Involvement of Vps33a in the Fusion of Uroplakin‐Degrading Multivesicular Bodies with Lysosomes

Abstract

The apical surface of the terminally differentiated mouse bladder urothelium is largely covered by urothelial plaques, consisting of hexagonally packed 16-nm uroplakin particles. These plaques are delivered to the cell surface by fusiform vesicles (FVs) that are the most abundant cytoplasmic organelles. We have analyzed the functional involvement of several proteins in the apical delivery and endocytic degradation of uroplakin proteins. Although FVs have an acidified lumen and Rab27b, which localizes to these organelles, is known to be involved in the targeting of lysosome-related organelles (LROs), FVs are CD63 negative and are therefore not typical LROs. Vps33a is a Sec1-related protein that plays a role in vesicular transport to the lysosomal compartment. A point mutation in mouse Vps33a (Buff mouse) causes albinism and bleeding (Hermansky-Pudlak syndrome) because of abnormalities in the trafficking of melanosomes and platelets. These Buff mice showed a novel phenotype observed in urothelial umbrella cells, where the uroplakin-delivering FVs were almost completely replaced by Rab27b-negative multivesicular bodies (MVBs) involved in uroplakin degradation. MVB accumulation leads to an increase in the amounts of uroplakins, Lysosomal-associated membrane protein (LAMP)-1/2, and the activities of β-hexosaminidase and β-glucocerebrosidase. These results suggest that FVs can be regarded as specialized secretory granules that deliver crystalline arrays of uroplakins to the cell surface, and that the Vps33a mutation interferes with the fusion of MVBs with mature lysosomes thus blocking uroplakin degradation.

Atg16L1 deficiency confers protection from uropathogenic Escherichia coli infection in vivo

“…1 G and H) (P < 0.05 and P < 0.01, respectively). Third, given that this vesicular system is responsible for uroplakin transport and recycling and that disruption in vesicular trafficking of FVs and MVBs is associated with aberrant MVB accumulation (28,30,33), we next determined the effect of Atg16L1 deficiency on uroplakin receptor expression. We found increased Up1a expression in Atg16L1 HM bladders ( Fig.…”

“…These cells are highly specialized to rapidly expand and shrink as the bladder fills and contracts, and this function requires large plaques of hexagonal arrays of uroplakin protein complexes, which are transported by discoidal fusiform vesicles (FVs) and multivesicular bodies (MVBs) to maintain cellular architecture and barrier properties (30,31). UPEC uses the uroplakins (Up1a) as receptors to facilitate invasion and entry into these urothelial cells (30)(31)(32). We reasoned that Atg16L1 deficiency might alter this membranous intracellular network, because changes in intracellular membranes associated with granule exocytosis are observed in the intestinal Paneth cell in Atg16L1 HM mice (11).…”

Expression and localization of four uroplakins in urothelial preneoplastic lesions

“…Small plaques are observed on a population of immature discoidal vesicles, which are derived from the trans-Golgi network (TGN). These vesicles, recognized by their slightly dilated profiles, are designated as immature fusiform vesicles (iFVs) (Guo et al 2009). Urothelial plaques gradually expand until they cover the entire surface the vesicles, which acquire a flattened, elongated disc configuration, leading to their designation as mature fusiform vesicles (mFVs) (Wu et al 1990;Tu et al 2002;Guo et al 2009).…”

“…These vesicles, recognized by their slightly dilated profiles, are designated as immature fusiform vesicles (iFVs) (Guo et al 2009). Urothelial plaques gradually expand until they cover the entire surface the vesicles, which acquire a flattened, elongated disc configuration, leading to their designation as mature fusiform vesicles (mFVs) (Wu et al 1990;Tu et al 2002;Guo et al 2009). Microridges and mFVs are therefore two morphological hallmarks of terminal urothelial cell differentiation (Romih and Jezernik 1996;Veranič et al 2004;Romih et al 2005).…”

Targeting protein-trafficking pathways alters melanoma treatment sensitivity

“…The VPS33A molecule has been implicated in mediating protein trafficking (9). Homozygous mutation of Vps33A in the buff mouse strain causes a lightened coat color and aberrantly formed eumelanosomes, the intracellular organelles in which brown/black melanin pigment is synthesized (10), suggesting a role for VPS33A in trafficking proteins targeted to eumelanosomes.…”