Disease relevance of NFAT5

• We provide evidence that both NFAT1, and the recently identified NFAT5 isoform, are expressed in invasive human ductal breast carcinomas and participate in promoting carcinoma invasion using cell lines derived from human breast and colon carcinomas [1].
• To investigate sequences or mutations associated with neurodegenerative disorders, we performed analyses for the NFAT5 gene, which is located in the candidate region for the autosomal dominantly inherited spinocerebellar ataxia type 4 (SCA4) [2].

High impact information on NFAT5

• We suggest that NFAT5 participates in specific aspects of host defense by upregulating TNF family genes and other target genes in T cells [3].
• Like Rel/NF-kappaB proteins but unlike the calcium-regulated NFAT proteins, NFAT5 is constitutively dimeric, and dimerization is essential for DNA binding and transcriptional activity [3].
• Using dominant-negative proteins that inhibit NFAT5 dimerization, we show that NFAT5 regulates expression of the TNFalpha and lymphotoxin-beta genes in osmotically stressed T cells [3].
• In addition, the transcriptional activity of NFAT5 is induced by alpha(6)beta(4) clustering in the presence of chemo-attractants, resulting in enhanced cell migration [1].
• Several kinases are known to contribute to signaling activation of TonEBP/OREBP, including ATM, which is a member of the phosphatidylinositol 3-kinase (PI3K)-like kinase family and is activated by DNA double-strand breaks [4].

Biological context of NFAT5

• Here we demonstrate that NFAT5 is necessary for optimal T cell development in vivo and allows for optimal cell growth ex vivo under conditions associated with osmotic stress [5].
• Recently, we mapped the human NFAT5 gene to chromosome 16 by PCR using DNA from hybrid cell lines [6].
• Genomic organization of the human NFAT5 gene: exon-intron structure of the 14-kb transcript and CpG-island analysis of the promoter region [7].
• Unlike NFAT1-4, whose nuclear import is tightly regulated by calcineurin-mediated dephosphorylation, NFAT5 is a constitutively nuclear phosphoprotein regardless of calcineurin activation [8].
• PCR based expression analyses detected NFAT5 transcripts with alternative splicing in 27 fetal and adult human tissues [2].

Anatomical context of NFAT5

• Here we demonstrate that this protein, designated NFATL1 (also known as tonicity enhancer binding protein and NFAT5) is expressed at high levels in the thymus but is undetectable in mature lymphocytes [9].
• However, NFATL1 can be induced in both primary quiescent T lymphocytes and differentiated Th1 and Th2 cell populations upon mitogen- or Ag receptor-dependent activation [9].
• We quantified TonEBP/OREBP in nuclear and cytoplasmic extracts from cultured cells by Western blot analysis [10].
• In COS-7 cells, wortmannin, an inhibitor of ATM, reduces high NaCl-induced nuclear translocation of TonEBP/OREBP [10].
• Consistently, small interfering RNA targeting NFAT5 gene enhanced myocyte death [11].

Associations of NFAT5 with chemical compounds

• NFAT1 and NFAT5 activity correlates with the expression of the alpha(6)beta(4) integrin [1].
• Assignment of transcription factor NFAT5 to human chromosome 16q22.1, murine chromosome 8D and porcine chromosome 6p1.4 and comparison of the polyglutamine domains [6].
• High urea and radiation also activate ATM, but they do not increase TonEBP/OREBP transcriptional activity like high NaCl does [12].
• High NaCl activates the transcription factor tonicity-responsive enhancer/osmotic response element-binding protein (TonEBP/OREBP), resulting in increased transcription of several protective genes, including the glycine betaine/gamma-aminobutyric acid transporter (BGT1) [12].
• The induction of NFATL1 protein, as well as NFATL1-dependent transcription, is inhibited by cyclosporin A and FK506, and expression of constitutively active calcineurin induces NFATL1-dependent transcription [9].

Physical interactions of NFAT5

• TonEBP/OREBP reciprocally coimmunoprecipitates with ATM kinase, demonstrating physical association [12].
• TonEBP [TonE (tonicity-responsive enhancer)-binding protein] is a transcriptional activator of the Rel family like NF-kappaB (nuclear factor kappaB) and NFAT (nuclear factor of activated T-cells) [13].
• The N- and C-termini of RHA bound the E'F loop of the DNA-binding domain of TonEBP [13].
• In hypertonic media there was activation of TauT and heat shock protein-70 (HSP-70) reporter activity and increased binding of TonEBP to the TonE motif [14].

Regulatory relationships of NFAT5

• The purpose of the present studies was to test whether ATM is also involved in high NaCl-induced TonEBP/OREBP nuclear translocation [10].
• Overexpression of RHA inhibited the activity of TonEBP; however, catalytic activity of RHA was dispensable for the inhibition [13].
• In conclusion, these results show that aldose reductase is upregulated by the transcriptional factor NFAT5 under high-glucose conditions in both PBMCs and HMCs [15].
• TonEBP protects the renal medulla from the deleterious effects of hyperosmolality and regulates the urinary concentration by stimulating aquaporin-2 and urea transporters [16].
• TonEBP stimulates genes whose products drive cellular accumulation of organic osmolytes and HSP70, which protect cells from the deleterious effects of hypertonicity and urea, respectively [17].

Other interactions of NFAT5

• TonEBP/OREBP contains ATM consensus phosphorylation sites at Ser-1197, Ser-1247, and Ser-1367 [12].
• Cyclophillin B and FK-associated binding protein, calcineurin A (alpha and beta), and NFATC3 and NFAT5 were detected in hTBEC cultures by RT-PCR [18].
• A fifth member of the NFAT family, NFAT5, controls the cellular response to osmotic stress, by a mechanism that requires dimer formation and is independent of calcineurin or of interaction with AP-1 [19].
• In the present paper, we report that TonEBP is associated in vivo with RHA (RNA helicase A) [13].
• Finally, the silencing of the NFAT5 gene in vitro reduced the expression of the aldose reductase gene [15].

Analytical, diagnostic and therapeutic context of NFAT5

• Chromatin immunoprecipitation experiments confirm that NFAT5 binds to the TNFalpha promoter in vivo [3].
• NFAT5 binding activity was quantitated using electrophoretic mobility shift assays for each of the OREs [15].
• Further, ubiquitin-conjugated NFAT5 was not detected in cultured cardiomyocytes treated with MG-132 and/or Dox, as assessed by immunoprecipitation assay, suggesting Dox-induced degradation through ubiquitin-independent proteasome pathway [11].
• Disruption of NES by site-directed mutagenesis yielded a mutant OREBP/TonEBP protein that accumulated in the nucleus under isotonic conditions but remained a target for hypotonicity-induced nuclear export [20].
• Confocal microscopy confirmed an increased nuclear translocation of TonEBP in response to NaCl-induced hypertonicity [21].

References