Functional activity of HERV-K-T47D-related long terminal repeats.
The human genome contains a family of endogenous retroviruses, HERV-K(HML-4), that comprises the full-length provirus HERV-K-T47D, five related elements, and hundreds of solitary long terminal repeats (LTRs). We here show that HERV-K-T47D-related LTRs are dispersed over all human chromosomes and have arisen after the divergence of Old and New World monkeys. By screening a cDNA library derived from the human mammary carcinoma cell line T47D with a HERV-K-T47D LTR probe, we isolated several clones containing LTR/cellular gene chimeras and assessed the transcriptional activity of these LTRs in transient transfection experiments. All LTRs were able to drive the expression of a reporter gene, thereby displaying distinct activities in different cell lines. We found that sequences located downstream of the LTR-U3 region modulate the level of gene expression. Based on the impact of the R region we distinguished between three different LTR types; the activity of type I LTRs was enhanced in the presence of the LTR-R region in all cell lines tested, whereas a type II LTR was downregulated. Type III LTRs are characterized by lacking or having a varying influence of the R region that was dependent on the cell line used. Finally, our results attribute to LTR-U5-gag sequences a role in determining LTR activity.
Baust
C
C
Medical Clinic III, Faculty of Clinical Medicine Mannheim, University of Heidelberg, D-68305 Mannheim, Germany. Corrina.Baust@urz.uni-heidelberg.de
Seifarth
W
W
Schön
U
U
Hehlmann
R
R
Leib-Mösch
C
C
D001483:Base Sequence; D015139:Blotting, Southern; D002461:Cell Line, Transformed; D002877:Chromosomes, Human / Q000235:genetics; D020077:Endogenous Retroviruses / Q000235:genetics* / Q000378:metabolism; D015967:Gene Expression Regulation, Viral / Q000235:genetics*; D015723:Gene Library; D017930:Genes, Reporter; D006801:Humans; D008156:Luciferases / Q000235:genetics; D008969:Molecular Sequence Data; D010957:Plasmids / Q000235:genetics; D020079:Terminal Repeat Sequences / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured
D008156:Luciferases