Importin-7 mediates glucocorticoid receptor nuclear import and is impaired by oxidative stress, leading to glucocorticoid insensitivity.
Some patients with severe inflammatory disease fail to respond to glucocorticoids, and oxidative stress contributes to this insensitivity. Importin receptors are associated with nuclear translocation of the glucocorticoid receptor (GR), which is essential for glucocorticoid function. We hypothesized that importin-7 is central to GR nuclear translocation and glucocorticoid sensitivity. We investigated the effects of importin-7 siRNA on fluticasone propionate (FP)-induced GR nuclear localization and suppression of IL-1β-induced CXCL8 and the effects of hydrogen peroxide (H2O2) plus IL-1β costimulation on importin-7 expression, function, and glucocorticoid responsiveness in a human macrophagecell line (U937). H2O2 significantly reduced FP-induced GR nuclear localization (3.4±0.51- vs. 5.7±0.85-fold increase, P<0.05) and suppression of IL-1β-induced CXCL8 (62.3±2.3 vs. 85.1±7.0%, P<0.05). Knockdown of importin-7 by 38.4 ± 11.5% (compared with control siRNA) significantly reduced FP-mediated GR nuclear localization (3.5±0.5- vs. 5.7±0.85-fold increase, P<0.05) and suppression of IL-1β-induced CXCL8 expression (40.2±16.1 vs. 68.4±3.0%, P<0.05). H2O2 plus IL-1β had no direct effect on importin-7 but caused a significant loss (61.2±12.6% compared with baseline) of nuclear RanGTP, an essential cofactor for importin-7-mediated nuclear import of cargo proteins. The importin-7 complex is essential for glucocorticoid function, and the expression of its cofactor RanGTP is reduced during oxidative stress-induced glucocorticoid insensitivity.
1National Heart and Lung Institute, Airway Disease Section, Imperial College London and Royal Brompton Hospital, Dovehouse St., London, SW3 6LY, UK. a.hakim08@imperial.ac.uk.
Amir
A
Hakim
Peter J
PJ
Barnes
Ian M
IM
Adcock
Omar S
OS
Usmani
D021581:Active Transport, Cell Nucleus; D000730:Androstadienes / Q000494:pharmacology; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000378:metabolism; D000068298:Fluticasone; D005938:Glucocorticoids / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D053583:Interleukin-1beta / Q000494:pharmacology; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism*; D018384:Oxidative Stress; D034741:RNA, Small Interfering / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D020298:U937 Cells; D020931:ran GTP-Binding Protein / Q000235:genetics / Q000378:metabolism
D000730:Androstadienes; C508606:CXCL8 protein, human; D005938:Glucocorticoids; C466996:IPO7 protein, human; D053583:Interleukin-1beta; D016209:Interleukin-8; D028884:Karyopherins; D034741:RNA, Small Interfering; D018160:Receptors, Cytoplasmic and Nuclear; D011965:Receptors, Glucocorticoid; D006861:Hydrogen Peroxide; D000068298:Fluticasone; D020931:ran GTP-Binding Protein
Ran-GTP; chronic obstructive pulmonary disease; hydrogen peroxide; inflammation; oxidative stress