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Multiple Biosynthetic Trafficking Routes for Apically Secreted Proteins in MDCK Cells
Author(s) -
Mattila Polly E.,
Youker Robert T.,
Mo Di,
Bruns Jennifer R.,
Cresawn Kerry O.,
Hughey Rebecca P.,
Ihrke Gudrun,
Weisz Ora A.
Publication year - 2012
Publication title -
traffic
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.677
H-Index - 130
eISSN - 1600-0854
pISSN - 1398-9219
DOI - 10.1111/j.1600-0854.2011.01315.x
Subject(s) - microbiology and biotechnology , biology , endocytic cycle , endosome , secretion , fluorescence recovery after photobleaching , apical membrane , transport protein , glycan , protein targeting , membrane protein , protein sorting signals , biochemistry , signal peptide , endocytosis , receptor , glycoprotein , intracellular , peptide sequence , membrane , gene
Many newly synthesized membrane proteins traverse endocytic intermediates en route to the surface in polarized epithelial cells; however, the biosynthetic itinerary of secreted proteins has not been elucidated. We monitored the trafficking route of two secreted proteins with different apical sorting signals: the N ‐glycan‐dependent cargo glycosylated growth hormone ( gGH ) and Ensol , a soluble version of endolyn whose apical sorting is independent of N ‐glycans. Both proteins were observed to colocalize in part with apical recycling endosome ( ARE ) markers. Cargo that lacks an apical targeting signal and is secreted in a nonpolarized manner did not localize to the ARE . Expression of a dominant‐negative mutant of myosin Vb , which disrupts ARE export of glycan‐dependent membrane proteins, selectively inhibited apical release of gGH but not Ensol . Fluorescence recovery after photobleaching ( FRAP ) measurements revealed that gGH in the ARE was less mobile than Ensol , consistent with tethering to a sorting receptor. However, knockdown of galectin‐3 or galectin‐4, lectins implicated in apical sorting, had no effect on the rate or polarity of gGH secretion. Together, our results suggest that apically secreted cargoes selectively access the ARE and are exported via differentially regulated pathways.