Stimulation of histamine release from human basophils by human platelet factor 4.

Signal transduction mechanisms associated with neutrophil activation by platelet factor 4 (PF4; CXCL4) are as yet poorly characterized. In a recent report, we showed that PF4-induced neutrophil functions (such as adhesion and secondary granule exocytosis) involve the activation of Src-kinases. By analyzing intracellular signals leading to adherence, we here demonstrate by several lines of evidence that in addition to Src-kinases, PF4 signaling involves the monomeric GTPase Ras, the tyrosine kinase Syk, and the MAP kinase JNK. Furthermore, on stimulation, GTPases Rac2 and RhoA were activated, and each was translocated to a different membrane compartment. As shown by inhibitor studies, Rac2 and JNK are located downstream of Syk and Ras. Most intriguingly, the latter 2 elements appear to control the activity of Rac2 and JNK independently of each other at different phases of the activation process. Although a first phase of Rac2 and JNK activation of up to 5 minutes is initiated by Ras, the second phase (5-30 minutes) depends predominantly on the activity of Syk. In summary, we describe that coordinated activity of Syk, Ras, and JNK mediates neutrophil adhesion to endothelial cells and that PF4 induces sequential activation of these elements. ( IntroductionPlatelet factor 4 (PF4; CXCL4) belongs to the family of CXC chemokines and shares 30% to 60% sequence identity and typical structural properties with other CXC chemokines, including the neutrophil-activating peptide-2 (NAP-2; CXCL7), interleukin-8 (IL-8; CXCL8), and interferon (IFN)-inducible protein 10 (IP-10; CXCL10). 1,2 However, with regard to its receptors, signal transduction, and biologic functions, the role of PF4 within the family of chemokines is exceptional. Unlike other chemokines, which affect only a limited set of target cells, PF4 was reported to be active on different cell types including basophils, T cells, NK cells, and monocytes. [3][4][5][6][7] In addition, PF4 supports the survival of hematopoietic stem cells and of progenitor cells, 8 and it inhibits endothelial cell proliferation and angiogenesis in vitro. 9-13 Recently, we described that PF4, in the absence of further costimuli, induces the differentiation of monocytes into HLA-DR-negative macrophages; in combination with IL-4, a specific type of antigen-presenting cell (APC) is developed. 6,14 In neutrophils, highly purified PF4 does not induce typical chemokine responses, such as chemotaxis, superoxide anion generation, or degranulation. 15 However, PF4 stimulates neutrophils to undergo extremely firm adhesion to unstimulated endothelial cells. 16 In the presence of an appropriate costimulus, such as the proinflammatory cytokine TNF, PF4 induces the exocytosis of secondary granule contents. 15,16 Although chemokines typically bind to 7-transmembrane domain G protein-coupled receptors, binding sites for PF4 are less well defined. In a recent report, Lasagni et al 11 described an alternatively spliced variant of CXCR3, also referred to as CXCR3-B, as a functional receptor for PF4 on endoth...

Section: Introductionmentioning

confidence: 99%

Neutrophil adhesion to endothelial cells induced by platelet factor 4 requires sequential activation of Ras, Syk, and JNK MAP kinases

Kasper

Brandt

Ernst

et al. 2006

“…Unlike other members of this group, which are active on a rather limited set of cell populations, PF-4 has been reported to affect a wide range of different cell types including basophils, eosinophils, endothelial cells, and fibroblasts. [8][9][10] Moreover, we recently could show that PF-4 is also active on human monocytes, preventing these cells from undergoing spontaneous apoptosis and inducing their differentiation into a certain subtype of macrophages. 11 However, PF-4 appears to be involved not only in the regulation of long-term biologic responses but can also mediate fast activation of neutrophils, a cell type that stands in the very first line of host defense.…”

mentioning

confidence: 97%

Platelet factor 4 (PF-4)–induced neutrophil adhesion is controlled by src-kinases, whereas PF-4–mediated exocytosis requires the additional activation of p38 MAP kinase and phosphatidylinositol 3-kinase

Kasper

Brandt

Bulfone–Paus∥

et al. 2004

IntroductionPlatelet factor 4 (PF-4; CXCL4), a CXC chemokine synthesized by megakaryocytes and stored in platelet ␣ granules as a noncovalent tetramer, becomes released in high concentrations on platelet activation. 1,2 PF-4 shares about 30% to 60% amino acid identity with other members of the CXC chemokine family, such as neutrophil-activating peptide 2 (NAP-2; CXCL7), interleukin 8 (IL-8; CXCL8), or interferon ␥-inducible protein 10 (IP-10; CXCL10). According to recent literature, CXC chemokines belong to 2 structurally different groups, depending on the presence or absence of a conserved tripeptide motif (Glu-Leu-Arg; ELR) within their N-terminus. The ELR motif has been demonstrated to be essential for the interaction of CXC chemokines with receptors CXCR1 and CXCR2 on neutrophils, 3 resulting in a rapid induction of cell functions such as chemotaxis, calcium mobilization, and degranulation (for reviews, see Rollins 4 and Baggiolini et al 5 ). However, CXC chemokines lacking the ELR motif fail to bind to CXCR1 and CXCR2 but instead interact with other 7-transmembrane-spanning G protein-coupled receptors expressed on different cell types (for reviews, see Baggiolini et al, 5 Zlotnik et al, 6 and Murdoch and Finn 7 ).With regard to its functional roles as well as to its receptor usage PF-4 appears to be an exception to the family of CXC chemokines. Unlike other members of this group, which are active on a rather limited set of cell populations, PF-4 has been reported to affect a wide range of different cell types including basophils, eosinophils, endothelial cells, and fibroblasts. [8][9][10] Moreover, we recently could show that PF-4 is also active on human monocytes, preventing these cells from undergoing spontaneous apoptosis and inducing their differentiation into a certain subtype of macrophages. 11 However, PF-4 appears to be involved not only in the regulation of long-term biologic responses but can also mediate fast activation of neutrophils, a cell type that stands in the very first line of host defense. In a recent report we have shown that with regard to neutrophils highly purified PF-4 lacks several biologic activities that are typical for chemokines, such as chemotaxis, calcium mobilization, or degranulation, on these cells. 12 Instead, a more specialized role for the chemokine was indicated by its requirement for a costimulus. In the presence of tumor necrosis factor (TNF), PF-4 stimulates neutrophils to undergo exocytosis of secondary granule contents or tight adhesion to different surfaces. 12 Interestingly, PF-4 stimulates neither release of primary granule contents nor tertiary granules or secretory vesicles. 12,13 So far, the only known function on neutrophils induced by PF-4 alone is their firm adhesion to endothelial cells. 13 Investigating PF-4-binding sites on neutrophils we could demonstrate that PF-4-induced functions were not elicited by binding to IL-8 receptors or another 7-transmembrane domain molecule, but by interaction with an integral chondroitin sulfate proteoglycan. 14,15 Neut...

“…21 On activation thrombocytes secrete proinflammatory cytokines and chemokines (eg, platelet factor 4, RAN-TES) and anti-inflammatory mediators (eg, transforming growth factor-␤). [22][23][24][25][26] In this work, we show for the first time that human platelets express receptors for the ER-resident heat shock protein Gp96. We investigate in detail the binding of Gp96 to the surfaces of human platelets and the consequences thereof concerning platelet function.…”

Section: Introductionmentioning

confidence: 70%

Human platelets express heat shock protein receptors and regulate dendritic cell maturation

Hilf

Singh‐Jasuja

Schwarzmaier

et al. 2002

Immunizations using the endoplasmic reticulum-resident heat shock protein Gp96 induce specific immune responses. Specificity is based on the major histocompatibility complex class I-restricted crosspresentation of Gp96-associated peptides derived from endogenous proteins. Initiation of the immune response depends on the ability of Gp96 to induce the production of proinflammatory cytokines by macrophages and dendritic cells (DCs) and of their maturation in a fashion presumably independent of associated peptide. Both events are mediated by Gp96 receptors on antigen-presenting cells. It is known that Gp96 is released from cells at necrosis induced, for example, by virus infection. Although this event supports the efficient induction of immune responses, it might also interfere with processes that are susceptible to chronic inflammation, such as wound healing after tissue damage. Therefore, Gp96-mediated stimulation of the immune system requires tight regulation. Here we show that human thrombocytes specifically interact with Gp96 and that binding of Gp96 to platelets is enhanced more than 10-fold on activation by thrombin. Gp96 interferes with neither thrombin-induced platelet activation nor platelet aggregation. However, the presence of platelets during Gp96-mediated DC activation reduces the secretion of proinflammatory cytokines and the activation of DCs. This effect is independent of soluble platelet factors and cell-to-cell contact between DCs and thrombocytes. Thus, we provide evidence for a regulatory mechanism that neutralizes Gp96 molecules systemically, especially in the blood. This effect might be of significance in wounds in which chronic inflammation and immune responses against autoantigens have to be prevented. IntroductionThe endoplasmic reticulum (ER)-resident heat shock protein (HSP) Gp96 plays multiple roles in mammalian organisms. As a chaperone, it assists protein folding and prevents aggregation of partially unfolded proteins in the ER. 1 In this key compartment of the major histocompatibility (MHC) class I presentation pathway, Gp96 is also one of the major peptide-binding proteins, and it associates with a peptide pool representative for the protein content of the cell. 2,3 Gp96 is released from cells after tissue damage caused by severe injury and resulting from necrotic cell death induced by freeze-thaw cycles 4 or virus infection. 5 Its presence in the extracellular space reveals surprising immunostimulatory properties: immunization with Gp96 preparations from tumor cells has been shown to elicit protective and therapeutic immune responses against the tumor from which the HSP had been purified. 6,7 The specificity of this immune response is attributed to tumor-derived peptides associated with Gp96. 6 After receptor-mediated endocytosis of Gp96 by professional antigen-presenting cells (APCs), 8 these peptides are presented on MHC class I molecules. 9 This process is usually referred to as cross-presentation, 10,11 and it is one of the key events during the priming of naive T cells. 12 In ...