Differential effects of the hsp70-binding protein BAG-1 on glucocorticoid receptor folding by the hsp90-based chaperone machinery.
The heat shock protein hsp70/hsc70 is a required component of a five-protein (hsp90, hsp70, Hop, hsp40, and p23) minimal chaperone system reconstituted from reticulocyte lysate that forms glucocorticoid receptor (GR).hsp90 heterocomplexes. BAG-1 is a cofactor that binds to the ATPase domain of hsp70/hsc70 and that modulates its chaperone activity. Inasmuch as BAG-1 has been found in association with several members of the steroid receptor family, we have examined the effect of BAG-1 on GR folding and GR.hsp90 heterocomplex assembly. BAG-1 was present in reticulocyte lysate at a BAG-1:hsp70/hsc70 molar ratio of approximately 0.03, and its elimination by immunoadsorption did not affect GR folding and GR. hsp90 heterocomplex assembly. At low BAG-1:hsp70/hsc70 ratios, BAG-1 promoted the release of Hop from the hsp90-based chaperone system without inhibiting GR.hsp90 heterocomplex assembly. However, at molar ratios approaching stoichiometry with hsp70, BAG-1 produced a concentration-dependent inhibition of GR folding to the steroid-binding form with corresponding inhibition of GR.hsp90 heterocomplex assembly by the minimal five-protein chaperone system. Also, there was decreased steroid-binding activity in cells that were transiently or stably transfected with BAG-1. These observations suggest that, at physiological concentrations, BAG-1 modulates assembly by promoting Hop release from the assembly complex; but, at concentrations closer to those in transfected cells and some transformed cell lines, hsp70 is continuously bound by BAG-1, and heterocomplex assembly is blocked.
Kanelakis
K C
KC
Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA.
Morishima
Y
Y
Dittmar
K D
KD
Galigniana
M D
MD
Takayama
S
S
Reed
J C
JC
Pratt
W B
WB
D000818:Animals; D016227:Benzoquinones; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D002460:Cell Line; D002474:Cell-Free System; D005591:Chemical Fractionation; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D018841:HSP90 Heat-Shock Proteins / Q000502:physiology*; D006360:Heat-Shock Proteins / Q000378:metabolism; D047029:Lactams, Macrocyclic; D051379:Mice; D018832:Molecular Chaperones / Q000502:physiology*; D011485:Protein Binding / Q000187:drug effects; D017510:Protein Folding; D011809:Quinones / Q000494:pharmacology; D011817:Rabbits; D011965:Receptors, Glucocorticoid / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D012156:Reticulocytes / Q000737:chemistry; D014157:Transcription Factors
C091732:BCL2-associated athanogene 1 protein; D016227:Benzoquinones; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D018832:Molecular Chaperones; D011809:Quinones; D011965:Receptors, Glucocorticoid; C489791:Stip1 protein, mouse; D014157:Transcription Factors; C001277:geldanamycin