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Disruption of Raf-1/heat shock protein 90 complex and Raf signaling by dexamethasone in mast cells
1Laboratory of Molecular Immunology, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-1760, USA.
The Journal of Biological Chemistry
|March 4, 2000
Summary
Dexamethasone disrupts the Raf-1.heat shock protein 90 (Hsp90) complex in mast cells, inhibiting extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) pathways. This mechanism explains dexamethasone
Area of Science:
- Immunology
- Cell Signaling
- Pharmacology
Background:
- Mast cells are activated by antigen-IgE receptor (FcepsilonRI) triggering Syk kinase and downstream signaling.
- Extracellular signal-regulated kinase (ERK) cascade activation is inhibited by dexamethasone prior to Raf-1 activation.
Purpose of the Study:
- To investigate the molecular mechanism by which dexamethasone inhibits mast cell signaling.
- To determine the effect of dexamethasone on the Raf-1.heat shock protein 90 (Hsp90) complex and its role in ERK and JNK cascades.
Main Methods:
- Cultured RBL-2H3 mast cells were treated with nanomolar concentrations of dexamethasone.
- Analysis of Raf-1.Hsp90 complex dissociation and subsequent membrane/Ras association.
- Assessment of upstream signaling events including Syk-dependent Shc phosphorylation and Ras activation.
- Investigation of MEKK-1 association with Hsp90 and its activation in response to dexamethasone.
Main Results:
- Dexamethasone treatment caused dissociation of the Raf-1.Hsp90 complex in mast cells.
- Raf-1 lacking Hsp90 failed to associate with the membrane or Ras upon antigen stimulation.
- Upstream signaling events (Syk, Shc, Grb2, Ras) remained unaffected by dexamethasone.
- Dexamethasone disrupted the Hsp90 association and activation of MEKK-1, a key component of the JNK cascade.
Conclusions:
- Dexamethasone inhibits ERK and JNK cascades by disrupting the Raf-1.Hsp90 and MEKK-1.Hsp90 complexes.
- This disruption at the level of Raf-1 and MEKK-1 explains dexamethasone's inhibitory effect on inflammatory mediator generation in mast cells.
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