Nuclear factor of activated T-cells, NFATC1, governs FLT3ITD-driven hematopoietic stem cell transformation and a poor prognosis in AML

Background

Acute myeloid leukemia (AML) patients with a high allelic burden of an internal tandem duplication (ITD)-mutated FMS-like Tyrosine Kinase-3 (FLT3) have a dismal outcome. FLT3^ITD triggers the proliferation of the quiescent hematopoietic stem cell (HSC) pool but fails to directly transform HSCs. While the inflammatory transcription factor nuclear factor of activated T-cells 2 (NFAT2, NFATC1) is overexpressed in AML, it is unknown whether it plays a role in FLT3^ITD-induced HSC transformation.

Methods

We generated a triple transgenic mouse model, in which tamoxifen-inducible Cre-recombinase targets expression of a constitutively nuclear transcription factor NFATC1 to FLT3^ITD positive HSC. Emerging genotypes were phenotypically, biochemically, and also transcriptionally characterized using RNA sequencing. We also retrospectively analyzed the overall survival of AML patients with different NFATC1 expression status.

Results

We find that NFATC1 governs FLT3^ITD-driven precursor cell expansion and transformation, causing a fully penetrant lethal AML. FLT3^ITD/NFATC1-AML is re-transplantable in secondary recipients and shows primary resistance to the FLT3^ITD-kinase inhibitor quizartinib. Mechanistically, NFATC1 rewires FLT3^ITD-dependent signaling output in HSC, involving augmented K-RAS signaling and a selective de novo recruitment of key HSC-transforming signaling pathways such as the Hedgehog- and WNT/B-Catenin signaling pathways. In human AML, NFATC1 overexpression is associated with poor overall survival.

Conclusions

NFATC1 expression causes FLT3^ITD-induced transcriptome changes, which are associated with HSC transformation, quizartinib resistance, and a poor prognosis in AML.

Electronic supplementary material

The online version of this article (10.1186/s13045-019-0765-y) contains supplementary material, which is available to authorized users.

Synergistic killing of FLT3ITD-positive AML cells by combined inhibition of tyrosine-kinase activity and N-glycosylation

Fms-like tyrosine kinase 3 (FLT3) with internal tandem duplications (ITD) is a major oncoprotein in acute myeloid leukemia (AML), and confers an unfavorable prognosis. Interference with FLT3ITD signaling is therefore pursued as a promising therapeutic strategy. In this study we show that abrogation of FLT3ITD glycoprotein maturation using low doses of the N-glycosylation inhibitor tunicamycin has anti-proliferative and pro-apoptotic effects on FLT3ITD-expressing human and murine cell lines. This effect is mediated in part by arresting FLT3ITD in an underglycosylated state and thereby attenuating FLT3ITD-driven AKT and ERK signaling. In addition, tunicamycin caused pronounced endoplasmatic reticulum stress and apoptosis through activation of protein kinase RNA-like endoplasmic reticulum kinase (PERK) and activation of the gene encoding CCAAT-enhancer-binding protein homologous protein (CHOP). PERK inhibition with a small molecule attenuated CHOP induction and partially rescued cells from apoptosis. Combination of tunicamycin with potent FLT3ITD kinase inhibitors caused synergistic cell killing, which was highly selective for cell lines and primary AML cells expressing FLT3ITD. Although tunicamycin is currently not a clinically applicable drug, we propose that mild inhibition of N-glycosylation may have therapeutic potential in combination with FLT3 kinase inhibitors for FLT3ITD-positive AML.

MYC-dependent downregulation of telomerase by FLT3 inhibitors is required for their therapeutic efficacy on acute myeloid leukemia

The somatic mutation of FLT3 occurs in 30% of acute myeloid leukemia (AML), with the majority of mutations exhibiting internal tandem duplication (ITD). On the other hand, the induction of telomerase reverse transcriptase (hTERT) and the activation of telomerase is a key step in AML development. Here, we sought to determine whether FLT3ITD regulates hTERT expression in AML cells and whether hTERT expression affects FLT3 inhibitors' therapeutic efficacy on AML. FLT3ITD-harboring AML cell lines and primary cells treated with the FLT3 inhibitor PKC412 displayed a rapid decline in the levels of hTERT mRNA and telomerase activity. Moreover, PKC412 inhibited hTERT gene transcription in a c-MYC-dependent manner. The ectopic expression of hTERT significantly attenuated the apoptotic effect of PKC412 on AML cells. Mechanistically, hTERT enhanced the activity of FLT3 downstream effectors or alternative RTK signaling, thereby enhancing AKT phosphorylation, in AML cells treated with PKC412. Collectively, PKC412 downregulates hTERT expression and telomerase activity in a MYC-dependent manner and this effect is required for its optimal anti-AML efficacy, while hTERT over-expression confers AML cells resistance to a targeted therapeutic agent PKC412. These findings suggest that the functional interplay between FLT3ITD and hTERT contributes to the AML pathogenesis and interferes with the efficacy of FLT3ITD-targeted therapy.