title: Dexamethasone Induces FcγRIIb 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 FcεRI-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 (FcεR) I and increased the mRNA levels of the inhibitory Fc receptor for IgG FcγRIIb. Interestingly, Dex stimulated transcriptions of other activating receptors such as Fc receptors for IgG (FcγR) I and FcγRIII. 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 FcγRI and FcγRIII mRNA levels potently, while FcεRI and FcγRIIb were minimally affected. Next, we examined expressions of the Fc receptors on cell surfaces by the flow cytometric method. Only FcγRIIb protein expression was significantly enhanced by Dex treatment, while FcγRI, FcγRIII and FcεRI 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 FcγRIIb.
authors.affiliation: Research Institute for Medical Sciences and Department of Biochemistry, College of Medicine, Chungnam National University, Daejeon 301-747, Korea.
authors.forename: Prashanta
authors.initials: P
authors.lastname: Silwal
authors.forename: Mi-Nam
authors.initials: MN
authors.lastname: Lee
authors.forename: Choong-Jae
authors.initials: CJ
authors.lastname: Lee
authors.forename: Jang-Hee
authors.initials: JH
authors.lastname: Hong
authors.forename: Uk
authors.initials: U
authors.lastname: Namgung
authors.forename: Zee-Won
authors.initials: ZW
authors.lastname: Lee
authors.forename: Jinhyun
authors.initials: J
authors.lastname: Kim
authors.forename: Kyu
authors.initials: K
authors.lastname: Lim
authors.forename: Gi Ryang
authors.initials: GR
authors.lastname: Kweon
authors.forename: Jong Il
authors.initials: JI
authors.lastname: Park
authors.forename: Seung Kiel
authors.initials: SK
authors.lastname: Park