More on Myb in myelofibrosis: molecular analyses of MYB and EP300 in 55 patients with myeloproliferative disorders

Clinical features and next-generation sequencing landscape of essential thrombocythemia, prefibrotic primary myelofibrosis, and overt fibrotic primary myelofibrosis: a Chinese monocentric retrospective study

OBJECTIVE

Since prefibrotic primary myelofibrosis (pre-PMF) was recognized as a separate entity in the 2016 revised classification of MPN differed from essential thrombocythemia (ET) or overt fibrotic primary myelofibrosis (overt PMF), it has been a subject of debate among experts due to its indefinite diagnosis.

METHODS

We retrospectively reviewed the clinical parameters, haematologic information, and genetic mutations of patients who were diagnosed with myeloproliferative neoplasms (MPNs) according to the WHO 2016 criteria in China, including 56 ET patients, 19 pre-PMF patients, and 43 overt PMF patients.

RESULTS

Pre-PMF patients exhibited higher leukocyte counts [14.2(6.0-28.1) × 10⁹/L vs 9.6(4.0-55.0) × 10⁹/L, P = 0.003], LDH values [307(233-479)U/L vs 241(129-1182)U/L, P < 0.001], onset ages [67(32-76) years vs 50(16-79) years, P = 0.006], a higher frequency of splenomegaly(47.4% vs 16.7%, P = 0.018) and hypertension (57.9 vs 23.2%, P = 0.005) than ET patients. On the other hand, pre-PMF patients had higher platelet counts [960(500-2245) × 10⁹/L vs 633(102-1720) × 10⁹/L, P = 0.017], haemoglobin levels [152(115-174)g/L vs 119(71-200)g/L, P = 0.003], lower LDH values [307(233-479)U/L vs 439(134-8100)U/L, P = 0.007] and a lower frequency of splenomegaly(47.4 vs 75.6%, P = 0.031) than overt PMF patients. Next-generation sequencing landscape was performed in 50 patients, revealed the frequency of EP300 mutations was significantly increased in pre-PMF patients compared with ET and overt PMF patients (60 vs 10 vs 15.79%, P = 0.033), and WT1 was more often overexpressed (WT1/ABL1 copies ≥ 1.0%) in patients with overt PMF than in those with ET or pre-PMF(54.55 vs 16.67 vs 17.65%, P = 0.009). In terms of outcome, male sex, along with symptoms including MPN10, anaemia (haemoglobin < 120 g/L), thrombocytopenia (platelet count < 100 × 10⁹/L), leucocytosis (leukocyte counts > 13 × 10⁹/L), high LDH value (> 350U/L), splenomegaly, WT1 overexpression(WT1/ABL1 copies ≥ 1.0%), KMT2A, ASXL1 and TP53 mutations, indicated a poor prognosis for PMF patients.

CONCLUSION

The results of this study indicated that a comprehensive evaluation of BM features, clinical phenotypes, haematologic parameters, and molecular profiles is needed for the accurate diagnosis and treatment of ET, pre-PMF, and overt PMF patients.

Predicting pathogenic genes for primary myelofibrosis based on a system‑network approach

The aim of the present study was to predict pathogenic genes for primary myelofibrosis (PMF) using a system‑network approach by combining protein‑protein interaction (PPI) network and gene expression data with known pathogenic genes. PMF gene expression profiles, known pathogenic genes and protein‑protein interactions were obtained. Using these data, differentially expressed genes (DEGs) were identified between PMF and normal conditions using significance analysis of microarrays, and seed genes were determined based on the intersection of known pathogenic genes and the PMF gene expression profile. A new network was constructed using the seed genes and their adjacent DEGs within the PPI network. Subsequently, a pathogenic network was extracted from the new network, and contained genes that interacted with at least two seed genes, and the candidate pathogenic genes were predicted based on the cohesion with seed genes. Cluster analysis was performed to mine the pathogenic modules from the pathogenic network, and functional analysis was performed to identify the putative biological processes of the candidate pathogenic genes. Results from the present study identified 845 DEGs between PMF and normal conditions, and 45 seed genes in PMF were screened. Subsequently, a pathogenic network comprising 103 nodes and 265 interactions was constructed, and 4 pathogenic modules (modules A‑D) were mined from the pathogenic network. There were nine candidate pathogenic genes contained within Module A and four potential pathogenic genes, including E1A‑binding protein p300, RAS‑like proto‑oncogene A, von Willebrand factor and RAF‑1 proto‑oncogene, serine/threonine kinase, were identified that may be involved in the same biological process with the seed genes. This study predicted 10 candidate pathogenic genes and several signaling pathways that may be related to the pathogenesis of PMF using a system‑network approach. These predictions may shed light on the PMF pathogenesis and may provide guidelines for future experimental verification.

MYB deregulation from a EWSR1-MYB fusion at leukemic evolution of a JAK2 (V617F) positive primary myelofibrosis

Background

Although Philadelphia-negative myeloproliferative neoplasms (Ph-MPN) are usually not aggressive, the type and the number of molecular lesions impact greatly on leukemic transformation. Indeed, the molecular background underlying progression is still largely unexplored even though ASXL1, IDH1/2, SRSF2, and TP53 mutations, together with adverse karyotypic changes, place the patient at high risk of leukemic transformation.

Case presentation

Our patient, a 64-year old man with a diagnosis of JAK2^V617F primary myelofibrosis (PMF) had an unusually rapid leukemic transformation. Genomic profiling showed that TET2 and SRSF2 mutations were also present. At leukemic transformation, the patient developed a complex chromosome rearrangement producing a EWSR1-MYB fusion. Remarkably, the expression of MYB and of its target BCL2 was, respectively, ≥4.7 and ≥2.8 fold higher at leukemic transformation than after chemotherapy, when the patient obtained the hematological remission. At this time point, the EWSR1-MYB fusion disappeared while JAK2^V617F, TET2, and SRSF2 mutations, as well as PMF morphological features persisted.

Conclusions

Rapid leukemic transformation of JAK2^V617F PMF was closely linked to a previously undescribed putative EWSR1-MYB transcription factor which was detected only at disease evolution. We hypothesize that the EWSR1-MYB contributed to leukemia transformation through at least two mechanisms: 1) it sustained MYB expression, and consequently deregulated its target BCL2, a putative onco-suppressor gene; and 2) ectopic EWSR1-MYB expression probably fulfilled its own oncogenic potential as demonstrated for other MYB-fusions. As our study confirmed that MYB is recurrently involved in chronic as well as leukemic transformation of PMF, it appears to be a valid molecular marker for tailored treatments.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-016-0277-1) contains supplementary material, which is available to authorized users.

Clonal evolution revealed by whole genome sequencing in a case of primary myelofibrosis transformed to secondary acute myeloid leukemia

Clonal architecture in myeloproliferative neoplasms (MPNs) is poorly understood. Here we report genomic analyses of a patient with primary myelofibrosis (PMF) transformed to secondary acute myeloid leukemia (sAML). Whole genome sequencing (WGS) was performed on PMF and sAML diagnosis samples, with skin included as a germline surrogate. Deep sequencing validation was performed on the WGS samples and an additional sample obtained during sAML remission/relapsed PMF. Clustering analysis of 649 validated somatic single-nucleotide variants revealed four distinct clonal groups, each including putative driver mutations. The first group (including JAK2 and U2AF1), representing the founding clone, included mutations with high frequency at all three disease stages. The second clonal group (including MYB) was present only in PMF, suggesting the presence of a clone that was dispensable for transformation. The third group (including ASXL1) contained mutations with low frequency in PMF and high frequency in subsequent samples, indicating evolution of the dominant clone with disease progression. The fourth clonal group (including IDH1 and RUNX1) was acquired at sAML transformation and was predominantly absent at sAML remission/relapsed PMF. Taken together, these findings illustrate the complex clonal dynamics associated with disease evolution in MPNs and sAML.

Ott1 (Rbm15) regulates thrombopoietin response in hematopoietic stem cells through alternative splicing of c-Mpl

Thrombopoietin (Thpo) signaling through the c-Mpl receptor promotes either quiescence or proliferation of hematopoietic stem cells (HSCs) in a concentration-dependent manner; however, in vivo Thpo serum levels are responsive to platelet mass rather than HSC demands, suggesting additional regulation exists. Ott1 (Rbm15), a spliceosomal component originally identified as a fusion partner in t(1;22)-associated acute megakaryocytic leukemia, is also essential for maintaining HSC quiescence under stress. Ott1 controls the alternative splicing of a dominant negative isoform, Mpl-TR, capable of inhibiting HSC engraftment and attenuating Thpo signaling. Ott1, which associates with Hdac3 and the histone methyltransferase, Setd1b, binds to both c-Mpl RNA and chromatin and regulates H4 acetylation and H3K4me3 marks. Histone deacetylase or histone methyltransferase inhibition also increases Mpl-TR levels, suggesting that Ott1 uses an underlying epigenetic mechanism to control alternative splicing of c-Mpl. Manipulation of Ott1-dependent alternative splicing may therefore provide a novel pharmacologic avenue for regulating HSC quiescence and proliferation in response to Thpo.

Genetic interaction between mutations in c-Myb and the KIX domains of CBP and p300 affects multiple blood cell lineages and influences both gene activation and repression

Adult blood cell production or definitive hematopoiesis requires the transcription factor c-Myb. The closely related KAT3 histone acetyltransferases CBP (CREBBP) and p300 (EP300) bind c-Myb through their KIX domains and mice homozygous for a p300 KIX domain mutation exhibit multiple blood defects. Perplexingly, mice homozygous for the same KIX domain mutation in CBP have normal blood. Here we test the hypothesis that the CBP KIX domain contributes subordinately to hematopoiesis via a genetic interaction with c-Myb. We assessed hematopoiesis in mice bearing compound mutations of c-Myb and/or the KIX domains of CBP and p300, and measured the effect of KIX domain mutations on c-Myb-dependent gene expression. We found that in the context of a p300 KIX mutation, the CBP KIX domain mutation affects platelets, B cells, T cells, and red cells. Gene interaction (epistasis) analysis provides mechanistic evidence that blood defects in KIX mutant mice are consistent with reduced c-Myb and KIX interaction. Lastly, we demonstrated that the CBP and p300 KIX domains contribute to both c-Myb-dependent gene activation and repression. Together these results suggest that the KIX domains of CBP, and especially p300, are principal mediators of c-Myb-dependent gene activation and repression that is required for definitive hematopoiesis.

Finding the needle in the hay stack: hematopoietic stem cells in Fanconi anemia

Fanconi anemia is a rare bone marrow failure and cancer predisposition syndrome. Childhood onset of aplastic anemia is one of the hallmarks of this condition. Supportive therapy in the form of blood products, androgens, and hematopoietic growth factors may boost blood counts temporarily. However, allogeneic hematopoietic stem cell transplantation (HSCT) currently remains the only curative treatment option for the hematologic manifestations of Fanconi anemia (FA). Here we review current clinical and pre-clinical strategies for treating hematopoietic stem cell (HSC) failure, including the experience with mobilizing and collecting CD34+ hematopoietic stem and progenitor cells as target cells for somatic gene therapy, the current state of FA gene therapy trials, and future prospects for cell and gene therapy.

Absence of FTL3 mutations in patients with JAK2V617F mutation negative essential thrombocythemia

A common point mutation in the JAK2 tyrosine kinase leads to constitutive hematopoietic growth factor receptor signaling and was recently described in many patients with myeloproliferative disorders (MPDs). However, this JAK2 mutation is present in only a subset (35-50%) of patients with essential thrombocythemia (ET). Thus, the proliferative signals responsible for MPDs in the absence of JAK2 mutations remain largely unknown. Despite intriguing pre-clinical data, where transgenic mice overexpressing FLT3-ITD developed a MPD resembling ET, none of the patient samples from ET patients who were JAK2(V617F)-negative demonstrated the presence of activating mutations in the FLT3 receptor.