<P> A hormone receptor is a receptor molecule that binds to a specific hormone . Hormone receptors are a wide family of proteins made up of receptors for thyroid and steroid hormones, retinoids and Vitamin D, and a variety of other receptors for various ligands, such as fatty acids and prostaglandins . There are two main classes of hormone receptors . Receptors for peptide hormones tend to be cell surface receptors built into the plasma membrane of cells and are thus referred to as trans membrane receptors . An example of this is insulin . Receptors for steroid hormones are usually found within the cytoplasm and are referred to as intracellular or nuclear receptors, such as testosterone . Upon hormone binding, the receptor can initiate multiple signaling pathways which ultimately lead to changes in the behavior of the target cells . </P> <P> Hormonal therapy and hormone receptors play a very large part in breast cancer treatment (therapy is not limited to only breast cancer). By influencing the hormones, the cells' growth can be changed along with its function . These hormones can cause cancer to not survive in the human body . </P> <P> Hormone receptor proteins bind to a hormone as a result of an accumulation of weak interactions . Because of the relatively large size of enzymes and receptors, the large amount of surface area provides the basis for these weak interactions to occur . This binding is actually highly specific because of the complementarity of these interactions between polar, non-polar, charged, neutral, hydrophilic, or hydrophobic residues . Upon binding, the receptor often undergoes a conformational change and may bind further signaling ligands in order to activate a signaling pathway . Because of these highly specific and high affinity interactions between hormones and their receptors, very low concentrations of hormone are needed to produce significant cellular response . Receptors can have various different structures depending on the function of the hormone and the structure of its ligand . Therefore, hormone binding to its receptor is a complex process which can be mediated by cooperative binding, reversible and irreversible interactions, and multiple binding sites . </P>

Where are target receptors for lipid soluble hormones located