Negative modulation of the chicken infectious anemia virus promoter by COUP-TF1 and an E box-like element at the transcription start site binding δEF1

Abstract

Expression of enhanced green fluorescent protein (EGFP) under control of the promoterenhancer of chicken infectious anemia virus (CAV) is increased in an oestrogen receptorenhanced cell line when treated with oestrogen and the promoter-enhancer binds unidentified proteins that recognize a consensus oestrogen response element (ERE). Co-transfection assays with the CAV promoter and the nuclear receptor chicken ovalbumin upstream promoter transcription factor 1 (COUP-TF1) showed that expression of EGFP was decreased by 50 to 60 % in DF-1 and LMH cells. The CAV promoter that included sequences at and downstream of the transcription start point had less expression than a short promoter construct. Mutation of a putative E box at this site restored expression levels. Electromobility shift assays showed that the transcription regulator delta-EF1 (dEF1) binds to this E box region. These findings indicate that the CAV promoter activity can be affected directly or indirectly by COUP-TF1 and dEF1.Chicken infectious anemia virus (CAV) is a small DNA virus of the family Circoviridae and has been classified as the sole member of the genus Gyrovirus (Pringle, 1999). CAV is present in virtually all commercial chicken operations (Yuasa, 1992; Yuasa et al., 1983). Clinical disease, characterized by anaemia, thymic and splenic atrophy and secondary infections including dermatitis (Schat, 2003), is limited to chickens less than 3 weeks of age. Older chickens may have decreased humoral immune responses causing poor vaccine responses, increased susceptibility to other infections (Adair, 2000) and decreased cell-mediated immune responses (MarkowskiGrimsrud & Schat, 2003;McConnell et al., 1993). CAV infects T cell precursors in the thymic cortex and CD8 + splenic lymphocytes and haemocytoblasts in the bone marrow (Adair, 2000;Jeurissen et al., 1992;Noteborn et al., 1994a). There is also evidence that CAV can be present in the reproductive system (Cardona et al., 2000a, b) and be vertically transmitted in antibody-positive or -negative hens (Miller et al., 2003).Sequences in the 59 non-transcribed region of the CAV genome are believed to be the sole promoter enhancer for CAV (Noteborn et al., 1994b;Phenix et al., 1994). This region has four or five direct repeat (DR) regions of 21 bases, with a 12 base insert between the first two (or three) and the last two DR. These regions are necessary for efficient viral transcription and replication (Noteborn et al., 1998(Noteborn et al., , 1994b. The DR regions contain the sequence AGCTCA, which varies by one nucleotide from the oestrogen response element (ERE) half site, (A)GGTCA. Oestrogen receptor (ER), a ligand-induced nuclear receptor, binds as a homodimer to EREs in oestrogen-regulated genes with promoters that contain perfect or imperfect ERE half sites (Driscoll et al., 1998) arranged as palindromes or as widely spaced direct repeats (Aumais et al., 1996;Kato et al., 1995;Klinge et al., 1997;Krieg et al., 2001). Other ligand-induced nuclear receptors, such as thyroid receptor (TR), retin...

Divergent gyroviruses in the feces of Tunisian children

“…Direct alignment between the partial NTR sequences of GyV6 and it’s the closest matches in HGyV/AGV2 and GyV3 revealed that 16 to 18 nucleotides were likely not sequenced. The GyV6 NTR possessed four tandem repeats of a CAV promoter (TGTACAGGGGGGGT ACGTCA ) containing a putative estrogen-response element ( ACGTCA ) that can upregulate transcription (Miller et al, 2005) and can be negatively regulated by COUP-TF1 (Miller et al, 2008). Four copies of this promoter element are found in CAV and HGyV/AGV2, while only one copy in GyV3.…”

Molecular identification and transcriptional regulation of porcine IFIT2 gene

“…DeltaEF1 factor, a zinc finger protein, is implicated in the regulation of a lot of viral and cellular genes with functionally diverse roles [21,22]. Through binding directly to the promoters, it represses transcription of epithelial splicing regulatory protein 2 [23], E-cadherin [24] and Plakophilin 3 genes [25], and suppresses promoter activity of chicken infectious anemia virus [26] as well. Here, we confirmed that deltaEF1 is also transcription repressor of pIFIT2 gene.…”

Biotic concerns in generating molecular diagnosis matrixes for 4 avian viruses with emphasis on Marek’s disease virus

“…The particular infection form of latency or pseudo-latency might also lead to difficulties to detect the infecting viruses. In these circumstances the infecting viruses are present in distinctively minute amounts, at least until reactivation, as in the case of herpesviruses, like ILTV (Guy et al, 1991;Hughes et al, 1991) and circoviruses, like CAV (Miller et al, 2008). In commercial flocks the infection is not synchronous, and the timing of sampling is dictated by the appearance of clinical signs in conjunction to other factors.…”