Previously, we have demonstrated the induction of Src in lipopolysaccharide (LPS)-stimulated macrophages. In this study, we observed that pharmacological blockade or knockout of inducible nitric-oxide synthase (iNOS) reduced LPS-mediated Src induction and macrophage migration. Either SNAP (a NO donor) or 8-Br-cGMP (a cGMP analogue) could rescue these defects in iNOS-null macrophages, which indicated the participation of NO/cGMP in LPS-elicited Src expression and mobilization. In addition, Src family kinase (SFK)-specific inhibitor, PP2, inhibited SNAP-and 8-Br-cGMP-evoked motility implicating the involvement of SFKs downstream of NO/cGMP. Analysis of the expression of SFKs indicated LPS dramatically induced Src, which could be attributable to the increased level of the src transcript. Attenuation of Src by src-specific siRNA reduced LPS-and SNAP-evoked mobilization in Raw264.7 macrophages, and reintroduction of avian Src could rescue their motility. Furthermore, LPS-mediated Src induction led to increased FAK Pi-Tyr-397 and Pi-Tyr-861, which was also iNOSdependent. With these findings, we concluded that iNOS was important for LPS-mediated macrophage locomotion and Src was a critical player in this process.Macrophages are important participants in innate immunity. Due to their ability to eliminate opsonized pathogens through a spectrum of surface receptors and antigen presentation to cells of the adaptive immunity, macrophage recruitment to sites of infection is an important physiological process in host defenses. Disturbed regulation of this event results in a variety of diseases such as sepsis, atherosclerosis, and autoimmune disorders.Nitric oxide (NO), 3 a unique diffusible messenger molecule, is produced via the oxidation of L-arginine by enzymes known as nitric-oxide synthases (NOSs) (1). Three distinct isoforms of the enzyme have been identified and characterized. Whereas Ca ϩ2 /calmodulin can regulate the activity of neuronal (n) and endothelial (e) NOS that are constitutively expressed, the activity of inducible (i) NOS is independent of Ca ϩ2 /calmodulin and only induced by bacterial products as well as inflammatory cytokines. A low level of constitutively produced NO is a crucial mediator for a spectrum of physiological functions such as regulation of neurotransmission, vasodilation, smooth muscle relaxation, and inhibition of platelet aggregation. In contrast, a high level of NO generated by macrophages and other effector cells under inducible conditions mediates host defense, including antibacterial and antitumor functions (2, 3). However, it is also well documented that some pathological processes such as inflammation and tumor can be induced by sustained, chronically produced NO (4, 5). As a main target of NO, sGC is a cytosolic, heme-containing heterodimer of ␣ and  subunits (6). When NO binds to the sGC heme prosthetic group, it activates the enzyme to convert guanosine 5Ј-triphosphate to cGMP, an intracellular second messenger (7). Accumulation of cGMP results in transmission of NO signals to t...
Toll‐like receptors (TLRs) are crucial in macrophage phagocytosis, which is pivotal in host innate immune response. However, the detailed mechanism is not fully defined. Here, we demonstrated the induction of Src and Eps8 in LPS‐treated macrophages was TLR4‐ and MyD88‐dependent, and their attenuation reduced LPS‐promoted phagocytosis. Confocal microscopy indicated the colocalization of Eps8 and TLR4 in the cytosol and at the phagosome. Consistently, both Eps8 and TLR4 were present in the same immunocomplex regardless of LPS stimulation. Inhibition of this complex formation by eps8 siRNA or overexpression of PH‐truncated Eps8 (i.e. 261‐p97Eps8) decreased LPS‐induced TLR4‐MyD88 interaction and the following activation of Src, FAK, and p38 MAPK. Importantly, attenuation of Eps8 impaired bacterium killing ability of macrophages. Thus, Eps8 is a key regulator of the LPS‐stimulated TLR4‐MyD88 interaction and contributes to macrophage phagocytosis. This work was supported by the National Science Council (NSC100‐2325‐B‐006‐011‐)
Previously, we demonstrated that iNOS/Src/FAK axis was a general mechanism of macrophage motility in response to various pathogen‐associated molecular patterns (PAMPs) and Eps8 participated in TLR4‐mediated signal transduction leading to enhanced phagocytosis and bacterial killing effect. However, the role of Eps8, an Src‐interacting protein, in PAMP‐mediated macrophage locomotion is still unclear. Here we observed that the expression of Eps8 was PAMP‐inducible, and the induction was iNOS/Src‐dependent. Attenuation of Eps8 simultaneously impaired Src activity and suppressed macrophage mobility. Remarkably, ectopic Eps8 could partly restore the reduced motility and Src activity in Src‐attenuated macrophages exposed to various PAMPs. Together, our findings indicated that Eps8 not only modulated TLR4‐mediated signal transduction but also participated in Src‐mediated cell migration in TLRs‐stimualted macrophages.
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