TonEBP/NFAT5 Stimulates Transcription of HSP70 in Response to Hypertonicity

Abstract

While hyperosmolality of the kidney medulla is essential for urinary concentration, it imposes a great deal of stress. Cells in the renal medulla adapt to the stress of hypertonicity (hyperosmotic salt) by accumulating organic osmolytes. Tonicity-responsive enhancer (TonE) binding protein (TonEBP) (or NFAT5) stimulates transcription of transporters and a synthetic enzyme for the cellular accumulation of organic osmolytes. We found that dominant-negative TonEBP reduced expression of HSP70 as well as the transporters and enzyme. Near the major histocompatibility complex class III locus, there are three HSP70 genes named HSP70-1, HSP70-2, and HSC70t. While HSP70-1 and HSP70-2 were heat inducible, only HSP70-2 was induced by hypertonicity. In the 5 flanking region of the HSP70-2 gene, there are three sites for TonEBP binding. In cells transfected with a reporter plasmid containing this region, expression of luciferase was markedly stimulated in response to hypertonicity. Coexpression of the dominant-negative TonEBP reduced the luciferase expression. Mutating all three sites in the reporter plasmid led to a complete loss of induction by hypertonicity. Thus, TonEBP rather than heat shock factor stimulates transcription of the HSP70-2 gene in response to hypertonicity. We conclude that TonEBP is a master regulator of the renal medulla for cellular protection against high osmolality via organic osmolytes and molecular chaperones.

The role of tonicity responsive enhancer sites in the transcriptional regulation of human hsp70-2 in response to hypertonic stress

“…About-250 bp region in the hsp70-2 promoter was responsible for the induction of hsp70 by hypertonic stress The human hsp70-2 promoter region contains three TonE (tonicity-responsive enhancer) sites, which have been reported to play an important role in the response to hypertonicity (Woo et al, 2002).…”

“…While many types of stress such as heat shock, heavy metals, and amino acids analogues induce both hsp70.1 and hsp70.3 simultaneously, hypertonic stress has been found to induce hsp70.1 selectively (Tanaka et al, 1988;Lee and Seo, 2002;Woo et al, 2002).…”

Activation of osmolyte pathways in inflammatory myopathy and Duchenne muscular dystrophy points to osmoregulation as a contributing pathogenic mechanism

“…We report prominent expression of AR, TauT, and SMIT in the perifascicular atrophic fibers of DM, accompanied by increased/induced expression of other known NFAT5 molecular targets HSP70, 27 iNOS, 28 and CCL2. 29 As was the case earlier for iNOS, 30 we could, however, not confirm a significant increase of AR protein levels in DM muscle extracts via western blotting, presumably because of its expression being limited to the affected perifascicular areas.…”

Hypertonicity-Induced Expression of Monocyte Chemoattractant Protein-1 through a Novel Cis-Acting Element and MAPK Signaling Pathways

“…It has been also reported that the consensus sequence of the TonE/ORE is the 59-(C/T)GGAANNN(C/T)N(C/T)-39 and/or 59-NGGAAA (A/T)(T/A/G)(C/A/T)(A/C)C-39 in the canine BGT1 gene (16) and/ or AR gene (17,18), respectively. In addition to the BGT1 and AR genes, the TonE/ORE has been identified in the proximal region of the 59-flanking region of stress protein genes, such as Hsp70 (19) and Osp94 (20), which protect cells from the deleterious effects of hyperosmolity. Recent studies on intracellular signaling pathways responsive to hypertonicity have suggested that MAPKs pathways play a role in the cellular mechanisms underling the regulation of gene expression in response to hypertonicity (21)(22)(23)(24).…”