Presence of atypical thrombopoietin receptor (MPL) mutations in triple-negative essential thrombocythemia patients.

Mutations in signaling molecules of the cytokine receptor axis play a central role in myeloproliferative neoplasm (MPN) pathogenesis. Polycythemia vera is mainly related to JAK2 mutations, whereas a wider mutational spectrum is detected in essential thrombocythemia (ET) with mutations in JAK2, the thrombopoietin (TPO) receptor (MPL), and the calreticulin (CALR) genes. Here, we studied the mutational profile of 17 ET patients negative for JAK2V617F, MPLW515K/L, and CALR mutations, using whole-exome sequencing and next-generation sequencing (NGS) targeted on JAK2 and MPL. We found several signaling mutations including JAK2V617F at very low allele frequency, 1 homozygous SH2B3 mutation, 1 MPLS505N, 1 MPLW515R, and 2 MPLS204P mutations. In the remaining patients, 4 presented a clonal and 7 a polyclonal hematopoiesis, suggesting that certain triple-negative ETs are not MPNs. NGS on 26 additional triple-negative ETs detected only 1 MPLY591N mutation. Functional studies on MPLS204P and MPLY591N revealed that they are weak gain-of-function mutants increasing MPL signaling and conferring either TPO hypersensitivity or independence to expressing cells, but with a low efficiency. Further studies should be performed to precisely determine the frequency of MPLS204 and MPLY591 mutants in a bigger cohort of MPN.

Sunitinib Treatment of VHL C162F Cells Slows Down Proliferation and Healing Ability via Downregulation of ZHX2 and Confers a Mesenchymal Phenotype.

von Hippel-Lindau (VHL) disease, due to mutations of the tumor suppressor VHL gene, is a rare hereditary syndrome with a high risk of developing clear cell renal cell carcinoma (ccRCC). We asked whether the VHL-C162F mutation interferes with proliferation, migration, healing and forming colony ability by using wild-type VHL (WT VHL) and VHL-C162F reconstituted cells. We then analyzed the in vitro impact of the sunitinib treatment on VHL-C162F cells. We showed that VHL-C162F mutations have no impact on cell morphology, colony formation and migration ability but confer a significant higher healing ability than in WT VHL cells. RNA sequencing analysis revealed that VHL-C162F mutation upregulates genes involved in hypoxia and epithelial mesenchymal transition (EMT) pathways by comparison with VHL WT cells. We next showed a decrease in healing ability in VHL-C162F cells depleting on ZHX2, an oncogenic driver of ccRCC, highlighting the potential involvement of ZHX2 in aggressiveness of the VHL-C162F cells. Moreover, we found that sunitinib treatment inhibits ZHX2 expression and induces a reduced proliferation correlating with downregulation of P-ERK. Sunitinib treatment also conferred a more mesenchymal profile to VHL-C162F cells with significant downregulation of E-cadherin and upregulation of N-cadherin, Slug and AXL. Sunitinib therapy may therefore promote disease progression in VHL-C162F patients.

NF-κB signaling controls H3K9me3 levels at intronic LINE-1 and hematopoietic stem cell genes in cis.

Ionizing radiations (IR) alter hematopoietic stem cell (HSC) function on the long term, but the mechanisms underlying these effects are still poorly understood. We recently showed that IR induces the derepression of L1Md, the mouse young subfamilies of LINE-1/L1 retroelements. L1 contributes to gene regulatory networks. However, how L1Md are derepressed and impact HSC gene expression are not known. Here, we show that IR triggers genome-wide H3K9me3 decrease that occurs mainly at L1Md. Loss of H3K9me3 at intronic L1Md harboring NF-κB binding sites motifs but not at promoters is associated with the repression of HSC-specific genes. This is correlated with reduced NFKB1 repressor expression. TNF-α treatment rescued all these effects and prevented IR-induced HSC loss of function in vivo. This TNF-α/NF-κB/H3K9me3/L1Md axis might be important to maintain HSCs while allowing expression of immune genes during myeloid regeneration or damage-induced bone marrow ablation.

The Most Common VHL Point Mutation R167Q in Hereditary VHL Disease Interferes with Cell Plasticity Regulation.

Von Hippel-Lindau disease (VHL) is a rare hereditary syndrome due to mutations of the VHL tumor suppressor gene. Patients harboring the R167Q mutation of the VHL gene have a high risk of developing ccRCCs. We asked whether the R167Q mutation with critical aspects of pseudo-hypoxia interferes with tumor plasticity. For this purpose, we used wild-type VHL (WT-VHL) and VHL-R167Q reconstituted cells. We showed that WT-VHL and VHL-R167Q expression had a similar effect on cell morphology and colony formation. However, cells transfected with VHL-R167Q display an intermediate, HIF2-dependent, epithelial-mesenchymal phenotype. Using RNA sequencing, we showed that this mutation upregulates the expression of genes involved in the hypoxia pathway, indicating that such mutation is conferring an enhanced pseudo-hypoxic state. Importantly, this hypoxic state correlates with the induction of genes belonging to epithelial-mesenchymal transition (EMT) and stemness pathways, as revealed by GSEA TCGA analysis. Moreover, among these deregulated genes, we identified nine genes specifically associated with a poor patient survival in the TCGA KIRC dataset. Together, these observations support the hypothesis that a discrete VHL point mutation interferes with tumor plasticity and may impact cell behavior by exacerbating phenotypic switching. A better understanding of the role of this mutation might guide the search for more effective treatments to combat ccRCCs.

Serial transplantation unmasks galectin-9 contribution to tumor immune escape in the MB49 murine model.

Mechanisms of tumor immune escape are quite diverse and require specific approaches for their exploration in syngeneic tumor models. In several human malignancies, galectin-9 (gal-9) is suspected to contribute to the immune escape. However, in contrast with what has been done for the infiltrating cells, the contribution of gal-9 produced by malignant cells has never been demonstrated in an animal model. Therefore, we derived isogenic clones-either positive or negative for gal-9-from the MB49 murine bladder carcinoma cell line. A progressive and consistent reduction of tumor growth was observed when gal-9-KO cells were subjected to serial transplantations into syngeneic mice. In contrast, tumor growth was unaffected during parallel serial transplantations into nude mice, thus linking tumor inhibition to the enhancement of the immune response against gal-9-KO tumors. This stronger immune response was at least in part explained by changing patterns of response to interferon-γ. One consistent change was a more abundant production of CXCL10, a major inflammatory factor whose production is often induced by interferon-γ. Overall, these observations demonstrate for the first time that serial transplantation into syngeneic mice can be a valuable experimental approach for the exploration of novel mechanisms of tumor immune escape.

Dynamic gene regulation by nuclear colony-stimulating factor 1 receptor in human monocytes and macrophages.

Despite their location at the cell surface, several receptor tyrosine kinases (RTK) are also found in the nucleus, as either intracellular domains or full length proteins. However, their potential nuclear functions remain poorly understood. Here we find that a fraction of full length Colony Stimulating Factor-1 Receptor (CSF-1R), an RTK involved in monocyte/macrophage generation, migrates to the nucleus upon CSF-1 stimulation in human primary monocytes. Chromatin-immunoprecipitation identifies the preferential recruitment of CSF-1R to intergenic regions, where it co-localizes with H3K4me1 and interacts with the transcription factor EGR1. When monocytes are differentiated into macrophages with CSF-1, CSF-1R is redirected to transcription starting sites, colocalizes with H3K4me3, and interacts with ELK and YY1 transcription factors. CSF-1R expression and chromatin recruitment is modulated by small molecule CSF-1R inhibitors and altered in monocytes from chronic myelomonocytic leukemia patients. Unraveling this dynamic non-canonical CSF-1R function suggests new avenues to explore the poorly understood functions of this receptor and its ligands.

Biology and prognostic impact of clonal plasmacytoid dendritic cells in chronic myelomonocytic leukemia.

Islands of CD123high cells have been commonly described in the bone marrow of patients with chronic myelomonocytic leukemia (CMML). Using a multiparameter flow cytometry assay, we detected an excess of CD123+ mononucleated cells that are lineage-negative, CD45+, CD11c-, CD33-, HLA-DR+, BDCA-2+, BDCA-4+ in the bone marrow of 32/159 (20%) patients. Conventional and electron microscopy, flow cytometry detection of cell surface markers, gene expression analyses, and the ability to synthesize interferon alpha in response to Toll-like receptor agonists identified these cells as bona fide plasmacytoid dendritic cells (pDCs). Whole-exome sequencing of sorted monocytes and pDCs identified somatic mutations in genes of the oncogenic RAS pathway in the two cell types of every patient. CD34+ cells could generate high amount of pDCs in the absence of FMS-like tyrosine kinase 3-ligand (FLT3L). Finally, an excess of pDCs correlates with regulatory T cell accumulation and an increased risk of acute leukemia transformation. These results demonstrate the FLT3L-independent accumulation of clonal pDCs in the bone marrow of CMML patients with mutations affecting the RAS pathway, which is associated with a higher risk of disease progression.

Engraftment of chronic myelomonocytic leukemia cells in immunocompromised mice supports disease dependency on cytokines.

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder that typically associates with mutations in epigenetic, splicing, and signaling genes. Genetically modified mouse models only partially recapitulate the disease phenotype, whereas xenotransplantation of CMML cells in immunocompromised mice has been rarely successful so far. Here, CMML CD34+ cells sorted from patient bone marrow (BM) or peripheral blood (PB) were injected intravenously into NSG (NOD/LtSz-scid IL2rγnull) mice and NSG mice engineered to express human granulo-monocyte colony-stimulating factor, stem cell factor, and interleukin-3 (NSGS mice). Fifteen out of 16 patient samples (94%) successfully engrafted into NSG or NSGS or both mouse strains. The expansion of human cells, predominant in the BM, was also observed in the spleen and the PB and was greatly enhanced in mice producing the 3 human cytokines. Gene mutations identified in engrafted cells were mostly similar to those identified in patient cells before injection. Successful secondary engraftment was obtained in NSGS mice in 3 out of 10 attempts. Thus, primary CMML leukemic cells expand much better in NSGS compared with NSG mice with limited efficacy of secondary transplant.