Interferon Regulatory Factor 2 Binding Protein 2 Is a New NFAT1 Partner and Represses Its Transcriptional Activity

Abstract

The nuclear factor of activated T cells (NFAT) family of transcription factors is expressed in a wide range of cell types and regulates genes involved in cell cycle, differentiation, and apoptosis. NFAT proteins share two well-conserved regions, the regulatory domain and the DNA binding domain. The N-and C-terminal ends are transactivation sites and show less sequence similarity, whereas their molecular functions remain poorly understood. Here, we identified a transcriptional repressor, interferon regulatory factor 2 binding protein 2 (IRF-2BP2), which specifically interacts with the C-terminal domain of NFAT1 among the NFAT family members. IRF-2BP2 was described as a corepressor by inhibiting both enhancer-activated and basal transcription. Gene reporter assays demonstrated that IRF-2BP2 represses the NFAT1-dependent transactivation of NFAT-responsive promoters. The ectopic expression of IRF-2BP2 in CD4 T cells resulted in decreased interleukin-2 (IL-2) and IL-4 production, supporting a repressive function of IRF-2BP2 for NFAT target genes. Furthermore, NFAT1 and IRF-2BP2 colocalized in the nucleus in activated cells, and the mutation of a newly identified nuclear localization signal in the IRF-2BP2 rendered it cytoplasmic, abolishing its repressive effect on NFAT1 activity. Collectively, our data demonstrate that IRF-2BP2 is a negative regulator of the NFAT1 transcription factor and suggest that NFAT1 repression occurs at the transcriptional level.The regulation of eukaryotic gene expression is a coordinated action of basal transcriptional machinery, chromatin remodeling factors, and transcriptional factors that bind specific elements in promoters and enhancers; these components form a complex network of protein-protein interactions for the proper regulation of mRNA transcription (37). Nuclear factor of activated T cells (NFAT) transcriptional factor, first identified as an inducible nuclear factor that binds the interleukin-2 (IL-2) promoter in activated T cells (57), plays an important role in the control of gene expression in a wide range of cell types and tissues (42, 65). The NFAT family consists of four members that are regulated by calcium and the calcineurin signaling pathway, known as NFAT1 (also called NFATp or NFATc2), NFAT2 (NFATc or NFATc1), NFAT3 (NFATc4), and NFAT4 (NFATx or NFATc3) (42, 52). A fifth member, NFAT5 (TonEBP or OREBP), is regulated by hyperosmotic stress (40, 45).All NFAT members share a highly conserved DNA binding domain (DBD) that is structurally related to the DBD of the Rel family of transcriptional factors and confers a common DNA-binding specificity to all NFAT proteins (52). The calcium-regulated members, NFAT1 to NFAT4, have a second conserved domain, the NFAT homology region (NHR). This region contains several serines that are phosphorylated when these proteins are in their inactive cytoplasmic forms, and it also contains the docking site for calcineurin and NFAT kinases (42, 52). The high degree of amino acid sequence conservation of the DBD and NHR among the different N...

IRF2BP2 transcriptional repressor restrains naive CD4 T cell activation and clonal expansion induced by TCR triggering

“…Although the majority of works available in the literature proposes a role for IRF2BP2 as a repressor in the regulation of diverse genes [4][5][6][7][8][9], there is some evidence that IRF2BP2 may also act as a positive regulator of gene expression [10,11]. The mechanisms by which IRF2BP2 mediates its repression or induction in the course of gene-expression regulation have not been established and may involve interaction with the DNA and/or with different proteins that vary according to the context.…”

“…Originally, IRF2BP proteins were identified as nuclear transcriptional corepressors that were dependent on IRF2; binding to IRF2 results in their recruitment to the DNA, where they can mediate their repressor function [4]. More recently, IRF2BP2 was identified as a transcriptional repressor in several other biologic contexts that did not necessarily require IRF2 participation [5][6][7][8][9].…”

“…Indeed, this protein has been described as a participant in at least 2 distinct transcriptional repressor complexes, in which it is dependent on either its zinc finger or RING domains [8,9]. As IRF2BP2 is ubiquitously expressed and has diverse roles described in several biologic contexts [4][5][6][7][8][9][10][11], more studies are necessary to investigate its possible roles in different cell types.…”

Genome-wide analysis of STAT3 binding in vivo predicts effectors of the anti-inflammatory response in macrophages

“…The latter are transcriptional corepressors that work in a histone deacetylation-independent manner to inhibit both enhancer-activated and basal transcription, such as that of the Irf2 gene, 41 or in combination with NFAT1 to repress NFAT-responsive genes such as IL-2 and IL-4 in CD4 ϩ T cells. 42 Irf-2bp1 and Irf-2bp2 are both expressed in macrophages, but their expression levels remain unchanged on IL-10 treatment. Finally, CIC is an HMG box-containing protein, and the Drosophila homologue (Capicua) acts as a repressor in dorsoventral patterning.…”

Molecular Characteristics and Clinical Significance of 12 Fusion Genes in Acute Promyelocytic Leukemia: A Systematic Review

“…The IRF2BP2 protein was recently described as a transcriptional corepressor and a repressor of transactivation of nuclear factors of activated T cells that regulate genes involved in the cell cycle, differentiation, and apoptosis [96]. IRF2BP2 has also been proven to be a direct target gene of p53, and its overexpression inhibits apoptosis by decreasing p53-mediated p21 and Bax gene transactivation [97].…”