Proviral Structure, Chromosomal Location, and Expression of HERV-K-T47D, a Novel Human Endogenous Retrovirus Derived from T47D Particles

Abstract

We previously described that type B retrovirus-like particles released from the human mammary carcinoma cell line T47D are pseudotypes and package retroviral RNA of different origins (W. Seifarth, H. Skladny, F. Krieg-Schneider, A. Reichert, R. Hehlmann, and C. Leib-Mösch, J. Virol. 69:6408–6416, 1995). One preferentially packaged retroviral sequence, ERV-MLN, has now been used to isolate the corresponding full-length provirus from a human genomic library. The 9,315-bp proviral genome comprises a complete retroviral structure except for a 3′ long terminal repeat (LTR) truncation. A lysine tRNA primer-binding site and phylogenetic analyses assign this human endogenous retroviral element, now called HERV-K-T47D, to the HML-4 subgroup of the HERV-K superfamily. The gag,prt, pol, and env genes exhibit 40 to 60% amino acid identity to HERV-K10. HERV-K-T47D is located on human chromosome 10, with five closely related elements on chromosomes 8, 9, 15, 16, and 19 and several hundred HERV-K-T47D-related solitary LTRs dispersed over the human genome. HERV-K-T47D-related sequences are detected in the genomes of higher primates and Old World monkeys but not in those of New World monkeys. High HERV-K-T47D transcription levels were observed in human placenta tissue, whereas transcription in T47D cells was strictly steroid dependent.

Solitary HERV‐K LTRs possess bi‐directional promoter activity and contain a negative regulatory element in the U5 region

“…A pGL3 vector lacks any eukaryotic promoter or enhancer and contains specific sequences to prevent transcription from any cryptic promoter located elsewhere in the plasmid as specified by the vendor. Nevertheless, we reproduced the results using another promoterless reporter pBV vector [14], thus confirming that the luciferase expression in transfected cells was the result of the LTR promoter activity and not the plasmid cryptic promoter activity boosted by the LTR enhancer. Until recently the ERV LTR promoter activity was studied mainly for ‘natural’ forward orientation relative to the provirus genes, though the reverse promoter activity of the U3 region of solitary HERV‐H LTRs [10] and murine IAP LTRs [15] has also been reported.…”

“…Gel purified PCR fragments were cloned in Sma I digested promoterless pGL‐3 Basic Vector (Promega). Plasmids pGLT47D were constructed by subcloning of Bam HI– Hin dII fragment containing 5′HERV‐K‐T47D LTR [14] into pGL3 Basic Vector (Promega).…”

Retroviruses and primate evolution

“…Possible involvement of LTRs in some genome functions is indirectly confirmed by the conservation of their functional motifs, such as potential enhancer and hormone responsive elements, TATA-box, and poly-A signal sequence. (43) Tissue-specific expression of HERVs themselves (21,22,24,40) supports their potential to direct the tissue specificity of the expression of neighboring genes. An example of new properties imparted by a nearby HERV element insertion was described recently for the human growth factor pleiotropin (PTN) gene.…”

Expression of human endogenous retrovirus K is stimulated by ultraviolet radiation in melanoma

“…Whereas HERV-K full-length mRNA is detectable in many tissues, the expression of retroviral proteins and the formation of virus-like particles have only been demonstrated in cell lines established from human teratocarcinoma (Boller et al, 1993), seminoma (Sauter et al, 1995), breast cancer (Seifarth et al, 1998), and melanoma (Buscher et al, 2005;Muster et al, 2003). To determine whether UVB irradiation leads to transcriptional activation of HERV-K and also increases retroviral protein expression in melanoma, the expression of the HERV-K-specific envelope protein (env) in response to UVB was analysed in immunofluorescence studies using a specifically designed rabbit anti-HERV-K-env antibody.…”