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Biochemical Reconstitution of Steroid Receptor•Hsp90 Protein Complexes and Reactivation of Ligand Binding

Biochemical Reconstitution of Steroid Receptor•Hsp90 Protein Complexes and Reactivation of Ligand Binding

Published on: September 21, 2011

From the structure of steroid receptors to their assessment by immunocytochemistry in target cells

J M Gasc¹, E E Baulieu

¹INSERM U 33, Lab. Hormones, Bicêtre, France.

Journal of Steroid Biochemistry

|January 1, 1987

Abstract:

Immunohistochemical studies with antibodies to steroid hormone receptors provide new insight in the mechanism of action of steroid hormones. Immunologically reactive estrogen and progesterone receptors are found exclusively in cell nuclei of target cells even in the absence of the hormonal ligand. A hormonal treatment inducing receptor transformation and "translocation" to the nucleus does not modify the intracellular distribution of the receptor. This result is in contradiction with most biochemical studies which show a displacement of receptor from the cytosolic fraction to the nuclear fraction after hormone-receptor complex formation. We propose that different affinity levels of the non-transformed and hormone-complexed receptor molecules for nuclear structure produce unequal losses of nuclear receptor during homogenization. A lesser loss appears as an increase in nuclear binding sites or immunologically reactive receptor. The glucocorticosteroid receptor differs from the others in that it shows an increase of nuclear immunoreactive receptor after hormone administration. This result was accepted as evidence for a nuclear translocation in the sense initially proposed for all steroid hormones. Alternatively, one may propose another explanation based on the same experimental artefact as invoked for the estrogen and progesterone cytosol receptors. A higher affinity of the hormone-complexed receptor entails a lesser loss from the nucleus during tissue processing, and consequently an apparent increase in nuclear staining. Such a possibility is currently tested in parallel with the progesterone receptor.

Insights

Immunohistochemistry reveals estrogen and progesterone receptors are nuclear, challenging translocation theories. A proposed artifact explains apparent nuclear increases, differing from glucocorticosteroid receptor behavior.

Area of Science:

Endocrinology
Cell Biology
Molecular Biology

Background:

Steroid hormone receptors mediate cellular responses.
Traditional models propose cytosolic receptors translocate to the nucleus upon hormone binding.
Immunohistochemical studies offer a novel approach to investigate receptor localization.

Purpose of the Study:

To investigate the intracellular localization of estrogen and progesterone receptors using immunohistochemistry.
To reconcile discrepancies between immunohistochemical and biochemical findings regarding steroid hormone receptor localization.
To propose an alternative explanation for observed changes in nuclear receptor levels.

Main Methods:

Immunohistochemical staining using antibodies against steroid hormone receptors.
Analysis of receptor distribution in target cells before and after hormonal treatment.
Comparison of immunohistochemical data with existing biochemical studies.

Main Results:

Estrogen and progesterone receptors are found exclusively in cell nuclei, irrespective of hormonal ligand presence.
Hormonal treatment does not alter the nuclear localization of these receptors, contradicting biochemical studies.
A proposed artifact due to differential affinity for nuclear structures during tissue homogenization explains apparent nuclear increases.

Conclusions:

Immunohistochemistry suggests estrogen and progesterone receptors reside in the nucleus, independent of hormone binding.
Observed increases in nuclear receptor levels may be an artifact of tissue processing, not true translocation.
Glucocorticosteroid receptor behavior may also be explained by this artifact, warranting further investigation.

Read full analysis

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