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| 2. |
- Alvarado-Kristensson, Maria, et al.
(författare)
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p38 Mitogen-activated protein kinase and phosphatidylinositol 3-kinase activities have opposite effects on human neutrophil apoptosis.
- 2002
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Ingår i: FASEB Journal. - : Wiley. - 1530-6860 .- 0892-6638. ; 16:1, s. 31-129
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Tidskriftsartikel (refereegranskat)abstract
- Neutrophil apoptosis is essential for resolution of inflammatory reactions. Here, we studied the role of two apoptosis/survival-associated protein kinases in this process. We discovered a previously undetected early and transient inhibition of the activity of p38 mitogen-activated protein kinase (p38 MAPK) during both spontaneous and Fas-induced apoptosis. Pharmacological inhibition of this enzyme augmented the activation of caspases and the apoptotic response, which suggests that the p38 MAPK signals survival in neutrophils. Our finding that caspase-3 activity was initiated during the transient inhibition of p38 MAPK suggests that apoptosis is initiated during this inhibition. Furthermore, such transient inhibition was counteracted by granulocyte-macrophage colony-stimulating factor, which elicits survival. We also found that neither this inhibition of p38 MAPK nor the spontaneous apoptotic response depended on Fas. Instead, the early inhibition of p38 MAPK concurred with a Fas-induced activation of phosphatidylinositol 3-kinase, inhibition of which reduced apoptosis. Thus, the Fas-induced augmentation of spontaneous apoptosis can be explained by its activation of phosphatidylinositol 3-kinase. We conclude that p38 MAPK activity represents a survival signal that is inactivated transiently during both spontaneous and Fas-induced apoptosis, whereas Fas-induced phosphatidylinositol 3-kinase activity is a proapoptotic signal in isolated human neutrophils.
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| 3. |
- Axelsson, Lena, et al.
(författare)
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Clustering of β2-integrins on human neutrophils activates dual signaling pathways to Ptdlns 3-kinase
- 2000
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Ingår i: Experimental Cell Research. - : Elsevier BV. - 0014-4827. ; 256:1, s. 257-263
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Tidskriftsartikel (refereegranskat)abstract
- The β2-integrins on leukocytes can serve as a signaling unit during cell adhesion and locomotion, and to further clarify this important property we investigated the possible mechanisms of β2-integrin-induced activation of PtdIns 3-kinase. It has previously been demonstrated that clustering of β2-integrins activates p21(ras) by a tyrosine kinase-dependent pathway, and here we show that active p21(ras) interacts with its downstream target, PtdIns 3-kinase. Engagement of β2-integrins also activates the tyrosine kinases p58(c-fgr) and p59/61(hck) and causes them to associate with the p85 subunit of PtdIns 3-kinase. These findings suggest a mechanism whereby p58(c- fgr) and p59/61(hck) are directly involved in the activation of PtdIns 3- kinase. No coupling between p58(c-fgr) and p59/61(hck) could be detected; hence these kinases probably trigger independent but parallel signals to PtdIns 3-kinase. The effect of β2-integrin clustering on PtdIns 3-kinase activity was monitored as the activation of protein kinase B (PKB). Stimulation of PKB by β2-integrins was abolished by genistein and wortmannin but not by using methyl transferase inhibitors to abrogate the influence of p21(ras)-related proteins. Thus, even if PtdIns 3-kinase is not activated by p21(ras), it can maintain full enzyme activity due to the mentioned interaction with p58(c-fgr) or p59/61(hck). These tyrosine kinases apparently activate similar pathways that operate in parallel and therefore have the potential to substitute for each other in mediating adhesion and regulating cell locomotion. (C) 2000 Academic Press.
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| 5. |
- Blomgran, Robert, et al.
(författare)
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Uropathogenic Escherichia coli triggers oxygen-dependent apoptosis in human neutrophils through the cooperative effect of type 1 fimbriae and lipopolysaccharide
- 2004
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Ingår i: Infection and Immunity. - 0019-9567 .- 1098-5522. ; 72:8, s. 4570-4578
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Tidskriftsartikel (refereegranskat)abstract
- Type 1 fimbriae are the most commonly expressed virulence factor on uropathogenic Escherichia coli. In addition to promoting avid bacterial adherence to the uroepithelium and enabling colonization, type 1 fimbriae recruit neutrophils to the urinary tract as an early inflammatory response. Using clinical isolates of type 1 fimbriated E. coli and an isogenic type 1 fimbria-negative mutant (CN1016) lacking the FimH adhesin, we investigated if these strains could modulate apoptosis in human neutrophils. We found that E. coli expressing type 1 fimbriae interacted with neutrophils in a mannose- and lipopolysaccharide (LPS)-dependent manner, leading to apoptosis which was triggered by the intracellular generation of reactive oxygen species. This induced neutrophil apoptosis was abolished by blocking FimH-mediated attachment, by inhibiting NADPH oxidase activation, or by neutralizing LPS. In contrast, CN1016, which did not adhere to or activate the respiratory burst of neutrophils, delayed the spontaneous apoptosis in an LPS-dependent manner. This delayed apoptosis could be mimicked by adding purified LPS and was also observed by using fimbriated bacteria in the presence of D-mannose. These results suggest that LPS is required for E. coli to exert both pro- and antiapoptotic effects on neutrophils and that the difference in LPS presentation (i.e., with or without fimbriae) determines the outcome. The present study showed that there is a fine-tuned balance between type 1 fimbria-induced and LPS-mediated delay of apoptosis in human neutrophils, in which altered fimbrial expression on uropathogenic E. coli determines the neutrophil survival and the subsequent inflammation during urinary tract infections.
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| 6. |
- Forsberg, Maria, 1973-, et al.
(författare)
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Activation of Rac2 and Cdc42 on Fc and complement receptor ligation in human neutrophils
- 2003
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Ingår i: Journal of Leukocyte Biology. - : Oxford University Press (OUP). - 0741-5400 .- 1938-3673. ; 74:4, s. 611-619
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Tidskriftsartikel (refereegranskat)abstract
- Phagocytosis is a complex process engaging a concerted action of signal-transduction cascades that leads to ingestion, subsequent phagolysosome fusion, and oxidative activation. We have previously shown that in human neutrophils, C3bi-mediated phagocytosis elicits a significant oxidative response, suggesting that activation of the small GTPase Rac is involved in this process. This is contradictory to macrophages, where only Fc receptor for immunoglobulin G (FcγR)-mediated activation is Rac-dependent. The present study shows that engagement of the complement receptor 3 (CR3) and FcγR and CR3- and FcγR-mediated phagocytosis activates Rac, as well as Cdc42. Furthermore, following receptor-engagement of the CR3 or FcγRs, a downstream target of these small GTPases, p21-activated kinase, becomes phosphorylated, and Rac2 is translocated to the membrane fraction. Using the methyltransferase inhibitors N-acetyl-S-farnesyl-L-cysteine and N-acetyl-S-geranylgeranyl-L-cysteine, we found that the phagocytic uptake of bacteria was not Rac2- or Cdc42-dependent, whereas the oxidative activation was decreased. In conclusion, our results indicate that in neutrophils, Rac2 and Cdc42 are involved in FcR- and CR3-induced activation and for properly functioning signal transduction involved in the generation of oxygen radicals.
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| 7. |
- Forsberg, Maria, et al.
(författare)
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Differential effects of invasion by and phagocytosis of Salmonella typhimurium on apoptosis in human macrophages : potential role of Rho–GTPases and Akt
- 2003
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Ingår i: Journal of Leukocyte Biology. - : Oxford University Press (OUP). - 0741-5400 .- 1938-3673. ; 74:4, s. 620-629
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Tidskriftsartikel (refereegranskat)abstract
- In addition to direct activation of caspase-1 and induction of apoptosis by SipB, invasive Salmonella stimulates multiple signaling pathways that are key regulators of host cell survival. Nevertheless, little is known about the relative contributions of these pathways to Salmonella-mediated death of macrophages. We studied human monocytic U937 cells and found that apoptosis was induced by invading wild-type Salmonella typhimurium but not by phagocytosed, serum-opsonized, noninvasive Salmonella mutants. Pretreating U937 cells with inhibitors of tyrosine kinases or phosphatidylinositol-3 kinase (PI-3K) completely blocked phagocytosis of opsonized Salmonella mutants but did not affect invasion by wild-type Salmonella or the apoptosis caused by invasion. However, pretreatment with GGTI-298, a geranylgeranyltransferase-1 inhibitor that prevents prenylation of Cdc42 and Rac1, suppressed Salmonella-induced apoptosis by ∼70%. Transduction of Tat fusion constructs containing dominant-negative Cdc42 or Rac1 significantly inhibited Salmonella-induced cell death, indicating that the cytotoxicity of Salmonella requires activation of Cdc42 and Rac. In contrast to phagocytosis of opsonized bacteria, invasion by S. typhimurium stimulated Cdc42 and Rac1, regardless of the activities of tyrosine- or PI-3K. Moreover, Salmonella infection activated Akt protein in a tyrosine-kinase or PI-3K-dependent manner, and a reduced expression of Akt by antisense transfection rendered the cells more sensitive to apoptosis induced by opsonized Salmonella. These results indicate that direct activation of Cdc42 and Rac1 by invasive Salmonella is a prerequisite of Salmonella-mediated death of U937 cells, whereas the simultaneous activation of Akt by tyrosine kinase and PI-3K during receptor-mediated phagocytosis protects cells from apoptosis.
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| 8. |
- Forsberg, Maria, 1973-, et al.
(författare)
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Tumour necrosis factor-α potentiates CR3-induced respiratory burst by activating p38 MAP kinase in human neutrophils
- 2001
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Ingår i: Immunology. - : Wiley. - 0019-2805 .- 1365-2567. ; 103:4, s. 465-472
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Tidskriftsartikel (refereegranskat)abstract
- CR3 and FcγRs are the main receptors involved in the phagocytic process leading to engulfment and killing of microbes by production of reactive oxygen intermediates (ROI) and degranulation. Various inflammatory mediators, such as tumour necrosis factor-α (TNF-α) and lipopolysaccharide (LPS), are known to prime neutrophils leading to increased bactericidal responses, but the underlying mechanism of priming has only been partially elucidated. The purpose of this study was to investigate how TNF-α primes neutrophils for subsequent stimuli via either CR3 or FcγR. The receptors were specifically activated with pansorbins (protein-A-positive Staphylococcus aureus) coated with anti-CR3, anti-FcγRIIa, or anti-FcγRIIIb monoclonal antibody. Activation of neutrophils with these particles resulted in ROI production as measured by chemiluminescence. Anti-CR3 pansorbins induced the most prominent ROI production in neutrophils. TNF-α potentiated the CR3-mediated respiratory burst but had little effect on that mediated by FcγRs. The priming effect of TNF-α on CR3-mediated ROI production is associated with an increased activation of p38 MAPK as well as tyrosine phosphorylation of p72syk. Pretreatment of neutrophils with the inhibitors for p38 MAPK and p72syk markedly suppressed the respiratory burst induced by CR3. Furthermore, TNF-α induced about a three-fold increase in the expression of CR3 in neutrophils, an effect which is blocked by the p38 MAPK inhibitor. Taken together, these results showed that TNF-α potentiates the CR3-mediated respiratory burst in neutrophils not only by triggering a p38 MAPK-dependent up-regulation of CD11b/CD18 but also by modulating the signalling pathways.
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| 9. |
- Perskvist, Nasrin, et al.
(författare)
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Activation of Human Neutrophils by Mycobacterium tuberculosis H37Ra Involves Phospholipase Cγ2, Shc Adapter Protein, and p38 Mitogen-Activated Protein Kinase
- 2000
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Ingår i: Journal of Immunology. - 0022-1767 .- 1550-6606. ; 164:2, s. 959-965
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have shown that human neutrophils play a significant protective role in mycobacteria infection. When encountered with mycobacteria, neutrophils exhibit the typical early bactericidal responses including phagocytosis and generation of reactive oxygen intermediates (ROI), but the underlying mechanisms are largely unknown. The present study shows that stimulation of neutrophils with an attenuated strain of Mycobacterium tuberculosis H37Ra (Mtb) led to a tyrosine kinase-dependent ROI production in these cells. Stimulation with Mtb induces a rapid and transient tyrosine phosphorylation of several proteins, one of which was identified as phospholipase Cγ2 (PLCγ2). Several tyrosine-phosphorylated proteins were associated with the PLCγ2 precipitates from Mtb-stimulated neutrophils, of which pp46 was characterized as the Shc adapter protein. A role for PLCγ2-Shc association in the generation of ROI is supported by the observations that stimulation with Mtb causes the activation of p38 mitogen-activated protein kinase (MAPK), a downstream target of the Shc/Ras signaling cascade, and that the effect of genistein on ROI production coincided with its ability to inhibit both PLCγ2-Shc association and p38 MAPK activation. Moreover, pretreatment of neutrophils with a PLC inhibitor markedly suppresses the Mtb-stimulated ROI production as well as p38 MAPK activation in these cells. Taken together, these results indicate that stimulation of neutrophils with Mtb triggers the tyrosine phosphorylation of PLCγ2 and its association with Shc, and that such association is critical for the Mtb-stimulated ROI production through activating p38 MAPK.
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| 10. |
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