title: Sialylation of N-linked glycans mediates apical delivery of endolyn in MDCK cells via a galectin-9-dependent mechanism.
abstract: The sialomucin endolyn is implicated in adhesion, migration, and differentiation of various cell types. Along rat kidney tubules, endolyn is variously localized to the apical surface and endosomal/lysosomal compartments. Apical delivery of newly synthesized rat endolyn predominates over direct lysosomal delivery in polarized Madin-Darby canine kidney cells. Apical sorting depends on terminal processing of a subset of lumenal N-glycans. Here we dissect the requirements of N-glycan processing for apical targeting and investigate the underlying mechanism. Modulation of glycan branching and subsequent polylactosamine elongation by knockdown of N-acetylglucosaminyltransferase III or V had no effect on apical delivery of endolyn. In contrast, combined but not individual knockdown of sialyltransferases ST3Gal-III, ST3Gal-IV, and ST6Gal-I, which together are responsible for addition of α2,3- and α2,6-linked sialic acids on N-glycans, dramatically decreased endolyn surface polarity. Endolyn synthesized in the presence of kifunensine, which blocks terminal N-glycan processing, reduced its interaction with several recombinant canine galectins, and knockdown of galectin-9 (but not galectin-3, -4, or -8) selectively disrupted endolyn polarity. Our data suggest that sialylation enables recognition of endolyn by galectin-9 to mediate efficient apical sorting. They raise the intriguing possibility that changes in glycosyltransferase expression patterns and/or galectin-9 distribution may acutely modulate endolyn trafficking in the kidney.
authors.affiliation: Renal Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
authors.forename: Di
authors.initials: D
authors.lastname: Mo
authors.forename: Simone A
authors.initials: SA
authors.lastname: Costa
authors.forename: Gudrun
authors.initials: G
authors.lastname: Ihrke
authors.forename: Robert T
authors.initials: RT
authors.lastname: Youker
authors.forename: Nuria
authors.initials: N
authors.lastname: Pastor-Soler
authors.forename: Rebecca P
authors.initials: RP
authors.lastname: Hughey
authors.forename: Ora A
authors.initials: OA
authors.lastname: Weisz
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D004285:Dogs; D004591:Electrophoresis, Polyacrylamide Gel; D051930:Endolyn / Q000235:genetics / Q000378:metabolism*; D037161:Galectins / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D061985:Madin Darby Canine Kidney Cells; D018613:Microscopy, Confocal; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism*; D034622:RNA Interference; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012794:Sialic Acids / Q000378:metabolism; D012799:Sialyltransferases / Q000235:genetics / Q000378:metabolism; D000094663:beta-Galactoside alpha-2,3-Sialyltransferase
chemical_list: D000470:Alkaloids; D051930:Endolyn; D037161:Galectins; D011134:Polysaccharides; D012794:Sialic Acids; C513912:galectin 9, rat; C065629:kifunensine; D017351:N-Acetylglucosaminyltransferases; C054599:beta-1,4-mannosyl-glycoprotein beta-1,4-N-acetylglucosaminyltransferase; C052254:alpha-1,6-mannosylglycoprotein beta 1,6-N-acetylglucosaminyltransferase; D012799:Sialyltransferases; D000094663:beta-Galactoside alpha-2,3-Sialyltransferase