Exosomes are membrane-bound extracellular vesicles (EVs) produced in the endosomal compartment of many eukaryotic cells. In animals, exosomes are found in biological fluids where they participate in functions including intercellular communication. Scientists researching the role of exosomes in cell-to-cell signaling often hypothesize that delivery of their cargo RNA can explain the biological effects that EVs exert on their target tissues. MicroRNAs (miRNA; non-coding RNA molecules 21 to 23 nucleotides in length) in exosomes are protected from RNase-dependent degradation and they can be stably detected in blood-based samples. Previous studies have shown that certain miRNA species carried by exosomes can serve as biomarkers and may in fact affect the progression of breast and brain cancer metastasis. Several recent studies have suggested that differences in miRNA signaling may underlie the pronounced discrepancies in breast cancer mortality seen, although the exact nature of miRNA involvement remains elusive.
In their recent Nature Communications article, Zhao et al. used microscopy-based, molecular, and in vivo analyses to identify exosome-delivered miR-1304-3p as the most upregulated miRNA in African American breast cancer patients and showed that its expression significantly correlated with poor outcomes in African American patients. To identify serum exosome miRNAs that were differentially expressed between African Americans and Caucasian Americans, the team first performed miRNA sequencing analysis on a cohort of patients’ serum exosomes. Using this technique, they established that miR-1304-3p expression is significantly overabundant in the serum of African American breast cancer patients. Next, a series of microscopy-based in vitro studies using human cells and in vivo experiments in mice, showed that exosomal miR-1304-3p was incorporated into adipocytes where it directly targeted the expression of factor GATA2, which is involved in promoting adipogenesis. This change was found to promote the secretion of triglycerides, which is suspected to fuel cancer cell growth. In the microscopy-based portion of these experiments, Biotium’s LipidSpot™ 610 was used to determine the effects that ectopically expressed miR-1304-3p, purified exosomes, or conditioned culture medium containing miR-1304-3p, had on differentiation and lipid accumulation in human cell lines (Figure 1). Altogether, this study highlights the critical role miR-1304-3 plays in breast cancer progression through the activation of cancer-associated adipocytes and in differential outcomes between African Americans and Caucasian Americans. This study also illustrates that serum exosomal miRNA offers a potential source of informative biomarkers for other types of cancers.
Figure: LipidSpot™ Lipid Droplet Stain helps show that miR-1304-3p promotes the growth of cancer-associated adipocytes. A) Human preadipocytes (BR-F) were first infected with either GFP-ctr (control) or GFP-miR-1304 (ectopically expressed miR-1304-3p). After differentiation, cells were stained with LipidSpot™ 610 and lipid droplets were imaged, quantified, and statistically analyzed (unpaired two-tailed student t-test, p=0.0005). Scalebar= 100μm. B) 50 ug of exosomes from either HCC1806miArrest-Ctr (inhibited control) or miArrest-1304-3p cells (express the highest level of miR-1304-3p) were added to the adipocyte medium. After differentiation, cells were stained with LipidSpot™ 610 and lipid droplets were imaged, quantified, and statistically analyzed (unpaired two-tailed student t-test, p = 0.000098). C) Conditioned medium from BRF-ctr or BRF-1304 adipocytes was added to MDA-MB-231 (human breast epithelial-like cell line), and after 24 hours, cells were stained with LipidSpot™ 610 and the number of lipid spots per cell was imaged, quantified, and statistically analyzed (Unpaired two-tailed student t-test, p = 0.0001). Scale bar = 10 μm. Credit: Modified from A. Zhao, et al. https://doi.org/10.1038/s41467-022-35305-2 reproduced under the Creative Commons license.
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Full Citation
Zhao, D., Wu, K., Sharma, S., Xing, F., Wu, S. Y., Tyagi, A., … & Watabe, K. (2022). Exosomal miR-1304-3p promotes breast cancer progression in African Americans by activating cancer-associated adipocytes. Nature Communications, 13(1), 7734. https://doi.org/10.1038/s41467-022-35305-2