Aberrant Microrna Expression In Chinese Patients with Chronic Lymphocytic Leukemia.

Abstract 4605

MicroRNAs (miRNAs) are a class of small endogenous RNAs that play important regulatory roles by targeting mRNAs for cleavage or translational repression. Many reports have indicated that microRNAs (miRNAs) play a critical role in malignancies, and regulations in the progression of leukemia. However, the miRNAs expression level in Chinese patients with chronic lymphocytic leukemia (CLL), and its prognostic value remain elusive. We identified various degrees of down-regulation of miR-15a, miR-16-1, miR-29b, miR-181a and miR-181b in CLL mononuclear cells of 138 patients. Moreover, we have identified that miR-29b, miR-181a and miR-181b expression was significantly correlated with IGHV mutatioal status (the P value was 0.057, 0.034 and 0.004, respectively). Down-expression of miR-181b was significantly associated (P=0.001) with overall survival in patients while expression for miR-181a was of borderline significant (P=0.09). To further determine the consequence of miR-181-down regulation, we sought to discover targets of miR-181 family. Transcript levels of predicted target genes BCL-2 and TCL-1 were determined, and the expression levels were significantly upregulated in CLL patients compared with normal controls (P<0.001). Higher expression of TCL-1 was significantly correlated with aggressive disease features. In addition, an inverse correlation was observed in the CLL samples between miRNAs (miR-16-1, miR-181a, miR-181b) and BCL-2 level (r=-0.216, P=0.012; r=-0.274, P=0.002; r=-0.184, P=0.036, respectively); furthermore, an inverse correlation was also observed between miRNAs (miR-16-1, miR-181a, miR-181b) and TCL-1 (r=-0.272, P=0.002; r =-0.224, P=0.009; r=-0.152, P=0.054, respectively), which suggest that these miRNAs may implicated in negatively regulating target mRNA at a transcriptional level. For further study, our study showed that miR-181a and miR-181b functioned as tumor suppressors that induced apoptosis in CLL cells by regulates BCL-2/MCL-1 protein expression. The luciferase activity of a BCL-2-3’-untranslated region-based reporter construct in CLL cells suggests that a new target site in the 3’UTR of BCL-2 of the mature miR-181a/b. MCL-1 is a BCL-2 family member and pro-survival protein associated with drug resistance in leukemia. Using a luciferase construct containing the MCL-1 3’ UTR we observed a decrease in luciferase expression upon miR-181b over-expression. It was suggested that miR-181b directly targets MCL-1 mRNA. In addition, enforced miR-181a/b expression in primary CLL cells (n= 52) reduced BCL-2/MCL-1 protein level and sensitized primary CLL B cells to fludarabine-induced apoptosis and also had effect in B-CLL cells from 7 p53 attenuated patients. Taken together, our results suggest that these deregulated miRNAs may play an important role in pathogenesis of CLL and might be applied for the assessment of prognosis in patients with CLL. Among which, miR-181a/b could function as tumor suppressors in human CLL cells, at least in part, by modulation of apoptosis via targeting BCL-2 and MCL-1.