Related Experiment Video
Updated: May 27, 2026

Imaging the Intracellular Trafficking of APP with Photoactivatable GFP
Published on: October 17, 2015
Multiple biosynthetic trafficking routes for apically secreted proteins in MDCK cells
Polly E Mattila1, Robert T Youker, Di Mo
1Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh, Pittsburgh, PA, USA.
None:
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.
Related Concept Videos
Overview of Secretory Vesicles
Various proteins regulate the aggregation of molecules inside the secretory vesicles. Chromogranins...
ER Retrieval Pathway
The ER uses many checkpoints to prevent the entry of incorrectly folded or a resident protein as cargo onto a transport vesicle. These mechanisms...
Introduction to Membrane Traffic
The transport of soluble and membrane proteins is mediated by transport vesicles that collect cargo from one cellular compartment and deliver it to another by fusing with the target organelle membrane. The Rab...
Clathrin Coated Vesicles
Post-translational Translocation of Proteins to the RER
Targeting proteins to the ER
Hsp40 and Hsp70 chaperone molecules bind the translated proteins in the cytosol to prevent their folding. The chaperone binding helps to keep the signal...
Bacterial Translocation and Protein Secretion

