Differential expression of apoptomiRs in myeloproliferative neoplasms

MicroRNAs are small non-coding RNAs that inhibit posttranscriptional gene expression through deadenylation and cleavage. Th ese molecules play crucial roles in regulating cell diff erentiation, proliferation and apoptosis [1]. MicroRNA expression levels are strongly associated with numerous human pathogenic diseases [2]. Th us, the discovery of microRNAs has opened up a wide range of possibilities regarding the understanding of disease pathophysiology and the development of new therapeutic agents. Recent studies show that microRNAs may participate in the regulation of apoptosis machinery (apoptomiRs). Apoptosis is a programmed cell death, orchestrated by the BCL-2 protein family, death receptors and inhibitor of apoptosis proteins (IAPs) [3]. Deregulated apoptosis is associated with tumorigenesis and autoimmunity [3] and seems to contribute to myeloproliferative neoplasms (MPNs), which are clonal disorders characterized by myeloaccumulation and in most cases by the presence of a somatic mutation in Janus kinase 2 (JAK2) [4]. Our research group previously described abnormal apoptosis in patients with MPNs [5 – 7]. We found abnormal expression of death-receptor pathway-related genes such as FAIM and C-FLIP in leukocytes and CD34 � hematopoietic stem cells (HSCs) [5], and deregulation of BCL-2 family members associated with JAK2 mutation [6,7]. Th ese fi ndings led us to investigate the molecular mechanisms associated with apoptosis deregulation in patients with MPNs. In this study, we sought to identify microRNAs whose targets are apoptosis-related genes, investigate their expression in patients with MPNs, and correlate this with the expression of apoptosis-related genes and JAK2 mutation allele burden using three algorithms (websites: http://www.diana.pcbi. upenn.edu/cgi-bin/miRGen/v3/Targets.cgi; Microcosm Targets: http://www.ebi.ac.uk/enright-srv/microcosm/cgi-bin/ targets/v5/hit_list.pl?genome_id � 2964; and Target Scan: http://www.targetscan.org). Th e microRNAs and their respective target genes (apoptosis-related genes) predicted by the bioinformatics tools are as follows: miR-15a: BIK and BCL-2; miR-16: BID, BIK, BCL-2 and BCL xl; miR-26a: C-FLIP, CIAP-2 and MCL-1; miR-130b: CIAP-2; miR-21: CIAP-2, FASL and BCL-2; miR-29c: CIAP-1 and MCL-1; and miR-let-7d: A1, BAX, FAS and FASL. In this study, we investigated apoptomiRs miR-26a, -130b, -21, -29c, -let-7d, -15a and -16. We quantifi ed their expression in bone marrow CD34 � HSCs and peripheral blood leukocytes in 27 patients with polycythemia vera (PV), 25 with essential thrombocythemia (ET) and 12 with primary myelofi brosis (PMF) (26 males and 38 females, mean age: 60.5 years). Th e bone marrow control group comprised 14 bone mar