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Sekhar P Reddy

Publications and source records attributed to Sekhar P Reddy.

18 recordsLinked to original sources
PubMed2007

Distinctive epidermal growth factor receptor/extracellular regulated kinase-independent and -dependent signaling pathways in the induction of airway mucin 5B and mucin 5AC expression by phorbol 12-myristate 13-acetate.

Elevated expression of gel-forming mucin (MUC) genes MUC5AC and MUC5B is a major pathological feature in various airway diseases. In this study, we show that phorbol 12-myristate 13-acetate (PMA) is a potent stimulator for MUC5B gene expression under air-liquid interface conditions in three airway epithelial cell systems: primary cultures of normal human bronchial epithelial cells, the immortalized normal bronchial epithelial cell line HBE1, and the human lung adenocarcinoma cell line A549. Stimulation was time- and dose-dependent, could be demonstrated by promoter-reporter gene transfection, and was sensitive to mithramycin A, suggesting the involvement of a specificity protein 1-based transcriptional mechanism in the stimulation. PMA-induced MUC5B message and promoter-reporter gene activity were specifically sensitive to inhibition of protein kinase C delta, which was further confirmed by the forced expression of dominant-negative mutant of protein kinase C delta. Regarding downstream transduction, PMA-induced MUC5B expression was sensitive to inhibitors and dominant-negative expression of signaling molecules involved in Ras/mitogen-activated protein kinase/extracellular signal-regulated kinase kinase kinase1-mediated c-Jun N-terminal kinase and p38 pathways. This contrasted with the inhibition of PMA-induced MUC5AC expression by inhibitors of the Ras/epidermal growth factor receptor/extracellular regulated kinase signaling pathway. These results demonstrate for the first time that PMA-stimulated MUC5AC and MUC5B expressions are regulated through distinctive epidermal growth factor receptor/extracellular regulated kinase-dependent and -independent signaling pathways.

Bronchi↗
PubMed2006

A JNK-independent signaling pathway regulates TNF alpha-stimulated, c-Jun-driven FRA-1 protooncogene transcription in pulmonary epithelial cells.

Among the several effectors that mediate TNF-alpha action is AP-1, which consists of transcription factors belonging to the JUN and FOS families. Although the effects of TNF-alpha in immune cells, such as the induction of NF-kappaBeta, are well known, the mechanisms by which it induces transcriptional activation of AP-1 in pulmonary epithelial cells are not well defined. In this study, we report that TNF-alpha stimulates the expression of the FRA-1 protooncogene in human pulmonary epithelial cells using c-Jun, acting via a 12-O-tetradecanoylphorbol-13 acetate response element located at -318. Although TNF-alpha stimulates phosphorylation of c-Jun, the inhibition of JNK activity had no significant effect on FRA-1 induction. Consistent with this result, ectopic expression of a c-Jun mutant lacking JNK phosphorylation sites had no effect on the TNF-alpha-induced expression of the promoter. In contrast, inhibition of the ERK pathway or ectopic expression of an ERK1 mutant strikingly reduced FRA-1 transcription. ERK inhibition not only blocked phosphorylation of Elk1, CREB, and ATF1, which constitutively bind to the FRA-1 promoter, but also suppressed the recruitment of c-Jun to the promoter. We found that short interfering RNA-mediated silencing of FRA-1 enhances TNF-alpha-induced IL-8 expression, whereas overexpression causes an opposite effect. Our findings collectively indicate that ERK signaling plays key roles in both Elk1, CREB, and ATF-1 activation and the subsequent recruitment of c-Jun to the FRA-1 promoter in response to TNF-alpha in pulmonary epithelial cells.

Animals↗
PubMed2006

EGFR-activated signaling and actin remodeling regulate cyclic stretch-induced NRF2-ARE activation.

Cyclic stretch (CS) associated with mechanical ventilation (MV) can cause excessive alveolar and endothelial distention, resulting in lung injury and inflammation. Antioxidant enzymes (AOEs) play a major role in suppressing these effects. The transcription factor Nrf2, via the antioxidant response element (ARE), alleviates pulmonary toxicant- and oxidant-induced oxidative stress by up-regulating the expression of several AOEs. Although gene expression profiling has revealed the induction of AOEs in the lungs of rodents exposed to MV, the mechanisms by which mechanical forces, such as CS, regulate the activation of Nrf2-dependent ARE-transcriptional responses are poorly understood. To mimic mechanical stress associated with MV, we have cultured pulmonary alveolar epithelial and endothelial cells on collagen I-coated BioFlex plates and subjected them to CS. CS exposure stimulated ARE-driven transcriptional responses and subsequent AOE expression. Ectopic expression of a dominant-negative Nrf2 suppressed the CS-stimulated ARE-driven responses. Our findings suggest that actin remodeling is necessary but not sufficient for high-level CS-induced ARE activation in both epithelial and endothelial cells. We also found that inhibition of EGFR activity by a pharmacologic agent ablated the CS-induced ARE transcriptional response in both cell types. Additional studies revealed that amphiregulin, an EGFR ligand, regulates this process. We further demonstrated that the PI3K-Akt pathway acts as the downstream effector of EGFR and regulates CS-induced ARE-activation in an oxidative stress-dependent manner. Collectively, these novel findings suggest that EGFR-activated signaling and actin remodeling act in concert to regulate the CS-induced Nrf2-ARE transcriptional response and subsequent AOE expression.

Actins↗
PubMed2006

Mechanical stress activates xanthine oxidoreductase through MAP kinase-dependent pathways.

Xanthine oxidoreductase (XOR) plays a prominent role in acute lung injury because of its ability to generate reactive oxygen species. We investigated the role of XOR in ventilator-induced lung injury (VILI). Male C57BL/6J mice were assigned to spontaneous ventilation (sham) or mechanical ventilation (MV) with low (7 ml/kg) and high tidal volume (20 ml/kg) for 2 h after which lung XOR activity and expression were measured and the effect of the specific XOR inhibitor allopurinol on pulmonary vascular leakage was examined. In separate experiments, rat pulmonary microvascular endothelial cells (RPMECs) were exposed to cyclic stretch (5% and 18% elongation, 20 cycles/min) for 2 h before intracellular XOR activity measurement. Lung XOR activity was significantly increased at 2 h of MV without changes in XOR expression. There was evidence of p38 MAP kinase, ERK1/2, and ERK5 phosphorylation, but no change in JNK phosphorylation. Evans blue dye extravasation and bronchoalveolar lavage protein concentration were significantly increased in response to MV, changes that were significantly attenuated by pretreatment with allopurinol. Cyclic stretch of RPMECs also caused MAP kinase phosphorylation and a 1.7-fold increase in XOR activity, which was completely abrogated by pretreatment of the cells with specific MAP kinase inhibitors. We conclude that XOR enzymatic activity is significantly increased by mechanical stress via activation of p38 MAP kinase and ERK and plays a critical role in the pathogenesis of pulmonary edema associated with VILI.

Animals↗
PubMed2006

A Phosphatidylinositol 3-kinase-regulated Akt-independent signaling promotes cigarette smoke-induced FRA-1 expression.

The FRA-1 proto-oncogene is overexpressed in a variety of human tumors and is known to up-regulate the expression of genes involved in tumor progression and invasion. The phosphatidylinositol 3-kinase (PI3K)-Akt pathway is also known to regulate these cellular processes. More importantly, respiratory toxicants and carcinogens activate both the PI3K-Akt pathway and FRA-1 expression in human bronchial epithelial (HBE) cells. In this study we investigated a potential link between the PI3K-Akt pathway and the cigarette smoke (CS)-stimulated epidermal growth factor receptor-mediated FRA-1 induction in non-oncogenic HBE cells. Treatment of cells with LY294002, an inhibitor of the PI3K-Akt pathway, completely blocked CS-induced FRA-1 expression. Surprisingly pharmacological inhibition of Akt had no significant effect on CS-induced FRA-1 expression. Likewise the inhibition of protein kinase C zeta, which is a known downstream effector of PI3K, did not alter FRA-1 expression. We found that the PI3K through p21-activated kinase 1 regulates FRA-1 proto-oncogene induction by CS and the subsequent activation of the Elk1 and cAMP-response element-binding protein transcription factors that are bound to the promoter in HBE cells.

Carcinogens↗
PubMed2006

Oxidants and signaling by mitogen-activated protein kinases in lung epithelium.

Oxidants in cigarette smoke and generated from asbestos fibers activate mitogen-activated protein kinase (MAPK) signaling cascades in lung epithelial cells in vitro and in vivo. These signaling pathways lead to the enhanced ability of Jun and Fos family members (i.e., components of the activator protein [AP]-1 transcription factor) to activate transcription of a number of AP-1-dependent target genes involved in cell proliferation or death, differentiation, and inflammation. Research by the Basbaum laboratory has been critical in showing that mucin transcription in response to cigarette smoke and gram-positive bacteria is mediated through activation of the epidermal growth factor receptor and MAPK cascades. Work from our laboratories supports the concept that MAPK signaling and AP-1 transactivation by cigarette smoke and asbestos may synergize in lung epithelial cell injury, compensatory proliferation of lung epithelial cells, and carcinogenesis, supporting a mechanistic framework for the striking increases in lung cancer incidence in asbestos workers who smoke. Targeting of MAPKs and inter-related signaling cascades may be critical to the prevention of lung cancers and control of mucin overproduction in a number of lung diseases including asthma, cystic fibrosis, chronic bronchitis, and chronic obstructive pulmonary disease.

Animals↗
PubMed2006

Nrf2 is a critical regulator of the innate immune response and survival during experimental sepsis.

Host genetic factors that regulate innate immunity determine susceptibility to sepsis. Disruption of nuclear factor-erythroid 2-related factor 2 (Nrf2), a basic leucine zipper transcription factor that regulates redox balance and stress response, dramatically increased the mortality of mice in response to endotoxin- and cecal ligation and puncture-induced septic shock. LPS as well as TNF-alpha stimulus resulted in greater lung inflammation in Nrf2-deficient mice. Temporal analysis of pulmonary global gene expression after LPS challenge revealed augmented expression of large numbers of proinflammatory genes associated with the innate immune response at as early as 30 minutes in lungs of Nrf2-deficient mice, indicating severe immune dysregulation. The expression profile indicated that Nrf2 has a global influence on both MyD88-dependent and -independent signaling. Nrf2-deficient mouse embryonic fibroblasts showed greater activation of NF-kappaB and interferon regulatory factor 3 in response to LPS and polyinosinic-polycytidylic acid [poly(I:C)] stimulus, corroborating the effect of Nrf2 on MyD88-dependent and -independent signaling. Nrf2's regulation of cellular glutathione and other antioxidants is critical for optimal NF-kappaB activation in response to LPS and TNF-alpha. Our study reveals Nrf2 as a novel modifier gene of sepsis that determines survival by mounting an appropriate innate immune response.

Animals↗
PubMed2005

Transcription repressor activity of spleen tyrosine kinase mediates breast tumor suppression.

Spleen tyrosine kinase (SYK) is a candidate tumor suppressor gene in breast. Loss of SYK expression in breast tumors as a result of DNA hypermethylation promotes tumor cell proliferation and invasion and predicts shorter survival of breast cancer patients. We previously reported that, in addition to its well-known cytoplasmic localization, the full-length Syk is also present in the nucleus and that Syk nuclear translocation is a rate-limiting step to determine Syk tumor suppressor function. Here, we show that the full-length form of Syk acts as a transcription repressor in the cell nucleus. Ectopic expression of Syk down-regulates the transcription of FRA1 and cyclin D1 oncogenes. This transcription-repressing activity of Syk is associated with its binding to members of the histone deacetylase family. Syk interacts with transcription factor Sp1 at the Sp1 DNA-binding site in the FRA1 promoter to repress Sp1-activated FRA1 transcription. Thus, breast tumorigenesis and progression resulting from the loss of SYK are underscored by the derepression of Sp1-mediated oncogene transcription.

Animals↗
PubMed2005

Mitogen regulated induction of FRA-1 proto-oncogene is controlled by the transcription factors binding to both serum and TPA response elements.

FRA-1, a member of the FOS family of transcription factors, is overexpressed in a variety of human tumors, and contributes to tumor progression. In addition to mitogens, various toxicants and carcinogens persistently induce FRA-1 expression in vitro and in vivo. Although the mitogen induced expression of c-FOS is relatively well understood, it is poorly defined in the case of FRA-1. Our recent analysis of the FRA-1 promoter has shown a critical role for a TRE located at -318 in mediating the TPA-induced expression. The -379 to -283 bp promoter segment containing a critical TRE (-318), however, is insufficient for the induction of FRA-1 promoter. Here, we show that a 40-bp (-276/-237) segment, comprising a TCF binding site and the CArG box (collectively known as serum response element, SRE), and an ATF site, is also necessary for the FRA-1 induction by TPA and EGF. Interestingly, the -283 to +32 bp FRA-1 promoter fragment containing an SRE and an ATF site alone was also insufficient to confer TPA sensitivity to a reporter gene. However, in association with the -318 TRE, the SRE and ATF sites imparted a strong TPA-inducibility to the reporter. Similarly, EGF also required these motifs for the full induction of this gene. Using ChIP assays we show that, in contrast to c-Jun, SRF, Elk1, ATF1 and CREB proteins bind to SRE and ATF sites of the FRA-1 promoter, constitutively. RNAi-mediated knockdown of endogenous SRF, ELK1 and c-JUN protein expression significantly reduced TPA-stimulated FRA-1 promoter activity. Thus, a bipartite enhancer formed by an upstream TRE and the downstream SRE and ATF sites and the cognate factors is necessary and sufficient for the regulation of FRA-1 in response to mitogens.

Activating Transcription Factors↗
PubMed2005

Gene expression profiling of NRF2-mediated protection against oxidative injury.

Nuclear factor E2 p45-related factor 2 (NRF2) contributes to cellular protection against oxidative insults and chemical carcinogens via transcriptional activation of antioxidant/detoxifying enzymes. To understand the molecular basis of NRF2-mediated protection against oxidative lung injury, pulmonary gene expression profiles were characterized in Nrf2-disrupted (Nrf2(-/-)) and wild-type (Nrf2(+/+)) mice exposed to hyperoxia or air. Genes expressed constitutively higher in Nrf2(+/+) mice than in Nrf2(-/-) mice included antioxidant defense enzyme and immune cell receptor genes. Higher basal expression of heat shock protein and structural genes was detected in Nrf2(-/-) mice relative to Nrf2(+/+) mice. Hyperoxia enhanced expression of 175 genes (> or = twofold) and decreased expression of 100 genes (> or =50%) in wild-type mice. Hyperoxia-induced upregulation of many well-known/new antioxidant/defense genes (e.g., Txnrd1, Ex, Cp-2) and other novel genes (e.g., Pkc-alpha, Tcf-3, Ppar-gamma) was markedly greater in Nrf2(+/+) mice than in Nrf2(-/-) mice. In contrast, induced expression of genes encoding extracellular matrix and cytoskeletal proteins was higher in Nrf2(-/-) mice than in Nrf2(+/+) mice. These NRF2-dependent gene products might have key roles in protection against hyperoxic lung injury. Results from our global gene expression profiles provide putative downstream molecular mechanisms of oxygen tissue toxicity.

Animals↗
PubMed2005

Development of monoclonal antibodies against GBF1 and their use in studying its functions.

Interferon-gamma (IFN-gamma) regulates a number of cellular genes using a variety of cellular signaling pathways. Previously, we identified a novel IFN-regulated element, IFN-gamma-activated transcriptional element (GATE), in the promoter of the murine IFN regulatory factor-9 (IRF-9) gene. This element binds to novel factors. We have recently characterized a novel regulatory factor, GATE binding factor 1 (GBF1), which promoted IFN-gamma-induced transcription. Although GBF1 was a potent inducer of transcription, it did not bind to DNA well in vitro. To understand its role in IFN-gamma-induced actions, we raised monoclonal antibodies (mAb) against GBF1. These antibodies are highly useful in Western, immunoprecipitation, and immunocytochemical analyses. Employing these antibodies, we show that GBF1 is recruited to the endogenous IRF-9 promoter. We also show GBF1 interacts with CAAAT/enhancer binding protein-beta (C/EBP-beta), the other GATE binding factor. Furthermore, other cytokines, such as interleukin-1 (IL-1) and IL-6, induced the expression of GBF1. These antibodies may be useful tools for investigating the role of GBF1 in cytokine-induced responses.

Animals↗
PubMed2004

Matrix metalloproteinase/epidermal growth factor receptor/mitogen-activated protein kinase signaling regulate fra-1 induction by cigarette smoke in lung epithelial cells.

Exposure to cigarette smoke (CS) can lead to the development of lung cancer, but the molecular mechanisms underlying this process remain unclear. Given that activator protein 1 (AP-1) regulates genes involved in both physiologic and pathophysiologic processes, we have investigated the effects of CS on Jun and Fos family member expression and regulation using a nonmalignant human bronchial epithelial cell line, 1HAEo. Exposure to CS caused a marked upregulation of c-Jun, c-Fos, and Fra-1, but not of Fra-2, Jun-B, and Jun-D expression. Because Fra-1 is overexpressed in various tumors and upregulates genes associated with tumor progression, we further elucidated the mechanisms that control CS-stimulated fra-1 induction. CS stimulated fra-1 induction primarily at the transcriptional level. However, epidermal growth factor receptor (EGFR)-specific inhibitor, AG1478, completely suppressed CS-stimulated fra-1 expression. Similarly, the specific inhibitors of extracellular signal-regulated kinase (ERK), c-Jun NH2 terminal kinase (JNK), and p38 kinase signaling markedly suppressed fra-1 induction. Consistent with this finding, AG1478 blocked CS-stimulated ERK, JNK, and p38 phosphorylation. These results suggest that EGFR-activated multiple kinase signaling is essential for fra-1 induction. Furthermore, treatment of cells with GM6001, which inhibits matrix metalloproteinase activity, significantly suppressed CS-stimulated EGF shedding, EGFR and ERK kinase phosphorylation, and subsequent fra-1 induction. Collectively, our findings indicate an obligatory role for metalloproteinase-EGFR-mediated mitogen-activated protein kinase signaling in controlling CS-induced fra-1 expression.

Cells, Cultured↗
PubMed2004

NADPH oxidase and ERK signaling regulates hyperoxia-induced Nrf2-ARE transcriptional response in pulmonary epithelial cells.

Oxidative stress plays a major role in hyperoxia-induced acute lung injury. We have shown previously that mice lacking the Nrf2 are more susceptible to hyperoxia than are wild-type mice. Nrf2 activates antioxidant response element (ARE)-mediated gene expression involved in cellular protection against toxic insults. The present study was designed to investigate the mechanisms that control the activation of Nrf2 by hyperoxia using a non-malignant murine alveolar epithelial cell line, C10. No significant alteration in the levels of Nrf2 mRNA and protein was found following exposure to hyperoxia. In contrast, hyperoxia caused the translocation of Nrf2 from the cytoplasm to the nucleus within 30-60 min of exposure. Consistent with these observations, gel shift and reporter analyses demonstrated a correlation between the hyperoxia-enhanced ARE DNA-binding activity of Nrf2 and an up-regulation of ARE-driven transcription. Inhibition of NADPH oxidase with diphenyleneiodonium (DPI) blocked both Nrf2 translocation and ARE-mediated transcription. Inhibition of the MEK/ERK pathway caused a similar effect. Consistent with this finding, hyperoxia stimulated ERK-1 and ERK-2 phosphorylation, whereas DPI or N-acetyl-l-cysteine blocked such activation. Hyperoxia stimulated the phosphorylation of endogenous Nrf2, but not in the presence of U0126, suggesting a critical role for ERK signaling in the activation of Nrf2. Consistent with this notion, hyperoxia did not stimulate the phosphorylation of Nrf2 in fibroblasts lacking the ERK-1. Collectively, our findings suggest that hyperoxia-induced, ARE-driven, Nrf2-dependent transcription is controlled by NADPH oxidase and ERK-1 signaling.

Active Transport, Cell Nucleus↗
PubMed2003

DEP-induced fra-1 expression correlates with a distinct activation of AP-1-dependent gene transcription in the lung.

Recent studies indicate a potential role for Fra-1, a heterodimeric partner of activator protein (AP)-1, in toxicant-induced epithelial injury, repair, and cellular transformation. Here we have investigated the effects of diesel exhaust particles (DEP) on fra-1 expression in C10 cells, a murine lung epithelial cell line. DEP markedly upregulated fra-1, but not fra-2, expression. The increase in fra-1 mRNA expression correlated well with its protein- and DNA-binding activity. DNA-binding assays also revealed a predominant presence of Jun-B and Jun-D in the AP-1 complex. Interestingly, DEP did not alter Jun-B and Jun-D protein levels. Transcriptional analysis revealed that fra-1 induction is regulated in part at the transcriptional level. The -379 to +32 bp 5'-flanking region mediated this induction. Furthermore, inhibitors of ERK1/2, JNK1, and p38 mitogen-activated protein kinases (MAPKs) significantly suppressed DEP-stimulated fra-1 transcription, suggesting their involvement in the induction process. Consistent with this finding, DEP stimulated phosphorylation of ERK1/2, JNK1, and p38 MAPKs with a distinct activation pattern. Overexpression of Fra-1 downregulated c-Jun and Nrf2 enhanced AP-1- and ARE-mediated reporter gene expression, respectively. In contrast, Fra-1 had the opposite effect on matrix metalloproteinase (MMP)-9 promoter activity. In particular, it bound to the functional AP-1 site of the MMP-9 promoter after DEP stimulation. Consistent with this result, DEP also markedly upregulated MMP-9 promoter activity. Collectively, these findings suggest that fra-1 induction by DEP may play a role in selectively regulating gene expression involved in alveolar epithelial cell injury and repair.

Animals↗
PubMed2003

Multiple cis-elements mediate the transcriptional activation of human fra-1 by 12-O-tetradecanoylphorbol-13-acetate in bronchial epithelial cells.

Recent studies indicate a potential role for Fra-1, a heterodimeric partner of activator protein 1 (AP1), in toxicant-induced epithelial injury, repair, and cellular transformation. Here, we have investigated the transcriptional regulation of fra-1 by 12-O-tetradecanoylphorbol-13-acetate (TPA) in human bronchial epithelial (HBE) cells, which are the direct targets of inhaled toxins/carcinogens. In contrast to a transient induction by H2O2, TPA persistently activated fra-1 transcription, principally at the transcriptional level. A deletion analysis of the fra-1 promoter revealed that several cis-elements located between -105/+32 and -283/-105 bp mediate minimal and basal promoter activities, respectively. A region between -379 and -283 bp, which harbors a putative TPA response element, a GC box, and an Ets-like binding site, was required for high level TPA-inducible expression. Mutations in any of these cis-elements markedly reduced both basal and TPA-inducible expression. Thus, cooperative interactions between factors binding to multiple cis-elements of the -379/-283 promoter region appear to regulate TPA-induced fra-1 transcription in HBE cells. Consistent with this finding, electrophoretic mobility shift assays indicated the formation of multiple complexes consisting of the AP1-, Sp-, and ETS-specific family of transcription factors with the -379/-283 fragment. Members of the AP1 family distinctly regulated the fra-1 promoter. In particular, coexpression of c-Jun, Jun-D, and Fra-2 up-regulated fra-1 transcription. Chromatin immunoprecipitation assays revealed an enhanced recruitment of c-Jun, Jun-D, and Fra-2 to the endogenous fra-1 promoter upon TPA stimulation. These results underscore the regulatory role of c-Jun, Jun-D, and Fra-2 in TPA-inducible fra-1 expression in HBE cells in vivo.

Base Sequence↗
PubMedDate not supplied

Hyperoxia stimulates an Nrf2-ARE transcriptional response via ROS-EGFR-PI3K-Akt/ERK MAP kinase signaling in pulmonary epithelial cells.

Nuclear factor erythroid 2-related factor (Nrf2) confers protection against cell death induced by hyperoxia and other proapoptotic stimuli. Because phosphoinositide-3-kinase (PI3K)/Akt signaling promotes cell survival, the significance of this pathway in mediating reactive oxygen species (ROS)-dependent hyperoxia-induced Nrf2 activation was investigated in the murine pulmonary epithelial cell line, C10. Inhibition of the PI3K pathway markedly attenuated hyperoxia-induced Nrf2 translocation and ARE (antioxidant response element)-mediated transcription. Consistent with this, hyperoxia markedly stimulated the activation of PI3K pathway, while an NADPH oxidase inhibitor and an antioxidant prevented such activation. The inhibition of Akt activity using a pharmacological inhibitor markedly attenuated Nrf2 translocation and ARE-driven expression. Moreover, overexpression of a dominant-negative Akt mutant attenuated the transcription, whereas a constitutively active mutant stimulated it. These results suggest that PI3K/Akt signaling regulates Nrf2 activation by hyperoxia. Inhibition of the PI3K pathway prevented hyperoxia-stimulated Akt and ERK1/2 kinase activation, which is critical for Nrf2-mediated transcription. Likewise, the epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, AG1478, blocked hyperoxia-stimulated Akt and ERK1/2 phosphorylation, Nrf2 nuclear accumulation, and ARE-driven transcription. Consistent with this result, an NADPH oxidase inhibitor blocked hyperoxia- stimulated EGFR phosphorylation, which was correlated with the attenuation of Akt and ERK activation. Collectively, our data suggest that EGFR-PI3K signaling through Akt and ERK kinases regulates ROS-dependent, hyperoxia-induced Nrf2 activation in pulmonary epithelial cells.

Animals↗
PubMedDate not supplied

Nrf2 defends the lung from oxidative stress.

Nuclear factor, erythroid 2 related factor 2 (Nrf2) belongs to the Cap'n'collar/basic region leucine zipper (CNC-bZIP) transcription factor family, and is activated by diverse oxidants, pro-oxidants, antioxidants, and chemopreventive agents. After phosphorylation and dissociation from the cytoplasmic inhibitor, Kelch-like ECH-associated protein 1 (Keap1), Nrf2 translocates to the nucleus and binds to an antioxidant response element (ARE). Through transcriptional induction of ARE-bearing genes that encode antioxidant-detoxifying proteins, Nrf2 activates cellular rescue pathways against oxidative injury, inflammation/immunity, apoptosis, and carcinogenesis. ARE-driven genes include direct antioxidants (e.g., GPx), thiol metabolism-associated detoxifying enzymes (e.g., GSTs), stress-response genes (e.g., HO-1), and others (e.g., PSMB5). Application of nrf2 germ-line mutant mice elucidated protective roles for Nrf2 in various models of human disorders in the liver, lung, kidney, brain, and circulation. In the lung, deficiency of nrf2 augmented injury caused by bleomycin and environmental oxidants including hyperoxia, diesel exhaust particles, and cigarette smoke. Microarray analyses of lungs from nrf2-deficient and -sufficient mice identified Nrf2-dependent genes that might be critical in pulmonary protection. Observations from these studies highlight the importance of the Nrf2-antioxidant pathway and may provide new therapeutic strategies for acute respiratory distress syndrome, idiopathic pulmonary fibrosis, cancer, and emphysema in which oxidative stress is implicated.

Animals↗