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

PAK1 as a Potential Therapeutic Target in Male Smokers with EGFR-Mutant Non-Small Cell Lung Cancer

P21-activated kinases (PAKs) are serine/threonine protein kinases that contribute to several cellular processes. Here, we aimed to determine the prognostic value of PAK1 and its correlation with the clinicopathological characteristics and five-year survival rates in patients with non-small cell lung cancer (NSCLC). We evaluated PAK1 mRNA and protein expression in NSCLC cells and resected tumor specimens, as well as in healthy human bronchial epithelial cells and adjacent healthy lung tissues, respectively, for effective comparison. Immunohistochemical tissue microarray analysis of 201 NSCLC specimens showed the correlation of PAK1 expression with clinicopathological characteristics. The mRNA and protein expression of PAK1 were 2.9- and 4.3-fold higher in six of seven NSCLC cell types and human tumors (both, p < 0.001) than in healthy human bronchial epithelial BEAS-2B cells and adjacent healthy lung tissues, respectively. Decreased survival was significantly associated with PAK1 overexpression in the entire cohort (χ² = 8.48, p = 0.0036), men (χ² = 17.1, p < 0.0001), and current and former smokers (χ² = 19.2, p < 0.0001). Notably, epidermal growth factor receptor (EGFR) mutation-positive lung cancer patients with high PAK1 expression showed higher mortality rates than those with low PAK1 expression (91.3% vs. 62.5%, p = 0.02). Therefore, PAK1 overexpression could serve as a molecular target for the treatment of EGFR mutation-positive lung cancer, especially among male patients and current/former smokers.

STK35 Is Ubiquitinated by NEDD4L and Promotes Glycolysis and Inhibits Apoptosis Through Regulating the AKT Signaling Pathway, Influencing Chemoresistance of Colorectal Cancer

The development of colorectal cancer (CRC) is often sporadic, but its etiology is multifactorial. Chemoresistance of CRC leads to tumor recurrence and poor prognosis in patients. The phosphorylation of protein kinase B (AKT) can activate metabolic reprogramming toward cellular glycolysis. Serine/threonine kinase 35 (STK35) regulates the cell cycle and is frequently associated with cancer progression, whereas little is known about its specific roles in CRC. In the current study, bioinformatics analyses were performed to investigate the relationship between STK35 and CRC prognosis. STK35 knockdown and overexpressing CRC cells were established to examine its functions in CRC. Fluorouracil (5-FU) was utilized to evaluate the effect of STK35 on CRC chemoresistance. Moreover, co-immunoprecipitation was performed to explore the ubiquitination of STK35. STK35 was highly expressed in CRC, and its protein expression was negatively correlated with the survival of CRC patients. Furthermore, STK35 overexpression could promote glycolysis, suppress apoptosis, upregulate p-AKT, and counteract the antitumor functions of 5-FU and neural precursor cell expressed developmentally downregulated gene 4-like (NEDD4L) in CRC cells. NEDD4L was associated with and could ubiquitinate STK35. STK35 could be a prognostic biomarker for CRC prognosis and has promotive effects on CRC cellular activities, partially through the AKT pathway. Moreover, STK35 also interferes with the chemosensitivity of CRC.

Effects of Extracellular Matrix Softening on Vascular Smooth Muscle Cell Dysfunction

Vascular smooth muscle cells (VSMCs) shift from a physiological contractile phenotype to an adverse proliferative or synthetic state, which is a major event leading to aortic disease. VSMCs are exposed to multiple mechanical signals from their microenvironment including vascular extracellular matrix (ECM) stiffness and stretch which regulate VSMC contraction. How ECM stiffness regulates the function and phenotype of VSMCs is not well understood. In this study, we introduce in vitro and in vivo models to evaluate the impact of ECM stiffnesses on VSMC function. Through unbiased transcriptome sequencing analysis, we detected upregulation of synthetic phenotype-related genes including osteopontin, matrix metalloproteinases, and inflammatory cytokines in VSMCs cultured using soft matrix hydrogels in vitro, suggesting VSMC dedifferentiation toward a synthetic phenotype upon ECM softening. For the in vivo model, the lysyl oxidase inhibitor β-aminopropionitrile monofumarate (BAPN) was administrated to disrupt the cross-linking of collagen to induce ECM softening. Consistently, decreased ECM stiffnesses promoted VSMC phenotypic switching to a synthetic phenotype as evidenced by upregulation of synthetic phenotype-related genes in the aortas of mice following BAPN treatment. Finally, BAPN-treated mice showed severe expansion and developed aortic dissection. Our study reveals the pivotal role of ECM softening in regulating the VSMC phenotype switch and provides a potential target for treating VSMC dysfunction and aortic dissection disease.

Expression and function of FRA1 protein in tumors

AP-1 is a dimeric complex that is composed of JUN, FOS, ATF and MAF protein families. FOS-related antigen 1 (FRA1) which encoded by FOSL1 gene, belongs to the FOS protein family, and mainly forms an AP-1 complex with the protein of the JUN family to exert an effect. Regulation of FRA1 occurs at levels of transcription and post-translational modification, and phosphorylation is the major post-translational modification. FRA1 is mainly regulated by the mitogen-activated protein kinases signaling pathway and is degraded by ubiquitin-independent proteasomes. FRA1 can affect biological functions, such as tumor proliferation, differentiation, invasion and apoptosis. Studies have demonstrated that FRA1 is abnormally expressed in many tumors and plays a relevant role, but the specific condition varies from the target organs. FRA1 is overexpressed in breast cancer, lung cancer, colorectal cancer, prostate cancer, nasopharyngeal cancer, thyroid cancer and other tumors. However, the expression of FRA1 is decreased in cervical cancer, and the expression of FRA1 in ovarian cancer and oral squamous cell carcinoma is still controversial. In this review, we present a detailed description of the regulatory factors and functions of FRA1, also, the expression of FRA1 in various tumors and its function in relative tumor.

Tobacco Exposure Enhances Human Papillomavirus 16 Oncogene Expression via EGFR/PI3K/Akt/c-Jun Signaling Pathway in Cervical Cancer Cells

High-risk human papillomavirus (HR-HPV) infection is not a sufficient condition for cervical cancer development because most infections are benign and naturally cleared. Epidemiological studies revealed that tobacco smoking is a cofactor with HR-HPV for cervical cancer initiation and progression, even though the mechanism by which tobacco smoke cooperates with HR-HPV in this malignancy is poorly understood. As HR-HPV E6/E7 oncoproteins overexpressed in cervical carcinomas colocalize with cigarette smoke components (CSC), in this study we addressed the signaling pathways involved in a potential interaction between both carcinogenic agents. Cervical cancer-derived cell lines, CaSki (HPV16; 500 copies per cell) and SiHa (HPV16; 2 copies per cell), were acutely exposed to CSC at various non-toxic concentrations and we found that E6 and E7 levels were significantly increased in a dose-dependent manner. Using a reporter construct containing the luciferase gene under the control of the full HPV16 long control region (LCR), we also found that p97 promoter activity is dependent on CSC. Non-synonymous mutations in the LCR-resident TPA (12-O-tetradecanoylphorbol 13-acetate)-response elements (TRE) had significantly decreased p97 promoter activation. Phosphoproteomic arrays and specific inhibitors revealed that CSC-mediated E6/E7 overexpression is at least in part reliant on EGFR phosphorylation. In addition, we showed that the PI3K/Akt pathway is crucial for CSC-induced E6/E7 overexpression. Finally, we demonstrated that HPV16 E6/E7 overexpression is mediated by JUN. overexpression, c-Jun phosphorylation and recruitment of this transcription factor to TRE sites in the HPV16 LCR. We conclude that acute exposure to tobacco smoke activates the transcription of HPV16 E6 and E7 oncogenes through p97 promoter activation, which involves the EGFR/PI3K/Akt/C-Jun signaling pathway activation in cervical cancer cells.

CHTM1, a novel metabolic marker deregulated in human malignancies

A better understanding of the link between cellular metabolism and tumorigenesis is needed. Here, we report characterization of a novel protein named Coiled-coil Helix Tumor and Metabolism 1 (CHTM1). We have found that CHTM1 is associated with cancer and cellular metabolism. CHTM1 localizes to mitochondria and cytosol, and its deficiency in cancer cells results in decreased mitochondrial oxygen consumption and ATP levels as well as oxidative stress indicating mitochondrial dysfunction. CHTM1-deficient cancer cells display poor growth under glucose/glutamine-deprived conditions, whereas cells expressing increased levels of exogenous CHTM1 exhibit enhanced proliferation and survival under similar conditions. CHTM1 deficiency also leads to defects in lipid metabolism resulting in fatty acid accumulation, which explains poor growth of CHTM1-deficient cells under glucose/glutamine deprivation since nutrient deprivation increases dependency on lipids for energy generation. We also demonstrate that CHTM1 mediates its effect via the PKC, CREB and PGC-1alpha signaling axis, and cytosolic accumulation of CHTM1during nutrient deprivation appears to be important for its effect on cellular signaling events. Furthermore, analyses of tissue specimens from 71 breast and 97 colon cancer patients show CHTM1 expression to be upregulated in the majority of tumor specimens representing these malignancies. Collectively, our findings are highly significant because CHTM1 is a novel metabolic marker that is important for the growth of tumorigenic cells under limiting nutrient supplies and thus, links cellular metabolism and tumorigenesis.

p120-Catenin Downregulation and PIK3CA Mutations Cooperate to Induce Invasion through MMP1 in HNSCC

Despite recent improvements in treatment for head and neck squamous cell carcinoma (HNSCC), half of all patients with a regional or advanced disease will die within 5 years from diagnosis. Therefore, identification of mechanisms driving the aggressive behavior of HNSCC is of utmost importance. Because p120-catenin (CTNND1/P120CTN) downregulation and PIK3CA mutations are commonly found in HNSCC, the objective of this study was to identify their impact on fundamental processes of metastasis, specifically, migration and invasion. Furthermore, this study aimed to identify the key effector proteins regulated by P120CTN downregulation and PIK3CA mutations. Studies using oral keratinocytes demonstrated that P120CTN downregulation and PIK3CA mutations increased migration and invasion. In addition, P120CTN downregulation and PIK3CA mutations resulted in elevated matrix metallopeptidase 1 (MMP1) levels. Inhibition of MMP1 resulted in decreased invasion, suggesting that MMP1 plays a critical role in HNSCC invasion. Moreover, analysis of HNSCC patient specimens from The Cancer Genome Atlas confirmed these findings. Tumors with low P120CTN and PI3K pathway mutations have higher levels of MMP1 compared to tumors with high P120CTN and no PI3K pathway mutations. In conclusion, this study demonstrates that P120CTN downregulation and PIK3CA mutations promote MMP1-driven invasion, providing a potential novel target for limiting metastasis in HNSCC.Implications: Because of its role in invasion, MMP1 represents a novel, potential target for limiting metastasis in a subset of HNSCCs with P120CTN downregulation and PIK3CA mutations. Mol Cancer Res; 15(10); 1398-409. ©2017 AACR.

Potentially functional polymorphisms in PAK1 are associated with risk of lung cancer in a Chinese population

P21-activated kinase 1(PAK1) plays an important role in the regulation of cell morphogenesis, motility, mitosis, and angiogenesis and has been implicated with tumorigenesis and tumor progression. We hypothesized that functional polymorphisms in PAK1 gene may modify the risk of lung cancer. We screened four potentially functional polymorphisms (rs2154754, rs3015993, rs7109645, and rs2844337) in PAK1 gene and evaluated the association between the genetic variants and lung cancer risk in a case–control study including 1341 lung cancer cases and 1982 cancer-free controls in a Chinese population. We found that variant allele of rs2154754 was significantly associated with a decreased risk of lung cancer (OR = 0.85, 95% CI: 0.77–0.95, P = 0.004), meanwhile the result of rs3015993 was marginal (OR = 0.90, 95%CI: 0.81–1.00, P = 0.044). After multiple comparisons, rs2154754 was still significantly associated with the lung cancer risk (P < 0.0125 for Bonferroni correction). We also detected a significant interaction between rs2154754 genotypes and smoking levels on lung cancer risk (P = 0.042). Combined analysis of these two polymorphisms showed a significant allele-dosage association between the number of protective alleles and reduced risk of lung cancer (P_trend = 0.008). These findings indicate that genetic variants in PAK1 gene may contribute to susceptibility to lung cancer in the Chinese population.

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.

In PC3 prostate cancer cells ephrin receptors crosstalk to β1-integrins to strengthen adhesion to collagen type I

Eph receptor (Eph) and ephrin signaling can play central roles in prostate cancer and other cancer types. Exposed to ephrin-A1 PC3 prostate cancer cells alter adhesion to extracellular matrix (ECM) proteins. However, whether PC3 cells increase or reduce adhesion, and by which mechanisms they change adhesion to the ECM remains to be characterized. Here, we assay how ephrin-A1 stimulates PC3 cells to adhere to ECM proteins using single-cell force spectroscopy. We find that PC3 cells binding to immobilized ephrin-A1 but not to solubilized ephrin-A1 specifically strengthen adhesion to collagen I. This Eph-ephrin-A1 signaling, which we suppose is based on mechanotransduction, stimulates β₁-subunit containing integrin adhesion via the protein kinase Akt and the guanine nucleotide-exchange factor cytohesin. Inhibiting the small GTPases, Rap1 or Rac1, generally lowered adhesion of PC3 prostate cancer cells. Our finding suggests a mechanism by which PC3 prostate cancer cells exposed to ephrins crosstalk to β₁-integrins and preferably metastasize in bone, a collagen I rich tissue.

Cigarette smoke-induced Ca2+ release leads to cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction

Chronic obstructive pulmonary disease affects 64 million people and is currently the fourth leading cause of death worldwide. Chronic obstructive pulmonary disease includes both emphysema and chronic bronchitis, and in the case of chronic bronchitis represents an inflammatory response of the airways that is associated with mucus hypersecretion and obstruction of small airways. Recently, it has emerged that exposure to cigarette smoke (CS) leads to an inhibition of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel, causing airway surface liquid dehydration, which may play a role in the development of chronic bronchitis. CS rapidly clears CFTR from the plasma membrane and causes it to be deposited into aggresome-like compartments. However, little is known about the mechanism(s) responsible for the internalization of CFTR following CS exposure. Our studies revealed that CS triggered a rise in cytoplasmic Ca(2+) that may have emanated from lysosomes. Furthermore, chelation of cytoplasmic Ca(2+), but not inhibition of protein kinases/phosphatases, prevented CS-induced CFTR internalization. The macrolide antibiotic bafilomycin A1 inhibited CS-induced Ca(2+) release and prevented CFTR clearance from the plasma membrane, further linking cytoplasmic Ca(2+) and CFTR internalization. We hypothesize that CS-induced Ca(2+) release prevents normal sorting/degradation of CFTR and causes internalized CFTR to reroute to aggresomes. Our data provide mechanistic insight into the potentially deleterious effects of CS on airway epithelia and outline a hitherto unrecognized signaling event triggered by CS that may affect the long term transition of the lung into a hyper-inflammatory/dehydrated environment.

Activation of uPAR is required for cigarette smoke extract-induced epithelial-mesenchymal transition in lung epithelial cells

Cigarette smoke is a major risk factor for lung cancer, which may contribute to lung cancer invasion and metastasis. However, the mechanism remains unclear. Epithelial-mesenchymal transition (EMT) is a critical phenotypic alteration of cells that triggers invasion and metastasis. The urokinase-type plasminogen activator receptor (uPAR) is originally thought to assist the directional invasion of migrating cells, and increasing evidences show that overexpression of uPAR in cancer cells promotes EMT. Therefore, we intend to study the role of uPAR in cigarette smoke extract (CSE)-induced EMT in lung epithelial cells. In this study, we showed that lung epithelial cells cultured after CSE treatment demonstrated changes consistent with EMT. E-cadherin was decreased, while vimentin, N-cadherin, and α-SMA expression was increased in both A549 and BEAS-2B cells. Cells acquired a mesenchymal-like morphology and increased cell motility and invasion. In addition, CSE-induced EMT was accompanied by increased expression of uPAR and activation of AKT downstream of uPAR. CSE-induced EMT and activation of AKT were blocked by uPAR gene silencing. Antagonizing PI3K also inhibits development of CSE-induced EMT. We conclude that CSE can induce EMT, and the activity of uPAR-dependent signal pathway in EMT is recapitulated in lung epithelial cells in vitro.

Both mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinases (ERK) 1/2 and phosphatidylinositide-3-OH kinase (PI3K)/Akt pathways regulate activation of E-twenty-six (ETS)-like transcription factor 1 (Elk-1) in U138 glioblastoma cells

Epidermal growth factor (EGF) and its receptor (EGFR) have been shown to play a significant role in the pathogenesis of glioblastoma. In our study, the EGFR was stimulated with EGF in human U138 glioblastoma cells. We show that the activated mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinases (ERK) 1/2 pathway phosphorylated the E twenty-six (ETS)-like transcription factor 1 (Elk-1) mainly at serine 383 residue. Mitogen-activated protein kinase kinase (MEK) 1/2 inhibitor, UO126 and ERK inhibitor II, FR180204 blocked the Elk-1 phosphorylation and activation. The phosphatidylinositide-3-OH kinase (PI3K)/Akt pathway was also involved in the Elk-1 activation. Activation of the Elk-1 led to an increased survival and a proliferative response with the EGF stimulation in the U138 glioblastoma cells. Knocking-down the Elk-1 using an RNA interference technique caused a decrease in survival of the unstimulated U138 glioblastoma cells and also decreased the proliferative response to the EGF stimulation. The Elk-1 transcription factor was important for the survival and proliferation of U138 glioblastoma cells upon the stimulation of EGFR with EGF. The MAPK/ERK1/2 and PI3K/Akt pathways regulated this response via activation of the Elk-1 transcription factor. The Elk-1 may be one of the convergence points for pathways located downstream of EGFR in glioblastoma cells. Utilization of the Elk-1 as a therapeutic target may lead to a novel strategy in treatment of glioblastoma.

Differential dephosphorylation of the protein kinase C-zeta (PKCζ) in an integrin αIIbβ3-dependent manner in platelets

Protein kinase C-zeta (PKCζ), an atypical isoform of the PKC family of protein serine/threonine kinases, is expressed in human platelets. However, the mechanisms of its activation and the regulation of its activity in platelets are not known. We have found that under basal resting conditions, PKCζ has a high phosphorylation status at the activation loop threonine 410 (T410) and the turn motif (autophosphorylation site) threonine 560 (T560), both of which have been shown to be important for its catalytic activity. After stimulation with agonist under stirring conditions, the T410 residue was dephosphorylated in a time- and concentration-dependent manner, while the T560 phosphorylation remained unaffected. The T410 dephosphorylation could be significantly prevented by blocking the binding of fibrinogen to integrin αIIbβ3 with an antagonist, SC-57101; or by okadaic acid used at concentrations that inhibits protein serine/threonine phosphatases PP1 and PP2A in vitro. The dephosphorylation of T410 residue on PKCζ was also observed in PP1cγ null murine platelets after agonist stimulation, suggesting that other isoforms of PP1c or another phosphatase could be responsible for this dephosphorylation event. We conclude that human platelets express PKCζ, and it may be constitutively phosphorylated at the activation loop threonine 410 and the turn motif threonine 560 under basal resting conditions, which are differentially dephosphorylated by outside-in signaling. This differential dephosphorylation of PKCζ might be an important regulatory mechanism for platelet functional responses.

Rtp801, a suppressor of mTOR signaling, is an essential mediator of cigarette smoke-induced pulmonary injury and emphysema

Rtp801, a stress – related protein triggered by adverse environmental conditions, inhibits mTOR and enhances oxidative stress – dependent cell death. We postulated that Rtp801 acts as potential amplifying switch in the development of cigarette smoke – induced lung injury, leading to emphysema. Rtp801 was overexpressed in human emphysematous lungs and in lungs of mice exposed to cigarette smoke. The upregulation of Rtp801 expression by cigarette smoke in the lung relied on oxidative stress – dependent activation of the CCAAT response element. Rtp801 was necessary and sufficient for NF – κ B activation in cultured cells and, when forcefully expressed in mouse lungs, it promoted NF – kB activation, alveolar inflammation, oxidative stress, and apoptosis of alveolar septal cells. On the other hand, Rtp801 ^{− / −} mice were markedly protected against acute cigarette smoke – induced lung injury, partly via increased mTOR signaling, and, when exposed chronically, against emphysema. Our data support the notion that Rtp801 may represent an important molecular sensor and mediator of lung injury to cigarette smoke.

Epidermal growth factor-induced cyclooxygenase-2 expression in oral squamous cell carcinoma cell lines is mediated through extracellular signal-regulated kinase 1/2 and p38 but is Src and nuclear factor-kappa B independent

The intracellular signalling cascade(s) mediating epidermal growth factor (EGF)-induced cyclooxygenase-2 (COX-2) expression is poorly defined in oral carcinomas. Investigation of two different oral squamous cell carcinoma (OSCC) cell lines with high EGF-induced COX-2 expression revealed, however, that this expression was dependent on two mitogen-activated protein kinase (MAPK) pathways [extracellular signal-regulated kinase 1/2 (ERK1/2) and p38] because combined inhibition of these pathways was needed to abolish EGF-induced COX-2 expression. Surprisingly, inhibition of phosphoinositide-3 kinase (PI3K) increased EGF-induced COX-2 expression in the basaloid OSCC cell line (C12), suggesting a PI3K-controlled, inhibitory COX-2-regulating pathway. Neither the transcription factor nuclear factor-kappaB (NF-kappaB), nor Src, was involved in EGF-induced COX-2 expression. The results suggest that EGF-induced COX-2 expression is regulated by several pathways, and emphasizes that individual tumors use different strategies for intracellular signalling.

PGE2 production in oral cancer cell lines is COX-2-dependent

It has been suggested that epithelial cyclooxygenase-2 (COX-2) promotes oral carcinogenesis and carcinoma malignancy through increased prostaglandin E(2) (PGE(2)) production. Although oral squamous cell carcinomas (OSCC) often express COX-2, they may also produce PGE(2) in a COX-1-dependent manner. We used 6 isolated cell lines to investigate which COX isoforms OSCC may use for PGE(2) production. COX-1 and -2 expression patterns divided the 6 OSCC cell lines into 3 distinct groups: both COX isoforms low, only COX-1 high, or both COX isoforms high. Multicolor immunohistofluorescence staining confirmed the COX-expression profiles in organotypic 3D cultures and the COX-2 dominance in OSCC tumors. Epidermal growth factor (EGF) stimulation induced COX-2 (but not COX-1) expression and increased PGE(2) production, which was attenuated by COX-2 (but not COX-1) specific inhibition or siRNA-mediated COX-2 gene knockdown. Thus, PGE(2) production in OSCC cell lines was COX-2-dependent.

The antioxidant response element and oxidative stress modifiers in airway diseases

Redox balance is particularly important in the airways because they are the first points of contact with environmental pollutants such as ozone, particles, and cigarette smoke, as well as pathogens such as bacteria and viruses. However, an imbalance between toxicant-induced reactive oxygen (ROS) and nitrogen (RNS) species and the antioxidant defense system leads to oxidative stress, which has been implicated in the development and/or perpetuation of airway diseases, including malignancy. Various antioxidant enzymes and proteins are critical to maintaining the reducing environment of the cell and preventing the damage to various biomolecules that is elicited by ROS/RNS. Emerging evidence indicates that transcriptional activation of the antioxidant response element (ARE) plays a crucial role in modulating oxidative stress and providing cytoprotection against prooxidant stimuli. This review focuses on the regulation and functional roles of key effectors that bind to the ARE and differentially (up- or down-) regulate gene expression in lung tissue/cell types in response to respiratory toxicants. It also provides a perspective on whether boosting ARE-mediated gene expression with dietary plants and synthetic plant products will offer a better therapeutic strategy for mitigating oxidative stress and respiratory pathogenesis.

The WNT signalling pathway and diabetes mellitus

The WNT signalling pathway is involved in many physiological and pathophysiological activities. WNT ligands bind to Frizzled receptors and co-receptors (LDL receptor-related protein 5/6), triggering a cascade of signalling events. The major effector of the canonical WNT signalling pathway is the bipartite transcription factor beta-catenin/T cell transcription factor (beta-cat/TCF), formed by free beta-cat and one of the four TCFs. The WNT pathway is involved in lipid metabolism and glucose homeostasis, and mutations in LRP5 may lead to the development of diabetes and obesity. beta-Cat/TCF is also involved in the production of the incretin hormone glucagon-like peptide-1 in the intestinal endocrine L cells. More recently, genome-wide association studies have identified TCF7L2 as a diabetes susceptibility gene, and individuals carrying certain TCF7L2 single nucleotide polymorphisms could be more susceptible to the development of type 2 diabetes. Furthermore, beta-cat is able to interact with forkhead box transcription factor subgroup O (FOXO) proteins. Since FOXO and TCF proteins compete for a limited pool of beta-cat, enhanced FOXO activity during ageing and oxidative stress may attenuate WNT-mediated activities. These observations shed new light on the pathogenesis of type 2 diabetes as an age-dependent disease.

A Fra-1-dependent, matrix metalloproteinase driven EGFR activation promotes human lung epithelial cell motility and invasion

We and others have shown a persistently high induction of Fra-1 transcription factor (a dimeric partner of AP-1) levels by respiratory carcinogens in pulmonary epithelial cells. Fra-1 is frequently overexpressed in various human tumors and cancer cells. We have recently shown that Fra-1 significantly promotes growth, motility, and invasion of human pulmonary epithelial cells, the precise molecular mechanisms by which this enhancement occurs are unclear. Because matrix metalloproteinases (MMPs) play key roles in wound healing and lung tumor metastasis, we tested the hypothesis that Fra-1 promotes lung epithelial cell motility and invasion via MMP activation. We show here that MMP-9 and MMP-2 activated signaling plays a critical role in regulating Fra-1-induced lung epithelial cell growth and invasion. Ectopic Fra-1 markedly stimulates MMP-2 and MMP-9 mRNA expression. Inhibition of MMP-2 and MMP-9 activity significantly attenuated Fra-1-driven cell motility and invasion. Furthermore, Fra-1 induced EGFR phosphorylation in an MMP-dependent manner, and an EGFR-specific inhibitor was able to block Fra-1-enhanced cell motility and invasion. Taken together, our data suggest that Fra-1 enhances lung cancer epithelial cell motility and invasion by inducing the activity of MMPs, in particular MMP-2 and MMP-9, and EGFR-activated signaling.

Late expression of granulysin by microbicidal CD4+ T cells requires PI3K- and STAT5-dependent expression of IL-2Rbeta that is defective in HIV-infected patients

Granulysin is a cytolytic effector molecule used by lymphocytes to kill tumor and microbial cells. Regulation of granulysin production is complex. A significant delay (5 days) following stimulation of CD4(+) T cells with IL-2 occurs before granulysin is produced. Unfortunately, the mechanisms responsible for this delay are unknown. We have recently demonstrated that granulysin-mediated killing of Cryptococcus neoformans by CD4(+) T cells is defective during HIV infection. This is because CD4(+) T cells from HIV-infected patients fail to produce granulysin in response to IL-2 activation. The present studies examined the mechanism of delayed production of granulysin and the mechanism of the defect in HIV patients. We demonstrate that IL-2 initially requires both STAT5 and PI3K activation to increase expression of IL-2Rbeta, produce granulysin, and kill C. neoformans. The increased expression of IL-2Rbeta precedes granulysin, and preventing the increased expression of IL-2Rbeta using small interfering RNA knockdown abrogates granulysin expression. Moreover, following the increased expression of IL-2Rbeta, blocking subsequent signaling by IL-2 using IL-2Rbeta-specific blocking Abs abrogates expression of granulysin. Finally, CD4(+) T cells from HIV-infected patients, who are defective in both STAT5 and PI3K signaling, fail to express IL-2Rbeta and fail to produce granulysin. These results suggest that IL-2 signals via PI3K and STAT5 to increase expression of IL-2Rbeta, which in turn is required for production of granulysin. These results provide a mechanism to explain the "late" production of granulysin during normal T cell responses, as well as for defective granulysin production by CD4(+) T cells in HIV-infected patients.

Cross talk between the insulin and Wnt signaling pathways: evidence from intestinal endocrine L cells

The proglucagon gene (glu) encodes the incretin hormone glucagon-like peptide-1 (GLP-1), produced in the intestinal endocrine L cells. We found previously that the bipartite transcription factor beta-catenin/T cell factor (cat/TCF), the major effector of the canonical Wnt signaling pathway, activates intestinal glu expression and GLP-1 production. We show here that 100 nm insulin stimulated glu expression and enhanced GLP-1 content in the intestinal GLUTag L cell line as well as in primary fetal rat intestinal cell cultures. Increased intestinal glu mRNA expression and GLP-1 content were also observed in vivo in hyperinsulinemic MKR mice. In the GLUTag cells, insulin-induced activation of glu expression occurred through the same TCF site that mediates cat/TCF activation. Phosphatidylinositol 3-kinase inhibition, but not protein kinase B inhibition, attenuated the stimulation by insulin. Furthermore, nuclear beta-catenin content in the intestinal L cells was increased by insulin. Finally, insulin enhanced the binding of TCF-4 and beta-catenin to the TCF site in the glu promoter G2 enhancer element, as determined by quantitative chromatin immunoprecipitation assay. Collectively, these findings indicate that enhancement of beta-catenin nuclear translocation and cat/TCF binding are among the mechanisms underlying cross talk between the insulin and Wnt signaling pathways in intestinal endocrine L cells.

Fra-1 governs cell migration via modulation of CD44 expression in human mesotheliomas

Silencing of Fra-1, a component of the dimeric transcription factor, activator protein-1 (AP-1), inhibits mRNA expression of c-met and cd44 in rat mesothelioma cells and is causally linked to maintenance of the transformed phenotype. However, the mechanisms of Fra-1 regulation and Fra-1 regulated gene expression in human malignant mesothelioma (MM) are unclear. We first show in a panel of human MM cells that Fra-1 mRNA expression in MM is complex and regulated by extracellular signal-regulated kinase (ERK1, ERK2), Src, and phosphatidyl-inositol-3-kinase (PI3K) pathways in a tumor-specific fashion. Cell lines with PI3K-dependent Fra-1 expression were SV40 positive and expressed the lowest basal Fra-1 levels. Levels of Fra-1 expression correlated with amounts of CD44 expression that were greater in simian virus 40 negative (SV40-) MM cells. Using dominant negative (dn), short hairpin (sh) and small interference (si) RNA constructs, we next demonstrate that expression of CD44, the principal hyaluronic receptor in MMs, correlates with Fra-expression in both simian virus 40 positive (SV40+) and SV40- MMs. Moreover, both Fra-1 and CD44 expression are linked to cell migration in SV40- MM cells. Lastly, in contrast to normal lung tissue, tissue microarrays revealed that Fra-1 was expressed in 33 of 34 human MMs, and that all CD44+ tumors were SV40-. These results suggest that Fra-1 is associated with cell migration in human MMs and that Fra-1 modulation of CD44 may govern migration of selected MMs.

Acquired resistance to erlotinib in A-431 epidermoid cancer cells requires down-regulation of MMAC1/PTEN and up-regulation of phosphorylated Akt

Erlotinib (Tarceva), an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, has clinical activity in advanced lung cancer, but disease that initially responds to erlotinib eventually progresses. The mechanism of this acquired resistance is unclear. We established two erlotinib-resistant pools of A-431 cells, a well-characterized epidermoid cancer cell line that constitutively overexpresses EGFR and is sensitive to erlotinib, by continuous exposure to erlotinib over a 6-month period. The extent of EGFR gene amplification or mutation of the EGFR tyrosine kinase domain was not altered in the resistant cells. Intracellular erlotinib concentrations, determined by liquid chromatography-tandem mass spectrometry, were almost the same in all three cell lines. Immunoprecipitation with EGFR antibody followed by detection with phosphotyrosine antibody revealed that erlotinib effectively reduced EGFR phosphorylation in both parental cells and resistant cells. Erlotinib induced mutated in multiple advanced cancers 1/phosphatase and tensin homologue (MMAC1/PTEN) and suppressed phosphorylated Akt (Ser(473)) but not in the erlotinib-resistant cells. Overexpression of MMAC1/PTEN by transfection with Ad.MMAC1/PTEN or by pharmacologic suppression of Akt activity restored erlotinib sensitivity in both resistant pools. Further, transfection of parental A-431 cells with constitutively active Akt was sufficient to cause resistance to erlotinib. We propose that acquired erlotinib resistance associated with MMAC1/PTEN down-regulation and Akt activation could be overcome by inhibitors of signaling through the phosphatidylinositol 3-kinase pathway.

Tumor-suppressive activity of the cell death activator GRIM-19 on a constitutively active signal transducer and activator of transcription 3

Signal transducers and activators of transcription 3 (STAT3) was originally identified as a transcription factor that mediates cytokine-induced responses. In these pathways, Janus-activated kinase (JAK)-induced transient tyrosine phosphorylation of STAT3 promotes gene expression in response to a number of cytokines, which is inhibited by feedback mechanisms. A number of studies have shown that STAT3 is constitutively activated in human cancer cells, leading to cell proliferation. It is unclear, apart from a chronic tyrosyl phosphorylation of STAT3, what mechanisms contribute to the STAT3 deregulation in tumors. Earlier, we have isolated a novel growth inhibitory gene product, gene associated with retinoid-IFN-induced mortality 19 (GRIM-19), using a genetic approach. GRIM-19 is an IFN/retinoic acid-regulated growth suppressor. Subsequent analyses have shown that GRIM-19 binds to STAT3 and prevents interleukin-6-induced transcription of cellular genes. However, its effects on a constitutively active STAT3 and cellular transformation are unknown. In this study, we show that GRIM-19 suppresses constitutive STAT3-induced cellular transformation in vitro and in vivo by down-regulating the expression of a number of cellular genes involved in cell proliferation and apoptosis.

FRA-1 proto-oncogene induces lung epithelial cell invasion and anchorage-independent growth in vitro, but is insufficient to promote tumor growth in vivo

FRA-1 forms activator protein-1 complexes in association with members of the JUN family and drives gene transcription. FRA-1 has been implicated in the development of airway squamous metaplasia and is frequently overexpressed in squamous cell carcinomas of the esophagus and stomach. We and others have shown a high level of persistent induction of FRA-1 by lung carcinogens, such as cigarette smoke and asbestos, in pulmonary epithelial cells. However, the exact roles of FRA-1 in regulating lung epithelial cell growth and invasion are poorly understood. To examine this aspect, we have stably overexpressed FRA-1 in human type-II-like alveolar malignant cell line (A549) and a nonmalignant bronchial epithelial cell line (BEAS-2B). FRA-1 greatly enhanced the rate of proliferation, motility, and invasion of A549 and BEAS-2B cells. In athymic nude mice, FRA-1, but not the control vector, rapidly enhanced tumor formation and metastasis by A549 cells. In contrast, FRA-1 failed to promote tumor formation by BEAS-2B. We suggest that FRA-1 can promote motility, invasion, and anchorage-independent growth of lung epithelial cells in vitro, but is insufficient for tumor formation.

Mechanisms of action of inhaled fibers, particles and nanoparticles in lung and cardiovascular diseases

BACKGROUND

A symposium on the mechanisms of action of inhaled airborne particulate matter (PM), pathogenic particles and fibers such as silica and asbestos, and nanomaterials, defined as synthetic particles or fibers less than 100 nm in diameter, was held on October 27 and 28, 2005, at the Environmental Protection Agency (EPA) Conference Center in Research Triangle Park, North Carolina. The meeting was the eighth in a series of transatlantic conferences first held in Penarth, Wales, at the Medical Research Council Pneumoconiosis Unit (1979), that have fostered long-standing collaborations between researchers in the fields of mineralogy, cell and molecular biology, pathology, toxicology, and environmental/occupational health.

RESULTS

The goal of this meeting, which was largely supported by a conference grant from the NHLBI, was to assemble a group of clinical and basic research scientists who presented and discussed new data on the mechanistic effects of inhaled particulates on the onset and development of morbidity and mortality in the lung and cardiovascular system. Another outcome of the meeting was the elucidation of a number of host susceptibility factors implicated in adverse health effects associated with inhaled pathogenic particulates.

CONCLUSION

New models and data presented supported the paradigm that both genetic and environmental (and occupational) factors affect disease outcomes from inhaled particulates as well as cardiopulmonary responses. These future studies are encouraged to allow the design of appropriate strategies for prevention and treatment of particulate-associated morbidity and mortality, especially in susceptible populations.

Agonist-modulated regulation of AMP-activated protein kinase (AMPK) in endothelial cells. Evidence for an AMPK -> Rac1 -> Akt -> endothelial nitric-oxide synthase pathway

The endothelial isoform of nitric-oxide synthase (eNOS), a key determinant of vascular homeostasis, is a calcium/calmodulin-dependent phosphoprotein regulated by diverse cell surface receptors. Vascular endothelial growth factor (VEGF) and sphingosine 1-phosphate (S1P) stimulate eNOS activity through Akt/phosphoinositide 3-kinase and calcium-dependent pathways. AMP-activated protein kinase (AMPK) also activates eNOS in endothelial cells; however, the molecular mechanisms linking agonist-mediated AMPK regulation with eNOS activation remain incompletely understood. We studied the role of AMPK in VEGF- and S1P-mediated eNOS activation and found that both agonists led to a striking increase in AMPK phosphorylation in pathways involving the calcium/calmodulin-dependent protein kinase kinase beta. Treatment with tyrosine kinase inhibitors or the phosphoinositide 3-kinase inhibitor wortmannin demonstrated differential effects of VEGF versus S1P. Small interfering RNA (siRNA)-mediated knockdown of AMPKalpha1or Akt1 impaired the stimulatory effects of both VEGF and S1P on eNOS activation. AMPKalpha1 knockdown impaired agonist-mediated Akt phosphorylation, whereas Akt1 knockdown did not affect AMPK activation, thus suggesting that AMPK lies upstream of Akt in the pathway leading from receptor activation to eNOS stimulation. Importantly, we found that siRNA-mediated knockdown of AMPKalpha1 abrogates agonist-mediated activation of the small GTPase Rac1. Conversely, siRNA-mediated knockdown of Rac1 decreased the agonist-mediated phosphorylation of AMPK substrates without affecting that of AMPK, implicating Rac1 as a molecular link between AMPK and Akt in agonist-mediated eNOS activation. Finally, siRNA-mediated knockdown of caveolin-1 significantly enhanced AMPK phosphorylation, suggesting that AMPK is negatively regulated by caveolin-1. Taken together, these results suggest that VEGF and S1P differentially regulate AMPK and establish a central role for an agonist-modulated AMPK --> Rac1 --> Akt axis in the control of eNOS in endothelial cells.

A JNK-Independent Signaling Pathway Regulates TNFα-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.