ARHGEF39 promotes tumor progression via activation of Rac1/P38 MAPK/ATF2 signaling and predicts poor prognosis in non-small cell lung cancer patients.

Rho guanine nucleotide exchange factor 39 (ARHGEF39), also called C9orf100, is a new member of the Dbl-family of guanine nucleotide exchange factors. Although ARHGEF39 has been proven to regulate tumor progression in hepatocellular carcinoma, the downstream signaling pathway of ARHGEF39 and its clinical associations in non-small cell lung cancer (NSCLC) are currently unknown. In the present study, using MTT, colony formation, flow cytometry, mice xenografts, wound healing, and transwell assays, we showed that ARHGEF39 promoted tumor proliferation, migration, and invasion. Furthermore, ARHGEF39 promoted the expression of Cyclin A2, Cyclin D1, and MMP2 by activating Rac1, leading to increased phosphorylation of P38 and ATF2. Treatment with a P38 inhibitor counteracted the effect of ARHGEF39 overexpression on the increase in Cyclin A2, Cyclin D1, and MMP2 expression. Moreover, the elevated levels of p-P38 and p-ATF2 caused by ARHGEF39 overexpression could be inhibited by expression of a dominant negative Rac1 mutant (T17N). In addition, the inhibition of the expression of p-P38 and p-ATF2 by ARHGEF39 RNAi could be restored by the expression of a constitutively active Rac1 mutant (Q61L). A similar impact on cell growth and invasion was observed after ARHGEF39 overexpression combined with the P38 inhibitor, Rac1 T17N, or Rac1 Q61L. Using immunohistochemistry, ARHGEF39 expression was observed to correlate positively with larger tumor size in clinical samples from 109 cases of NSCLC (P = 0.008). The Kaplan-Meier test revealed that ARHGEF39 expression significantly affected the overall survival of patients with NSCLC (52.55 ± 6.40 months vs. 64.30 ± 5.40 months, P = 0.017). In conclusion, we identified that ARHGEF39 promotes tumor growth and invasion by activating the Rac1-P38-ATF2 signaling pathway, as well as increasing the expression of Cyclin A2, Cyclin D1, and MMP2 in NSCLC cells. ARHGEF39 may be a useful marker to predict poor prognosis of patients with NSCLC.

The role of Nrf2 and ATF2 in resistance to platinum-based chemotherapy.

PURPOSE: Nrf2 and its role in controlling levels of the AKR family of aldo-keto reductases which have been implicated in resistance to platinum-based chemotherapy was studied in ovarian, cervical and lung cell lines. METHODS: Nrf2 shRNA knockdowns of cells from different tumor origins were prepared to determine the role of this factor in producing resistance to platinum chemotherapy. RESULTS: Nrf2 knockdowns resulted in marked decreases in AKR1C1, AKR1C2 and to a lesser extent AKR1C3. Additionally, all other candidate enzymes GSTπ and TRX1 were decreased, but their role was difficult to correlate to cytotoxicity. Nrf2 knockdowns exhibited marked increases in mitochondrial membrane depolarization and ROS production following cisplatin treatment, with the cervical ME180R knockdowns exhibiting the greatest effect (AKR1C1 and AKR1C2 levels were decreased in the ME180R and SKOV3 cells to near zero). Oxaliplatin tended to parallel cisplatin, except it markedly stimulated O2- production not [Formula: see text] by oxaliplatin treatment of the ME180R cells. The pJNK/p38 pathway has been implicated in cisplatin cytotoxicity, and significant phosphorylation of pJNK was observed in the SKOV3 and ME180R and p38 in the SKOV3 knockdowns. Phosphorylation of ATF2 was decreased in the Nrf2 knockdowns (Crf38, Srf6, Arf5) which could affect its interaction with JNK and p38. Oxaliplatin treatment showed minimal effects on the JNK/p38 pathway, showing that its mode of action is different although ROS generation appeared an initial step with both drugs. CONCLUSIONS: Nrf2 controls a multitude of different candidate genes; however, it did markedly modulate cisplatin resistance through the AKR family. This involved ROS production and activation of the pJNK/p38 pathway with involvement of ATF2.

A Protective Mechanism of Visible Red Light in Normal Human Dermal Fibroblasts: Enhancement of GADD45A-Mediated DNA Repair Activity.

The phototherapeutic effects of visible red light on skin have been extensively investigated, but the underlying biological mechanisms remain poorly understood. We aimed to elucidate the protective mechanism of visible red light in terms of DNA repair of UV-induced oxidative damage in normal human dermal fibroblasts. The protective effect of visible red light on UV-induced DNA damage was identified by several assays in both two-dimensional and three-dimensional cell culture systems. With regard to the protective mechanism of visible red light, our data showed alterations in base excision repair mediated by growth arrest and DNA damage inducible, alpha (GADD45A). We also observed an enhancement of the physical activity of GADD45A and apurinic/apyrimidinic endonuclease 1 (APE1) by visible red light. Moreover, UV-induced DNA damages were diminished by visible red light in an APE1-dependent manner. On the basis of the decrease in GADD45A-APE1 interaction in the activating transcription factor-2 (ATF2)-knockdown system, we suggest a role for ATF2 modulation in GADD45A-mediated DNA repair upon visible red light exposure. Thus, the enhancement of GADD45A-mediated base excision repair modulated by ATF2 might be a potential protective mechanism of visible red light.

miR-204 suppresses the development and progression of human glioblastoma by targeting ATF2.

In human cancers, miRNAs are important regulators of multiple cellular processes, and aberrant miRNA expression has been observed, and their alterations contribute to multiple cancer development and progression. Till now, little has been known about the role of miR-204 in human glioblastoma (GBM). In the present study, we used in-vitro assays to investigate the mechanisms of miR-204 in GBM cell lines and 60 cases of GBM tissues. Here, we found that miR-204 expression is downregulated in both GBM cell lines A172, U87 and U251 cells and GBM tissues as compared with NHA cells and normal tissues (all p<0.001). In addition, the ectopic expression of miR-204 suppressed A172 and U87 cell proliferation, migration and invasion. Meanwhile, miR-204 over-expression extremely inhibited the protein expression of ATF2. Notably, the enforced expression of ATF2 in A172 and U87 cells with the over-expression of miR-204 attenuated the inhibitory effects of miR-204 on proliferation, migration and invasion. In conclusion, our findings suggest that miR-204 suppressed cell proliferation, migration and invasion through inhibition of ATF2, thus, miR-204 may function as a useful drug target in the treatment and diagnosis of GBM.

Sensitisation of c-MYC-induced B-lymphoma cells to apoptosis by ATF2.

Transcription factors ATF2 (activating transcription factor 2) and ATF7 (activating transcription factor 7) are highly homologous members of the activator protein 1 (AP-1) family. Their activities are growth factor and stress stimulated and they strictly require phosphorylation by mitogen-activated protein (MAP) kinases for their transcriptional functions. In samples of human B-cell lymphomas as well as Eµ-Myc-driven mouse B-cell lymphomas, we find that ATF2 as well as MAP kinase c-Jun N-terminal kinase (JNK) are significantly up-regulated compared with normal human B-cell lines and mouse B cells, respectively. The B cell-specific deletion of ATF2 and ATF7 in mice results in significantly accelerated onset of Eµ-Myc-induced lymphoma. In addition, loss of ATF2/7 desensitises Eµ-Myc lymphoma cells to spontaneous as well as stress-induced apoptosis. Our results therefore suggest that c-MYC induces stress-mediated activation of ATF2 and ATF7 and that these transcription factors regulate apoptosis in response to oncogenic transformation of B cells.

In vitro studies on the antimicrobial peptide human beta-defensin 9 (HBD9): signalling pathways and pathogen-related response (an American Ophthalmological Society thesis).

PURPOSE: Human ß-defensins (HBDs) are an important part of the innate immune host defense at the ocular surface. Unlike other defensins, expression of HBD9 at the ocular surface is reduced during microbial infection, but activation of toll-like receptor 2 (TLR2) in corneal epithelial cells has been shown to up-regulate HBD9. Our purpose was to test the hypothesis that TLR2 has a key role in the signalling pathway(s) involved in the overexpression or underexpression of HBD9, and accordingly, different pathogens would induce a different expression pattern of HBD9. METHODS: The in vitro RNAi silencing method and response to dexamethasone were used to determine key molecules involved in signalling pathways of HBD9 in immortalized human corneal epithelial cells. The techniques included cell culture with exposure to specific transcription factor inhibitors and bacteria, RNA extraction and cDNA synthesis, quantitative real-time polymerase chain reaction, and immunohistology. RESULTS: This study demonstrates that TLR2 induces HBD9 mRNA and protein expression in a time- and dose-dependent manner. Transforming growth factor-ß-activated kinase 1 (TAK1) plays a central role in HBD9 induction by TLR2, and transcription factors c-JUN and activating transcription factor 2 are also involved. Dexamethasone reduces TLR2-mediated up-regulation of HBD9 mRNA and protein levels in mitogen-activated protein kinase phosphatase 1 (MKP1)-dependent and c-JUN-independent manner. HBD9 expression differs with gram-negative and gram-positive bacteria. CONCLUSIONS: TLR2-mediated MKPs and nuclear factor-κB signalling pathways are involved in HBD9 expression. TAK-1 is a key molecule. These molecules can be potentially targeted to modulate HBD9 expression. Differential expression of HBD9 with different bacteria could be related to differences in pathogen-associated molecular patterns of these organisms.

Circadian rhythms: An electric jolt to the clock.

The animal circadian pacemaker is composed of two transcriptional feedback loops, which regulate electrical activity in circadian neurons. Surprisingly, a new study reports that electrical activity can reprogram circadian transcription, and identifies CREB proteins as candidates for this reprograming.

Electrical activity can impose time of day on the circadian transcriptome of pacemaker neurons.

BACKGROUND: Circadian (∼24 hr) rhythms offer one of the best examples of how gene expression is tied to behavior. Circadian pacemaker neurons contain molecular clocks that control 24 hr rhythms in gene expression that in turn regulate electrical activity rhythms to control behavior. RESULTS: Here we demonstrate the inverse relationship: there are broad transcriptional changes in Drosophila clock neurons (LN(v)s) in response to altered electrical activity, including a large set of circadian genes. Hyperexciting LN(v)s creates a morning-like expression profile for many circadian genes while hyperpolarization leads to an evening-like transcriptional state. The electrical effects robustly persist in per(0) mutant LN(v)s but not in cyc(0) mutant LN(v)s, suggesting that neuronal activity interacts with the transcriptional activators of the core circadian clock. Bioinformatic and immunocytochemical analyses suggest that CREB family transcription factors link LN(v) electrical state to circadian gene expression. CONCLUSIONS: The electrical state of a clock neuron can impose time of day to its transcriptional program. We propose that this acts as an internal zeitgeber to add robustness and precision to circadian behavioral rhythms.

Driving transcriptional regulators in melanoma metastasis.

The progression of melanoma toward the metastatic phenotype occurs in a defined stepwise manner. While many molecular changes take place early in melanoma development, progression toward the malignant phenotype, most notably during the transition from the radial growth phase (RGP) to the vertical growth phase (VGP) involves deregulated expression of several transcription factors. For example, the switch from RGP to VGP is associated with the loss of the transcription factor AP2α and gain of transcriptional activity of cAMP-responsive element binding protein. Together with the upregulation of microphthalmia-associated transcription factor, activating transcription factor 2, nuclear factor kappa B, and other transcription factors, these changes lead to dysregulated expression or function of important cellular adhesion molecules, matrix degrading enzymes, survival factors, as well as other factors leading to metastatic melanoma. Additionally, recent evidence suggests that microRNAs and RNA editing machinery influence the expression of transcription factors or are regulated themselves by transcription factors. Many of the downstream signaling molecules regulated by transcription factors, such as protease activated receptor-1, interleukin-8, and MCAM/MUC18 represent new treatment prospects.

Molecular mechanisms responsible for the selective and low-grade induction of proinflammatory mediators in murine macrophages by lipopolysaccharide.

Low-dose endotoxemia is prevalent in humans with adverse health conditions, and it correlates with the pathogenesis of chronic inflammatory diseases such as atherosclerosis, diabetes, and neurologic inflammation. However, the underlying molecular mechanisms are poorly understood. In this study, we demonstrate that subclinical low-dose LPS skews macrophages into a mild proinflammatory state, through cell surface TLR4, IL-1R-associated kinase-1, and the Toll-interacting protein. Unlike high-dose LPS, low-dose LPS does not induce robust activation of NF-κB, MAPKs, PI3K, or anti-inflammatory mediators. Instead, low-dose LPS induces activating transcription factor 2 through Toll-interacting protein-mediated generation of mitochondrial reactive oxygen species, allowing mild induction of proinflammatory mediators. Low-dose LPS also suppresses PI3K and related negative regulators of inflammatory genes. Our data reveal novel mechanisms responsible for skewed and persistent low-grade inflammation, a cardinal feature of chronic inflammatory diseases.

NADPH oxidase-mediated redox signal contributes to lipoteichoic acid-induced MMP-9 upregulation in brain astrocytes.

BACKGROUND: Lipoteichoic acid (LTA) is a component of gram-positive bacterial cell walls and may be elevated in the cerebrospinal fluid of patients suffering from meningitis. Among matrix metalloproteinases (MMPs), MMP-9 has been observed in patients with brain inflammatory diseases and may contribute to the pathology of brain diseases. Moreover, several studies have suggested that increased oxidative stress is implicated in the pathogenesis of brain inflammation and injury. However, the molecular mechanisms underlying LTA-induced redox signal and MMP-9 expression in brain astrocytes remain unclear. OBJECTIVE: Herein we explored whether LTA-induced MMP-9 expression was mediated through redox signals in rat brain astrocytes (RBA-1 cells). METHODS: Upregulation of MMP-9 by LTA was evaluated by zymographic and RT-PCR analyses. Next, the MMP-9 regulatory pathways were investigated by pretreatment with pharmacological inhibitors or transfection with small interfering RNAs (siRNAs), Western blotting, and chromatin immunoprecipitation (ChIP)-PCR and promoter activity reporter assays. Moreover, we determined the cell functional changes by migration assay. RESULTS: These results showed that LTA induced MMP-9 expression via a PKC(α)-dependent pathway. We further demonstrated that PKCα stimulated p47phox/NADPH oxidase 2 (Nox2)-dependent reactive oxygen species (ROS) generation and then activated the ATF2/AP-1 signals. The activated-ATF2 bound to the AP-1-binding site of MMP-9 promoter, and thereby turned on MMP-9 gene transcription. Additionally, the co-activator p300 also contributed to these responses. Functionally, LTA-induced MMP-9 expression enhanced astrocytic migration. CONCLUSION: These results demonstrated that in RBA-1 cells, activation of ATF2/AP-1 by the PKC(α)-mediated Nox(2)/ROS signals is essential for upregulation of MMP-9 and cell migration enhanced by LTA.

Tumor cell-derived angiopoietin-like protein ANGPTL2 is a critical driver of metastasis.

Strategies to inhibit metastasis have been mainly unsuccessful in part due to insufficient mechanistic understanding. Here, we report evidence of critical role for the angiopoietin-like protein 2 (ANGPTL2) in metastatic progression. In mice, Angptl2 has been implicated in inflammatory carcinogenesis but it has not been studied in human tumors. In patients with lung cancer, elevated levels of ANGPTL2 expression in tumor cells within the primary tumor were associated with a reduction in the period of disease-free survival after surgical resection. Transcription factors NFATc, ATF2, and c-Jun upregulated in aggressive tumor cells promoted increased Angptl2 expression. Most notably, tumor cell-derived ANGPTL2 increased in vitro motility and invasion in an autocrine/paracrine manner, conferring an aggressive metastatic tumor phenotype. In xenograft mouse models, tumor cell-derived ANGPTL2 accelerated metastasis and shortened survival whereas attenuating ANGPTL2 expression in tumor cells-blunted metastasis and extended survival. Overall, our findings showed that tumor cell-derived ANGPTL2 drives metastasis and provided an initial proof of concept for blockade of its action as a strategy to antagonize the metastatic process.

Caspase-3 is a target gene of c-Jun:ATF2 heterodimers during apoptosis induced by activity deprivation in cerebellar granule neurons.

Caspase-3, a key executor of neuronal apoptosis, is up-regulated and activated during apoptosis induced by activity deprivation in cerebellar granule neurons (CGNs). However, the transcriptional mechanism regulating caspase-3 during CGN apoptosis remains unknown. Here, we show that the caspase-3 gene is transactivated and its induction is preceded by c-Jun NH(2)-terminal kinase (JNK)/c-Jun:ATF2 pathway activation following activity deprivation in CGNs. We observed that caspase-3 induction is abolished by pharmacological inhibition of the JNK/c-Jun:ATF2 pathway. Destroying c-Jun:ATF2 heterodimers with dominant negative mutants of c-Jun and ATF2 or knockdown by small RNA interference reduced caspase-3 promoter activity and mRNA level. Furthermore, chromatin immunoprecipitation showed increased binding of c-Jun:ATF2 heterodimers to the caspase-3 promoter in response to activity deprivation in vivo. Site-directed mutagenesis of the caspase-3 promoter revealed that caspase-3 transcriptional activation depends primarily on an ATF site -233 to -225 nucleotides upstream of the start site. Taken together, these data demonstrate that caspase-3 is a target gene of c-Jun:ATF2 heterodimers during apoptosis induced by activity deprivation in CGNs.

Loss of ATF2 function leads to cranial motoneuron degeneration during embryonic mouse development.

The AP-1 family transcription factor ATF2 is essential for development and tissue maintenance in mammals. In particular, ATF2 is highly expressed and activated in the brain and previous studies using mouse knockouts have confirmed its requirement in the cerebellum as well as in vestibular sense organs. Here we present the analysis of the requirement for ATF2 in CNS development in mouse embryos, specifically in the brainstem. We discovered that neuron-specific inactivation of ATF2 leads to significant loss of motoneurons of the hypoglossal, abducens and facial nuclei. While the generation of ATF2 mutant motoneurons appears normal during early development, they undergo caspase-dependent and independent cell death during later embryonic and foetal stages. The loss of these motoneurons correlates with increased levels of stress activated MAP kinases, JNK and p38, as well as aberrant accumulation of phosphorylated neurofilament proteins, NF-H and NF-M, known substrates for these kinases. This, together with other neuropathological phenotypes, including aberrant vacuolisation and lipid accumulation, indicates that deficiency in ATF2 leads to neurodegeneration of subsets of somatic and visceral motoneurons of the brainstem. It also confirms that ATF2 has a critical role in limiting the activities of stress kinases JNK and p38 which are potent inducers of cell death in the CNS.

Activating transcription factor 2 (ATF2) controls tolfenamic acid-induced ATF3 expression via MAP kinase pathways.

Tolfenamic acid (TA) is a non-steroidal anti-inflammatory drug associated with anti-tumorigenic and pro-apoptotic properties in animal and in vitro models of cancer. However, the underlying cellular mechanisms by which TA exerts its effects are only partially understood. Activating transcription factor 3 (ATF3) is a member of the ATF/CREB subfamily of the basic region-leucine zipper family and has been known as a tumor suppressor in human colorectal cancer cells. The present study was performed to observe whether ATF3 mediates TA-induced apoptosis and to elucidate the molecular mechanism of ATF3 transcription induced by TA. TA treatment and ectopic expression of ATF3 increased apoptosis, whereas knockdown of ATF3 resulted in significant repression of TA-activated apoptosis. The TA treatment also induced ATF3 promoter activity. Internal deletion and point mutation of the predicted ATF/C/EBP binding site in ATF3 promoter abolished luciferase activation by TA. Overexpression of ATF2 resulted in significant increase in ATF3 promoter activity, and electrophoretic mobility shift assay identified this region as a core sequence to which ATF2 binds. TA treatment resulted in an increase in ATF2 phosphorylation, which was followed by a subsequent increase in ATF3 transcription. Knock down of ATF2 abolished TA-induced ATF3 expression. We further provide evidence that TA leads to increases in phospho-p38 MAPK, JNK and ERK levels. Inhibition of these pathways using selective inhibitors and dominant negative constructs ameliorated TA-induced ATF3 expression and promoter activities. The current study shows that TA stimulates ATF3 expression and subsequently induces apoptosis. These pathways are mediated through phosphorylation of ATF2, which is mediated by p38 MAPK-, JNK- and ERK-dependent pathways.

The role of ATF-2 family transcription factors in adipocyte differentiation: antiobesity effects of p38 inhibitors.

ATF-2 is a member of the ATF/CREB family of transcription factors and is activated by stress-activated protein kinases, such as p38. To analyze the physiological role of ATF-2 family transcription factors, we have generated mice with mutations in Atf-2 and Cre-bpa, an Atf-2-related gene. The trans-heterozygotes of both mutants were lean and had reduced white adipose tissue (WAT). ATF-2 and CRE-BPa were required for bone morphogenetic protein 2 (BMP-2)-and p38-dependent induction of peroxisome proliferator-activated receptor gamma2 (PPARgamma2), a key transcription factor mediating adipocyte differentiation. Since stored fat supplies have been recognized as a possible target for antiobesity treatments, we tested whether inhibition of the p38-ATF-2 pathway suppresses adipocyte differentiation and leads to reduced WAT by treating mice with a p38 inhibitor for long periods of time. High-fat diet (HFD)-induced obesity was significantly reduced in mice fed the p38 inhibitor. Furthermore, the p38 inhibitor alleviated HFD-induced insulin resistance. In p38 inhibitor-treated mice, macrophage infiltration into WAT was reduced and the tumor necrosis factor alpha (TNF-alpha) levels were lower than control mice. Thus, p38 inhibitors may provide a novel antiobesity treatment.

Arachidonic acid induces Fas and FasL upregulation in human leukemia U937 cells via Ca2+/ROS-mediated suppression of ERK/c-Fos pathway and activation of p38 MAPK/ATF-2 pathway.

Arachidonic acid (AA)-induced apoptotic death of human leukemia U937 cells was characteristic of increase in intracellular Ca(2+) concentration ([Ca(2+)]i), ROS generation, ERK inactivation, p38 MPAK activation, degradation of procaspase-8 and production of truncated Bid (tBid). Moreover, AA treatment upregulated Fas/FasL protein expression and transcription of Fas/FasL mRNA. Downregulation of FADD blocked AA-induced procaspase-8 degradation and rescued viability of AA-treated cells. BAPTA-AM (Ca(2+) chelator) pretreatment abolished AA-induced ROS generation, while N-acetylcysteine (NAC, ROS scavenger) was unable to alter AA-elicited [Ca(2+)]i increase. Pretreatment with BAPTA-AM or NAC abrogated p38 MAPK activation and restored ERK activation. Suppression of p38 MAPK or transfection of constitutively active MEK1 abolished AA-induced Fas and FasL upregulation. AA treatment repressed ERK-mediated c-Fos phosphorylation but evoked p38 MAPK-mediated ATF-2 phosphorylation. Knockdown of c-Fos and ATF-2 by siRNA reflected that c-Fos counteracted the effect of ATF-2 on Fas/FasL upregulation. Taken together, our data indicate that Fas/FasL upregulation in AA-treated U937 cells is elicited by Ca(2+)/ROS-mediated suppression of ERK/c-Fos pathway and activation of p38 MAPK/ATF-2, and suggest that autocrine Fas-mediated apoptotoic mechanism is involved in AA-induced cell death.

Coordination of multiple dual oxidase-regulatory pathways in responses to commensal and infectious microbes in drosophila gut.

All metazoan guts are in permanent contact with the microbial realm. However, understanding of the exact mechanisms by which the strength of gut immune responses is regulated to achieve gut-microbe mutualism is far from complete. Here we identify a signaling network composed of complex positive and negative mechanisms that controlled the expression and activity of dual oxidase (DUOX), which 'fine tuned' the production of microbicidal reactive oxygen species depending on whether the gut encountered infectious or commensal microbes. Genetic analyses demonstrated that negative and positive regulation of DUOX was required for normal host survival in response to colonization with commensal and infectious microbes, respectively. Thus, the coordinated regulation of DUOX enables the host to achieve gut-microbe homeostasis by efficiently combating infection while tolerating commensal microbes.

Integrative decomposition procedure and Kappa statistics for the distinguished single molecular network construction and analysis.

Our method concentrates on and constructs the distinguished single gene network. An integrated method was proposed based on linear programming and a decomposition procedure with integrated analysis of the significant function cluster using Kappa statistics and fuzzy heuristic clustering. We tested this method to identify ATF2 regulatory network module using data of 45 samples from the same GEO dataset. The results demonstrate the effectiveness of such integrated way in terms of developing novel prognostic markers and therapeutic targets.