Expression of the human endogenous retrovirus HERV-W family in various human tissues and cancer cells.

We examined the structural genes (gag, pol and env) of the human endogenous retrovirus (HERV-W) family from 12 normal human tissues and 18 human cancer cell lines using RT-PCR. For the gag and pol genes, their expression patterns showed tissue or cell specificity, depending on the samples, whereas the env gene was expressed in all tissues and cancer cells examined. To identify active HERV-W elements in tissues and cancer cells, the RT-PCR products were cloned and sequenced. Ninety-five clones for the env gene, 55 clones for the pol gene and 17 clones for the gag gene of the HERV-W family were isolated from human tissues and sequenced, while 85 clones for the env gene, 61 clones for the pol gene and no clones for the gag gene of the HERV-W family were isolated and sequenced from cancer cells. Among these clones, 50 clones from tissues and 44 from cancer cells showed putative amino acids of the HERV-W env gene, while only two clones from cancer cells showed putative amino acids of the HERV-W pol gene. Phylogenetic analysis indicated that several clones identified previously from human monochromosomes had sister relationships with the clones from the different tissues and cancer cells. These data suggest that HERV-W elements are actively expressed in human tissues and cancer cells. These active HERV-W elements deserve further investigation as potential causative agents of various human diseases including cancers.