Expression and regulation of NFAT (nuclear factors of activated T cells) in human CD34+ cells: down-regulation upon myeloid differentiation

Abstract

The calcineurin-dependent, cyclosporin A (CsA)-sensitive transcription factor nuclear factor of activated T cells (NFAT) represents a group of proteins, which is well-characterized as a central regulatory element of cytokine expression in activated T cells. In contrast, little is known about the expression or function of NFAT family members in myeloid cells; moreover, it is unclear whether they are expressed by hematopoietic stem/progenitor cells. Here, we show that NFATc2 (NFAT1) is expressed at high levels in CD34+ cells and megakaryocytes but not in cells committed to the neutrophilic, monocytic, or erythroid lineages. Cytokine-induced in vitro differentiation of CD34+ cells into neutrophil granulocytes results in the rapid suppression of NFATc2 RNA and protein. NFATc2 dephosphorylation/rephosphorylation as well as nuclear/cytoplasmic translocation in CD34+ cells follow the same calcineurin-dependent pattern as in T lymphocytes, suggesting that NFATc2 activation in these cells is equally sensitive to inhibition with CsA. Finally, in vitro proliferation, but not differentiation, of CD34+ cells cultured in the presence of fms-like tyrosine kinase 3 ligand (FLT3L), stem cell factor, granulocyte macrophage-colony stimulating factor (GM-CSF), interleukin-3, and G-CSF is profoundly inhibited by treatment with CsA in a dose-dependent manner. These results suggest a novel and unexpected role for members of the NFAT transcription factor family in the hematopoietic system.

Requirement for balanced Ca/NFAT signaling in hematopoietic and embryonic development

“…This is most likely due to a mild inability of the AV-NFAT1-expressing cell populations to compete with cells in which the hyperactivable protein is not expressed. These findings are consistent with a previous report showing that as hematopoietic stem cells begin to differentiate, expression of all NFAT family members is downregulated (38,39); in contrast, hyperactivable NFAT1 proteins expressed from the R26 locus would not be downregulated, and progenitor cells expressing these proteins, even at low levels, would display inappropriately sustained NFAT activity, potentially conferring a competitive disadvantage on those cell populations. NFAT1 has been shown to repress expression of the G 0 /G 1 checkpoint kinase cyclin-dependent kinase 4 (CDK4) (40).…”

Osteomyelosclerosis, anemia and extramedullary hematopoiesis in mice lacking the transcription factor NFATc2

“…Our previous studies showed that members of the NFAT family are expressed in hematopoietic progenitor cells and are regulated during myeloid commitment in a lineage-specific manner. 15,16 These results prompted us to investigate the role of NFATc2 in hematopoiesis.…”

“…Of note, NFATc2 is expressed by both hematopoietic stem cells and stromal cells. 15,26,27 and thus both direct and indirect mechanisms have to be considered as causes for the hematopoietic insufficiency in the bone marrow of NFATc2-deficient animals. Our results suggest that NFATc2 is neither directly nor indirectly involved in the myeloid differentiation of hematopoietic progenitor cells, as the capacity for erythroid and granulocytic differentiation of these cells was maintained in the absence of NFATc2, both within the local bone marrow environment and in extramedullary organs.…”

“…15,16 We, therefore, set out to determine whether NFATc2 was necessary for the intrinsic megakaryocytic differentiation potential of hematopoietic progenitor cells, and also extended this question to other NFAT family members. Of note, activation of NFAT proteins strictly requires posttranslational modification (i.e.…”

“…Our previous studies show that all members of the NFAT family, except for NFATc4, are expressed in CD34 + HSC and that their expression is differentially regulated during the lineage-specific differentiation of myeloid cells. 15,16 For example, while NFATc4 is not expressed in HSC and remains almost undetectable in differentiated neutrophil, eosinophil and erythroid cells, its expression is strongly induced during megakaryocyte differentiation. In contrast, the expression of NFATc2, which is abundantly found in HSC, is rapidly and almost completely suppressed upon their differentiation into neutrophil granulocytes, but is maintained in the megakaryocyte lineage.…”