title: Polarized GP2 secretion in MDCK cells via GPI targeting and apical membrane-restricted proteolysis.
abstract: The major zymogen granule membrane protein in the exocrine pancreas is glycoprotein 2 (GP2), a glycosyl phosphatidylinositol (GPI)-linked membrane protein. Despite its GPI anchor, GP2 is secreted into the pancreatic duct. We examined the mechanism underlying the secretion of GP2 in isolated pancreatic acini and transfected Madin-Darby canine kidney (MDCK) cells (MDCK-GP2). MDCK-GP2 cells release GP2 almost exclusively (> 95%) from the apical membrane. Using GP2 as a model, we defined a novel mechanism of polarized protein secretion in which a secretory protein is targeted via a GPI anchor to the apical plasma membrane, whereupon the mature form is released by proteolysis. Furthermore, we described two features of MDCK cells that enhance the polarized release of GP2: an apical plasma membrane-restricted distribution of the protease responsible for GP2 membrane cleavage, and a transcytotic pathway to reroute basolateral plasma membrane GP2 to the apical cell surface.
authors.affiliation: Department of Medicine, Stanford University, California 94305-5487, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Fritz
authors.forename: A W
authors.initials: AW
authors.lastname: Lowe
mesh_terms: D000818:Animals; D000976:Antipain / Q000494:pharmacology; D007611:Aprotinin / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D016764:Cell Polarity; D003594:Cytoplasmic Granules / Q000378:metabolism; D004285:Dogs; D010450:Endopeptidases / Q000378:metabolism; D058851:GPI-Linked Proteins; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D007976:Leupeptins / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D008970:Molecular Weight; D010179:Pancreas / Q000166:cytology / Q000378:metabolism; D010447:Peptide Hydrolases / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: D058851:GPI-Linked Proteins; D017261:Glycosylphosphatidylinositols; C066161:Gp2 protein, rat; D007976:Leupeptins; D008562:Membrane Glycoproteins; D011480:Protease Inhibitors; D000976:Antipain; D007611:Aprotinin; D010738:Type C Phospholipases; D010450:Endopeptidases; D010447:Peptide Hydrolases; C032854:leupeptin