The role of microRNAs in breast development and breast cancer pathogenesis
Final Report Abstract
MicroRNAs (miRNAs) are a class of small non-coding RNA, which regulate gene expression on a post-transcriptional level. They play a key role in development but also in specific biological processes such as cell proliferation, differentiation, and apoptosis. Altered miRNA expression has been implicated in various human diseases including cancer. In human breast cancer, complex de-regulated miRNA expression patterns were found. My research project investigated the temporal miRNA expression during postnatal mammary gland development. The overall goal was to analyze individual miRNA expression levels throughout a 16-point developmental fime course including juvenile, puberty, mature virgin, gestation, lactation, and involution stages. Subsequently, tissue-specific miRNA profiles were established by analyzing the expression of 318 murine miRNAs using a bead-based flowcytometric profiling of whole mouse mammary glands. In addition, whole-genome messenger RNA data reflecting gene expression were obtained. The main findings were: i) one third (n=102) of all murine miRNAs are present during mammary gland development, ii) miRNAs are highly co-regulated during all development stages and expressed in seven temporal clusters, iii) None of the investigated single miRNAs or miRNA clusters are exclusively associated with a particular development stage. However, miRNAs which were found to be up-regulated in breast cancer are overrepresented in two of the clusters. One cluster was highly expressed during puberty and gestation, which is dominated by proliferation and invasion and the second cluster directly before and afler puberty and gestation. The findings suggest that biological processes such as proliferation or invasion are not regulated by single or few miRNAs but rather determined by a complex contribution of miRNA clusters as shown during postnatal breast development. Regarding whole-genome messenger RNA analysis, we determined the expression of computationally predicted miRNA target genes. There were no systematic changes in target gene expression for most miRNAs. However, for few miRNA families, i.e. let-7, predicted target genes were down-regulated during time points when the miRNA was highly expressed and up-regulated when the miRNA was expressed at low levels. In an additional project, distinct mammary gland cell populations including luminal, basal, and stromal cells were isolated using fluorescent activated cell sorting (FACS) and analyzed by gene expression profiling. This data is currently being analyzed by a biostatistician in comparison with the gene expression profiles of breast cancer molecular subtypes. My next goal is to continue breast cancer related miRNA research at the Institute of Pathology, Technische Universität Munich. A subsequent grant application will propose to investigate differential expression patterns of miRNAs in the pathogenesis and malignant progression of breast cancer. Specific aims are to further investigate the temporal expression of specific candidate miRNAs, which represent one of the clusters identified earlier i) in breast cancer cells in-vitro ii) in a mouse breast cancer model iii) in human fissue including in-situ carcinoma and invasive cancer with and without metastases and iiii) for prediction of treatment response.
Publications
- MicroRNA: implications for cancer. Virchows Arch (2008),452:1-10
Sassen S, Miska EA, Caldas C
