Glucocorticoid‐induced leucine zipper is downregulated in human alveolar macrophages upon Toll‐like receptor activation

Abstract

Induction of the glucocorticoid-induced leucine zipper (GILZ) by glucocorticoids plays a role in their antiinflammatory action, whereas GILZ expression is reduced under inflammatory conditions. The mechanisms regulating GILZ expression during inflammation, however, have not yet been characterized. Here, we investigated GILZ expression in human alveolar macrophages (AMs) following Toll-like receptor (TLR) activation. Macrophages were shown to predominantly express GILZ transcript variant 2. Lipopolysaccharide-treated AMs, THP-1 cells, and lungs of lipopolysaccharide-exposed mice displayed decreased GILZ protein and mRNA levels. The effect was strictly dependent on the adapter molecule MyD88, as shown by using specific ligands or a knockdown strategy. Investigations on the functional significance of GILZ downregulation performed by GILZ knockdown revealed a proinflammatory response, as indicated by increased cytokine expression and NF-κB activity. We found that TLR activation reduced GILZ mRNA stability, which was mediated via the GILZ 3 -untranslated region. Finally, involvement of the mRNA-binding protein tristetraprolin (TTP) is suggested, since TTP overexpression or knockdown modulated GILZ expression and TTP was induced in a MyD88-dependent fashion. Taken together, our data show a MyD88-and TTP-dependent GILZ downregulation in human macrophages upon TLR activation. Suppression of GILZ is mediated by mRNA destabilization, which might represent a regulatory mechanism in macrophage activation.Keywords: GILZ transcript variants · Inflammation · Innate immunity · mRNA stability · Pulmonary macrophages IntroductionInflammatory processes in the lung play an important role in different diseases, such as viral and bacterial infections. Moreover, noninfectious diseases such as chronic obstructive pulmonary disCorrespondence: Prof. Alexandra K. Kiemer e-mail: pharm.bio.kiemer@mx.uni-saarland.de ease (COPD) are characterized by chronic inflammatory processes. Asthma and allergic diseases are other examples of chronic inflammatory lung diseases with major clinical relevance [1,2].Toll-like receptors (TLRs) represent an important family of innate immune receptors, which act as a first line of defense of host immunity against various pathogens. Presently, ten human TLRs are known, which recognize pathogen-associated molecular patterns including bacterial cell wall components, such as lipoproteins (TLR1/2 or TLR1/6 dimers) or lipopolysaccharide (LPS, TLR4), C 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2012. 42: 1282-1293 Innate immunity 1283 bacterial flagellin (TLR5), viral RNA (TLR3, 7 and 8), as well as bacterial DNA (TLR9) [3]. Except for TLR3, all TLRs signal via the adapter molecule MyD88. The MyD88-independent pathway used by TLR3 can also be utilized by TLR4. The different signaling pathways employ different protein kinase complexes and show distinct cytokine profiles, but all activate NF-κB [4]. In addition to their role in pathogen defense, TLRs also play a dominant role in ...

The Role and Effects of Glucocorticoid-Induced Leucine Zipper in the Context of Inflammation Resolution

“…15); that is, resident cells of the pleural cavity express GILZ and during the productive phase of LPS-induced pleurisy GILZ expression is inhibited. Indeed, it has been demonstrated that GILZ is downregulated in human alveolar macrophages upon TLR activation (33) and in HUVECs and macrophages upon treatment with TNF-a (34). In contrast, during the resolution phase, 48-72 h after LPS, GILZ expression was upregulated, and cells producing GILZ and AnxA1 were mostly Mres and M2 macrophages.…”

Glucocorticoid-Induced Leucine Zipper: A Critical Factor in Macrophage Endotoxin Tolerance

“…Examples include NF-kB and AP-1 (1)(2)(3)(4). GILZ was first isolated as a dexamethasone-responsive gene from a thymus subtraction library (5).…”

“…GILZ was first isolated as a dexamethasone-responsive gene from a thymus subtraction library (5). It is widely expressed in many tissues, such as lung, spleen, liver, kidney, brain, heart, and skeletal muscle, as well as in a variety of cells such as macrophages, T lymphocytes, and endothelial cells (1,3,4,6,7).…”

Les protéines de la famille TSC-22D

“…Jusqu'à présent, il était admis que l'expression génique de GILZ était induite par différents signaux anti-inflammatoires, comme les glucocorticoïdes, mais aussi par les interleukines-4 (IL-4), -13 et -10 dans les monocytes et les macrophages, l'IL-10 dans les mastocytes et les cellules dendritiques (DC) humaines dérivées de monocytes (MoDC) [8,[19][20][21], ou par le TGF- dans les MoDC. Inversement, il a été décrit que l'expression de GILZ était réprimée par des signaux pro-inflammatoires ou infectieux, comme dans les macrophages alvéolaires humains, en réponse à l'activation par le LPS (lipopolysaccharide) du récepteur Toll-like 4 (TLR4) [22]. Mais, les travaux de l'équipe d'Éric Morand ont suggéré que GILZ pouvait être exprimée dans des situations inflammatoires.…”

“…Le promoteur de Gilz comporte aussi des sites potentiels de fixation pour les facteurs de transcription STAT6 (signal transducer and activator of transcription 6), NFAT (nuclear factor of activated T cell), OCT-1 (octamer binding transcription factor-1) et c-Myc [25]. Enfin, un mécanisme de régulation post-transcriptionnelle de Gilz a été décrit dans lequel l'activation par le LPS (lipopolysaccharide) déstabilise l'ARNm de Gilz dans la région 3'UTR (untranslated region), diminuant ainsi son expression [22]. Tsc-22 est régulé positivement par la dexaméthasone dans la lignée d'ostéoblastes murins MC3T3 E1 [2], bien qu'aucune séquence GRE n'ait été identifiée à ce jour dans le promoteur de Tsc-22 [2,26].…”