Implications of MicroRNAs in Normal Hematopoiesis and Human Leukemia

MicroRNAs (miRNAs) are small noncoding RNAs with important regulatory functions, including hematopoietic differentiation. The advent of high-throughput methods to detect miRNA expression has allowed the study of miRNA levels during normal hematopoiesis and have revealed a widespread aberrant miRNA expression in leukemic cells with respect to the normal hematopoietic cells, suggesting a role for miRNAs in human leukemogenesis. Studies have demonstrated that miRNAs are indeed involved in the initiation and progression of human leukemias. Mutations in miRNA genes and in their target sites could predispose to cancer by altering miRNA expression or by affecting its regulatory function on the target messenger RNA. Furthermore, miRNA expression profiling could also distinguish patients with leukemia with poor outcome independent from other biomarkers. Herein, we review the main studies investigating the role of miRNAs in normal human hematopoiesis as well as in acute and chronic leukemias. In addition, we will discuss the emerging role of other noncoding RNAs (namely the ultraconserved regions) in leukemia.