NF45 and NF90 Regulate HS4-dependent Interleukin-13 Transcription in T Cells

Abstract

Expression of the cytokine interleukin-13 (IL13) is critical forThe T cell-derived cytokine interleukin (IL) 2 -13 plays a pivotal effector role in T helper type 2 (Th2) immune responses to extracellular parasites (1). When dysregulated by genetic and/or environmental factors, IL13 expression is essential for the pathogenesis of allergic diseases (2). Indeed, experimental animal models have shown that IL-13 is necessary and sufficient to induce all the cardinal features of allergic lung inflammation, including airway hyper-responsiveness, eosinophilia, goblet cell metaplasia and mucus hyper-secretion, epithelial cell damage, and fibrosis (3-5). IL13 expression and IL-13-dependent events are also amplified in human allergy (6, 7), and high IL-13 production in early life is strongly associated with the subsequent development of allergic sensitization (8 -10).The IL13 gene lies within the Th2 cytokine locus on human chromosome 5q31, which also includes IL4 and IL5. Th2 cytokine gene expression has been shown to be tightly coordinated and fine-tuned by multiple local and distant cis-regulatory elements that are located throughout the Th2 locus and are marked by developmentally conserved DNase I-hypersensitive (HS) sites (11). HS sites typically reflect the DNA binding activity of sequence-specific trans-acting factors that induce destabilization or displacement of local nucleosomes (12) and mark the location of enhancers, silencers, or locus control regions (13). In the murine Th2 locus, nuclease HS regions appear to work cooperatively (14, 15) and engage in local and long range intra-chromosomal interactions that are essential for concerted Th2 cytokine expression (16).We recently characterized the dynamic modifications in DNase I hypersensitivity and epigenetic marks that occur at the human IL13 locus during the differentiation of naive CD4ϩ Th cells into a polarized IL-13/IL-4 secreting Th2 phenotype (17). Our study demonstrated that distinct regions of the IL13 locus exhibit distinct patterns of chromatin accessibility at defined stages of the Th cell differentiation process. In naive T cells, chromatin at the proximal promoter, the transcription unit, and the IL13/IL4 intergenic region was in an inaccessible state, marked by the absence of HS sites and by extensive CpG hypermethylation. During Th2 differentiation, these regions underwent profound remodeling, revealed by the appearance of numerous HS sites that co-localized with DNA hypomethylation. In contrast, the distal IL13 promoter contained two closely spaced, novel HS sites, HS4 and HS5, which were detectable in unstimulated naive CD4 ϩ T cells and persisted throughout Th cell differentiation (17). Detection of constitutive HS sites in naive CD4ϩ T cells was intriguing because these cells rapidly express substantial amounts of IL-13 upon T cell receptor cross-linking (18). Early accessibility of the distal promoter suggested occupancy of HS4 and HS5 by constitutive transcription * This work was supported, in whole or in part, by National Institutes of Hea...

The NF45/NF90 Heterodimer Contributes to the Biogenesis of 60S Ribosomal Subunits and Influences Nucleolar Morphology

“…The NF45/NF90 heterodimer has been previously implicated in a plethora of cellular pathways (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17). The involvement of NF45/NF90 in ribosome synthesis identified here adds a very basic cellular pathway to its functional repertoire and could well explain why NF90 is essential in vertebrates.…”

“…Over recent years, NF45/NF90 has been implicated in a great variety of biological processes. Apart from regulation of transcription (5)(6)(7), the heterodimer has also been linked to numerous other pathways, such as DNA damage response (8,9), mRNA metabolism (10,11), microRNA (miRNA) biogenesis (12), and viral infection (13)(14)(15)(16)(17). NF90 knockout mice display severe defects in skeletal muscle formation leading to respiratory failure soon after birth (18), indicating an essential role of NF90 function in vertebrate development.…”

Nucleotide Composition of Cellular Internal Ribosome Entry Sites Defines Dependence on NF45 and Predicts a Posttranscriptional Mitotic Regulon

“…NF45 was first identified as a nuclear factor of activated T cells (NFAT)-related transcription factor that regulates interleukin-2 transcription, together with its binding partner NF90 (8). Therefore, a general reduction in the polysome loading of APAF1 could reflect an indirect transcriptional effect of NF45 and its binding partner, NF90, in a complex that is known to target a wide array of genes (9,45). Moreover, we showed previously that the attenuation of cIAP1 IRES-dependent translation induction in d5 cells during ER stress can be rescued by reexpression of NF45 but not NF90 (7); this further argues that the NF45-NF90 transcriptional effects are independent of the function of NF45 as an ITAF.…”

“…Indeed, NF45 was shown to interact directly with the cIAP1 IRES and positively affect its activity, resulting in the increased translation of its mRNA during thapsigargin-induced endoplasmic reticulum (ER) stress. This was the first report of NF45 having a bona fide function in IRESmediated translation, although there have been reports of the involvement of NF45 and its binding partner NF90 in transcription (8,9), viral replication (10)(11)(12), and microRNA processing (13,14).…”

Overexpression of NF90-NF45 Represses Myogenic MicroRNA Biogenesis, Resulting in Development of Skeletal Muscle Atrophy and Centronuclear Muscle Fibers

“…We previously showed that the NF90-NF45 complex suppresses pri-miRNA cleavage and mature miRNA production through binding to pri-miRNAs in HEK293T cells (27). In addition, it has been reported that NF90 or the NF90-NF45 complex is involved in mRNA stabilization (28), translational repression (29,30), replication of viral RNA (31), and transcription (32,33) in vitro. However, the physiological functions of NF90 and/or NF45 remain largely unknown because NF90 or NF45 knockout (KO) mice exhibit perinatal lethality due to respiratory failure or embryonic lethality (32,34).…”