Tissue inhibitors of metalloproteinases (TIMPs) are endogenous inhibitors of matrix metalloproteinases (MMPs) and the balance between MMPs/TIMPs regulates the extracellular matrix (ECM) turnover and remodeling during normal development and pathogenesis. Increasing evidence indicates a much more complex role for TIMPs during tumor progression and angiogenesis, in addition to their regulation of MMP-mediated ECM degradation. In this article, we review both the MMP-dependent and -independent actions of TIMPs for the regulation of cell death, cell proliferation, and angiogenesis, with a particular emphasis on TIMP-1 in the regulation of tetraspanin/integrin-mediated cell survival signal transduction pathways.

This study identified CD63, a member of the tetraspanin family, as a TIMP-1 interacting protein by yeast twohybrid screening. Immunoprecipitation and confocal microscopic analysis confirmed CD63 interactions with TIMP-1, integrin b1, and their co-localizations on the cell surface of human breast epithelial MCF10A cells. TIMP-1 expression correlated with the level of active integrin b1 on the cell surface independent of cell adhesion. While MCF10A cells within a three-dimensional (3D) matrigel matrix form polarized acinar-like structures, TIMP-1 overexpression disrupted breast epithelial cell polarization and inhibited caspase-mediated apoptosis in centrally located cells, necessary for the formation and maintenance of the hollow acinar-like structures. Small hairpin RNA (shRNA)-mediated CD63 downregulation effectively reduced TIMP-1 binding to the cell surface, TIMP-1 colocalization with integrin b1, and consequently reversed TIMP-1-mediated integrin b1 activation, cell survival signaling and apoptosis inhibition. CD63 downregulation also restored polarization and apoptosis of TIMP-1 overexpressing MCF10A cells within a 3D-matrigel matrix. Taken together, the present study identified CD63 as a cell surface binding partner for TIMP-1, regulating cell survival and polarization via TIMP-1 modulation of tetraspanin/integrin signaling complex.

Galectin-3 is a multifunctional oncogenic protein found in the nucleus and cytoplasm and also the extracellular milieu. Although recent studies demonstrated an anti-apoptotic activity of galectin-3, neither the functional site nor the mechanism of how galectin-3 regulates apoptosis is known. In this study, we examined the subcellular localization of galectin-3 during apoptosis and investigated its anti-apoptotic actions. We report that galectin-3 translocates to the perinuclear membrane following a variety of apoptotic stimuli. Confocal microscopy and biochemical analysis revealed that galectin-3 is enriched in the mitochondria and prevents mitochondrial damage and cytochrome c release. Using a yeast two-hybrid system, we screened for galectin-3-interacting proteins that regulate galectin-3 localization and anti-apoptotic activity. Synexin, a Ca 2؉ -and phospholipid-binding protein, was one of the proteins identified. We confirmed direct interaction between galectin-3 and synexin by glutathione S-transferase pulldown assay in vitro. We showed that galectin-3 failed to translocate to the perinuclear membranes when expression of synexin was down-regulated using an oligodeoxyribonucleotide complementary to the synexin mRNA, suggesting a role for synexin in galectin-3 trafficking. Furthermore, synexin down-regulation abolished anti-apoptotic activity of galectin-3. Taken together, these results suggest that synexin mediates galectin-3 translocation to the perinuclear mitochondrial membranes, where it regulates mitochondrial integrity critical for apoptosis regulation.Galectin-3 is a 31-kDa member of the ␤-galactoside-binding family of proteins found widely in epithelial and immune cells. Expression of galectin-3 is associated with neoplastic progression and metastatic potential (1-5) in head and neck (6), thyroid (7), gastric (3), and colon (8) cancers, suggesting a role in oncogenesis. Galectin-3 modulates a variety of cellular processes. Extracellular galectin-3 mediates cell migration, cell adhesion, and cell/cell interactions, whereas nuclear galectin-3 is involved in pre-mRNA splicing (9 -11). Interestingly, recent studies showed that cytoplasmic, but not nuclear, galectin-3 is associated with tumor progression (12, 13). Yet, the role of cytoplasmic galectin-3 is unknown.We (15-17) and others (14,18,19) have previously shown that galectin-3 inhibits T-cell apoptosis induced by anti-Fas antibody and epithelial cell apoptosis induced by staurosporine, cisplatin, genistein, and anoikis. The anti-apoptotic activity of galectin-3 was also demonstrated in galectin-3-deficient mice. Peritoneal macrophages from galectin-3-deficient mice were more sensitive to apoptotic stimuli than those from control mice (20). The ability of galectin-3 to protect cells against apoptosis induced by agents working through different mechanisms suggests that galectin-3 regulates the common apoptosis commitment step.During the past decade, explosive progress has been made toward understanding the molecular basis for the regulation of the a...