UPK3A

UPK3A, or uroplakin 3A, is a human gene encoding a member of the uroplakin family of urothelial membrane proteins. Uroplakins are major constituents of specialized membrane plaques that cover the apical surface of superficial urothelial cells and contribute to the barrier and structural properties of the urinary tract epithelium.

The UPK3A protein is a single-pass transmembrane glycoprotein that localizes to the apical membrane of umbrella cells in the urothelium. It participates in the formation of urothelial plaques through interactions with other uroplakins, aiding the assembly of stable, organized membrane domains that support the bladder’s expanding and contracting surface during filling and voiding.

Expression of UPK3A is most prominent in urothelial tissues, including the bladder, ureters, and renal pelvis, with limited expression in most other tissues. Its presence helps maintain barrier function against urine and protects underlying tissues from mechanical stress.

Clinical and research notes indicate that altered expression or mislocalization of UPK3A has been observed in urothelial disorders, including urothelial carcinomas. Because uroplakins are markers of urothelial differentiation, UPK3A is often evaluated in pathology to help characterize urothelial origin of tumors. The gene is conserved across mammals, reflecting an evolutionarily important role in urothelial biology. While no single inherited disease has been definitively linked to UPK3A, ongoing research continues to clarify its contributions to urothelial health and disease.