The Mus cervicolor MuLV isolate M813 is highly fusogenic and induces a T-cell lymphoma associated with large multinucleated cells

M813 is a type-C murine leukemia virus (MuLV) isolated from the Asian roden t Mus cervicolor. We have recently demonstrated that M813 defines a distinc t MuLV receptor interference group. Here we show that M813 rapidly induces fusion of MuLV-expressing fibroblasts from "without" with syncytia being ob served within 1 h after exposure to virus. Infection of fibroblasts with Mu LV from all tested receptor-interference groups imparts susceptibility to M 813-induced fusion, provided the cells also express the M813 receptor. Sync ytium induction is also observed in vivo; mice infected with M813 develop a peripheral T-cell lymphoma, which is associated with large multinucleated cells of macrophage origin. A recombinant Moloney MuLV/M813 chimeric virus demonstrated that syncytium induction is a function of the Env SU protein. We postulate that the highly fusogenic property of M813 is attributable to either its unique receptor usage or sequences in the proline-rich domain of the Env protein. (C) 2001 Academic Press.