Correlation of MicroRNA Expressions with mutated and unmutated IgVH gene groups in chronic lymphocytic leukemia

Abstract

B-cell chronic lymphocytic leukemia is the most common leukemia in the adult population of Western developed countries. In 2005, an estimated 9,730 adults in the United States will be diagnosed with B-CLL and an estimated 4,600 deaths will occur. B-CLL is a common heterogeneous malignant disease with variable outcome. B-CLL is divided into two groups based on whether somatic hypermutation is observed in the variable region of the immunoglobulin heavy-chain locus (IgVH). The two distinct groups are named mutated and unmutated. The B-CLL mutated group has a more favorable prognosis than the unmutated group.

Gene expression profiling has been used successfully to decipher the biological and clinical diversity of many leukemias and lymphomas. Recently, other small RNAs (microRNAs) have been shown to be important in hematopoiesis. MicroRNAs are small 20-28 nucleotide RNAs that are believed to control many important cellular and developmental processes by posttranscriptional gene silencing, translational repression, and modulating epigenetic events.

We are interested in whether microRNA expression correlates with the mutational status of IgVH. This study is significant in the following ways: (1) microRNAs may become surrogate markers for the mutational status of IgVH of B-CLL, which implies a more rapid diagnostic means as compared to the current practice, and (2) microRNAs, in the particular context of B-CLL, may play some significant roles in a gene regulatory network that is further responsible for chromosomal abnormalities found in B-CLL.

This thesis presents a study comparing microRNA expression in mutated and unmutated B-CLL groups. Instead of using a genome-wide expression profiling strategy, we selected a specific set of microRNAs based on their chromosome locations and mRNA targets. Specifically, we chose the following eight microRNAs (with their chromosomal abnormalities): mir16-1 (deletion 13), let-7i (trisomy 12), mir196-2 (trisomy 12), mir26a-2 (trisomy 12), mir-34b (deletion 11), mir-125b (deletion 11), mir-181C (trisomy 19), mir-125a (trisomy 19). We used solution hybridization assays to monitor the expression of microRNAs. We successfully characterized the microRNA expression in twelve B-CLL patient samples (eight mutated and four unmutated). Among the eight microRNAs examined, three (mir196-2, mir-125a, mir-125b) are not expressed in the two B-CLL groups, four (mir16-1, mir26a-2, let-7i, mir-34b) have significant differences in expressions over the two groups, and one (mir-181c) has no significant difference in expressions over the two groups.