INVESTIGADORES
GALIGNIANA Mario Daniel
artículos
Título:
Protein phosphatase 5 is a major component of glucocorticoid receptor.hsp90 complexes with properties of an FK506-binding immunophilin
Autor/es:
SILVERSTEIN AM, GALIGNIANA MD, CHEN MS, OWENS-GRILLO JK, CHINKERS M, PRATT WB
Revista:
JOURNAL OF BIOLOGICAL CHEMISTRY
Editorial:
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
Referencias:
Año: 1997 vol. 272 p. 16224 - 16230
ISSN:
0021-9258
Resumen:
Steroid receptors are recovered from hormone-free cells in multiprotein
complexes containing hsp90, p23, an immunophilin, and often some hsp70.
The immunophilin, which can be of the FK506- or cyclosporin A-binding
class, binds to hsp90 via its tetratricopeptide repeat (TPR) domain, and
different receptor heterocomplexes exist depending upon which
immunophilin occupies the TPR-binding region of hsp90. We have recently
reported that a protein serine/threonine phosphatase that is designated
PP5 and contains four TPRs binds to hsp90 and is co-purified with the
glucocorticoid receptor (GR) (Chen, M.-S., Silverstein, A. M., Pratt, W.
B., and Chinkers, M. (1996) J. Biol. Chem. 271, 32315-32320). In this
work, we show that PP5 is recovered with both GR that is nuclear and GR
that is cytoplasmic in hormone-free cells. Approximately one-half of the
GR.hsp90 heterocomplexes in L cell cytosol contains an immunophilin
with high affinity FK506 binding activity, such as FKBP51 or FKBP52, and
approximately 35% contains PP5. Only a small (but undetermined)
fraction of the native GR.hsp90 heterocomplexes contain the cyclosporin
A-binding immunophilin CyP-40. PP5, FKBP52, and CyP-40 exist in separate
heterocomplexes with hsp90, and competition binding experiments with
the PP5 TPR domain suggest that the three proteins occupy a common
binding site on hsp90. A 55-residue connecting region between the
N-terminal TPR domain of human PP5 and its C-terminal phosphatase domain
has 50% amino acid homology and 22% identity with the central portion
of the peptidylprolyl isomerase domain of human FKBP52. Of the 9
residues in this portion of FKBP52 involved in high affinity
interactions with FK506, 3 residues are retained and 4 have homologous
substitutions in PP5. Although immunoadsorbed PP5 did not bind
[3H]FK506, we found that both rabbit PP5 in reticulocyte lysate and
purified rat PP5 were specifically retained by an FK506 affinity matrix.
Thus, we propose that PP5 possesses properties of an immunophilin with
low affinity FK506 binding activity and that it determines a major
portion of the native GR heterocomplexes in L cell cytosol.