Dexamethasone up-regulates A3 adenosine receptors in rat basophilic leukemia (RBL-2H3) cells.
The cross-linking of surface IgE receptors by multi-functional Ags promotes the degranulation of mast cells. Previous studies have indicated that the nucleoside adenosine potentiates this response by activating putative A3 adenosine receptors (AR) coupled to phospholipase C in mast cells or their cultured analogues, rat basophilic leukemia (RBL-2H3) cells. Moreover, it has been shown that exposure of RBL-2H3 cells to dexamethasone attenuated antigen-mediated mast cell degranulation, but potentiated the response elicited by adenosine. To determine whether the A3AR is a potential site of action of dexamethasone, we have assessed the status of these receptors in RBL-2H3 cells treated with and without dexamethasone. Treatment with dexamethasone (100 nM) for 24 h resulted in an increase in the number of A3AR to 217 +/- 50% of control. The increased receptor expression was both time- and concentration-dependent, with optimal increases observed following 16 h of treatment and using 100 nM of dexamethasone. No increase in the level of the A2aAR was detectable following dexamethasone treatment. Northern blotting studies indicated a 2.7 +/- 0.3-fold increase in A3AR mRNA in RBL-2H3 cells treated with dexamethasone for 24 h. Dexamethasone also increased the expression of G protein alpha i2, alpha i3, alpha s, and beta subunits by two- to threefold. Activation of the A3AR by aminophenylethyladenosine (APNEA) following dexamethasone treatment enhanced the production of inositol phosphates and the mobilization of intracellular Ca2+. From these data, it is concluded that dexamethasone increases the expression of both A3AR and G proteins in RBL-2H3 cells which contributes to the enhanced response to adenosine.
Ramkumar
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Department of Pharmacology, Southern Illinois University School of Medicine, Springfield 62794, USA.
Wilson
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Dhanraj
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Gettys
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Ali
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D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000032:analysis; D003907:Dexamethasone / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000096:biosynthesis* / Q000187:drug effects; D007295:Inositol Phosphates / Q000032:analysis; D015471:Leukemia, Basophilic, Acute; D008407:Mast Cells / Q000187:drug effects*; D051381:Rats; D018047:Receptors, Purinergic P1 / Q000096:biosynthesis* / Q000187:drug effects*; D014407:Tumor Cells, Cultured; D015854:Up-Regulation; D001619:beta-N-Acetylhexosaminidases / Q000378:metabolism
D007295:Inositol Phosphates; D018047:Receptors, Purinergic P1; D003907:Dexamethasone; D001619:beta-N-Acetylhexosaminidases; D019204:GTP-Binding Proteins; D002118:Calcium