Hormone receptor

A hormone receptor is a molecule that can bind to a specific hormone. Receptors for peptide hormones tend to be found on the plasma membrane of cells, whereas receptors for lipid-soluble hormones are usually found within the cytoplasm. Upon hormone binding, the receptor can initiate multiple signaling pathways which ultimately lead to changes in the behaviour of the target cells.

Water-soluble hormone receptors

Water-soluble hormones include glycoproteins, catecholamines and peptide hormones composed of polypeptides, e.g. thyroid-stimulating hormone, follicle-stimulating hormone, luteinizing hormone and insulin. These molecules are not lipid-soluble and therefore cannot diffuse through cell membranes. Consequently, receptors for peptide hormones are located on the plasma membrane.

The main two types of transmembrane hormone receptor are the G-protein-coupled receptor and the enzyme-coupled receptor. These receptors generally function via intracellular second messengers, including cyclic AMP (cAMP), cyclic GMP (cGMP), inositol 1,4,5-trisphosphate (IP3) and the calcium (Ca²⁺)-calmodulin system.

Lipid-soluble hormone receptors

Steroid hormone receptors and related receptors are generally soluble proteins that function through gene activation. Their response elements are DNA sequences (promoters) that are bound by the complex of the steroid bound to its receptor. The receptors themselves are zinc-finger proteins. These receptors include those for glucocorticoids, estrogens, androgens, thyroid hormone (T3), calcitriol (the active form of vitamin D), and the retinoids (vitamin A).