The novel functions of TIMP-1: Regulation of apoptosis and epithelial-mesenchymal transition in breast epithelial cells

Recent studies demonstrate that Tissue inhibitor of metalloproteinase-1 (TIMP-1) is a potent inhibitor of apoptosis in a variety of cell types through either a MMP-dependent or -independent mechanism. Recently, we identified CD63, a member of the tetraspanin family of proteins, as a cell surface binding partner for TIMP-1 which modulates integrin-mediated survival pathways in the human breast epithelial cell line MCF10A. In addition, I have made a novel finding that TIMP-1 expression in MCF10A cells induces phenotypic changes in cell morphology, cell-cell adhesion, cytoskeletal remodeling and migrative phenotype taking on the hallmarks of an epithelial-mesenchymal transition (EMT). This is evidenced by loss of the epithelial cell adhesion molecules E-cadherin and beta-catenin, with an increase in the mesenchymal markers vimentin, N-cadherin, fibronectin. TIMP-1 overexpression resulted in an increase in MCF10A cell migration dependent of CD63. Treatment with rTIMP-1 also led to a loss of E-cadherin in MCF10A cells. Interestingly, TIMP-1 signaling induced Twist expression, an EMT master transcription factor known to suppress E-cadherin gene transcription and upregulate mesenchymal markers. SiRNA-mediated Twist knockdown restored E-cadherin expression in TIMP-1 overexpressing MCF10A cells, demonstrating a functional significance of Twist in TIMP-1 mediated EMT. We further demonstrated that TIMP-1 induces Twist expression and EMT-like changes in a CD63-dependent manner. Furthermore, analysis of TIMP-1 structural mutants unveiled that TIMP-1 interaction with CD63, activation of cell survival signaling, and induction of EMT in MCF10A cells does not require the MMP-inhibitory domain of TIMP-1. Taken together, we hypothesize that TIMP-1 binding to CD63 activates intracellular signal transduction pathways and leads to inhibition of apoptosis and induction of EMT-like changes in breast epithelial cells, potentially facilitating breast cancer progression. Our study of the pleiotropic activities of TIMP-1 at the molecular level may enhance our understanding of TIMP-1's multi-functions during tumor progression and metastasis. This information may also be useful in designing more rational, mechanism-based therapeutic interventions aimed at modulating the activities of MMPs and TIMPs.