MicroRNA-206 is differentially expressed in Brca1-deficient mice and regulates epithelial and stromal cell compartments of the mouse mammary gland

MicroRNAs: A Link between Mammary Gland Development and Breast Cancer

Breast cancer is among the most common cancers in women, second to skin cancer. Mammary gland development can influence breast cancer development in later life. Processes such as proliferation, invasion, and migration during mammary gland development can often mirror processes found in breast cancer. MicroRNAs (miRNAs), small, non-coding RNAs, can repress post-transcriptional RNA expression and can regulate up to 80% of all genes. Expression of miRNAs play a key role in mammary gland development, and aberrant expression can initiate or promote breast cancer. Here, we review the role of miRNAs in mammary development and breast cancer, and potential parallel roles. A total of 32 miRNAs were found to be expressed in both mammary gland development and breast cancer. These miRNAs are involved in proliferation, metastasis, invasion, and apoptosis in both processes. Some miRNAs were found to have contradictory roles, possibly due to their ability to target many genes at once. Investigation of miRNAs and their role in mammary gland development may inform about their role in breast cancer. In particular, by studying miRNA in development, mechanisms and potential targets for breast cancer treatment may be elucidated.

MicroRNAs, DNA damage response and ageing

Ageing is a multifactorial and integrated gradual deterioration affecting the most of biological process of cells. MiRNAs are differentially expressed in the cellular senescence and play important role in regulating of genes expression involved in features of ageing. The perception of miRNAs functions in ageing regulation can be useful in clarifying the mechanisms underlying ageing and designing of therapeutic strategies. The preservation of genomic integrity through DNA damage response (DDR) is related to the process of cellular senescence. The recent studies have shown that miRNAs has directly regulated the expression of numerous proteins in DDR pathways. In this review study, DDR pathways, miRNA biogenesis and functions, current finding on DDR regulations, molecular biology of ageing and the role of miRNAs in these processes have been studied. Finally, a brief explanation about the therapeutic function of miRNAs in ageing regarding its regulation of DDR has been provided.

MiR-16a Regulates Milk Fat Metabolism by Targeting Large Tumor Suppressor Kinase 1 (LATS1) in Bovine Mammary Epithelial Cells

Milk contains a number of beneficial fatty acids including short and medium chain and unsaturated conjugated and nonconjugated fatty acids. In this study, microRNA sequencing of mammary tissue collected in early-, peak-, mid-, and late-lactation periods was performed to determine the miRNA expression profiles. miR-16a was one of the differentially expressed miRNA and was selected for in-depth functional studies pertaining to fatty acid metabolism. The mimic of miR-16a impaired fat metabolism [triacylglycerol (TAG) and cholesterol] while knock-down of miR-16a promoted fat metabolism in vitro in bovine mammary epithelial cells (BMECs). In addition, the in vitro work with BMECs also revealed that miR-16a had a negative effect on the cellular concentration of cis 9-C18:1, total C18:1, C20:1, and C22:1 and long-chain polyunsaturated fatty acids. Therefore, these data suggesting a negative effect on fatty acid metabolism extend the discovery of the key role of miR-16a in mediating adipocyte differentiation. Through a combination of bioinformatics analysis, target gene 3' UTR luciferase reporter assays, and western blotting, we identified large tumor suppressor kinase 1 (LATS1) as a target of miR-16a. Transfection of siRNA-LATS1 into BMECs led to increases in TAG, cholesterol, and cellular fatty acid concentrations, suggesting a positive role of LATS1 in mammary cell fatty acid metabolism. In summary, data suggest that miR-16a regulates biological processes associated with intracellular TAG, cholesterol, and unsaturated fatty acid synthesis through LATS1. These data provide a theoretical and experimental framework for further clarifying the regulation of lipid metabolism in mammary cells of dairy cows.

A miR-206 regulated gene landscape enhances mammary epithelial differentiation

miR‐206 is known to suppress breast cancer. However, while it is expressed in mammary stem cells, its function in such nontumor cells is not well understood. Here, we explore the role of miR‐206 in undifferentiated, stem‐like mammary cells using the murine mammary differentiation model HC11, genome‐wide gene expression analysis, and functional assays. We describe the miR‐206‐regulated gene landscape and propose a network whereby miR‐206 suppresses tumor development. We functionally demonstrate that miR‐206 in nontumor stem‐like cells induces a G1–S cell cycle arrest, and reduces colony formation and epithelial‐to‐mesenchymal transition markers. Finally, we show that addition of miR‐206 accelerates the mammary differentiation process along with related accumulation of lipids. We conclude that miR‐206 impacts a network of signaling pathways, and acts as a regulator of proliferation, stemness, and mammary cell differentiation in nontumor stem‐like mammary cells. Our study provides a broad insight into the breast cancer suppressive functions of miR‐206.

MiR-29b-1-5p is altered in BRCA1 mutant tumours and is a biomarker in basal-like breast cancer

Depletion of BRCA1 protein in mouse mammary glands results in defects in lactational development and increased susceptibility to mammary cancer. Extensive work has focussed on the role of BRCA1 in the normal breast and in the development of breast cancer, the cell of origin for BRCA1 tumours and the protein-coding genes altered in BRCA1 deficient cells. However, the role of non-coding RNAs in BRCA1-deficient cells is poorly understood. To evaluate miRNA expression in BRCA1 deficient mammary cells, RNA sequencing was performed on the mammary glands of Brca1 knockout mice. We identified 140 differentially expressed miRNAs, 9 of which were also differentially expressed in human BRCA1 breast tumours or familial non-BRCA1 patients and during normal gland development. We show that BRCA1 binds to putative cis-elements in promoter regions of the miRNAs with the potential to regulate their expression, and that four miRNAs (miR-29b-1-5p, miR-664, miR-16-2 and miR-744) significantly stratified the overall survival of basal-like tumours. Importantly the prognostic value of miR-29b-1-5p was higher in significance than several commonly used clinical biomarkers. These results emphasise the role of Brca1 in modulating expression of miRNAs and highlights the potential for BRCA1 regulated miRNAs to be informative biomarkers associated with BRCA1 loss and survival in breast cancer.

MicroRNAs in the development and neoplasia of the mammary gland

Study on the role of microRNAs (miRs) as regulators of gene expression through posttranscriptional gene silencing is currently gaining much interest,due to their wide involvement in different physiological processes. Understanding mammary gland development, lactation, and neoplasia in relation to miRs is essential. miR expression profiling of the mammary gland from different species in various developmental stages shows their role as critical regulators of development. miRs such as miR-126, miR-150, and miR-145 have been shown to be involved in lipid metabolism during lactation. In addition, lactogenic hormones influence miR expression as evidenced by overexpression of miR-148a in cow mammary epithelial cells, leading to enhanced lactation. Similarly, the miR-29 family modulates lactation-related gene expression by regulating DNA methylation of their promoters. Besides their role in development, lactation and involution, miRs are responsible for breast cancer development. Perturbed estrogen (E2) signaling is one of the major causes of breast cancer. Increased E2 levels cause altered expression of ERα, and ERα-miR cross-talk promotes tumour progression. miRs, such as miR-206, miR-34a, miR-17-5p, and miR-125 a/b are found to be tumour suppressors; whereas miR-21, miR-10B, and miR-155 are oncogenes. Oncogenic miRs like miR-21, miR-221, and miR-210 are overexpressed in triple negative breast cancer cases which can be diagnostic biomarker for this subtype of cancer.  This review focuses on the recent findings concerning the role of miRs in developmental stages of the mammary gland (mainly lactation and involution stages) and their involvement in breast cancer progression. Further studies in this area will help us to understand the molecular details of mammary gland biology, as well as miRs that could be therapeutic targets of breast cancer.