An envelope glycoprotein of the human endogenous retrovirus HERV-W is expressed in the human placenta and fuses cells expressing the type D mammalianretrovirus receptor

A new human endogenous retrovirus (HERV) family, termed HERV-W, was recentl y described (J.-L. Blond, F. Beseme, L. Duret, O. Bouton, F, Bedin, H. Perr on, B. Mandrand, and F, Mallet, J, Virol. 73:1175-1185, 1999), HERV-W mRNAs were found to be specifically expressed in placenta cells, and an env cDNA containing a complete open reading frame was recovered. In cell-cell fusio n assays, we demonstrate here that the product of the HERV-W env gene is a highly fusogenic membrane glycoprotein, Transfection of an HERV-W Env expre ssion vector in a panel of cell lines derived from different species result ed in formation of syncytia in primate and pig cells upon interaction with the type D mammalian retrovirus receptor. Moreover, envelope glycoproteins encoded by HERV-W were specifically detected in placenta cells, suggesting that they may play a physiological role during pregnancy and placenta forma tion.