Cell adhesion molecule involved in the establishment and/or maintenance of cell integrity. Involved in the formation and regulation of the tight junction (TJ) paracellular permeability barrier in epithelial cells. Plays a role in VAMP3-mediated vesicular transport and recycling of different receptor molecules through its interaction with VAMP3. Plays a role in the regulation of cell shape and movement by modulating the Rho-family GTPase activity through its interaction with ARHGEF25/GEFT. Induces primordial adhesive contact and aggregation of epithelial cells in a Ca(2+)-independent manner. Important for skeletal muscle and heart development. Also involved in striated muscle regeneration and repair and in the regulation of cell spreading (By similarity). Important for the maintenance of cardiac function. Plays a regulatory function in heart rate dynamics mediated, at least in part, through cAMP-binding and, probably, by increasing cell surface expression of the potassium channel KCNK2 and enhancing current density. Is a caveolae-associated protein important for the preservation of caveolae structural and functional integrity as well as for heart protection against ischemia injury (By similarity). Homodimer. Homodimerization requires the C-terminus cytoplasmic region (By similarity). Interacts (via the C-terminus cytoplasmic tail) with TJP1. Interacts (via the C-terminus cytoplasmic tail) with ARHGEF25/GEFT (via the DH domain). Interacts (via the C-terminus cytoplasmic tail) with VAMP3. Interacts with KCNK2; the interaction enhances KCNK2 surface expression and is inhibited by cAMP (By similarity). Interacts with CAV3 (By similarity). Colocalizes with VAMP3 at the cell-cell contact in cardiac and skeletal muscle (By similarity). Its movement from the cytoplasm to membrane is an early event occurring concurrently with cell-cell contact. Colocalizes in epithelial cells with OCLN and TJP1 in an apical-lateral position within the z axis. Detected at cell-cell contact but never observed at the free surface of epithelial cells (By similarity). Strongly expressed in heart and skeletal muscle. Weakly expressed in brain, spleen, liver, kidney and lung. Belongs to the popeye family.