Evidence for the existence of an oligomeric, non-DNA-binding complex of the progesterone receptor in the cytoplasm.

Steroid receptors are found as a hetero-oligomeric complex in cell extracts. Due to the dynamic interaction between receptor-associated proteins and receptors, it is difficult to study the oligomeric complex in living cells. Here this was attempted in cells in which the interaction was stabilized by introducing molybdate into the cells or by incubating the cells at low temperature.

The C-terminal half of Hsp90 is responsible for its cytoplasmic localization.

With some exceptions, research so far has shown heat shock protein (Hsp) 90 to be a cytoplasmic protein. Here, we studied the sequence determinants which dictate the subcellular localization of Hsp90. By constructing hybrid molecules between a nuclear protein, progesterone receptor (PR), and parts of Hsp90, we demonstrated that the C-terminal but not the N-terminal half of Hsp90 can prevent nuclear translocation of the PR.

Heat shock protein 90 and the nuclear transport of progesterone receptor.

Steroid receptors exist as large oligomeric complexes in hypotonic cell extracts. In the present work, we studied the nuclear transport of the 2 major components of the oligomeric complex, the receptor itself and the heat shock protein 90 (Hsp90), by using different in vitro transport systems: digitonin permeabilized cells and purified nuclei. We demonstrate that the stabilized oligomeric complex of progesterone receptor (PR) cannot be transported into the nucleus and that unliganded PR salt dissociated from Hsp90 is transported into the nucleus.

Only a small portion of the cytoplasmic progesterone receptor is associated with Hsp90 in vivo.

In cell extracts all of the nonliganded steroid receptor molecules are found as an oligomeric complex with Hsp90 and other proteins. In previous studies we have shown that Wild-type Hsp90 and progesterone receptor (PR) are located in different cell compartments (Tuohimaa et al. [1993] Proc.

Reappraisal of the role of heat shock proteins as regulators of steroid receptor activity.

Almost 30 years have passed since the original demonstration that steroid receptors, comprising a subfamily of the nuclear receptor (NR) superfamily, exist as large (6-8S) non-DNA-binding complexes in hypotonic extracts (cytosol) of target cells; later such complexes were shown to correspond to a heterooligomer composed of receptor, heat shock (Hsp), and other proteins. Subsequently, an impressive number of studies have dealt with the composition of the "nonactive" complex, its dissociation and/or reassembly in vitro, possible functions of the non-receptor components, and their subcellular compartmentalization. While there is little dispute about the chaperoning role of some Hsps in such a complex, there is still no final proof of an association in vivo of NRs and Hsps in the nuclei of target cells, which is requisite for a direct regulatory involvement of Hsps in NR function.