HERV-H family is the most abundant HERV families in the human genome with more 
than 1000 copies including full-length, truncated form, and solitary LTRs. We 
investigated envelope (env) gene fragments of HERV-H family in various human 
tissues and cancer cells. The env fragments were detected in mRNA of several 
human tissues (placenta, skeletal muscle, spleen, and thymus) and cancer cells 
(RT4, BT-474, HCT-116, TE-1, UO-31, Jurkat, HepG2, A549, MCF7, OVCAR-3, 
MIA-PaCa-2, PC3, LOX-IMVI, AZ521, 2F7, U-937, and C-33A) by RT-PCR approach. The 
RT-PCR products were cloned and sequenced. New 12 clones from human tissues and 
48 clones from cancer cells of env gene sequences belonging to the HERV-H family 
showed 84.3-98.1% sequence similarity to that of HERV-H (AF108843). Deduced 
amino acid sequences of 60 clones from human tissues and cancer cell lines 
showed multiple frameshifts and termination codons caused by deletion/insertion 
or point mutation with the exception of eight clones as following: HHE9-1, 
HHE9-5 (skeletal muscle), HHE10-5 (spleen), CHE10-9 (MCF7), CHE12-4, CHE12-5 
(MIA-PaCa-2), and CHE18-1, CHE18-3 (C-33A) to that of HERV-H (AF108843). A 
phylogenetic tree of the HERV-H family was constructed to understand their 
relationship, indicating that they were divided into three groups, one major 
(group I) and two minor (group II and III), through sequence divergence. The 
HERV-H families in group I has been proliferated on human genome during hominoid 
evolution. These active HERV-H elements are worthy of further investigations as 
potential pathogenic effects to various human diseases including cancers.