Serine/threonine protein phosphatase 5 (PP5) participates in the regulation of glucocorticoid receptor nucleocytoplasmic shuttling.
BACKGROUND
In most cells glucocorticoid receptors (GR) reside predominantly in the cytoplasm. Upon hormone binding, the GR translocates into the nucleus, where the hormone-activated GR-complex regulates the transcription of GR-responsive genes. Serine/threonine protein phosphatase type 5 (PP5) associates with the GR-heat-shock protein-90 complex, and the suppression of PP5 expression with ISIS 15534 stimulates the activity of GR-responsive reporter plasmids, without affecting the binding of hormone to the GR.


RESULTS
To further characterize the mechanism by which PP5 affects GR-induced gene expression, we employed immunofluorescence microscopy to track the movement of a GR-green fluorescent fusion protein (GR-GFP) that retained hormone binding, nuclear translocation activity and specific DNA binding activity, but is incapable of transactivation. In the absence of glucocorticoids, GR-GFP localized mainly in the cytoplasm. Treatment with dexamethasone results in the efficient translocation of GR-GFPs into the nucleus. The nuclear accumulation of GR-GFP, without the addition of glucocorticoids, was also observed when the expression of PP5 was suppressed by treatment with ISIS 15534. In contrast, ISIS 15534 treatment had no apparent effect on calcium induced nuclear translocation of NFAT-GFP.


CONCLUSIONS
These studies suggest that PP5 participates in the regulation of glucocorticoid receptor nucleocytoplasmic shuttling, and that the GR-induced transcriptional activity observed when the expression of PP5 is suppressed by treatment with ISIS 15534 results from the nuclear accumulation of GR in a form that is capable of binding DNA yet still requires agonist to elicit maximal transcriptional activation.
Dean
D A
DA
Division of Pulmonary and Critical Care Medicine, Northwestern University, Chicago, IL 60611, USA. dean@northwestern.edu
Urban
G
G
Aragon
I V
IV
Swingle
M
M
Miller
B
B
Rusconi
S
S
Bueno
M
M
Dean
N M
NM
Honkanen
R E
RE
D021581:Active Transport, Cell Nucleus; D002467:Cell Nucleus / Q000201:enzymology*; D003593:Cytoplasm / Q000201:enzymology; D003907:Dexamethasone / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D019319:Okadaic Acid / Q000494:pharmacology; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000502:physiology*; D054735:Phosphorothioate Oligonucleotides; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; D005938:Glucocorticoids; C120289:ISIS 15534; D009687:Nuclear Proteins; D016376:Oligonucleotides, Antisense; D054735:Phosphorothioate Oligonucleotides; D011965:Receptors, Glucocorticoid; D011993:Recombinant Fusion Proteins; D019319:Okadaic Acid; D003907:Dexamethasone; D010749:Phosphoprotein Phosphatases; C089641:protein phosphatase 5