Specific Depletion of Leukemic Stem Cells: Can MicroRNAs Make the Difference?

MicroRNA-21 over expression in umbilical cord blood hematopoietic stem progenitor cells by leukemia microvesicles

Microvesicles are able to induce the cell of origin's phenotype in a target cell. MicroRNA-21, as an oncomir, is up-regulated in almost all cancer types such as leukemia which results in cell proliferation. In this study, we examine the ability of leukemia microvesicles to induce proliferation in hematopoietic stem progenitor cells (HSPCs) via microRNA-21 dysregulation. Herein, leukemia microvesicles were isolated from HL-60 and NB-4 cell lines by ultracentrifugation, and then their protein content was measured. Normal HSPCs were isolated from umbilical cord blood samples by a CD-34 antibody. These cells were treated with 20 and 40 μg/mL leukemia microvesicles for 5 and 10 days, respectively. Cell count, CD-34 analysis, and a microRNA-21 gene expression assay were done at days 5 and 10. HSPCs showed a significant increase in both microRNA-21 gene expression and cell count after treating with leukemia microvesicles compared with the control group. CD-34 analysis as stemness proof did not show any difference among the studied groups. This data suggests that HSPC proliferation followed by microRNA-21 gene over expression can be another evidence of a leukemia-like phenotype induction in a healthy target cell by leukemia microvesicles.

Genome-wide identification of microRNA signatures associated with stem/progenitor cells in Philadelphia chromosome-positive acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a malignant transformation with uncontrolled proliferation of lymphoid precursor cells within bone marrow including a dismal prognosis after relapse. Survival of a population of quiescent leukemia stem cells (LSCs, also termed leukemia-initiating cells (LICs)) after treatment is one of the relapse reasons in Ph⁺ ALL patient. MicroRNAs (miRNAs) are known as highly conserved 19-24 nucleotides non-protein-coding small RNAs that regulate the expression of human genes. miRNAs are often involved in the tuning of hematopoiesis. Therefore, the deregulation of miRNA expression and function in hematopoietic cells can cause cancer and promote its progression. This is the first comprehensive analysis of miRNA expression differences between CD34⁺CD38^- LSCs and CD34⁺CD38⁺ leukemic progenitors (LPs) from the same Ph⁺ B-ALL bone marrow samples using high-throughput sequencing technologies. We identified multiple differentially expressed miRNAs including hsa-miR-3143, hsa-miR-6503-3p, hsa-miR-744-3p, hsa-miR-1226-3p, hsa-miR-10a-5p, hsa-miR-4658 and hsa-miR-493-3p related to LSC and LP populations which have regulatory functions in stem-cell associated biological processes. The deregulation of these miRNAs could affect leukemogenesis, clonogenic and stemness capacities in these subpopulations of Ph⁺ B-ALL. Therefore, identification of these LSC associated miRNAs may improve the diagnosis and management of B-ALL. These findings may also lead to future strategies to eliminate the presence of resistant LSCs, either by induction of apoptosis or by sensitizing these cells to chemotherapy.

Cell Cycle Regulation of Stem Cells by MicroRNAs

MicroRNAs (miRNAs) are a class of small non-coding RNA molecules involved in the regulation of gene expression. They are involved in the fine-tuning of fundamental biological processes such as proliferation, differentiation, survival and apoptosis in many cell types. Emerging evidence suggests that miRNAs regulate critical pathways involved in stem cell function. Several miRNAs have been suggested to target transcripts that directly or indirectly coordinate the cell cycle progression of stem cells. Moreover, previous studies have shown that altered expression levels of miRNAs can contribute to pathological conditions, such as cancer, due to the loss of cell cycle regulation. However, the precise mechanism underlying miRNA-mediated regulation of cell cycle in stem cells is still incompletely understood. In this review, we discuss current knowledge of miRNAs regulatory role in cell cycle progression of stem cells. We describe how specific miRNAs may control cell cycle associated molecules and checkpoints in embryonic, somatic and cancer stem cells. We further outline how these miRNAs could be regulated to influence cell cycle progression in stem cells as a potential clinical application.

MicroRNAs as New Biomarkers for Diagnosis and Prognosis, and as Potential Therapeutic Targets in Acute Myeloid Leukemia

Acute myeloid leukemias (AML) are clonal disorders of hematopoietic progenitor cells which are characterized by relevant heterogeneity in terms of phenotypic, genotypic, and clinical features. Among the genetic aberrations that control disease development there are microRNAs (miRNAs). miRNAs are small non-coding RNAs that regulate, at post-transcriptional level, translation and stability of mRNAs. It is now established that deregulated miRNA expression is a prominent feature in AML. Functional studies have shown that miRNAs play an important role in AML pathogenesis and miRNA expression signatures are associated with chemotherapy response and clinical outcome. In this review we summarized miRNA signature in AML with different cytogenetic, molecular and clinical characteristics. Moreover, we reviewed the miRNA regulatory network in AML pathogenesis and we discussed the potential use of cellular and circulating miRNAs as biomarkers for diagnosis and prognosis and as therapeutic targets.