Galectin-3 translocates to the perinuclear membranes and inhibits cytochrome c release from the mitochondria. A role for synexin in galectin-3 translocation.
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 pull-down 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.
Yu
Fei
F
Department of Pathology, Wayne State University School of Medicine and Karmanos Cancer Institute, Detroit, Michigan 48201, USA.
Finley
Russell L
RL
Raz
Avraham
A
Kim
Hyeong-Reh Choi
HR
D017310:Annexin A7 / Q000378:metabolism*; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001943:Breast Neoplasms / Q000473:pathology; D020169:Caspases / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000378:metabolism; D005260:Female; D037502:Galectin 3; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism*; D009685:Nuclear Envelope / Q000378:metabolism*; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D017310:Annexin A7; D000943:Antigens, Differentiation; D003574:Cytochrome c Group; D037502:Galectin 3; D008562:Membrane Glycoproteins; D011993:Recombinant Fusion Proteins; D003576:Electron Transport Complex IV; D020169:Caspases; D019311:Staurosporine