Component of the asymmetric unit membrane (AUM); a highly specialized biomembrane elaborated by terminally differentiated urothelial cells. May play an important role in regulating the assembly of the AUM (By similarity). Interacts with uroplakin-1a (UPK1A). Heterodimer formation with UPK1A is a prerequisite to exit out of the endoplasmic reticulum (ER). Expressed only in the urothelium. Localizes to urothelial superficial cells. Belongs to the uroplakin-2 family.