Regulation of MT1-MMP in breast carcinoma by microenvironmental cues

Matrix metalloproteinases (MMPs) play a major role in the degradation of the extracellular matrix during cancer progression. A lot of interest has been recently directed to Membrane Type-1 Matrix Metalloproteinase (MT1-MMP), a surface metalloproteinase closely involved in the invasive process. The expression of MT1-MMP in different breast carcinoma cell lines positively correlated with the invasive potential of the cells and negatively correlated with their Estrogen Receptor-α (ER-α) status. Since little is known about gene regulation of MT1-MMP in cancer cells, we studied the role of different growth factors and hormones on the transcriptional modulation of MT1-MMP. Treatment of breast carcinoma cell lines with transforming growth factor-β (TGF-β) upregulated the expression of MT1-MMP at the mRNA level and promoted invasion through a basement membrane matrix. However, we did not observe transcriptional regulation of MT1-MMP when promoter reporter assays were used. Moreover, the stability of the MT1-MMP message was not affected by TGF-β treatment as determined by Actinomycin-D treatments. Alternative mechanisms could include changes in chromatin structure and DNA modifications that may affect MT1-MMP expression induced by TGF-β. ^ The role of hypoxic microenvironments on MT1-MMP function was also investigated. Hypoxia markedly increased the invasion capacity of the MT1-MMP expressing cells, MDA-MB-435 and MDA-MB-231. Blocking either MT1-MMP or MMP-2 was effective in reducing the hypoxia-induced invasion. Serum-free reconstitution experiments confirmed the involvement of the MT1-MMP/MMP2/TIMP-2 complex in this hypoxia-induced response. Overexpression of MT1MMP in a poorly invasive breast cancer cell line, T47-D, promoted hypoxia-induced invasion and MMP-2 activation. Cell surface accumulation and activation of MT1-MMP without apparent regulation at the mRNA or protein levels indicated a post-translational adaptive response to hypoxia. Inhibition of the small GTPase RhoA eliminated the hypoxia-induced invasion and blocked the localization of MT1-MMP to the plasma membrane. Zymographic and molecular analysis of human breast tumors showed a strong correlation between hypoxic microenvironments and MMP-2 activation without changes in MT1-MMP expression. Our studies suggest that hypoxic tumor microenvironments promote breast cancer invasion through an MT1-MMP dependent mechanism.