Galectin-3 Translocates to the Perinuclear Membranes and Inhibits Cytochrome c Release from the Mitochondria

Abstract

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...

Expression of galectin-3 correlates with apoptosis in pituitary adenoma cells

“…Gal-3 may inhibit the apoptosis of epithelial cells induced by staurosporine, cis-diamminedichloroplatinum (DDP), genistein and anoikis [10] . In some human cancers, Gal-3 level shows a direct correlation with the progress of cancers.…”

Plant Pectin: A Potential Source for Cancer Suppression

“…Several investigations suggest that targeting galectin-3 increases cancer cell sensitivity towards various chemotherapeutic agents such as cisplatin, staurosporine (Yu et al, 2002), etoposide (Fukumori et al, 2006) and doxorubicin (Johnson et al, 2007). From these studies it is clear that pectin, CP and MCP, as a galectin-3 inhibitor, may hold a significant role in cancer chemotherapy.…”

Galectin-3 in apoptosis, a novel therapeutic target

“…This protein was shown to modulate cell growth, to control the cell cycle, and to be involved in the regulation of apoptosis. Galectin-3 has been shown to translocate either from the cytosol or from the nucleus to the mitochondria following exposure to apoptotic stimuli (Yu et al, 2002) and to block changes in the mitochondrial membrane potential, thereby preventing apoptosis (Matarrese et al, 2000). It is indicated that galectin-3 might exert its anti-apoptotic activity by interacting with other apoptosis regulators that function in the mitochondria.…”