Endothelial cell-specific membrane protein involved in the formation of the diaphragms that bridge endothelial fenestrae. It is also required for the formation of stomata of caveolae and transendothelial channels. Functions in microvascular permeability, endothelial fenestrae contributing to the passage of water and solutes and regulating transcellular versus paracellular flow in different organs. Plays a specific role in embryonic development. Homodimer. Membrane-associated protein of caveolae. Found in fenestral and stomatal diaphragms in fenestrated endothelia and transendothelial channels. Also colocalized with CAV1 in perinuclear region. Expressed in lung, kidney, heart, aorta, placenta, muscle, pituitary gland, adrenals, mammary gland, bladder, lymph node, bone marrow, trachea, digestive tract, liver and tumor-associated endothelium. By phorbol myristate acetate (PMA) or VEGF in endothelial cell culture. The disease is caused by variants affecting the gene represented in this entry.