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Am J Physiol. 1996 Jan;270(1 Pt 1):G176-83.

Polarized GP2 secretion in MDCK cells via GPI targeting and apical membrane-restricted proteolysis.

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Department of Medicine, Stanford University, California 94305-5487, USA.


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.

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