Inhibition of Rous sarcoma virus assembly by treatment with 2',5' adenosine nucleotides

We have investigated the influence of 2',5' adenosine nucleotides on the replication and transformation of cells by Rous sarcoma virus (RSV). Treatment with the nucleotides ppp2',5'A4 and 2',5'A4 causes a striking reduction (50-fold) in the yield of infectious progeny virus, while ppp2',5A2 and 2',5'A3 had virtually no effect. The reduction in infectivity seen with 2',5'A4 nucleotides is paralleled by a smaller but significant (three- to four-fold) reduction in the amount of particles released as measured by reverse transcriptase activity and levels of viral structural proteins. The reduced infectivity of released particles is not due to viral RNA being missing since the amount of genomic RNA in particles from 2',5'A4-treated cultures was likewise only reduced by a factor of 2-3. Pulse-chase radioactive label experiments showed that processing of both viral group-specific antigens (gag) and viral envelope glycoprotein (env) gene products was completely normal in nucleotide-treated cultures, but that the rate of appearance of viral proteins in mature virus in the culture supernatants was reduced by a factor of about 3-4. Taken together, the data show that assembly of viral structural proteins into virions which can be released into the medium is slowed, and that assembly of virus particles with reduced infectivity follows upon nucleotide treatment. This inhibition of infectious virus production takes place without significant toxic effects on the cell; host protein synthesis is only 20% inhibited. There is also no significant effect on the secretory ability of the cells as measured by total protein release into the medium or release of fibronectin. The transformed cell phenotype was also subtly affected by 2',5'A4, but not by other oligomers. Plasminogen activator protease activity was sharply reduced upon treatment, while other typical features of RSV-transformed cells such as elevated hexose transport, and pp60src-associated protein phosphokinase activity, were little affected.