Cell Biology

Ghosts of Infections Past

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Science  03 Mar 2000:
Vol. 287, Issue 5458, pp. 1557
DOI: 10.1126/science.287.5458.1557d

The human genome contains numerous human endogenous retrovirus (HERVs) sequences that are relicts of past infections. For some time, there have been worries about the potential threat HERVs pose to xenotransplantation or as carcinogens. However, one of these genomic “fossils” appears to have been adopted by its host for a more benign purpose. A characteristic of the pathology of retroviruses like human immunodeficiency virus (HIV) is their ability to make their host cells fuse together into a syncytium. In retroviral diseases, the viral envelope protein (Env) mediates such cell fusion. HERVs are known to be expressed in the placenta, and the fetal-maternal interface, or syncytiotrophoblast, is a thin layer of fused fetal trophoblast cells.

Mi et al. have found a protein with significant homology to Env, which they called syncytin, that is expressed at high levels in the syncytiotrophoblast, placenta, and testis, but nowhere else. A cancerous trophoblastic cell line expressed high levels of syncytin, and recombinant syncytin induced cell fusion in several cell types. Cell fusion could be blocked in a trophoblast cell line by using antibodies against syncytin. Although the evidence looks strong, these authors could not rule out that syncytin may be acting in conjunction with another protein to cause syncytiotrophoblast formation, and that such an interaction might be the essential part of the mechanism. The authors suggest that syncytin disregulation may contribute to certain pathologies such as preeclampsia.—CA

Nature403, 785 (2000).

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