Glycosylated phosphatidylinositol molecules as second messengers

Glycosylated phosphatidylinositol (GPI) lipids are a structurally and functionally diverse molecular family. One of the most interesting and controversial aspects of GPI function is their ability to participate in signaling mechanisms or to directly function as second messengers of biological receptors. For example, while there is little dispute that subsets of GPI molecules are hydrolyzed following receptor ligation, there is no consensus as to the subsequent roles of intact GPI molecules or their cleavage products. The importance of these observations is underscored by two facts; many GPI anchored proteins participate in the regulation of cell proliferation, and several hormones metabolize GPI forms that are not linked to proteins. The purpose of this review is to outline the major structural and biological features of GPI molecules as they relate to their role in cellular signaling.