EXPRESSION OF AN ENDOGENOUS RETROVIRAL GENE-PRODUCT IN HUMAN PLACENTA

To investigate the presence and potential pathophysiological role of e ndogenous retroviruses in humans, we prepared a recombinant protein us ing clone 4-1, a proviral sequence. DNA fragments containing the env r egion of clone 4-1 were subcloned into a prokaryotic expression vector (pET3), and 2 fusion proteins, SU413 and SU415, were then expressed i n Escherichia coli after treatment with isopropyl-beta-thiogalactopyra noside (IPTG). By sonicating lysates of the transformed E. coli, the r ecombinant protein SU413 was successfully separated from the native ba cterial components, and was used to raise an antiserum in rabbits. In immunoblot analysis, this antiserum specifically recognized the recomb inant protein, but did not react with other components of E. coli. Thi s antiserum was then used for an immunofluorescence study of human pla centa, in which the env gene transcript has been reported. As a result , the anti-SU413 serum detected substance sin syncytiotrophoblasts and vascular endothelia from a human placenta. No such reactivity was det ected in human kidney or human liver. Immunoblot analysis revealed tha t this antiserum reacted to a single molecule of 38-kDa in placenta, a nd its reactivity was reduced by the antiserum absorbed with SU413 ant igen. These findings suggest that human placental syncytiotrophoblasts and vascular endothelia preferentially express a molecule encoded by human endogenous retrovirus clone 4-1. (C) 1994 Wiley-Liss, Inc.