Comparative study of RSV rescue from RSV‐transformed mammalian cells

Abstract

All individual heterokaryons obtained by fusion of cells of the five different mammalian RSV-transformed virogenic cells with indicator chicken fibroblasts produced infectious RSV. In contrast, non-virogenic mammalian cells derived from tumours which arose in mice injected with RSV did not give rise to infectious RSV, even when fused with chicken fibroblasts preinfected with three different "helper viruses". Fusion of four lines of vlrogenic cells with mammalian fibroblasts as well as of virogenic Chinese hamster cells with chicken liver, mesonephros, thymus and macrophage cells did not lead to the formation of detectable RSVor RSV coat antigen. Similarly, experiments on complementation by mutual fusion of virogenic cells in five different crosses were negative. The presence of a " natural" Gs antigen in the indicator cells is not necessary for RS V rescue because the fusion ofcells derived from Gs negative chicken and duck embryos with virogenic cells leads to the formation of infectious RSV.The results are discussed in relation to the specificity of the cells participating in the induction of RS V formation by cell fusion.

Fusion Injection of Rous Sarcoma Virus Proteins into Rous Sarcoma Virus-transformed, Non-producing Hamster Cells Causes Release of Infectious Virus

“…In contrast to this successful virus release from RBH cells, the rat TWERC cells could not be induced to release RSV subgroup C, This failure cannot be due to a lower fusion frequency of rat TWERC cells with loaded erythrocyte ghosts because in previous experiments with rat TWERC cells (vonder Helm et aI., 1980), we had found an even higher fusion frequency (50%) than with RBH cells; neither can it be due to an insufficient precursor cleavage since pr76 was cleaved as well in both RBH and TWERC cells upon fusion injection of p15, as shown in our previous work (vonder Helm et al, 1980). These results may reflect the fact that the TWERC cells are non-virogenic in contrast to RBH cells and corroborate the hypothesis that the virus in rat TWERC cells is not rescuable due to defects in the virus genome (Svoboda et aL, 1971).…”

“…Mammalian cells are only non-productively infected and transformed by ASV, although minute amounts of virus group-specific antigen (gag) can be detected in the form of their precursor protein pr76 (Eisenman et al, 1974;Aupoix & Vigier, 1976). When such ASV-transformed mammalian cells were co-cultivated or fused with uninfected chicken embryo fibroblasts, virus is rescued and released (Svoboda & Hlozanek, 1970;Svoboda et al, 1971Svoboda et al, , 1977Steimer & Boettger, 1977), but the molecular mechanism of this process is not fully understood. The protein precursor pr76 is not detectably cleaved in ASVtransformed mammalian cells (Svoboda et al, 1977;von der Helm et al, 1980), presumably because no free protein p15 (the precursor of the virus protease that causes processing) is present.…”

“…At present, we cannot offer an explanation for the molecular mechanism which determines rescue of the infectious virus; clearly, p15 plays an essential role, but apparently other virus proteins are also important. It could be speculated that those factors which have been postulated (Svoboda et al, 1971;Vigier, 1972) to be required for induction of avian virus from transformed, non-producing mammalian cells might have similar function(s) as the injected virus proteins.…”

Characterization of Transforming Viruses Rescued from a Hamster Tumour Cell Line Harbouring the v-src Gene Flanked by Long Terminal Repeats

“…These results suggested that the provirus is generated from a processed src mRNA because F6 and F6-NP had been established from rescued virus and therefore only RNA correctly spliced had been encapsidated. Previous attempts to obtain transforming virus after fusion of similar mouse (Svoboda et al, 1971) or rat (Hughes et al, 1978) cells with chick embryo fibroblasts infected by RAV-1 or transformation-defective avian sarcoma virus (ASV) mutants failed. This might be due to the experimental procedures used in which only free transforming virus in the supernatant of heterokaryons was measured.…”

Molecular Events Accompanying Rous Sarcoma Virus Rescue from Rodent Cells and the Role of Viral Gene Complementation

“…So far, it is known that RSV-transformed rodent cells are not complemented when different independently obtained cell lines are fused one with the other (45). Similarly it was revealed that infection of transformed cells with rodent retroviruses does not lead to RSV rescue in spite of the fact that rodent retroviruses complete their replication cycle (46).…”