Epithelial membrane protein-1 (EMP-1) is a four pass transmembrane protein consisting of 160 amino acids. It is a member of a small family of epithelial membrane proteins. EMP-1 is very similar in structure to its close relative, Peripheral Myelin Protein 22 (PMP22). It is most predominantly expressed in tissues of the gastrointestinal tract but has also been found to be a junctional protein in the liver expressed along the intercellular border. EMP-1 directly interacts with the C-terminus of the P2X7 receptor and may be involved in membrane blebbing. EMP-1 may also be an important regulator in cell communication, signaling, and adhesion. When EMP-1 is overexpressed, cell proliferation is inhibited, S phase is arrested and G1 phase is prolonged in esophogeal cancer cells. EMP-1 may play a role in tumorigenesis and has been identified as a biomarker for gefitinib treatment resistance for patients with lung cancer.