Human Endogenous Retrovirus Family HERV-K(HML-2) RNA Transcripts Are Selectively Packaged into Retroviral Particles Produced by the Human Germ Cell Tumor Line Tera-1 and Originate Mainly from a Provirus on Chromosome 22q11.21

Abstract

The human germ cell tumor line Tera-1 produces retroviral particles which are encoded by the human endogenous retrovirus family HERV-K(HML-2). We show here, by quantitative reverse transcriptase PCR, that HML-2 gag and env RNA transcripts are selectively packaged into Tera-1 retroviral particles, whereas RNAs from cellular housekeeping genes and from other HERV families (HERV-H and HERV-W) are nonselectively copackaged. Assignment of cloned HML-2 gag and env cDNAs from Tera-1 retroviral particles to individual HML-2 loci in the human genome demonstrated that HML-2 RNA transcripts packaged into Tera-1 retroviral particles originate almost exclusively from an HML-2 provirus on chromosome 22q11.21. Based on relative cloning frequencies, this provirus was the most active among a total of eight transcribed HML-2 loci identified in Tera-1 cells. These data suggest that at least one HML-2 element, that is, the HML-2 provirus on 22q11.21, has retained the capacity for packaging RNA into HML-2-encoded retroviral particles. Given its elevated transcriptional activity and the presence of a full-length Gag open reading frame, the 22q11.21 HML-2 provirus may also significantly contribute to Gag protein and thus particle production in Tera-1 cells. Our findings provide important clues to the generation and biological properties of HML-2-encoded particles. In addition, copackaging of non-HML-2 HERV transcripts in HML-2-encoded particles should inform the debate about endogenous retroviral particles putatively encoded by non-HML-2 HERV families that have previously been described for other human diseases, such as multiple sclerosis.

Human Endogenous Retrovirus Type K (HERV-K) Particles Package and Transmit HERV-K–Related Sequences

“…The levels of gapdh transcripts decreased in IP samples compared to those of the raw supernatant. The residual low levels of gapdh in IP samples is expected, as this has been reported in studies of other retroviruses (32,(69)(70)(71)(72)(73)(74)(75)(76), which can package different nonviral RNA sequences at low levels. Further, enrichment of HK2 gag and Bogota neo transcripts found in HK2 VLPs was 5 to 20 times greater than that of gapdh transcripts (Fig.…”

“…3C). In order to determine the packaging efficiency of these transcripts into the pelleted retroviral VLPs, we compared the levels of transcripts found in the pelleted retroviral VLPs to the ones found in the cellular RNA using a previously validated methodology (32,77,78). Of these transcripts, HK2 genes and Bogota HK2 appear to be the most abundant retroviral transcripts in NCCIT cellular RNA.…”

“…While no single human endogenous retrovirus sequence thus far identified in the genome encodes a complete infectious virus, the diverse HK2 loci in the human genome retain coding capacity for every functional retroviral protein (4,10,(28)(29)(30): the Gag protein, necessary for particle formation and release (31)(32)(33)(34)(35); the Pro protein, necessary for cleavage and maturation of viral proteins (35)(36)(37); the Pol protein, necessary for RNA-dependent DNA replication and integration (38)(39)(40)(41)(42); the accessory protein Rec, which exports unspliced viral RNA from the nucleus to the cytoplasm (43,44); and functional Env proteins (45). Recombination or trans-complementation between these proviruses could lead to the formation of viruses that would be able to package and transmit HK2 sequences (9,(46)(47)(48), as seen with endogenous retroviruses in mice (49)(50)(51).…”

A Single Amino Acid Substitution in a Segment of the CA Protein within Gag That Has Similarity to Human Immunodeficiency Virus Type 1 Blocks Infectivity of a Human Endogenous Retrovirus K Provirus in the Human Genome

“…obtained here with a cDNA clone from a MGCT show that K101 can contribute to production of these particles. Others have shown that K101 and K108 are transcribed in MGCTs (23,54), and RNAs from these proviruses are packaged into particles produced in MGCTs (54). HERV-K particle production has also been reported to occur in normal human placenta (21,29,58), and K101, K108, and K109 are candidates for encoding those particles.…”

Retroelements: molecular features and implications for disease

“…Evidence indicates that multiple sclerosis-related virus (MSRV) pol derived from HERV-W and HERV-K is expressed in the brain tissues of MS patients and is associated with the cause of MS (Johnston et al, 2001;Antony et al, 2011). As described above, HERVs play a role in the development of malignant transformation or tumor growth via the production of HERVencoded oncogenic proteins such as Rec/Np9, and insertional mutation disturb binding of tumor suppressors like P53 and tissue specific expression alteration (Ruprecht et al, 2008;Belancio et al, 2010). HERV-K has been detected in germ cell tumors and in primary or metastatic human melanomas (Gallus et al, 2010).…”