NCI: A molecule inside or on the surface of a cell that binds to a specific substance and causes a specific physiologic effect in the cell.,CSP: diverse family of binding proteins which mediate the biological effects of regulatory molecules such as hormones; many are intrinsic membrane proteins; others (such as the steroid receptors) are cytoplasmic carriers; postcoordinate this term with specific ligand terms.,NCI: A protein located on the cell surface, or in the cytoplasm, that binds to a specific signaling factor, such as a hormone, antigen, or neurotransmitter, causing a conformational and functional change in the receptor molecule. The ligand-bound receptor then alters its interaction with target molecules, which leads to changes in cellular physiology through modification of the activity of one or more signal transduction pathways.