Regulation of Src family tyrosine kinase activities in adherent human neutrophils. Evidence that reactive oxygen intermediates produced by adherent neutrophils increase the activity of the p58c-fgr and p53/56lyn tyrosine kinases

The TGF-β/NADPH Oxidases Axis in the Regulation of Liver Cell Biology in Health and Disease

The Transforming Growth Factor-beta (TGF-β) pathway plays essential roles in liver development and homeostasis and become a relevant factor involved in different liver pathologies, particularly fibrosis and cancer. The family of NADPH oxidases (NOXs) has emerged in recent years as targets of the TGF-β pathway mediating many of its effects on hepatocytes, stellate cells and macrophages. This review focuses on how the axis TGF-β/NOXs may regulate the biology of different liver cells and how this influences physiological situations, such as liver regeneration, and pathological circumstances, such as liver fibrosis and cancer. Finally, we discuss whether NOX inhibitors may be considered as potential therapeutic tools in liver diseases.

AUF1 Promotes Proliferation and Invasion of Thyroid Cancer via Downregulation of ZBTB2 and Subsequent TRIM58

The pathogenesis of papillary thyroid cancer (PTC), the most common type of thyroid cancer, is not yet fully understood. This limits the therapeutic options for approximately 7% of invasive PTC patients. The critical role of AUF1 in the progression of thyroid cancer was first reported in 2009, however, its molecular mechanism remained unclear. Our study used CRISPR/Cas 9 system to knockdown AUF1 in IHH4 and TPC1 cells. We noticed that the expression of TRIM58 and ZBTB2 were increased in the AUF1 knockdown IHH4 and TPC1 cells. When TRIM58 and ZBTB2 were inhibited by small hairpin RNAs (shRNAs) against TRIM58 (shTRIM58) and ZBTB2 (shZBTB2), respectively, the proliferation, migration, and invasion ability of the AUF1-knockdown IHH4 and TPC1 cells were increased. In addition, two ZBTB2 binding sites (-719~-709 and -677~-668) on TRIM58 promoter and two AUF1 binding sites (1250-1256 and 1258-1265) on ZBTB2 3’-UTR were identified. These results suggested that AUF1 affecting thyroid cancer cells via regulating the expression of ZBTB2 and TRIM58.

SIX1 Activates STAT3 Signaling to Promote the Proliferation of Thyroid Carcinoma via EYA1

As a critical member of the Retinal Determination Gene Network (RDGN), SIX1 has been regarded as a tumor promoter in various types of cancer. However, its role in papillary thyroid carcinoma (PTC) has never been investigated. In this study, thyroid carcinoma tissue microarray staining was employed to identify the expression patterns of SIX1 and its co-activator EYA1. Papillary thyroid cancer cell lines, BCPAP, and TPC-1 cells were used to investigate the potential mechanism of SIX1 in vitro and in vivo. Flow cytometry analysis, MTT assay, the growth curve assay, colony formation assay, EdU incorporation and xenograft assay were performed to demonstrate the role of SIX1 in the malignant change of PTC cells. Western blot and Real-time PCR were used to detect the interaction among the SIX1, EYA1, and STAT3 signaling. In comparison with normal tissue, high expressions of SIX1 and EYA1 were associated with a malignant tumor. Importantly, SIX1 strongly correlated with EYA1 in thyroid carcinoma tissue microarray. Functional assays indicated SIX1 increased EYA1 expression by stabilizing EYA1 at the post-transcriptional level. Besides, SIX1 promoted the proliferation and invasion of thyroid carcinoma via activation of STAT3 signaling and its downstream targets in an EYA1-dependent manner. SIX1 can integrate with EYA1 to contribute to PTC development via activation of the classical STAT3 signaling. These data suggested targeting the abnormal activation of the SIX1/EYA1 complex may represent a novel therapeutic strategy for advanced PTC patients.

The Importance of Tyrosine Phosphorylation Control of Cellular Signaling Pathways in Respiratory Disease: pY and pY Not

Reversible phosphorylation of proteins on tyrosine residues is an essential signaling mechanism by which diverse cellular processes are closely regulated. The tight temporal and spatial control of the tyrosine phosphorylation status of proteins by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) is critical to cellular homeostasis as well as to adaptations to the external environment. Via regulation of cellular signaling cascades involving other protein kinases and phosphatases, receptors, adaptor proteins, and transcription factors, PTKs and PTPs closely control diverse cellular processes such as proliferation, differentiation, migration, inflammation, and maintenance of cellular barrier function. Given these key regulatory roles, it is not surprising that dysfunction of PTKs and PTPs is important in the pathogenesis of human disease, including many pulmonary diseases. The roles of various PTKs and PTPs in acute lung injury and repair, pulmonary fibrosis, pulmonary vascular disease, and inflammatory airway disease are discussed in this review. It is important to note that although there is overlap among many of these proteins in various disease states, the mechanisms by which they influence the pathogenesis of these conditions differ, suggesting wide-ranging roles for these enzymes and their potential as therapeutic targets.

Redox modification of caveolar proteins in the cardiovascular system- role in cellular signalling and disease

Rapid and coordinated release of a variety of reactive oxygen species (ROS) such as superoxide (O₂^.-), hydrogen peroxide (H₂O₂) and peroxynitrite, in specific microdomains, play a crucial role in cell signalling in the cardiovascular system. These reactions are mediated by reversible and functional modifications of a wide variety of key proteins. Dysregulation of this oxidative signalling occurs in almost all forms of cardiovascular disease (CVD), including at the very early phases. Despite the heavily publicized failure of "antioxidants" to improve CVD progression, pharmacotherapies such as those targeting the renin-angiotensin system, or statins, exert at least part of their large clinical benefit via modulating cellular redox signalling. Over 250 proteins, including receptors, ion channels and pumps, and signalling proteins are found in the caveolae. An increasing proportion of these are being recognized as redox regulated-proteins, that reside in the immediate vicinity of the two major cellular sources of ROS, nicotinamide adenine dinucleotide phosphate oxidase (Nox) and uncoupled endothelial nitric oxide synthase (eNOS). This review focuses on what is known about redox signalling within the caveolae, as well as endogenous protective mechanisms utilized by the cell, and new approaches to targeting dysregulated redox signalling in the caveolae as a therapeutic strategy in CVD.

Coincident signals from GPCRs and receptor tyrosine kinases are uniquely transduced by PI3Kβ in myeloid cells

Class I phosphoinositide 3-kinases (PI3Ks) catalyze production of the lipid messenger phosphatidylinositol 3,4,5-trisphosphate (PIP3), which plays a central role in a complex signaling network regulating cell growth, survival, and movement. This network is overactivated in cancer and inflammation, and there is interest in determining the PI3K catalytic subunit (p110α, p110β, p110γ, or p110δ) that should be targeted in different therapeutic contexts. Previous studies have defined unique regulatory inputs for p110β, including direct interaction with Gβγ subunits, Rac, and Rab5. We generated mice with knock-in mutations of p110β that selectively blocked the interaction with Gβγ and investigated its contribution to the PI3K isoform dependency of receptor tyrosine kinase (RTK) and G protein (heterotrimeric guanine nucleotide-binding protein)-coupled receptor (GPCR) responses in primary macrophages and neutrophils. We discovered a unique role for p110β in supporting synergistic PIP3 formation in response to the coactivation of macrophages by macrophage colony-stimulating factor (M-CSF) and the complement protein C5a. In contrast, we found partially redundant roles for p110α, p110β, and p110δ downstream of M-CSF alone and a nonredundant role for p110γ downstream of C5a alone. This role for p110β completely depended on direct interaction with Gβγ, suggesting that p110β transduces GPCR signals in the context of coincident activation by an RTK. The p110β-Gβγ interaction was also required for neutrophils to generate reactive oxygen species in response to the Fcγ receptor-dependent recognition of immune complexes and for their β2 integrin-mediated adhesion to fibrinogen or poly-RGD+, directly implicating heterotrimeric G proteins in these two responses.

Extracellular matrix-specific Caveolin-1 phosphorylation on tyrosine 14 is linked to augmented melanoma metastasis but not tumorigenesis

Caveolin-1 (CAV1) is a scaffolding protein that plays a dual role in cancer. In advanced stages of this disease, CAV1 expression in tumor cells is associated with enhanced metastatic potential, while, at earlier stages, CAV1 functions as a tumor suppressor. We recently implicated CAV1 phosphorylation on tyrosine 14 (Y14) in CAV1-enhanced cell migration. However, the contribution of this modification to the dual role of CAV1 in cancer remained unexplored. Here, we used in vitro [2D and transendothelial cell migration (TEM), invasion] and in vivo (metastasis) assays, as well as genetic and biochemical approaches to address this question in B16F10 murine melanoma cells. CAV1 promoted directional migration on fibronectin or laminin, two abundant lung extracellular matrix (ECM) components, which correlated with enhanced Y14 phosphorylation during spreading. Moreover, CAV1-driven migration, invasion, TEM and metastasis were ablated by expression of the phosphorylation null CAV1(Y14F), but not the phosphorylation mimicking CAV1(Y14E) mutation. Finally, CAV1-enhanced focal adhesion dynamics and surface expression of beta1 integrin were required for CAV1-driven TEM. Importantly, CAV1 function as a tumor suppressor in tumor formation assays was not altered by the Y14F mutation. In conclusion, our results provide critical insight to the mechanisms of CAV1 action during cancer development. Specific ECM-integrin interactions and Y14 phosphorylation are required for CAV1-enhanced melanoma cell migration, invasion and metastasis to the lung. Because Y14F mutation diminishes metastasis without inhibiting the tumor suppressor function of CAV1, Y14 phosphorylation emerges as an attractive therapeutic target to prevent metastasis without altering beneficial traits of CAV1.

The Emerging Hallmarks of Cancer Metabolism

Tumorigenesis is dependent on the reprogramming of cellular metabolism as both direct and indirect consequence of oncogenic mutations. A common feature of cancer cell metabolism is the ability to acquire necessary nutrients from a frequently nutrient-poor environment and utilize these nutrients to both maintain viability and build new biomass. The alterations in intracellular and extracellular metabolites that can accompany cancer-associated metabolic reprogramming have profound effects on gene expression, cellular differentiation, and the tumor microenvironment. In this Perspective, we have organized known cancer-associated metabolic changes into six hallmarks: (1) deregulated uptake of glucose and amino acids, (2) use of opportunistic modes of nutrient acquisition, (3) use of glycolysis/TCA cycle intermediates for biosynthesis and NADPH production, (4) increased demand for nitrogen, (5) alterations in metabolite-driven gene regulation, and (6) metabolic interactions with the microenvironment. While few tumors display all six hallmarks, most display several. The specific hallmarks exhibited by an individual tumor may ultimately contribute to better tumor classification and aid in directing treatment.

4-Hydroxynonenal activates Src through a non-canonical pathway that involves EGFR/PTP1B

Src, a non-receptor protein tyrosine kinase involved in many biological processes, can be activated through both redox-dependent and independent mechanisms. 4-Hydroxy-2-nonenal (HNE) is a lipid peroxidation product that is increased in pathophysiological conditions associated with Src activation. This study examined how HNE activates human c-Src. In the canonical pathway Src activation is initiated by dephosphorylation of pTyr530 followed by conformational change that causes Src auto-phosphorylation at Tyr419 and its activation. HNE increased Src activation in both dose- and time-dependent manner, while it also increased Src phosphorylation at Tyr530 (pTyr530 Src), suggesting that HNE activated Src via a non-canonical mechanism. Protein tyrosine phosphatase 1B inhibitor (539741), at concentrations that increased basal pTyr530 Src, also increased basal Src activity and significantly reduced HNE-mediated Src activation. The EGFR inhibitor, AG1478, and EGFR silencing, abrogated HNE-mediated EGFR activation and inhibited basal and HNE-induced Src activity. In addition, AG1478 also eliminated the increase of basal Src activation by a PTP1B inhibitor. Taken together these data suggest that HNE can activate Src partly through a non-canonical pathway involving activation of EGFR and inhibition of PTP1B.

TGFβ1 rapidly activates Src through a non-canonical redox signaling mechanism

Transforming growth factor-β1 (TGF-β) is involved in multiple cellular processes through Src activation. In the canonical pathway, Src activation is initiated by pTyr530 dephosphorylation followed by a conformational change allowing Tyr419 auto-phosphorylation. A non-canonical pathway in which oxidation of cysteine allows bypassing of pTyr530 dephosphorylation has been reported. Here, we examined how TGF-β activates Src in H358 cells, a small cell lung carcinoma cell line. TGF-β increased Src Tyr419 phosphorylation, but surprisingly, Tyr530 phosphorylation was increased rather than decreased. Vanadate, a protein tyrosine phosphatase inhibitor, stimulated Src activation itself, but rather than inhibiting Src activation by TGF-β, activation by vanadate was additive with TGF-β showing that pTyr530 dephosphorylation was not required. Thus, the involvement of the non-canonical oxidative activation was suspected. TGF-β increased extracellular H2O2 transiently while GSH-ester and catalase abrogated Src activation by TGF-β. Apocynin, a NADPH oxidase inhibitor, inhibited TGF-β-stimulated H2O2 production. Furthermore, mutation of cysteines to alanine, 248C/A, 277C/A, or 501C/A abrogated, while 490C/A significantly reduced, TGF-β-mediated Src activation. Taken together, the results indicate that TGF-β-mediated Src activation operates largely through a redox dependent mechanism, resulting from enhanced H2O2 production through an NADPH oxidase and that cysteines 248, 277, 490, and 501 are critical for this activation.

Matrix metalloproteinases and protein tyrosine kinases: potential novel targets in acute lung injury and ARDS

Acute lung injury (ALI) and ARDS fall within a spectrum of pulmonary disease that is characterized by hypoxemia, noncardiogenic pulmonary edema, and dysregulated and excessive inflammation. While mortality rates have improved with the advent of specialized ICUs and lung protective mechanical ventilation strategies, few other therapies have proven effective in the management of ARDS, which remains a significant clinical problem. Further development of biomarkers of disease severity, response to therapy, and prognosis is urgently needed. Several novel pathways have been identified and studied with respect to the pathogenesis of ALI and ARDS that show promise in bridging some of these gaps. This review will focus on the roles of matrix metalloproteinases and protein tyrosine kinases in the pathobiology of ALI in humans, and in animal models and in vitro studies. These molecules can act independently, as well as coordinately, in a feed-forward manner via activation of tyrosine kinase-regulated pathways that are pivotal in the development of ARDS. Specific signaling events involving proteolytic processing by matrix metalloproteinases that contribute to ALI, including cytokine and chemokine activation and release, neutrophil recruitment, transmigration and activation, and disruption of the intact alveolar-capillary barrier, will be explored in the context of these novel molecular pathways.

Activated neutrophils induce epithelial cell apoptosis through oxidant-dependent tyrosine dephosphorylation of caspase-8

Activated neutrophils can injure host cells through direct effects of oxidants on membrane phospholipids, but an ability to induce apoptotic cell death has not previously been reported. We show that neutrophils activated in vivo in patients who have sustained multiple trauma or in vitro by exposure to bacterial lipopolysaccharide promote epithelial cell apoptosis through SHP-1-mediated dephosphorylation of epithelial cell caspase-8. Epithelial cell apoptosis induced by circulating neutrophils from patients who had sustained serious injury depended on the generation of neutrophil-derived reactive oxygen intermediates and was blocked by inhibition of NADPH oxidase or restoration of intracellular glutathione. Caspase-8 was constitutively tyrosine phosphorylated in a panel of resting epithelial cells, but underwent SHP-1-dependent dephosphorylation in response to hydrogen peroxide, activated neutrophils, or inhibition of Src kinases. Cells transfected with a mutant caspase-8 in which tyrosine residues at Tyr397 or Tyr465 are replaced by nonphosphorylatable phenylalanine underwent accelerated apoptosis, whereas either mutation of these residues to phosphomimetic glutamic acid or transfection with the Src kinases Lyn or c-Src inhibited hydrogen peroxide-induced apoptosis. Exposure to either hydrogen peroxide or lipopolysaccharide-stimulated neutrophils increased phosphorylation and activity of the phosphatase SHP-1, increased activity of caspases 8 and 3, and accelerated epithelial cell apoptosis. These observations reveal a novel mechanism for neutrophil-mediated tissue injury through oxidant-dependent, SHP-1-mediated dephosphorylation of caspase-8 resulting in enhanced epithelial cell apoptosis.

Neutrophil migration: moving from zebrafish models to human autoimmunity

There has been a resurgence of interest in the neutrophil's role in autoimmune disease. Classically considered an early responder that dies at the site of inflammation, new findings using live imaging of embryonic zebrafish and other modalities suggest that neutrophils can reverse migrate away from sites of inflammation. These 'inflammation-sensitized' neutrophils, as well as the neutrophil extracellular traps and other products made by neutrophils in general, may have many implications for autoimmunity. Here, we review what is known about the role of neutrophils in three different autoimmune diseases: rheumatoid arthritis, systemic lupus erythematosus, and small vessel vasculitis. We then highlight recent findings related to several cytoskeletal regulators that guide neutrophil recruitment including Lyn, Rac2, and SHIP. Finally, we discuss how our improved understanding of the molecules that control neutrophil chemotaxis may impact our knowledge of autoimmunity.

Modulation of Neutrophil Apoptosis and the Resolution of Inflammation through β2 Integrins

Precise control of the neutrophil death program provides a balance between their defense functions and safe clearance, whereas impaired regulation of neutrophil death is thought to contribute to a wide range of inflammatory pathologies. Apoptosis is essential for neutrophil functional shutdown, removal of emigrated neutrophils, and timely resolution of inflammation. Neutrophils receive survival and pro-apoptosis cues from the inflammatory microenvironment and integrate these signals through surface receptors and common downstream mechanisms. Among these receptors are the leukocyte-specific membrane receptors β2 integrins that are best known for regulating adhesion and phagocytosis. Accumulating evidence indicate that outside-in signaling through the β2 integrin Mac-1 can generate contrasting cues in neutrophils, leading to promotion of their survival or apoptosis. Binding of Mac-1 to its ligands ICAM-1, fibrinogen, or the azurophilic granule enzyme myeloperoxidase suppresses apoptosis, whereas Mac-1-mediated phagocytosis of bacteria evokes apoptotic cell death. Mac-1 signaling is also target for the anti-inflammatory, pro-resolving mediators, including lipoxin A4, aspirin-triggered lipoxin A4, and resolvin E1. This review focuses on molecular mechanisms underlying Mac-1 regulation of neutrophil apoptosis and highlights recent advances how hierarchy of survival and pro-apoptosis signals can be harnessed to facilitate neutrophil apoptosis and the resolution of inflammation.

Cigarette smoke extract stimulates epithelial-mesenchymal transition through Src activation

Epithelial-mesenchymal transition (EMT) is implicated in the pathogenesis of lung fibrosis and cancer metastasis, two conditions associated with cigarette smoke (CS). CS has been reported to promote the EMT process. CS is the major cause of lung cancer and nearly half of lung cancer patients are active smokers. Nonetheless, the mechanism whereby CS induces EMT remains largely unknown. In this study we investigated the induction of EMT by CS and explored the underlying mechanisms in the human non-small-cell lung carcinoma (H358) cell line. We demonstrate that exposure to an extract of CS (CSE) decreases E-cadherin and increases N-cadherin and vimentin, markers of EMT, in H358 cells cultured in RPMI 1640 medium with 1% fetal bovine serum. Pretreatment with N-acetylcysteine (NAC), a potent antioxidant and precursor of glutathione, abrogated changes in these EMT markers. In addition, CSE activated Src kinase (shown as increased phosphorylation of Src at Tyr418), and the Src kinase inhibitor PP2 inhibited CS-stimulated EMT changes, suggesting that Src is critical in CSE-stimulated EMT induction. Furthermore, NAC treatment abrogated CSE-stimulated Src activation. However, co-incubation with catalase had no effect on CSE-mediated Src activation. Finally, acrolein, an unsaturated aldehyde present in CSE, caused Src activation. Taken together, these data suggest that CSE initiates EMT through Src, which is activated by CS through redox modification.

Lyn is a redox sensor that mediates leukocyte wound attraction in vivo

Tissue wounding induces the rapid recruitment of leukocytes. Wounds and tumours--a type of 'unhealed wound'--generate hydrogen peroxide (H(2)O(2)) through an NADPH oxidase (NOX). This extracellular H(2)O(2) mediates recruitment of leukocytes, particularly the first responders of innate immunity, neutrophils, to injured tissue. However, the sensor that neutrophils use to detect the redox state at wounds is unknown. Here we identify the Src family kinase (SFK) Lyn as a redox sensor that mediates initial neutrophil recruitment to wounds in zebrafish larvae. Lyn activation in neutrophils is dependent on wound-derived H(2)O(2) after tissue injury, and inhibition of Lyn attenuates neutrophil wound recruitment. Inhibition of SFKs also disrupted H(2)O(2)-mediated chemotaxis of primary human neutrophils. In vitro analysis identified a single cysteine residue, C466, as being responsible for direct oxidation-mediated activation of Lyn. Furthermore, transgenic-tissue-specific reconstitution with wild-type Lyn and a cysteine mutant revealed that Lyn C466 is important for the neutrophil wound response and downstream signalling in vivo. This is the first identification, to our knowledge, of a physiological redox sensor that mediates leukocyte wound attraction in multicellular organisms.

Oxidative stress-mediated bimodal regulation of polymorphonuclear leukocyte spreading by polyphenolic compounds

Pyrogallol-bearing polyphenolic compounds induce spreading of polymorphonuclear leukocytes (PMNL), although their optimal concentrations for induction of spreading are quite different (2000, 200, and 2 μM for pyrogallol, (-)-epigallocatechin gallate (EGCG), and tannic acid (TA), respectively), and TA tends to inhibit spreading at higher concentrations. In this study, we examined the involvement of oxidative stress in the regulation of PMNL spreading by these compounds. All three compounds in solution generated H(2)O(2) to a similar extent. Adsorption of the polyphenols to cell surfaces and their accumulation within cells were assessed by detection of the H(2)O(2) precursor O(2)(-) produced by the compounds through reduction of cytochrome c and p-nitro-blue tetrazolium, respectively. TA showed the highest degree of adsorption. EGCG adhered only to PMNL pre-fixed by paraformaldehyde, whereas pyrogallol did not adhere. None of the compounds caused intracellular O(2)(-) generation. A non-pyrogallic compound, 1,2,4-benzenetriol (BT), also produced H(2)O(2); it had no stimulatory effect on PMNL spreading, but inhibited spreading induced by other stimuli. BT did not adhere to PMNL but accumulated within them, and generated O(2)(-) in the presence of glycine. Thiol antioxidants abrogated all of the above spreading-regulatory effects of the polyphenolic compounds. We conclude that H(2)O(2)-generating polyphenols bimodally regulate the spreading of PMNL by subjecting them to oxidative stress. The ability of polyphenol to adhere to, or accumulate within, PMNL may govern the nature of the oxidative stress and determine the optimal concentration of each compound for induction of spreading, as well as whether spreading is promoted or inhibited.

Rituximab sensitizes a Burkitt lymphoma cell line to cell killing by X-irradiation

Clinical trials with rituximab in combination with chemotherapeutic regimens have shown promising results. Data on the effects of rituximab treatment in combination with irradiation are, however, limited and inconsistent. This study aims to investigate the effects of rituximab (R) on cell death induced by X-irradiation in Raji lymphoma cells and to evaluate its mechanisms. We found the cell growth inhibition by irradiation was enhanced by additional rituximab exposure both in cells precultured with rituximab followed by irradiation (R + irradiation) or in cells treated in the reverse sequence (irradiation + R). R + irradiation combination treatment induced more apoptotic cells than irradiation and irradiation + R treatment as early as 12 h after treatment. At 24 h, both combination treatments, R + irradiation and irradiation + R, showed apoptotic cells, which were significantly different from irradiation alone. G2/M cell cycle arrest was observed after irradiation alone and the combination treatment. The combination treatment revealed an elevation in reactive oxygen species (ROS) generation in a radiation dose-dependent manner. In addition, rituximab enhanced the cell growth inhibition and apoptotic cell death induced by the oxidative agent, H(2)O(2). We propose that rituximab mediates a significant in vitro radiosensitizing effect and induces cell cycle changes and apoptosis in Raji cells. ROS probably play an important role in these events.

Downstream targets and intracellular compartmentalization in Nox signaling

Reactive oxygen species (ROS) have become recognized for their role as second messengers in a multitude of physiologic responses. Emerging evidence points to the importance of the NADPH oxidase family of ROS-producing enzymes in mediating redox-sensitive signal transduction. However, a clear paradox exists between the specificity required for signaling and the nature of ROS as both diffusible and highly reactive molecules. We seek to understand the targets and compartmentalization of the NADPH oxidase signaling to determine how NADPH oxidase-derived ROS fit into established signaling paradigms. Herein we review recent data that link cellular NADPH oxidase enzymes to ROS signaling, with a particular focus on the mechanism(s) involved in achieving signaling specificity.

Biphasic regulation of polymorphonuclear leukocyte spreading by polyphenolic compounds with pyrogallol moieties

Green tea polyphenols have been reported to have anti-inflammatory activities, although the molecular mechanisms responsible for this effect remain unclear. In the present study, we examined the effect of green tea extract and a variety of polyphenolic compounds on spreading of peripheral blood polymorphonuclear leukocytes (PMNs) over fibrinogen-coated surfaces. Green tea extract exerted a biphasic effect on PMN spreading; it induced or suppressed spreading at low and high concentrations, respectively. We also found that pyrogallol-bearing compounds have spreading induction activity. Among the compounds tested, tannic acid (TA) had the strongest activity; the concentrations required for induction of maximal spreading were 2 microM for TA, 200 microM for (-)-epigallocatechin gallate, and 2000 microM for the other active compounds. Furthermore, TA was the only compound showing a biphasic effect similar to that of green tea extract; TA at 20 or 200 microM suppressed spreading. The spreading-stimulatory signal was still latent during PMN exposure to TA at concentrations that inhibited spreading, because the pre-exposed PMNs underwent spreading when plated after removal of free TA by centrifugation. The spreading-inhibitory effect of TA at high concentrations overcame the induction of spreading by other stimuli, including phorbol 12-myristate 13-acetate, hydrogen peroxide, denatured fibrinogen surfaces, and naked plastic surfaces. These results suggest that TA as well as green tea extract is bi-functional, having pro-inflammatory and anti-inflammatory effects at low and high concentrations, respectively. Pharmacological use of TA may thus provide new strategies aimed at regulation of PMN spreading for control of inflammation.

The NOX family of ROS-generating NADPH oxidases: physiology and pathophysiology

For a long time, superoxide generation by an NADPH oxidase was considered as an oddity only found in professional phagocytes. Over the last years, six homologs of the cytochrome subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the phagocyte NADPH oxidase itself (NOX2/gp91(phox)), the homologs are now referred to as the NOX family of NADPH oxidases. These enzymes share the capacity to transport electrons across the plasma membrane and to generate superoxide and other downstream reactive oxygen species (ROS). Activation mechanisms and tissue distribution of the different members of the family are markedly different. The physiological functions of NOX family enzymes include host defense, posttranlational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. NOX enzymes also contribute to a wide range of pathological processes. NOX deficiency may lead to immunosuppresion, lack of otoconogenesis, or hypothyroidism. Increased NOX activity also contributes to a large number or pathologies, in particular cardiovascular diseases and neurodegeneration. This review summarizes the current state of knowledge of the functions of NOX enzymes in physiology and pathology.

Src protein tyrosine kinase family and acute inflammatory responses

Acute inflammatory responses are one of the major underlying mechanisms for tissue damage of multiple diseases, such as ischemia-reperfusion injury, sepsis, and acute lung injury. By use of cellular and molecular approaches and transgenic animals, Src protein tyrosine kinase (PTK) family members have been identified to be essential for the recruitment and activation of monocytes, macrophages, neutrophils, and other immune cells. Src PTKs also play a critical role in the regulation of vascular permeability and inflammatory responses in tissue cells. Importantly, animal studies have demonstrated that small chemical inhibitors for Src PTKs attenuate tissue injury and improve survival from a variety of pathological conditions related to acute inflammatory responses. Further investigation may lead to the clinical application of these inhibitors as drugs for ischemia-reperfusion injury (such as stroke and myocardial infarction), sepsis, acute lung injury, and multiple organ dysfunction syndrome.

Src protein tyrosine kinase family and acute lung injury

Acute inflammatory responses are one of the major underlying mechanisms for tissue damage of multiple diseases, such as sepsis and acute lung injury. Inflammatory mediators released from a variety of cells in response to acute inflammations can interact with immune cells, microvascular endothelial cells and other tissue cells, to elicit a series of intracellular signaling reactions where activation of Src protein tyrosine kinase (PTK) family members is involved. Using cellular and molecular approaches and transgenic animals, Src PTK family members have been identified to be essential for the recruitment and activation of monocytes, macrophages, neutrophils and other immune cells. Src PTK family members also play a critical role in the regulation of vascular permeability and inflammatory responses in tissue cells. Importantly, animal studies have demonstrated that small chemical inhibitors for Src PTKs attenuated acute lung injury. Further investigation may lead to the clinical application of these inhibitors as drugs for acute lung injury.

Neutrophil beta2 integrins: moderators of life or death decisions

Beta2 integrins are leukocyte-specific membrane receptors that are crucial for host defense. They are best known for promoting neutrophil recruitment into inflamed tissue and pathogen phagocytosis. More recent data suggest that they also modulate neutrophil apoptosis. Neutrophils are terminally differentiated cells, which undergo constitutive apoptosis, and their apoptosis and clearance is required for the resolution of inflammation. Engagement of the beta2 integrin Mac-1 through its adhesion to its ligands, intercellular adhesion molecule-1 (ICAM-1) and fibrinogen, signals survival cues in neutrophils. However, in the presence of pro-apoptotic signals, such as tumor necrosis factor (TNF), Mac-1 engagement accelerates apoptosis. Furthermore, Mac-1-dependent phagocytosis of complement-opsonized pathogens triggers rapid neutrophil apoptosis, which is dependent on NADPH oxidase-generated reactive oxygen species and caspase activation. This is also associated with changes in the transcription profiles of pro- and anti-apoptotic genes. In this review, the beta2 integrin-dependent mechanisms that modulate the decision between life and death in neutrophils are overviewed.

p40phox: The last NADPH oxidase subunit

The phagocytic NADPH-oxidase is a multiprotein system activated during the inflammatory response to produce superoxide anion (O2-), which is the substrate for formation of additional reactive oxygen species (ROS). The importance of this system for innate immunity is established by chronic granulomatous disease (CGD), a primary immunodeficiency caused by defects in the NADPH oxidase. In this review, we present and discuss recent knowledge about p40phox, the last NADPH oxidase component to be identified. Furthermore, its interaction with cellular pathways outside of the NADPH oxidase is discussed. Described in this review is evidence that p40phox participates in NADPH oxidase dynamics within cells, what is known about its role in the oxidase, the possibility that p40phox participates in non-NADPH oxidase processes in phagocytic and non-phagocytic cells and whether p40phox could mediate a similar function in other NADPH oxidases. An improved understanding of p40phox should provide new insights about NADPH oxidase, the physiology of phagocytic cells and the innate immune system.

The proto-oncogene Fgr regulates cell migration and this requires its plasma membrane localization

Fgr participates in integrin signaling in myeloid leukocytes. To examine the role of its specific domains in regulating cell migration, we expressed various Fgr molecules in COS-7 cells. Full-length, membrane-bound Fgr, but not an N-terminal truncation mutant that distributed to an intracellular compartment, increased cell migration on fibronectin and enhanced phosphorylation of the p85 subunit of phosphatidylinositol 3-kinase (PI3K), cortactin and focal adhesion kinase (FAK) at Y397 and Y576. Fgr increased Rac GTP loading, and phosphorylation of the Rac GEF Vav2, and bound to a protein complex formed by the Rho inhibitor p190RhoGAP and FAK, increasing p190RhoGAP phosphorylation, in a manner absolutely dependent on membrane localization. A kinase-defective truncation mutant of Fgr increased cell migration, albeit to a much lower extent than full-length Fgr, and was found to associate with the plasma membrane, to activate Rac and to form complexes with p190RhoGAP/FAK. Formation of complexes between p190RhoGAP, Fgr, and the FAK-related protein Pyk2 were also detected in murine macrophages. These findings suggest that the proto-oncogene Fgr regulates cell migration impinging on a signaling pathway implicating FAK/Pyk2 and leading to activation of Rac and the Rho inhibitor p190RhoGAP.

Role of oxidative modifications in atherosclerosis

This review focuses on the role of oxidative processes in atherosclerosis and its resultant cardiovascular events. There is now a consensus that atherosclerosis represents a state of heightened oxidative stress characterized by lipid and protein oxidation in the vascular wall. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis. In support of this hypothesis, oxidized LDL can support foam cell formation in vitro, the lipid in human lesions is substantially oxidized, there is evidence for the presence of oxidized LDL in vivo, oxidized LDL has a number of potentially proatherogenic activities, and several structurally unrelated antioxidants inhibit atherosclerosis in animals. An emerging consensus also underscores the importance in vascular disease of oxidative events in addition to LDL oxidation. These include the production of reactive oxygen and nitrogen species by vascular cells, as well as oxidative modifications contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption. Despite these abundant data however, fundamental problems remain with implicating oxidative modification as a (requisite) pathophysiologically important cause for atherosclerosis. These include the poor performance of antioxidant strategies in limiting either atherosclerosis or cardiovascular events from atherosclerosis, and observations in animals that suggest dissociation between atherosclerosis and lipoprotein oxidation. Indeed, it remains to be established that oxidative events are a cause rather than an injurious response to atherogenesis. In this context, inflammation needs to be considered as a primary process of atherosclerosis, and oxidative stress as a secondary event. To address this issue, we have proposed an "oxidative response to inflammation" model as a means of reconciling the response-to-injury and oxidative modification hypotheses of atherosclerosis.

Formyl-Met-Leu-Phe induces calcium-dependent tyrosine phosphorylation of Rel-1 in neutrophils

Chemoattractant priming and activation of PMNs results in changes in cytosolic Ca2+ concentration, tyrosine kinase activity, and gene expression. We hypothesize that the initial signaling for the activation of a 105kDa protein (Rel-1) requires Ca2+-dependent tyrosine phosphorylation. A rapid and time-dependent tyrosine phosphorylation of Rel-1 occurred following formyl-Met-Leu-Phe (fMLP) stimulation of human PMNs at concentrations that primed or activated the NADPH oxidase (10(-9) to 10(-6)M), becoming maximal after 30s. Pretreatment with pertussis toxin (Ptx) or tyrosine kinase inhibitors abrogated this phosphorylation and inhibited fMLP activation of the oxidase. The fMLP concentrations employed also caused a rapid increase in cytosolic Ca2+ but chelation negated the effects, including the cytosolic Ca2+ flux, oxidase activation, and the tyrosine phosphorylation of Rel-1. Conversely, chelation of extracellular Ca2+ decreased the fMLP-mediated Ca2+ flux, had no affect on the oxidase, and augmented tyrosine phosphorylation of Rel-1. Phosphorylation of Rel-1 was inhibited when PMNs were preincubated with a p38 MAP kinase (MAPK) inhibitor (SB203580). In addition, fMLP elicited rapid activation of p38 MAPK which was abrogated by chelation of cytosolic Ca2+. Thus, fMLP concentrations that prime or activate the oxidase cause a rapid Ca2+-dependent tyrosine phosphorylation of Rel-1 involving p38 MAPK activation.

TNF-Induced β2 Integrin Activation Involves Src Kinases and a Redox-Regulated Activation of p38 MAPK

We previously demonstrated that the TNF-alpha-induced inside-out signaling leading to beta(2) integrin activation is redox regulated. To identify kinases involved in this pathway, the effects of kinase inhibitors on the expression of beta(2) integrin activation neoepitope (clone 24) were investigated. We show that both p38 MAPK (inhibited by SB203580) and Src kinases (inhibited by PP2) are involved in beta(2) integrin activation by TNF and oxidants in human neutrophils. Src kinases appeared constitutively active in resting neutrophils and not further activated by TNF or oxidants in nonadherent conditions. However, PP2 blocked both TNF-induced expression of the 24 epitope and cell adhesion promoted by the integrin activating anti-CD18 KIM185 mAb, showing that both the inside-out and the outside-in signaling involve Src kinases. p38 MAPK was activated by TNF and oxidants in nonadherent conditions i.e., with 10 mM EDTA. This activation in EDTA resulted in CD11b, CD35 and CD66 up-regulation and in an oxidative response, all blocked by SB203580 and PP2. p38 MAPK was not activated upon direct integrin activation by KIM185 mAb. Thus, p38 activation allows the study to distinguish the initial transduction pathway leading to beta(2) integrin activation from the signaling resulting from integrin engagement. Finally, p38 MAPK activation by TNF was blocked by diphenylene iodonium, an inhibitor of flavoprotein oxidoreductase, and by the free radical scavenger N-acetylcystein. Taken together, these results demonstrate, for the first time, that constitutively activated Src tyrosine kinases and a redox-regulated activation of p38 MAPK are involved in TNF inside-out signaling leading to beta(2) integrin activation.

Distinct subcellular localizations of Nox1 and Nox4 in vascular smooth muscle cells

OBJECTIVE

Reactive oxygen species (ROS) that act as signaling molecules in vascular smooth muscle cells (VSMC) and contribute to growth, hypertrophy, and migration in atherogenesis are produced by multi-subunit NAD(P)H oxidases. Nox1 and Nox4, two homologues to the phagocytic NAD(P)H subunit gp91phox, both generate ROS in VSMC but differ in their response to growth factors. We hypothesize that the opposing functions of Nox1 and Nox4 are reflected in their differential subcellular locations.

METHODS AND RESULTS

We used immunofluorescence to visualize the NAD(P)H subunits Nox1, Nox4, and p22phox in cultured rat and human VSMC. Optical sectioning using confocal microscopy showed that Nox1 is co-localized with caveolin in punctate patches on the surface and along the cellular margins, whereas Nox4 is co-localized with vinculin in focal adhesions. These immunocytochemical distributions are supported by membrane fractionation experiments. Interestingly, p22phox, a membrane subunit that interacts with the Nox proteins, is found in surface labeling and in focal adhesions in patterns similar to Nox1 and Nox4, respectively.

CONCLUSIONS

The differential roles of Nox1 and Nox4 in VSMC may be correlated with their differential compartmentalization in specific signaling domains in the membrane and focal adhesions.

Oxygen radical production in neutrophils interacting with platelets and surface-immobilized plasma proteins: Role of tyrosine phosphorylation

The interaction between neutrophil granulocytes and platelets is considered to play an important role in the inflammatory process induced by an implanted foreign material. However, the cellular mechanisms involved remain incompletely understood. We used a luminol-dependent chemiluminescence (CL) technique to analyze the generation of reactive oxygen species (ROS) in human neutrophils interacting with different plasma protein-coated surfaces in the presence or absence of unstimulated or stimulated platelets. The role of tyrosine phosphorylation in the regulation of NADPH oxidase activity was evaluated with quantitative fluorescence microscopy and the specific tyrosine kinase inhibitor genistein. We found that the ROS-production is 2 to 3 times higher in neutrophils on immunoglobulin G (IgG)-coated surfaces than in cells interacting with albumin- or fibrinogen-coated surfaces. Incubation with superoxide dismutase and catalase revealed that about 45% of the ROS was released extracellularly on IgG surfaces whereas corresponding values were 90% and 85% in neutrophils interacting with albumin and fibrinogen, respectively. The presence of platelets markedly increased the extracellular generation of ROS, mainly in neutrophils interacting with IgG- or fibrinogen-coated surfaces whereas the intracellular production was only modestly affected. Quantitative fluorescence microscopy of neutrophils stained with FITC-conjugated anti-phosphotyrosine antibodies showed a correlation between tyrosine phosphorylation, cell spreading, and ROS production. Platelets markedly amplified the anti-phosphotyrosine staining on both fibrinogen- and IgG-coated surfaces whereas the low level of tyrosine phosphorylation in neutrophils on albumin-coated surfaces was not further elevated by platelets. Furthermore, the tyrosine kinase inhibitor genistein inhibited both extra- and intracellular ROS production in neutrophils regardless of the presence of platelets. We demonstrate that plasma protein coating and the presence of platelets are crucial for the inflammatory response of adhering neutrophils and that the oxidative response correlates with the extent of tyrosine phosphorylation of proteins in focal contacts.

Down-regulation of Rac activity during beta 2 integrin-mediated adhesion of human neutrophils

In human neutrophils, beta2 integrin engagement mediated a decrease in GTP-bound Rac1 and Rac2. Pretreatment of neutrophils with LY294002 or PP1 (inhibiting phosphatidylinositol 3-kinase (PI 3-kinase) and Src kinases, respectively) partly reversed the beta2 integrin-induced down-regulation of Rac activities. In contrast, beta2 integrins induced stimulation of Cdc42 that was independent of Src family members. The PI 3-kinase dependence of the beta2 integrin-mediated decrease in GTP-bound Rac could be explained by an enhanced Rac-GAP activity, since this activity was blocked by LY204002, whereas PP1 only had a minor effect. The fact that only Rac1 but not Rac2 (the dominating Rac) redistributed to the detergent-insoluble fraction and that it was independent of GTP loading excludes the possibility that down-regulation of Rac activities was due to depletion of GTP-bound Rac from the detergent-soluble fraction. The beta2 integrin-triggered relocalization of Rac1 to the cytoskeleton was enabled by a PI 3-kinase-induced dissociation of Rac1 from LyGDI. The dissociations of Rac1 and Rac2 from LyGDI also explained the PI 3-kinase-dependent translocations of Rac GTPases to the plasma membrane. However, these accumulations of Rac in the membrane, as well as that of p47phox and p67phox, were also regulated by Src tyrosine kinases. Inasmuch as Rac GTPases are part of the NADPH oxidase and the respiratory burst is elicited in neutrophils adherent by beta2 integrins, our results indicate that activation of the NADPH oxidase does not depend on the levels of Rac-GTP but instead requires a beta2 integrin-induced targeting of the Rac GTPases as well as p47phox and p67phox to the plasma membrane.

Neutrophil survival on biomaterials is determined by surface topography

PURPOSE

Cardiovascular device-centered infections are a major cause of hospital morbidity, mortality, and expense. Caused by opportunistic bacteria, this phenomenon is thought to arise because of a defect in neutrophil bacterial killing. We have shown that neutrophils that adhere to polystyrene remain viable, whereas neutrophils that adhere to the vascular biomaterials expanded polytetrafluoroethylene (ePTFE) and Dacron undergo a rapid nonapoptotic death. This study was designed to test the hypothesis that surface topography is a determinant of the nonapoptotic death response of neutrophils to biomaterials.

METHODS

We took advantage of the ease with which a polystyrene surface can be manipulated to examine the effect of surface topography on neutrophil viability. Neutrophils were exposed to smooth or roughened polystyrene surfaces both in vivo and in vitro. Changes in cell membrane permeability and production of reactive oxygen species by individual cells were monitored with fluorescent dyes.

RESULTS

Host cells and isolated human neutrophils died rapidly after adhesion to roughened polystyrene. Neutrophils adherent to roughened surfaces produced more reactive oxygen intermediates than those adherent to smooth surfaces and were first to die. The cell death response precipitated by expanded polytetrafluoroethylene, Dacron, or the roughened surfaces was significantly reduced with treatment of the neutrophils with catalase, diphenylene iodonium, or the src kinase inhibitor PP2 before adhesion.

CONCLUSIONS

Neutrophil adhesion to roughened materials triggers rapid production of reactive oxygen species and precipitates a nonapoptotic cell death. Understanding the material properties that trigger these responses is essential to development of the next generation of implantable biomaterials.

Chemoattractant receptor-stimulated F-actin polymerization in the human neutrophil is signaled by 2 distinct pathways

We characterized the overall rate of F-actin polymerization in the pseudopod region by measuring the rate of extension of single pseudopods stimulated by f-Met-Leu-Phe. The rate of pseudopod extension was measured in the presence of inhibitors for signaling molecules that are known to be involved in motility. Our data show the existence of 2 distinct signaling pathways of actin polymerization in the pseudopod region: a phosphoinositide 3-kinase gamma (PI3Kgamma)-dependent and -independent pathway. The PI3Kgamma dependent signaling of F-actin polymerization also depends on protein kinase C zeta and protein kinase B (Akt/PKB). The PI3Kgamma-independent pathway depends on GTPase RhoA, the RhoA ROCK kinase, Src family tyrosine kinases, and NADPH, and is modulated by cAMP.

Src kinase induces calcium release in Xenopus egg extracts via PLCgamma and IP3-dependent mechanism

Mobilization of intracellular calcium is an indispensable step of fertilization-induced egg activation. Recently, this process has been shown to require the sequential activation of Src family tyrosine kinases, phospholipase Cgamma (PLCgamma), and inositol-1,4,5-trisphosphate (IP3)-dependent receptor of endoplasmic reticulum. In the present study, we made an attempt to recapitulate the early events of egg activation by stimulating Src kinase activity in the cell-free extracts of Xenopus eggs. We found that enhanced Src kinase activity can initiate calcium response of low magnitude in cytostatic factor (CSF)-arrested mitotic extracts without releasing them into interphase. The addition of catalytically active recombinant Src kinase, as well as the activation of endogenous Xenopus Src family kinase by hydrogen peroxide (H2O2), increased total tyrosine phosphorylation, tyrosine phosphorylation of PLCgamma, and IP3 production in the extracts. The treatment with the Src family kinase-specific inhibitor, PP1, or PLC inhibitor, U73122, or IP3 receptor antagonist, heparin, prevented calcium release in the extracts. We conclude, therefore, that possible mechanism of Src/H2O2 action in the extracts might involve tyrosine phosphorylation and activation of PLCgamma, accompanied by the increase in IP3 content and subsequent calcium release from IP3-regulated calcium stores. These results also suggest that monitoring calcium signals induced in the Xenopus egg extracts by various components of signaling pathways may provide a particularly useful approach to investigating their role in the signal transduction.

Soluble fibrinogen modulates neutrophil functionality through the activation of an extracellular signal-regulated kinase-dependent pathway

The integrin family not only mediates the recruitment of polymorphonuclear leukocytes (PMN) to sites of inflammation but also regulates several effector functions by binding to specific ligands. We have recently demonstrated that soluble fibrinogen (sFbg) is able to trigger an activating signal in PMN through an integrin-dependent mechanism. This activation results in degranulation, phagocytosis enhancement, and apoptosis delay. The aim of the present work was to further elucidate the molecular events that follow sFbg interaction with CD11b in human PMN, and the participation of this signaling pathway in the regulation of neutrophil functionality. We demonstrate that sFbg triggers a cascade of intracellular signals that lead to focal adhesion kinase and extracellular signal-regulated kinase 1/2 tyrosine phosphorylation. The activation of this mitogen-activated protein kinase pathway plays a central role in the sFbg modulation of secondary granule degranulation, Ab-dependent phagocytosis, and apoptosis. However, fibrinogen-induced secretory vesicle degranulation occurs independently of the signaling transduction pathways investigated herein. In the context of an inflammatory process, the intracellular signal pathway activated by sFbg may be an early event influencing the functionality of PMN.

Preservation of the pattern of tyrosine phosphorylation in human neutrophil lysates. II. A sequential lysis protocol for the analysis of tyrosine phosphorylation-dependent signalling

In stimulated neutrophils, the majority of tyrosine phosphorylated proteins are concentrated in Triton X-100 or NP-40 insoluble fractions. Most immunobiochemical studies, whose objective is to study the functional relevance of tyrosine phosphorylation are, however, performed using the supernatants of cells lysed in non-ionic detergent-containing buffers (RIPA lysis buffers). This observation prompted us to develop an alternative lysis protocol. We established a procedure involving the sequential lysis of neutrophils in buffers of increasing tonicities that not only preserved and solubilized tyrosine phosphorylated proteins but also retained their enzymatic activities. The sequential lysis of neutrophils in hypotonic, isotonic and hypertonic buffers containing non-ionic detergents resulted in the solubilisation of a significant fraction of tyrosine phosphorylated proteins. Furthermore, we observed that in monosodium urate crystals-stimulated neutrophils, Lyn activity was enhanced in the soluble fraction recovered from the hypertonic fraction, but not from that of the first hypotonic lysis. The distribution of tyrosine phosphorylated proteins between the NP-40 soluble and insoluble fractions was both substrate- and agonist-dependent. In neutrophils stimulated with fMet-Leu-Phe, MSU crystals or by CD32 ligation, the tyrosine phosphorylated proteins were mostly insoluble. On the other hand, in GM-CSF-treated cells, the phosphoproteins were more equally distributed between the two fractions. The results of this study provide a new experimental procedure for the investigation of tyrosine phosphorylation pathways in activated human neutrophils which may also be applicable to other cell types.

Tumor necrosis factor alpha stimulates invasion of Src-activated intestinal cells

BACKGROUND & AIMS

Src activation is correlated with progression of colorectal cancer (CRC). CRCs accompanied by ulcerative colitis, chronic inflammation in the colon, often have elevated Src activity, and ulcerative colitis-related CRCs are more likely to become invasive, whereas Ras activation is rarely associated with this disease. The aim of this study was to investigate the effects of a proinflammatory cytokine, tumor necrosis factor alpha (TNF-alpha), on the invasive properties of epithelial cells constitutively expressing activated Ras or Src.

METHODS

A cell line derived from intestinal epithelia was transfected with a v-src- or v-H-ras-expressing vector. The effect of TNF-alpha on morphologic changes in colonies cultured in soft agar was determined. Src protein kinase activity, peroxide production, E-cadherin expression levels, and the phosphorylation status of beta-catenin and E-cadherin were determined. The invasive potential of these cells was determined by measuring cell motility and using an in vitro invasion assay.

RESULTS

TNF-alpha altered the colony morphology of src-, but not ras-expressing cells. TNF-alpha increased peroxide production, leading to Src protein expression as well as Src activity in src transfectants. Activation of Src by TNF-alpha led to reduced E-cadherin levels and enhanced invasion of src transfectants. Pyrrolidine dithiocarbamate and herbimycin A inhibited these effects.

CONCLUSION

These results indicate that Src kinase activation enhances the response of epithelial cells to TNF-alpha leading to increased invasion through mechanisms that involve production of reactive oxygen intermediates.

Oxidant-dependent phosphorylation of p40phox in B lymphocytes

As with the neutrophil NADPH oxidase, the B lymphocyte NADPH oxidase consists of a membrane-bound flavocytochrome b and regulatory factors including Rac and the cytosolic phox protein triad p67phox, p47phox, and p40phox. Here we demonstrate by phosphoamino acid analysis and the use of the potent PKC inhibitor GFX that, in response to stimulation of B lymphocytes with sodium orthovanadate and H(2)O(2), the p40phox component of the cytosolic phox triad is selectively phosphorylated on serine and threonine residues by a PKC-type protein kinase. The pattern of p40phox phosphorylation was closely related to the kinetics of tyrosine phosphorylation of PKC-delta, the main PKC isotype of B lymphocytes. Blocking H(2)O(2)-dependent tyrosine phosphorylation of PKC by genistein resulted in inhibition of p40phox phosphorylation. The correlation between the tyrosine phosphorylation of PKC-delta and the serine/threonine phosphorylation of p40phox, together with the inhibition of p40phox phosphorylation by rottlerin, a selective inhibitor of PKC-delta, makes the activated PKC-delta a likely candidate in the process of the oxidant-dependent phosphorylation of p40phox in B cells.

Platelet/polymorphonuclear leukocyte adhesion: a new role for SRC kinases in Mac-1 adhesive function triggered by P-selectin

Adhesion of polymorphonuclear leukocytes (PMNLs) to activated platelets requires a P-selectin-triggered, tyrosine kinase-dependent adhesiveness of Mac-1 and is accompanied by tyrosine phosphorylation of a 110-kd protein (P-110) in PMNLs. Inhibitors of SRC tyrosine kinases were found to inhibit PMNL adhesion to activated platelets or to P-selectin expressing Chinese hamster ovary (CHO-P) cells and the tyrosine phosphorylation of P-110. Adhesion of PMNLs to activated platelets or to CHO-P cells stimulated activity of LYN and HCK. Monoclonal antibody blockade of P-selectin or beta2-integrins reduced the activation of both kinases. In PMNLs either adherent to platelets or aggregated by P-selectin-IgG chimera, Mac-1 was rapidly redistributed to the Triton X-100-insoluble cytoskeletal fraction, and large clusters of Mac-1 colocalized with patches of F-actin at the sites of cell-cell contact. In PMNLs stimulated by P-selectin-IgG chimera, SRC kinase inhibition impaired Mac-1 clustering, F-actin accumulation, and CD18 redistribution to the cytoskeleton. Disruption of the actin filament network by cytochalasin D prevented PMNL-platelet adhesion and P-selectin-induced PMNL aggregation and impaired the clustering of Mac-1. In agreement with the requirement for the beta2-integrin in the functional up-regulation of LYN and HCK, integrin blockade by monoclonal antibodies resulted in a complete inhibition of P-selectin-induced Mac-1 clustering and F-actin accumulation. Taken together, the results indicate that, after an initial P-selectin-triggered beta2-integrin interaction with the ligand, SRC kinases are activated and allow the remodeling of cytoskeleton-integrin linkages and integrin clustering that finally strengthen cell-cell adhesion. This model highlights a new role for SRC kinases in a regulatory loop by which the Mac-1 promotes its own adhesive function.

Nonstructural 3 protein of hepatitis C virus triggers an oxidative burst in human monocytes via activation of NADPH oxidase

It has been shown that oxidative stress occurs in chronic hepatitis C. Release of reactive oxygen species (ROS) from sequestered phagocytes and activated resident macrophages represents the predominant component of oxidative stress in the liver. However, little is known about the ability of the monocyte to produce ROS in response to protein of hepatitis C virus. In this study, we investigated the ROS production in human monocytes stimulated by several viral proteins of hepatitis C virus. Human monocytes from healthy blood donors were incubated with recombinant viral protein: Core, NS3, NS4, and NS5. ROS production was measured by chemiluminescence. Only NS3 triggered ROS production in human monocytes. Generated ROS were mainly the anion superoxide. NS3 also induced a rapid and transient increase in intracellular calcium concentration measured by a video digital microscopy technique. By using different metabolic inhibitors, we showed that ROS production requires calcium influx, tyrosine kinases, and the stress-activated protein kinase, p38. The study of p47(PHOX) phosphorylation and translocation showed that NADPH oxidase was activated and involved in ROS production induced by NS3. In a second experiment, NS3 inhibited the oxidative burst induced by phorbol 12-myristate 13-acetate. These results indicate that NS3 activates NADPH oxidase and modulates ROS production, which may be involved in the natural history of hepatitis C infection.

Peroxynitrite-dependent activation of src tyrosine kinases lyn and hck in erythrocytes is under mechanistically different pathways of redox control

Peroxynitrite, the product of superoxide and nitric oxide radicals, is considered one of the major oxidants formed in vivo under intense oxidative stress. We have previously reported the upregulation by peroxynitrite of src kinase activity in red blood cells. In this study, we investigated the mechanisms of peroxynitrite action and we demonstrate that two src kinases (lyn and hck) are activated through different pathways involving cysteine-dependent or -independent oxidations. Activation of hck by peroxynitrite or by hydrogen peroxide could be explained by reversible SH redox changes, whereas lyn was unaffected by hydrogen peroxide and its direct activation by peroxynitrite occurred through a still unknown modification(s) not reverted by SH reduction or inhibited by SH alkylation. Moreover, lyn could be activated also downstream by peroxynitrite-activated hck. The cross talk between lyn and hck was selective, since activated hck did not activate the non-src kinase syk. This study illustrates the complexity of redox-dependent src regulation and suggests that one reason for src heterogeneity may be a peculiar difference in their sensitivity to physiological oxidants. Irrespectively of the activation pathway, the final effect of peroxynitrite is the amplification of tyrosine-dependent signaling, a finding of general interest in nitric oxide-related pathophysiology.

Mycobacterium tuberculosis phagosomes exhibit altered calmodulin-dependent signal transduction: contribution to inhibition of phagosome-lysosome fusion and intracellular survival in human macrophages

Mycobacterium tuberculosis successfully parasitizes macrophages by disrupting the maturation of its phagosome, creating an intracellular compartment with endosomal rather than lysosomal characteristics. We have recently demonstrated that live M. tuberculosis infect human macrophages in the absence of an increase in cytosolic Ca(2+) ([Ca(2+)](c)), which correlates with inhibition of phagosome-lysosome fusion and intracellular viability. In contrast, killed M. tuberculosis induces an elevation in [Ca(2+)](c) that is coupled to phagosome-lysosome fusion. We tested the hypothesis that defective activation of the Ca(2+)-dependent effector proteins calmodulin (CaM) and CaM-dependent protein kinase II (CaMKII) contributes to the intracellular pathogenesis of tuberculosis. Phagosomes containing live M. tuberculosis exhibited decreased levels of CaM and the activated form of CaMKII compared with phagosomes encompassing killed tubercle bacilli. Furthermore, ionophore-induced elevations in [Ca(2+)](c) resulted in recruitment of CaM and activation of CaMKII on phagosomes containing live M. tuberculosis. Specific inhibitors of CaM or CaMKII blocked Ca(2+) ionophore-induced phagosomal maturation and enhanced the bacilli's intracellular viability. These results demonstrate a novel role for CaM and CaMKII in the regulation of phagosome-lysosome fusion and suggest that defective activation of these Ca(2+)-activated signaling components contributes to the successful parasitism of human macrophages by M. tuberculosis.

PLA(2) dependence of diaphragm mitochondrial formation of reactive oxygen species

Contraction-induced respiratory muscle fatigue and sepsis-related reductions in respiratory muscle force-generating capacity are mediated, at least in part, by reactive oxygen species (ROS). The subcellular sources and mechanisms of generation of ROS in these conditions are incompletely understood. We postulated that the physiological changes associated with muscle contraction (i.e., increases in calcium and ADP concentration) stimulate mitochondrial generation of ROS by a phospholipase A(2) (PLA(2))-modulated process and that sepsis enhances muscle generation of ROS by upregulating PLA(2) activity. To test these hypotheses, we examined H(2)O(2) generation by diaphragm mitochondria isolated from saline-treated control and endotoxin-treated septic animals in the presence and absence of calcium and ADP; we also assessed the effect of PLA(2) inhibitors on H(2)O(2) formation. We found that 1) calcium and ADP stimulated H(2)O(2) formation by diaphragm mitochondria from both control and septic animals; 2) mitochondria from septic animals demonstrated substantially higher H(2)O(2) formation than mitochondria from control animals under basal, calcium-stimulated, and ADP-stimulated conditions; and 3) inhibitors of 14-kDa PLA(2) blocked the enhanced H(2)O(2) generation in all conditions. We also found that administration of arachidonic acid (the principal metabolic product of PLA(2) activation) increased mitochondrial H(2)O(2) formation by interacting with complex I of the electron transport chain. These data suggest that diaphragm mitochondrial ROS formation during contraction and sepsis may be critically dependent on PLA(2) activation.