HspBP1 Is the Negative Regulator of the Bovine Progesterone Receptor

K. M. Park,J. W. Song

doi:10.5713/ajas.2003.1261

Abstract

We have investigated whether HspBP1, a Hsp70 binding protein, could have effect on the assembly of the bovine progesterone receptor (bPR) with a chaperone complex consisting of bovine Hsp90 (bHsp90), bovine Hsp70 (bHsp70), Hop, Ydj-1, and p23. The bPR, isolated in its native conformation, loses its function to interact with progesterone hormone in the absence of this protein complex. However, in the presence of bHsp90, bHsp70, Hop, p23 and Ydj-1, its function could be restored in vitro. Our findings here indicate that the inclusion of HspBP1 to five-protein system prevented the proper assembly of progesterone receptor-chaperone complex and induce the loss of bPR ability to interact with hormone. Immunoprecipitation assays of bPR with HspBP1 show that the presence of HspBP1 did not have any effect on the assembly of Ydj-1 and bHsp70 with the progesterone receptor. However, further assembly of Hsp90, Hop and p23 was completely prevented and the function of the bPR was lost. In vitro competition and protein folding assays indicated that the binding of HspBP1 to bHsp70 prevented the ternary complex formation of bHsp70, bHsp90, and Hop. These results indicate that HspBP1 is a negative regulator of the assembly of Hsp90, Hop and Hsp70, and thus, prevent the proper maturation of unliganded bPR with chaperones assembly system. (Asian-Aust. J. Anim. Sci. 2003. Vol 16, No. 9 : 1261-1267)

Highlights

Progesterone Receptor (PR) is a member of the nuclear receptors, a large and diverse group of proteins that mediate transcriptional activation or repression in the presence of ligand, progesterone (Jensen, 1991; Smith and Toft, 1993).PR, upon binding to progesterone hormone, functions as a transcriptional factor and plays an important role in controlling cell proliferation and differentiation in many organs
In vitro competition and protein folding assays indicated that the binding of HspBP1 to bovine Hsp70 (bHsp70) prevented the ternary complex formation of bHsp70, bovine Hsp90 (bHsp90), and Hop. These results indicate that HspBP1 is a negative regulator of the assembly of Hsp90, Hop and Hsp70, and prevent the proper maturation of unliganded bovine progesterone receptor (bPR) with chaperones assembly system
Proteins added to the reaction mixtures were shown by Western blot analysis for bPR

Summary

INTRODUCTION

Progesterone Receptor (PR) is a member of the nuclear receptors, a large and diverse group of proteins that mediate transcriptional activation or repression in the presence of ligand, progesterone (Jensen, 1991; Smith and Toft, 1993). Unliganded PR complexes were assembled by incubating purified proteins including Hsp, Hsp, Hsp, Hop and p23 with unliganded PR (Barent et al, 1998; Chen and Smith; 1998, Dittmar et al, 1998; Kosano et al, 1998). Among those proteins, Hsp, Hsp and Hsp are three chaperones, which are necessary for maturation of hormone binding ability of PR in vitro. Hsp and Hop are dissociated from the complex as p23, a Hsp interacting protein, binds to Hsp in the presence of ATP (Johnson and Toft, 1995; Hernandez et al, 2002). HspBP1 caused the Hsp90-Hop dissociation from Hsp and this process inhibited the ligand binding ability of bovine PR to progesterone

MATERIALS AND METHODS

RESULTS AND DISCUSSION

HspBP1