Abstract
Uroplakins (UPs) play an essential role in maintaining an effective urothelial permeability barrier at the level of superficial urothelial cell (UC) layer. Although the organization of UPs in the apical plasma membrane (PM) of UCs is well known, their transport in UCs is only partially understood. Here, we dissected trafficking of UPs and its differentiation-dependent impact on Golgi apparatus (GA) architecture. We demonstrated that individual subunits UPIb and UPIIIa are capable of trafficking from the endoplasmic reticulum to the GA in UCs. Moreover, UPIb, UPIIIa or UPIb/UPIIIa expressing UCs revealed fragmentation and peripheral redistribution of Golgi-units. Notably, expression of UPIb or UPIb/UPIIIa triggered similar GA fragmentation in MDCK and HeLa cells that do not express UPs endogenously. The colocalization analysis of UPIb/UPIIIa-EGFP and COPI, COPII or clathrin suggested that UPs follow constitutively the post-Golgi route to the apical PM. Depolymerisation of microtubules leads to complete blockade of the UPIb/UPIIIa-EGFP post-Golgi transport, while disassembly of actin filaments shows significantly reduced delivery of UPIb/UPIIIa-EGFP to the PM. Our findings show the significant effect of the UPs expression on the GA fragmentation, which enables secretory Golgi-outpost to be distributed as close as possible to the sites of cargo delivery at the PM.
Highlights
Plasma membrane proteins must be correctly synthesized, processed and transported to the plasma membrane (PM) in order to perform their specialized function
Scanning electron microscopy (EM) analysis of the cell surface topography revealed an apical PM of superficial urothelial cell (UC) mainly shaped in rounded ridges and rarely in microvilli (Fig. 1B), which is all in line with our previously published results[32,33]
fracture replica immunolabeling (FRIL) showed that anti-UPs antibodies recognized intramembrane particles that most likely represent 16-nm UP particles, which were organized into urothelial plaques (Fig. 1D)
Summary
Plasma membrane proteins must be correctly synthesized, processed and transported to the plasma membrane (PM) in order to perform their specialized function. The uroplakins (UPs), i.e., UPIa (27 kDa), UPIb (28 kDa), UPII (15 kDa) and UPIIIa (47 kDa)[1,2,3,4,5] are expressed in a differentiation-dependent manner[2,6] and are highly organized in so called urothelial plaques in the apical PM of highly differentiated superficial urothelial cells (UCs)[7,8]. When they are correctly assembled in the apical PM they provide the structural basis for the blood-urine barrier in the urinary bladder. Actin filaments (AFs) are greatly retracted from the subapical cytoplasm of terminally differentiated superficial UCs29 and microtubules (MTs) are rearranged during the differentiation of UCs26,30
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
