Sequence and functional properties of African green monkey CD4 silencer

We reported previously that in African green monkey (AGM) CD4 lymphocytes, CD4 mRNA expression undergoes a decrease following in vitro activation, and CD4 cells are therefore subject to loss of CD4 expression on the cell surf ace. To examine the transcriptional regulation of the CD4 gene in this spec ies, we analyzed the CD4 silencer, which has been identified as a regulator y element responsible for the down regulation of CD4 transcription in CD8 c ell lineage cells. Sequence analysis indicated that the CD4 silencer of the AGM was highly homologous to that of humans. However, two nucleotide subst itutions were present in one of the nuclear protein binding sites, which wa s characterized as the FP II site having a strong enhancing effect on trans gene expression in CD4 cells. By performing transient transfection assays, we found that the enhancing activities of the CD4 silencer or FP II-contain ing fragment of the AGM were greatly reduced in a human CD4 cell line as co mpared to those of human materials. The CD4 mRNA level was significantly de creased in the human CD4 cell line when synthetic oligonucleotide correspon ding to the human FP II sequence was added to the culture. These observatio ns imply that FP II-protein interaction might be required for the maintenan ce of sufficient expression of the CD4 gene, and the enhancing activity med iated by the above interaction might be decreased in the AGM CD4 silencer, due probably to the nucleotide changes occurring at the FP II site. (C) 200 0 Elsevier Science B.V. All rights reserved.