Abstract 3175: Genomic and transcriptomic data integration in chronic myelomonocytic leukemia reveals a novel fusion gene involving onco-miR-125b-2
Authors: Muntasir M. Majumder, Mika Kontro, Henrik Edgren, Daniel Nicorici, Alun Parsons, Riikka Karjalainen, Samuli Eldfors, Pirkko Mattila, Maija Lepistö, Pekka Ellonen, Henrikki Almusa, Hannele Rintala, Jonathan K c Knowles, Janna Saarela, Krister Wennerberg, Satu Mustjoki, Maija Wolf, Olli Kallioniemi, Kimmo Porkka, Caroline A. Heckman
Journal: Cancer Research (2012)

Abstract Chronic myelomonocytic leukemia (CMML) is a rare malignancy characterized by increased peripheral monocytosis and dysplasia in a single- or multilineage fashion. Gene mutations so far reported in CMML include TET2, CBL, NRAS, KRAS, RUNX1 and EZH2 but their pathogenic role and driver status in the disease remains unclear. Altered expression of the microRNA miR-125b has been implicated in the pathogenesis of many types of cancers, including myeloid leukemias and Down syndrome-associated acute myeloid leukemia (DS-AML). In addition, this miRNA has been shown to play an important role in hematopoiesis and the regulation of immune cell response. Here, integration of data from next-generation transcriptome sequencing, exome sequencing and array-CGH in a CMML patient (trisomy 21 by cytogenetics) led to the identification of a novel gene fusion event involving the nuclear receptor interacting protein NRIP1 gene and the open reading frame C21orf34 (both at 21q21 approximately 1 MB apart). The fusion was validated by capillary sequencing and found to involve two copy number transition breaks, inversion of the intervening region and the upregulation of the 3′ end of C21orf34. This intronic region harbors a cluster of three miRNAs: miR-let7c, miR-99a, and miR-125b-2. Based on genomic breakpoint analysis, the gene fusion took place just upstream of miR-125b-2. Consistent with this, only miR-125b-2 was highly expressed in the sample, and was processed to a mature miRNA. By RT-PCR, increased expression of miR-125b-2 was also observed in four other CMML patients and five CML patients when compared to healthy bone marrow controls. In contrast, five AML cases studied showed expression levels similar to or lower than that of controls. Interestingly, one AML patient with trisomy 21 had very high levels of miR-125b-2. We found the NRIP1-C21orf34 fusion only in our index patient and therefore other mechanisms of miRNA deregulation at 21q21 in CMML/CML and AML+21 will also exist. In conclusion, we describe for the first time a fusion gene involving miR-125b-2 in CMML, a previously recognized and well-studied onco-miR, which is known to impact on self-renewal of hematopoietic cell precursors. We also detected overexpression of miR-125b-2 in all CMML samples studied suggesting a key pathogenetic driver gene role for this micro-RNA. The assessment of miR-125b-2 levels could potentially be applied to the diagnosis and follow-up of patients with CMML. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3175. doi:1538-7445.AM2012-3175