Newly synthesized and recycling pools of the apical protein gp135 do not occupy the same compartments

Abstract
Polarized epithelial cells sort newly synthesized and recycling plasma membrane proteins into distinct trafficking pathways directed to either the apical or basolateral membrane domains. While the trans Golgi network is a well‐established site of protein sorting, increasing evidence indicates a key role for endosomes in the initial trafficking of newly synthesized proteins. Both basolateral and apical proteins have been shown to traverse endosomes en route to the plasma membrane. In particular, apical proteins traffic through either subapical early or recycling endosomes. Here we use the SNAP tag system to analyze the trafficking of the apical protein gp135, also known as podocalyxin. We show that newly synthesized gp135 traverses the apical recycling endosome, but not the apical early endosomes. In contrast, post‐endocytic gp135 is delivered to the apical early endosome before recycling back to the apical membrane. The pathways pursued by the newly synthesized and recycling gp135 populations do not detectably intersect, demonstrating that the biosynthetic and post‐endocytic pools of this protein are subjected to distinct sorting processes.

In polarized epithelial cells, apical or basolateral membrane proteins are sorted in endosomal compartments en route to their target membranes. We used the SNAP tag system to study the intracellular trafficking of the apical protein gp135. Newly synthesized gp135 was shown to traverse the apical recycling endosome (ARE), wh...

Source: Traffic - September 20, 2016 Category: Research Authors: Emily H. Stoops, Michael Hull, Michael J. Caplan Tags: Original Article Source Type: research