TM4SF4 is a member of the transmembrane 4 superfamily, also known as the tetraspanin family. Most of these members are cell-surface proteins that are characterized by the presence of four hydrophobic domains. The proteins mediate signal transduction events that play a role in the regulation of cell development, activation, growth and motility. TM4SF4 is a cell surface glycoprotein that regulates the adhesive and proliferative status of intestinal epithelial cells and can mediate density-dependent cell proliferation. Glycosylation is required for the growth inhibitory effect.