UPK3B

UPK3B, short for uroplakin 3B, is a gene that encodes a member of the uroplakin family of integral membrane proteins expressed in the urothelium, the lining of the urinary tract. Uroplakins form rigid,22– to 32-meric plaques on the apical surface of umbrella cells, contributing to the urothelial barrier that protects underlying tissues from urine and helps regulate permeability. UPK3B is one of several uroplakin proteins that cooperate to assemble these plaques and maintain epithelial integrity.

Expression and localization of UPK3B are greatest in the urothelium of the bladder and are also detectable in other parts of the urinary tract, such as the ureter and renal pelvis. The protein is associated with urothelial differentiation and the maintenance of the specialized apical membrane characteristic of umbrella cells. In tissue, UPK3B localizes to urothelial plaques, where it is thought to participate in membrane organization and barrier function in concert with other uroplakins.

Structure and interactions of UPK3B reflect its role in plaque formation. As a uroplakin family member, UPK3B is a transmembrane protein that participates in the assembly of urothelial plaques, contributing to the stability and impermeability of the urothelium. Its exact molecular interactions are still being studied, but it is commonly discussed alongside other uroplakins such as UPK1, UPK2, and UPK3A in the context of plaque architecture.

Clinical significance is not fully established. Altered expression of uroplakins, including UPK3B, has been observed in urothelial carcinomas and other urothelial disorders, suggesting potential diagnostic or prognostic value in some contexts. However, UPK3B remains a relatively less characterized member of the family, and there is no widely recognized inherited disease linked specifically to germline UPK3B mutations. Further research is ongoing to clarify its roles in health and disease.