Simian Virus 40-transformed Hamster Cells Research Articles

Blocked herpes simplex virus type 2-specific DNA synthesis in simian virus 40-transformed hamster cells permissive for herpes simplex virus type 1

Simian virus 40-transformed hamster cells (LL-1) permissive to herpes simplex virus type 1 (HSV-1) were shown to be relatively nonpermissive to HSV-2. When LL-1 cells were infected with HSV-2, there was a 3- to 4-log reduction in infectious viral progeny at 24 h postinfection as compared with HSV-1 under identical cultured conditions. HSV-2 could be carried in the LL-1 cell line for up to 12 passages without any appreciable cytopathology. Various early functions of the replicative cycle of HSV-2 appeared to be normal. Experiments demonstrated that early enzyme activity, HSV-2 thymidine kinase, and DNA polymerase appeared at permissive levels in extracts of HSV-2-infected LL-1 cells. However, DNA analysis of HSV-2 infected LL-1 cells demonstrated a block in HSV-2-specific DNA synthesis, although HSV-2 was capable of inhibiting DNA synthesis in LL-1 cells. Furthermore, indirect immunofluorescence studies indicate that late HSV-2 structural protein synthesis was inhibited in infected LL-1 cells. Thus, the inability of HSV-2 to replicate in LL-1 cells is due to a block at or before HSV-specific DNA synthesis, resulting in a reduction of the structural protein synthesis required for viral maturation.

Resistance of simian virus 40-transformed hamster cells to the cytolytic effect of activated macrophages: a possible factor in species-specific viral oncogenicity.

Simian virus 40 (SV40)-transformed hamster cells were relatively resistant to the lytic effect of activated macrophages from animals with chronic intracellular infections. Conversely, SV40-transformed mouse and rat cells and adenovirus 2-transformed hamster cells were highly susceptible to destruction by tumoricidal activated macrophages. The pattern of resistance or susceptibility of SV40-transformed rodent cells was the same whether activated macrophage effectors were obtained from mice, random-bred hamsters, or the inbred LSH hamsters from which some of the SV40-transformed hamster lines were derived. The results suggest that resistance of transformed cells to macrophage-mediated cytolysis may explain in part the species-specific oncogenicity of this DNA virus.

Presence of allograft-rejection resistance in simian virus 40-transformed hamster cells and its possible role in tumor development.

LSH Syrian hamster cells transformed in vitro by simian virus 40, which is oncogenic for hamsters, are resistant to rejection by adult allogeneic CB hamsters. In contrast, simian virus 40-transformed cells from other species are usually not oncogenic in immunocompetent autologous or isologous hosts. The ability of simian virus 40 to convey resistance to an allograft-type host response to transformed hamster cells may be important in determining the tumor-inducing capacity of these cells and could, in part, explain the species-specific oncogenicity of this virus.

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.

N-(Phosphonacetyl)-l-Aspartate, a Potent Transition State Analog Inhibitor of Aspartate Transcarbamylase, Blocks Proliferation of Mammalian Cells in Culture

Abstract N-(phosphonacetyl)-l-aspartate (PALA) is an analog of the activated complex for the reaction catalyzed by aspartate transcarbamylase and has previously been shown to be a potent and specific inhibitor of the enzymes from Escherichia coli and mouse spleen. PALA is now shown to be a potent inhibitor of de novo pyrimidine nucleotide biosynthesis in five lines of mammalian cells in culture. When the concentration of PALA in the medium is 10-4 m, simian virus 40-transformed hamster cells do not divide and, within about 2 days, have detached from the culture dishes and appear dead. The toxicity of 10-4 m PALA is prevented completely if 10-4 m uridine is present in the medium, showing that PALA inhibits uridylic acid biosynthesis specifically. The same effect can be observed with the other cell lines. When the external concentration of radioactive PALA is in the range 10-4 to 10-5 m, its concentration in the cytosol is approximately equal to the external concentration. Most of the PALA recovered from cells remains undegraded. In crude cell extracts, the Ki for PALA is about 1 x 10-9 m at 37° and pH 7.5. Addition of 1 x 10-7 m PALA in vitro to an extract of transformed hamster cells inhibits by 60% the incorporation of radioactivity from CO2 into UMP and CMP; approximately 10-6 m PALA is required to give comparable inhibition of incorporation from carbamyl-P. Higher concentrations give virtually complete inhibition in both cases. These results suggest that PALA may find clinical use in suppressing cellular proliferation. A small number of the virus-transformed hamster cells become resistant to 10-4 m PALA in culture and retain resistance after they are grown for many generations in the absence of the drug. Resistance is accompanied by a large increase in aspartate transcarbamylase activity.