Loss of the KN Motif and AnKyrin Repeat Domain 1 (KANK1) Leads to Lymphoid Compartment Dysregulation in Murine Model.

The KN Motif and AnKyrin Repeat Domain 1 (KANK1) is proposed as a tumour suppressor gene, as its expression is reduced or absent in several types of tumour tissue, and over-expressing the protein inhibited the proliferation of tumour cells in solid cancer models. We report a novel germline loss of heterozygosity mutation encompassing the KANK1 gene in a young patient diagnosed with myelodysplastic neoplasm (MDS) with no additional disease-related genomic aberrations. To study the potential role of KANK1 in haematopoiesis, we generated a new transgenic mouse model with a confirmed loss of KANK1 expression. KANK1 knockout mice did not develop any haematological abnormalities; however, the loss of its expression led to alteration in the colony forming and proliferative potential of bone marrow (BM) cells and a decrease in hematopoietic stem and progenitor cells (HSPCs) population frequency. A comprehensive marker expression analysis of lineage cell populations indicated a role for Kank1 in lymphoid cell development, and total protein analysis suggests the involvement of Kank1 in BM cells' cytoskeleton formation and mobility.

TP53 mutations identify younger mantle cell lymphoma patients who do not benefit from intensive chemoimmunotherapy.

Despite recent advances in lymphoma treatment, mantle cell lymphoma (MCL) remains incurable, and we are still unable to identify patients who will not benefit from the current standard of care. Here, we explore the prognostic value of recurrent genetic aberrations in diagnostic bone marrow (BM) specimens from 183 younger patients with MCL from the Nordic MCL2 and MCL3 trials, which represent current standard-of-care regimens. In the univariate model, mutations of TP53 (11%) and NOTCH1 (4%), and deletions of TP53 (16%) and CDKN2A (20%), were significantly associated with inferior outcomes (together with MIPI, MIPI-c, blastoid morphology, and Ki67 > 30%); however, in multivariate analyses, only TP53 mutations (HR, 6.2; P < .0001) retained prognostic impact for overall survival (OS), whereas TP53 mutations (HR, 6.9; P < .0001) and MIPI-c high-risk (HR, 2.6; P = .003) had independent prognostic impact on time to relapse. TP53-mutated cases had a dismal outcome, with a median OS of 1.8 years, and 50% relapsed at 1.0 years, compared to a median OS of 12.7 years for TP53-unmutated cases (P < .0001). TP53 mutations were significantly associated with Ki67 > 30%, blastoid morphology, MIPI high-risk, and inferior responses to both induction- and high-dose chemotherapy. In conclusion, we show that TP53 mutations identify a phenotypically distinct and highly aggressive form of MCL with poor or no response to regimens including cytarabine, rituximab, and autologous stem-cell transplant (ASCT). We suggest patients with MCL should be stratified according to TP53 status, and that patients with TP53 mutations should be considered for experimental frontline trials exploring novel agents.

Forced expression of human macrophage colony-stimulating factor in CD34+ cells promotes monocyte differentiation in vitro and in vivo but blunts osteoclastogenesis in vitro.

OBJECTIVES: Here, we tested the hypothesis that human M-CSF (hM-CSF) overexpressed in cord blood (CB) CD34+ cells would induce differentiation and survival of monocytes and osteoclasts in vitro and in vivo. METHODS: Human M-CSF was overexpressed in cord blood CD34+ cells using a lentiviral vector. RESULTS: We show that LV-hM-CSF-transduced CB CD34+ cells expand 3.6- and 8.5-fold more with one or two exposures to the hM-CSF-expressing vector, respectively, when compared to control cells. Likewise, LV-hM-CSF-transduced CB CD34+ cells show significantly higher levels of monocytes. In addition, these cells produced high levels of hM-CSF. Furthermore, they are able to differentiate into functional bone-resorbing osteoclasts in vitro. However, osteoclast differentiation and bone resorption were blunted compared to control CD34+ cells receiving exogenous hM-CSF. NSG mice engrafted with LV-hM-CSF-transduced CB CD34+ cells have physiological levels of hM-CSF production that result in an increase in the percentage of human monocytes in peripheral blood and bone marrow as well as in the spleen, lung and liver. CONCLUSION: In summary, ectopic production of human M-CSF in CD34+ cells promotes cellular expansion and monocyte differentiation in vitro and in vivo and allows for the formation of functional osteoclasts, albeit at reduced levels, without an exogenous source of M-CSF, in vitro.

The tyrosine phosphatase SHP2 is required for cell transformation by the receptor tyrosine kinase mutants FIP1L1-PDGFRα and PDGFRα D842V.

Activated forms of the platelet derived growth factor receptor alpha (PDGFRα) have been described in various tumors, including FIP1L1-PDGFRα in patients with myeloproliferative diseases associated with hypereosinophilia and the PDGFRα(D842V) mutant in gastrointestinal stromal tumors and inflammatory fibroid polyps. To gain a better insight into the signal transduction mechanisms of PDGFRα oncogenes, we mutated twelve potentially phosphorylated tyrosine residues of FIP1L1-PDGFRα and identified three mutations that affected cell proliferation. In particular, mutation of tyrosine 720 in FIP1L1-PDGFRα or PDGFRα(D842V) inhibited cell growth and blocked ERK signaling in Ba/F3 cells. This mutation also decreased myeloproliferation in transplanted mice and the proliferation of human CD34(+) hematopoietic progenitors transduced with FIP1L1-PDGFRα. We showed that the non-receptor protein tyrosine phosphatase SHP2 bound directly to tyrosine 720 of FIP1L1-PDGFRα. SHP2 knock-down decreased proliferation of Ba/F3 cells transformed with FIP1L1-PDGFRα and PDGFRα(D842V) and affected ERK signaling, but not STAT5 phosphorylation. Remarkably, SHP2 was not essential for cell proliferation and ERK phosphorylation induced by the wild-type PDGF receptor in response to ligand stimulation, suggesting a shift in the function of SHP2 downstream of oncogenic receptors. In conclusion, our results indicate that SHP2 is required for cell transformation and ERK activation by mutant PDGF receptors.

Platelet-derived growth factors and their receptors in normal and malignant hematopoiesis.

Platelet-derived growth factors (PDGF) bind to two closely related receptor tyrosine kinases, PDGF receptor α and ß, which are encoded by the PDGFRA and PDGFRB genes. Aberrant activation of PDGF receptors occurs in myeloid malignancies associated with hypereosinophilia, due to chromosomal alterations that produce fusion genes, such as ETV6-PDGFRB or FIP1L1-PDGFRA. Most patients are males and respond to low dose imatinib, which is particularly effective against PDGF receptor kinase activity. Recently, activating point mutations in PDGFRA were also described in hypereosinophilia. In addition, autocrine loops have been identified in large granular lymphocyte leukemia and HTLV-transformed lymphocytes, suggesting new possible indications for tyrosine kinase inhibitor therapy. Although PDGF was initially purified from platelets more than 30 years ago, its physiological role in the hematopoietic system remains unclear. Hematopoietic defects in PDGF-deficient mice have been reported but appear to be secondary to cardiovascular and placental abnormalities. Nevertheless, PDGF acts directly on several hematopoietic cell types in vitro, such as megakaryocytes, platelets, activated macrophages and, possibly, certain lymphocyte subsets and eosinophils. The relevance of these observations for normal human hematopoiesis remains to be established.

ETV6-PDGFRB and FIP1L1-PDGFRA stimulate human hematopoietic progenitor cell proliferation and differentiation into eosinophils: the role of nuclear factor-κB.

BACKGROUND: ETV6-PDGFRB (also called TEL-PDGFRB) and FIP1L1-PDGFRA are receptor-tyrosine kinase fusion genes that cause chronic myeloid malignancies associated with hypereosinophilia. The aim of this work was to gain insight into the mechanisms whereby fusion genes affect human hematopoietic cells and in particular the eosinophil lineage. DESIGN AND METHODS: We introduced ETV6-PDGFRB and FIP1L1-PDGFRA into human CD34(+) hematopoietic progenitor and stem cells isolated from umbilical cord blood. RESULTS: Cells transduced with these oncogenes formed hematopoietic colonies even in the absence of cytokines. Both oncogenes also stimulated the proliferation of cells in liquid culture and their differentiation into eosinophils. This model thus recapitulated key features of the myeloid neoplasms induced by ETV6-PDGFRB and FIP1L1-PDGFRA. We next showed that both fusion genes activated the transcription factors STAT1, STAT3, STAT5 and nuclear factor-κB. Phosphatidylinositol-3 kinase inhibition blocked nuclear factor-κB activation in transduced progenitor cells and patients' cells. Nuclear factor-κB was also activated in the human FIP1L1-PDGFRA-positive leukemia cell line EOL1, the proliferation of which was blocked by bortezomib and the IκB kinase inhibitor BMS-345541. A mutant IκB that prevents nuclear translocation of nuclear factor-κB inhibited cell growth and the expression of eosinophil markers, such as the interleukin-5 receptor and eosinophil peroxidase, in progenitors transduced with ETV6-PDGFRB. In addition, several potential regulators of this process, including HES6, MYC and FOXO3 were identified using expression microarrays. CONCLUSIONS: We show that human CD34(+) cells expressing PDGFR fusion oncogenes proliferate autonomously and differentiate towards the eosinophil lineage in a process that requires nuclear factor-κB. These results suggest new treatment possibilities for imatinib-resistant myeloid neoplasms associated with PDGFR mutations.

PRDM16 (1p36) translocations define a distinct entity of myeloid malignancies with poor prognosis but may also occur in lymphoid malignancies.

The PRDM16 (1p36) gene is rearranged in acute myeloid leukaemia (AML) and myelodysplastic syndrome (MDS) with t(1;3)(p36;q21), sharing characteristics with AML and MDS with MECOM (3q26.2) translocations. We used fluorescence in situ hybridization to study 39 haematological malignancies with translocations involving PRDM16 to assess the precise breakpoint on 1p36 and the identity of the partner locus. Reverse-transcription polymerase chain reaction (PCR) was performed in selected cases in order to confirm the partner locus. PRDM16 expression studies were performed on bone marrow samples of patients, normal controls and CD34(+) cells using TaqMan real-time quantitative PCR. PRDM16 was rearranged with the RPN1 (3q21) locus in 30 cases and with other loci in nine cases. The diagnosis was AML or MDS in most cases, except for two cases of lymphoid proliferation. We identified novel translocation partners of PRDM16, including the transcription factors ETV6 and IKZF1. Translocations involving PRDM16 lead to its overexpression irrespective of the consequence of the rearrangement (fusion gene or promoter swap). Survival data suggest that patients with AML/MDS and PRDM16 translocations have a poor prognosis despite a simple karyotype and a median age of 65 years. There seems to be an over-representation of late-onset therapy-related myeloid malignancies.

Multiple oligomerization domains of KANK1-PDGFRß are required for JAK2-independent hematopoietic cell proliferation and signaling via STAT5 and ERK.

BACKGROUND: KANK1-PDGFRB is a fusion gene generated by the t(5;9) translocation between KANK1 and the platelet-derived growth factor receptor beta gene PDGFRB. This hybrid was identified in a myeloproliferative neoplasm featuring severe thrombocythemia, in the absence of the JAK2 V617F mutation. DESIGN AND METHODS: KANK1-PDGFRB was transduced into Ba/F3 cells and CD34(+) human progenitor cells to gain insights into the mechanisms whereby this fusion gene transforms cells. RESULTS: Although platelet-derived growth factor receptors are capable of activating JAK2, KANK1-PDGFRß did not induce JAK2 phosphorylation in hematopoietic cells and a JAK inhibitor did not affect KANK1-PDGFRß-induced cell growth. Like JAK2 V617F, KANK1-PDGFRß constitutively activated STAT5 transcription factors, but this did not require JAK kinases. In addition KANK1-PDGFRß induced the phosphorylation of phospholipase C-γ, ERK1 and ERK2, like wild-type PDGFRß and TEL-PDGFRß, another hybrid protein found in myeloid malignancies. We next tested various mutant forms of KANK1-PDGFRß in Ba/F3 cells and human CD34(+) hematopoietic progenitors. The three coiled-coil domains located in the N-terminus of KANK1 were required for KANK1-PDGFRß-induced cell growth and signaling via STAT5 and ERK. However, the coiled-coils were not essential for KANK1-PDGFRß oligomerization, which could be mediated by another new oligomerization domain. KANK1-PDGFRß formed homotrimeric complexes and heavier oligomers. CONCLUSIONS: KANK1-PDGFRB is a unique example of a thrombocythemia-associated oncogene that does not signal via JAK2. The fusion protein is activated by multiple oligomerization domains, which are required for signaling and cell growth stimulation.