TEACHING EDITORIAL Radiochemicai Probes for Steroid Hormone Receptors

Steroid hormone receptors are thermolabile, specific, high-affinity binding proteins that are necessary for steroid hormone action at the cellular level in steroid hormone-responsive cells. Ac cording to our present understanding of the mechanism of steroid hormone action, circulating ste roids are first taken up by target cells and then bind to specific cytoplasmic receptor molecules, forming hormone-receptor complexes. These complexes undergo an activation step and are trans located into the nucleus where the activated receptor-hormone complexes interact with cell chro matin, the final result being quantitative or qualitative alterations in specific gene transcription. The newly synthesized RNA undergoes processing, is transported to the cytoplasm, and translated into protein, eventually bringing about changes in the cell phenotype. This sequence of events is presentedto demonstratethecomplexityof hormoneactionandshouldbeconsideredin thefinal interpretation of the results obtained with receptor assays. Thus, in this long chain of interactions, proof of the presence of specific receptors is not necessarily identical with proof of steroid respon siveness, since theme exist several possible points for interruption, which might prevent hormone responsiveness. It has been approximately two decades since radiolabeled steroid hormones were first synth