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The Zap1 transcriptional activator also acts as a repressor by binding downstream of the TATA box in ZRT2.

ABSTRACT: The zinc-responsive transcriptional activator Zap1 regulates the expression of both high- and low-affinity zinc uptake permeases encoded by the ZRT1 and ZRT2 genes. Zap1 mediates this response by binding to zinc-responsive elements (ZREs) located within the promoter regions of each gene. ZRT2 has a remarkably different expression profile in response to zinc compared to ZRT1. While ZRT1 is maximally induced during zinc limitation, ZRT2 is repressed in low zinc but remains induced upon zinc supplementation. In this study, we determined the mechanism underlying this paradoxical Zap1-dependent regulation of ZRT2. We demonstrate that a nonconsensus ZRE (ZRT2 ZRE3), which overlaps with one of the ZRT2 transcriptional start sites, is essential for repression of ZRT2 in low zinc and that Zap1 binds to ZRT2 ZRE3 with a low affinity. The low-affinity ZRE is also essential for the ZRT2 expression profile. These results indicate that the unusual pattern of ZRT2 regulation among Zap1 target genes involves the antagonistic effect of Zap1 binding to a low-affinity ZRE repressor site and high-affinity ZREs required for activation.

SUBMITTER: Bird AJ

PROVIDER: S-EPMC380977 | biostudies-literature | 2004 Mar

REPOSITORIES: biostudies-literature

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The Zap1 transcriptional activator also acts as a repressor by binding downstream of the TATA box in ZRT2.

Bird Amanda J AJ Blankman Elizabeth E Stillman David J DJ Eide David J DJ Winge Dennis R DR

The EMBO journal 20040219 5

The zinc-responsive transcriptional activator Zap1 regulates the expression of both high- and low-affinity zinc uptake permeases encoded by the ZRT1 and ZRT2 genes. Zap1 mediates this response by binding to zinc-responsive elements (ZREs) located within the promoter regions of each gene. ZRT2 has a remarkably different expression profile in response to zinc compared to ZRT1. While ZRT1 is maximally induced during zinc limitation, ZRT2 is repressed in low zinc but remains induced upon zinc supple ...[more]

PMID: 14976557

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Project description:HIV-1 is transcriptionally active in activated T helper (Th)-cells and inactive in naive or resting memory Th-cells. Ets-2 is a preinduction transcriptional repressor of the IL-2 gene in naive Th-cells and a candidate transcriptional repressor of HIV-1 in the same cells, because the -279 to -250 upstream region of HIV-1-LTR [repressor-activator target sequence (RATS)], that participates in HIV-1-LTR transcriptional silencing, encompasses the AAGGAG Ets-2 binding site. In this proof of concept study, we investigated whether Ets-2 represses the expression of HIV-1. To assess whether Ets-2 can repress HIV-1 transcriptional activation acting through RATS, we transfected Jurkat cells with an Ets-2 overexpression plasmid (pCDNA3-ets-2) or Ets-2 silencing plasmids (ets-2-shRNA) and, as target genes, plasmids carrying the whole HIV-1-LTR sequence (HIV-1-LTR-CAT) or two copies of the RATS sequence (2× RATS-CAT) or a point mutation in the Ets-2 binding site (2× mutantRATS-CAT) or CMV-CAT (control). Ets-2 overexpression resulted in a significant reduction of HIV-1-LTR-CAT and 2× RATS-CAT activities in stimulated cells, but not of the 2× mutantRATS-CAT or CMV-CAT. Ets-2 silencing led to increased activities of HIV-1-LTR-CAT and 2× RATS-CAT in unstimulated cells, but had no effect on the activities of 2× mutantRATS-CAT and CMV-CAT. To assess Ets-2 binding to HIV-1-LTR-RATS in naive Th-cells, we isolated naive Th-cell nuclear proteins and passed them through an Ets-2 antibody column; electrophoretic mobility shift assays were performed using an RATS probe mixed with consecutive protein eluates. Ets-2 bound to the HIV-1-LTR-RATS in a dose-dependent manner. To assess Ets-2 binding to RATS in vivo, Jurkat cells were transfected with 2× RATS-CAT and stained for the Ets-2 protein and the RATS sequence by combining immunofluorescence and fluorescence in situ hybridization techniques. In unstimulated cells, Ets-2 bound to RATS, whereas no binding was observed in stimulated cells. To test for RATS specificity, the same experiments were performed with 2× mutantRATS-CAT, and no binding of Ets-2 was observed. The results were corroborated by chromatin immunoprecipitation assays performed with the same cells. Our results show that Ets-2 is a transcriptional repressor of HIV-1. Repression of HIV-LTR-RATS mediated by Ets-2 may account for the low-level transcription and replication of HIV-1 in naive Th-cells, and contribute to the viral latency and maintenance of viral reservoirs in patients, despite long-term therapy.

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The Zap1 transcriptional activator also acts as a repressor by binding downstream of the TATA box in ZRT2.

Publications

The Zap1 transcriptional activator also acts as a repressor by binding downstream of the TATA box in ZRT2.

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