A characterization and comparison of the microRNA expression profile in breast cancer cell lines and exosomes

Abstract

Breast cancer is the leading cause in cancer deaths among woman worldwide, and one in ten women will experience the disease during their lifetime. Breast cancer accounted for 23% of the total new cancer incidences and 14% of the total cancer deaths in Norway in 2008. One way to potentially improve long-term cancer survival statistics is earlier detection. That includes the discovery and characterization of minimally invasive and unique breast cancer biomarkers to aid early diagnosis. The presence of circulating microRNAs (miRNAs) in blood components (including serum and plasma) has been repeatedly observed in cancer patients as well as healthy controls. Since the deregulation of miRNA is associated with cancer development and progression, profiling of circulating miRNAs has been used in a number of studies that aim to identify novel miRNA biomarkers. MiRNAs are small RNA molecules that regulate gene expression post-transcriptionally. They play a key role in diverse biological processes, including development, cell proliferation, differentiation, and apoptosis. Hence, altered miRNA expression contributes to the development and progression of human disease, including cancer. In this thesis, we used a strategy of small RNA profiling by Applied Biosystem’s next-generation sequencing system (SOLiD) to analyze the different genome-wide miRNA expression profiles in breast cancer cell lines and exosomes originating from breast cancer cell lines. We found a number of key miRNAs that were highly expressed in both the breast cancer cell lines and exosomes; miRNAs that could have potential as biomarkers for early breast cancer detection. We also sequenced miRNA from 14 breast cancer cell lines of different subtypes and miRNA from exosomes from 9 of those cell lines. This was done to investigate the potential differences in the miRNA expression patterns, both between the different subtypes of breast cancer cell lines and the exosomes originating from the cell lines. We identified miRNAs with a consistent high expression among all the cell lines and exosomes and miRNAs that were differentially expressed between the cell lines and exosomes. Finally, a comparison of the miRNA expression pattern between the exosomes and the cell lines revealed that the miRNA profiles in exosomes did not reflect the miRNA profiles observed in the parental cells.