NFAT2 Isoforms Differentially Regulate Gene Expression, Cell Death, and Transformation through Alternative N-Terminal Domains

Abstract

bThe NFAT (nuclear factor of activated T cells) family of transcription factors is composed of four calcium-responsive proteins (NFAT1 to -4). The NFAT2 (also called NFATc1) gene encodes the isoforms NFAT2␣ and NFAT2␤ that result mainly from alternative initiation exons that provide two different N-terminal transactivation domains. However, the specific roles of the NFAT2 isoforms in cell physiology remain unclear. Because previous studies have shown oncogenic potential for NFAT2, this study emphasized the role of the NFAT2 isoforms in cell transformation. Here, we show that a constitutively active form of NFAT2␣ (CA-NFAT2␣) and CA-NFAT2␤ distinctly control death and transformation in NIH 3T3 cells. While CA-NFAT2␣ strongly induces cell transformation, CA-NFAT2␤ leads to reduced cell proliferation and intense cell death through the upregulation of tumor necrosis factor alpha (TNF-␣). CA-NFAT2␤ also increases cell death and upregulates Fas ligand (FasL) and TNF-␣ in CD4 ؉ T cells. Furthermore, we demonstrate that differential roles of NFAT2 isoforms in NIH 3T3 cells depend on the N-terminal domain, where the NFAT2␤-specific N-terminal acidic motif is necessary to induce cell death. Interestingly, the NFAT2␣ isoform is upregulated in Burkitt lymphomas, suggesting an isoform-specific involvement of NFAT2 in cancer development. Finally, our data suggest that alternative N-terminal domains of NFAT2 could provide differential mechanisms for the control of cellular functions.

NFATc1 is a tumor suppressor in hepatocellular carcinoma and induces tumor cell apoptosis by activating the FasL‐mediated extrinsic signaling pathway

“…Correlation analysis by IHC and TCGA dataset also revealed that there were positive correlations between NFATc1 and FasL. Consistent with our results, many studies have shown that NFATc1 binds FasL promoter to induce its expression in many other types of cells and tissues . Both dysregulation of the extrinsic and intrinsic apoptosis pathways are well known to be involved in cancer .…”

“…However, other studies suggested NFATc1 might function as a tumor suppressor in some types of cancer. [33][34][35][36][37][38] Lucena et al 39 found that different murine Nfatc1 isoforms played distinct roles in NIH 3T3 cells. While Nfatc1 isoform 3 induced cell transformation, Nfatc1 isoform 1 reduced cell proliferation and induce apoptosis.…”

“…Consistent with our results, many studies have shown that NFATc1 binds FasL promoter to induce its expression in many other types of cells and tissues. [39][40][41] Both dysregulation of the extrinsic and intrinsic apoptosis pathways are well known to be involved in cancer. 42 FasL is a key protein that triggers the extrinsic apoptosis pathway, 43 and its expression is regulated by many transcriptional factors such as Jun, NF-κB, NFAT, EGR-3, and SP1 in human tumors.…”

Transcription Factors in Cancer: When Alternative Splicing Determines Opposite Cell Fates

“…Burkitt lymphoma patients show high levels of NFAT2α associated to low NFAT2β levels, in opposition to what was observed in peripheral blood mononuclear cells from health donors. These data corroborated a pro-oncogenic role of NFAT2α in Burkitt lymphomas [82]. NFAT2α TAD [78,82]…”

“…NFAT2α and NFAT2β could compete for the transcription of cell death genes to prevent or promote the apoptosis of activated T or B cells [78]. Indeed, NFAT2β may induce the up-regulation apoptotic genes, such as Tnf-α and FasL, more potently than NFAT2α through its conserved N-terminal TAD [78,82]. Burkitt lymphoma patients show high levels of NFAT2α associated to low NFAT2β levels, in opposition to what was observed in peripheral blood mononuclear cells from health donors.…”