GCUNC-45 Is a Novel Regulator for the Progesterone Receptor/hsp90 Chaperoning Pathway

Abstract

The hsp90 chaperoning pathway is a multiprotein system that is required for the production or activation of many cell regulatory proteins, including the progesterone receptor (PR). We report here the identity of GCUNC-45 as a novel modulator of PR chaperoning by hsp90. GCUNC-45, previously implicated in the activities of myosins, can interact in vivo and in vitro with both PR-A and PR-B and with hsp90. Overexpression and knockdown experiments show GCUNC-45 to be a positive factor in promoting PR function in the cell. GCUNC-45 binds to the ATP-binding domain of hsp90 to prevent the activation of its ATPase activity by the cochaperone Aha1. This effect limits PR chaperoning by hsp90, but this can be reversed by FKBP52, a cochaperone that is thought to act later in the pathway. These findings reveal a new cochaperone binding site near the N terminus of hsp90, add insight on the role of FKBP52, and identify GCUNC-45 as a novel regulator of the PR signaling pathway.The activities of the progesterone receptor (PR) are intimately linked to its associations with other proteins that are essential for normal progesterone action. Unliganded PR is associated with a multifunctional complex of proteins which includes the heat shock proteins hsp70 and hsp90 plus several cochaperone proteins. This heterocomplex is responsible for correct assembly and folding of the PR as well as preventing its degradation (36). Recent studies indicate additional roles for molecular chaperones in receptor trafficking and in the maintenance of receptor function in the nucleus (11,12). Hormone binding promotes conformational changes in the PR and its release from the chaperone complex. The resulting PR dimer is then able to associate with specific coactivators and general transcription factors as well as progestin response elements in the promoters of target genes (13,19,27,44,50).Cell-free systems using the purified proteins have been of crucial importance in dissecting the ordered pathway that leads to the hormone-responsive state of the receptor (36,39,52). This hsp90-dependent chaperoning pathway is initiated by hsp40 and hsp70 binding to PR, followed by the binding of Hop-hsp90 to hsp70 (16). This intermediate complex is then modified by loss of hsp70 and Hop and recruitment of p23, resulting in a receptor able to bind hormone. In the cell, this last step also incorporates the cochaperone FKBP51, FKBP52, or Cyp40, but this step has eluded dissection in vitro.Although the overall mechanism might be as described above, details and dynamics of this process are still unclear. Furthermore, several additional proteins have been discovered recently that interact with hsp90 or hsp70, such as Chip, Bag1, TPR2, and Aha1 (23,31,36,39,52). These are all likely to have important roles in some aspect of hsp70/hsp90 chaperoning to provide a more intricate and versatile process than that described in the current model. There are also a number of proteins that interact with the PR as transcriptional coregulators or to relate PR functions with other cell signa...

Effect of nuclear export inhibition on estrogen receptor regulation in breast cancer cells

“…Of note, radicicol by itself caused a marked decrease of PgR level. This confirmed previous work (Lange et al 2000, Chadli et al 2006 showing that Hsp90 interacts with this receptor and contributes to its stability.…”

Conformational dynamics of the molecular chaperone Hsp90

“…Aha1 stimulates ATPase activity * p50 blocks ATPase activity and is thought to be kinase specific * Cpr6 TPR-containing and peptidy-prolyl-isomerase (Johnson et al, 2007) FKBP52 TPR-containing and peptidy-prolyl-isomerase (Riggs et al, 2003) GCUNC-45 TPR-containing that blocks progression of cycle (Chadli et al, 2006) Hop TPR-containing and scaffolds Hsp70-Hsp90 interaction * Hsp70 recruits substrates to Hsp90 * NudC CHORD-domain containing (Te et al, 2007) p23 blocks ATPase activity and traps client proteins in complex with Hsp90 * PP5 TPR-containing and phosphatase * Sse1 part of Hsp90 complex in budding yeast (Liu et al, 1999) Tah1 TPR-containing For a list of additional co-chaperones see http://www.picard.ch/downloads/Hsp90interactors.pdf * References can be found in the text.…”

Functional Protein Interactions in Steroid Receptor-Chaperone Complexes

“…General cell UNC-45 (GCUNC-45), a member of the UNC-45/Cro1/She4p (UCS) protein family, is a TPR protein that regulates PR chaperoning by Hsp90 by preventing activation of Hsp90 ATPase activity (Chadli et al, 2006). Hsp90-binding experiments in the presence of Hop revealed a novel GCUNC-45 TPR recognition site in the N-terminal domain of Hsp90, which also bound FKBP52 (Chadli et al, 2008a).…”