Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P11021 (BiP)
 2,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To be in a conformation that binds steroid, the hormone-binding domain of the glucocorticoid receptor (GR) must be bound to the 90 kDa heat shock protein (hsp90). Rabbit reticulocyte lysate contains a protein chaperone system that assembles the receptor into a heterocomplex with hsp90 and converts it from a non-steroid-binding to a steroid-binding form. Assembly of the GR-hsp90 heterocomplex requires hsp70, and in this work we examine the activities of four members of the hsp70 protein family in GR-hsp90 heterocomplex assembly. Rabbit reticulocyte lysate was depleted of hsp70 by passing it through a column of ATP agarose, resulting in the inactivation of its GR-hsp90 heterocomplex assembly activity. Addition of purified animal (mouse) or plant (wheat germ) hsp70 to the hsp70-depleted lysate permits assembly of a GR-hsp90 heterocomplex with a high affinity steroid binding site. However, purified hsp70 homologues from bacteria (DnaK) or the endoplasmic reticulum (BiP) do not promote heterocomplex formation, despite the fact that both DnaK and BiP bind to the GR in the assay system. When added to whole (i.e. hsp70-containing) reticulocyte lysate, DnaK and BiP inhibit GR-hsp90 heterocomplex assembly. Wheat germ lysate forms a heterocomplex between mouse GR and plant hsp90, but the addition of purified rabbit hsp70 to the wheat germ lysate does not increase the amount of receptor-wheat hsp90 complex produced, despite the fact that the rabbit hsp70 binds to the GR when it is added to the wheat chaperone system. The conclusion is that binding of hsp70 to receptors does not necessarily reflect a physiologically meaningful interaction. When native receptor heterocomplexes isolated from cytosols contain hsp70, it is likely that the hsp70-bound receptors represent a minority of receptors that have not yet proceeded fully through the receptor heterocomplex assembly process, which includes the dissociation of hsp70 after the binding of hsp90.
 ...
PMID:Ability of various members of the hsp70 family of chaperones to promote assembly of the glucocorticoid receptor into a functional heterocomplex with hsp90. 883 60

Calreticulin is a ubiquitously expressed Ca2+-binding protein of the endoplasmic reticulum (ER), which inhibits DNA binding in vitro and transcriptional activation in vivo by steroid hormone receptors. Transient transfection assays were carried out to investigate the effects of different intracellular targeting of calreticulin on transactivation mediated by glucocorticoid receptor. BSC40 cells were transfected with either calreticulin expression vector (ER form of calreticulin) or calreticulin expression vector encoding calreticulin minus leader peptide, resulting in cytoplasmic localization of the recombinant protein. Transfection of BSC40 cells with calreticulin expression vector encoding the ER form of the protein led to 40-50% inhibition of the dexamethasone-sensitive stimulation of luciferase expression. However, in a similar experiment, but using the calreticulin expression vector encoding cytoplasmic calreticulin, dexamethasone-stimulated activation of the luciferase reporter gene was inhibited by only 10%. We conclude that the ER, but not cytosolic, form of calreticulin is responsible for inhibition of glucocorticoid receptor-mediated gene expression. These effects are specific to calreticulin, since overexpression of the ER lumenal proteins (BiP, ERp72, or calsequestrin) has no effect on glucocorticoid-sensitive gene expression. The N domain of calreticulin binds to the DNA binding domain of the glucocorticoid receptor in vitro; however, we show that the N+P domain of calreticulin, when synthesized without the ER signal sequence, does not inhibit glucocorticoid receptor function in vivo. Furthermore, expression of the N domain of calreticulin and the DNA binding domain of glucocorticoid receptor as fusion proteins with GAL4 in the yeast two-hybrid system revealed that calreticulin does not interact with glucocorticoid receptor under these conditions. We conclude that calreticulin and glucocorticoid receptor may not interact in vivo and that the calreticulin-dependent modulation of the glucocorticoid receptor function may therefore be due to a calreticulin-dependent signaling from the ER.
 ...
PMID:Endoplasmic reticulum form of calreticulin modulates glucocorticoid-sensitive gene expression. 891 Jun 10