The Osmoprotective Function of the NFAT5 Transcription Factor in T Cell Development and Activation

Abstract

The NFAT5/TonEBP transcription factor, a recently identified rel/NF-κB family member, activates transcription of osmocompensatory genes in response to extracellular hyperosmotic stress. However, the function of NFAT5 under isosmotic conditions present in vivo remains unknown. 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. Transgenic mice expressing an inhibitory form of NFAT5 in developing and mature T cells exhibited a 30% reduction in thymic cellularity evenly distributed among thymic subsets, consistent with the uniform expression and nuclear localization of NFAT5 in each subset. This was associated with a 25% reduction in peripheral CD4+ T cells and a 50% reduction in CD8+ T cells. While transgenic T cells exhibited no impairment in cell growth or cytokine production under normal culture conditions, impaired cell growth was observed under both hyperosmotic conditions and isosmotic conditions associated with osmotic stress. Transgenic thymocytes also demonstrated increased sensitivity to osmotic stress. Consistent with this, the system A amino acid transporter gene ATA2 exhibited NFAT5 dependence under hypertonic conditions but not in response to amino acid deprivation. Expression of the TNF-α gene, a putative NFAT5 target, was not altered in transgenic T cells. These results not only demonstrate an osmoprotective function for NFAT5 in primary cells but also show that NFAT5 is necessary for optimal thymic development in vivo, suggesting that developing thymocytes within the thymic microenvironment are subject to an osmotic stress that is effectively countered by NFAT5-dependent responses.

Degradation of NFAT5, a Transcriptional Regulator of Osmotic Stress-related Genes, Is a Critical Event for Doxorubicin-induced Cytotoxicity in Cardiac Myocytes

“…Several data presented here illustrate the physiological significance of NFAT5 for cell survival in cardiac myocytes, consistent with previous reports concerning the cytoprotective roles of the transcriptional targets of NFAT5 in mammalian cells (16,19,20). TauT is a major factor in maintaining a high gradient of cardiac tissue/plasma taurine concentration (46,47).…”

“…Expression vector of truncated NFAT5 construct consists of a DNA-binding domain (212-543 amino acids) as described previously (10). Other investigators have revealed that the deletion mutant inhibits endogenous NFAT5 activity, interfering with NFAT5 dimerization but not the transcriptional activity of the other NFATs, NF B and AP-1 (16,25).…”

“…Recent studies have demonstrated that disruption of NFAT5 gene results in late gestational lethality and that surviving NFAT5 Ϫ/Ϫ mice develop a remarkable atrophy of kidney medulla (19). Similarly, suppression of NFAT5 transcriptional activity resulted in impaired cell proliferation with increased cell death in T-cell (16) and lens fiber cells (20). Interestingly, NFAT5, unlike the other members of the NFAT family of protein, is localized not only in cytosol but also in nucleus in isotonic conditions (9).…”

“…NFAT5 also induces molecular chaperones, such as heat shock protein 70-2 (Hsp70-2) (14) and osmotic stress protein of 94 kDa (Osp94) (15). Importantly, inhibition of NFAT5 led to an increase in susceptibility to hypertonic stress (16).…”

Downregulation of NFAT5 by RNA interference reduces monoclonal antibody productivity of hybridoma cells

“…The release of and response to ATP plays a key role in the mechanism through which hypertonic stress regulates the function of T cells [26]. NFAT5 is also necessary for optimal T-cell development in vivo and allows for optimal cell growth ex vivo under conditions associated with osmotic stress [27]. Furthermore, William Go and his co-workers [21,28] measured lymphoid tissue osmolality directly by using a vapor pressure osmometer and they found that in contrast to brain and lung, lymphoid tissues were significantly hypertonic relative to serum.…”