Developing concepts in receptor research.

Recent advances in molecular biology and protein chemistry have permitted spectacular progress in understanding the chemistry and cell biology of cell surface receptors for hormones and drugs. Methodological approaches, such as the use of radiolabeled ligands and direct receptor assays, have permitted the characterization, categorization, and purification of many receptors. The knowledge gained in understanding fundamental hormone-receptor interactions can form the basis of future, rational new drug design. Another important advance relates to the dynamic nature of receptors in their membrane environment. Upon binding of hormones such as insulin and epidermal growth factor, the complexes rearrange topographically on the cell surface, forming microclusters that are internalized into "receptosomes" via receptor-mediated endocytosis (which utilizes coated pits). The internalized receptor-hormone complex can have various fates, including the generation of selective signals for controlling cell growth and differentiation. In at least one case (epidermal growth factor), the latter may be dependent on the processes that occur in an acidic endosomal compartment within the cell.