Dexamethasone Induces FcgammaRIIb Expression in RBL-2H3 Cells

ABSTRACT

Mast cells are involved in allergic responses, protection against pathogens and autoimmune diseases. Dexamethasone (Dex) and other glucocorticoids suppress FcepsilonRI-mediated release of inflammatory mediators from mast cells. The inhibition mechanisms were mainly investigated on the downstream signaling of Fc receptor activations. Here, we addressed the effects of Dex on Fc receptor expressions in rat mast cell line RBL-2H3. We measured mRNA levels of Fc receptors by real-time PCR. As expected, Dex decreased the mRNA levels of activating Fc receptor for IgE (FcepsilonR) I and increased the mRNA levels of the inhibitory Fc receptor for IgG FcgammaRIIb. Interestingly, Dex stimulated transcriptions of other activating receptors such as Fc receptors for IgG (FcgammaR) I and FcgammaRIII. To investigate the mechanisms underlying transcriptional regulation, we employed a transcription inhibitor actinomycin D and a translation inhibitor cycloheximide. The inhibition of protein synthesis without Dex treatment enhanced FcgammaRI and FcgammaRIII mRNA levels potently, while FcepsilonRI and FcgammaRIIb were minimally affected. Next, we examined expressions of the Fc receptors on cell surfaces by the flow cytometric method. Only FcgammaRIIb protein expression was significantly enhanced by Dex treatment, while FcgammaRI, FcgammaRIII and FcepsilonRI expression levels were marginally changed. Our data showed, for the first time, that Dex regulates Fc receptor expressions resulting in augmentation of the inhibitory receptor FcgammaRIIb.