Glucocorticoids inhibit IL-4 and mitogen-induced IL-4Rα chain expression by different posttranscriptional mechanisms,☆☆,,★★,

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Abstract

Background: A high level of expression of IL-4Rα chain on the surface of lymphocytes has been described in certain allergic and inflammatory autoimmune diseases. Progression of these diseases are usually controlled by steroid treatment. One mechanism by which these drugs exert their antiinflammatory and immunosuppressive effects is by widely repressing or enhancing the production of cytokines and their receptors. Objectives: The effect of glucocorticoids on IL-4Rα chain expression has not been previously studied, and this is the aim of the present report. For this purpose, human lymphocytes were induced to express IL-4Rα chain by means of protein kinase C (PKC) activation with phorbol myristate acetate (PMA) or by triggering the Janus kinase-Stat pathway with IL-4 in the presence or absence of pharmacologic doses of dexamethasone. Methods: IL-4Rα cell surface expression was studied by flow cytofluorometry. The levels and stability of mRNA were assessed by Northern blot analysis. The effect of dexamethasone on the IL-4Rα rate of transcription was determined by nuclear run-on experiments. Results: Dexamethasone significantly downregulated PMA-induced IL-4Rα mRNA and protein levels in total peripheral blood mononuclear cells and in isolated T cells. The mechanism involved a posttranscriptional regulation of IL-4Rα expression because dexamethasone decreased the PMA-induced IL-4Rα mRNA half-life. However, we found that PMA did not influence the transcription rate of IL-4Rα gene, irrespective of the presence or absence of dexamethasone. This immunosuppressor also diminished the IL-4–induced IL-4Rα expression on the surface of isolated T and B lymphocytes but, interestingly, without modifying mRNA levels that indicates that dexamethasone downregulated IL-4–dependent IL-4Rα expression by acting at a translational or posttranslational level. In fact, we observed that the drug did not affect IL-4–induced IL-4Rα gene transcription rate nor did it shorten mRNA half-life. The effect of dexamethasone on the IL-4Rα was steroid specific because it was totally reversed by the glucocorticoid receptor antagonist RU486. Conclusion: Our results support that dexamethasone may influence the course of allergic and inflammatory diseases by downregulating the expression of IL-4Rα. (J Allergy Clin Immunol 1998;102:968-76.)

Section snippets

Reagents

Human recombinant IL-4 (rIL-4) was purchased from Genzyme Corp (Cambridge, Mass). PMA and dexamethasone were from Sigma Chemical Co (St Louis, Mo). PMA was dissolved in dimethyl sulfoxide, and dexamethasone was water soluble. The glucocorticoid antagonist RU486 was provided by Roussel Uclaf (Romainville, France) and was dissolved in ethanol. PMA and RU486 were diluted in culture medium, and the final concentration of dimethyl sulfoxide and ethanol in cultures was less than 0.01%. Actinomycin D

Decreased IL-4Rα protein expression by dexamethasone

The effect of dexamethasone on the IL-4Rα expression induced by means of protein kinase C (PKC) by PMA was analyzed by flow cytometry with the IL-4Rα–specific mAb M57 in both freshly isolated PBMCs and in highly purified T cells (Table I, Fig 1).

. Dexamethasone-mediated downregulation of IL-4Rα protein expression induced by PMA

Empty CellIL-4Rα MFI
Empty Cell24 h48 h72 h
PBMCs
 Medium7.00 ± 2.1616.00 ± 2.1614.33 ± 6.18
 PMA24.00 ± 6.2428.00 ± 4.3536.33 ± 15.04
 PMA + DEX6.00 ± 1.73*15.66 ± 0.57*9.33 ± 3.51
T cells
 Medium5.66

DISCUSSION

Regulation of immunoresponses by glucocorticoids is widely due to their capacity to enhance or repress the production of cytokines and their receptors. In this study a dexamethasone-mediated downregulation of PMA- or IL-4-induced IL-4Rα expression is described, and evidence is also shown that the glucocorticoid modulates IL-4Rα levels by different regulatory mechanisms, depending on the nature of the activation signal.

Pharmacologic doses of dexamethasone clearly exerted a downmodulatory effect

Acknowledgements

The authors thank Dr S. Gillis and Dr P. Beckmann for providing the IL-4R cDNA probe and the M57 mAb, Roussel Uclaf for the supply of RU 486, Dr Achsah D. Keegan for the critical reading of the manuscript, and David Wallace for the English correction.

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    From a the Department of Immunology, Hospital Central de Asturias, Centro Universitario, Oviedo; and b Functional Biology, Universidad de Oviedo, Oviedo.

    ☆☆

    José Zamorano is currently affiliated with the Immunology Department, American Red Cross, Rockville, Md.

    Supported by Grants FIS 92/102 and 97/955 from the Fondo de Investigaciones Sanitarias de la Seguridad Social.

    ★★

    Reprint requests: Carmen Gutiérrez, MD, Servicio de Inmunología, Hospital Central de Asturias, Julián Clavería s/n, 33006 Oviedo, Spain.

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