Genetic disruption of Fra-1 decreases susceptibility to endotoxin-induced acute lung injury and mortality in mice

FOSL1's Oncogene Roles in Glioma/Glioma Stem Cells and Tumorigenesis: A Comprehensive Review

This review specifically examines the important function of the oncoprotein FOSL1 in the dimeric AP-1 transcription factor, which consists of FOS-related components. FOSL1 is identified as a crucial controller of invasion and metastatic dissemination, making it a potential target for therapeutic treatment in cancer patients. The review offers a thorough examination of the regulatory systems that govern the influence exerted on FOSL1. These include a range of changes that occur throughout the process of transcription and after the translation of proteins. We have discovered that several non-coding RNAs, such as microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), play a significant role in regulating FOSL1 expression by directly interacting with its mRNA transcripts. Moreover, an investigation into the functional aspects of FOSL1 reveals its involvement in apoptosis, proliferation, and migration. This work involves a comprehensive analysis of the complex signaling pathways that support these diverse activities. Furthermore, particular importance is given to the function of FOSL1 in coordinating the activation of several cytokines, such as TGF-beta, and the commencement of IL-6 and VEGF production in tumor-associated macrophages (TAMs) that migrate into the tumor microenvironment. There is a specific emphasis on evaluating the predictive consequences linked to FOSL1. Insights are now emerging on the developing roles of FOSL1 in relation to the processes that drive resistance and reliance on specific treatment methods. Targeting FOSL1 has a strong inhibitory effect on the formation and spread of specific types of cancers. Despite extensive endeavors, no drugs targeting AP-1 or FOSL1 for cancer treatment have been approved for clinical use. Hence, it is imperative to implement innovative approaches and conduct additional verifications.

Bioinformatic and systems biology approach revealing the shared genes and molecular mechanisms between COVID-19 and non-alcoholic hepatitis

Introduction: Coronavirus disease 2019 (COVID-19) has become a global pandemic and poses a serious threat to human health. Many studies have shown that pre-existing nonalcoholic steatohepatitis (NASH) can worsen the clinical symptoms in patients suffering from COVID-19. However, the potential molecular mechanisms between NASH and COVID-19 remain unclear. To this end, key molecules and pathways between COVID-19 and NASH were herein explored by bioinformatic analysis. Methods: The common differentially expressed genes (DEGs) between NASH and COVID-19 were obtained by differential gene analysis. Enrichment analysis and protein-protein interaction (PPI) network analysis were carried out using the obtained common DEGs. The key modules and hub genes in PPI network were obtained by using the plug-in of Cytoscape software. Subsequently, the hub genes were verified using datasets of NASH (GSE180882) and COVID-19 (GSE150316), and further evaluated by principal component analysis (PCA) and receiver operating characteristic (ROC). Finally, the verified hub genes were analyzed by single-sample gene set enrichment analysis (ssGSEA) and NetworkAnalyst was used for the analysis of transcription factor (TF)-gene interactions, TF-microRNAs (miRNA) coregulatory network, and Protein-chemical Interactions. Results: A total of 120 DEGs between NASH and COVID-19 datasets were obtained, and the PPI network was constructed. Two key modules were obtained via the PPI network, and enrichment analysis of the key modules revealed the common association between NASH and COVID-19. In total, 16 hub genes were obtained by five algorithms, and six of them, namely, Kruppel-like factor 6 (KLF6), early growth response 1 (EGR1), growth arrest and DNA-damage-inducible 45 beta (GADD45B), JUNB, FOS, and FOS-like antigen 1 (FOSL1) were confirmed to be closely related to NASH and COVID-19. Finally, the relationship between hub genes and related pathways was analyzed, and the interaction network of six hub genes was constructed with TFs, miRNAs, and compounds. Conclusion: This study identified six hub genes related to COVID-19 and NASH, providing a new perspective for disease diagnosis and drug development.

The PMN-MDSC - A key player in glucocorticoid resistance following combined physical and psychosocial trauma

Stress-associated somatic and psychiatric disorders are often linked to non-resolving low-grade inflammation, which is promoted at least in part by glucocorticoid (GC) resistance of distinct immune cell subpopulations. While the monocyte/macrophage compartment was in the focus of many clinical and preclinical studies, the role of myeloid-derived suppressor cells (MDSCs) in stress-associated pathologies and GC resistance is less understood. As GC resistance is a clear risk factor for posttraumatic complications in patients on intensive care, the exact interplay of physical and psychosocial traumatization in the development of GC resistance needs to be further clarified. In the current study we employ the chronic subordinate colony housing (CSC) paradigm, a well-characterized mouse model of chronic psychosocial stress, to study the role of myeloid cells, in particular of MDSCs, in innate immune activation and GC resistance following combined psychosocial and physical (e.g., bite wounds) trauma. Our findings support the hypothesis that stress-induced neutrophils, polymorphonuclear (PMN)-MDSCs and monocytes/monocyte-like (MO)-MDSCs get primed and activated locally in the bone marrow as determined by toll-like receptor (TLR)2 upregulation and increased basal and lipopolysaccharide (LPS)-induced in vitro cell viability. These primed and activated myeloid cells emigrate into the peripheral circulation and subsequently, if CSC is accompanied by significant bite wounding, accumulate in the spleen. Here, PMN-MDSCs and monocytes/MO-MDSCs upregulate TLR4 expression, which exclusively in PMN-MDSCs promotes NF-κB hyperactivation upon LPS-stimulation, thereby exceeding the anti-inflammatory capacities of GCs and resulting in GC resistance.

The Fra-1: Novel role in regulating extensive immune cell states and affecting inflammatory diseases

Fra-1(Fos-related antigen1), a member of transcription factor activator protein (AP-1), plays an important role in cell proliferation, apoptosis, differentiation, inflammation, oncogenesis and tumor metastasis. Accumulating evidence suggest that the malignancy and invasive ability of tumors can be significantly changed by directly targeting Fra-1. Besides, the effects of Fra-1 are gradually revealed in immune and inflammatory settings, such as arthritis, pneumonia, psoriasis and cardiovascular disease. These regulatory mechanisms that orchestrate immune and non-immune cells underlie Fra-1 as a potential therapeutic target for a variety of human diseases. In this review, we focus on the current knowledge of Fra-1 in immune system, highlighting its unique importance in regulating tissue homeostasis. In addition, we also discuss the possible critical intervention strategy in diseases, which also outline future research and development avenues.

Functional reprogramming of monocytes in acute and convalescent severe COVID-19 patients

Severe COVID-19 disease is associated with dysregulation of the myeloid compartment during acute infection. Survivors frequently experience long-lasting sequelae, but little is known about the eventual persistence of this immune alteration. Herein, we evaluated TLR-induced cytokine responses in a cohort of mild to critical patients during acute or convalescent phases (n = 97). In the acute phase, we observed impaired cytokine production by monocytes in the patients with the most severe COVID-19. This capacity was globally restored in convalescent patients. However, we observed increased responsiveness to TLR1/2 ligation in patients who recovered from severe disease, indicating that these cells display distinct functional properties at the different stages of the disease. In patients with acute severe COVID-19, we identified a specific transcriptomic and epigenomic state in monocytes that can account for their functional refractoriness. The molecular profile of monocytes from recovering patients was distinct and characterized by increased chromatin accessibility at activating protein 1 (AP1) and MAF loci. These results demonstrate that severe COVID-19 infection has a profound impact on the differentiation status and function of circulating monocytes, during both the acute and the convalescent phases, in a completely distinct manner. This could have important implications for our understanding of short- and long-term COVID-19–related morbidity.

Identification of the Fosl1/AMPK/autophagy axis involved in apoptotic and inflammatory effects following spinal cord injury

Strategies for reducing spinal cord injury (SCI) have become a research focus because an effective treatment of SCI is unavailable. The objective of this study was to explore the underlying mechanisms of Fosl1 following SCI. Based on the analysis of the Gene Expression Omnibus (GEO) database, Fosl1 was found to be highly enhanced in SCI. This result was confirmed in our animal model, and Fosl1 was found to be obviously expressed in neurons. Next, we treated PC-12 cells with H₂O₂ to mimic injured neurons and further verified that Fosl1 silencing upregulated AMPK expression, promoted autophagy and inhibited inflammation and apoptosis. Subsequently, a special inhibitor of AMPK was used to examine the role of AMPK, and we learned that the inhibition of AMPK suppressed autophagy and promoted inflammation and apoptosis following Fosl1 silencing. These changes completely reversed the beneficial effects of Fosl1 silencing on injured PC-12 cells. Moreover, treatment with an AMPK activator resulted in effects that were opposite those of the inhibitor. Finally, rats were injected intrathecally with si-Fosl1 to detect its role in vivo. The results showed that si-Fosl1 improved neurological function and decreased apoptosis and inflammation at 14 d postoperation, and the activator further benefited the rats of si-Fosl1 treatment. In conclusion, Fosl1 inhibits autophagy and promotes inflammation and apoptosis through the AMPK signaling pathway following SCI in vivo and in vitro.

Role of the Transcription Factor FOSL1 in Organ Development and Tumorigenesis

The transcription factor FOSL1 plays an important role in cell differentiation and tumorigenesis. Primarily, FOSL1 is crucial for the differentiation of several cell lineages, namely adipocytes, chondrocytes, and osteoblasts. In solid tumors, FOSL1 controls the progression of tumor cells through the epithelial-mesenchymal transformation. In this review, we summarize the available data on FOSL1 expression, stabilization, and degradation in the cell. We discuss how FOSL1 is integrated into the intracellular signaling mechanisms and provide a comprehensive analysis of FOSL1 influence on gene expression. We also analyze the pathological changes caused by altered Fosl1 expression in genetically modified mice. In addition, we dedicated a separate section of the review to the role of FOSL1 in human cancer. Primarily, we focus on the FOSL1 expression pattern in solid tumors, FOSL1 importance as a prognostic factor, and FOSL1 perspectives as a molecular target for anticancer therapy.

Serum Amyloid A Aggravates Lipopolysaccharide-Induced Injury of BEAS-2B Cells by Activating Toll-Like Receptor 2/Activator Protein-1 Signaling

The serum amyloid A (sAA) is a common sensitive indicator for the diagnosis of infectious diseases, and sAA levels are increased in pneumonia. However, the detailed molecular mechanism is unknown. Previous studies have demonstrated the participation of Toll-like receptor (TLR) 2 and its downstream protein activator protein-1 (AP-1) in inflammatory lung injury. This study aimed to investigate the effect of sAA on LPS-induced BEAS-2B cells injury and uncover the possible mechanism. The human bronchial epithelial cell line BEAS-2B was exposed to sAA with or without lipopolysaccharide (LPS) treatment, then cell viability, inflammation and apoptosis were evaluated. The effects of TLR2 knockout on sAA + LPS-treated BEAS-2B cells were also determined. Results revealed that sAA treatment reduced cell viability in a concentration-dependent manner and the effect of 500 nM sAA on cell viability was approximately equivalent to LPS. The levels of inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-8, monocyte chemotactic protein (MCP)-1 and IL-6 as well as cell apoptosis and expression of proteins related to apoptosis were significantly increased upon sAA or LPS stimulation. The expression of TLR2 and AP-1 was also elevated in cells challenged with sAA or LPS. Besides, sAA and LPS co-treatment further enhanced the actions of LPS. However, the knockdown of TLR2 obviously blunted the effects of LPS and sAA co-treatment on cell viability, inflammation and apoptosis. Taken together, our results revealed that sAA could exert an enhanced effect on LPS-induced BEAS-2B cells injury via promoting TLR2/AP-1 expression.

Transcription factor-mediated signaling pathways' contribution to the pathology of acute lung injury and acute respiratory distress syndrome

The 2019 novel coronavirus (2019-nCoV) is still spreading rapidly around the world, and one cause of lethality for patients infected with 2019-nCoV is acute respiratory distress syndrome (ARDS). ARDS is a severe syndrome of acute lung injury (ALI) that is predominantly triggered by inflammation and results in a sudden loss of, or damage to, kidney function. Emerging studies reveal that multiple transcription factor-associated signaling pathways are activated in the pathology of ALI/ARDS. Of these pathways, the activation of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells), AP-1 (activator protein 1), IRFs (interferon regulatory factors), STATs (signal transducer and activator of transcription), Wnt/β-catenin-TCF/LEF (T-cell factor/lymphoid enhancer-binding factor), and CtBP2 (C-Terminal binding protein 2)-associated transcriptional complex contributes to ALI/ARDS pathology through diverse mechanisms, such as inducing proinflammatory cytokine levels and mediating macrophage polarization. In this review, we present an updated summary of the mechanisms underlying these signaling activations and regulations, as well as their contribution to the pathogenesis of ALI/ARDS. We aim to develop a better understanding of how ALI/ARDS occurs and improve ALI/ARDS therapy.

FOSL1 is a novel mediator of endotoxin/lipopolysaccharide-induced pulmonary angiogenic signaling

Systemic sepsis is a known risk factor for bronchopulmonary dysplasia (BPD) in premature infants, a disease characterized by dysregulated angiogenesis and impaired vascular and alveolar development. We have previoulsy reported that systemic endotoxin dysregulates pulmonary angiogenesis resulting in alveolar simplification mimicking BPD in neonatal mice, but the underlying mechanisms remain unclear. We undertook an unbiased discovery approach to identify novel signaling pathways programming sepsis-induced deviant lung angiogenesis. Pulmonary endothelial cells (EC) were isolated for RNA-Seq from newborn C57BL/6 mice treated with intraperitoneal lipopolysaccharide (LPS) to mimic systemic sepsis. LPS significantly differentially-regulated 269 genes after 6 h, and 1,934 genes after 24 h. Using bioinformatics, we linked 6 h genes previously unknown to be modulated by LPS to 24 h genes known to regulate angiogenesis/vasculogenesis to identify pathways programming deviant angiogenesis. An immortalized primary human lung EC (HPMEC-im) line was generated by SV40 transduction to facilitate mechanistic studies. RT-PCR and transcription factor binding analysis identified FOSL1 (FOS like 1) as a transcriptional regulator of LPS-induced downstream angiogenic or vasculogenic genes. Over-expression and silencing studies of FOSL1 in immortalized and primary HPMEC demonstrated that baseline and LPS-induced expression of ADAM8, CXCR2, HPX, LRG1, PROK2, and RNF213 was regulated by FOSL1. FOSL1 silencing impaired LPS-induced in vitro HPMEC angiogenesis. In conclusion, we identified FOSL1 as a novel regulator of sepsis-induced deviant angiogenic signaling in mouse lung EC and human fetal HPMEC.

Silencing lncRNA AGAP2-AS1 Upregulates miR-195-5p to Repress Migration and Invasion of EC Cells via the Decrease of FOSL1 Expression

The interaction of long non-coding RNAs (lncRNAs), microRNAs (miRNAs), and mRNAs has been implicated in various types of cancers, including esophageal cancer (EC). The current study aimed to investigate the role of AGAP2-AS1/miR-195-5p/Fos-like antigen-1 (FOSL1) in EC progression. The expression of AGAP2-AS1, miR-195-5p, and FOSL1 in tumor tissues isolated from EC patients and EC cell lines was determined by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), the results of which illustrated that AGAP2-AS1 and FOSL1 were increased while miR-195-5p was reduced in EC. Next, the ectopic expression, knockdown, and reporter assay experiments were all employed to elucidate the mechanism of AGAP2-AS1/miR-195-5p/FOSL1 in the processes of EC cell proliferation, cell cycle, apoptosis, invasion, and migration as well as tumor growth. Knockdown of AGAP2-AS1 or overexpression of miR-195-5p reduced EC cell proliferation, migration, and invasion, blocked cell cycle entry, and elevated apoptosis. FOSL1 was found to be specifically targeted by miR-195-5p. AGAP2-AS1 was observed to upregulate FOSL1 by binding to miR-195-5p. Silencing of AGAP2-AS1 was observed to restrain the development of EC both in vitro and in vivo through upregulating miR-195-5p and downregulating FOSL1. Taken together, AGAP2-AS1 knockdown exercises suppressive effects on the development of EC through miR-195-5p-dependent downregulation of FOSL1. Therefore, targeting AGAP2-AS1 could be a future direction to develop a novel molecule-targeted therapeutic strategy for EC.

Transcription factor Fra-1 targets arginase-1 to enhance macrophage-mediated inflammation in arthritis

The polarization of macrophages is regulated by transcription factors such as nuclear factor kappa B (NF-κB) and activator protein 1 (AP-1). In this manuscript, we delineated the role of the transcription factor Fos-related antigen 1 (Fra-1) during macrophage activation and development of arthritis. Network level interaction analysis of microarray data derived from Fra-1- or Fra-2-deficient macrophages revealed a central role of Fra-1, but not of Fra-2 in orchestrating the expression of genes related to wound response, toll-like receptor activation and interleukin signaling. Chromatin-immunoprecipitation (ChIP)-sequencing and standard ChIP analyses of macrophages identified arginase 1 (Arg1) as a target of Fra-1. Luciferase reporter assays revealed that Fra-1 down-regulated Arg1 expression by direct binding to the promoter region. Using macrophage-specific Fra-1- or Fra-2- deficient mice, we observed an enhanced expression and activity of Arg1 and a reduction of arthritis in the absence of Fra-1, but not of Fra-2. This phenotype was reversed by treatment with the arginase inhibitor Nω-hydroxy-nor-L-arginine, while ʟ-arginine supplementation increased arginase activity and alleviated arthritis, supporting the notion that reduced arthritis in macrophage-specific Fra-1-deficient mice resulted from enhanced Arg1 expression and activity. Moreover, patients with active RA showed increased Fra-1 expression in the peripheral blood and elevated Fra-1 protein in synovial macrophages compared to RA patients in remission. In addition, the Fra-1/ARG1 ratio in synovial macrophages was related to RA disease activity. In conclusion, these data suggest that Fra-1 orchestrates the inflammatory state of macrophages by inhibition of Arg1 expression and thereby impedes the resolution of inflammation.

c-Jun Is Required for Nuclear Factor-κB-Dependent, LPS-Stimulated Fos-Related Antigen-1 Transcription in Alveolar Macrophages

Previously, we have reported that Fos-related antigen-1 (Fra-1) transcription factor promotes LPS-induced acute lung injury and mortality, and that LPS-induced Fra-1 expression in the lung occurs predominantly in alveolar macrophages. Nuclear factor-κB (NF-κB) and c-Jun transcription factors play key roles in modulating inflammatory and immune responses induced by infectious and non-infectious insults. Here, we report that NF-κB and c-Jun coregulate Fra-1 induction by LPS in alveolar macrophages and that this regulation occurs through both the NF-κB and the extracellular signal-regulated protein kinase (ERK) signaling pathways. Transient transfections with Fra-1 promoter-reporter constructs and inhibitor studies revealed that the transcriptional activation of Fra-1 by LPS in alveolar macrophages is mediated by NF-κB and ERK1/2 signaling. Importantly, chromatin immunoprecipitation assays revealed the recruitment of c-Jun and NF-κB to the endogenous Fra-1 promoter after LPS stimulation. We found that inhibition of ERK1/2 signaling reduced LPS-stimulated c-Jun and NF-κB recruitment to the promoter. Likewise, NF-κB inhibitor blocked LPS-induced NF-κB and c-Jun binding to the promoter. ERK1/2 inhibition had no effect on c-Jun activation but suppressed LPS-stimulated NF-κB phosphorylation. Finally, functional assays showed reduced levels of LPS-stimulated NF-κB regulated proinflammatory IL-1β and macrophage inflammatory protein-1α expression and increased antiinflammatory IL-10 expression in lung alveolar macrophages of Fra-1-null mice in vivo. Thus, our studies indicate that NF-κB and c-Jun coregulate LPS-induced Fra-1 transcription and that Fra-1 selectively modulates LPS-stimulated inflammatory cytokine expression in lung alveolar macrophages during inflammatory lung injury.

Myeloid-specific Fos-related antigen-1 regulates cigarette smoke-induced lung inflammation, not emphysema, in mice

Heightened lung inflammation is a cardinal feature of chronic obstructive pulmonary disease (COPD). Cigarette smoke (CS)-induced macrophage recruitment and activation, accompanied by abnormal secretion of a number of inflammatory cytokines and matrix metalloproteinases, play a major role in the pathophysiology of COPD. The Fos-related antigen-1 (Fra-1) transcription factor differentially regulates several cellular processes that are implicated in COPD, such as inflammation and immune responses, cell proliferation and death, and extracellular remodeling. Although CS stimulates Fra-1 expression in the lung, the precise role of this transcription factor in the regulation of CS-induced lung inflammation in vivo is poorly understood. Here, we report that myeloid-specific Fra-1 signaling is important for CS-induced lung macrophagic inflammatory response. In response to chronic CS exposure, mice with Fra-1 specifically deleted in myeloid cells showed reduced levels of CS-induced lung macrophagic inflammation, accompanied by decreased expression levels of proinflammatory cytokines compared with their wild-type counterparts. Consistent with this result, bone marrow-derived Fra-1-null macrophages treated with CS showed decreased levels of proinflammatory mediators and matrix metalloproteinases. Interestingly, deletion of Fra-1 in myeloid cells did not affect the severity of emphysema. We propose that Fra-1 plays a key role in promoting chronic CS-induced lung macrophagic inflammation in vivo, and that targeting this transcription factor may be useful in dampening persistent lung inflammation in patients with COPD.

Visualization of Fra-1/AP-1 activation during LPS-induced inflammatory lung injury using fluorescence optical imaging

Inappropriate lung inflammatory response following oxidant and toxicant exposure can lead to abnormal repair and disease pathogenesis, including fibrosis. Thus early detection of molecular and cellular processes and mediators promoting lung inflammation is necessary to develop better strategies for therapeutic intervention and disease management. Previously, we have shown that transcription factor Fra-1/AP-1 plays key roles in lung inflammatory response, as Fra-1-null mice are less susceptible than wild-type mice to LPS-induced lung injury and mortality. Herein, we developed a transgenic reporter mouse model expressing tdTomato under the control of FRA-1 (human) promoter (referred to as FRA-1(TdTg) mice) to monitor its activation during inflammatory lung injury using fluorescence protein-based optical imaging and molecular analysis in vivo and ex vivo. A higher red fluorescent signal was observed in the lungs of LPS-treated FRA-1(TdTg) mice compared with vehicle controls, and Western blot and qRT-PCR analyses revealed a significant correlation with the FRA-1-tdTomato reporter expression. Immunocolocalization demonstrated expression of FRA-1-tdTomato largely in lung alveolar macrophages and to some extent in epithelial cells. Moreover, we validated these results with a second reporter mouse model that expressed green fluorescent protein upon activation of endogenous Fra-1 promoter. Additionally, we demonstrated increased expression of FRA-1 in alveolar macrophages in human lung instilled with Escherichia coli ex vivo. Collectively, our data obtained from two independent reporter mouse models and from human samples underscore the significance of Fra-1 activation in alveolar macrophages during inflammatory lung injury and may aid in developing strategies to target this transcription factor in lung injury and repair.

Fra-1/AP-1 transcription factor negatively regulates pulmonary fibrosis in vivo

The Fra-1/AP-1 transcription factor plays a key role in tumor epithelial cell progression; however, its role in pathogenic lung fibrosis remains unclear. In the present study, using a genetic approach (Fra-1 deficient mice), we have demonstrated a novel regulatory (protective) role for Fra-1 in lung fibrosis. We found greater levels of progressive interstitial fibrosis, characterized by increased levels of inflammation, collagen accumulation, and profibrotic and fibrotic gene expression in the lungs of Fra-1^Δ/Δ mice than in those of Fra-1^+/+ mice following bleomycin treatment. Fra-1 knockdown in human lung epithelial cells caused the upregulation of mesenchymal marker N-cadherin, concomitant with a downregulation of the epithelial phenotype marker E-cadherin, under basal conditions and in response to bleomycin and TGF-β1. Furthermore, Fra-1 knockdown caused an enhanced expression of type 1 collagen and the downregulation of collagenase (MMP-1 and MMP-13) gene expression in human lung epithelial cells. Collectively, our findings demonstrate that Fra-1 mediates anti-fibrotic effects in the lung through the modulation of proinflammatory, profibrotic and fibrotic gene expression, and suggests that the Fra-1 transcription factor may be a potential target for pulmonary fibrosis, a progressive disorder with poor prognosis and treatment.

Oxidant-induced cell death and Nrf2-dependent antioxidative response are controlled by Fra-1/AP-1

AP-1 (Jun/Fos) transcription factors play key roles in various biological processes, including cell death. Here we report a novel role for Fra-1 in oxidant-induced cell death controlled by modulating antioxidant gene expression. Fra-1-deficient (Fra-1(Δ/Δ)) mouse embryonic fibroblasts (MEFs) and primary lung fibroblasts (PLFs) were remarkably resistant to H(2)O(2)- and diquat-induced cell death, compared to their wild-type (Fra-1(+/+)) counterparts. Fra-1 deficiency ablated oxidant-induced mitochondrion-dependent apoptosis. Fra-1(Δ/Δ) cells had elevated basal levels of antioxidant enzymes and intracellular glutathione (GSH), which were further stimulated by oxidants. Loss of Fra-1 led to an increased half-life of transcription factor Nrf2 and increased recruitment of this protein to the promoters of antioxidant genes and increased their expression. Depletion of intracellular GSH or RNA interference (RNAi)-mediated knockdown of Nqo1, Hmox1, and Nrf2 restored oxidant-induced cell death in Fra-1(Δ/Δ) cells. Thus, Fra-1 appears to increase susceptibility to oxidants and promotes cell death by attenuating Nrf2-driven antioxidant responses.