NFAT5 participates in Inducible Nitric Oxide Synthase activation by hypoxia in MEF cells.

We previously described the protective role of NFAT5 during hypoxia, in an independent way of HIF-1. Alternatively, inducible NO synthase (iNOS) is also induced by hypoxia. The aim of this study was to establish the NFAT5 target gene in mouse embryonic fibroblasts (MEF) cell stimulated by hypoxia. NFAT5, iNOS, NO level, aquaporin 1 (AQP1) and urea transporter 1 (UTA1) were induced by low oxygen levels in MEF cells. Additionally, NFAT5 and UTA1 were induced in reoxygenation (after 24hrs of hypoxia). NFAT5 transactivation domain (TAD) was induced during hypoxia and hypoxia/reoxygenation. Two MEF cells line independently produced for altered NFAT5 (Knockout and DBD-mutant) lost the iNOS and AQP1 induction by low oxygen. The iNOS induction was recovered in NFAT5-KO MEF cells, when recombinant NFAT5 protein expression was reconstituted, but not for NFAT5 DBD-mutant MEF cells, explained by its dominant negative effect. Finally, we found a negative feedback loop of iNOS effect over NFAT5 protein abundance. This work provides a relevant information about signaling pathway of NFAT5 during adaptive responses to oxygen depletion.