TonEBP/NFAT5 stimulates transcription of HSP70 in response to hypertonicity.
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.
Department of Medicine, Johns Hopkins University, Baltimore, Maryland, USA.
Seung Kyoon
SK
Woo
Sang Do
SD
Lee
Ki Young
KY
Na
Won Kun
WK
Park
H Moo
HM
Kwon
D024506:5' Flanking Region / Q000235:genetics; D000818:Animals; D002458:Cell Fractionation; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005091:Exons / Q000235:genetics; D017930:Genes, Reporter; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007679:Kidney Medulla / Q000166:cytology; D051379:Mice; D008822:Mice, Transgenic; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins / Q000378:metabolism; D009997:Osmotic Pressure; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D015398:Signal Transduction / Q000502:physiology; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic
D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D014157:Transcription Factors