Steroid hormone receptors: intracellular distribution

Area of Science:

• Endocrinology
• Molecular Biology
• Cell Biology

Background:

• The established two-step model of steroid hormone action posits cytoplasmic, unliganded receptors translocating to the nucleus upon hormone binding.
• This model relies on a hypothetical nuclear translocation mechanism to explain receptor localization changes.

Purpose of the Study:

• To review recent biochemical and morphological evidence that challenges the conventional two-step model of steroid hormone action.
• To discuss the implications of new findings on the understanding of steroid hormone receptor localization and function.

Main Methods:

• Review of recent biochemical and morphological studies.
• Analysis of experimental data contradicting the nuclear translocation hypothesis.

Main Results:

• New data indicate the absence of steroid hormone receptors in the cytoplasm.
• Receptors are consistently found in the nucleus regardless of ligand-bound status.
• These findings render the hypothesized nuclear translocation mechanism obsolete.

Conclusions:

• The traditional two-step model of steroid hormone action requires revision.
• Steroid hormone receptors appear to reside in the nucleus constitutively.
• A new conceptual framework is needed to explain steroid hormone mechanisms.