Analysis of the dissociated steroid RU24858 does not exclude a role for inducible genes in the anti-inflammatory actions of glucocorticoids.
Although repression of inflammatory gene expression makes glucocorticoids powerful anti-inflammatory agents, side effects limit usage and drive the search for improved glucocorticoid receptor (GR) ligands. In A549 pulmonary cells, dexamethasone and the prototypical dissociated ligand RU24858 (Mol Endocrinol 11:1245-1255, 1997) repress interleukin (IL)-1beta-induced expression of cyclooxygenase (COX)-2 and IL-8. Although RU24858 is a weaker GR ligand, both glucocorticoids showed similar efficacies on transrepression of nuclear factor kappaB (NF-kappaB)-dependent transcription, whereas RU24858 yielded less than 12% of the response to dexamethasone on a classic glucocorticoid response element (GRE) reporter (transactivation). Modest NF-kappaB-dependent transrepression ( approximately 40%), along with analysis of IL-8 transcription rate and the accumulation of unspliced nuclear RNA, indicates that transrepression does not fully account for the repression of genes such as IL-8. This was confirmed by the finding that mRNA degradation is increased by both dexamethasone and RU24858. Analysis of IL-1beta-induced steady-state mRNA levels for IL-8 and COX-2 show that dexamethasone- and RU24858-dependent repression of these genes is attenuated by inhibitors of transcription and protein synthesis. Because similar effects were observed with respect to COX-2 and IL-8 protein expression, we conclude that glucocorticoid-dependent gene expression is necessary for repression by both glucocorticoids. Despite RU24858 being defective at classic GRE-dependent transactivation, both dexamethasone and RU24858 induced the expression of potentially anti-inflammatory genes and metabolic genes, suggesting the importance of nontraditional glucocorticoid-dependent gene expression. Thus, classic transactivation- and transrepressionbased screens for anti-inflammatory "dissociated" GR ligands may be flawed because they may not reflect the effects on real glucocorticoid-inducible genes.
Chivers
Joanna E
JE
Department of Cell Biology & Anatomy, Respiratory Research Group, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
Gong
Wei
W
King
Elizabeth M
EM
Seybold
Joachim
J
Mak
Judith C
JC
Donnelly
Louise E
LE
Holden
Neil S
NS
Newton
Robert
R
D000893:Anti-Inflammatory Agents / Q000494:pharmacology*; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers; D003609:Dactinomycin / Q000494:pharmacology; D003899:Desoximetasone / Q000031:analogs & derivatives; D003907:Dexamethasone / Q000494:pharmacology*; D015232:Dinoprostone / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D006889:Hydroxycorticosteroids / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic
D000893:Anti-Inflammatory Agents; D017931:DNA Primers; D006889:Hydroxycorticosteroids; D012333:RNA, Messenger; C000589029:RU24858; D003609:Dactinomycin; D003899:Desoximetasone; D003907:Dexamethasone; D015232:Dinoprostone