About UPK / Uroplakin:
The urothelium is considered a specialized epithelium found in the interior cover of the urinary tract. Uroplakin, a urothelial plaque found in glycoprotein heteropolymer, is among the structures that give the urothelium its unique features. Uroplakin has four distinct complexes; UPIa, UPIb, UPII, UPIII.
Uroplakin is mainly found in urine, blood, and tissues. Urothelial plaque formation is one of the most complex processes. Accordingly, the disturbances associated with this process result in incorrect plaque formation, which is sometimes associated with various pathological states. Uroplakins are also associated with some pathological processes, such as urothelial cancer and urinary tract infection.
Generally, uroplakins are proteins in the cell membrane that form urothelial plaques, especially on each urothelial cell surface. Uroplakin proteins, such as UPK2 and UPK3A in the human body, are glycoproteins with sugar residues crucial during protein synthesis and functions. Another form of uroplakin II does not have sugar residue. This is usually a mature form.
Two forms of uroplakin (27kDa and 28kDa) are transmembrane proteins with four chains with two hydrophilic fragments on the inside of the bladder and a localized cell plasma fragment. This structure classifies the two forms under tetraspanins.
The primary function of uroplakins is to protect the urinary tract against toxic substances found in urine. This protein ensures these toxins do not penetrate back to the bloodstream. Uroplakin lines the ureter, renal pelvis, bladder, and some parts of the urethra.