Figure 10. .

Model depicting requirements of V-ATPase activity for biosynthetic sorting and trafficking of apical membrane proteins. V-ATPase activity promotes apical sorting of O-glycosylated membrane proteins in the TGN and subsequent trafficking of both O- and N-glycosylated membrane proteins through distinct Rab8 and Rab11 carriers. In the absence of V-ATPase activity, O-glycosylated membrane proteins become randomly missorted to basolateral and apical trafficking routes. Additionally, apical delivery through Rab11 carriers is acutely blocked, and Rab8 tubular carriers collapse into vacuoles. Over time, aberrant vacuoles fuse with apical compartments and accumulate apical and lysosomal membrane proteins.