Department of Cell Biology and Cell Pathology, Philipps-Universität Marburg, D-35033, Marburg, Germany.
Traffic. 2013 Sep;14(9):1014-27. doi: 10.1111/tra.12086. Epub 2013 Jun 25.
The β-galactoside binding protein galectin-3 is highly expressed in a variety of epithelial cell lines. Polarized MDCK cells secrete this lectin predominantly into the apical medium by non-classical secretion. Once within the apical extracellular milieu, galectin-3 can re-enter the cell followed by passage through endosomal organelles and modulate apical protein sorting. Here, we could show that galectin-3 is internalized by non-clathrin mediated endocytosis. Within endosomal organelles this pool associates with newly synthesized neurotrophin receptor in the biosynthetic pathway and assists in its membrane targeting. This recycling process is accompanied by transient interaction of galectin-3 with detergent insoluble membrane microdomains in a lactose- and pH-dependent manner. Moreover, in the presence of lactose, apical sorting of the neurotrophin receptor is affected following endosomal deacidification. Taken together, our results suggest that internalized galectin-3 directs the subcellular targeting of apical glycoproteins by membrane recycling.
β-半乳糖苷结合蛋白半乳糖凝集素-3在多种上皮细胞系中高度表达。极化的 MDCK 细胞通过非经典分泌将这种凝集素主要分泌到顶端培养基中。一旦进入顶端细胞外环境，半乳糖凝集素-3可以重新进入细胞，然后通过内体细胞器传递，并调节顶端蛋白分拣。在这里，我们可以证明半乳糖凝集素-3是通过非网格蛋白介导的内吞作用内化的。在内体细胞器中，该池与生物合成途径中新生的神经营养因子受体结合，并协助其膜靶向。这个回收过程伴随着半乳糖凝集素-3与去污剂不溶性膜微区的瞬时相互作用，这种相互作用依赖于乳糖和 pH 值。此外，在乳糖存在的情况下，内体去酸化后，神经营养因子受体的顶端分拣受到影响。总之，我们的结果表明，内化的半乳糖凝集素-3通过膜回收来指导顶端糖蛋白的亚细胞靶向。
