Distinct Expression Patterns of Human microRNAs in Myeloid Differentiation and Acute Myeloid Leukemia.

MicroRNAs (miRNAs) play an important role in differentiation, regulation of cell growth, cell death and potentially cancer pathogenesis. In the current study, we profiled expression of 154 human miRNAs by using a stem-loop reverse transcription and real-time PCR approach in 50 patients with AML and 12 control samples (normal bone marrow (NBM) samples and CD34+ cells). All of these samples were simultaneously analysed by whole genome mRNA microarrays. Out of all miRNAs tested, more than 30 were analyzed in a second, independent group of 48 AML samples and 4 controls. Five miRNAs showed differentiation associated expression changes which were confirmed by in-vitro differentiation of HL-60 cells with all-trans retinoic acid (ATRA) or 12-O-tetradecanoylphorbol-13-acetate (TPA). Overall, we found six miRNAs, including the miR-221 and 222 cluster, that showed substantially different expression between AML and CD34+ cells/ NBM. In class prediction analyses using support vector machines, 92% of the AML samples and 100% of the control samples were correctly predicted. We also looked for differentially regulated miRNAs in FAB subtypes and identified several miRNAs with significantly different expression. For example, high expression levels of miR-26a, 23a and 27b occurred in FAB M5. mRNA levels were analyzed with regard to differences in miRNA expression. Significant negative correlations with specific mRNAs were observed for several miRNAs, for example miR-23b. When mRNA expression patterns were analyzed for dichotomized miRNA levels, close associations between specific miRNAs and gene expression clusters were observed. For example, miR-10a levels were closely associated with the expression of hox genes. Taken together, the distinct expression patterns of miRNAs observed in AML strongly suggest involvement of the described miRNAs in both hematopoietic differentiation and pathogenesis of AML.