of prevention, diagnosis and treatment for breast cancer.

MMTV-LIKE virus and c-myc over-expression are associated with invasive breast cancer

Development and progression of breast cancer is an outcome of strong interplay between proto-oncogenes as well as environmental factors. Among proto-oncogenes, c-myc, a multifunctional transcription factor (TF), is one of the most highlighted one, whereas among environmental factors Mouse Mammary Tumor Virus (MMTV)-like virus is a widely discussed agent. Both, c-myc and MMTV-like virus, are known to individually correlate with the poor prognosis of breast cancer. However, no study has ever been reported to determine their mutual association in breast cancer patients. In this study, our aim was to quantify and compare c-myc mRNA in MMTV-like virus-positive and virus-negative-histopathological types of breast cancer. At first, biopsy samples of 105 breast cancer patients with known histopathological types were collected and screened for the presence of MMTV-like virus. To quantify mRNA level of c-myc, quantitative-Polymerase Chain Reaction (qPCR) was used. Next, c-myc expression was compared in MMTV-like virus-positive and virus-negative-histopathological types as of breast cancer. Statistical analysis was done using GraphPad Prism 7 Software. Molecular analysis revealed that 69 (65.72%) out of 105 samples were positive for MMTV-like virus. Moreover, invasive types of breast cancer exhibited increased (3-13 folds higher) expression of c-myc as compared to baseline representing normal control comprising of 15 tumor-free biopsy samples of breast cancer patients. Whereas, non-invasive types of breast cancer showed only 1-3 folds increase in the expression of c-myc as compared to normal control. Furthermore, virus-positive and virus-negative samples had different levels of c-myc mRNA. Positive status of MMTV-like virus was noticed to significantly associate with c-myc expression increasing it from 1.87-folds in virus-negative patient samples to 4.31-folds in virus-positive patient samples (p-value: <0.0001). Whereas, increase in the expression of c-myc was only 1.14-folds higher in 2 (13.33%) virus-positive-normal control samples as compared to 13 (86.67%) virus-negative-normal control samples (P-value: <0.01). In conclusion, it is suggested that presence of MMTV-like virus and over-expression of c-myc may be used as markers of invasion of breast cancer.

Involvement of a mouse mammary tumor virus (MMTV) homologue in human breast cancer: Evidence for, against and possible causes of controversies

Breast cancer (BC) is a complex and heterogeneous disease whose evolution depends on the tumor-host interaction. This type of cancer occurs when the mammary cells begin to grow wildly and become able to invade nearby tissues and/or promote metastases. Mouse mammary tumor virus (MMTV) is the accepted etiological agent of mammary tumors in mice. The identification of MMTV-like sequences and antigens in human mammary carcinoma has supported the theory that a virus homologous to MMTV (namely, HMTV) may be involved in human BC, but the role of retroviral elements in this disease remains elusive, as results from different research groups were contradictory. In the present review we present works for and against the involvement of HMTV in BC and discuss possible causes of divergences among studies. In the final section we fit current data regarding this issue to stablished causality criteria. We conclude that there is convincing data supporting the association of HMTV with BC, however there is still a need for epidemiological and basic research studies focusing on carcinogenic mechanisms for this virus in humans to fully understand its role in BC. This knowledge may open the way for the development of new preventive and therapeutic approaches in human BC.

Viral infections and breast cancer - A current perspective

Sporadic human breast cancer is the most common cancer to afflict women. Since the discovery, decades ago, of the oncogenic mouse mammary tumour virus, there has been significant interest in the potential aetiologic role of infectious agents in sporadic human breast cancer. To address this, many studies have examined the presence of viruses (e.g. papillomaviruses, herpes viruses and retroviruses), endogenous retroviruses and more recently, microbes, as a means of implicating them in the aetiology of human breast cancer. Such studies have generated conflicting experimental and clinical reports of the role of infection in breast cancer. This review evaluates the current evidence for a productive oncogenic viral infection in human breast cancer, with a focus on the integration of sensitive and specific next generation sequencing technologies with pathogen discovery. Collectively, the majority of the recent literature using the more powerful next generation sequencing technologies fail to support an oncogenic viral infection being involved in disease causality in breast cancer. In balance, the weight of the current experimental evidence supports the conclusion that viral infection is unlikely to play a significant role in the aetiology of breast cancer.

Occurrence of renal cell carcinoma and hematologic malignancies (predominantly lymphoid) in individuals and in families

The relationship between renal cell cancer (RCC) and hematologic malignancy (HM) in the same individual has been reported for more than 20 years, and is noted in SEER database studies. Family histories suggest a familial association as well. This study evaluates the occurrence of renal cell cancer and hematologic malignancies in individual patients and families, and the occurrence of age-of-onset anticipation among generations. Family history data from our familial patient registry, including more than 700 pedigrees of familial hematologic malignancies, and 700 patients with renal cell cancer, were reviewed. Twenty-six patients with a personal history of both RCC and HM are reported. Seventy four patients with RCC are noted to have 95 family members with HM. Consistent with past reports, there was male predominance among the patients with both diseases (71 %), and among the RCC patients' relatives with HM (57 %). Also consistent was a predominance of lymphoid malignancies in those with both diseases (92 %) and in the HMs among family members of RCC patients (79 %). The majority (95 %) of HM relatives were first or second degree relatives of the patient with RCC. Thirty of 34 parent/child pairs demonstrated age of onset anticipation in which the child developed either disease at a younger age than the parent. The co-occurrence of RCC and HM in the same patient has been shown to be significantly greater than expected. Families also appear to have an increased association. The appearance of anticipation suggests that genetic factors may be significant in this association of RCC and HM.

Primary cardiac lymphoma in a patient with concomitant renal cancer

Primary cardiac lymphoma is defined as non-Hodgkin lymphoma involving the heart and/or pericardium. It is a rare cancer that primarily affects the right heart and in particular the right atrium. By contrast, renal cell carcinoma is a relatively common cancer, which in rare circumstances can metastasize to the heart. It is now known that there is an association between non-Hodgkin lymphoma and renal cell carcinoma, although the underlying mechanisms are not fully understood. The authors present a case of primary cardiac non-Hodgkin lymphoma in a patient with concomitant renal cell carcinoma and explore the possible reasons for this association.

Synchronous invasive ductal carcinoma and intravascular large B-cell lymphoma of the breast: a case report and review of the literature

Primary breast lymphomas (PBLs) represent less than 1% of all breast malignancies. Intravascular large B-cell lymphoma (ILBCL) is a rare, aggressive form of extranodal lymphoma. Breast involvement has only been described in the literature once previously. ILBCL is characterized by the proliferation of tumour cells within the lumen of small vessels of involved organs, resulting in their eventual occlusion. Clinical features are often vague, diagnosis is difficult and delayed, and prognosis is usually poor. We report the first ever case of synchronous ILBCL and invasive ductal carcinoma (IDC) of the breast in a patient presenting with pyrexia of unknown origin and altered mental status who underwent modified radical mastectomy and subsequent chemotherapy, and review the literature regarding intravascular large B-cell lymphoma, PBLs and synchronous carcinomas and lymphomas of the breast.

Chronic lymphocytic leukemia involving the breast parenchyma, mimicker of invasive breast cancer: differentiation on breast MRI

Leukemic involvement of the breast is rare, particularly involvement by chronic lymphocytic leukemia (CLL). While concurrent invasive ductal carcinoma and CLL manifesting as a collision tumor in the breast is extremely rare, this association (CLL and carcinoma) has been described in other organs. We report here a case of a 58-year-old woman with concurrent invasive ductal carcinoma and CLL and describe the imaging features of CLL, particularly the differentiation on MRI.

Are viruses associated with human breast cancer? Scrutinizing the molecular evidence

The three viruses most studied as possible causes of human breast cancer are mouse mammary tumor virus-like sequences (MMTV-LS), Epstein-Barr virus (EBV), and oncogenic (high risk) types of human papilloma virus (HPV). The first step in fulfilling traditional criteria for inferring that a cancer is caused by a virus is to demonstrate the virus in the affected tissue. Molecular techniques, compared to host antibody assessment and immunohistochemistry, are the most definitive in establishing viral presence. Results of 85 original molecular research investigations to detect one or more of the three viruses have been extremely divergent with no consensus reached. We evaluated the methodology of these studies for the following: type of molecular assay, DNA/RNA quality control, positive and negative assay controls, type of fixation, genome targets, methods for preventing and detecting molecular contamination, pathology of specimens processed, sample size, and proportion of specimens positive for the viral genome region targeted. Only seven of the studies convincingly demonstrated the presence of an oncogenic virus biomarker (EBV: 4/30 studies (13%); HPV 3/29 studies (10%), whereas 25 convincingly demonstrated absence of the virus studied (MMTV-LS: 4/25 (16%); EBV: 15/30 (50%); 6/29 (21%). The remainder of the studies suffered shortcomings, which, in our opinion, prevented a definitive conclusion. Only one of the studies compared frequency of the virus in breast tissue of breast cancer patients versus appropriate normal control subjects with no history of breast cancer. None of the studies were designed as epidemiologic studies to determine if the presence of the virus was significantly associated with breast cancer. Based on our evaluation, the data in the publications reviewed here remain preliminary, and do not justify a conclusion that MMTV-LS, HPV, or EBV are causally associated with breast cancer. However, they form a valuable basis for redirecting future studies.

DNA of mouse mammary tumor virus-like virus is present in human tumors influenced by hormones

Mouse mammary tumor virus (MMTV) is a hormonally regulated, oncogenic virus of mice. MMTV-like virus DNA has previously been detected in human breast cancers, liver disease, and liver cancers. It is hypothesized that local hormonal effects might be of primary importance in determining MMTV-like virus detection in human tumors. MMTV-like virus envelope (env) DNA was determined using nested PCR in 89 ovarian, 147 prostate, 50 endometrial, 141 skin, and 51 lung cancers. Viral-positive sequences were compared with published MMTV-like viral sequences from human breast cancer, liver cancer and MMTV. Immunohistochemistry for estrogen receptor (ER-alpha) and progesterone receptor (PgR) was performed on a subset of tumors. MMTV-like virus env DNA was detected in ovarian cancers (14/89; 16%), prostate cancers (53/147; 36%), endometrial cancers (5/50; 10%), skin cancers (13/141; 9%) but not in lung cancers (0/51). Phylogenetic analysis of the viral-positive sequences showed no clustering of the isolates according to tissue type. A significant association was observed between the presence of hormone receptors and detection of MMTV-like virus in the human cancers screened (P = 0.01). A significant association between MMTV-like virus and PgR was noted in skin cancers (P = 0.003). Therefore, unlike the mouse model, the detection of MMTV-like env sequences in human cancers in addition to breast indicates that MMTV-like viral expression is not breast cancer-specific and may relate to hormone-dependent viral expression.

Human mammary tumor virus in inflammatory breast cancer

The authors have found that retroviral sequences with 85% to 95% homology to the mouse mammary tumor virus were present in 40% of the sporadic breast cancers of American women. These sequences were not found in normal breasts or other tumors. A whole proviral structure was detected in 2 tumors. Breast cancer cells in culture were shown to contain and shed betaretroviral particles. This virus was designated human mammary tumor virus (HMTV). The authors have investigated the presence of HMTV sequences in a variety of breast conditions and geographic locations. Here they report that inflammatory breast cancer from American women shows a higher incidence of viral sequences (71%) than sporadic breast cancers. Similar incidence has been found in inflammatory breast cancers from Tunisia, and in gestational breast cancers. Because these conditions represent highly invasive malignancies, it is concluded that HMTV is sometimes associated with a particularly malignant phenotype.

Concomitant Hodgkin's lymphoma and gastric adenocarcinoma: a rare coincidence

Gastric adenocarcinomas may be seen together with colon, prostate, breast, liver, lung and gynecological malignancies as synchronous or metachronous cancer. However, Hodgkin's lymphoma (HL) is rarely diagnosed with solid tumors. Herein, a 72-year-old man with both gastric adenocarcinoma and HL has been presented. Mass lesions far away from the primary tumor in cancer patients can be not only the sign of distant metastasis but also another primary malignancy. In the English literature, synchronous gastric adenocarcinoma and HL has been rarely reported, and as far as we know, this is the third case to be reported.

Detection of human mammary tumor virus proteins in human breast cancer cells

Mouse mammary tumor virus (MMTV) has been proven to induce mammary cancer in mice. MMTV-like env gene sequences have been detected in one-third of the human breast tumors studied. The whole proviral structure with 95% homology to MMTV was found in two human breast tumors and was designated as human mammary tumor virus (HMTV). HMTV viral particles with betaretroviral features have been isolated. In addition, a retrovirus called human betaretrovirus (HBRV), homologous to the mentioned retroviruses, has been isolated from tissues of patients with primary biliary cirrhosis. In this report, the expression of HMTV envelope (Env) and capsid (Ca) was detected in 10 primary cultures of human breast cancer containing HMTV sequences (MSSM) by Western blot and fluorescence activated cell sorting (FACS), using a panel of antibodies against HMTV Env, HBRV Env and Ca and the MMTV Env Gp36 and Ca P27 proteins. By contrast, HMTV proteins did not react with antibody against the MMTV Env Gp52 protein. All the antibodies detected MMTV proteins with exception of two out of four monoclonal antibodies against HMTV Env. Approximately 13% of the MSSM cells showed HMTV protein expression by FACS analysis. This report shows the expression of HMTV proteins for the first time in human breast cancer cells using a panel of antibodies against HMTV, HBRV and MMTV proteins. This should be taken into consideration when MMTV antibodies are used to detect HMTV proteins in human tissues.

Bilateral breast cancer in a survivor of acute lymphoblastic leukemia: a case report

Although breast cancer is the most common disease for women, bilateral breast cancer is a rare situation. Development of a second malignancy which is the most frightening side effect, may be related with genetic predisposition or cancer treatment. Because our case is a survivor of acute lymphoblastic leukemia, development of bilateral breast cancer which occurs rarely in early ages, is discussed with the help of literature.

Do viruses cause breast cancer?

Because mouse mammary tumor virus (MMTV; the Bittner virus) is the proven cause of breast cancer in both field and experimental mice, similar viruses have long been suspects as a potential cause of human breast cancer. MMTV-like viral genetic material has been identified in human breast tumors, but there is no definitive evidence whether MMTV is causal and not merely an innocuous infection in humans. High-risk human papilloma viruses (HPVs), Epstein-Barr (EBV), and other viruses also have been identified in human breast tumors, but again there is no definitive evidence for a causal role. Any viral hypothesis as a cause of breast cancer must take into account the most striking epidemiologic feature of human breast cancer, the three- to sixfold differences in mortality and up to eightfold differences in incidence between some Asian and Western populations. These differences dramatically lessen to a two- to threefold difference within one or two generations of migration of females from low to high risk of breast cancer countries. In this chapter, a plausible explanation for these phenomena is offered; that is, the hypothesis that oncogenic viruses such as MMTV and high-risk HPVs may initiate some breast cancers in most populations. Furthermore, dietary patterns are suggested to determine circulating sex hormone levels, which in turn promote the replication of the hormone-dependent viruses MMTV and HPV. In addition, diet and hormones promote growth of both normal and malignant cells. Finally, the hypothesis that migrants from low to high risk of breast cancer countries change their food consumption patterns is suggested, which leads to higher circulating hormone levels, which in turn promotes viral replication, which initiates breast oncogenesis, which is enhanced by sex and growth hormones.

Rev and Rex proteins of human complex retroviruses function with the MMTV Rem-responsive element

Background

Mouse mammary tumor virus (MMTV) encodes the Rem protein, an HIV Rev-like protein that enhances nuclear export of unspliced viral RNA in rodent cells. We have shown that Rem is expressed from a doubly spliced RNA, typical of complex retroviruses. Several recent reports indicate that MMTV can infect human cells, suggesting that MMTV might interact with human retroviruses, such as human immunodeficiency virus (HIV), human T-cell leukemia virus (HTLV), and human endogenous retrovirus type K (HERV-K). In this report, we test whether the export/regulatory proteins of human complex retroviruses will increase expression from vectors containing the Rem-responsive element (RmRE).

Results

MMTV Rem, HIV Rev, and HTLV Rex proteins, but not HERV-K Rec, enhanced expression from an MMTV-based reporter plasmid in human T cells, and this activity was dependent on the RmRE. No RmRE-dependent reporter gene expression was detectable using Rev, Rex, or Rec in HC11 mouse mammary cells. Cell fractionation and RNA quantitation experiments suggested that the regulatory proteins did not affect RNA stability or nuclear export in the MMTV reporter system. Rem had no demonstrable activity on export elements from HIV, HTLV, or HERV-K. Similar to the Rem-specific activity in rodent cells, the RmRE-dependent functions of Rem, Rev, or Rex in human cells were inhibited by a dominant-negative truncated nucleoporin that acts in the Crm1 pathway of RNA and protein export.

Conclusion

These data argue that many retroviral regulatory proteins recognize similar complex RNA structures, which may depend on the presence of cell-type specific proteins. Retroviral protein activity on the RmRE appears to affect a post-export function of the reporter RNA. Our results provide additional evidence that MMTV is a complex retrovirus with the potential for viral interactions in human cells.

The possible involvement of virus in breast cancer

It is well known that the etiology of human breast cancer is significantly affected by environmental factors. Virus-associated cancer refers to a cancer where viral infection results in the malignant transformation of the host's infected cells. Human papillomaviruses (HPV), mouse mammary tumor virus (MMTV) and Epstein-Barr (EBV) virus are prime candidate viruses as agents of human breast cancer. The precise role that viruses play in tumorigenesis is not clear, but it seems that they are responsible for causing only one in a series of steps required for cancer development. The idea that a virus could cause breast cancer has been investigated for quite some time, even though breast cancer could be a hereditary disease; however, hereditary breast cancer is estimated to account for a small percentage of all breast cancer cases. Based on current research, this review present at moment, substantial, but not conclusive, evidence that HPV, EBV and MMTV may be involved in breast cancer.

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

Background

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.

Results

MMTV-like envelope (env) and long terminal repeat (LTR) sequences containing the MMTV superantigen gene (sag) were detected in the malignant tissues of all three family members. The amplified env gene sequences were 98.0%–99.6% homologous to the MMTV env sequences found in the GR, C3H, and BR6 mouse strains. The amplified LTR sequences containing sag sequences segregated to specific branches of the MMTV phylogenetic tree and did not form a distinct branch of their own.

Conclusion

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.

Concurrent Invasive Ductal Carcinoma and Chronic Lymphocytic Leukemia Manifesting as a Collision Tumor in Breast

Collision tumors are rare clinical entities in which two histologically distinct tumor types show involvement in the same site. The occurrence of these tumors in the breast is extremely rare. Here, we present a case of a patient with both invasive ductal carcinoma and chronic lymphocytic leukemia in the breast. Wide excision with sentinel lymph node biopsy revealed palpably abnormal lymph nodes negative for breast carcinoma on frozen section. Histopathological examination of these lymph nodes showed extensive involvement by lymphoma and review of the breast specimen demonstrated the same lymphoma at the periphery of the ductal carcinoma. We review the literature and discuss possible etiologies for the dual presentation of both cancers.

MMTV-like sequences in human breast cancer: a fluorescent PCR/laser microdissection approach

The hypothesis that a retrovirus homologous to the mouse mammary tumour virus (MMTV) is involved in human breast cancer aetiology has fascinated scientists from many years, but it has never been convincingly demonstrated. Renewed interest in this hypothesis developed when an MMTV env gene-like sequence was found in 38% of human breast cancer tissues. Whereas some subsequent studies confirmed these findings, others did not. The main reasons for this discrepancy, among others, are the different sensitivities and technical details of current molecular approaches to the detection of these sequences. This study is an attempt to find sensitive and reproducible conditions capable of detecting MMTV env-like sequence in human samples. To this end, we first developed a fluorescence nested-PCR (FN-PCR) method that was able to detect very low copies of the viral genome, and then screened a panel of 45 frozen breast cancer samples obtained by laser microdissection. The MMTV env gene-like sequence was found in 15 (33%) of the human breast cancers analysed, whereas the same sequence was detectable neither in normal tissues nor in other types of tumour. Sequence analysis revealed 96% homology with the MMTV genome, but no other significant similarities with the human genome. The combined use of frozen material, microdissected cell populations and FN-PCR provides a novel, sensitive, robust, non-radioactive and fast methodology for the molecular detection of human-MTV. This approach might be successfully used in large molecular studies that aim to investigate the hypothesis of a retroviral aetiology of human breast cancer.

Viruses and human breast cancer

There are well-established risk factors for breast cancer, most of which relate to estrogens and growth hormones in females. These include early-age menarche, late-age menopause, postmenopausal obesity and use of hormone therapy. However, these factors do not account for the sixfold difference in breast cancer incidence and mortality between countries and the fact that these differences dramatically lessen after migration; nor do they account for male breast cancer. Accordingly, hormone-responsive viruses have become major suspects as etiological agents for human breast cancer. Human papillomaviruses, mouse mammary tumor virus and Epstein-Barr virus are the prime candidate viruses as causes of human breast cancer. Human papillomaviruses and the mouse mammary tumor virus have hormone responsive elements that appear to be associated with enhanced replication of these viruses in the presence of corticosteroid and other hormones. This biological phenomenon is particularly relevant because of the hormone dependence of breast cancer. Viral genetic material for each of these candidate viruses has been identified by polymerase chain reaction in breast tumors but rarely in normal breast tissue controls. Pooled data from controlled studies show substantial odds ratios for the presence of viral genetic material in breast tumors compared with normal controls. These and additional data provide substantial, but not conclusive, evidence that human papillomavirus, the mouse mammary tumor virus and Epstein-Barr virus may have a role in the etiology of human breast cancer. If conclusive evidence for a role of these viruses in breast carcinogenesis can be developed, there is a practical possibility of primary prevention.

Renal parenchymal tumors and lymphoma in the same patient: case series and review of the literature

We reviewed the incidence of diagnosis of renal cell carcinoma and lymphoma in the same patient and analyzed the characteristics of this association. Nine patients in 4 years had the diagnosis of renal cell carcinoma (RCC) and lymphoma, including 2 with Hodgkin disease, 1 with chronic lymphocytic leukemia (CLL), and 3 each with low-grade follicular and intermediate-grade non-Hodgkin lymphoma (NHL). In SEER data, the observed/expected (O/E) ratio of NHL and RCC is 1.86 to 2.07. In our series, 2 patients were diagnosed with NHL after the diagnosis of RCC, 1 was diagnosed concurrently, and in the other 6, lymphoma preceded diagnosis of RCC. In reviews of second malignancies following treatment of Hodgkin disease, RCC is less common (O/E 1.5, with 1/3 being transitional cell carcinoma and 2/3 being adenocarcinoma). We report 2 cases with Hodgkin disease preceding RCC, and in both, Hodgkin disease occurred as an adult. There is a male predominance for patients with both diagnoses, which is greater than the male predominance for either RCC or NHL alone (2.2 vs. 2.0 vs. 1.2). There is an increased likelihood of the lymphoma being extranodal. There is an increased association of RCC and NHL more often among male patients, and often with extranodal lymphoma. Potential common etiological factors include prior treatment for malignancy, genetic predisposition, environmental factors, including a search for viral sequences, and possible immune dysregulation generating the lymphoma and subsequently leading to solid tumors such as RCC or melanoma.

Identification of the segments of the mouse transferrin receptor 1 required for mouse mammary tumor virus infection

Most enveloped viruses enter cells through binding of virion surface envelope proteins to receptors found on the plasma membrane of the cell. The beta retrovirus mouse mammary tumor virus (MMTV) uses transferrin receptor 1 (TfR1) to enter cells in a pH-dependent mechanism, probably co-trafficking with TfR1 to an acidic compartment where virus entry occurs. We have shown here that, although mouse and rat TfR1 function as entry receptors, cat, dog, hamster, or human TfR1s do not support MMTV infection. We also demonstrated that MMTV entry is independent of transferrin, iron, and the TfR1 cofactor hereditary hematochromatosis HFE protein. Using chimeric mouse/human hybrid TfR1 constructs, we determined the site of interaction with MMTV and found that it maps to two segments physically disparate from the TfR and HFE binding sites. Thus, MMTV has apparently evolved to enter cells independently of the iron status of the host.

Human, rhesus macaque, and feline sequences highly similar to mouse mammary tumor virus sequences

Sequences highly similar (>95%) to the mouse mammary tumor virus (MMTV) env gene have been amplified from human DNA samples, including DNA samples from patients with breast cancer (BC) and persons who did not have BC. The sequences from human DNA were distinct from the MMTV sequences used as controls in these PCR reactions, indicating that these results are not simply due to contamination. In addition to both, mouse and human-related sequences were also amplified from some monkey and cat genomic DNA samples. These products were shown to be distinct from, but highly related to, the MMTV env gene, whereas, testing of other sources (lambda phage, snake, cockroach, sea urchin, chicken, or dog) demonstrated no specific amplification. A sequence 90% similar to the MMTV group antigen gene (gag) was amplified from cat DNA. These results indicate that DNA from vertebrate species other than rodents, including some but not all humans, monkeys, and cats, can contain sequences closely related to MMTV.

Of mice, cats, and men: Is human breast cancer a Zoonosis?

Mouse mammary tumor virus (MMTV), a member of the betaretroviridae, is the most common cause of breast cancer (BC) in mice. MMTV is transmitted in mice both in the germline as endogenous proviruses and exogenously as infectious virions. Here, we review a variety of evidence accumulated for six decades that has suggested that a human homologue of MMTV may exist. The findings include recent studies from several independent laboratories that have detected sequences very closely related to MMTV in DNA isolated from human BC tumors. Other laboratories, however, have failed to detect the MMTV-related sequences in human DNA samples, and conclusive evidence for a human mammary tumor virus has been elusive. We also reviewed additional studies, suggesting that betaretroviruses are present in a much wider range of species than previously known, including rodents, felines, and primates. The observation that a subset of cats may be infected with a close homologue of MMTV may be of epidemiological significance for human BC. Cats may become infected by MMTV from mice, and in turn may transmit the virus to humans, possibly after selection for variants with an expanded host range.