Disease relevance of TEF

• The purified VBP and a1/EBP bacterial fusion proteins bind overlapping but distinct subsets of CCAAT/enhancer elements in the closely related ALV and Rous sarcoma virus (RSV) LTR enhancers [1].
• VBP and a1/EBP could mediate the high rates of ALV and RSV LTR-enhanced transcription in bursal lymphoma cells and many other cell types [1].
• VBP and RelA regulate avian leukosis virus long terminal repeat-enhanced transcription in B cells [2].
• As with vertically transmitted endogenous ALV of subgroup E, the oncornavirus recovered from kidney tumor cell cultures failed to replicate in chicken embryo fibroblast (CEF) cultures of the C/E phenotype, but did replicate in turkey embryo fibroblasts (TEF), which are permissive for replication of endogenous ALV of subgroup E [3].

High impact information on TEF

• These oncornavirus particles served as a helper virus to form Rous sarcoma virus pseudotypes, which produced foci in TEF cultures but not in CEF cultures of the C/E phenotype [3].
• Studies have established that cryoprecipitates of the plasma of tumor patients contain a biological activity enhancing morphological cell transformation (transformation-enhancing factor; TEF) in cultures of chicken embryo fibroblasts infected with temperature-sensitive mutants of Rous sarcoma virus [4].
• VBP binds to one of the most important positive elements in the VTGII promoter and appears to play a pivotal role in the estrogen-dependent regulation of this gene [5].
• Thus, the optimal binding sites for VBP and DBP may be distinct [5].
• We now report the isolation of a cDNA clone that encodes a complete open reading frame for a VBP isoform that differs from the previously reported sequence at both the amino-terminal and carboxyl-terminal ends [6].

Biological context of TEF

• An analysis of the VBP gene revealed that the two different amino-terminal sequences map to alternative first exons and that the two different carboxyl-terminal sequences reflect an optional splicing event which can occur only on transcripts that are polyadenylated at the more distal of two polyadenylation sites [6].
• 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 [2].
• The LTR-binding activities of VBP, a1/EBP, and B-cell nuclear extract protein were compared and mapped by gel shift, DNase I footprinting, and methylation interference assays [1].
• The VBP and a1/EBP leucine zipper factors bind overlapping subsets of avian retroviral long terminal repeat CCAAT/enhancer elements [1].
• To investigate whether VBP is involved in apoVLDL II gene expression, we examined its capacity to enhance apoVLDL II transcription and its presence in liver [7].

Anatomical context of TEF

• Results of viral isolation procedures in turkey embryo chorioallantoic membrane (CAM) and yolk sac, as well as in turkey embryo fibroblast (TEF) and turkey kidney cell (TKC) cultures, were negative [8].

Physical interactions of TEF

• Previous studies showed that VBP can bind simultaneously with the estrogen receptor to the putative complex regulatory element E1D [7].

Other interactions of TEF

• The partial a3/EBP cDNA clone encodes amino acids 84 to 313 of vitellogenin gene-binding protein (VBP), a leucine zipper factor that binds the avian vitellogenin II gene promoter (S. Iyer, D. Davis, and J. Burch, Mol. Cell. Biol. 11:4863-4875, 1991) [1].

Analytical, diagnostic and therapeutic context of TEF

• An RT-PCR analysis further revealed that a total of four VBP isoforms are encoded by the combinatorial use of these two splicing options [6].
• Circular dichroism (CD) spectroscopy measured the thermal stability of eight proteins derived from the basic region leucine zipper domain of chicken VBP, the mammalian TEF at seven pHs and three KCl concentrations [9].
• However, VBP could not be detected in liver by Western-blots or immuno-electro mobility shift assays (EMSAs) using antibodies against different moieties of the protein [7].
• Flow cytometric analysis and immunoprecipitation experiments demonstrated specific binding between the TEF CAR1-related protein and an immunoadhesin composed of the surface (SU) envelope protein of subgroup E (RAV-0) virus fused to the constant region of a rabbit immunoglobulin [10].

References