Noncancerous Exosomes Establish a Growth Promoting Paracrine Effect on Triple Negative Breast Cancer Cells

Previous studies have demonstrated that breast cancer cells secrete exosomes into the tumor microenvironment, promoting tumor progression. However, the paracrine influence of noncancerous breast epithelial cells on the growth of triple-negative breast cancer (TNBC) cells has largely been overlooked. We hypothesize that exosomes from noncancerous breast epithelial cells are secreted into the tumor microenvironment, stimulating TNBC growth.

Exosome-containing media were prepared using exosomes isolated from triple-negative patient-derived xenografts (PDX) or noncancerous MCF-10A breast epithelial cells and used to treat MCF-7 or TNBC cells. Exosome-containing media from MCF-10A cells were characterized using ELISA. Subsequently, MDA-MB-231 and MDA-MB-468 cells treated with the MCF-10A exosome-containing media, and their impact on proliferation, migration, protein expression and gene expression were analyzed using Alamar blue assays, wound healing assays, western blotting, immunofluorescence, and gene expression arrays, respectively.

Exosomes extracted from the PDX and MCF-10A cells stimulated the growth of all examined cell lines. The MCF-10A exosome-containing media expressed CD9 and CD63; however, the MDA-MB-231 and MDA-MB-468 cells treated with these media exhibited differential expression of these proteins. Exposure of MDA-MB-231 and MDA-MB-468 cells to the MCF-10A exosome-containing media stimulated their growth and migration. Exposure of MDA-MB-231 cells to MCF-10A exosome-containing media caused down-regulation of genes involved in cell-cell adhesion, DNA damage response, epithelial-mesenchymal transition drivers, tumor suppression, and up-regulation of the MYC oncogene.

Secreted factors from noncancerous cells, identified as exosomes, induce cancer cell proliferation and prime the tumor microenvironment by enhancing disease progression-associated pathways.