Monomer molecular weight of T antigen from simian virus 40-infected and transformed cells

T-antigens from simian virus 40 (SV 40)-transformed and lytically infected cells have been isolated by immunoprecipitation and their molecular weights estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. T-antigen from SV40-transformed mouse and hamster cells has an apparent molecular weight of 94,000 whereas that from several lines of SV40-infected monkey cells is 84,000. In a wheat germ cell-free system, mRNA from either transformed or productively infected cells is translated into a 94,000 species. Experiments with the protease inhibitors L-l-(tosylamide-2-phenyl)ethylchloromethyl ketone HCl and N-alpha-p-tosyl-L-lysylchloromethyl ketone HCl suggest that the 84,000 species of T-antigen found in infected cells is derived from the larger species by proteolytic cleavage. Further, the cleavage pathway probably involves a two-step reaction with an 89,000 intermediate. The biological significance of the two molecular weight forms of T-antigen is unknown, but the possibility that they have different physiological activities is discussed.

Excision of viral DNA from host cell DNA after induction of simian virus 40-transformed hamster cells

Simian virus 40-transformed hamster cells were induced to produce infectious virus by treatment with mitomycin C or gamma-irradiation. A portion of the simian virus-40 DNA, which is integrated into the host cell genome in uninduced cells, was recovered in a pool of relatively low-molecular-weight DNA early after induction treatment in the absence of DNA replication. The data indicte that excision of the viral genome occurs subsequent to the induction stimulus.

Effect of passage in culture on a clone of BALB/c 3T3 cells transformed by simian virus 40

Most simian virus 40 (SV40)-transformed BALB/c 3T3 clones employed for biochemical studies have been used without regard to passage level. To determine whether virus-induced properties are stable as a function of passage, we have extensively characterized one transformed clone, FNE, which was isolated after SV40 infection BALB/c 3T3 cells in factor-free medium. From the initial testing at passage 5 and for at least 50 subsequent subcultures, the cells stably maintained many transformed growth properties, including high saturation density, morphology, colony formation on contact-inhibited monolayers, tumorigenicity, and synthesis of viral-specific RNA. However, other properties varied as a function of passage. There was a slight decrease in viral genome equivalents per cell from 1.1 copy/cell at passage 5 to 0.7 copies at passage 40. Initially, the cells were negative for all type C virus; however, cells carried at low density for 13 to 20 passages (65 to 100 generations) began to release an endogenous type C virus that then persisted in the culture. Spontaneous release of type C virus did not occur in control BALB/c 3T3 cells carried under identical culture conditions for 90 passages. When the cultures were releasing type C viruses they stained uniformly and brightly positive for SV40 tumor (T) antigen by immunofluorescence, whereas T antigen staining was variable at early passage. These experiments suggest that subtle but perhaps important differences in viral gene expression can occur as a function of passage; they also demonstrate the importance of evaluating the interactions between SV40 and endogenous type C viruses.

Characterization of simian cells tranformed by temperature-sensitive mutants of simian virus 40

Seven lines derived from primary African green monkey kidney cells, which had survived lytic infection by wild-type simian virus 40 (SV40) or temperature-sensitive mutants belonging to the A and B complementation groups, were established. These cultures synthesize SV40 tumor (T) antigen constitutively and have been passaged more than 60 times in vitro. The cells released small amounts of virus even at high passage levels but eventually became negative for the spontaneous release of virus. Virus rescued from such "nonproducer" cells by the transfection technique exhibited the growth properties of the original inoculum virus. Four of the cell lines were tested for the presence of altered growth patterns commonly associated with SV40-induced transformation. Although each of the cell lines was greater than 99% positive for T antigen, none of the cultures could be distinguished from primary or stable lines of normal simian cells on the basis of morphology, saturation density in high or low serum concentrations, colony formation on plastic or in soft agar, hexose transport, or concanavalin A agglutinability. However, the cells could be distinguished from the parental green monkey kidney cells by a prolonged life span, the presence of T antigen, a resistance to the replication of superinfecting SV40 virus or SV40 viral DNA, and, with three of the four lines, an ability to complement the growth of human adenovirus type 7. These properties were expressed independent of the temperature of incubation. These results indicate that the presence of an immunologically reactive SV40 T antigen is not sufficient to ensure induction of phenotypic transformation and suggest that a specific interaction between viral and cellular genes and/or gene products may be a necessary requirement.

Systematic variables affecting simian virus 40-induced T-antigen expression and transformation in human cells

Simian virus 40 (SV40) infection of human skin fibroblast and human tumor cells resulted in the expression of T-antigen and transformed foci. By examining various conditions of input virus multiplicity and initial cell density, the systematic variation of T-antigen determination was minimized. The most uniform results were obtained at multiplicities of about 275 plaque-forming units/cell. Within limits (5 X 10(4) to 2 X 10(5) cells/dish), initial cell density had little effect on T-antigen expression. Volume of virus inoculum was critical for some cell lines, but not for others. Cell passage level had no general effect on T-antigen expression, although specific cell lines demonstrated increased or decreased levels of T-antigen expression with serial passage for no apparent reason. T-antigen expression correlated with virus-induced cell transformation (focus formation) at two different multiplicities. In addition, T-antigen assays at 3 days gave consistently more reproducible results than transformation assays at 21 days in seven cell lines tested at two multiplicities of infection. These results defined input multiplicity as the major source of systematic variability and will permit development of a more reproducible tool in the evaluation of individuals at high risk of cancer.

Simian virus 40-specific polypeptides in AD2+ ND1- and Ad2+ ND4-infected cells

A comparison of the proteins synthesized in human cells at late times after infection with adenovirus (Ad2) and with the adeno-simian virus 40 (SV40) hybrid viruses revealed polypeptides of 30,000 and 92,000 molecular weight specific for the hybrid viruses Ad2+ND1 and Ad2+ND4, respectively. Cell-free translation of SV40-specific mRNA, prepared from these cells by hybridization of total cytoplasmic RNA to SV40 DNA, showed that the mRNA's specifying these two polypeptides were at least partially encoded by the SV40 portion of the hybrid viruses. Cell-free translation of SV40-specific mRNA prepared from monkey cells infected with SV40 produced polypeptides of 40,000, 43,000, 48,500, and 92,000 molecular weight. The SV40 and Ad2+ND4 92,000-molecular-weight polypeptides made in vitro were very similar in electrophoretic mobility in sodium dodecyl sulfate-polyacrylamide gels to the polypeptide precipitated by Tegtmeyer (1974) with SV40 anti-T serum.

Construction and analysis of viable deletion mutants of simian virus 40

Viable mutants of simian virus 40 (SV40), with deletions ranging in size from 15 to 200 base pairs, have been obtained by infecting CV-1P cells with circularly permuted linear SV40 DNA. The linear DNA was produced by cleavage of closed circular DNA with DNase I in the presence of Mn2+, followed, in some cases, by mild digestion with lambda 5'-exonuclease. The SV40 map location and the size of each deletion were determined by using the S1 nuclease mapping procedure (Shenk et al., 1975) and the change in size of fragments produced by Hind II + III endonuclease cleavage. Deletions in at least three regions of the SV40 chromosome have slight or no effect on the rate or yield of viral multiplication and on vira-induced cellular transformation. These regions are located at the following coordinates on the SV40 physical map: 0.17 to 0.18; 0.54 to 0.59; and 0.68 to 0.74.

A scanning electron microscopic study of SV40 infected cells

The surface of the SV40-infected African green monkey kidney (AGMK) cells was studied morphologically by scanning electron microscopy. In 24 hr post infection (p.i.), the cell surface was covered with slightly elongated microvilli. The microvilli increased in number. In 96 hr.p.i. most of the cells showed SV40-specific cytopathic effects (CPE). Nuclear swellings and the elongation of microvilli were eminent. Microvilli were observed projecting with high densities especially on the nuclear portions of the cell surfaces. Features suggesting cytoplasmic vacuolization were also observed in some cells. Spherical particles viewed in some of the cells at the late stage of infection were considered SV40 virions. Their origin was also discussed.

Cell killing by simian virus 40: variation in the pattern of lysosomal enzyme release, cellular enzyme release, and cell death during productive infection of normal and simian virus 40-transformed simian cell lines

Simian virus 40 (SV40) growth on rhesus kidney cells and on the T-22 line of SV40-transformed green monkey kidney (GMK) cells is largely limited by the low plating efficiency of SV40 on these cells. In addition, a fraction of the rhesus kidney and T-22 cells are resistant to infection by SV40. Nevertheless, 72-h viral yields per infected rhesus kidney and T-22 cell are nearly equivalent to that obtained on normal GMK cells and are independent of the multiplicity of infection. Despite the production of high viral yields, infected rhesus kidney and T-22 cells are killed slowly by SV40. Monolayers of these cells are also refractory to plaque formation by SV40. SV40 induces the release of lysosomal N-acetyl-beta-glucosaminidase into the cytoplasmic fractions of rhesus kidney and T-22 cells to an extent equal to that observed during infection of rapidly killed normal GMK cells. In contrast, damage to the plasma membrane, as indicated by the release of the cellular enzymes lactic dehydrogenase and glutamic oxaloacetic transaminase into the overlay media, occurred to a much greater extent in the normal GMK cells than in the rhesus kidney or T-22 cells. Neither a lysosomal hydrolase mechanism nor viral release appear to be responsible for this phenomenon. The different rates and extents of the SV40 cytocidal process on these cells do not result from the differences in the viral plating efficiency on them.

Construction and propagation of a defective simian virus 40 genome bearing an operator from bacteriophage lambda

A 2400 base pair DNA segment containing the leftward operator (OL) of phage lambda was covalently joined in vitro to a fragment of simian virus 40 (SV40) DNA harboring the SV40 replication origin. The recombinant molecule was propagated in the presence of helper wild-type SV40 DNA in monkey kidney cells and partially cloned by an infectious center procedure. After propagation in monkey cells and purification, the hybrid DNA could be distinguished from wild-type SV40 DNA by its shortened length (about 80% that of SV40), specific hybridization to denatured lambda DNA immobilized on filters, specific affinity for lambda repressor, and preservation of a large part (about 2300 base pairs) of the lambda immunity region as determined by restriction nuclease cleavage patterns and electron microscopic heteroduplex analysis. These results indicate that defective SV40 replicons can serve as vectors for propagating foreign DNA in mammalian cells.

Fluctuation in activity of the molecular forms of cellular DNA polymerase during infection by SV40

Infection of BSC-1 cells by SV40 brings about an increase of 7--11-fold in DNA polymerase activity, found in the nuclei and cytoplasm, respectively. The overall ratio between activites of DNA polymerase beta (3.1S) and DNA polymerase alpha (5.5S) remains fairly constant throughout infection. However,there is a large increase in DNA polymerase alpha2 (7.1S) in the cytoplasm, and its appearance in the nuclei late in infection. The addition of 1 M NaCl to infected cytoplasm,causes an aggregation of DNA polymerase alpha into a higher sedimenting form (9.8S), termed DNA polymerase alpha3. DNA polymerase alpha1, alpha2 and alpha3 are different molecular forms of the same enzyme, as can be seen by their similar inhibition by N-ethyl-maleimide, heparin and NaCl. However, this new activity, alpha3, is stimulated by dithiothreitol to a greater extent at pH 9.30 than at pH 7.94. The conformational changes induced in DNA polymerase and its increase in activity during infection with SV40 are discussed.

Regulatory mechanism of simian virus 40 gene expression in permissive and in nonpermissive cells

Primary or continuous lines of mouse cells (3T3) are nonpermissive for simian virus 40 (SV40). Abortively infected cells synthesize tumor antigen (T antigen but not viral DNA and virus capsid protein (V antigen). V antigen, however, was obtained when SV40 DNA was injected into 3T3 cells. This late gene expression also appears to be correlated with the quantity of injected DNA molecules per 3T3 cell. T antigen formation can be detected after microinjection of only 1 to 2 DNA molecules, but the intensity of intranuclear T antigen fluorescence is significantly brighter with injection of higher concentrations of viral DNA. In permissive cells (TC7), early and late SV40 gene expression is directly related to the number of injected molecules. Microinjection of 1DNA molecule induced T and V antigen formation with the same efficiency as microinjection of 2,000 to 4,000 molecules. The question of weather late SV40 gene expression is directly related to the quantity of an early virus-specific product was approached by microinjection of early SV40 complementary RNA together with small amounts of viral DNA. V antigen was obtained in a high proportion of recipient 3T3 cells at conditions where microinjection of viral DNA alone induced T but not V antigen synthesis.

Complementation between BK human papovavirus and a simian virus 40 tsA mutant

Complementation tests between BK human papovavirus and SV40 temperature-sensitive mutants tsA58 and tsB11 were performed. Under the reported experimental conditions, BKV complemented the "early" mutant tsA58 but failed to complement the "late" mutant tsB11.

Simian virus 40-chinese hamster kidney cell interaction. II. The semipermissivity of the cell system

Throughout in vitro passages, Chinese hamster kidney (CHK) cells progressively lost susceptibility to SV 40 virus infection while remaining continuously susceptible to viral DNA infection. Upon infection with SV 40 virus or viral DNA, the CHK cell line supported viral DNA and virus replication at a low level. SV 40 transformed CHK cell lines spontaneously produced small amounts of viral DNA and virions. The percentage of virus-producing cells was low. Various clones derived from each of these lines behaved as the parental cell population, leading to the conclusion that each CHK cell, whether transformed or not with SV 40, is potentially permissive for this virus.

Analysis of simian virus 40 wild-type and mutant virions by agarose gel electrophoresis

Intact wild-type simian virus 40 particles can be separated and resolved from a temperature-sensitive mutant and from a number of other viruses by agarose gel electrophoresis. The relative mobilities of the viruses appear to be a function of both virion size and surface composition. The virions of a temperature-sensitive strain of simian virus 40, tsB204, have significantly greater mobility than those of wild-type simian virus 40, when electrophoresis was conducted toward the cathode at pH 5.0. When electrophoresis was performed toward the anode at pH 7.0, TSB204 viruses have a slightly slower mobility as compared with that of the wild type. The data indicated that the virions of tsB204 have a greater positive charge at their surface than those of wild-type particles. No differences were detected in the finger print patterns of the tryptic peptides of VP1 and VP3 of these two virus strains. Although it was not possible to identify the structural polypeptide directly affected by the tsB204 mutation, we have shown that this mutation affects charge distribution on the surface of the virion.

Endonucleases and simian virus 40 virions: origin of a virion-associated endonuclease

The origin and role of the endonuclease activity associated with purified virions of simian virus 40, previously described by this and other laboratories, have been further investigated. We found that the enzymatic activity from virions of temperature-sensitive (ts) mutants is not more heat labile than that from wild-type virions. This result was obtained for a variety of ts mutants, including three of the tsA class, and in experiments in which the enzyme was tested in both the presence and absence of viral particles. Comparison of the viron enzyme with endonucleases prepared from either serum or nuclei of uninfected cells reveals a similarity between the viron and serum enzymes based on chromatographic behavior and relative activity with different cations. Virus particles prepared free of this endonuclease were still infectious. We were unsuccessful in uncovering endonuclease in such preparations upon disruption. These data emphasize the necessity for caution in interpreting the role of particle-associated enzymes.

Variable response of normal and transformed mouse cells to interferon inducers

Balb/3T3 mouse cells, normal and SV40-transformed, produced interferon when induced with Newcastle disease and influenza viruses; transformed cells failed to respond to double-stranded RNA inducers.

Chromatin-like structures in polyoma virus and simian virus 10 lytic cycle

Nucleoprotein complexes containing viral DNA and cellular histones were extracted from nuclei of permissive cells infected with polyoma virus or simian virus 40 (SV40) and examined by electron microscopy. Polyoma and SV40 nucleoprotein complexes are almost identical. They appear as relaxed circular molecules consisting of 20 to 21 globular particles interconnected by thin filaments. Their contour length in 0.02 M salt is 2.7 times shorter than that of viral DNA form I obtained after dissociation of the proteins in 1 M NaCl. The nucleosomes have an average diameter of 12.5 nm. Each nucleosome contains 175 to 205 DNA base pairs condensed fivefold in length. The nucleosomes are regularly spaced on the circular molecule. The internucleosomal filaments are made of naked DNA, and each filament contains about 55 base pairs. The partial sensitivity of the nucleoprotein complex to cleavage by EcoR1 endonuclease suggests that the nucleosomes are not formed at specific sites on the viral genome. Faster sedimenting nucleoprotein complexes containing replicative intermediates were studied. Isopycnic centrifugation in metrizamide gradients in the absence of aldehyde fixation showed that these molecules conserved the same DNA-to-protein ratio as the form I DNA-containing complexes.

Studies on morphological transformation of BALB/3T3-derived clones by murine leukemia virus

We have described a cell line, UC1-B, derived spontaneously from BALB/3T3 mouse embryo cells, which, unlike the standard BALB/3T3, are morphologically transformed and produce bizarre viral forms in response to murine leukemia virus. Although UC1-B and BALB/3T3 are morphologically similar, and both form contact-inhibited monolayers at confluence, the UC1-B cells are partially transformed because: they grow to a slightly higher saturation density than 3T3 cells, they grow in medium lacking serum growth factors, and they produce tumors in mice. Another clone, 12A-3, derived from BALB/3T3, also transforms and produces bizarre viral forms after infection with murine leukemia virus. Unlike UC1-B cells, the 12A3-8 cells are identical in growth properties to BALB/3T3; therefore, a partially altered morphology is not required for the induction of transformation by murine leukemia virus.

Tumorigenicity of mouse-human diploid hybrids in nude mice

Somatic cell hybrids between normal mouse cells and simian virus 40 (SV40)-transformed human cells, which contained a diploid complement of mouse chromosomes and the human chromosome 7 carrying the genome of SV40, were tumorigenic in nude mice. One single copy of human chromosome 7 per hybrid cell appeared to be sufficient for the tumorigenicity of the hybrids.