Functional analysis of the endogenous retroviral promoter of the XXXX endothelin B receptor gene.

@entity1 @entity45925 @entity1627 @entity377
We previously reported that the long terminal repeats (LTRs) of retroviral elements belonging to the HERV-E family contribute to the expression of the @entity1 @entity45925 ( @entity45925 ) and endothelin B receptor ( @entity1627 ) genes by providing alternative promoters. While both LTRs were shown to promote transcription in vivo and in vitro, their respective activity and tissue specificity appeared to differ even though they shared a high degree of sequence identity. In the present study, we further characterized the promoter of the @entity1627 LTR and delineated the regions and motifs required for strong activity. We confirmed the placenta-restricted expression of the LTR by transient transfections and quantitative real-time PCR and determined that the retroviral promoter contributes significantly to the level of @entity1627 transcripts in placenta, where chimeric mRNAs were found to represent 15% of overall @entity1627 mRNAs. Transient transfection of 5' deletion constructs in cells of placental origin identified a motif, named LPE1, between positions 111 and 122 of the @entity1627 LTR necessary for transcriptional activity. Removal of this region, which contains a putative SP1 binding site, abolished promoter activity. A second enhancing region resides between positions 175 and 215 of the LTR and was termed LPE2. Interestingly, this section contained three binding sites that were not present in the @entity45925 LTR due to minor @entity377 differences. The predicted motifs in the @entity1627 LTR were found to likely act in symbiosis as modifications to any of the three sites reduced transcription by one-third while alterations to all three eliminated promoter activity. The results from this study illustrate how slight variations in transcriptional regulatory sequences can have a profound effect on promoter activity and demonstrate the complex regulatory effects of @entity1 endogenous retrovirus elements on @entity1 gene expression.
