442920

MIR196B

MIRN196B|miR-196b|miRNA196B;microRNA 196b;MIR196B;microRNA 196b

hsa-mir-196b

7p15.2

ncRNA

Keeping in view the fact that genes coding microRNAs (miRNAs) have been found to be localized in chromosomal regions susceptible to genetic translocations, this study was addressed to identify and characterize the miRNAs that are present near/within the regions involved in genetic translocations characteristic of B-cell acute lymphoblastic leukemia (B-cell ALL). Out of six such identified miRNAs miR-196b was not only found to be significantly down-regulated in both EB-3 cell line as well as B-cell ALL patients as compared to that found in the corresponding controls, but also had the inherent capacity to down-regulate the highly expressed c-myc gene, a consequence of genetic translocation characteristic of EB-3 cells at both transcriptional and translational level. This phenomenon was in conformity with the observed reciprocal relationship between the expressed genes coding for miR-196b and c-myc in B-cells derived from ALL patients as well as c-myc gene was found to be a putative target of miR-196b as predicted by bioinformatic algorithms. Also down-regulation of c-myc gene was accompanied by decreased expressions of c-myc effector genes coding for hTERT, Bcl-2, and AATF. Based upon these results, we propose for the first time that miR-196b has the inherent capacity to down-regulate the overamplified c-myc gene recognized as a common pathognomonic feature leading to cancer in general and B-cell ALL in particular. Hence miR-196b can be assigned with the tumor suppressor function and can be of therapeutic importance in paving the way toward the treatment of B-cell ALL.

Huge data accumulated in last few years have shown that differential expression of candidate miRNAs in normal versus transformed cell provides important insights into the pathogenesis of cancer including leukemias. In our previous report, we have revealed that miR-196b was significantly down-regulated in both EB-3 cells as well as B-cell ALL (acute lymphoblastic leukemia) patients as compared to their respective controls. We have unambiguously proven that miR-196b restoration in EB-3 cells leads to significant down-regulation of c-myc and its effector genes, i.e., human telomerase reverse transcriptase (hTERT), B-cell lymphoma/leukemia-2 (Bcl-2), apoptosis antagonizing transcription factor (AATF), and qualifies for tumor suppressor function in B-cell ALL. Keeping in view these results, the present study was aimed at dissecting the role of miR-196b and other miRNAs present near/within the genomic regions involved in genetic translocations characteristic of ALL in T-cell ALL cell lines and patient samples. We have demonstrated significant down-regulation in the expression of miR-196b in MOLT-4 and T-cell ALL patients with respect to the respective control cells. Transfection experiments revealed that none of the six identified miRNAs were able to knock down the expression of c-myc gene. Interestingly, it was found that miR-196b loses its ability to down-regulate c-myc gene expression in T-cell ALL as a consequence of mutations in target 3-untranslated region (3-UTR) of the c-myc gene. Results of the present study revealed that miR-196b becomes non-functional in T-cell ALL as a consequence of mutations in 3-UTR of c-myc gene in T-cell ALL cellular models.