The Contribution of “Alternative Approaches” to Understanding Steroid Hormone Action

In the 47 yr since the first evidence for a steroid hormone receptor was presented at an international congress to an audience of five persons, the concept of “alternative approach” has played an important role in providing new understanding. By asking not what does an estrogenic hormone do to cellular processes in responsive tissues but what do these cells do to the hormone, it was shown that rat uterus contains a characteristic protein with which the hormone associates to promote growth. In the following decade, it was established that this substance is a true receptor, involved in hormonal action. Furthermore, estradiol was found not to undergo a chemical change as it exerts its effect. Finally, estrogenic action was established as a two-step process in which association with the hormone converts the receptor from an inactive to an active form that can bind tightly in the nucleus to modify transcription. These findings, obtained by studying the fate of the hormone itself, disproved the then accepted concept that estrogens interact with enzyme systems, and opened a new field of research. Soon various laboratories identified intracellular receptors for all classes of steroid hormones, the action of which involves a similar two-step process. Several laboratories then attempted, without success, to obtain antibodies to these receptors by conventional techniques. The unconventional approach of gradient ultracentrifugation, using radioactive estradiol as a marker for the receptor, gave a means of recognizing the soluble immune complexes formed with estrogen receptor and provided the first antibodies to any steroid hormone receptor, permitting its cloning. Finally, the knowledge that estrogens act through a receptor suggested that measuring the receptor content of an excised tumor specimen could identify, in advance, two thirds of the human breast cancers that are not estrogen dependent. These patients will not benefit from endocrine ablation or antiestrogen treatment and should be placed directly on chemotherapy. This is now standard clinical practice.