The Role of Microrna-196a-1 and Microrna-196b in Acute T-Lymphoblastic Leukemia and Acute Myeloid Leukemia.

Overexpression of the gene ERG (v-ets erythroblastosis virus E26 oncogene homolog) is an adverse prognostic factor in adult patients with acute T-lymphoblastic leukemia (T-ALL) and acute myeloid leukemia (AML). However, the underlying biology remains unknown. The aim of this study was to investigate the regulation of ERG expression by microRNAs (miRNAs) and to explore their potential role in acute leukemia and normal hematopoiesis. METHODS: A bioinformatic database search was carried out using the Targetscan, Pictar, and Human microRNA target tools to predict ERG regulating miRNAs. Verification of ERG as potential target of predicted miRNAs was performed by AMAXA transfection of miRNA precursor molecules in the myeloid leukemic cell line KG1a. After 24 hours (hrs) and 48 hrs total RNA was extracted using the Trizol reagent. Overexpression of the miRNAs was confirmed by TaqMan MicroRNA assays and ERG expression was determined by real-time RT-PCR. Moreover, specific binding of miRNAs to the 3'UTR of ERG was verified by luciferase reporter assays co-transfecting the ERG 3'UTR cloned into the psiCHECK-2 luciferase vector with miRNA precursor molecules. To investigate the expression of miRNAs during hematopoietic maturation, CD34 positive bone marrow cells from healthy individuals were in vitro cultured using the cytokines SCF and IL-3 (maintenance culture) with the addition of EPO or G-/GM-CSF. Cells were harvested after 3, 6, 9, 13, 16, and 20 days and miRNA expression levels were measured. The expression of miR-196a-1 and miR-196b was also studied in acute leukemias including bone marrow samples of adult patients with newly diagnosed T-ALL (n=105) and AML (n=34). RESULTS: By the database search, a total of 13 miRNAs were predicted to potentially regulate ERG and were further studied. Of these, only the miRNAs miR-196a-1 and miR-196b induced a significant reduction of ERG expression levels. After 24 hrs ERG was significantly down-regulated by 36% (after miR-196a-1 transfection) and by 42% (after miR-196b transfection) as well as after 48 hrs by 43% (after miR-196a-1 transfection) and by 47% (after miR-196b transfection) compared to the controls. The luciferase assays revealed a 30% and 40% luciferase activity reduction in miR-196a-1 and miR-196b transfected cells, respectively, compared to the miRNA-missense transfected cells. This confirmed the direct binding of these miRNAs to the ERG 3'UTR. During hematopoietic differentiation of normal CD34 positive progenitors, expression of miR-196a-1 was constant over time using the different cytokine conditions. In contrast, the expression of miR-196b decreased substantially during the in vitro differentiation (maintenance culture: 20-fold reduction; EPO: 18-fold reduction; G-/GM-CSF: 13-fold reduction - from day 0 to day 9). In acute leukemia, we found that miR-196a-1 was significantly higher expressed in AML compared to bone marrow samples of healthy donors (P=0.02). In T-ALL, miR-196a-1 was significantly up-regulated in patients with aberrant expression of myeloid markers (P=0.04), and miR-196b expression correlated with CD34 expression (P=0.003). In contrast to the reported adverse prognostic impact of ERG, expression of these miRNAs had no prognostic significance in T-ALL. CONCLUSION: This study identifies miR196a-1 and miR-196b as ERG regulators. We show that miR-196b is specifically down-regulated during hematopoietic differentiation, thus indicating a specific role of this miRNA in hematopoiesis. Moreover, the aberrant expression of miR-196a-1 and miR-196b in T-ALL and AML points to a potential role of these miRNAs in acute leukemias.

No relevant conflicts of interest to declare.