Src family kinases mediate neutrophil adhesion to adherent platelets

Induction of an inflammatory monocyte phenotype by activated platelets is implicated in the pathogenesis of inflammatory diseases, including atherosclerosis. In this study, we investigated the early signaling events associated with this platelet-induced inflammatory phenotype. We report that coculture of human monocytes with activated platelets induces phosphorylation of Akt, together with rapid mobilization of intracellular Ca2+, and show that these signaling events can be uncoupled from monocyte binding to activated platelets. Specifically, Ab-inhibition studies and incubation of monocytes with activated platelet supernatant highlighted a role for secreted product(s) of activated platelets. We also identified a role for pertussis toxin–sensitive G protein–coupled receptors and excluded key candidates platelet-activating factor receptor and CCR5. Our results suggest that inhibition of monocyte–platelet interactions via PSGL-1 or P-selectin is not sufficient to prevent platelet-mediated monocyte activation in an inflammatory context. These findings have important implications for the development of therapeutics to treat diseases in which platelet–monocyte complexes are implicated in pathogenesis.

Section: The Uncoupling Of Monocyte-platelet Interactions From the Inmentioning

confidence: 99%

The Uncoupling of Monocyte–Platelet Interactions from the Induction of Proinflammatory Signaling in Monocytes

Stephen

Emerson

Fox

et al. 2013

“…In Jurkat T cells, crosslinking of LFA-1 results in formation of an actin cloud that is dependent on the presence of the Src kinase Lyn (60). Downstream of Syk, phosphorylation of FAK and Pyk was found to be impaired upon integrin engagement in Syk-deficient neutrophils and macrophages (61). Also, SLP76 (62), ADAP (63), and its homolog PRAM-1 (64) were identified to be essential for intact outside-in signaling events in neutrophils, suggesting a dual role for SLP76 and ADAP for outside-in and inside-out signaling.…”

Section: Leukocyte Recruitmentmentioning

confidence: 99%

Integrin Regulation during Leukocyte Recruitment

Herter

Zarbock

2013

168

138

Integrins are recognized as vital players in leukocyte recruitment. Integrin malfunction causes severe disease patterns characterized by the inability to fight pathogens. Although inflammatory reactions are beneficial and necessary for host defense, these reactions have to be controlled to prevent tissue destruction and harmful sequelae. In this review, we discuss the different signaling pathways leading to the change of integrin adhesiveness in neutrophils, monocytes, and lymphocytes. We thereby focus on the importance of integrin activation for the different steps of the leukocyte recruitment cascade, including rolling, adhesion, postadhesion strengthening, intravascular crawling, and transmigration, as each step necessitates the proper functioning of a distinct set of integrin molecules that has to be activated specifically. Additionally, we discuss endogenous mechanisms that balance and counteract integrin activation and limit leukocyte recruitment at the site of inflammation. Further insight into these complex mechanisms may provide new approaches for developing new anti-inflammatory therapies.

“…Dantrolene inhibits Pyk2 by blocking ryanodine receptor-mediated intracellular calcium release, which is required for Pyk2 activation (44 -46). Another agent often used as a Pyk2 inhibitor is AG17, which blocks calcium releaseactivated calcium (CRAC) channel-mediated intracellular calcium (47)(48)(49). As shown in Fig.…”

Section: Il-1␤ Induction By Gp120 Involves Focal Adhesion-related Kinmentioning

confidence: 99%

Signaling Mechanism of HIV-1 gp120 and Virion-Induced IL-1β Release in Primary Human Macrophages

Cheung

Ravyn

Wang

et al. 2008

HIV-1 envelope glycoprotein gp120 induces, independently of infection, the release of proinflammatory cytokines, including IL-1β from macrophages, that are implicated in the pathogenesis of HIV-associated dementia. However, the signal transduction pathways involved have not been fully defined. Previously, our laboratory reported that soluble gp120 activates multiple protein kinases in primary human monocyte-derived macrophages, including the Src family kinase Lyn, PI3K, and the focal adhesion-related proline-rich tyrosine kinase Pyk2. In this study we showed that gp120 induces IL-1β release from macrophages in a time- and concentration-dependent manner through binding to the chemokine receptor CCR5 and coupling to Giα protein. Using pharmacological inhibitors and small interfering RNA gene knockdown, we demonstrated that concomitant activation of Lyn, Pyk2, and class IA PI3K are required for gp120-induced IL-1β production. By coimmunoprecipitation and immunofluorescence confocal microscopy, we showed that CCR5 activation by gp120 triggered the assembly of a signaling complex involving endogenous Lyn, PI3K, and Pyk2 and is associated with PI3K and Pyk2 translocation from the cytoplasm to the membrane where they colocalized with Lyn. Finally, we demonstrated that virion-associated gp120 induced similar response, as structurally intact whole virions also triggered IL-1β release and re-localization of PI3K and Pyk2. This study identifies a novel signaling mechanism for HIV-1-induced IL-1β production by primary human macrophages that may be involved in the neuropathogenesis of HIV-associated dementia.