NIPBL: a new player in myeloid cell differentiation

Abstract

The nucleophosmin 1 gene ( NPM1 ) is the most frequently mutated gene in acute myeloid leukemia. Notably, NPM1 mutations are always accompanied by additional mutations such as those in cohesin genes RAD21 , SMC1A , SMC3 , and STAG2 but not in the cohesin regulator, nipped B-like ( NIPBL ). In this work, we analyzed a cohort of adult patients with acute myeloid leukemia and NPM1 mutation and observed a specific reduction in the expression of NIPBL but not in other cohesin genes. In our zebrafish model, overexpression of the mutated form of NPM1 also induced downregulation of nipblb , the zebrafish ortholog of human NIPBL . To investigate the hematopoietic phenotype and the interaction between mutated NPM1 and nipblb , we generated a zebrafish model with nipblb downregulation which showed an increased number of myeloid progenitors. This phenotype was due to hyper-activation of the canonical Wnt pathway: myeloid cells blocked in an undifferentiated state could be rescued when the Wnt pathway was inhibited by dkk1b mRNA injection or indomethacin administration. Our results reveal, for the first time, a role for NIPBL during zebrafish hematopoiesis and suggest that an interplay between NIPBL/NPM1 may regulate myeloid differentiation in zebrafish and humans through the canonical Wnt pathway and that dysregulation of these interactions may drive leukemic transformation.

Dysregulation of NIPBL leads to impaired RUNX1 expression and haematopoietic defects

“…Second, it has been reported that the chromatin structure at the spi1b /PU.1 locus could be differentially regulated during the different stages of haematopoiesis, 11 suggesting the possibility that other mechanisms than RUNX1 might control spi1b expression. For example, we demonstrated that the canonical Wnt pathway, modulated by nipblb , has a pivotal role in regulating spi1b myeloid expression during definitive haematopoiesis in zebrafish 34 . Moreover, in vitro and in vivo studies demonstrated that forced expression of gata1 down‐regulates spi1b , while forced expression of spi1b down‐regulates gata1 48–50 .…”

“…We previously showed that NIPBL transcript abundance is decreased in AML patients carrying the mutated NUCLEOPHOSMIN1 (NPM1) , which transfers NPM1 in the cytoplasm (NPMc+), compared to the NPM1 wild‐type (NPM1wt) 34 . Therefore, we analysed the correlation between the expression of NIPBL and RUNX1 in BM cells derived from 20 patients NPMc+, selected among the 34 AML patients, compared to 14 patients NPM1wt and found a significant positive correlation in NPMc+ but not in NPM1wt AML patients (Figure 1E‐F).…”

“…To confirm the positive correlation between NIPBL and RUNX1 observed in human, we took advantage of a zebrafish model with down‐regulation of nipblb , the orthologue of the human NIPBL , previously generated in our laboratory 34 . The expression of runx1 was analysed in embryos at 30 and 48 hpf as definitive HSCs arise from the vascular endothelium from these developmental stages.…”

Cohesin mutations are synthetic lethal with stimulation of WNT signaling

“…Scale bar, 50 µm. For Tg(7xTCF-Xla.Siam:nlsmCherry) ia5 control embryos n=15/15; and for Tg(7xTCF-Xla.Siam:nlsmCherry) ia5 ;rad21 nz171 cohesin mutant, n=4/4 with the same expression pattern.b Tg(7xTCF-Xla.Siam:nlsmCherry) ia5Tg(7xTCF-Xla.Siam:nlsmCherry) ia5 ;rad21 nz171 canonical Wnt signaling is hyperactivated in cohesin loader nipblb-lossof-function zebrafish embryos[60]. Altogether, the results suggest that hyperactivation of Wnt signaling is a conserved feature of cohesin deficient cells, and that enhanced sensitivity to Wnt is at least in part due to stabilization of b-catenin.DiscussionThecohesin complex and its regulators are encoded by several different loci, and genetic alterations in any one of them may occur in up to 26% of patients included in The Cancer Genome Atlas (TCGA) studies [61].…”

HDAC8: A Promising Therapeutic Target for Acute Myeloid Leukemia

“…Alternatively, in double immunofluorescence staining analyses, we injected water as a control. For canonical Wnt inhibition, zebrafish dkk1b mRNA was injected at the concentration of 50 pg/embryo (Mazzola et al, 2019). PCI treatment were done in 24-well plates, 30 embryos/well.…”