Steroid hormone receptors: intracellular distribution.

Recent reports, both biochemical and morphological, have challenged the widely accepted two-step model of steroid hormone action. This model proposed that steroid hormone receptors existed under two different forms: the unliganded receptor in the cytoplasm and the hormone-bound receptor complex in the nucleus. A nuclear translocation mechanism was hypothesized as a necessary link between the two forms. In contradiction with this model, new studies have concluded to the absence of receptor in the cytoplasm and its presence in the nucleus under all hormonal conditions, thus rendering the hypothetical nuclear translocation unnecessary. In this review, we discuss how our concept of the mechanism of action of steroid hormone ought to be revised in the light of the new data.