Fusion of normal primate cells: A common biological property of the D-type retroviruses

Abstract

Three different D-type oncoviruses, Mason-Pfizer monkey virus (M-PMV), squirrel monkey retrovirus (SMRV), and langur virus (PO-1-Lu), have been shown to induce cell fusion in different nontransformed human and nonhuman primate cell lines. This therefore represents the first report that cell fusion is a common property of all three D-type retroviruses. In contrast, primate and feline C-type retroviruses (baboon endogenous virus, woolly monkey leukemia virus, and RD-114) fail to induce syncytia in parallel experiments. Inhibitor studies indicate that the three D-type oncoviruses induce multinucleate cell formation by a common mechanism, different from that of either the paramyxoviruses or the syncytia-forming foamy viruses. Increasing doses of ultraviolet irradiation reduce the syncytia-forming ability of these viruses with single-hit kinetics. However, proviral DNA synthesis is not required for cell fusion since the addition of cytosine arabinoside has no significant effect on multinucleate cell formation at concentrations which inhibit virus replication. This result indicates that virus replication is not required for multinucleate cell formation and that the two are independent events of virus infection. The addition of cycloheximide during the first 12 hr of infection, on the other hand, significantly reduces cell fusion, indicating that de novo protein synthesis is required. The possibility that cell fusion involves translation of input viral RNA is discussed. Pre-infection of target cells with the replicating component of M-PMV blocks fusion by all three D-type viruses. The degree of interference observed correlates with the molecular relatedness of the three viruses.