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Integrative analysis of copy number and gene expression data suggests novel pathogenic mechanisms in Primary Myelofibrosis

ABSTRACT: Primary myelofibrosis (PMF) is a Myeloproliferative Neoplasm (MPN) characterized by megakaryocyte hyperplasia, progressive bone marrow fibrosis, extramedullary hematopoiesis and transformation to Acute Myeloid Leukemia (AML). Beginning in early 2005, a number of novel mutations involving JAK2, CALR, MPL, TET2, ASXL1, DNMT3a, CBL, IDH1 and IDH2 have been described in MPNs, depicting a really complex genomic landscape for MPNs. To shed light on the genomic lesions that can contribute to disease phenotype and/or development, we integrated gene expression and copy number signals and identified several genomic abnormalities leading to a concordant alteration in gene expression levels. In particular, copy number gain in the polyamine oxidase (PAOX) gene locus is accompanied by a coordinated transcriptional up-regulation in PMF patients. Inhibition of PAOX resulted in rapid cell death in PMF progenitor cells, but not in normal cells, suggesting that PAOX inhibition could represent a therapeutic strategy to selectively target PMF cells without affecting normal hematopoietic cells’ survival. Moreover, copy number loss in the chromatin modifier HMGXB4 gene correlates with a concomitant transcriptional down-regulation in PMF patients. Interestingly, silencing of HMGXB4 induces megakaryocyte differentiation, while inhibiting erythroid development, in human hematopoietic stem/progenitor cells. These results highlight a previously un-reported, yet potentially interesting role of HMGXB4 in the hematopoietic system suggesting that genomic and transcriptional imbalances of HMGXB4 could contribute to the aberrant expansion of the megakaryocytic lineage that characterize PMF patients. In this study, the authors take advantage of the integrative analysis of gene expression and copy number data to identify the concordant gain/up-regulation of the polyamine oxidase PAOX and the loss/down-regulation of the chromatin modifier HMGXB4. This work sheds light on the influence of genomic abnormalities on gene expression regulation in PMF CD34+ cells and on their contribution to specific features of PMF, such as a hyperplastic megakaryopoiesis.

ORGANISM(S): Homo sapiens

PROVIDER: GSE69161 | GEO | 2018/05/21

REPOSITORIES: GEO

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Project description:Ph-negative myeloproliferative neoplasms (MPNs) are characterized by many somatic mutations which have already been shown useful in the prognostic assessment of MPN patients. Moreover, aberrant microRNA (miRNA) expression seems to add to the molecular complexity of MPNs, as specific miRNA signatures capable of discriminating MPN cells from those of normal donors were previously reported. In order to have a comprehensive picture of miRNA deregulation and its relationship with differential gene expression in primary myelofibrosis (PMF) cells, we obtained gene- (GEP) and miRNA expression profiles (miEP) of CD34+ cells from 31 healthy donors and 42 PMF patients using Affymetrix technology (HG-U219 and miRNA 2.0 arrays). Differentially expressed genes (DEG) and miRNAs (DEM) were sorted out by means of Partek Genomic Suite vs 6.6. Since each miRNA can target many mRNAs while a single mRNA can be targeted by multiple miRNAs, we performed Integrative Analysis (IA) by means of Ingenuity Pathway Analysis (IPA) to untangle this combinatorial complexity. In particular, IPA points out DEM-DEG pairs among experimentally validated interactions from TarBase, miRecords and Ingenuity Expert Findings as well as predicted microRNA-mRNA interactions from TargetScan. IPA microRNA Target Filter was then employed to select only the DEM-DEG pairs showing an anti-correlated expression pattern and to build regulatory networks. Finally, 3'UTR luciferase reporter assays were performed to validate IPA predicted miRNA-mRNA interactions. This study allowed the identification of different networks possibly involved in PMF onset and progression, highlighting an aberrant cross-regulation in miRNA-targets involved in malignant hematopoiesis. Furthermore, Integrative analysis was proved a powerful tool to unravel miRNA-mRNA interactions in functional networks, shedding light on the potential contribution of miRNAs to PMF pathogenesis. Gene expression profile (GEP) and miRNA expression profile (miEP) were performed starting from the same totalRNA of CD34+ cells from 42 PMF patients and 31 healthy donors (n=16 PB CD34+, n=15 BM CD34+) (1 replicate for each sample). In particular, GEP and miEP were performed on 23 PMF patients carrying the mutation JAK2V617F and 19 wild-type samples.

Project description:Even though mutations in epigenetic regulators frequently occur in myeloproliferative neoplasms, their effects on the epigenome have not been well studied. Furthermore, even though primary myelofibrosis (PMF) has a markedly worse prognosis compared to essential thrombocytosis (ET) or polycythemia vera (PV), the molecular distinctions between these subgroups are not well elucidated. We performed the HELP (HpaII tiny fragment enriched by LM-PCR) assay to study genome-wide methylation in PV, ET and PMF samples compared with healthy controls. We determined that PV and ET are characterized by aberrant promoter hypermethylation while PMF is an epigenetically distinct subgroup characterized by both aberrant hyper and hypomethylation. Aberrant hypomethylation in PMF was seen to occur in non CpG island loci, demonstrating further qualitative differences between the disease subgroups. The differentially methylated genes in PV and ET were involved predominantly in cell signaling pathways and were enriched for binding sites of GATA1 and other transcription factors. In contrast, aberrantly methylated genes in PMF were involved in inflammatory pathways and were enriched for NF1 (NFI), LEF1 and other transcription factors. Within the PMF subgroup, cases with ASXL1 disruptions formed an epigenetically distinct subgroup with relatively increased methylation. Cases of MPNs with TET2 mutations demonstrated decreased levels of hydroxymethylation and distinct set of hypermethylated genes. In contrast, the JAK2V617F mutation did not drive epigenetic clustering within MPNs. Finally, the significance of aberrant methylation was demonstrated by sensitivity of MPN derived cell lines to decitabine. These results demonstrate epigenetic differences between PMF and PV/ET and reveal methylomic signatures of ASXL1 and TET2 mutations. The study population consisted of 26 MPN patients (6 cases of ET, 8 cases of PV and 12 cases of PMF) and 3 healthy controls. Individual HpaII restriction digest profiles were compared to an internal MspI digest control, to yield differentially methylated fragments for every sample. The purpose of this study was to assess genome wide patterns of DNA methylation across the MPN stratified by disease class.

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Integrative analysis of copy number and gene expression data suggests novel pathogenic mechanisms in Primary Myelofibrosis

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