Overexpression of matrix metalloproteinase‐9 in breast cancer cell lines remarkably increases the cell malignancy largely via activation of transforming growth factor beta/SMAD signalling

OBJECTIVES: Matrix metalloproteinase 9 (MMP‐9) has been frequently noticed in the breast cancers. In this study, we aim to investigate the associations of MMP‐9 with the activation of transforming growth factor beta (TGF‐β)/SMAD signalling and the malignancy of breast malignant tumour cells. MATERIALS AND METHODS: The distributions of MMP‐9 and TGF‐β in the tissues of canine breast cancers were screened by immunohistochemical assays. A recombinant plasmid expressing mouse MMP‐9 was generated and transiently transfected into three different breast cancer cell lines. Cell Counting Kit‐8 and colony formation assay were used to study cell viability. Migration and invasion ability were analysed by wound assay and transwell filters. Western blot and quantitative real‐time PCR were used to determine the protein and mRNA expression. RESULT: Remarkable strong MMP‐9 and TGF‐β signals were observed in the malignant tissues of canine breast cancers. In the cultured three cell lines receiving recombinant plasmid expressing mouse MMP‐9, the cell malignancy was markedly increased, including the cell colony formation, migration and epithelial‐mesenchymal transition. The levels of activated TGF‐β, as well as SMAD4, SMAD2/3 and phosphorylation of SMAD2, were increased, reflecting an activation of TGF‐β/SMAD signalling. We also demonstrated that the inhibitors specific for MMP‐9 and TGF‐β sufficiently blocked the overexpressing MMP‐9 induced the activation of SMAD signalling and enhancement on invasion in the tested breast cancer cell lines. CONCLUSION: Overexpression of MMP‐9 increases the malignancy of breast cancer cell lines, largely via activation of the TGF‐β/SMAD signalling.