Relationship between A-type and C-type particles in cells infected by Rous sarcoma virus.

Abstract

Chicken cells infected with avian RNA tumor virus often contain small cytoplasmic A-type particles which commonly exist as clusters of 50-100 particles when viewed in thin sections. These particles were found more consistently in Rous sarcoma virus-infected than Rous-associated virus-infected cultures, but were generally present in only a small fraction of the total infected cells. The results of the survey of cells infected with various strains of leukosissarcoma viruses led to the hypothesis that the A particles develop in cells undergoing cytopathological degeneration. The hypothesis explains also the evanescent nature of the appearance of these particles in infected cells. The application of immunoelectron microscopic methods using monospecific antisera against viral internal proteins revealed that the A particles contain components immunologically related to the proteins of C-type virus.The process of assembly, release by budding, and maturation of the oncogenic RNA agents, including particles classified morphologically as C-type viruses (1, 2), occurs at the plasma membrane of infected cells (3-5). In avian systems one generally does not observe any recognizable precursor internal structures at the site of egress equivalent to the "A"-type particles found in murine and other infections. However, commencing with the report by Bernhard et al. (6), presence of aggregates of cytoplasmic A particles 60-70 nm in diameter has been described (7-10). Since such particles are not an invariable component of virus-producing avian cells they were considered to be not essential for replication. By contrast, in the case of murine agents A particles are present consistently, notably in tissue of mouse mammary carcinoma (2, 11), plasma cell tumors, and lymphomas (12)(13)(14) (19,20). For most experiments, chicken cells negative for group-specific antigen (gs) and chicken helper factor (chf) (18) were used.Antisera and Immunoelectron Microscopy. Monospecific antisera against purified RAV-2 proteins P27, P19, and P15 were obtained from immunized rats as described previously (21, 22). The specificity of each serum was determined by means of radioimmunoassay employing as antigen each respective polypeptide purified on guanidine-hydrochloride agarose columns and indicated less than 1% cross reactivity with any other antigen (22). Since antibody does not penetrate the plasma membrane of living cells, prior to immunological tagging the cells were released from monolayer by trypsin, washed repeatedly in cold Dulbecco's phosphate-buffered saline, made permeable by exposure for 2 min to 0.005% Nonidet P40 (NP40) to rupture the membrane, centrifuged at 800 X g for 10 min into a pellet, resuspended in Eagle's MEM nutrient medium (23), and incubated with monospecific antiserum at 370 for 30 min with continuous agitation. Unattached antibody was removed by centrifuging the cells and resuspending in nutrient medium twice. In some cases when the indirect immunoferritin technique (24) was employed the ruptured cells were exposed fi...

Effects of Dexamethasone on the Morphogenesis of Two Mutants of Rous Sarcoma Virus

“…A relationship between cytotoxicity and the incidence of A-lype particles has been reported [30], In our hands, the treatment of BH RSV(-)Q with dexamethasone at a concentration higher than 10 5 M caused cytotoxicity and resulted in no incidence of A-type particles. It seems unlikely in this case that the cytotoxicity of the drug played a role in the appearance of A-type particles.…”

“…In the avian C-type virus system, core assembly occurs under the plasma mem brane, forming a crescent shape at the time of early budding. Intracyto plasmic A-type particles can rarely be observed and are reported as aberrant avian tumor viruses [30][31][32][33][34][35][36]. The incidence of intracytoplasmic A-type par ticles was suggested to be caused by the disturbance of late assembly of avian C-type viruses [33][34][35],…”

Biological and electron microscopic studies on the phenotypic mixing of the thermolabile mutant of vesicular stomatitis virus,tl-17, with avian RNA tumor viruses

“…at the plasma membrane or in intracytoplasmic vacuoles. The intracytpplasmic A-type particles observed were morphologically indistinguishable from those of A-type particles detected by other groups (6,10) in ATV transformed CEC.…”