MicroRNAs (miRNAs) are short RNA molecules encoded by plant, animal, and viral genomes that have garnered significant interest for their ability to regulate gene expression. Many critical biological processes are regulated by miRNAs, and recent evidence has shown that alterations in miRNA expression is involved in human tumor development and metastasis.
Investigations into the role of miRNAs in cancer up until now have largely focused on the function and expression of individual miRNAs, but miRNA function is more complex and interwoven. "MicroRNAs were always considered as singles, generally unrelated to each other in the miRNA world," said Ohio State University researcher Carlo Croce. "We did not know much about how miRNAs cooperate."
Because a single miRNA is likely to regulate many genes, and each target gene may be regulated by more than one miRNA, Croce and an international team of colleagues suggested that in order to capture the complex patterns of miRNA expression in cancer, the system must be thought of as a "social network" that coordinates the delicate balance of gene regulation.
Croce explained that in healthy tissues, miRNAs are connected in networks and different cell types have different network connections. In cancer, it is likely that normal network interactions have become disrupted or rewired, contributing to disease.
The group analyzed patterns of miRNA expression levels in a large set of normal and cancerous tissue samples, mapping groups of miRNAs exhibiting highly related patterns of expression. Once relationships were recognized, they could then build a genetic network revealing the most highly connected miRNAs, called "hubs."
When comparing the miRNA networks built from normal tissues to the networks built from tumor samples, Croce's team found cases where the miRNA networks have been reprogrammed in cancer. In some cases, they found that the highly connected miRNA hubs changed between cancer and normal tissues.
They also identified even more extreme cases of tumor network changes. "Groups of miRNAs go awry and exit from the 'social network' altogether," Croce said. "In solid cancers there can be a few, or more, groups of such misbehaved miRNAs, while in leukemias we found only one or two." Some of these "unsocial" miRNAs have well-known roles in cancer, but others had not been implicated until now.
This work is particularly significant in that novel cancer genes have been discovered utilizing a strategy based on relationships, rather than up or down regulation of expression. "The miRNAs we discovered can now be used as targets for drug development," Croce added, "or to pinpoint candidate proteins, which, in turn, they regulate."
Scientists from the Ohio State University (Columbus, OH), the University of Ferrara (Ferrara, Italy), The Scripps Research Institute (La Jolla, CA), the University of California, Los Angeles (Los Angeles, CA), Thomas Jefferson University (Philadelphia, PA), the National Institutes of Health (Bethesda, MD), the University of California, San Diego, (La Jolla, CA), the Charité - Universitätsmedizin Berlin (Berlin, Germany), Institut Pasteur (Paris, France), MD Anderson Cancer Center (Houston, TX), and the University of Rome (Rome, Italy) contributed to this study.
This work was primarily funded by grants from the National Cancer Institute, with additional support from the Italian Association for Cancer Research (Associazione Italiana per la Ricerca sul Cancro), the Ministry of Education, University and Research (Italy), and BioPharmaNet.
Carlo M. Croce, MD is available for more information by contacting Darrell E. Ward, Associate Director of Media Relations at The Ohio State University Medical Center (+1-614-293-3737; firstname.lastname@example.org).
Interested reporters may obtain copies of the manuscript from Peggy Calicchia, Editorial Secretary, Genome Research (email@example.com; +1-516-422-4012).
About the article:
The manuscript will be published online and in print on May 3, 2010. Its citation is as follows: Volinia S, Galasso M, Costinean S, Tagliavini L, Gamberoni G, Drusco A, Marchesini J, Mascellani N, Sana ME, Abu Jarour R, et al. Reprogramming of miRNA networks in cancer and leukemia. Genome Res doi:10.1101/gr.098046.109.
About Genome Research:
Launched in 1995, Genome Research (www.genome.org) is an international, continuously published, peer-reviewed journal that focuses on research that provides novel insights into the genome biology of all organisms, including advances in genomic medicine. Among the topics considered by the journal are genome structure and function, comparative genomics, molecular evolution, genome-scale quantitative and population genetics, proteomics, epigenomics, and systems biology. The journal also features exciting gene discoveries and reports of cutting-edge computational biology and high-throughput methodologies.
About Cold Spring Harbor Laboratory Press:
Cold Spring Harbor Laboratory is a private, nonprofit institution in New York that conducts research in cancer and other life sciences and has a variety of educational programs. Its Press, originating in 1933, is the largest of the Laboratory's five education divisions and is a publisher of books, journals, and electronic media for scientists, students, and the general public.
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