FK506 binding to the 56-kilodalton immunophilin (hsp56) in the glucocorticoid receptor heterocomplex has no effect on receptor folding or function

Abstract

It has recently been reported that the hsp56 component of glucocorticoid receptor heterocomplexes is an immunophilin of the FK506 binding class [Yem, A. W., Tomasselli, A. G., Heinrikson, R. L., Zurcher-Neely, H., Ruff, V. A., Johnson, R. A., & Deibel, M. R. (1992) J. Biol. Chem. 267, 2868-2871; Tai, P. K., Albers, M. W., Chang, H., Faber, L. E., & Schreiber, S. L. (1992) Science 256, 1315-1318]. The existence of binding proteins for these two potent groups of immunosuppressants in the same molecular complex compels us to ask whether FK506 affects glucocorticoid receptor function. We show here that hsp56 is a component of the native L-cell glucocorticoid receptor heterocomplex and that [3H]FK506 binds to the immunopurified, untransformed receptor complex. However, at concentrations in excess of those required to occupy all of its binding sites on hsp56, FK506 does not affect the steroid binding activity of the receptor nor does it stabilize or dissociate the receptor-hsp90 complex. FK506 does not affect steroid-mediated hsp90 dissociation from the receptor in vitro, and it does not affect steroid-mediated nuclear transfer of the receptor or steroid-mediated transcriptional enhancement from a reporter in intact cells. When immunopurified mouse glucocorticoid receptor is reconstituted into a heat shock protein complex by rabbit reticulocyte lysate, hsp56 is present in the reconstituted complex in addition to hsp90 and hsp70. FK506, however, does not affect reconstitution of the complex or return of the receptor to the steroid binding state, a change of conformation that occurs upon receptor association with hsp90.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclosporin A potentiates the dexamethasone-induced mouse mammary tumor virus-chloramphenicol acetyltransferase activity in LMCAT cells: a possible role for different heat shock protein-binding immunophilins in glucocorticosteroid receptor-mediated gene expression.

“…FKBP59 is a 90-kDa hsp-binding immunophilin, as indicated previously (11,12). Exposure of different receptors to FK506 or CsA in vitro (8,33,34), as well as in cells (this work), does not apparently modify the protein composition of unliganded receptors. From CsA-affinity purification experiments (Fig.…”

An FK506-sensitive Transporter Selectively Decreases Intracellular Levels and Potency of Steroid Hormones

“…However, FK506 has little or no effect on the affinity of GR for Dex or TA (42,45), and the effects of FK506 analogs on Dex responsiveness do not correlate with their inhibition of peptidylprolyl isomerase (FKBP-59) or calcineurin activity (42). FK506 also potentiates the response of progesterone receptor in yeast to the steroid R5020, an effect that was attributed to enhanced steroid-induced receptor phosphorylation by sub-saturating levels of R5020 (46).…”

Effect of immunosuppressive agents on glucocorticoid receptor function in A6 cells

“…We therefore decided to revisit the question of inhibition of GRmediated effects in A6 cells to determine whether this was in fact due to transcriptional inhibition by these agents. Earlier reports had suggested variable effects of FK-506 on GR-mediated transcription but not complete inhibition (9,14). We have examined this issue with the use of GR-reporter constructs.…”

“…In support of this latter possibility are observations that agents that bind to HSP90 such as geldanamycin alter the kinetics of receptor translocation (21,27) and the suggestion that the immunophilin component of the complex may be required for translocation (16), possibly because it binds both HSP90 and cytoplasmic dynein (6,22). However, initial studies using FK-506, which binds to immunophilins and inhibits their peptidylprolyl isomerase activity, either failed to show an effect on transcriptional activation by ligand-bound glucocorticoid receptor (GR) or suggested an enhancement of activity (9,14).…”