Dental Stem Cells SV40, a new cell line developed in vitro from human stem cells of the apical papilla

AIM

To establish and fully characterize a new cell line from human stem cells of the apical papilla (SCAPs) through immortalization with an SV40 large T antigen.

METHODOLOGY

Human SCAPs were isolated and transfected with an SV40 large T antigen and treated with puromycin to select the infected population. Expression of human mesenchymal surface markers CD73, CD90 and CD105 was assessed in the new cell line named Dental Stem Cells SV40 (DSCS) by flow cytometry at early and late passages. Cell contact inhibition and proliferation were also analysed. To evaluate trilineage differentiation, quantitative polymerase chain reaction and histological staining were performed.

RESULTS

DSCS cell flow cytometry confirmed the expression of mesenchymal surface markers even in late passages [100% positive for CD73 and CD90 and 98.9% for CD105 at passage (P) 25]. Fewer than 0.5% were positive for haematopoietic cell markers (CD45 and CD34). DSCS cells also showed increased proliferation when compared to the primary culture after 48 h, with a doubling time of 23.46 h for DSCS cells and 40.31 h for SCAPs, and retained the capacity to grow for >45 passages (150 population doubling) and their spindle-shaped morphology. Trilineage differentiation potential was confirmed through histochemical staining and gene expression of the chondrogenic markers SOX9 and COL2A1, adipogenic markers CEBPA and LPL, and osteogenic markers COL1A1 and ALPL.

CONCLUSIONS

The new cell line derived from human SCAPs has multipotency, retains its morphology and expression of mesenchymal surface markers and shows higher proliferative capacity even at late passages (P45). DSCS cells can be used for in vitro study of root development and to achieve a better understanding of the regenerative mechanisms.

GRK2 mediates β-arrestin interactions with 5-HT(2) receptors for JC polyomavirus endocytosis

JC polyomavirus (JCPyV) infects the majority of the population, establishing a lifelong, asymptomatic infection in the kidney of healthy individuals. People that become severely immunocompromised may experience JCPyV reactivation, which can cause progressive multifocal leukoencephalopathy (PML), a neurodegenerative disease. Due to a lack of therapeutic options, PML results in fatality or significant debilitation among affected individuals. Cellular internalization of JCPyV is mediated by serotonin 5-hydroxytryptamine subfamily 2 receptors (5-HT₂Rs) via clathrin-mediated endocytosis. The JCPyV entry process requires the clathrin-scaffolding proteins β-arrestin, adaptor protein 2 (AP2), and dynamin. Further, a β-arrestin interacting domain, the Ala-Ser-Lys (ASK) motif, within the C-terminus of 5-HT_2AR is important for JCPyV internalization and infection. Interestingly, 5-HT₂R subtypes A, B, and C equally support JCPyV entry and infection, and all subtypes contain an ASK motif, suggesting a conserved mechanism for viral entry. However, the role of the 5-HT₂R ASK motifs and the activation of β-arrestin-associated proteins during internalization has not been fully elucidated. Through mutagenesis, the ASK motifs within 5-HT_2BR and 5-HT_2CR were identified as critical for JCPyV internalization and infectivity. Further, utilizing biochemical pulldown techniques, mutagenesis of the ASK motifs in 5-HT_2BR and 5-HT_2CR resulted in reduced β-arrestin binding. Utilizing small-molecule chemical inhibitors and RNA interference, G-protein receptor kinase 2 (GRK2) was determined to be required for JCPyV internalization and infection by mediating interactions between β-arrestin and the ASK motif of 5-HT₂Rs. These findings demonstrate that GRK2 and β-arrestin interactions with 5-HT₂Rs are critical for JCPyV entry by clathrin-mediated endocytosis and resultant infection.IMPORTANCE As intracellular parasites, viruses require a host cell to replicate and cause disease. Therefore, virus-host interactions contribute to viral pathogenesis. JC polyomavirus (JCPyV) infects most of the population, establishing a lifelong asymptomatic infection within the kidney. Under conditions of severe immunosuppression JCPyV may spread to the central nervous system, causing the fatal demyelinating disease progressive multifocal leukoencephalopathy (PML). Individuals living with HIV or undergoing immunomodulatory therapies are at risk for developing PML. The mechanisms of how JCPyV uses specific receptors on the surface of host cells to initiate internalization and infection is a poorly understood process. We have further identified cellular proteins involved in JCPyV internalization and infection and elucidated their specific interactions that are responsible for activation of receptors. Collectively, these findings illuminate how viruses usurp cellular receptors during infection, contributing to current development efforts for therapeutic options for the treatment or prevention of PML.

Viral gene delivery vectors: the next generation medicines for immune-related diseases

Viruses have evolved to efficiently express their genes in host cells, which makes them ideally suited as gene delivery vectors for gene and immunotherapies. Replication competent (RC) viral vectors encoding foreign or self-proteins induce strong T-cell responses that can be used for the development of effective cancer treatments. Replication-defective (RD) viral vectors encoding self-proteins are non-immunogenic when introduced in a host naïve for the cognate virus. RD viral vectors can be used to develop gene replacement therapies for genetic disorders and tolerization therapies for autoimmune diseases and allergies. Degenerative/inflammatory diseases are associated with chronic inflammation and immune responses that damage the tissues involved. These diseases therefore strongly resemble autoimmune diseases. This review deals with the use of RC and RD viral vectors for unraveling the pathogenesis of immune-related diseases and their application to the development of the next generation prophylactics and therapeutics for todays' major diseases.

Genomic Perspective on Mouse Liver Cancer Models

Selecting the most appropriate mouse model that best recapitulates human hepatocellular carcinoma (HCC) allows translation of preclinical mouse studies into clinical studies. In the era of cancer genomics, comprehensive and integrative analysis of the human HCC genome has allowed categorization of HCC according to molecular subtypes. Despite the variety of mouse models that are available for preclinical research, there is a lack of evidence for mouse models that closely resemble human HCC. Therefore, it is necessary to identify the accurate mouse models that represent human HCC based on molecular subtype as well as histologic aggressiveness. In this review, we summarize the mouse models integrated with human HCC genomic data to provide information regarding the models that recapitulates the distinct aspect of HCC biology and prognosis based on molecular subtypes.

Crystallization, Reentrant Melting, and Resolubilization of Virus Nanoparticles

Crystallization is a fundamental and ubiquitous process that is well understood in the case of atoms or small molecules, but its outcome is still hard to predict in the case of nanoparticles or macromolecular complexes. Controlling the organization of virus nanoparticles into a variety of 3D supramolecular architectures is often done by multivalent ions and is of great interest for biomedical applications such as drug or gene delivery and biosensing, as well as for bionanomaterials and catalysis. In this paper, we show that slow dialysis, over several hours, of wild-type Simian Virus 40 (wt SV40) nanoparticle solution against salt solutions containing MgCl₂, with or without added NaCl, results in wt SV40 nanoparticles arranged in a body cubic center crystal structure with Im3m space group, as a thermodynamic product, in coexistence with soluble wt SV40 nanoparticles. The nanoparticle crystals formed above a critical MgCl₂ concentrations. Reentrant melting and resolubilization of the virus nanoparticles took place when the MgCl₂ concentrations passed a second threshold. Using synchrotron solution X-ray scattering we determined the structures and the mass fraction of the soluble and crystal phases as a function of MgCl₂ and NaCl concentrations. A thermodynamic model, which balances the chemical potentials of the Mg²⁺ ions in each of the possible states, explains our observations. The model reveals the mechanism of both the crystallization and the reentrant melting and resolubilization and shows that counterion entropy is the main driving force for both processes.

De Novo Collapsing Glomerulopathy in Renal Allograft in Association with BK Virus Nephropathy in a Child and Stabilization of Renal Function by Elimination of Viremia

Well-recognized association between HIV 1 infection and collapsing glomerulopathy (CG) raises the possibility that intrarenal infection by other viruses may also contribute to the development of this lesion in native or post-transplant kidneys. There is evidence in literature about association of these lesions with cytomegalovirus, Epstein–Barr virus, hepatitis C virus, and parvovirus B19 infections. Here, we present a case report of post-transplant BK virus nephropathy in a male child who was found to have CG in subsequent biopsy 2 months later. His renal function and proteinuria were stabilized on elimination of viremia.

RNA encapsidation by SV40-derived nanoparticles follows a rapid two-state mechanism

Remarkably, uniform virus-like particles self-assemble in a process that appears to follow a rapid kinetic mechanism. The mechanisms by which spherical viruses assemble from hundreds of capsid proteins around nucleic acid, however, are yet unresolved. Using time-resolved small-angle X-ray scattering (TR-SAXS), we have been able to directly visualize SV40 VP1 pentamers encapsidating short RNA molecules (500mers). This assembly process yields T = 1 icosahedral particles comprised of 12 pentamers and one RNA molecule. The reaction is nearly one-third complete within 35 ms, following a two-state kinetic process with no detectable intermediates. Theoretical analysis of kinetics, using a master equation, shows that the assembly process nucleates at the RNA and continues by a cascade of elongation reactions in which one VP1 pentamer is added at a time, with a rate of approximately 10(9) M(-1) s(-1). The reaction is highly robust and faster than the predicted diffusion limit. The emerging molecular mechanism, which appears to be general to viruses that assemble around nucleic acids, implicates long-ranged electrostatic interactions. The model proposes that the growing nucleo-protein complex acts as an electrostatic antenna that attracts other capsid subunits for the encapsidation process.

Malignant mesothelioma: facts, myths, and hypotheses

Malignant mesothelioma (MM) is a neoplasm arising from mesothelial cells lining the pleural, peritoneal, and pericardial cavities. Over 20 million people in the US are at risk of developing MM due to asbestos exposure. MM mortality rates are estimated to increase by 5-10% per year in most industrialized countries until about 2020. The incidence of MM in men has continued to rise during the past 50 years, while the incidence in women appears largely unchanged. It is estimated that about 50-80% of pleural MM in men and 20-30% in women developed in individuals whose history indicates asbestos exposure(s) above that expected from most background settings. While rare for women, about 30% of peritoneal mesothelioma in men has been associated with exposure to asbestos. Erionite is a potent carcinogenic mineral fiber capable of causing both pleural and peritoneal MM. Since erionite is considerably less widespread than asbestos, the number of MM cases associated with erionite exposure is smaller. Asbestos induces DNA alterations mostly by inducing mesothelial cells and reactive macrophages to secrete mutagenic oxygen and nitrogen species. In addition, asbestos carcinogenesis is linked to the chronic inflammatory process caused by the deposition of a sufficient number of asbestos fibers and the consequent release of pro-inflammatory molecules, especially HMGB-1, the master switch that starts the inflammatory process, and TNF-alpha by macrophages and mesothelial cells. Genetic predisposition, radiation exposure and viral infection are co-factors that can alone or together with asbestos and erionite cause MM. J. Cell. Physiol. 227: 44-58, 2012. © 2011 Wiley Periodicals, Inc.

Simian virus 40 induces lamin A/C fluctuations and nuclear envelope deformation during cell entry

The canonical gate of viruses and viral genomes into the nucleus in non-dividing cells is the nuclear pore, embedded within the nuclear envelope. However, we found that for SV40, the nuclear envelope poses a major hurdle to infection: FISH analysis revealed that the majority of viral DNA remains trapped in the ER; silencing of Lamin A/C rendered the cells more susceptible to infection; and proliferating cells are more susceptible to infection than quiescent cells. Surprisingly, we observed that following SV40 infection the nuclear envelope, including lamins A/C, B1, B2 and the nuclear pore complex, was dramatically deformed, as seen by immunohistochemistry. The infection induced fluctuations in the level of lamin A/C, dephosphorylation of an unknown epitope and leakage to the cytoplasm just prior to and during nuclear entry. Deformations were transient, and the spherical structure of the nuclear envelope was restored subsequent to nuclear entry. Nuclear envelope deformations and lamin A/C dephosphorylation depended on caspase-6 cleavage of lamin A/C. Notably, we have previously reported that inhibition of caspase-6 abolishes SV40 infection. Taken together the results suggest that alterations of the nuclear lamina, induced by the infecting virus, are involved in the nuclear entry of the SV40 genome. We propose that SV40 utilize this unique, previously unknown mechanism for direct trafficking of its genome from the ER to the nucleus. As SV40 serves as a paradigm for the pathogenic human BK, JC and Merkel cell polyomavirus, this study suggests nuclear entry as a novel drug target for these infections.

Induction of interferon-stimulated genes by Simian virus 40 T antigens

Simian virus 40 (SV40) large T antigen (TAg) is a multifunctional oncoprotein essential for productive viral infection and for cellular transformation. We have used microarray analysis to examine the global changes in cellular gene expression induced by wild-type T antigen (TAg(wt)) and TAg-mutants in mouse embryo fibroblasts (MEFs). The expression profile of approximately 800 cellular genes was altered by TAg(wt) and a truncated TAg (TAg(N136)), including many genes that influence cell cycle, DNA-replication, transcription, chromatin structure and DNA repair. Unexpectedly, we found a significant number of immune response genes upregulated by TAg(wt) including many interferon-stimulated genes (ISGs) such as ISG56, OAS, Rsad2, Ifi27 and Mx1. Additionally, we also observed activation of STAT1 by TAg(wt). Our genetic studies using several TAg-mutants reveal an unexplored function of TAg and indicate that the LXCXE motif and p53 binding are required for the upregulation of ISGs.

Cellular transformation by Simian Virus 40 and Murine Polyoma Virus T antigens

Simian Virus 40 (SV40) and Mouse Polyoma Virus (PY) are small DNA tumor viruses that have been used extensively to study cellular transformation. The SV40 early region encodes three tumor antigens, large T (LT), small T (ST) and 17KT that contribute to cellular transformation. While PY also encodes LT and ST, the unique middle T (MT) generates most of the transforming activity. SV40 LT mediated transformation requires binding to the tumor suppressor proteins Rb and p53 in the nucleus and ST binding to the protein phosphatase PP2A in the cytoplasm. SV40 LT also binds to several additional cellular proteins including p300, CBP, Cul7, IRS1, Bub1, Nbs1 and Fbxw7 that contribute to viral transformation. PY MT transformation is dependent on binding to PP2A and the Src family protein tyrosine kinases (PTK) and assembly of a signaling complex on cell membranes that leads to transformation in a manner similar to Her2/neu. Phosphorylation of MT tyrosine residues activates key signaling molecules including Shc/Grb2, PI3K and PLCgamma1. The unique contributions of SV40 LT and ST and PY MT to cellular transformation have provided significant insights into our understanding of tumor suppressors, oncogenes and the process of oncogenesis.

High prevalence of human polyomavirus JC VP1 gene sequences in pediatric malignancies

The oncogenic potential of human polyomavirus JC (JCV), a ubiquitous virus that establishes infection during early childhood in approximately 70% of the human population, is unclear. As a neurotropic virus, JCV has been implicated in pediatric central nervous system tumors and has been suggested to be a pathogenic agent in pediatric acute lymphoblastic leukemia. Recent studies have demonstrated JCV gene sequences in pediatric medulloblastomas and among patients with colorectal cancer. JCV early protein T-antigen (TAg) can form complexes with cellular regulatory proteins and thus may play a role in tumorigenesis. Since JCV is detected in B-lymphocytes, a retrospective analysis of pediatric B-cell and non-B-cell malignancies as well as other HIV-associated pediatric malignancies was conducted for the presence of JCV gene sequences. DNA was extracted from 49 pediatric malignancies, including Hodgkin disease, non-Hodgkin lymphoma, large cell lymphoma and sarcoma. Polymerase chain reaction (PCR) was conducted using JCV specific nested primer sets for the transcriptional control region (TCR), TAg, and viral capsid protein 1 (VP1) genes. Southern blot analysis and DNA sequencing were used to confirm specificity of the amplicons. A 215-bp region of the JCV VP1 gene was amplified from 26 (53%) pediatric tumor tissues. The JCV TCR and two JCV gene regions were amplified from a leiomyosarcoma specimen from an HIV-infected patient. The leiomyosarcoma specimen from the cecum harbored the archetype strain of JCV. Including the leiomyosarcoma specimen, three of five specimens sequenced were typed as JCV genotype 2. The failure to amplify JCV TCR, and TAg gene sequences in the presence of JCV VP1 gene sequence is surprising. Even though JCV TAg gene, which is similar to the SV40 TAg gene, is oncogenic in animal models, the presence of JCV gene sequences in pediatric malignancies does not prove causality. In light of the available data on the presence of JCV in normal and cancerous colon epithelial tissue and our data on amplification of JCV from the cecum of an HIV-infected pediatric patient, further studies are warranted on the role of colon epithelium in the pathogenesis of JCV infection.

Normal and SV40 transfected human peritoneal mesothelial cells produce IL-6 and IL-8: implication for gynaecological disease

High levels of interleukin-6 (IL-6) and interleukin-8 (IL-8) have been demonstrated in the peritoneal fluid of benign and malignant gynaecological disease. Peritoneal monocytes and macrophages, endometrial cells, endometrial and peritoneal stromal cells and tumour cells produce these cytokines in vitro. To investigate whether normal human peritoneal mesothelial cells (HPMC) produce IL-6 and IL-8, HPMC were isolated from omental biopsies. Primary HPMC (P-HPMC) were transfected with pSV3-neo encoding SV40 large T antigen (T-HPMC) to generate sufficient cells. T-HPMC preserved the characteristics of P-HPMC as assessed by phase contrast microscopy, electron microscopy, immunocytochemistry and flow cytometry (FACS) analysis. T-HPMC retained a stable phenotype up to passage 14-19, whereas P-HPMC proliferated poorly and became senescent by passage 4-6. T-HPMC and P-HPMC constitutively expressed IL-6 and IL-8 at both protein and mRNA level. IL-6 and IL-8 production was stimulated by recombinant human interleukin-1beta (hIL-1beta) or human tumour necrosis factor-alpha (hTNF-alpha) alone in a dose-dependent manner. Moreover, hIL-1beta or hTNF-alpha up-regulated IL-6 and IL-8 gene expression as determined by competitive PCR. In contrast, human interferon-gamma (hIFN-gamma) or lipopolysaccharide (LPS) showed no effect. These data indicate that (1) T-HPMC lines mimic the morphological and functional features of P-HPMC, (2) P-HPMC and T-HPMC constituitively produce IL-6 and IL-8, which is enhanced by hIL-1beta and hTNF-alpha and (3) HPMC in vivo may participate in the pathogenesis of benign and malignant gynaecological disease.

Thirty-five year mortality following receipt of SV40- contaminated polio vaccine during the neonatal period

Early poliovirus vaccines, both inactivated and live attenuated, were inadvertently contaminated with simian virus 40 (SV40), a monkey virus known to be oncogenic for newborn hamsters. Although large epidemiologic studies have not identified an elevated cancer risk in persons who received SV40-contaminated vaccines, fragments of SV40 DNA have recently been identified in certain human tumours. We report the follow-up of a cohort of 1073 persons, unique because they received SV40-contaminated poliovirus vaccines as newborns in 1961-63. A previous report of the status of these subjects as of 1977-79 identified 15 deaths, none due to cancer. The present study utilized the National Death Index to identify deaths in the cohort for the years 1979-96. Expected deaths were calculated from Cleveland area sex-, age-, race- and year-specific mortality rates. Increased mortality from all causes was not found. 4 deaths from cancer were found compared to 3.16 expected (P = 0.77). However, 2 deaths from testicular cancer occurred, compared to 0.05 expected (P = 0.002), which may be a chance finding due to multiple comparisons. There were 2 deaths due to leukaemia, a non-significant finding, and no deaths due to tumours of the types putatively associated with SV40. Although these results are, for the most part, consistent with other negative epidemiologic investigations of risks from SV40-contaminated vaccines, further study of testicular cancer may be warranted, and it will be important to continue monitoring this cohort which is now reaching middle-age.

Investigation of the SV40--human cancer association: look for the full signature of the virus

In the controversy about the association of simian virus 40 with human cancers, the greatest problem is the ascertainment of SV40 exposure. This difficulty would be resolved if one were to look for all components of SV40 infection. How does SV 40 circulate in the human community? Do cancer patients with SV40-positive tumors have serological correlates of SV 40 infection and of SV40-induced cancer? SV40 association with a cancer should be studied in the context of the known risk factors for that cancer. The tumor cell-virus relationship should be characterized with respect to viral integration and viral localization to the tumor cell. Specimens should be masked and the assays should include panels of specimens to estimate analytic sensitivity and specificity. In view of the rarity of some of the tumors reported to be associated with SV40, a multi-institutional investigation initiated and coordinated by the NIH would be most effective.

High incidence of SV40-like sequences detection in tumour and peripheral blood cells of Japanese osteosarcoma patients

Recent studies have revealed the evidence for the significance of SV40 genome in human malignancies. In this paper, the presence of SV40-like sequences was investigated in 54 Japanese osteosarcomas in which mutations of the retinoblastoma (Rb), p53, MDM2, and CDK4 genes had been already analysed. Using polymerase chain reaction and Southern hybridization, SV40-like sequences were detected in 25 cases (46.3%). In most cases, only a part of SV40 genome was detected, and the regulatory region containing enhancer sequences was most frequently found (21/54, 38.9%). There was no apparent relationship between the presence of SV40-like sequences and tumour suppressor genes mutations in each tumour. The SV40-like sequences were also detected in peripheral blood cells of substantial proportion of the patients (43.3%), whereas the incidence was much lower (4.7%) in normal healthy controls. This difference is statistically highly significant (P < 0.0001), suggesting that the presence of SV40-like sequences, even if only a part, may play some roles to predispose individuals to osteosarcoma.

Changes in membrane structure associated with cell contact

Ultrastructural analysis of 3T3 fibroblasts by freeze-cleavage has demonstrated significant changes in cell-membrane structure associated with cell-to-cell contact and malignant transformation. These changes consist of a rearrangement and redistribution of intramembranous particles on the membrane fracture faces exposed by freeze-cleavage. The results show that noncontacted 3T3 cells in low density contain randomly distributed intramembranous particles. With the development of cell-to-cell contacts during the logarithmic phase of growth however, a pronounced aggregation of intramembranous particles is seen. A direct correlation between the degree of cell contact and the percentage of cells showing intramembranous-particle aggregation has been established. By contrast, transformed SV3T3 and SP3T3 cells show no evidence of intramembranous-particle aggregation even at cell densities where cell-to-cell contact is extensive. In view of recent reports that intramembranous particles represent foci of interaction between certain intrinsic membrane proteins and lipids, we propose that cell-to-cell contact of nontransformed 3T3 cells may initiate a change in the distribution of intrinsic membrane proteins associated with intramembranous particles and that these changes may influence control of cell proliferation.

A factor from a transformed cell line that affects cell migration

When a monolayer culture of normal Balb/c3T3 cells is wounded by scraping away part of the cell sheet, the cells do not migrate into the cleared area unless there is serum in the culture medium. By contrast, SV40-transformed Balb/c3T3 cells do migrate into the wound area without serum. A quantitative assay for the migration of Balb/c3T3 cells into wounds is described. This assay is used in the partial purification of a migration factor released into serum-free medium by SV28 cells. SV28 is a line of BHK21/13 hamster cells transformed by SV40 chosen for its malignancy. The most purified fractions have about 1500 times the specific activity of whole calf serum. These fractions have an activity that promotes overgrowth of Balb/c3T3 cells to high density and an activity that prolongs cell survival without serum. The SV28 migration factor is not extractable from the medium of untransformed BHK21/13 cells or from serum. This migration factor might contribute to the malignancy of SV28 cells.

Cleavage of DNA by R 1 restriction endonuclease generates cohesive ends

R(1) restriction endonuclease cleaves duplex DNA at a specific sequence, probably 6 nucleotide pairs in length, by making two single-strand staggered cleavages, generating 5'-phosphoryl and 3'-hydroxyl termini. The single-strand ends produced at each break have identical and complementary sequences of 4 or 6 nucleotides in length. Therefore, the cleavage site possesses a 2-fold rotational axis of symmetry perpendicular to the helix axis. The ends of full-length linear SV40 DNA, generated by R(1) endonuclease cleavage, can be joined by Escherichia coli ligase to regenerate duplex, fully infectious, covalently-closed circular molecules. It was further found that all R(1) endonuclease-generated ends are identical and complementary. Therefore, any two DNA molecules with R(1) sites can be "recombined" at their restriction sites by the sequential action of R(1) endonuclease and DNA ligase to generate hybrid DNA molecules.

Extensive symmetrical transcription of Simian Virus 40 DNA in virus-yielding cells

Rapidly labeled RNA was extracted from monkey cells after infection with Simian Virus 40 (SV40) and exposure to short pulses of [5-(3)H]uridine late in infection. When this RNA was self-annealed, it became resistant to digestion with ribonuclease. The fraction of RNA that resisted the ribonuclease treatment decreased with increased labeling time, or when a short pulse of radioactivity was followed by incubation with unlabeled uridine and actinomycin D. The RNase-resistant RNA was isolated by chromatography on Sephadex G-100 and shown to be double-stranded by its susceptibility to ribonuclease as a function of salt concentration and temperature. This behavior was not due to RNA-DNA hybrid formation, since deoxyribonuclease had no effect upon the double-stranded molecules, even after their denaturation. The relation of the double-stranded RNA to SV40 was demonstrated by the hybridization of about 50% (corrected value, >90%) of the separated RNA strands with component I of SV40 DNA from plaque-purified virus. After self-annealing in formamide at low temperature, about 10% of the rapidly labeled, viral RNA sedimented at 13 S. This value corresponds in size to about 60% of the SV40 DNA.These observations indicate that late in infection of monkey cells, SV40 DNA is transcribed symmetrically over a considerable portion of its length, and that subsequently some sequences from one or both of the RNA strands are degraded.

Loss of simian virus 40 DNA-RNA hybrids from nitrocellulose membranes; implications for the study of virus--host DNA interactions

Complete hybrids of simian virus 40 (SV40)DNA and its complementary RNA (cRNA) are not retained on nitrocellulose membranes. At saturating cRNA concentrations, retention of the hybrids indicates incomplete homology between DNA and RNA, probably due to incorporation of host DNA in the viral DNA; this effect is most pronounced when DNA is produced in cells infected at high multiplicity. Hybrids between DNA of Chinese hamster cells transformed by SV40 and cRNA are retained if the DNA fragments are long, but they are lost if the DNA is sheared to less than the length of an SV40 DNA molecule. Hence, in cells examined with about six SV40 genomes per cell, each genome is individually integrated. The results may explain previous discrepancies in the estimation of the number of viral genomes in transformed cells.

Patterns of Simian Virus 40 DNA transcription after acute infection of permissive and nonpermissive cells

Small amounts of fractionated, denatured, (32)P-labeled DNA from SV40 virus were incubated with a large excess of the complementary RNA of SV40 prepared in vitro with Escherichia coli RNA polymerase; the viral DNA strands were separated on hydroxyapatite columns. The RNA present in green monkey cells late in the lytic cycle reacted with 40-42% of the strand complementary to the in vitro complementary RNA (minus strand), and 60-64% of the opposite (plus) strand. "Early lytic" RNA failed to significantly interact with the plus strand, but formed stable duplex molecules with 35-39% of the minus strand. The RNA prepared from mouse embryo cells 24 hr after infection with SV40 combined with 35-38% of the minus strand and 60-62% of the plus strand. In all cases, the same regions of either the plus or minus strand appear to be transcribed in permissive and nonpermissive infections.

Increased uptake of amino acids and 2-deoxy-D-glucose by virus-transformed cells in culture

Transformed and nontransformed cells in tissue culture differ in their rate of uptake of certain nutrients, as determined by a polyester-coverslip technique. A 2.5- to 3.5-fold increased rate of uptake of alpha-aminoisobutyric acid, cycloleucine, and 2-deoxy-D-glucose was observed with polyoma virus-transformed baby hamster kidney (BHK) 21 cells and simian virus 40 (SV40)-transformed BALB/3T3 (mouse fibroblast) cells, compared to their nontransformed counterparts. Kinetic analysis suggested that the increased uptake by cells transformed with virus was associated with a 3-fold greater V(max), with no detectable changes in apparent K(m). Limited studies also revealed increased initial rates of uptake by murine sarcoma virus-transformed rat liver cells, as compared to the parental line. Exposure of cells to concanavalin A and wheat-germ agglutinin led to significant reductions in amino-acid uptake by both transformed and nontransformed cells; however, transformed cells showed a greater decrease in uptake after exposure to wheat-germ agglutinin. Increased initial rates of uptake of certain amino acids and sugars may be a feature common to transformed cells, compared to their parental control.

Mutation causing temperature-sensitive expression of cell transformation by a tumor virus (SV40-3T3 mouse cells-growth control)

A procedure has been devised to isolate 3T3 mouse fibroblasts transformed by simian virus 40 (SV40) that express their transformed phenotype at low (32 degrees C) but not at high (39 degrees C) temperature. Three parameters typical of malignant growth in vitro: (a) high saturation density in culture, (b) ability to form colonies on monolayers of normal 3T3 cells, and (c) lack of contact inhibition of DNA synthesis, are temperature sensitive. These phenotypic changes are fully reversible. The serum requirement for growth appears to be largely unchanged by temperature. These cells seem to owe their behavior to a cellular, rather than to a viral, alteration since after fusion of the temperature-sensitive transformed cells with permissive monkey cells, a procedure that leads to rescue (i.e., multiplication of the virus), wild-type SV40 virus is produced.