Galectin-4 and sulfatides in apical membrane trafficking in enterocyte-like cells.
Bottom Line: Moreover, galectin-4 depletion altered the DRM association characteristics of apical proteins.Sulfatides with long chain-hydroxylated fatty acids, which were also enriched in DRMs, were identified as high-affinity ligands for galectin-4.Together, our data propose that interaction between galectin-4 and sulfatides plays a functional role in the clustering of lipid rafts for apical delivery.
Affiliation: Unité INSERM 560, 59045 Lille Cedex, France.
We have previously reported that 1-benzyl-2-acetamido-2-deoxy-alpha-D-galactopyranoside (GalNAc alpha-O-bn), an inhibitor of glycosylation, perturbed apical biosynthetic trafficking in polarized HT-29 cells suggesting an involvement of a lectin-based mechanism. Here, we have identified galectin-4 as one of the major components of detergent-resistant membranes (DRMs) isolated from HT-29 5M12 cells. Galectin-4 was also found in post-Golgi carrier vesicles. The functional role of galectin-4 in polarized trafficking in HT-29 5M12 cells was studied by using a retrovirus-mediated RNA interference. In galectin-4-depleted HT-29 5M12 cells apical membrane markers accumulated intracellularly. In contrast, basolateral membrane markers were not affected. Moreover, galectin-4 depletion altered the DRM association characteristics of apical proteins. Sulfatides with long chain-hydroxylated fatty acids, which were also enriched in DRMs, were identified as high-affinity ligands for galectin-4. Together, our data propose that interaction between galectin-4 and sulfatides plays a functional role in the clustering of lipid rafts for apical delivery.
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Mentions: The 2-D gel electrophoresis pattern of DRMs is shown in Fig. 1, and the identity of corresponding proteins in Table I. Besides flotillin-1, an ubiquitous marker of DRMs, the proteins identified could be divided into eight groups: (1) G proteins (G(i) α1,2,3, G11, GTPase-activating protein for Rab6); (2) proteins of SNARE machinery (NSF, SNAP23); (3) proteins of vesicular structures (Rab22a, annexin II); (4) chaperone proteins (heat-shock protein 90 (hsp90), BiP, endoplasmin, hsp73); (5) ionic pumps (V-ATPase, voltage-dependent anion channel 2); (6) membrane cytoskeleton and intermediate filament-associated proteins (αII-spectrin, α4-actinin, myosin light chain, periplakin, mitofilin, cytokeratins 8, 18, 19, and 20); (7) apical membrane glycoproteins dipeptidylpeptidase-IV (DPP-IV), carcinoembryonic antigen (CEA), nonspecific cross-reacting antigen, 5′-nucleotidase, CD59); and (8) a member of the galectin family of lectins, galectin-4. Proteins of the three latter groups were the major proteins of the DRMs.