A microRNA study of the genetic origins of acute myeloid leukaemia

PhDMicroRNAs (miRNAs), a group of highly-conserved, small (19-26 nucleotides), non-coding RNAs, are one of the largest gene families of the genome. They are believed to control several pathways including haematopoiesis and are implicated in a number of cancers. The genetic basis of acute myeloid leukaemia (AML) has been extensively studied, however its aetiology is not fully understood. Analysis of new markers, such as miRNAs, may suggest areas for further exploration. Expression levels of 157 miRNAs in 100 AML samples representing the known spectrum of karyotypes, 2 leukaemic cell lines and bone marrow from 2 healthy donors were measured by real time-PCR, designed to amplify only from the mature miRNA. Unsupervised hierarchical clustering revealed molecular signatures associated with the major translocation-mediated gene-fusion events implicated in AML. In particular, the acute promyelocytic leukaemia (APML) samples harbouring a t(15;17) showed a distinct pattern characterised by high expression of a subset of genes located within an imprinted region on chromosome 14. Two of the miRNAs located within this region were examined in situ. A novel method for the detection of miRNAs in haematopoietic cells was devised using locked nucleic acid (LNA)-modified probes and confocal microscopy demonstrated their spatial localisation. The method was modified further to incorporate probes for the detection of the abnormal blast population and was applied to paired, diagnostic and remission, samples. Functional analyses were performed on cell lines and patient samples using a precursor molecule and a knockdown molecule for miR-127. Cell cycle and gene expression analysis was undertaken. This miRNA was not directly involved in the cell cycle or apoptotic pathways, however gene expression analyses identified a number of potential gene targets. These findings provide new insights into the role of miRNAs in the genetic origins of AML and highlight their potential as biomarkers for disease stratification and drug-targeted therapy