SETBP1 and miR_4319 dysregulation in primary myelofibrosis progression to acute myeloid leukemia

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Abstract

The molecular pathogenesis underlying the primary myelofibrosis (PMF) progression to acute myeloid leukemia (AML) is still not well defined. The involvement of microRNA (miRNA) is actually helping to shed light on an important issue in the occurrence of myeloproliferative neoplasms (MPNs). However, the role of intronic miRNA, derived from the intron regions of gene transcripts, has never been reported in MPNs. In this study, we describe a PMF case evolved to AML with a t(12;18)(p13;q12) rearrangement showing the downregulation of the intronic miR_4319 and the overexpression of its host gene, SET binding protein ( SETBP1). A possible molecular mechanism regulating the PMF progression to AML is discussed.

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Structure and activity of putative intronic miRNA promoters.

Yi Xing, Luis Tecedor, Alex Mas Monteys … (2010)

MicroRNAs (miRNAs) are RNA sequences of approximately 22 nucleotides that mediate post-transcriptional regulation of specific mRNAs. miRNA sequences are dispersed throughout the genome and are classified as intergenic (between genes) or intronic (embedded into a gene). Intergenic miRNAs are expressed by their own promoter, and until recently, it was supposed that intronic miRNAs are transcribed from their host gene. Here, we performed a genomic analysis of currently known intronic miRNA regions and observed that approximately 35% of intronic miRNAs have upstream regulatory elements consistent with promoter function. Among all intronic miRNAs, 30% have associated Pol II regulatory elements, including transcription start sites, CpG islands, expression sequence tags, and conserved transcription factor binding sites, while 5% contain RNA Pol III regulatory elements (A/B box sequences). We cloned intronic regions encompassing miRNAs and their upstream Pol II (miR-107, miR-126, miR-208b, miR-548f-2, miR-569, and miR-590) or Pol III (miR-566 and miR-128-2) sequences into a promoterless plasmid, and confirmed that miRNA expression occurs independent of host gene transcription. For miR-128-2, a miRNA overexpressed in acute lymphoblastic leukemia, ChIP analysis suggests dual regulation by both intronic (Pol III) and host gene (Pol II) promoters. These data support complex regulation of intronic miRNA expression, and have relevance to disregulation in disease settings.

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SETBP1 overexpression is a novel leukemogenic mechanism that predicts adverse outcome in elderly patients with acute myeloid leukemia.

Nora J. Rifon, Ion Cristóbal, D L Orti … (2010)

Acute myeloid leukemias (AMLs) result from multiple genetic alterations in hematopoietic stem cells. We describe a novel t(12;18)(p13;q12) involving ETV6 in a patient with AML. The translocation resulted in overexpression of SETBP1 (18q12), located close to the breakpoint. Overexpression of SETBP1 through retroviral insertion has been reported to confer growth advantage in hematopoietic progenitor cells. We show that SETBP1 overexpression protects SET from protease cleavage, increasing the amount of full-length SET protein and leading to the formation of a SETBP1-SET-PP2A complex that results in PP2A inhibition, promoting proliferation of the leukemic cells. The prevalence of SETBP1 overexpression in AML at diagnosis (n = 192) was 27.6% and was associated with unfavorable cytogenetic prognostic group, monosomy 7, and EVI1 overexpression (P < .01). Patients with SETBP1 overexpression had a significantly shorter overall survival, and the prognosis impact was remarkably poor in patients older than 60 years in both overall survival (P = .015) and event-free survival (P = .015). In summary, our data show a novel leukemogenic mechanism through SETBP1 overexpression; moreover, multivariate analysis confirms the negative prognostic impact of SETBP1 overexpression in AML, especially in elderly patients, where it could be used as a predictive factor in any future clinical trials with PP2A activators.

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PP2A impaired activity is a common event in acute myeloid leukemia and its activation by forskolin has a potent anti-leukemic effect.

M Calasanz, I Cristóbal, M Alonso … (2011)

Protein phosphatase 2A (PP2A) is a human tumor suppressor that inhibits cellular transformation by regulating the activity of several signaling proteins critical for malignant cell behavior. PP2A has been described as a potential therapeutic target in chronic myeloid leukemia, Philadelphia chromosome-positive acute lymphoblastic leukemia and B-cell chronic lymphocytic leukemia. Here, we show that PP2A inactivation is a recurrent event in acute myeloid leukemia (AML), and that restoration of PP2A phosphatase activity by treatment with forskolin in AML cells blocks proliferation, induces caspase-dependent apoptosis and affects AKT and ERK1/2 activity. Moreover, treatment with forskolin had an additive effect with Idarubicin and Ara-c, drugs used in standard induction therapy in AML patients. Analysis at protein level of the PP2A activation status in a series of patients with AML at diagnosis showed PP2A hyperphosphorylation in 78% of cases (29/37). In addition, we found that either deregulated expression of the endogenous PP2A inhibitors SET or CIP2A, overexpression of SETBP1, or downregulation of some PP2A subunits, might be contributing to PP2A inhibition in AML. In conclusion, our results show that PP2A inhibition is a common event in AML cells and that PP2A activators, such as forskolin or FTY720, could represent potential novel therapeutic targets in AML.

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Author and article information

Journal

Journal ID (nlm-ta): J Hematol Oncol

Journal ID (iso-abbrev): J Hematol Oncol

Title: Journal of Hematology & Oncology

Publisher: BioMed Central

ISSN (Electronic): 1756-8722

Publication date Collection: 2012

Publication date (Electronic): 8 August 2012

Volume: 5

Page: 48

Affiliations

[1 ]Department of Emergency and Organ Transplantation (D.E.T.O.) - Hematology Section, University of Bari, 70124, Bari, Italy

[2 ]Hematology, Azienda Ospedaliera Universitaria Policlinico, P.zza G. Cesare, 11 70124, Bari, Italy

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Publisher ID: 1756-8722-5-48

DOI: 10.1186/1756-8722-5-48

PMC ID: 3470981

PubMed ID: 22873195

SO-VID: 6b7a14e8-82a1-4073-994b-58353a867c96

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This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

SETBP1 and miR_4319 dysregulation in primary myelofibrosis progression to acute myeloid leukemia

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Most cited references 7

Structure and activity of putative intronic miRNA promoters.

SETBP1 overexpression is a novel leukemogenic mechanism that predicts adverse outcome in elderly patients with acute myeloid leukemia.

PP2A impaired activity is a common event in acute myeloid leukemia and its activation by forskolin has a potent anti-leukemic effect.

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