Reduction in Migratory Phenotype in a Metastasized Breast Cancer Cell Line via Downregulation of S100A4 and GRM3

To investigate phenotypic and genotypic alterations before and after bone metastasis, we conducted genome-wide mRNA profiling and DNA exon sequencing of two cell lines (TMD and BMD) derived from a mouse xenograft model. TMD cells were harvested from the mammary fat pad after transfecting MDA-MB-231 breast cancer cells, while BMD cells were isolated from the metastasized bone. Compared to BMD cells, TMD cells exhibited higher cellular motility. In contrast, BMD cells formed a spheroid with a smoother and more circular surface when co-cultured with osteoblasts. In characterizing mRNA expression using principal component analysis, S100 calcium-binding protein A4 (S100A4) was aligned to a principal axis associated with metastasis. Partial silencing of S100A4 suppressed migratory capabilities of TMD cells, while Paclitaxel decreased the S100A4 level and reduced TMD's cellular motility. DNA mutation analysis revealed that the glutamate metabotropic receptor 3 (GRM3) gene gained a premature stop codon in BMD cells, and silencing GRM3 in TMD cells altered their spheroid shape closer to that of BMD cells. Collectively, this study demonstrates that metastasized cells are less migratory due in part to the post-metastatic downregulation of S100A4 and GRM3. Targeting S100A4 and GRM3 may help prevent bone metastasis.