MicroRNAs in chronic lymphocytic leukemia pathogenesis and disease subtypes

MicroRNAs (miRNAs) are short, non-coding RNAs, which function as evolutionary conserved regulators of a gene expression. They have essential roles in development, cell differentiation, proliferation, apoptosis and chromosome structure. MiRNAs constitute about 3-5% of predicted genes in the human genome (i.e. about 1000); and 20-30% of the protein-coding genes are estimated to be regulated by the miRNAs. The primary evidence that miRNAs possibly act as a novel class of oncogenes/tumor-suppressors comes from the discovery of the miR-15a and miR-16-1 in 13q14 region deleted in chronic lymphocytic leukemia (CLL). Moreover, miRNA signatures have been used to classify tumor types. There have recently been several reports on the miRNAs role in CLL pathogenesis and disease subtypes (according to IgVH mutation status). In this report, we will review the published observations and present our miRNA profiling data in aggressive CLL with TP53 abnormalities (deletion and/or mutation of p53 gene). We have identified a deregulated miRNA expression pattern (down regulation of miR-34a, miR-29 and miR-17-5p) in these samples, compared to cells with wild-type TP53. It has previously been shown that miR-34a is directly regulated by p53 and targets BCL-2, miR-29c regulates the MCL-1 and TCL-1 proto-oncogenes and the miR-17-5p targets important cell cycle regulatory molecules. Consequently, these three miRNAs could potentially play important roles in the pathogenesis of aggressive CLL.