MicroRNA expression profiles classify human cancers

Abstract

MicroRNAs are regulatory, non-coding RNAs about 22 nucleotides in length: over 200 have been identified in humans, and their functions are beginning to be pinned down. It has been suggested that like other regulatory molecules they might be involved in tumour formation, and three papers in this issue confirm that this is the case. One cluster of microRNAs, known as mir-17–92, is shown to be a potential oncogene by its action in an in vivo model of human B-cell lymphoma. A cluster of microRNAs on human chromosome 13 has been found to be regulated by c-Myc, an important transcription factor that is overexpressed in many human cancers. And analysis of microRNA expression in over 300 individuals shows that microRNA profiles could be of value in cancer diagnosis. There is a global downregulation of microRNA in tumours, and the microRNA profile also reflects the origin and differentiation state of the tumours. Recent work has revealed the existence of a class of small non-coding RNA species, known as microRNAs (miRNAs), which have critical functions across various biological processes1,2. Here we use a new, bead-based flow cytometric miRNA expression profiling method to present a systematic expression analysis of 217 mammalian miRNAs from 334 samples, including multiple human cancers. The miRNA profiles are surprisingly informative, reflecting the developmental lineage and differentiation state of the tumours. We observe a general downregulation of miRNAs in tumours compared with normal tissues. Furthermore, we were able to successfully classify poorly differentiated tumours using miRNA expression profiles, whereas messenger RNA profiles were highly inaccurate when applied to the same samples. These findings highlight the potential of miRNA profiling in cancer diagnosis.