Glucocorticoid-induced leucine zipper inhibits the Raf-extracellular signal-regulated kinase pathway by binding to Raf-1.
Glucocorticoid-induced leucine zipper (GILZ) is a leucine zipper protein, whose expression is augmented by dexamethasone (DEX) treatment and downregulated by T-cell receptor (TCR) triggering. Stable expression of GILZ in T cells mimics some of the effects of glucocorticoid hormones (GCH) in GCH-mediated immunosuppressive and anti-inflammatory activity. In fact, GILZ overexpression inhibits TCR-activated NF-kappaB nuclear translocation, interleukin-2 production, FasL upregulation, and the consequent activation-induced apoptosis. We have investigated the molecular mechanism underlying GILZ-mediated regulation of T-cell activation by analyzing the effects of GILZ on the activity of mitogen-activated protein kinase (MAPK) family members, including Raf, MAPK/extracellular signal-regulated kinase (ERK) 1/2 (MEK-1/2), ERK-1/2, and c-Jun NH(2)-terminal protein kinase (JNK). Our results indicate that GILZ inhibited Raf-1 phosphorylation, which resulted in the suppression of both MEK/ERK-1/2 phosphorylation and AP-1-dependent transcription. We demonstrate that GILZ interacts in vitro and in vivo with endogenous Raf-1 and that Raf-1 coimmunoprecipitated with GILZ in murine thymocytes treated with DEX. Mapping of the binding domains and experiments with GILZ mutants showed that GILZ binds the region of Raf interacting with Ras through the NH(2)-terminal region. These data suggest that GILZ contributes, through protein-to-protein interaction with Raf-1 and the consequent inhibition of Raf-MEK-ERK activation, to regulating the MAPK pathway and to providing a further mechanism underlying GCH immunosuppression.
Ayroldi
Emira
E
Department of Clinical and Experimental Medicine, Section of Pharmacology. Department of Drug Chemistry and Technology, University of Perugia, 06100 Perugia, Italy.
Zollo
Ornella
O
Macchiarulo
Antonio
A
Di Marco
Barbara
B
Marchetti
Cristina
C
Riccardi
Carlo
C
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D016762:Genes, fos; D016758:Genes, jun; D005938:Glucocorticoids / Q000494:pharmacology; D007376:Interleukin-2 / Q000378:metabolism; D016350:Leucine Zippers; D008213:Lymphocyte Activation; D020935:MAP Kinase Signaling System / Q000502:physiology*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D016415:Sequence Alignment; D013601:T-Lymphocytes / Q000166:cytology / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; C498608:Dsip1 protein, mouse; D005938:Glucocorticoids; D007376:Interleukin-2; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D003907:Dexamethasone; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases