Fusion of transformed human cells by simian retroviruses

Mason-Pfizer monkey virus (MPMV), baboon endogenous virus (BaEV) and simian sarcoma virus associated virus (SSAV) induced fusion in cultured human cells derived from tumors or transformed in vitro. Not only virus-transformed cells, but also cells transformed spontaneously by 4-nitroquinoline 1-oxide (4-NQO) treatment or by 60Co-gamma ray irradiation were fused by these simian retroviruses. Non-transformed cells derived from normal human embryos were not fused by any of these viruses. Of these tumor or transformed cells, cells carrying Rous sarcoma virus (RSV) genome were most extensively fused by these simian retroviruses. Anti-MPMV, anti-BaEV and anti-SSAV sera blocked the cell fusion mediated by MPMV, BaEV and SSAV, respectively, and not that by other viruses, indicating that the cell fusion was virus-specific.