MicroRNAs (miRNAs) are noncoding RNAs that regulate processes involved in proliferation and differentiation. Since abnormal proliferation and differentiation is the hallmark of cancer, miRNAs may have a role in the pathogenesis of cancer. Here we examined the miRNA expression in various subtypes of Childhood Acute Lymphoblastic Leukemia (ALL) including MLL-rearranged ALL (n = 16), T-ALL (n = 10) and precursor B-ALL patients positive for TEL-AML1 (n = 10), BCR-ABL (n = 10), E2A-PBX (n = 8) or hyperdiploidy (more than 50 chromosomes, n = 10) and other precursor B-ALL patients that are negative for all major genetic abnormalities in ALL (n = 19). We have found that miR-196b is highly expressed only in MLL-rearranged ALL and its expression level is ∼400 to 700-fold (P < 0.05) higher than the levels in all other precursor B-ALL subtypes and T-ALL cases. Moreover, all precursor B-ALL subtypes including TEL-AML1, BCR-ABL, E2A-PBX and hyperdiploid positive cases have a 250- to 6500- fold upregulation (P ≤0.01) of miR-708 compared to MLL-rearranged ALL and T-ALL patients. Interestingly, it is known that MLL-translocated ALL arises in an earlier stage of B-lineage development compared to other precursor B-ALL subtypes negative for MLL rearrangements, thus subtype-specific expression of miR-196b and miR-708 could reflect a difference in maturation status. However, miR-196b and miR-708 expression levels do not seem to correlate with the differentiation status of the leukemia cells based on the immunoglobulin (Ig) and T-cell receptor (TCR) rearrangements in case of precursor B-ALL and EGIL classification in case of T-ALL. Furthermore, miR-196b is located between the HOXA9 and HOXA10 genes, which are known to be upregulated in MLL-translocated patients. Here we find a positive correlation between miR-196b expression and HOXA9/HOXA10 expression within MLL- rearranged and T-ALL patients. Further research has to reveal whether high expression of miR-196b actively contributes to leukemogenesis like HOX genes or whether it is an epiphenomenon of HOXA upregulation in MLL-rearranged ALL patients. All together, our present study suggests that the expression level of miR-196b and miR-708 reflects differences between genetic subtypes rather than differences in differentiation status and emphasizes the need to further investigate the role of these miRNAs in leukemogenesis.
Disclosure: No relevant conflicts of interest to declare.