Sachiko Omura

Syncytium formation induced by baboon endogenous virus in several transformed human cell lines

Abstract Several types of cultured human cells derived from malignant tumors and transformedin vitro by DNA tumor viruses. RNA tumor viruses, chemical carcinogens, or60Co γ radiation were fused into syncytia when cocultivated with baboon endogenous virus producing human embryonic cells (BaEV-HEC). On the other hand, neither diploid human cell lines nor cells from normal human embryos were fused when cocultivated with BaEV-HEC. Thus, syncytium formation induced by BaEV is dependent upon transformation of human indicator cells rather than upon transforming agents themselves. Concentrated cell-free BaEV suspensions also induced syncytia in human indicator cells within 2 hr after inoculation. The presence of cycloheximide in culture medium had no effect on early syncytium formation. Human indicator cells exposed to low concentrations of BaEV did not form syncytia but produced the virus. These findings strongly suggest that cell fusion induced by BaEV is fusion from without. Specific antiserum against BaEV (M7) blocked this syncytium formation but did not block cell fusion mediated by Mason-Pfizer monkey virus or simian sarcoma virus type I. These observations indicate that the syncytium formation is BaEV specific. The findings in this study suggest that syncytium formation induced by BaEV is a specific characteristic of malignant or transformed human cells.