Comparison of miRNA Expression Profiles in Leukemia-Derived Microvesicles and Corresponding Leukemia Cells and Analysis of Their Roles in Leukemia

Abstract 1388

Microvesicles(MVs) are small exosomes of endocytic origin released by normal healthy or damaged cell types, including leukemic cells. MVs have been considered as cell dust, however, recent data bring evidences that MVs generated during cell activation or apoptosis can transfer biologic messages between different cell types.

MicroRNAs (miRNAs) have been demonstrated to be aberrantly expressed in leukemia and the overall miRNA expression could differentiate normal versus leukemia. The MVs expressing miRNAs were found in the primary tumors. However it is currently unknown whether miRNA content changes in MVs derived from leukemic cells. Here we compared the miRNA expression in leukemia-derived MVs to corresponding leukemia cells and analysed their roles in leukemia. K562 cells were cultured and collected. MVs derived from K562 cells were also isolated. The presence and levels of specific miRNAs from both MVs derived from K562 cells and K562 cells were determined by Agilent miRNA microarray analysis probing for 888 miRNAs. Some selected miRNAs were verified by real time qRT-PCR. Bioinformatic software tools were used to predict the target genes of identified miRNAs and define their function.

Our results showed that 77 and 122 miRNAs were only expressed in MVs and K562 cells, respectively. There were significant differences in miRNA expression profiles between MVs and K562 cells. We also found that 112 miRNAs were co-expressed in MVs and K562 cells. This observaton may suggest that compartmentalization of miRNAs from cells into to MVs, for at least some miRNAs, is an active (selective) process.

Among those abnormally expressed miRNAs, some have been proposed oncomiRNAs or tumor suppressors. For example, miR-155, has been proposed as oncomiRNA, was abnormally expressed only in MVs in our study, suggesting that oncomiRNA was present in MVs. Further analysis revealed that 39 potential target genes regulated by miR-155. Among them, 4 genes involed in oncogenes and the signal genes.

OncomiRNAs such as miR-27a and miR-21 expressed in both MVs and corresponding cells, indicating that MVs bear miRNA characteristic of the cell origin. MVs, released into the leukemia microenvironment, play an important role in leukemia.

In contrast to oncomiRNAs, if miRNA is associated with tumor suppressive activity, it is regarded as a tumor suppressor (oncosuppressor). The aberrantly expressed miR-125a-3p, miR-125-5p,miR-27b, which have implicated as tumor suppressors, appear in both cellular and MVs of leukemia in our study. MiR-125a-3p, miR-125-5p and miR-27b regulated 308 potential target genes. To our knowledge, 10 of them are tumor suppression genes. It is possible that these aberrantly expressed tumor suppressor miRNAs decreased or lost their roles of tumor suppression, which led to decrease or loss their roles of regulating their target genes including oncogenes, consequently resulted in leukemia.

Since K562 cells presented t(9;22), we further examined the predicted function of the 6 expressed miRNAs located in chrosome 9 (hsa-miR-188-5p,hsa-miR-602)and 22(hsa-let-7b,hsa-miR-1249,hsa-miR-130b,hsa-miR-185), which expressed both in the MVs and K562 cells. Using the TargetScan, we found 442 predicted targets regulated by 6 miRNAs. Those miRNAs may play roles in leukemia via these 422 genes.

This study is the first to identify and define miRNA expression between K562 cells presented t(9;22), derived from K562 cells and their corresponding cells. We found significant differences in miRNA expression between MVs and corresponding leukemia. K562 cells released MVs riched in miRNAs including oncomiRNAs or tumor suppressor miRNAs into leukemia microenvironment, which play a role in leukemia via regulating their targer genes including oncogenes, consequently resulted in leukemia.