p38 Mitogen-activated protein kinase-induced glucocorticoid receptor phosphorylation reduces its activity: role in steroid-insensitive asthma.
BACKGROUND
Although glucocorticoids are the most effective treatment for chronic inflammatory diseases, such as asthma, some patients show a poor response. IL-2 combined with IL-4 can alter glucocorticoid receptor (GR) ligand-binding affinity and modulate glucocorticoid function.


OBJECTIVE
We sought to confirm the altered ligand-binding affinity in a distinct group of steroid-dependent asthmatic subjects and examine the mechanism by which IL-2 and IL-4 modify the ligand-binding affinity of the GR.


METHODS
We examined PBMCs from healthy subjects, subjects with mild asthma, and steroid-dependent subjects with severe asthma using dexamethasone-binding assays and Western blot analysis of GR and phosphorylated activated transcription factor 2 expression. GR phosphorylation was measured after orthophosphate labeling and immunoprecipitation and cytokine production by means of ELISA.


RESULTS
GR ligand-binding affinity was reduced in the nucleus but not in the cytoplasm of steroid-dependent asthmatic subjects compared with that seen in healthy subjects (dissociation constant, 39.8 +/- 4.6 vs. 6.79 +/- 0.8 nmol/L). This difference in ligand-binding affinity could be mimicked by IL-2 and IL-4 cotreatment and was blocked by the p38 mitogen-activated kinase (MAPK) inhibitor SB203580. Activation of p38 MAPK by IL-2 and IL-4, as shown by means of phosphorylation of activated transcription factor 2, resulted in GR phosphorylation and reduced dexamethasone repression of LPS-stimulated GM-CSF release. p38 MAPK phosphorylation of CD2(+) T cells occurred on serine residues. The ability of dexamethasone to modulate IL-10 release was also inhibited by IL-2 and IL-4 cotreatment. These effects were also inhibited by SB203580.


CONCLUSIONS
These data show that p38 MAPK inhibitors may have potential in reversing glucocorticoid insensitivity and reestablishing the beneficial effects of glucocorticoids in patients with severe asthma.
Irusen
Elvis
E
Thoracic Medicine, Imperial College School of Medicine at the National Heart and Lung Institute, London, United Kingdom.
Matthews
John G
JG
Takahashi
Atsushi
A
Barnes
Peter J
PJ
Chung
Kian F
KF
Adcock
Ian M
IM
D000284:Administration, Oral; D000328:Adult; D001249:Asthma / Q000188:drug therapy* / Q000503:physiopathology; D004351:Drug Resistance; D005260:Female; D005541:Forced Expiratory Volume; D005938:Glucocorticoids / Q000627:therapeutic use*; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000378:metabolism; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D016753:Interleukin-10 / Q000378:metabolism; D007376:Interleukin-2 / Q000494:pharmacology; D015847:Interleukin-4 / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D010766:Phosphorylation; D011725:Pyridines / Q000494:pharmacology; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases
D005938:Glucocorticoids; D007093:Imidazoles; D007376:Interleukin-2; D011725:Pyridines; D011965:Receptors, Glucocorticoid; D016753:Interleukin-10; D015847:Interleukin-4; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580