Defective glucocorticoid receptor nuclear translocation and altered histone acetylation patterns in glucocorticoid-resistant patients.
BACKGROUND
Most chronic inflammatory diseases are well controlled by glucocorticoids. However, a minority of patients fails to respond adequately to this treatment.


OBJECTIVE
We wished to determine whether glucocorticoid insensitivity in a group of steroid-resistant (SR) and steroid-dependent (SD) asthmatic subjects resulted from an inability of the glucocorticoid receptor (GR) to translocate into the nucleus.


METHODS
Glucocorticoid receptor nuclear translocation was determined in PBMCs by immunocytochemistry and GR function measured by suppression of TNF-alpha-induced GM-CSF release and effects of dexamethasone on histone acetylation.


RESULTS
Glucocorticoid repression of TNF-alpha-induced GM-CSF release was reduced in PBMCs from SD and SR patients. This inhibition correlated with a failure of GR to translocate into the nucleus and induce histone acetylation in response to dexamethasone. In addition, dexamethasone failed to inhibit TNF-alpha-induced histone acetyltransferase activity, which predominantly targeted histone residues lysine (K)8 and K12. However, in a subset of patients, even high levels of GR nuclear translocation failed to produce histone acetylation in response to dexamethasone. Histone H4 K5 acetylation, a marker of dexamethasone transactivation, was specifically reduced in this group. However, cells from this subset of steroid-insensitive subjects were still capable of inhibiting TNF-alpha-induced histone acetylation.


CONCLUSIONS
We have identified a novel mechanism of glucocorticoid insensitivity in a group of SR and SD subjects. These data suggest that most patients respond to glucocorticoids according to the degree of GR nuclear translocation occurring, but some subjects with steroid resistance have a reduced response because of a failure of steroids to transactivate, rather than transrepress.
Matthews
John G
JG
Thoracic Medicine, National Heart and Lung Institute, Imperial College of Science, Technology and Medicine, Dovehouse Street, London SW3 6LY, United Kingdom.
Ito
Kazuhiro
K
Barnes
Peter J
PJ
Adcock
Ian M
IM
D000107:Acetylation; D021581:Active Transport, Cell Nucleus; D000328:Adult; D003907:Dexamethasone / Q000494:pharmacology*; D004351:Drug Resistance; D005260:Female; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D006657:Histones / Q000378:metabolism*; D006801:Humans; D008239:Lysine / Q000378:metabolism; D008297:Male; D011965:Receptors, Glucocorticoid / Q000032:analysis / Q000378:metabolism*; D015203:Reproducibility of Results; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D006657:Histones; D011965:Receptors, Glucocorticoid; D014409:Tumor Necrosis Factor-alpha; D003907:Dexamethasone; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D008239:Lysine