VBP and RelA regulate avian leukosis virus long terminal repeat-enhanced transcription in B cells.
The avian leukosis virus (ALV) long terminal repeat (LTR) contains a compact transcription enhancer that is active in many cell types. A major feature of the enhancer is multiple CCAAT/enhancer element motifs that could be important for the strong transcriptional activity of this unit. The contributions of the three CCAAT/enhancer elements to LTR function were examined in B cells, as this cell type is targeted for ALV tumor induction following integration of LTR sequences next to the c-myc proto-oncogene. One CCAAT/enhancer element, termed a3, was found to be the most critical for LTR enhancement in transiently transfected B lymphoma cells, while in chicken embryo fibroblasts all three elements contributed equally to enhancement. Gel shift assays demonstrated that vitellogenin gene-binding protein (VBP), a member of the PAR subfamily of C/EBP factors, is a major component of the nuclear proteins binding to the a3 CCAAT/enhancer element. VBP activated transcription through the a3 CCAAT/enhancer element, supporting the idea that VBP is important for LTR enhancement in B cells. A member of the Rel family of proteins was also identified as a component of the a3 protein binding complex in B cells. Gel shift and immunoprecipitation assays indicated that this factor is RelA. Gel shift assays demonstrated that while RelA does not bind directly to the LTR CCAAT/enhancer elements, it does interact with VBP to potentiate VBP DNA binding activity. The synergistic interaction of VBP and RelA increased CCAAT/enhancer element-mediated transcription, indicating that both factors may be important for viral LTR regulation and also for expression of many cellular genes.
Curristin
S M
SM
Department of Microbiology and Immunology and Cancer Center, University of Rochester, School of Medicine and Dentistry, New York 14642, USA.
Bird
K J
KJ
Tubbs
R J
RJ
Ruddell
A
A
D000818:Animals; D001354:Avian Leukosis Virus / Q000235:genetics*; D030161:Avian Proteins; D001402:B-Lymphocytes / Q000821:virology*; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins / Q000502:physiology*; D002642:Chick Embryo; D004742:Enhancer Elements, Genetic; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism / Q000494:pharmacology*; D012091:Repetitive Sequences, Nucleic Acid; D051996:Transcription Factor RelA; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic
D030161:Avian Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; D016328:NF-kappa B; D051996:Transcription Factor RelA; D014157:Transcription Factors