UPK3A (uroplakin 3A) is a structural component of the asymmetric unit membrane (AUM) in terminally differentiated urothelial cells, playing a critical role in maintaining bladder barrier integrity. The protein contributes to AUM-cytoskeleton interactions and formation of the urothelial glycocalyx, which protects against bacterial adherence 1. In healthy bladders, UPK3A+ umbrella cells form a specialized differentiated layer essential for normal barrier function. UPK3A expression is significantly reduced in Hunner-type interstitial cystitis/bladder pain syndrome (HIC), where urothelial damage and barrier dysfunction predominate 1. The TLR3-NR2F6 signaling axis has been identified as a key pathway responsible for UPK3A+ umbrella cell injury in HIC, suggesting therapeutic targets for restoring urothelial barrier function 1. Beyond bladder physiology, elevated urinary UPK3A serves as a sensitive biomarker for bladder cancer detection (83% sensitivity and specificity at optimal cutoff) 2, outperforming cytology and NMP22 testing. Ectopic UPK3A expression in gastric cancer promotes malignant progression by suppressing p53 signaling 3. Additionally, UPK3A mutations are implicated in congenital kidney disorders in Phelan-McDermid syndrome and vesicoureteral reflux, and UPK3A hypermethylation occurs in meningiomas with increasing frequency across tumor grades 456.