Critical role of proline-rich tyrosine kinase 2 in reversion of the adhesion-mediated suppression of reactive oxygen species generation by human neutrophils

The Adhesome Network: Key Components Shaping the Tumour Stroma

Beyond the conventional perception of solid tumours as mere masses of cancer cells, advanced cancer research focuses on the complex contributions of tumour-associated host cells that are known as "tumour microenvironment" (TME). It has been long appreciated that the tumour stroma, composed mainly of blood vessels, cancer-associated fibroblasts and immune cells, together with the extracellular matrix (ECM), define the tumour architecture and influence cancer cell properties. Besides soluble cues, that mediate the crosstalk between tumour and stroma cells, cell adhesion to ECM arises as a crucial determinant in cancer progression. In this review, we discuss how adhesome, the intracellular protein network formed at cell adhesions, regulate the TME and control malignancy. The role of adhesome extends beyond the physical attachment of cells to ECM and the regulation of cytoskeletal remodelling and acts as a signalling and mechanosensing hub, orchestrating cellular responses that shape the tumour milieu.

SKAP2 is required for defense against K. pneumoniae infection and neutrophil respiratory burst

Klebsiella pneumoniae is a respiratory, blood, liver, and bladder pathogen of significant clinical concern. We show that the adaptor protein, SKAP2, is required for protection against K. pneumoniae (ATCC 43816) pulmonary infections. Skap2-/- mice had 100-fold higher bacterial burden when compared to wild-type and burden was controlled by SKAP2 expression in innate immune cells. Skap2-/- neutrophils and monocytes were present in infected lungs, and the neutrophils degranulated normally in response to K. pneumoniae infection in mice; however, K. pneumoniae-stimulated reactive oxygen species (ROS) production in vitro was abolished. K. pneumoniae-induced neutrophil ROS response required the activity of SFKs, Syk, Btk, PLCγ2, and PKC. The loss of SKAP2 significantly hindered the K. pneumoniae-induced phosphorylation of SFKs, Syk, and Pyk2 implicating SKAP2 as proximal to their activation in pathogen-signaling pathways. In conclusion, SKAP2-dependent signaling in neutrophils is essential for K. pneumoniae-activated ROS production and for promoting bacterial clearance during infection.

Klebsiella pneumoniae is a type of bacteria that can cause life-threatening infections – including pneumonia, blood stream infections, and urinary tract infections – in hospitalized patients. These infections can be difficult to treat because some K. pneumoniae are resistant to antibiotics. The bacteria are normally found in the human intestine, and they do not usually cause infections in healthy people. This implies that healthy people’s immune systems are better able to fend off K. pneumoniae infections; learning how could help scientists develop new ways to treat or prevent infections in hospitalized patients.

In healthy people, a type of immune cell called neutrophils are the first line of defense against bacterial infections. Several different proteins are needed to activate neutrophils, including a protein called SKAP2. But the role of this protein in fighting K. pneumoniae infections is not clear.

To find out what role SKAP2 plays in the defense against pneumonia caused by K. pneumoniae, Nguyen et al. compared infections in mice with and without the protein. Mice lacking SKAP2 in their white blood cells had more bacteria in their lungs than normal mice. The experiments showed that neutrophils from mice with SKAP2 produce a burst of chemicals called “reactive oxygen species”, which can kill bacteria. But neutrophils without the protein do not. Without SKAP2, several proteins that help produce reactive oxygen species do not work.

Understanding the role of SKAP2 in fighting infections may help scientists better understand the immune system. This could help clinicians to treat conditions that cause it to be hyperactive or ineffective. More studies are needed to determine if SKAP2 works the same way in human neutrophils and if it works against all types of K. pneumoniae. If it does, then scientists might be able use this information to develop therapies that help the immune system fight infections.

TNF and ROS Crosstalk in Inflammation

Tumor necrosis factor (TNF) is tremendously important for mammalian immunity and cellular homeostasis. The role of TNF as a master regulator in balancing cell survival, apoptosis and necroptosis has been extensively studied in various cell types and tissues. Although these findings have revealed much about the direct impact of TNF on the regulation of NF-κB and JNK, there is now rising interest in understanding the emerging function of TNF as a regulator of the generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS). In this review we summarize work aimed at defining the role of TNF in the control of ROS/RNS signaling that influences innate immune cells under both physiological and inflammatory conditions.

TNF receptor-associated factor 4 (TRAF4) is a novel binding partner of glycoprotein Ib and glycoprotein VI in human platelets

BACKGROUND

Reactive oxygen species generation is one consequence of ligand engagement of platelet glycoprotein (GP) receptors GPIb-IX-V and GPVI, which bind VWF/collagen and initiate thrombosis at arterial shear; however, the precise molecular mechanism coupling redox pathway activation to engagement of these receptors is unknown.

OBJECTIVE

The objective of this study was to identify novel binding partners for GPIb-IX-V and GPVI that could provide a potential link between redox pathways and early platelet signaling events.

METHODS AND RESULTS

Using protein array analysis and affinity-binding assays, we demonstrated that the orphan TNF receptor-associated factor (TRAF) family member, TRAF4, selectively binds cytoplasmic sequences of GPIbβ and GPVI. TRAF4, p47(phox) [of the NADPH oxidase (Nox2) enzyme complex] and other redox relevant signaling proteins such as Hic-5, co-immunoprecipitate with GPIb/GPVI from human platelet lysates whilst MBP-TRAF4 or MBP-p47(phox) fusion proteins specifically pull-down GPIb/GPVI. GPIb- or GPVI-selective agonists induce phosphorylation of the TRAF4-associated proteins, Hic-5 and Pyk2, with phosphorylation attenuated by Nox2 inhibition.

CONCLUSION

These results describe the first direct association of TRAF4 with a receptor, and identify a novel binding partner for GPIb-IX-V and GPVI, providing a potential link between these platelet receptors and downstream TRAF4/Nox2-dependent redox pathways.

Radiation-induced liver fibrosis is mitigated by gene therapy inhibiting transforming growth factor-β signaling in the rat

PURPOSE

We determined whether anti-transforming growth factor-β (TGF-β) intervention could halt the progression of established radiation-induced liver fibrosis (RILF).

METHODS AND MATERIALS

A replication-defective adenoviral vector expressing the extracellular portion of human TβRII and the Fc portion of immunoglobulin G fusion protein (AdTβRIIFc) was produced. The entire rat liver was exposed to 30 Gy irradiation to generate a RILF model (RILFM). Then, RILFM animals were treated with AdTβRIIFc (1 × 10(11) plaque-forming units [PFU] of TβRII), control virus (1 × 10(11) PFU of AdGFP), or saline. Delayed radiation liver injury was assessed by histology and immunohistochemistry. Chronic oxidative stress damage, hepatic stellate cell activation, and hepatocyte regeneration were also analyzed.

RESULTS

In rats infected with AdTβRIIFc, fibrosis was significantly improved compared with rats treated with AdGFP or saline, as assessed by histology, hydroxyproline content, and serum level of hyaluronic acid. Compared with AdGFP rats, AdTβRIIFc-treated rats exhibited decreased oxidative stress damage and hepatic stellate cell activation and preserved liver function.

CONCLUSIONS

Our results demonstrate that TGF-β plays a critical role in the progression of liver fibrosis and suggest that anti-TGF-β intervention is feasible and ameliorates established liver fibrosis. In addition, chronic oxidative stress may be involved in the progression of RILF.

Regulation of TNF-induced oxygen radical production in human neutrophils: role of delta-PKC

In human neutrophils, TNF-elicited O(2)(-) production requires adherence and integrin activation. How this cooperative signaling between TNFRs and integrins regulates O(2)(-) generation has yet to be fully elucidated. Previously, we identified delta-PKC as a critical early regulator of TNF signaling in adherent neutrophils. In this study, we demonstrate that inhibition of delta-PKC with a dominant-negative delta-PKC TAT peptide resulted in a significant delay in the onset time of TNF-elicited O(2)(-) generation but had no effect on Vmax, indicating an involvement of delta-PKC in the initiation of O(2)(-) production. In contrast, fMLP-elicited O(2)(-) production in adherent and nonadherent neutrophils was delta-PKC-independent, suggesting differential regulation of O(2)(-) production. An important step in activation of the NADPH oxidase is phosphorylation of the cytosolic p47phox component. In adherent neutrophils, TNF triggered a time-dependent association of delta-PKC with p47phox, which was associated with p47phox phosphorylation, indicating a role for delta-PKC in regulating O(2)(-) production at the level of p47phox. Activation of ERK and p38 MAPK is also required for TNF-elicited O(2)(-) generation. TNF-mediated ERK but not p38 MAPK recruitment to p47phox was delta-PKC-dependent. delta-PKC activity is controlled through serine/threonine phosphorylation, and phosphorylation of delta-PKC (Ser643) and delta-PKC (Thr505) was increased significantly by TNF in adherent cells via a PI3K-dependent process. Thus, signaling for TNF-elicited O(2)(-) generation is regulated by delta-PKC. Adherence-dependent cooperative signaling activates PI3K signaling, delta-PKC phosphorylation, and delta-PKC recruitment to p47phox. delta-PKC activates p47phox by serine phosphorylation or indirectly through control of ERK recruitment to p47phox.

Human neutrophils coordinate chemotaxis by differential activation of Rac1 and Rac2

Rac1 and Rac2, members of the small Rho GTPase family, play essential roles in coordinating directional migration and superoxide production during neutrophil responses to chemoattractants. Although earlier studies in Rac1 and Rac2 knockout mice have demonstrated unique roles for each Rac isoform in chemotaxis and NADPH oxidase activation, it is still unclear how human neutrophils use Rac1 and Rac2 to achieve their immunological responses to foreign agent stimulation. In the current study, we used TAT dominant-negative Rac1-T17N and Rac2-T17N fusion proteins to acutely alter the activity of Rac1 and Rac2 individually in human neutrophils. We demonstrate distinct activation kinetics and different roles for Rac1 and Rac2 in response to low vs high concentrations of fMLP. These observations were verified using neutrophils from mice in which Rac1 or Rac2 was genetically absent. Based on these results, we propose a model to explain how human neutrophils kill invading microbes while limiting oxidative damage to the adjacent surrounding healthy tissue through the differential activation of Rac1 and Rac2 in response to different concentrations of chemoattractant.

Review article: Leukocyte-endothelial dysregulation in systemic small vessel vasculitis

Aberrant interaction between the leukocyte and the endothelial cell (EC) results in the uncontrolled inflammation seen in systemic small vessel vasculitis. This review discusses our current understanding of this process and includes consideration of the role of adhesion molecules, proteases and the neutrophil respiratory burst. The effects of anti-neutrophil cytoplasm antibodies and anti-endothelial cell antibodies and their pathogenic roles are examined, and we look at experimental disease models. Specificity of disease-targetted endothelial beds and the role of circulating EC are discussed.

Dietary salt activates an endothelial proline-rich tyrosine kinase 2/c-Src/phosphatidylinositol 3-kinase complex to promote endothelial nitric oxide synthase phosphorylation

Although many laboratories have shown that dietary NaCl (salt) intake increases NO production in rodents and humans, the mechanism has not been uncovered. In the present study, pharmacological and dominant-negative strategies were used to show that feeding a formulated diet containing increased amounts of salt to young male Sprague-Dawley rats induced the formation of an endothelial cell-signaling complex that contained proline-rich tyrosine kinase 2, c-Src (also known as pp60(c-src)), and phosphatidylinositol 3-kinase. In the setting of a high-salt diet, proline-rich tyrosine kinase 2 served as the scaffold for c-Src-mediated phosphatidylinositol 3-kinase activation. Phosphatidylinositol 3-kinase was the upstream activator of protein kinase B (Akt), which was responsible for phosphorylation of the rat endothelial isoform of NO synthase at S1176 and thereby promoted the increase in NO production. The combined findings illustrated the crucial role for a proline-rich tyrosine kinase 2-signaling complex in the endothelial response to salt intake.

Transduction of proteins into intact neutrophils

Neutrophils and related phagocytic leukocytes are notoriously difficult to transfect, making the introduction of proteins into these cells for biological studies problematic. We describe here two methods that have been successfully used to introduce proteins into intact primary human neutrophils while maintaining normal functional responses. The first utilizes a lipid-based reagent that transports proteins into intact neutrophils. This method is quick, easy, and is capable of transducing greater than 90% of the neutrophils in the population being studied. The second method involves the addition of a sequence derived from the HIV TAT protein to the protein to be introduced into the neutrophil. This requires both molecular biology to generate the initial construct as well as special procedures for protein isolation and renaturation. However, it also results in highly effective functional protein delivery into human neutrophils.

Human mesenchymal stem cells inhibit neutrophil apoptosis: a model for neutrophil preservation in the bone marrow niche

Mesenchymal stem cells (MSC) establish close interactions with bone marrow sinusoids in a putative perivascular niche. These vessels contain a large storage pool of mature nonproliferating neutrophils. Here, we have investigated the effects of human bone marrow MSC on neutrophil survival and effector functions. MSC from healthy donors, at very low MSC:neutrophil ratios (up to 1:500), significantly inhibited apoptosis of resting and interleukin (IL)-8-activated neutrophils and dampened N-formyl-l-methionin-l-leucyl-l-phenylalanine (f-MLP)-induced respiratory burst. The antiapoptotic activity of MSC did not require cell-to-cell contact, as shown by transwell experiments. Antibody neutralization experiments demonstrated that the key MSC-derived soluble factor responsible for neutrophil protection from apoptosis was IL-6, which signaled by activating STAT-3 transcription factor. Furthermore, IL-6 expression was detected in MSC by real-time reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. Finally, recombinant IL-6 was found to protect neutrophils from apoptosis in a dose-dependent manner. MSC had no effect on neutrophil phagocytosis, expression of adhesion molecules, and chemotaxis in response to IL-8, f-MLP, or C5a. These results support the following conclusions: (a) in the bone marrow niche, MSC likely protect neutrophils of the storage pool from apoptosis, preserving their effector functions and preventing the excessive or inappropriate activation of the oxidative metabolism, and (b) a novel mechanism whereby the inflammatory potential of activated neutrophils is harnessed by inhibition of apoptosis and reactive oxygen species production without impairing phagocytosis and chemotaxis has been identified.

Signaling requirements for translocation of P-Rex1, a key Rac2 exchange factor involved in chemoattractant-stimulated human neutrophil function

PI 3,4,5-trisphosphate [PI(3,4,5)P3; PIP3]-dependent Rac exchanger 1 (P-Rex1) is a Rac-specific guanine nucleotide exchange factor abundant in neutrophils and myeloid cells. As a selective catalyst for Rac2 activation, P-Rex1 serves as an important regulator of human neutrophil NADPH oxidase activity and chemotaxis in response to a variety of extracellular stimuli. The exchange activity of P-Rex1 is synergistically activated by the binding of PIP3 and betagamma subunits of heterotrimeric G proteins in vitro, suggesting that the association of P-Rex1 with membranes is a prerequisite for cellular activation. However, the spatial regulation of endogenous P-Rex1 has not been well defined, particularly in human neutrophils activated through G protein-coupled receptors. Upon stimulation of neutrophil chemoattractant receptors, we observed that P-Rex1 translocated from cytoplasm to the leading edge of polarized cells in a G protein betagamma subunit- and PIP3-dependent manner, where it colocalized with F-actin and its substrate, Rac2. Redistribution of P-Rex1 to the leading edge was also dependent on tyrosine kinase activity and was modulated by cell adhesion. Furthermore, we observed that activation of cAMP-dependent protein kinase A (PKA), which phosphorylates and inactivates P-Rex1, inhibited its translocation. Our data indicate that endogenous P-Rex1 translocates to areas of Rac2 and cytoskeletal activation at the leading edge in response to chemoattractant stimuli in human neutrophils and that this translocation can be negatively modulated by activation of PKA and by cell adhesion.

Regulation of the phagocyte NADPH oxidase by Rac GTPase

Phagocytic leukocytes generate reactive oxygen species important for the killing of invading microorganisms. The source of these oxidants is the NADPH oxidase, a tightly controlled multicomponent enzyme made up of a membrane-associated catalytic moiety and cytosolic regulatory components that must assemble to form the active oxidase. The phagocyte NADPH oxidase was the first mammalian system shown to be directly regulated by a Rac GTPase. We review here our understanding of NADPH oxidase regulation by Rac, as well as the regulation of Rac itself, in phagocytic leukocytes. Rather than viewing Rac as a "cog" in the NADPH oxidase machinery, we argue for a view of Rac GTPases as critical "molecular switches" regulating the formation of ROS by phagocytic leukocytes under physiologic and pathologic conditions.

The effect of acute exercise on endothelial function following a high-fat meal

The transient impairment of endothelial function following a high-fat meal is well established. Brachial artery flow-mediated dilation (FMD) decreases between 2 and 6 h post ingestion. Whether this impairment can be reduced with acute aerobic exercise has not been investigated. The purpose of this study was to investigate if a single sustained aerobic exercise session can counteract the postprandial attenuation in brachial artery FMD associated with the ingestion of a high-fat meal. Eight apparently healthy adults (five men, three women), age 25.5 +/- 0.8 years, performed three treatment conditions in a counter-balanced design: (1) low-fat meal alone (LFM), (2) high-fat meal alone (HFM), and (3) one session of aerobic exercise presented 2 h after ingesting a high-fat meal (HFM-EX). The examination of brachial artery FMD was performed at baseline and 4 h following the ingestion of the meal for each treatment condition. A 3 x 2 (treatment x time) repeated measures ANOVA exhibited a significant interaction (P = 0.019). Preprandial FMDs were similar (P = 0.863) among all three treatment conditions. The FMDs following the LFM (7.18 +/- 1.31%) and HFM-EX (8.72 +/- 0.94%) were significantly higher (P = 0.001) than the FMD following the HFM (4.29 +/- 1.64%). FMD was significantly elevated above preprandial values following the HFM-EX (5.61 +/- 1.54 to 8.72 +/- 0.94%, P = 0.005) but was unchanged following the LFM (6.17 +/- 0.94 to 7.18 +/- 1.31%, P = 0.317) and the HFM (5.73 +/- 1.23 to 4.29 +/- 1.64%, P = 0.160). These findings suggest that a single aerobic exercise session cannot only counteract the postprandial endothelial dysfunction induced by the ingestion of a high-fat meal, but also increase brachial artery FMD in apparently healthy adults.

A comparison between active- and reactive-hyperaemia-induced brachial artery vasodilation

The measurement of brachial artery vasodilation in response to a hyperaemic stimulus has been used extensively to assess changes in endothelial function. However, whether or not similar changes occur in response to an active hyperaemic stimulus is unknown. The purpose of the present study was to compare brachial artery vasodilation in response to an active compared with a reactive hyperaemic stimulus following a known perturbation of endothelial function. Eight apparently healthy adults were assigned to four treatment conditions in a counter-balanced design: (i) low-fat meal with active hyperaemic stimulus (LFM-A), (ii) high-fat meal with active hyperaemic stimulus (HFM-A), (iii) low-fat meal with reactive hyperaemic stimulus (LFM-R), and (iv) high-fat meal with reactive hyperaemic stimulus (HFM-R). Meals were ingested at 08:00 hours on each treatment day. Brachial artery vasodilation was assessed via ultrasound 4 h after ingestion of each meal. The active hyperaemic stimulus was induced by 5 min of rhythmic handgrip exercise, whereas reactive hyperaemia was induced by 5 min of forearm occlusion. Brachial artery vasodilation was expressed as the percentage change in diameter from baseline to post-active/reactive hyperaemia. Using a 2x2 repeated measures ANOVA, a significant stimulusxmeal interaction (P=0.025) was found. Simple main effects revealed no difference (P=0.541) in brachial artery vasodilation between LFM-A (5.75+/-1.64%) and HFM-A (6.39+/-1.45%); however, a significant decrease (P=0.014) in brachial artery vasodilation was found in the HFM-R (4.29+/-1.64%) compared with the LFM-R (7.18+/-1.13%) treatment. In conclusion, the measurement of brachial artery vasodilation in response to active hyperaemia did not detect a change in endothelial function following a single perturbation meal, whereas reactive hyperaemia did.

Continuous assay of protein tyrosine phosphatases based on fluorescence resonance energy transfer

An assay method that continuously measures the protein tyrosine phosphatase (PTP)-catalyzed dephosphorylation reaction based on fluorescence resonance energy transfer (FRET) was developed as an improvement of our previously reported discontinuous version [M. Nishikata, K. Suzuki, Y. Yoshimura, Y. Deyama, A. Matsumoto, Biochem. J. 343 (1999) 385-391]. The assay uses oligopeptide substrates that contain (7-methoxycoumarin-4-yl)acetyl (Mca) group as a fluorescence donor and 2,4-dinitrophenyl (DNP) group as a fluorescence acceptor, in addition to a phosphotyrosine residue located between these two groups. In the assay, a PTP solution is added to a buffer solution containing a FRET substrate and chymotrypsin. The PTP-catalyzed dephosphorylation of the substrate and subsequent chymotryptic cleavage of the dephosphorylated substrate results in a disruption of FRET, thereby increasing Mca fluorescence. In this study, we used FRET substrates that are much more susceptible to chymotryptic cleavage after dephosphorylation than the substrate used in our discontinuous assay, thus enabling the continuous assay without significant PTP inactivation by chymotrypsin. The rate of fluorescence increase strictly reflected the rate of dephosphorylation at appropriate chymotrypsin concentrations. Since the continuous assay allows the measurement of initial rate of dephosphorylation reaction, kinetic parameters for the dephosphorylation reactions of FRET substrates by Yersinia, T-cell and LAR PTPs were determined. The continuous assay was compatible with the measurement of very low PTP activity in a crude enzyme preparation and was comparable in sensitivity to assays that use radiolabeled substrates.