Uroplakin 1B (UPK1B)

TSPAN20 is a member of the transmembrane 4 superfamily. Most of these members are cell-surface proteins that are characterized by the presence of four hydrophobic domains. These proteins mediate signal transduction events that play a role in the regulation of cell development, activation, growth and motility. This encoded protein is found in the asymmetrical unit membrane (AUM) where it can form a complex with other transmembrane 4 superfamily proteins. It may play a role in normal bladder epithelial physiology, possibly in regulating membrane permeability of superficial umbrella cells or in stabilizing the apical membrane through AUM/cytoskeletal interactions. The AUM is believed to be involved in strengthening the cells that line the bladder, thus preventing these cells from rupturing during bladder distension.