Calcium signals lead to the translocation of nuclear factor of activated T cells (NFAT) from the cytoplasm to the nucleus. This process is regulated by the calcium-activated phosphatase calcineurin, which can be cotransported with NFAT to the nucleus to maintain it transcriptionally active for the duration of calcium signaling. When the calcium signal ceases, NFAT is exported to the cytoplasm, and different NFAT kinases have been reported to oppose calcineurin activities and regulate the nuclear export of NFAT. Here we show that p38 MAPK phosphorylates in vitro and interacts in vivo with NFATp. Furthermore, the activation of this pathway in HeLa cells by cotransfection with activated MKK6 and p38 counteracts the calcium-induced nuclear accumulation of NFATp but not that of NFATc. By contrast, activation of JNK or ERK pathways failed to modify the nuclear shuttling of NFATp. Consistently, activation of p38, but not the JNK MAPK pathway, results in the inhibition of NFATp-driven transcription. In addition, the inhibition of the nuclear accumulation of NFATp by p38 appears to be mediated through the activation of NFATp nuclear export and takes place in a Leptomycin B-sensitive fashion, suggesting the involvement of the exportin CRM1 in this process. Thus, the p38 signal transduction pathway appears to play an important role in the regulation of the nuclear shuttling of NFATp and in cellular homeostasis.
Biological Transport Calcium