Morphological and molecular characterization of the human breast epithelial cell line M13SV1 and its tumorigenic derivatives M13SV1-R2-2 and M13SV1-R2-N1

The estrogen receptor-positive M13SV1 breast epithelial cell line was proposed to be a suitable in vitro model for breast cancer research since two derivatives with graduated tumorigenicity-M13SV1-R2-2 and M13SV1-R2-N1-are available for this cell line. In the present study, these three cell lines were comparatively examined for their morphological and their biochemical properties on the molecular level.

Due to the molecular and morphological features, the M13SV1 cell line and its tumorigenic derivatives seem to be less suitable as in vitro models than other cell lines such as the MCF-10A cell line which displays proper acini formation in 3D culture.

A transcriptomic approach (gene array analysis) was chosen to unravel differences in gene expression among the three cell lines. Network analysis was conducted to identify deregulated signaling pathways. Cellular viability was determined by impedance measurements as well as by neutral red uptake assay. Apoptosis was determined by using a caspase assay. For morphological characterization, cells were grown in three-dimensional cell culture, and cellular differentiation and spheroid formation was followed by immunofluorescence staining by using confocal laser scanning microscopy.

The gene array results indicated that there were only marginal differences in gene expression among the three cell lines. Network analysis predicted the R2-N1 derivative (1) to display enhanced apoptosis and (2) to have a higher migration capability compared to its parent cell line M13SV1. Enhanced apoptosis was confirmed by elevated caspase activity, and increased migration was observed in 3D culture when cells migrated out of the globular spheroids. In 3D cell culture, all three cell lines similarly formed spheroids within three days, but there was no acini formation until day 21 which is indicated by a growth arrest around day 15, cellular polarization, and the formation of hollow lumen inside the spheroids. These characteristics, however, are crucial to study, e.g., the differentiation process of breast epithelial cells in vitro.