Protection of Measles Virus by Sulfate Ions Against Thermal Inactivation

Rapp, Fred (Baylor University College of Medicine, Houston, Tex.), Janet S. Butel, and Craig Wallis. Protection of measles virus by sulfate ions against thermal inactivation. J. Bacteriol. 90:132-135. 1965.-The infectivity of measles virus in water is rapidly destroyed at temperatures of 37 C and above. More than 50% of the infectivity is lost after 1 hr at 25 C, and almost 90% loss of infectivity occurs within 24 hr at 4 C. Magnesium chloride enhances the inactivation of the virus at all temperatures tested. Addition of either magnesium or sodium sulfate protects the virus against thermal inactivation. The stabilizing effect is demonstrable at temperatures ranging from 4 to 56 C, but is especially pronounced through 45 C. Prolonged storage (up to 6 weeks) of the virulent virus at 4 C in 1 m magnesium sulfate permits retention of substantial infectivity, whereas storage at 4 C in either water or 1 m magnesium chloride results in a loss of infectivity approximating 99% after 2 weeks. Magnesium chloride also enhances inactivation of the attenuated vaccine strain of measles virus. The attenuated virus, however, is strongly protected by magnesium sulfate against thermal inactivation, and retention of infectivity for long periods of time at 4 C seems feasible when the virus is kept in 1 m magnesium sulfate.

Detection of antibodies to polyomavirus SV40 in two central European countries

Simian virus 40 (SV40) is significantly associated with some human cancers. However, the frequency of tumor-associated virus detection differs by geographic regions, so it is important to understand the status of SV40 infections in different populations. Poliovaccines potentially containing live SV40 were used in well-documented nationwide vaccination programs in Hungary and the Czech Republic that are reported here. We analyzed serum samples from periodic surveillance programs in those two countries for antibodies to SV40 using a specific plaque reduction neutralization assay. The prevalence of antibodies was between 1.3 and 8.7% in Hungary and from 1.0 to 4.0% in the Czech Republic. Females had a higher rate of antibodies than males, reaching in certain age groups 15.6% in Hungary and 8.3% in the Czech Republic. Antibodies to SV40 were found in similar proportions in both countries among persons not directly exposed to poliovaccines and subjects vaccinated in the era of SV40-free vaccines. Complexities and limitations of current serological approaches to epidemiological studies of SV40 in humans are discussed. These data suggest that SV40 may be present in these populations and emphasize the importance of follow-up studies to determine the pathogenesis of infections by this emerging human agent.

Wnt-1 and int-2 mammary oncogene effects on the beta-catenin pathway in immortalized mouse mammary epithelial cells are not sufficient for tumorigenesis

Development of strategies for prevention of breast cancer development requires an understanding of the effects of mammary oncogenes on mammary cells at early stages in neoplastic transformation. As mammary oncogenes wnt-1 and int-2 affect different signal transduction pathways, we investigated their effects on established mouse mammary epithelial cell lines (MMECLs) reflecting early stages in tumorigenesis. Normal interactions between beta-catenin and E-cadherin were abrogated in all three immortalized MMECLs and the cells lacked beta-catenin-mediated transactivation activity, detectable using a reporter assay, suggesting that alterations in cell adhesion may be very early events in mammary tumorigenesis. Immortalized FSK4 and EL12 cells and hyperplastic TM3 cells were stably transfected with expression vectors encoding wnt-1 or int-2 or the control vector, and drug-selected pooled cells from each line were confirmed by reverse transcription-polymerase chain reaction to express the transfected oncogene; this expression persisted in the cells analysed in vitro and in vivo. Resultant phenotypic changes depended both on the oncogene and the target mammary cell line. In FSK4 cells, expression of wnt-1 or int-2 resulted in proliferative changes in vitro, including reduced contact inhibition, increased beta-catenin expression, and decreased p53 transcriptional activity, but neither oncogene conferred upon those cells the ability to produce tumors in vivo. EL12 cells were highly refractory to the effects of both oncogenes, with the only measurable changes being increased E-cadherin levels induced by both oncogenes and increased proliferation of the int-2-transfected cells in the absence of serum. Parental TM3 cells were phenotypically similar to wnt-1- or int-2-transfected FSK4 cells and displayed an increased rate of proliferation in vitro and markedly increased tumorigenicity in vivo following transfection with int-2 but not with wnt-1. These results suggest that wnt-1 signaling is redundant in the hyperplastic TM3 cells and indicate that wnt-1-induced effects in the immortalized FSK4 and EL12 cells were not sufficient to mediate a tumorigenic phenotype. This study showed that the wnt-1 and int-2 oncogenes have similar but distinguishable effects on immortalized MMECLs and that the genetic background of the mammary cells greatly influences the consequences of oncogene expression at early stages of cell transformation.

Simian virus 40 regulatory region structural diversity and the association of viral archetypal regulatory regions with human brain tumors

The regulatory region (RR) of simian virus 40 (SV40) contains enhancer/promoter elements and an origin of DNA replication. Natural SV40 isolates from simian brain or kidney tissues typically have an archetypal RR arrangement with a single 72-basepair enhancer element. A rare simpler, shorter SV40 RR exists that lacks a duplicated sequence in the G/C-rich region and is termed protoarchetypal. Occasionally, SV40 strain variants arise de novo that have complex RRs, which typically contain sequence reiterations, rearrangements, and/or deletions. These variants replicate faster and to higher titers in tissue culture; we speculate that such faster-growing variants were selected when laboratory strains of SV40 were initially recovered. SV40 strains with archetypal RRs have been found in some human brain tumors. The possible implications of these findings and a brief review of the SV40 RR structure are presented.

Increasing evidence for involvement of SV40 in human cancer

SV40, a small DNA virus, is known to possess strong oncogenic potential. Millions of people were exposed to SV40 as an unknown contaminant of some early poliovaccines. This article briefly summarizes the increasing evidence of the association of SV40 with certain types of human cancer, including mesotheliomas and brain tumors. Unanswered questions pertaining to the pathogenesis of human infections by SV40 and the functional role of the virus in tumor development are noted. It is concluded that SV40 should be considered a candidate human tumor virus and that vigorous efforts to clarify the role of the virus in human disease should be supported.

Molecular characterization of SV40 DNA in multiple samples from a human mesothelioma

BACKGROUND

Prolonged exposure to asbestos, a potent carcinogen, has been the generally accepted factor responsible for the development of human mesotheliomas. Recent reports documenting the detection of SV40 DNA in human mesotheliomas suggest the possibility that this known tumor virus may be an additional factor involved in the development of some tumors.

METHODS

A detailed analysis was performed by polymerase chain reaction and DNA sequencing of the genetic characteristics of SV40 viral DNA detected in samples taken from multiple sites of a human mesothelioma.

RESULTS

A single virus variant was detected within the tumor that encoded a novel variable region at the C-terminus of the large T-antigen oncoprotein. The viral regulatory region was predominantly archetypal in sequence (lacking duplications of the enhancer), typical of natural isolates.

CONCLUSIONS

These data confirm previous reports from several laboratories showing an association of SV40 DNA with human mesotheliomas and provide the first evidence of a novel virus variant present in separated regions of a mesothelioma.

Viral carcinogenesis: revelation of molecular mechanisms and etiology of human disease

The RNA and DNA tumor viruses have made fundamental contributions to two major areas of cancer research. Viruses were vital, first, to the discovery and analysis of cellular growth control pathways and the synthesis of current concepts of cancer biology and, second, to the recognition of the etiology of some human cancers. Transforming retroviruses carry oncogenes derived from cellular genes that are involved in mitogenic signalling and growth control. DNA tumor viruses encode oncogenes of viral origin that are essential for viral replication and cell transformation; viral oncoproteins complex with cellular proteins to stimulate cell cycle progression and led to the discovery of tumor suppressors. Viral systems support the concept that cancer development occurs by the accumulation of multiple cooperating events. Viruses are now accepted as bona fide etiologic factors of human cancer; these include hepatitis B virus, Epstein-Barr virus, human papillomaviruses, human T-cell leukemia virus type I and hepatitis C virus, plus several candidate human cancer viruses. It is estimated that 15% of all human tumors worldwide are caused by viruses. The infectious nature of viruses distinguishes them from all other cancer-causing factors; tumor viruses establish long-term persistent infections in humans, with cancer an accidental side effect of viral replication strategies. Viruses are usually not complete carcinogens, and the known human cancer viruses display different roles in transformation. Many years may pass between initial infection and tumor appearance and most infected individuals do not develop cancer, although immunocompromised individuals are at elevated risk of viral-associated cancers. Variable factors that influence viral carcinogenesis are reviewed, including possible synergy between viruses and environmental cofactors. The difficulties in establishing an etiologic role for a virus in human cancer are discussed, as well as the different approaches that proved viral links to cancer. Future directions for tumor virus studies are considered.

A mammary-specific model demonstrates the role of the p53 tumor suppressor gene in tumor development

Although alterations in the p53 tumor suppressor gene are detected frequently in human breast cancers, mammary tumors are observed infrequently in p53(null) mice. This has led to the suggestion that absence of p53 alone is not sufficient for induction of mammary tumors. However, early death of p53(null) mice from thymic lymphomas may obscure tumor phenotypes that would develop later. Therefore, p53(null) mammary epithelium was transplanted into cleared mammary fat pads of wild type p53 BALB/c hosts to allow long-term analysis of mammary tumor phenotypes. Five treatments were compared for their effects on tumor incidence in hosts bearing transplants of p53(null) and p53wt mammary epithelium. The treatment groups were: (1) untreated; (2) continuous hormone stimulation with pituitary isografts; (3) multiple pregnancies; (4) DMBA alone; and (5) DMBA+pituitary isografts. The tumor incidences in p53(null) vs p53wt mammary transplants for each treatment group were 62% vs 0%, 100% vs 0%, 68% vs 0%, 60% vs 4% and 91% vs 14%, respectively. The mammary tumors that developed in the p53(null) mammary epithelium were all adenocarcinomas and were frequently aneuploid. These data demonstrate that the absence of p53 is sufficient to cause development of mammary tumors and that hormonal stimulation enhances the tumorigenicity of p53(null) mammary epithelium to a greater extent than DMBA exposure alone. This model provides an in situ approach to examine the molecular basis for the role of p53 in the regulation of mammary tumorigenesis.

Simian virus 40, poliovirus vaccines, and human cancer: research progress versus media and public interests

From 1955 through early 1963, millions of people were inadvertently exposed to simian virus 40 (SV40) as a contaminant of poliovirus vaccines; the virus had been present in the monkey kidney cultures used to prepare the vaccines and had escaped detection. SV40 was discovered in 1960 and subsequently eliminated from poliovirus vaccines. This article reviews current knowledge about SV40 and considers public responses to reports in the media. SV40 is a potent tumour virus with broad tissue tropism that induces tumours in rodents and transforms cultured cells from many species. It is also an important laboratory model for basic studies of molecular processes in eukaryotic cells and mechanisms of neoplastic transformation. SV40 neutralizing antibodies have been detected in individuals not exposed to contaminated poliovirus vaccines. There have been many reports of detection of SV40 DNA in human tumours, especially mesotheliomas, brain tumours and osteosarcomas; and DNA sequence analyses have ruled out the possibility that the viral DNA in tumours was due to laboratory contamination or that the virus had been misidentified. However, additional studies are necessary to prove that SV40 is the cause of certain human cancers. A recently published review article evaluated the status of the field and received much media attention. The public response emphasized that there is great interest in the possibility of health risks today from vaccinations received in the past.

Evidence of SV40 infections in hospitalized children

Simian virus 40 (SV40) is known to have contaminated poliovirus vaccines used between 1955 and 1963. Accumulating reports have described the presence of SV40 DNA in human tumors and normal tissues, although the significance of human infections by SV40 is unknown. We investigated whether unselected hospitalized children had evidence of SV40 infections and whether any clinical correlations were apparent. Serum samples were examined for SV40 neutralizing antibody using a specific plaque reduction test; of 337 samples tested, 20 (5.9%) had antibody to SV40. Seropositivity increased with age and was significantly associated with kidney transplants (6 of 15 [40%] positive, P < .001). Many of the antibody-positive patients had impaired immune systems. Molecular assays (polymerase chain reaction and DNA sequence analysis) on archival tissue specimens confirmed the presence of SV40 DNA in 4 of the antibody-positive patients. This study, using 2 independent assays, shows the presence of SV40 infections in children born after 1980. We conclude that SV40 causes natural infections in humans.

Molecular evidence of simian virus 40 infections in children

Recent studies have detected simian virus 40 (SV40) DNA in certain human tumors and normal tissues. The significance of human infections by SV40, which was first discovered as a contaminant of poliovirus vaccines used between 1955 and 1963, remains unknown. The occurrence of SV40 infections in unselected hospitalized children was evaluated. Polymerase chain reaction and DNA sequence analyses were done on archival tissue specimens from patients positive for SV40 neutralizing antibody. SV40 DNA was identified in samples from 4 of 20 children (1 Wilms' tumor, 3 transplanted kidney samples). Sequence variation among SV40 regulatory regions ruled out laboratory contamination of specimens. This study shows the presence of SV40 infections in pediatric patients born after 1982.

Expression of MDM2 during mammary tumorigenesis

The MDM2 oncoprotein encodes a 90 kDa nuclear phosphoprotein capable of abrogating the growth suppressive functions of p53 and pRb tumor suppressor proteins by direct interaction. Alternative splicing of MDM2 protein coding sequences has been documented during tumor progression in human ovarian and bladder carcinomas. The aim of this study was to determine whether alternative splicing of MDM2 occurs during breast tumorigenesis in mice and humans and whether protein coding sequences were affected. Specimens representing normal and malignant breast tissues from the murine D2 mammary tumor model system and human breast carcinomas were examined. Three distinct mdm2 mRNA transcripts of 3.3, 1.6 and 1.5 kb were detected in normal and malignant murine mammary tissues by Northern blot analysis using a full-length mdm2 cDNA probe. Additional Northern blot analysis using a probe derived from exon 12 of murine mdm2 demonstrated that the 1.5 and 1.6 kb transcripts lack sequences encoding the C-terminus of the protein. No evidence of internal deletions of protein coding sequences of mdm2 was detected in any of the normal mammary tissues or D2 murine mammary tumors examined by reverse transcription PCR (RT-PCR). Three distinct MDM2 transcripts of 6.7, 4.7 and 1.9 kb were detected in malignant human breast tissue by Northern blot analysis using a cDNA probe specific for the complete open reading frame of human MDM2. However, a cDNA probe specific for the last exon of human MDM2 hybridized only to the 6.7 and 4.7 kb transcripts, demonstrating that the 1.9 kb transcript lacked protein coding sequences contained in exon 12. Similarly, no internal deletions were detected in a panel of malignant human breast tissues using RT-PCR and analogous primers within human MDM2. Therefore, breast tumors differ from other solid tumors reported previously in that no internal deletions of MDM2 protein coding sequences were observed. However, the data document the presence of multiple MDM2 mRNA transcripts in both normal and malignant breast tissues. A subset of MDM2 transcripts were shown to lack the last exon which contains sequences coding for the RING and zinc fingers and domains which are targets for caspase-3 mediated proteolytic degradation and are required to target p53 for proteosomal degradation.

Polyomaviruses and human tumors: a brief review of current concepts and interpretations

Polyomaviruses are small DNA viruses that typically establish persistent but inapparent infections of their natural hosts, although cytolytic disease may develop if the host becomes immunocompromised. Most polyomaviruses have the ability to induce tumor formation when introduced into certain foreign hosts and are considered oncoviruses. Some polyomaviruses, including those that infect humans, have occasionally been detected in cancerous tissue of their natural hosts. This article briefly reviews the biology of polyomaviruses and explores issues pertaining to the significance of association of polyomaviruses with human tumors.

Cell and molecular biology of simian virus 40: implications for human infections and disease

Simian virus 40 (SV40), a polyomavirus of rhesus macaque origin, was discovered in 1960 as a contaminant of polio vaccines that were distributed to millions of people from 1955 through early 1963. SV40 is a potent DNA tumor virus that induces tumors in rodents and transforms many types of cells in culture, including those of human origin. This virus has been a favored laboratory model for mechanistic studies of molecular processes in eukaryotic cells and of cellular transformation. The viral replication protein, named large T antigen (T-ag), is also the viral oncoprotein. There is a single serotype of SV40, but multiple strains of virus exist that are distinguishable by nucleotide differences in the regulatory region of the viral genome and in the part of the T-ag gene that encodes the protein's carboxyl terminus. Natural infections in monkeys by SV40 are usually benign but may become pathogenic in immunocompromised animals, and multiple tissues can be infected. SV40 can replicate in certain types of simian and human cells. SV40-neutralizing antibodies have been detected in individuals not exposed to contaminated polio vaccines. SV40 DNA has been identified in some normal human tissues, and there are accumulating reports of detection of SV40 DNA and/or T-ag in a variety of human tumors. This review presents aspects of replication and cell transformation by SV40 and considers their implications for human infections and disease pathogenesis by the virus. Critical assessment of virologic and epidemiologic data suggests a probable causative role for SV40 in certain human cancers, but additional studies are necessary to prove etiology.

Consideration of PCR methods for the detection of SV40 in tissue and DNA specimens

SV40 is capable of infecting humans, although its association with human diseases remains controversial. Recently, a subgenomic SV40 DNA sequence was detected by polymerase chain reaction (PCR) in certain types of human tumour tissue as well as in normal pituitary tissue. However, due to the limited DNA sequence information that was obtained in those experiments, SV40 could not be authenticated, and it was uncertain whether a related or hybrid virus (or endogenous DNA) accounted for the PCR-amplified DNA. To gain more insight into these observations, we are experimenting with PCR primers directed at various sites of the SV40 genome, as well as with various parameters of the PCR assay. In this communication, we describe methodology we currently use in our studies and discuss problems associated with the PCR detection of SV40 in various types of samples.

Detection of authentic SV40 DNA sequences in human brain and bone tumours

This report summarizes our follow-up studies of SV40 DNA sequences in human brain tumors of early childhood and our confirmation of the presence of SV40 DNA in human osteosarcomas. We examined brain tumors and osteosarcoma samples by the polymerase chain reaction (PCR) using primers from four separated regions of the SV40 genome. Sequence analysis confirmed that authentic SV40 DNA was present. The regulatory region of each tumor-associated viral DNA was of archetypal length (non-duplicated enhancer); sequence variation was noted at the extreme C-terminus of the large T-antigen (T-ag) genes. Infectious SV40 was recovered from one brain tumor. We sequenced the entire early genomic region from three human isolates of SV40 and two laboratory strains originally recovered from monkeys. The predicted amino acid sequence of the large T-ags showed remarkable sequence conservation among isolates, except for a small variable region identified at the C-terminus of the protein. There were no human-isolate-specific changes detected that could serve to distinguish a human variant of SV40 nor were any tumor-type-specific viral markers observed. Based on these data, we conclude that authentic SV40 is associated with some human brain and bone tumors and that multiple SV40 strains can infect humans.

Cytotoxic T lymphocyte recognition sequences as markers for distinguishing among tumour antigens encoded by SV40, BKV and JCV

Simian virus 40 (SV40) has been shown to be associated with a number of human tumours. Two other human papova viruses, BKV and JCV, infect humans at a relatively high frequency and are activated upon immune suppression. The T antigens of both of these viruses share considerable homologies with the transforming protein T antigen of SV40. We have used SV40 T antigen specific cytotoxic T lymphocyte (CTL) clones to discriminate among the T antigens of SV40, BKV and JCV. These CTL clones directed to four distinct CTL epitopes serve as specific probes and can differentiate subtle alterations or deletions in the CTL epitopes relative to SV40 T antigen. Using this strategy, we have been able to authenticate three SV40 viruses isolated from humans as all four distinct CTL epitopes in the T antigens encoded by these three SV40 human isolates (SVCPC, SVMEN, and SVPML-1) were found to be identical to prototype SV40. We have further identified a 198 amino acid deletion T antigen variant of SVCPC. The finding of a deletion mutant in the SVCPC virus population suggests that the cellular immune response may play a role in the selection of antigenic loss variants.

Radiation-induced tumorigenesis in preneoplastic mouse mammary glands in vivo: significance of p53 status and apoptosis

In mouse mammary tumorigenesis, p53 mutations facilitate tumorigenesis in concert with other oncogenic alterations. Ionizing radiation enhances tumorigenesis in preneoplastic mammary outgrowth lines and induces p53-dependent apoptosis. We asked if normal p53 function modulates radiation-induced tumorigenesis in preneoplastic mammary lesions by affecting the apoptotic pathway of cell deletion. Three different hyperplastic outgrowth lines were compared. Outgrowth line D1 overexpressed wild-type p53 and responded to irradiation with enhanced tumorigenicity but no induction of apoptosis. Outgrowth line TM12 exhibited normal wild-type p53 expression and responded to irradiation with no alteration in tumorigenicity but with a marked increase in apoptosis. Outgrowth line TM2L also exhibited normal wild-type p53 expression and responded to irradiation with a marked enhancement in both tumorigenicity and apoptosis. These results indicate that the two radiation-induced responses, apoptosis and tumorigenesis, are dissociable events in the mammary gland. Furthermore, radiation-induced tumorigenicity was not abrogated by either enhanced wild-type p53 expression or a robust apoptotic response. The radiation dose of 5 Gy most likely induces multiple genetic alterations in surviving cells, including genomic instability, and this may account for the tumorigenicity. Future experiments will examine lower doses of irradiation that still induce a significant apoptotic response but significantly less genomic instability.

Natural isolates of simian virus 40 from immunocompromised monkeys display extensive genetic heterogeneity: new implications for polyomavirus disease

Simian virus 40 (SV40) DNAs in brain tissue and peripheral blood mononuclear cells (PBMCs) of eight simian immunodeficiency virus-infected rhesus monkeys with SV40 brain disease were analyzed. We report the detection, cloning, and identification of five new SV40 strains following a quadruple testing-verification strategy. SV40 genomes with archetypal regulatory regions (containing a duplication within the G/C-rich regulatory region segment and a single 72-bp enhancer element) were recovered from seven animal brains, two tissues of which also contained viral genomes with nonarchetypal regulatory regions (containing a duplication within the G/C-rich regulatory region segment as well as a variable duplication within the enhancer region). In contrast, PBMC DNAs from five of six animals had viral genomes with both regulatory region types. It appeared, based on T-antigen variable-region sequences, that nonarchetypal virus variants arose de novo within each animal. The eighth animal exclusively yielded a new type of SV40 strain (SV40-K661), containing a protoarchetypal regulatory region (lacking a duplication within the G/C-rich segment of the regulatory region and containing one 72-bp element in the enhancer region), from both brain tissue and PBMCs. The presence of SV40 in PBMCs suggests that hematogenous spread of viral infection may occur. An archetypal version of a virus similar to SV40 reference strain 776 (a kidney isolate) was recovered from one brain, substantiating the idea that SV40 is neurotropic as well as kidney-tropic. Indirect evidence suggests that maternal-infant transmission of SV40 may have occurred in one animal. These findings provide new insights for human polyomavirus disease.

Serological evidence of SV40 infections in HIV-infected and HIV-negative adults

SV40 is a simian polyomavirus that was a contaminant of some viral vaccines administered to people between 1955 and 1962. SV40 DNA has recently been found associated with several types of human tumors, suggesting that the virus is present in humans. We examined sera from patients infected with human immunodeficiency virus type 1 (HIV-1) as well as from HIV-1-negative controls to determine the prevalence of SV40 neutralizing antibodies using a specific plaque reduction assay. We found that 16.1% of HIV-infected patients (n = 236) were seropositive for SV40, as compared to 12.0% of HIV-negative control volunteers (n = 108) and 11.1% of HIV-negative patients (n = 72). These differences were not statistically significant. As individuals born between 1941 and 1962 had the highest chance of having received SV40-contaminated poliovaccines, we analyzed SV40 seropositivity rates based on year of birth. SV40 antibody rates for HIV-infected patients born before 1941, between 1941 and 1962, and after 1962 were 17.1%, 16.3%, and 11.8%, respectively. For the HIV-negative subjects, the rates were 12.5%, 12.0%, and 9.7%, respectively. There was no correlation between SV40 seropositivity and either the stage of disease in HIV-infected patients or the race/ethnicity. Also, there was no correlation between the presence of SV40 neutralizing antibody and the titer of neutralizing antibody to human polyomavirus BKV. The SV40 seropositivity rates in the patients born between 1941 and 1962 may be explained by the likelihood of those individuals having received SV40-contaminated vaccines, but the detection of SV40 neutralizing antibody in individuals born after 1962 (with no risk of having received contaminated vaccines) is significant. Although cross-reactive antibodies might theoretically contribute to the observed reactivities, these results suggest that SV40 neutralizing antibodies are present in certain individuals and raise the possibility that SV40 continues to infect humans long after vaccines were freed from contamination.

Sequence analyses of human tumor-associated SV40 DNAs and SV40 viral isolates from monkeys and humans

SV40 DNA has been found associated with several types of human tumors. We now report a sequence comparison of SV40 DNAs from pediatric brain tumors and from osteosarcomas with viral isolates from monkeys and from humans. We analyzed the entire genomic sequences of five isolates, Baylor and VA45-54 strains from monkeys and SVCPC, SVMEN, and SVPML-1 recovered from humans, and compared them to the reference virus SV40-776. The viral sequences were highly conserved, but isolates could be distinguished by variations in the structure of the viral regulatory region and in the nucleotide sequence of the variable domain at the C-terminus of the large T-antigen gene. We conclude that multiple strains of SV40 exist that can be identified on the basis of sequences in these regions of the viral genome. The isolates were more similar to each other and to the Baylor strain than to the reference strain SV40-776. Human isolates SVCPC and SVMEN were found to be identical. The DNAs present in some human brain and bone tumors were authentic SV40 sequences. Many of the C-terminal T-ag sequences associated with human tumors were unique, but some sequences were shared by independent sources. There was no compelling evidence for human-specific strains of SV40 or for tumor type-specific associations, suggesting that SV40 has a relatively broad host range. The source of the viral DNA found in human tumors remains unknown.

Hepatitis B virus X protein interferes with cellular DNA repair

The hepatitis B virus X protein (HBx) is a broadly acting transactivator implicated in the development of liver cancer. Recently, HBx has been reported to interact with several different cellular proteins, including our report of its binding to XAP-1, the human homolog of the simian repair protein UVDDB. In the present study, several HBx mutants were used to localize the minimal domain of HBx required for binding to XAP-1/UVDDB to amino acids 55 to 101. The normal function of XAP-1/UVDDB is thought to involve binding to damaged DNA, the first step in nucleotide excision repair (NER); therefore, we hypothesized that this interaction may affect the cell's capacity to correct lesions in the genome. When tested in two independent assays that measure NER (unscheduled DNA synthesis and host cell reactivation), the expression of HBx significantly inhibited the ability of cells to repair damaged DNA. Under the assay conditions, HBx was expressed at a level similar to that previously observed during natural viral infection and was able to transactivate several target reporter genes. These results are consistent with a model in which HBx acts as a cofactor in hepatocarcinogenesis by preventing the cell from efficiently repairing damaged DNA, thus leading to an accumulation of DNA mutations and, eventually, cancer. An adverse effect on cellular DNA repair processes suggests a new mechanism by which a tumor-associated virus might contribute to carcinogenesis.

SV40 DNA in human osteosarcomas shows sequence variation among T-antigen genes

Authentic simian virus 40 (SV40) has been detected in association with human choroid plexus and ependymoma tumors, and SV40-like DNA sequences have been found in some human osteosarcomas. We report here an analysis of human osteosarcoma samples for the presence of SV40 DNA using PCR and primers directed at 4 distinct sites of the SV40 genome, coupled with sequence analysis. Authentic SV40 DNA sequences were detected in 5 of 10 osteosarcoma tumor samples. The SV40 regulatory region in each case was identical and of archetypal length (non-duplicated enhancer), as is usually found in natural isolates of SV40 from monkeys and in human brain tumors. A section of the gene that encodes a viral late gene product (VP1) was detected in 5 of 10 tumors and had an exact match with the known sequence of SV40. Two separated segments of the large T-antigen (T-ag) gene were found in the same 5 tumors. Analysis of the DNA sequences encoding the T-ag carboxy terminus revealed sequence variation among the tumors, as observed previously in viral DNA associated with human brain tumors. There does not appear to be a preferential association of a T-ag variable domain sequence with a given tumor type. No sequences from the regulatory region of human polyomaviruses JCV and BKV were detected in the bone tumors. We also noted less efficient recovery of SV40 DNA from tumor samples fixed in paraffin as compared to frozen tumors. Our results confirm the presence of SV40 DNA in human bone tumors and, based on the sequence variation observed for the carboxy terminus of the T-ag gene, suggest that there is not a specific SV40 strain associated with human osteosarcomas.

Loss of T-antigen sequences allows SV40-transformed human cells in crisis to acquire a senescent-like phenotype

Normal human cells transfected with SV40 DNA exhibit an extended proliferative potential compared with controls, but they eventually enter a phase known as "crisis." During crisis, extensive cell death occurs and the cells exhibit some gene expression changes similar to senescent cells. This article presents results which indicate that crisis most likely depends on expression of the viral gene T-antigen. We have obtained a unique subpopulation of cells that have deleted the T-antigen gene and, rather than dying as cells do in crisis, remain viable and exhibit some senescent-like characteristics. We also found that the SV40 promoter is poorly expressed in senescent versus young cells. We hypothesize that decreased activity of the viral promoter may result in decreased expression of T-antigen, which is challenged by over-expression of the cell cycle inhibitors such as p21Sdi1. Conflicting signals to proceed/halt cells cycle progression result in the cell death associated with crisis.

Interaction of the UV-damaged DNA-binding protein with hepatitis B virus X protein is conserved among mammalian hepadnaviruses and restricted to transactivation-proficient X-insertion mutants

We carried out a comparative analysis of several proposed host protein partners of the human hepatitis B virus X protein (HBx) using both the GAL4- and the LexA-based yeast two-hybrid system. We showed that the interaction of HBx with the UV-damaged DNA-binding protein (UVDDB) is positive in both yeast systems, detectable in cotransfected human cells, conserved by rodent hepadnavirus X proteins (known to transactivate in human cells), and tightly correlated with the transactivation proficiency of X-insertion mutants. Taken together, our results strongly suggest that UVDDB is involved in X-mediated transactivation.

Tissue culture adaptation of natural isolates of simian virus 40: changes occur in viral regulatory region but not in carboxy-terminal domain of large T-antigen

The regulatory region of natural isolates of simian virus 40 (SV40) is different from that of laboratory-adapted strains of the virus. The latter have a nucleotide sequence duplication within the enhancer region which varies slightly with each strain, whereas the duplication is lacking in fresh isolates of SV40, which contain an 'archetypal' regulatory region. Many isolates also display nucleotide differences in the DNA encoding the carboxy terminus of large tumour antigen (T-ag). To determine whether genetic changes in these two regions of the SV40 genome were detectable during laboratory adaptation and long-term passage, low-passage virus stocks of two laboratory strains which had detailed passage histories spanning more than 25 years (Baylor strain and VA45-54) were analysed using PCR, cloning and sequencing assays. Both laboratory and archetypal regulatory regions were present in low-passage stocks. Following duplication in the regulatory region, no additional changes were detectable. The variable region at the T-ag carboxy terminus did not undergo any change with tissue culture passage and may serve as a useful site for taxonomic classification of different strains of SV40. Cloned genomes containing single or duplicated enhancers derived from both SV40 strains were viable in CV-1 cells. Attempts to induce regulatory region duplications by 14 serial passages of SV40 archetypal strains in monkey cells were not successful. The results are compatible with tissue culture adaptation of SV40, reflecting either selection of a rare variant pre-existing in the original sample or generation of a rare regulatory region duplication in infected cells.

Unscheduled DNA replication precedes apoptosis of photoreceptors expressing SV40 T antigen

Expression of simian virus 40 T antigen (Tag) in the rod photoreceptors of transgenic mice leads to cell death that is completed by the end of the third week of postnatal development. To understand the mechanistic link between Tag expression and the death of the expressing photoreceptors, cell cycle activity was followed in a transgenic mouse family that expresses Tag directed by the mouse opsin promoter. Tag-expressing photoreceptors also expressed rhodopsin suggesting that these cells were differentiated. The presence of Tag in the photoreceptors induced the expression of both proliferating cell nuclear antigen (PCNA) and thymidine kinase (TK). The abnormally high levels of PCNA and TK continued until the complete disappearance of the cells expressing Tag. Photoreceptor cell death was also associated with continued DNA synthesis that ceased shortly after postnatal day 16. The specific loss of the rod photoreceptors that re-entered the cell cycle accounted entirely for the loss of photoreceptors from the outer nuclear layer. The antiproliferative nature of the mature retina is directly involved in the apoptotic death of photoreceptors expressing Tag.

A coupled PCR and restriction digest method for the detection and analysis of the SV40 regulatory region in infected-cell lysates and clinical samples

The polymerase chain reaction (PCR) is an increasingly popular analytical tool for the detection of virus sequences in laboratory preparations as well as in human clinical samples. In studies involving papovaviruses SV40, BK virus (BKV), and JC virus (JCV), one of the primary targets for analysis is the viral regulatory region, as that section of the papovavirus genome is distinct. A primary concern with PCR-based studies is whether amplified DNA sequences may be derived from laboratory contaminants. Recognizing that common sources of PCR contamination are the positive control templates, we devised a facile method to distinguish between real and false-positive PCR-amplified SV40 regulatory region DNAs. SV40 constructs that had been engineered to contain different combinations of 72-basepair (bp) enhancer elements and 21-bp repeats, as well as two introduced unique restriction enzyme sites, were used as positive control templates for PCR amplification. Cleavage of PCR-amplified DNA identifies products from the engineered control plasmids. The procedure is rapid, simple and cost-effective. We also report that primer sets predicted to be specific for the SV40 regulatory region can be used to amplify BKV and JCV regulatory region sequences under conditions of reduced stringency.

Apolipoprotein B gene regulatory factor-2 (BRF-2) is structurally and immunologically highly related to hepatitis B virus X associated protein-1 (XAP-1)

Hepatic cell-specific expression of the human apolipoprotein B (apoB) gene is controlled by at least four cis-acting elements located between positions -128 and +122 [Chuang, S. S., & Das, H. K. (1996) Biochem. Biophys. Res. Commun. 220, 553-562]. The distal element (-128 to -85) appears to be liver specific because it shows positive activity in HepG2 cells and negative activity in HeLa cells. ApoB gene regulatory factor-2 (BRF-2) interacts with the sequence (-104 to -85). BRF-2 has been purified from rat liver nuclear extract, and its molecular weight has been determined to be approximately 120 kDa [Zhuang et al. (1992) Mol. Cell. Biol. 12, 3183-3191]. In this paper we report the isolation of two isoforms of BRF-2 by further purification using high-performance liquid chromatography. Both isoforms produced a single approximately 120-kDa band in sodium dodecyl sulfate polyacrylamide gel electrophoresis detected by silver stain. The amino acid sequences of two tryptic peptides derived from HPLC-purified heavier BRF-2 isoform were determined to be YLAIAPPIIK and ALYYLQIHPQELR. These two peptides were found to share 100% sequence homology with human hepatitis B virus X associated protein-1 (XAP-1) and monkey UV-damaged DNA-binding protein (UV-DDB). Anti-peptide antisera raised against two synthetic peptides of XAP-1 recognized a approximately 120-kDa polypeptide band in both BRF-2 isoforms in a western blot analysis. By using apoB promoter fragments containing various internal deletions and a substitution mutation as templates for gel mobility shift assays, we identified the region between -104 and -85 as crucial for binding by the high-molecular weight form. In contrast, the lower molecular weight isoform bound to all apoB mutants tested. Anti-peptide 2 antiserum directed against XAP-1 was found to inhibit in vitro transcription of the apoB gene in rat liver nuclear extracts by 50%. These results suggest that BRF-2 and XAP-1 are structurally and immunologically highly related trans-activators of the apoB gene. We propose that BRF-2 exists both as a monomer (BRF-2M) and as a homooligomer. probably a homodimer (BRF-2D), in solution; oligomerization appears to be an essential step for imparting sequence-specificity to BRF-2 protein and thereby facilitating its role as a trans-activator of the apoB gene.

High-fidelity PCR amplification of infectious copies of the complete simian virus 40 genome from plasmids and virus-infected cell lysates

We describe here a long-polymerase chain reaction (PCR) method that can be used to amplify complete simian virus 40 (SV40) DNA with high fidelity, and we show that authentic, viable virus can be produced from molecular clones of the PCR-amplified viral DNAs. A commercial long-PCR kit that employed a combination of Taq and GB-D polymerases was used, together with a pair of overlapping primers that recognized a unique EcoRI site in the SV40 genome. Efficient amplification required linearization of the circular SV40 genomic DNAs with EcoRI. Entire SV40 genomes were successfully PCR-amplified from an SV40 plasmid and from two different SV40-infected cell lysates and were cloned into pUC-19. Three separate segments of the cloned viral genomes were DNA sequenced, and no nucleotide changes relative to the parental virus were detected, suggesting that the viral DNAs had been amplified with high fidelity. Each PCR clone was infectious, and no differences were detected in the growth characteristics of viruses derived from these clones as compared to the original viral strain. The procedure we utilized shortens and simplifies the molecular cloning of small double-stranded DNA viruses and will be useful for viral diagnostic tests and for recovery of virus from clinical samples. The results of these experiments have broad implications, as the methodology is applicable to many systems.

Activation of the HTLV-I long terminal repeat by the hepatitis B virus X protein

The human T-cell leukemia virus type I (HTLV-I) Tax protein and the hepatitis B virus (HBV) X protein have each been shown to activate transcription of their respective viral promoters as well as a subset of cellular gene promoters. Here we show that the HTLV-I long terminal repeat (LTR) is responsive to HBV X transactivation. Maximum levels of X-mediated transactivation of the LTR were 8-fold. An X-responsive-region (XRR) of the LTR is located between nucleotides -355 and -276 and contains an AP-2 binding site, a previously recognized X-responsive element. We demonstrated that Tax and X synergize to activate transcription from the HTLV-I LTR, although the AP-2 binding site was not required for this synergy. These results raise the possibility that the HBV X protein may affect the level of HTLV-I gene expression in co-infected individuals.

Identification of a variable region at the carboxy terminus of SV40 large T-antigen

The entire early regions of three human isolates of simian virus 40 (SV40), as well as two laboratory strains recovered from monkeys, were sequenced. The early coding region of each isolate contains a number of nucleotide differences when compared to the reference strain SV40-776. These differences result in some changes in the predicted amino acid sequence of the unique region of small t-antigen and in the carboxy (C) terminus of large T-antigen. The amino acid sequence of the remainder of large T-antigen was absolutely conserved among all isolates. Thus, SV40 large T-antigen contains a variable domain at the C-terminal end of the molecule.

Increased sensitivity to the hepatocarcinogen diethylnitrosamine in transgenic mice carrying the hepatitis B virus X gene

The role of the hepatitis B virus (HBV) X protein in liver tumorigenesis is unresolved. Transgenic mice harboring the X gene (nt 1376-1840 under the control of the human alpha-1-antitrypsin regulatory elements) (ATX mice) display only minor histopathologic alterations of the liver. To determine if ATX mice are more susceptible to the effects of hepatocarcinogens, 12- to 15-d-old male ATX and control littermate mice were injected with a single dose (2 microgram/g body weight) of diethylnitrosamine (DEN). The animals were killed 6-10 mo after exposure and were analyzed for histological changes in the liver. One hundred percent of the DEN-treated AXT mice developed abnormal liver lesions. Then their liver tissues were compared by stereological analysis with those of non-transgenic animals, the ATX mice had a relative twofold increase in the total number of focal lesion and a twofold increase in the incidence of hepatocellular carcinoma. Elevated levels of X protein and p53 protein were not detected in carcinogen-induced nodules or tumors. These results are consistent with a model in which the expression of the HBV X protein potentiates the induction of DEN-mediated liver disease.

Increased sensitivity to the hepatocarcinogen diethylnitrosamine in transgenic mice carrying the hepatitis B virus X gene

The role of the hepatitis B virus (HBV) X protein in liver tumorigenesis is unresolved. Transgenic mice harboring the X gene (nt 1376-1840 under the control of the human alpha-1-antitrypsin regulatory elements) (ATX mice) display only minor histopathologic alterations of the liver. To determine if ATX mice are more susceptible to the effects of hepatocarcinogens, 12- to 15-d-old male ATX and control littermate mice were injected with a single dose (2 microgram/g body weight) of diethylnitrosamine (DEN). The animals were killed 6-10 mo after exposure and were analyzed for histological changes in the liver. One hundred percent of the DEN-treated AXT mice developed abnormal liver lesions. Then their liver tissues were compared by stereological analysis with those of non-transgenic animals, the ATX mice had a relative twofold increase in the total number of focal lesion and a twofold increase in the incidence of hepatocellular carcinoma. Elevated levels of X protein and p53 protein were not detected in carcinogen-induced nodules or tumors. These results are consistent with a model in which the expression of the HBV X protein potentiates the induction of DEN-mediated liver disease.

Increased sensitivity to the hepatocarcinogen diethylnitrosamine in transgenic mice carrying the hepatitis B virus X gene

The role of the hepatitis B virus (HBV) X protein in liver tumorigenesis is unresolved. Transgenic mice harboring the X gene (nt 1376-1840 under the control of the human alpha-1-antitrypsin regulatory elements) (ATX mice) display only minor histopathologic alterations of the liver. To determine if ATX mice are more susceptible to the effects of hepatocarcinogens, 12- to 15-d-old male ATX and control littermate mice were injected with a single dose (2 microgram/g body weight) of diethylnitrosamine (DEN). The animals were killed 6-10 mo after exposure and were analyzed for histological changes in the liver. One hundred percent of the DEN-treated AXT mice developed abnormal liver lesions. Then their liver tissues were compared by stereological analysis with those of non-transgenic animals, the ATX mice had a relative twofold increase in the total number of focal lesion and a twofold increase in the incidence of hepatocellular carcinoma. Elevated levels of X protein and p53 protein were not detected in carcinogen-induced nodules or tumors. These results are consistent with a model in which the expression of the HBV X protein potentiates the induction of DEN-mediated liver disease.

Increased sensitivity to the hepatocarcinogen diethylnitrosamine in transgenic mice carrying the hepatitis B virus X gene

The role of the hepatitis B virus (HBV) X protein in liver tumorigenesis is unresolved. Transgenic mice harboring the X gene (nt 1376-1840 under the control of the human alpha-1-antitrypsin regulatory elements) (ATX mice) display only minor histopathologic alterations of the liver. To determine if ATX mice are more susceptible to the effects of hepatocarcinogens, 12- to 15-d-old male ATX and control littermate mice were injected with a single dose (2 microgram/g body weight) of diethylnitrosamine (DEN). The animals were killed 6-10 mo after exposure and were analyzed for histological changes in the liver. One hundred percent of the DEN-treated AXT mice developed abnormal liver lesions. Then their liver tissues were compared by stereological analysis with those of non-transgenic animals, the ATX mice had a relative twofold increase in the total number of focal lesion and a twofold increase in the incidence of hepatocellular carcinoma. Elevated levels of X protein and p53 protein were not detected in carcinogen-induced nodules or tumors. These results are consistent with a model in which the expression of the HBV X protein potentiates the induction of DEN-mediated liver disease.

Natural simian virus 40 strains are present in human choroid plexus and ependymoma tumors

Simian virus 40 (SV40) sequences for large tumor antigen (T-ag) were recently detected in a significant fraction of certain human brain tumors of early childhood (Bergsagel et al., N. Engl. J. Med. 326, 988-993, 1992). In the current study, we sought to determine whether authentic SV40 was present in the choroid plexus and ependymoma tumors previously examined. Polymerase chain reaction and DNA sequence analysis revealed authentic SV40 regulatory region and major capsid (VP1) sequences in 14 of 17 tumors tested. Only one 72-basepair element was detected in the SV40 enhancer region of positive tumor samples, an arrangement designated as "archetypal." The C terminus of the T-ag gene was detected in the same 14 tumors and was sequenced from 5 tumors; some nucleotide changes were found that would result in amino acid changes in T-ag. Infectious SV40 was isolated from one sample after lipofection of tumor DNA into monkey kidney cells. Sequence analysis of the rescued virus SVCPC revealed (i) an archetypal regulatory region, (ii) nucleotide changes in the C terminus of the T-ag gene that distinguished it from SV40 laboratory strains 776 and SV40-B2 and from human isolate SVPML-1, and (iii) identity with previous human brain tumor isolate SVMEN in the three genomic regions sequenced. No human-isolate-specific distinguishing features were detected among the viral sequences analyzed. Thus, authentic SV40 is present in humans and associated with two tumor types known to be induced experimentally by the virus.

Expression of the mouse mammary tumor virus long terminal repeat open reading frame promotes tumorigenic potential of hyperplastic mouse mammary epithelial cells

The retrovirus mouse mammary tumor virus (MMTV) 3' long terminal repeat (LTR) contains an open reading frame (ORF) for a 36-kDa protein and encodes a superantigen activity [pORF(sag)]. We have tested the potential oncogenic activity of pORF(sag) in two immortalized mouse mammary epithelial cells. We subcloned MMTV LTR ORF DNA into the pRc/CMV mammalian expression vector in order to place LTR ORF transcription under the control of the constitutive CMV promoter. Mouse mammary epithelial cell lines TM3 and FSK7e4 were transfected and G418-resistant cell clones were isolated. Reverse transcription-polymerase chain reaction and Northern blot analyses revealed modest overexpression of LTR RNA in several transfected cell clones of each line. Individual cell clones were transplanted into cleared mammary gland fat pads of syngeneic BALB/c mice. The parental cell lines and FSK7e4-derived clones did not form tumors, whereas ORF-transfected clones derived from the TM3 cells formed tumors within 8 weeks in 100% of transplanted fat pads in multiple experiments. The tumor cells expressed exogenous LTR ORF RNA and were proven to be derivatives of TM3 cells based on a marker p53 mutation. Immunohistochemistry using a polyclonal antiserum raised against pORF(sag) expressed in insect cells revealed a cytoplasmic reaction in TM3-CMV-LTR tumor cells; a much weaker cytoplasmic reaction was detected in the transfected tissue culture cells. These observations suggest that MMTV pORF(sag) may act as an oncogene in certain mouse mammary epithelial cells and raise the possibility that pORF(sag) may have a role in mammary tumorigenesis. As the parental FSK7 cell line has produced only ductal outgrowths upon transplantation in vivo and the TM3 cell line produces a nontumorigenic hyperplasia, the results suggest further that pORF(sag) may influence the latter stages of mammary tumorigenesis, namely, the preneoplastic to neoplastic transformation.

Detection of retroviral superantigen and products of the envelope gene from endogenous mouse mammary tumor virus in B cells from BALB/c mice

Minor lymphocyte-stimulating antigens and other superantigens have been shown to be encoded by the 3' long terminal repeat (LTR) open reading frame (ORF) of the endogenous and exogenous mammary tumor viruses. We have previously reported the presence of an antigen(s) related to mouse mammary tumor virus (MMTV) env products in splenic B cells of BALB/c mice. By Western blots an MMTV-related molecule of 68 kDa was detected in splenic preparations of B lymphocytes, but not in T cells. Antibodies against the MMTV envelope proteins gp52 and gp36, obtained by elution after binding to nitrocellulose in the presence of purified MMTV, reacted in Western blots with a 68-kDa protein present in B cells, indicating that this molecule is related to both MMTV envelope proteins. Using antibody against the MMTV 3' LTR ORF coding sequence, 10-15% of splenic B cells reacted by immunoperoxidase staining with this reagent, while no such staining was observed in splenic T cell preparations. Furthermore, in preparations of splenic B cells, but not T cells, two bands of 68 and 33 kDa, respectively, were detected by Western blots using the anti-ORF. These results demonstrate that the superantigen protein is present in B cells of BALB/c mice in two distinct forms, i.e., as a 68-kDa molecule, possibly associated with products of the env gene, and as a 33-kDa form.

Inhibition of HIV-1 by a double transdominant fusion gene

A double transdominant fusion gene (trev) designed to inhibit two essential HIV functions simultaneously was constructed by linking tat and rev transdominant mutants. Trev independently inhibited both Tat and Rev functions, localized within the nucleus and cells transfected with trev showed a stable inhibition of HIV-1-mediated cytopathicity. A retroviral vector of trev was made and shown also to confer protection from HIV cytopathic effects. Simultaneous inhibition of two essential viral genes presents significant advantages for potential gene therapy treatment of HIV infection over conventional single effect molecules.

Hepatitis B virus X protein interacts with a probable cellular DNA repair protein

The mechanism of action of hepatitis B virus (HBV) X protein in transcriptional transactivation and in tumorigenesis remains obscure. We have used the yeast two-hybrid system to identify a cellular protein that can interact with HBV X protein. This protein, designated X-associated protein 1 (XAP-1), is a human homolog of the UV-damaged DNA-binding protein (UV-DDB) recovered from a monkey cell cDNA library. UV-DDB is presumed to be involved in DNA repair. The interaction between X protein and XAP-1 protein was verified by immunoprecipitation of yeast cell lysates expressing both proteins and by in vitro mixing with X protein expressed as a glutathione S-transferase fusion protein and XAP-1 protein either in HeLa cell extracts or synthesized by in vitro translation. We speculate that the interaction of X protein with a DNA repair protein may recruit cellular proteins to repair the partially double-stranded HBV genome or may modify cellular transcription processes. An effect on the cellular DNA repair system may explain a cofactor role for HBV in liver cancer development.

Artificial modification of the viral regulatory region improves tissue culture growth of SV40 strain 776

We describe here changes in the regulatory region of SV40 that influence its growth potential in cultured cells. Laboratory strains of papovaviruses BK and JC differ in the sequence of their regulatory regions from archetypes that have not been passaged in cell culture. These archetypes lack sequence repeats in the regulatory region; duplications that occur upon passage in cell culture confer selective growth advantage. Changes within the enhancer-promoter region of the well-characterized 776 strain of papovavirus SV40 that might affect its growth in tissue culture cells have not been documented. We measured the effect upon the growth of SV40 (776 strain) in CV-1 cells either of adding an additional 72-basepair (bp) enhancer element or of duplicating the entire 21-bp repeat region. SV40 growth in tissue culture was improved by reiteration of enhancer elements, whereas no growth advantage was conferred by tandem duplication of the 21-bp repeats. Viral DNA infectivity in CV-1 cells was directly proportional to the number of 72-bp elements but was unaffected by tandemly repeated 21-bp repeat elements. This study suggests that the 776 strain of SV40 is an evolutionary intermediate and that tissue-culture-adapted strains of SV40 do not accurately reflect the replication potential of natural isolates from primate hosts.

Tumor suppressor p53 mutations and breast cancer: a critical analysis

Alterations in the tumor suppressor gene p53 are the most commonly identified changes in cancer, including neoplasia of the breast. The activity of p53 is regulated post-translationally. Phosphorylation state, subcellular localization, and interaction with any of a number of cellular proteins are likely to influence the function of p53. The exact effect of p53-mediated growth suppression seems to be cell-type specific but appears to be directly related to the ability of p53 to act as a specific transcriptional activator. The role that transcriptional repression plays in the function of WT p53 is less clear. It is also possible that p53 has a more direct activity in DNA replication and repair. Most documented p53 mutations result in single amino acid substitutions which may confer one or more of a spectrum of transforming abilities on the protein. Mutation may lead to nuclear accumulation of p53 protein; however, inactivation of p53 by nuclear exclusion and interaction with the mdm2 protein also appear to be important in tumorigenesis. Used in conjunction with other established factors, accumulation of cellular p53 may be a useful prognostic indicator in breast cancer. A syngeneic mouse model system yielded evidence that p53 mutations are important in the early, preneoplastic stages of mammary tumorigenesis. This murine system may provide the ability to investigate the functions of p53 in the early stages of breast cancer which are technically difficult to examine in the human system.