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Pharmacol Res. 2014 Mar;81:10-6. doi: 10.1016/j.phrs.2014.01.002. Epub 2014 Jan 22.

Corticosteroids modulate the expression of the PKC-anchoring protein RACK-1 and cytokine release in THP-1 cells.

Author information

1
Laboratory of Toxicology, DiSFeB, Università degli Studi di Milano, Milan, Italy. Electronic address: emanuela.corsini@unimi.it.
2
Department of Drug Sciences - Pharmacology, University of Pavia, Pavia, Italy.
3
Laboratory of Toxicology, DiSFeB, Università degli Studi di Milano, Milan, Italy.

Abstract

We demonstrated that cortisol reduces the expression of RACK-1 (Receptor for Activated C Kinase-1), a protein required for immune cell activation. The aim of this study was to evaluate whether and to what extent other clinically relevant corticosteroids may modulate RACK-1 expression. We used the human promyelocytic cell line THP-1 to investigate the effects of cortisol, prednisone, prednisolone, budesonide, betamethasone and methylprednisolone on RACK-1 expression and cytokine production. As anticipated, all corticosteroids inhibited at non-cytotoxic concentrations in a dose and time related manner LPS-induced TNF-α and IL-8 release, with budesonide, betamethasone and methylprednisolone being the most active followed by prednisolone, cortisol and prednisone. To a similar extent, all corticosteroids also reduced RACK-1 mRNA expression and RACK-1 protein levels as assessed by Real Time PCR and Western blot, respectively. Prednisone was the least potent compound while betamethasone and methylprednisolone where the most active. A good correlation was observed between RACK-1 mRNA or protein levels and cytokine release (Pearson r=0.7376, p=0.0471 for RACK-1 mRNA and TNF-α release, and Pearson r=0.8108, p=0.0252 for RACK-1 protein and IL-8 release). Mifepristone, a potent glucocorticoid receptor (GR) antagonist, completely prevented the effect of cortisol, demonstrating that RACK-1 downregulation is via GR. Furthermore, to by-pass the defective PKC activation due to the decrease in RACK-1, we used a RACK-1 pseudosubstrate, that directly activates PKC-beta. RACK-1 pseudosubstrate was able to restore LPS-induced cytokine production affected by cortisol, supporting the role of RACK-1 in the anti-inflammatory effect of corticosteroids. These results confirm the involvement of RACK-1 in immune cell activation and identify this protein as a novel transcriptional target of corticosteroid-induced anti-inflammatory effects.

KEYWORDS:

Corticosteroids; Cytokines; Protein kinase C; Signal transduction

PMID:
24462857
DOI:
10.1016/j.phrs.2014.01.002
[Indexed for MEDLINE]
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