Binding of heat shock proteins to the avian progesterone receptor.

Abstract

The protein composition of the avian progesterone receptor was analyzed by immune isolation of receptor complexes and gel electrophoresis of the isolated proteins. Nonactivated cytosol receptor was isolated in association with the 90-kilodalton (kDa) heat shock protein, hsp9O, as has been described previously. A 70-kDa protein was also observed and was shown by Western immunoblotting to react with an antibody specific to the 70-kDa heat shock protein. Thus, two progesterone receptor-associated proteins are identical, or closely related, to heat shock proteins. When the two progesterone receptor species, A and B, were isolated separately in the absence of hormone, both were obtained in association with hsp9O and the 70-kDa protein. However, activated receptor isolated from oviduct nuclear extracts was associated with the 70-kDa protein, but not with hsp9O. A hormone-dependent dissociation of hsp9O from the cytosolic form of the receptor complex was observed within the first hour of in vivo progesterone treatment, which could explain the lack of hsp9O in nuclear receptor complexes. In a cell-free system, hsp9O binding to receptor was stabilized by molybdate but disrupted by high salt. These treatments, however, did not alter the binding of the 70-kDa protein to receptor. Association of the 70-kDa protein with the receptor could be disrupted by the addition of ATP at elevated temperatures (23°C). The receptor-associated 70-kDa protein is an ATP-binding protein, as demonstrated by its affinity labeling with azido[32P]ATP. These results indicate that the two receptor-associated proteins interact with the progesterone receptor by different mechanisms and that they are likely to affect the structure or function of the receptor in different ways.

Functional Interaction of Human Cdc37 with the Androgen Receptor but Not with the Glucocorticoid Receptor

“…There is evidence for persistent Hsp70 association with ligand bound receptors (48), although the functional significance of this interaction remains unknown. A new study on the Drosophila Ecdysone receptor, however, showed that Hsp90 and several other co-chaperones facilitate heterodimerization with RXR and DNA binding (49).…”

Heat and Chemical Shock Potentiation of Glucocorticoid Receptor Transactivation Requires Heat Shock Factor (HSF) Activity

“…Although it is interesting to speculate that one of the major known heat shock proteins may serve the function of product X in our system, to date no direct evidence for this possibility has been found. However, there is evidence that HSPs can affect the DNA-binding properties of steroid receptors, since the glucocorticoid (49), progesterone (50,51), and estrogen receptors (52) have been shown to remain tightly complexed to HSP70 even after hormone-induced transformation of these receptors to the DNA-binding state. Moreover, purified HSP70 has been shown to enhance the in vitro DNA binding properties of the estrogen receptor (52).…”

Identification of a 60-kilodalton stress-related protein, p60, which interacts with hsp90 and hsp70.

“…For glucocorticoid receptors, hsp90 binding to receptor is required to maintain high-affinity ligand binding (3,26,40), but other steroid receptors that have been examined do not show this same dependency on hsp90. In all hsp90-nuclear receptor complexes, ligand-dependent activation of the receptor DNA-binding ability is accompanied by dissociation of hsp90 (14,17,31,43), and it appears likely that one hsp90 function is to repress DNA binding by receptor.Steroid receptor-hsp9O interactions provide a model for understanding hsp90 function, but exploiting this model has been hindered by the inability to reversibly assemble receptor-hsp90 complexes in vitro. This drawback was recently overcome by establishing certain physicochemical conditions that permit the use of rabbit reticulocyte lysate as a cell-free medium for assembly of hsp90 with chick progesterone receptor (PR) (44, 45) and rat glucocorticoid receptor (40).…”

“…For glucocorticoid receptors, hsp90 binding to receptor is required to maintain high-affinity ligand binding (3,26,40), but other steroid receptors that have been examined do not show this same dependency on hsp90. In all hsp90-nuclear receptor complexes, ligand-dependent activation of the receptor DNA-binding ability is accompanied by dissociation of hsp90 (14,17,31,43), and it appears likely that one hsp90 function is to repress DNA binding by receptor.…”