Table 2.
Details of several Class I and Class II human endogenous retroviruses: full details provided in references [3,7,9]
| Family | Family members | No. of copies /previous classification | mRNA expression | Protein expression | Genome structure | Primer binding site | Chromosomal location | Comment | |
|---|---|---|---|---|---|---|---|---|---|
| HERV-H/RTVL-HClass I | RTVL-H2; RGH2 | Multicopy type C; 800–1000 copies plus ∼ 1000 solitary LTRs | LTR-gag-pol-env-LTR mRNA expression in lung squamous cell carcinoma, teratocarcinoma cell line, multiple sclerosis derived B-lymphoblastoid cell lines | 62 kDa protein detected for env gene | Severely truncated provirus | tRNAHis | Copies in all chromosomes with concentration on chromosomes 1p and 7q | Complementation and full expression may occur under circumstances yet to be described | |
| HERV-EClass I | HERV-E clone 4–1 | Multicopy type C retrovirus; 50–100 copies | Several LTR and en- containing mRNAs are expressed in normal placenta, breast and colon carcinoma cells | 38 kDa env protein, no particle formation | Full length genome = 8·8-kilobase Truncate genome = 6-kilobase (lack env sequence) | tRNAGlu | Altered tissue-specific gene expression in salivary gland for the amylase gene complex due to insertion of HERV-E LTR into its promoter region | ||
| ERV-9Class I | Type C retroviruses | Detected ERV-9 RNA transcripts of 8, 2, and 1·5 kb in undifferen- tiated NT2/D1cells, teratocarcinoma cells | Severely truncated provirus | tRNAArg | Selective expression of zinc finger protein in cell lineages associated with an ERV9 promoter | ||||
| HERV-RClass I | ERV3 | Single copy type C retrovirus | High expression in placenta and cell line U937, low expression in thymus, breast, lung, pancreas | 65 KDa env protein | Full length = 9·9 kilobase | tRNAArg | Chromosome 7 | mRNA expression mediated by steroid hormones | |
| HRES-1Class I | Single copy element per haploid genome | Detected for LTR, gag regions | Encodes a 28 kDa gag protein in H9 human T cells | Mapped to a common fragile site: chromosome 1 at 1q42 | Antibodies to HRES-1 specific synthetic peptides were found in patients with MS, SLE, Sjogren syndrome | ||||
| HERV-W(MSRV)Class I | Multicopy type C retrovirus | LTR-gag-pol-env-LTR mRNA expression in placenta and testis | env gene codes for Syncytin protein (65 kDa env) | Detected in MS, human genome contain at least 70 100, and 30 HERV-W-related gag, pro, and env regions, respectively | |||||
| HERV-KClass II | HERV-K10 | Multicopy mosaic- type endogenous proviruses; 50 copies per haploid genome | LTR-gag-pol-env-LTR, rev mRNA expression; high in teratocarcinoma cell lines, testicular tumours; expression of HERV-K env gene in human breast cancer cells; low in placenta and normal tissues; expressed in peripheral blood lymphocytes | gag, cORF, protease, integrase, polymerase, env; rev, retroviral particle formation | Complete nucleotide sequence of the HERV-K10 clone = 8·8-kilobase | tRNALys | Induced HERV-K mRNA expression in human breast cancer cells by addition of oestradiol and progesterone | ||
| HERV-LClass II | Multicopy type | pol, LTR-gag-pol mRNA expression; tissues: rheumatoid arthritis, synovial fluid cells, placenta, breast cancer | Unknown | tRNALeu |