Glucocorticoid-induced Leucine Zipper Overexpression Research Articles

Immunomodulation by glucocorticoid-induced leucine zipper in macrophages: enhanced phagocytosis, protection from pyroptosis, and altered mitochondrial function.

Glucocorticoids, which have long served as fundamental therapeutics for diverse inflammatory conditions, are still widely used, despite associated side effects limiting their long-term use. Among their key mediators is glucocorticoid-induced leucine zipper (GILZ), recognized for its anti-inflammatory and immunosuppressive properties. Here, we explore the immunomodulatory effects of GILZ in macrophages through transcriptomic analysis and functional assays. Bulk RNA sequencing of GILZ knockout and GILZ-overexpressing macrophages revealed significant alterations in gene expression profiles, particularly impacting pathways associated with the inflammatory response, phagocytosis, cell death, mitochondrial function, and extracellular structure organization activity. GILZ-overexpression enhances phagocytic and antibacterial activity against Salmonella typhimurium and Escherichia coli, potentially mediated by increased nitric oxide production. In addition, GILZ protects macrophages from pyroptotic cell death, as indicated by a reduced production of reactive oxygen species (ROS) in GILZ transgenic macrophages. In contrast, GILZ KO macrophages produced more ROS, suggesting a regulatory role of GILZ in ROS-dependent pathways. Additionally, GILZ overexpression leads to decreased mitochondrial respiration and heightened matrix metalloproteinase activity, suggesting its involvement in tissue remodeling processes. These findings underscore the multifaceted role of GILZ in modulating macrophage functions and its potential as a therapeutic target for inflammatory disorders, offering insights into the development of novel therapeutic strategies aimed at optimizing the benefits of glucocorticoid therapy while minimizing adverse effects.

Glucocorticoid-induced leucine zipper protects noise-induced apoptosis in cochlear cells by inhibiting endoplasmic reticulum stress in rats.

Endoplasmic reticulum (ER) stress-mediated apoptosis has been reported to be involved in the noise-induced hearing loss (NIHL). Glucocorticoid-induced leucine zipper (GILZ) protein has been reported to have different regulatory effects on apoptosis according to cell types. However, whether GILZ regulates apoptosis in cochlear cells is unclear. Our study aimed to investigate the mechanism by which GILZ protected ER stress-mediated cochlear apoptosis induced by noise exposure. In our trials, forty-eight male Spraque-Dawley rats were randomized into the noise, OE-GILZ-rLV + noise (ON), shRNA-GILZ-rLV + noise (SN), and control group. Rats in noise and control groups were pre-treated by administration of Blank-rLV. Before and on days 1, 4, 14 after noise exposure, auditory brainstem response (ABR) and cochlear apoptosis were detected. Changes in GILZ, GRP78, CHOP, Bcl-xL, Bax, and cleaved caspase-3 levels were investigated. Noise exposure increased ABR threshold shifts and cochlear apoptosis in parallel with downregulation of Bcl-xL and upregulation of GRP78, CHOP, Bax and cleaved caspase-3. GILZ overexpression significantly reduced ABR threshold shifts and apoptotic cochlear cells owing to noise exposure. GILZ overexpression in the cochlea further increased GRP78 elevation, decreased expression of CHOP, Bax and cleaved caspase-3, and increased expression of Bcl-xL. GILZ silencing demonstrated the opposite effect on these effects. GILZ protects cochlea from ER stress-mediated apoptosis induced by noise exposure through reduction of CHOP and regulation of ER stress-associated apoptotic proteins.

Clock represses preadipocytes adipogenesis via GILZ.

Adiposity is a worldwide health threat that needs to be prevented. Circadian gene Clock (circadian locomotor output cycles kaput) is closely correlated to adiposity; for example, weight gain, adipocytes size expansion, and serum lipid level rise in ClockΔ19 mice compared to C57BL/6J mice. However, the precise role of Clock during adipogenic differentiation is unknown. Herein, the circadian gene Clock is shown to regulate adipogenesis mediated by GILZ. Clock-mediated attenuation and upregulation influenced lipid synthesis and affected the levels of adipogenic transcriptional factors, C/EBP-β, C/EBP-α, PPAR-γ, and FABP4, both in vivo and in vitro (primary adipose-derived stromal cells and 3T3-L1 cells). Chromatin immunoprecipitation (ChIP) assay, reporter gene assay, and serum shock assay found that Clock transcriptionally regulated the glucocorticoid-induced leucine zipper (GILZ). Furthermore, GILZ attenuation could relieve the inhibitory effect of Clock on lipid synthesis and GILZ overexpression also reduced the promotion role of Clock attenuation in adipogenesis suggesting that Clock inhibits adipogenic differentiation of preadipocytes via GILZ. The current results demonstrate how circadian genes are likely to regulate adiposity, affecting the adipogenic differentiation process, as well as, increasing the fat cells number. Therefore, this study may provide novel insights into the underlying mechanism explaining the correlation between Clock mutation and adiposity.

Glucocorticoid-Induced Leucine Zipper Protects the Retina From Light-Induced Retinal Degeneration by Inducing Bcl-xL in Rats

The aim of the present study was to investigate the neuroprotective effects of glucocorticoid-induced leucine zipper (GILZ) in a light-induced retinal degeneration model and to explore the underlying mechanisms. Intravitreal injection of recombinant GILZ-overexpressing lentivirus (OE-GILZ-rLV) and short hairpin RNA targeting GILZ recombinant lentivirus (shRNA-GILZ-rLV) was performed to up- and downregulate retinal GILZ, respectively. Three days after stable transduction, rats were exposed to continuous bright light (5000 lux) for 2 days. Retinal function was assessed by full-field electroretinography (ERG), and the retinal structure was examined for photoreceptor survival and death in rats kept under a 12-hour light:2-hour dark cycle following light exposure. The expression levels of retinal Bcl-xL, caspase-9, and caspase-3 were examined by Western blotting or real-time PCR at 1, 3, 5, and 7 days after light exposure. Exposure to bright light downregulated retinal GILZ in parallel with the downregulation of Bcl-xL and the upregulation of active caspase-3. Overexpression of retinal GILZ attenuated the decrease of Bcl-xL and the activation of caspase-9 and caspase-3 at 1, 3, 5, and 7 days after bright light exposure, respectively. GILZ silencing aggravated the downregulation of Bcl-xL induced by bright light exposure. Bright light exposure reduced the amplitude of ERG, increased the number of apoptotic photoreceptor cells, and decreased retinal thickness; and GILZ overexpression could attenuate all these effects. Overexpression of GILZ by OE-GILZ-rLV transduction protected the retina from light-induced cellular damage by activating antiapoptotic pathways.

Metabolic rewiring in cancer cells overexpressing the glucocorticoid-induced leucine zipper protein (GILZ): Activation of mitochondrial oxidative phosphorylation and sensitization to oxidative cell death induced by mitochondrial targeted drugs

Cancer cell metabolism is largely controlled by oncogenic signals and nutrient availability. Here, we highlighted that the glucocorticoid-induced leucine zipper (GILZ), an intracellular protein influencing many signaling pathways, reprograms cancer cell metabolism to promote proliferation. We provided evidence that GILZ overexpression induced a significant increase of mitochondrial oxidative phosphorylation as evidenced by the augmentation in basal respiration, ATP-linked respiration as well as respiratory capacity. Pharmacological inhibition of glucose, glutamine and fatty acid oxidation reduced the activation of GILZ-induced mitochondrial oxidative phosphorylation. At glycolysis level, GILZ-overexpressing cells enhanced the expression of glucose transporters in their plasmatic membrane and showed higher glycolytic reserve. 1H NMR metabolites quantification showed an up-regulation of amino acid biosynthesis. The GILZ-induced metabolic reprograming is present in various cancer cell lines regardless of their driver mutations status and is associated with higher proliferation rates persisting under metabolic stress conditions. Interestingly, high levels of OXPHOS made GILZ-overexpressing cells vulnerable to cell death induced by mitochondrial pro-oxidants. Altogether, these data indicate that GILZ reprograms cancer metabolism towards mitochondrial OXPHOS and sensitizes cancer cells to mitochondria-targeted drugs with pro-oxidant activities.

Glucocorticoid-induced leucine zipper overexpression inhibits lipopolysaccharide-induced retinal inflammation in rats

Glucocorticoid-induced leucine zipper (GILZ) mediates several effects of glucocorticoids and has important anti-inflammatory properties. Here, we explored the role of GILZ in inhibiting retinal inflammation. Endotoxin-induced uveitis (EIU) was established in rats by intravitreal injection of lipopolysaccharide (LPS). GILZ levels decreased in the EIU retina after LPS injection. Retinal GILZ was downregulated by recombinant lentivirus-delivered short-hairpin RNA targeting GILZ (shRNA-GILZ-rLV) and upregulated by recombinant lentivirus-mediated GILZ overexpression (Oe-GILZ-rLV). GILZ silencing attenuated the anti-inflammatory effects of intravitreal injection of triamcinolone acetonide (TA) in the EIU retina, as demonstrated by increased retinal interleukin (IL)-1β, monocyte chemoattractant protein (MCP)-1and intercellular cell adhesion molecule-1 expression at 18 h after TA injection. A Bio-Plex cytokine assay and western blotting demonstrated that GILZ overexpression inhibited the effects of LPS, downregulating retinal IL-1β, MCP-1, MIP-1α, and IL-17 and inhibiting LPS-induced activation of the retinal toll-like receptor 4–myeloid differentiation factor 88 signaling pathway. At 48 and 72 h after LPS injection, the clinical score of inflammation was significantly lower in Oe-GILZ-rLV–transfected eyes than in blank-rLV–transfected eyes. Histological examination showed a 67.85% reduction of infiltrating inflammatory cells in the anterior chamber and a 58.97% reduction in vitreous cavity of Oe-GILZ-rLV transfected eyes at 48 h after LPS injection. Taken together, our results suggest that GILZ is a novel therapeutic target for the treatment of retinal inflammatory diseases.

Low expression of the GILZ may contribute to adipose inflammation and altered adipokine production in human obesity

The glucocorticoid-induced leucine zipper (GILZ), a primary target of glucocorticoids, is expressed in human adipocytes, but its importance in adipocyte function is unknown. Because TNFα is increased in obese adipose tissue and antagonizes a number of glucocorticoid actions, we investigated the interplay of these pathways. GILZ knockdown increased and GILZ overexpression decreased interleukin-6 (IL-6) and leptin mRNA and protein secretion. GILZ knockdown increased the magnitude of the glucocorticoid effect on leptin secretion, but did not affect the glucocorticoid suppression of IL-6. Although GILZ silencing decreased adiponectin mRNA levels, it did not affect the amount of adiponectin secreted. GILZ negatively modulated pro-inflammatory signaling pathways, blocking basal and TNFα-stimulated (1 h) p65 nuclear factor κB nuclear translocation and transcriptional activity by binding to p65 in the cytoplasm. GILZ silencing increased basal ERK1/2 and JNK phosphorylation, and decreased MAPK phosphatase-1 protein levels. Longer term TNFα (4 h or 24 h) treatment decreased GILZ expression in human adipocytes. Furthermore, adipose tissue GILZ mRNA levels were reduced in proportion to the degree of obesity and expression of inflammatory markers. Overall, these results suggest that GILZ antagonizes the pro-inflammatory effects of TNFα in human adipocytes, and its downregulation in obesity may contribute to adipose inflammation and dysregulated adipokine production, and thereby systemic metabolism.

Glucocorticoid-Induced Leucine Zipper Is Expressed in Human Neutrophils and Promotes Apoptosis through Mcl-1 Down-Regulation

Glucocorticoid-induced leucine zipper (GILZ) is a potent anti-inflammatory protein, the expression of which is mainly induced by glucocorticoids (GCs) in haematopoietic cells. GILZ regulates signal transduction pathways of inflammation and plays a role in cell survival. The objective of this study was to evaluate the expression and mechanisms of action of GILZ in the apoptosis of human neutrophils. GILZ expression was induced by GCs in human neutrophils, enhanced upon phosphatidylinositol 3-kinase inhibition and resulted in apoptosis amplification. We then stably transfected PLB-985 cells with the human gilz gene and differentiated both control and GILZ-overexpressing clones in neutrophil-like cells. GILZ overexpression in PLB-985 cells led to an exacerbated apoptosis, associated with caspase-3, caspase-9 and caspase-8 activations, and a loss of mitochondrial potential, suggesting that GILZ-induced apoptosis used the mitochondrial pathway. The expression of BH3 interacting domain death agonist, Bcl-2 interacting mediator of cell death, annexin-A1 and Bcl-2-associated X was not affected in PLB-985-GILZ clones, but phosphorylation and subsequent proteasomal degradation of myeloid cell leukemia-1 (Mcl-1) were observed. Noteworthy, Mcl-1 phosphorylation was related to a significant and sustained activation of c-Jun N-terminal kinase (JNK) in PLB-985-GILZ clones. These results reveal GILZ to be a new actor in apoptosis regulation in neutrophil-like cells involving JNK and Mcl-1.

GILZ Promotes Production of Peripherally Induced Treg Cells and Mediates the Crosstalk between Glucocorticoids and TGF-β Signaling

Regulatory T (Treg) cells expressing the transcription factor forkhead box P3 (FoxP3) control immune responses and prevent autoimmunity. Treatment with glucocorticoids (GCs) has been shown to increase Treg cell frequency, but the mechanisms of their action on Treg cell induction are largely unknown. Here, we report that glucocorticoid-induced leucine zipper (GILZ), a protein induced by GCs, promotes Treg cell production. In mice, GILZ overexpression causes an increase in Treg cell number, whereas GILZ deficiency results in impaired generation of peripheral Treg cells (pTreg), associated with increased spontaneous and experimental intestinal inflammation. Mechanistically, we found that GILZ is required for GCs to cooperate with TGF-β in FoxP3 induction, while it enhances TGF-β signaling by binding to and promoting Smad2 phosphorylation and activation of FoxP3 expression. Thus, our results establish an essential GILZ-mediated link between the anti-inflammatory action of GCs and the regulation of TGF-β-dependent pTreg production.

Glucocorticoid Induced Leucine Zipper inhibits apoptosis of cardiomyocytes by doxorubicin

Doxorubicin (Dox) is an indispensable chemotherapeutic agent for the treatment of various forms of neoplasia such as lung, breast, ovarian, and bladder cancers. Cardiotoxicity is a major concern for patients receiving Dox therapy. Previous work from our laboratory indicated that glucocorticoids (GCs) alleviate Dox-induced apoptosis in cardiomyocytes. Here we have found Glucocorticoid-Induced Leucine Zipper (GILZ) to be a mediator of GC-induced cytoprotection. GILZ was found to be induced in cardiomyocytes by GC treatment. Knocking down of GILZ using siRNA resulted in cancelation of GC-induced cytoprotection against apoptosis by Dox treatment. Overexpressing GILZ by transfection was able to protect cells from apoptosis induced by Dox as measured by caspase activation, Annexin V binding and morphologic changes. Western blot analyses indicate that GILZ overexpression prevented cytochrome c release from mitochondria and cleavage of caspase-3. When bcl-2 family proteins were examined, we found that GILZ overexpression causes induction of the pro-survival protein Bcl-xL. Since siRNA against Bcl-xL reverses GC induced cytoprotection, Bcl-xL induction represents an important event in GILZ-induced cytoprotection. Our data suggest that GILZ functions as a cytoprotective gene in cardiomyocytes.

Glucocorticoid-induced leucine zipper (GILZ) promotes apoptosis in vitro in neutrophil-like cells.

Event Abstract Back to Event Glucocorticoid-induced leucine zipper (GILZ) promotes apoptosis in vitro in neutrophil-like cells. Marie-Alix Espinasse1*, Pascale Piednoir2, Guillaume Dufour2, Philippe Montravers2, Sylvie Chollet-Martin1, 2, Marc Pallardy1 and Armelle Biola-Vidamment1 1 INSERM UMRS 996, Université Paris-Sud, France 2 APHP-Bichat, Intensive Care Unit, France Glucocorticoid-induced leucine zipper (GILZ) is an ubiquitous potent anti-inflammatory protein whose expression is induced by glucocorticoids, TGF- or IL-10 in haematopoietic cells. We and others have evidenced that GILZ regulates inflammation -involved signal transduction pathways, such as AP-1, NF-kappaB or FOXO. Moreover, we recently detected GILZ expression in blood neutrophils of patients suffering from acute respiratory distress syndrome (ARDS). The objective of this study was to evaluate the role of GILZ in human neutrophils apoptosis. For this purpose, we used neutrophil-like PLB-985 differentiated cells. We generated GILZ overexpressing cells stably transfected with the human gilz gene. These cells were then differentiated in neutrophil-like cells using all trans-retinoic acid (ATRA) and dimethylformamid (DMF). We measured CD11b expression, oxidative burst, phagocytosis capacity and verified the presence of multi-lobed nuclei. Differentiated PLB-985 cells were then characterized for their spontaneous and activation-induced apoptosis using PMA through SubG1 analysis and AnnexinV/7AAD staining. We found that GILZ overexpression led to an exacerbated apoptosis, characterized by caspase 3, 9 and 8 activation and loss of mitochondrial potential. These results suggested that GILZ-induced apoptosis involved the mitochondrial pathway. Interestingly, apoptosis of PLB-985 GILZ clones was associated with a downregulation of Mcl-1, whereas BID or BIM were not involved. This model suggests that in neutrophils, GILZ could participate in the control of apoptosis, essential to the resolution of inflammation in vivo. Further investigations of GILZ functions in neutrophils are ongoing both in vitro and ex vivo during ARDS. Keywords: Neutrophils, Apoptosis Regulatory Proteins, GILZ, Inflammation, Mcl-1 Conference: 15th International Congress of Immunology (ICI), Milan, Italy, 22 Aug - 27 Aug, 2013. Presentation Type: Abstract Topic: Innate immunity Citation: Espinasse M, Piednoir P, Dufour G, Montravers P, Chollet-Martin S, Pallardy M and Biola-Vidamment A (2013). Glucocorticoid-induced leucine zipper (GILZ) promotes apoptosis in vitro in neutrophil-like cells.. Front. Immunol. Conference Abstract: 15th International Congress of Immunology (ICI). doi: 10.3389/conf.fimmu.2013.02.00730 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 14 Jun 2013; Published Online: 22 Aug 2013. * Correspondence: Miss. Marie-Alix Espinasse, INSERM UMRS 996, Université Paris-Sud, Chatenay-Malabry, France, marie-alix.espinasse@u-psud.fr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Marie-Alix Espinasse Pascale Piednoir Guillaume Dufour Philippe Montravers Sylvie Chollet-Martin Marc Pallardy Armelle Biola-Vidamment Google Marie-Alix Espinasse Pascale Piednoir Guillaume Dufour Philippe Montravers Sylvie Chollet-Martin Marc Pallardy Armelle Biola-Vidamment Google Scholar Marie-Alix Espinasse Pascale Piednoir Guillaume Dufour Philippe Montravers Sylvie Chollet-Martin Marc Pallardy Armelle Biola-Vidamment PubMed Marie-Alix Espinasse Pascale Piednoir Guillaume Dufour Philippe Montravers Sylvie Chollet-Martin Marc Pallardy Armelle Biola-Vidamment Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Identification of the Chemokine CX3CL1 as a New Regulator of Malignant Cell Proliferation in Epithelial Ovarian Cancer

BackgroundLittle is known about the molecules that contribute to the growth of epithelial ovarian carcinomas (EOC), which remain the most lethal gynecological cancer in women. The chemokine Fractalkine/CX3CL1 has been widely reported to play a biologically relevant role in tumor growth and spread. We report here the first investigation of the expression and role of CX3CL1 in EOC.ResultsEpithelial cells from the surface of the ovary and the Fallopian tubes and from benign, borderline and malignant tumors all stained positive for CX3CL1. In tumor specimens from 54 women who underwent surgical treatment for EOC diagnosis, CX3CL1 immunoreactivity was unevenly distributed in epithelial tumor cells, and ranged from strong (33%) to absent (17%). This uneven distribution of CX3CL1 did not reflect the morphological heterogeneity of EOC. It was positively correlated with the proliferation index Ki-67 and with GILZ (glucocorticoid-induced leucine zipper), previously identified as an activator of the proliferation of malignant EOC cells. Hierarchical clustering analysis, including age at diagnosis, tumor grade, FIGO stage, Ki-67 index, CX3CL1, SDF-1/CXCL12 and GILZ immunostaining scores, distinguished two major clusters corresponding to low and high levels of proliferation and differing in terms of GILZ and CX3CL1 expression. GILZ overexpression in the carcinoma-derived BG1 cell line resulted in parallel changes in CX3CL1 products. Conversely, CX3CL1 promoted through its binding to CX3CR1 AKT activation and proliferation in BG1 cells. In a mouse subcutaneous xenograft model, the overexpression of GILZ was associated with higher expression of CX3CL1 and faster tumor growth.ConclusionOur findings highlight the previously unappreciated constitutive expression of CX3CL1 preceding tumorigenesis in ovarian epithelial cells. Together with GILZ, this chemokine emerges as a regulator of cell proliferation, which may be of potential clinical relevance for the selection of the most appropriate treatment for EOC patients.

Glucocorticoid‐induced leucine zipper is an endogenous antiinflammatory mediator in arthritis

Glucocorticoid-induced leucine zipper (GILZ) is a glucocorticoid-induced protein, the reported molecular interactions of which suggest that it functions to inhibit inflammation. However, the role of endogenous GILZ in the regulation of inflammation in vivo has not been established. This study was undertaken to examine the expression and function of GILZ in vivo in collagen-induced arthritis (CIA), a murine model of rheumatoid arthritis (RA), and in RA synoviocytes. GILZ expression was detected in mouse and human synovium by immunohistochemistry and in cultured cells by real-time polymerase chain reaction and permeabilization flow cytometry. GILZ function was assessed in vivo by small interfering RNA (siRNA) silencing using cationic liposome-encapsulated GILZ or control nontargeting siRNA and was assessed in vitro using transient overexpression. GILZ was readily detectable in the synovium of mice with CIA and was up-regulated by therapeutic doses of glucocorticoids. Depleting GILZ expression in vivo increased the clinical and histologic severity of CIA and increased synovial expression of tumor necrosis factor and interleukin-1 (IL-1), without affecting the levels of circulating cytokines or anticollagen antibodies. GILZ was highly expressed in the synovium of patients with active RA and in cultured RA synovial fibroblasts, and GILZ overexpression in synovial fibroblasts inhibited IL-6 and IL-8 release. Our findings indicate that GILZ functions as an endogenous inhibitor of chronic inflammation via effects on cytokine expression and suggest that local modulation of GILZ expression could be a beneficial therapeutic strategy.

Expression and regulation of glucocorticoid-induced leucine zipper in the developing anterior pituitary gland

The expression profile of glucocorticoid-induced leucine zipper (GILZ) in the anterior pituitary during the second half of embryonic development in the chick is consistent with in vivo regulation by circulating corticosteroids. However, nothing else has been reported about the presence of GILZ in the neuroendocrine system. We sought to characterize expression and regulation of GILZ in the chicken embryonic pituitary gland and determine the effect of GILZ overexpression on anterior pituitary hormone levels. Pituitary GILZ mRNA levels increased during embryogenesis to a maximum on the day of hatch, and decreased through the first week after hatch. GILZ expression was rapidly upregulated by corticosterone in embryonic pituitary cells. To determine whether GILZ regulates hormone gene expression in the developing anterior pituitary, we overexpressed GILZ in embryonic pituitary cells and measured mRNA for the major pituitary hormones. Exogenous GILZ increased prolactin mRNA above basal levels, but not as high as that in corticosterone-treated cells, indicating that GILZ may play a small role in lactotroph differentiation. The largest effect we observed was a twofold increase in FSH beta subunit in cells transfected with GILZ but not treated with corticosterone, suggesting that GILZ may positively regulate gonadotroph development in a manner not involving glucocorticoids. In conclusion, this is the first report to characterize avian GILZ and examine its regulation in the developing neuroendocrine system. We have shown that GILZ is upregulated by glucocorticoids in the embryonic pituitary gland and may regulate expression of several pituitary hormones.

Regulation of Mesenchymal Stem Cell Osteogenic Differentiation by Glucocorticoid-induced Leucine Zipper (GILZ)

Mesenchymal stem cells (MSCs) can differentiate into multiple cell lineages, including osteoblasts and adipocytes. We reported previously that glucocorticoid-induced leucine zipper (GILZ) inhibits peroxisome proliferator-activated receptor gamma-2 (Ppargamma2) expression and blocks adipocyte differentiation. Here we show that overexpression of GILZ in mouse MSCs, but not MC3T3-E1 osteoblasts, increases alkaline phosphatase activity and enhances mineralized bone nodule formation, whereas knockdown of Gilz reduces MSC osteogenic differentiation capacity. Consistent with these observations, real-time reverse transcription-PCR analysis showed that both basal and differentiation-induced transcripts of the lineage commitment gene Runx2/Cbfa1, as well as osteoblast differentiation marker genes including alkaline phosphatase, type I collagen, and osteocalcin, were all increased in GILZ-expressing cells. In contrast, the mRNA levels of adipogenic Ppargamma2 and C/ebpalpha were significantly reduced in GILZ-expressing cells under both osteogenic and adipogenic conditions. Together, our results demonstrate that GILZ functions as a modulator of MSCs and that overexpression of GILZ shifts the balance between osteogenic and adipogenic differentiation of MSCs toward the osteogenic pathway. These data suggest that GILZ may have therapeutic value for stem cell-based therapies of metabolic bone diseases, such as fracture repair.

GILZ, a new target for the transcription factor FoxO3, protects T lymphocytes from interleukin-2 withdrawal–induced apoptosis

AbstractInterleukin-2 (IL-2) withdrawal is a physiologic process inducing cell death in activated T lymphocytes. Glucocorticoid-induced leucine zipper (GILZ) has recently been identified as a protein modulating T-cell receptor activation by repressing various signaling pathways. We report here that IL-2 deprivation leads to expression of GILZ in T lymphocytes. We then characterized the human gilz promoter and showed that FoxO3 (Forkhead box class O3) binding to the Forkhead responsive elements identified in the promoter is necessary for induction of gilz expression upon IL-2 withdrawal. To assess the functional consequences of this induction, we used 2 strategies, GILZ overexpression and GILZ silencing in murine IL-2–dependent CTLL-2 cells. GILZ overexpression protects CTLL-2 cells from IL-2 withdrawal–induced apoptosis, whereas cell death is accelerated in cells unable to express GILZ. Concomitantly, the expression of Bim is inhibited in GILZ-overexpressing cells and enhanced when GILZ expression is impaired. Furthermore, GILZ inhibits FoxO3 transcriptional activity that leads to inhibition of Bim expression but also to down-regulation of GILZ itself. Therefore, GILZ is a transiently expressed protein induced upon IL-2 withdrawal that protects T cells from the onset of apoptosis.