title: Carbachol-induced MUC17 endocytosis is concomitant with NHE3 internalization and CFTR membrane recruitment in enterocytes.
abstract: We have reported that transmembrane mucin MUC17 binds PDZ protein PDZK1, which retains MUC17 apically in enterocytes. MUC17 and transmembrane mucins MUC3 and MUC12 are suggested to build the enterocyte apical glycocalyx. Carbachol (CCh) stimulation of the small intestine results in gel-forming mucin secretion from goblet cells, something that requires adjacent enterocytes to secrete chloride and bicarbonate for proper mucin formation. Surface labeling and confocal imaging demonstrated that apically expressed MUC17 in Caco-2 cells and Muc3(17) in murine enterocytes were endocytosed upon stimulation with CCh. Relocation of MUC17 in response to CCh was specific as MUC3 and MUC12 did not relocate following CCh stimulation. MUC17 colocalized with PDZK1 under basal conditions, while MUC17 relocated to the terminal web and into early endosomes after CCh stimulation. CCh stimulation concomitantly internalized the Na(+/)H(+) exchanger 3 (NHE3) and recruited cystic fibrosis transmembrane conductance regulator (CFTR) to the apical membranes, a process that was important for CFTR-mediated bicarbonate secretion necessary for proper gel-forming mucin unfolding. The reason for the specific internalization of MUC17 is not understood, but it could limit the diffusion barrier for ion secretion caused by the apical enterocyte glycocalyx or alternatively act to sample luminal bacteria. Our results reveal well-orchestrated mucus secretion and trafficking of ion channels and the MUC17 mucin.
authors.affiliation: Department of Medical Biochemistry, University of Gothenburg, Gothenburg, Sweden.
authors.forename: Thaher
authors.initials: T
authors.lastname: Pelaseyed
authors.forename: Jenny K
authors.initials: JK
authors.lastname: Gustafsson
authors.forename: Ida J
authors.initials: IJ
authors.lastname: Gustafsson
authors.forename: Anna
authors.initials: A
authors.lastname: Ermund
authors.forename: Gunnar C
authors.initials: GC
authors.lastname: Hansson
mesh_terms: D000818:Animals; D019921:Biotinylation; D018938:Caco-2 Cells; D002217:Carbachol / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects* / Q000378:metabolism; D018679:Cholinergic Agonists / Q000494:pharmacology*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000187:drug effects* / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects*; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism; D020895:Enterocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D008297:Male; D008565:Membrane Proteins; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D009077:Mucins / Q000378:metabolism*; D021381:Protein Transport; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013997:Time Factors
chemical_list: C505032:CFTR protein, human; D002352:Carrier Proteins; D018679:Cholinergic Agonists; C450720:MUC17 protein, human; D008565:Membrane Proteins; D009077:Mucins; C484659:PDZK1 protein, human; C000613385:SLC9A3 protein, human; C000613386:Slc9a3 protein, mouse; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D002217:Carbachol
keywords: CFTR; MUC17; Muc3(17), PDZK1; NHE3