Non-genomic inhibitory effect of glucocorticoids on activated peripheral blood basophils through suppression of lipid raft formation

Abstract

SummaryWe investigated the non-genomic effects of glucocorticoids (GCs) on inhibition of plasma membrane lipid raft formation in activated human basophils. Human basophils obtained from house dust mite (HDM)-sensitive volunteers were pretreated with hydrocortisone (CORT) or dexamethasone (Dex) for 30 min and then primed with phorbol 12-myristate 13-acetate (PMA, 10 ng/ml) or HDM (10 mg/ml). The expression of CD63, a basophil activation marker, was assessed by flow cytometry. Membrane-bound GC receptors (mGCRs) were analysed by flow cytometry and confocal laser microscopy. Lipid rafts were assessed using a GM1 ganglioside probe and visualization by confocal laser microscopy. Pretreatment of basophils with CORT (10 -4 M and 10 -5 M) and Dex (10 -7 M) significantly inhibited CD63 expression 20 min after addition of PMA or HDM. The inhibitory effects of GCs were not altered by the nuclear GC receptor (GCR) antagonist RU486 (10 -5 M) or the protein synthesis inhibitor cycloheximide (10 -4 M) (P < 0·05). CORT coupled to bovine serum albumin (BSA-CORT) mimicked the rapid inhibitory effects of CORT, suggesting the involvement of mGCRs. mGCRs were detectable on the plasma membrane of resting basophils and formed nanoclusters following treatment with PMA or HDM. Pretreatment of cells with BSA-CORT inhibited the expression of mGCRs and nanoclustering of ganglioside GM1 in lipid rafts. The study provides evidence that non-genomic mechanisms are involved in the rapid inhibitory effect of GCs on the formation of lipid raft nanoclusters, through binding to mGCRs on the plasma membrane of activated basophils.

The Influence of Tissue-Specific Glucocorticoid System on the Inflammatory Microenviroment: A Mini-Review

“…Recently, researchers hypothesised that both mechanisms can regulate cell and tissue functions. Although the genomic pathway is thought to be more important regarding inflammation, more rapid functions by inhibition of calcium and sodium cycling through the plasma membrane are carried out by membrane-bound glucocorticoid receptors (mGRS) [6]. There is a major role of GC influence on T regulatory (Treg) cells generation.…”

New target for asthma treatment: Inhibition of cluster formation of lipid rafts

“…Among the nongenomic effects, GCs exhibit rapid onset and therefore occur through acute regulation of intracellular signal-ling cascades. Several studies 11,14 have reported that non-genomic effects contribute to GC inhibition of granule exocytosis by basophils or mast cells. Because membrane-impermeable bovine serum albumin (BSA)-conjugated GC exhibits the same effect as non-conjugated GC, the inhibitory effects have been suggested to occur, at least in part, through binding to membrane-bound GC receptors (mGRs) 11 .…”

“…Several studies 11,14 have reported that non-genomic effects contribute to GC inhibition of granule exocytosis by basophils or mast cells. Because membrane-impermeable bovine serum albumin (BSA)-conjugated GC exhibits the same effect as non-conjugated GC, the inhibitory effects have been suggested to occur, at least in part, through binding to membrane-bound GC receptors (mGRs) 11 . Non-genomic inhibitory effects of GCs through suppression of cluster formation of lipid rafts lead to inhibition of granule exocytosis from basophils or mast cells.…”

“…Pretreatment with GCs inhibits the expression of mGR and GM1 gangliosides, which are enriched in lipid rafts and can be detected using a probe of cholera toxin-B (CT-b), in HDM-treated basophils from HDM-sensitive subjects (Figure 2). Non-genomic mechanisms are involved in the rapid inhibitory effect of GCs on cluster formation of lipid rafts, through binding to mGRs on the plasma membranes of activated basophils 11 .…”

“…)11 . However, glucocorticoids (GCs) did not inhibit cluster formation of IgE crosslinking on HDMtreated basophils.After crosslinking of FcεRI, the process of granule exocytosis, including translocation of the vesicle, docking and fusion to the inner membrane, occurs successively on grounded lipid rafts.…”