Lipopolysaccharide (LPS)-induced Macrophage Activation and Signal Transduction in the Absence of Src-Family Kinases Hck, Fgr, and Lyn

Abstract

Lipopolysaccharide (LPS) stimulates immune responses by interacting with the membrane receptor CD14 to induce the generation of cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-1, and IL-6. The mechanism by which the LPS signal is transduced from the extracellular environment to the nuclear compartment is not well defined. Recently, an increasing amount of evidence suggests that protein tyrosine kinases especially the Src-family kinases Hck, Fgr, and Lyn, play important roles in LPS signaling. To directly address the physiological function of Hck, Fgr and Lyn in LPS signaling, a genetic approach has been used to generate null mutations of all three kinases in a single mouse strain. hck −/− fgr −/− lyn −/− mice are moderately healthy and fertile; macrophages cultured from these mice express normal levels of CD14 and no other Src-family kinases were detected. Although the total protein phosphotyrosine level is greatly reduced in macrophages derived from hck −/− fgr −/− lyn −/− mice, functional analyses indicate that both elicited peritoneal (PEMs) and bone marrow–derived macrophages (BMDMs) from triple mutant mice have no major defects in LPS-induced activation. Nitrite production and cytokine secretion (IL-1, IL-6, and TNF-α) are normal or even enhanced in hck −/− fgr −/− lyn −/− macrophages after LPS stimulation. The development of tumor cell cytotoxicity is normal in triple mutant BMDMs and only partially impaired in PEMs after LPS stimulation. Furthermore, the activation of the ERK1/2 and JNK kinases, as well as the transcription factor NF-κB, are the same in normal and mutant macrophages after LPS stimulation. The current study provides direct evidence that three Src-family kinases Hck, Fgr, and Lyn are not obligatory for LPS-initiated signal transduction.

Toll-Like receptor 4 mediates inflammatory signaling by bacterial lipopolysaccharide in human hepatic stellate cells

“…45 In macrophages, activated JNKs mediate the expression of cytokines such as TNF-␣, IL-1, and IL-6 46 and chemokines such as RANTES, 47 all of which often lead to inflammatory responses. We demonstrated that LPS is an effective inducer of JNK activation in activated human HSCs.…”

Deficiency of Src family kinases compromises the repopulating ability of hematopoietic stem cells

“…Mice lacking various members of hematopoietic-specific SFKs (Hck, Fgr, and Lyn) have been backcrossed into C57BL/6 strain (CD45.2 allele) for more than 20 generations [27,28]. Mice lacking the expression of different combinations of the three hematopoietic-specific Src kinases have been generated and used in these studies: Lyn −/− , Fgr −/− , Hck −/− , and Lyn/Fgr/Hck −/− (SFK −/− ).…”

Cyclic AMP Modulates the Functional Plasticity of Immature Dendritic Cells by Inhibiting Src-like Kinases through Protein Kinase A-mediated Signaling

“…In this context, it has been also shown that stimulation of human monocytes by LPS rapidly activates CD14-associated Lyn, and the treatment with herbimycin, a tyrosine kinase inhibitor, prevented the production of TNF-␣ (25). Data from the triple knockout hckϪ/Ϫ, fgrϪ/Ϫ, and lynϪ/Ϫ macrophages are contrasting; the absence of these kinases did not affect the response to LPS (26). However, even in this murine model, treatment with herbimycin was effective in preventing TNF-␣ release showing the involvement of an Src-like kinase other than Hck, Fgr, and Lyn in the LPS signaling pathway (26).…”

“…Data from the triple knockout hckϪ/Ϫ, fgrϪ/Ϫ, and lynϪ/Ϫ macrophages are contrasting; the absence of these kinases did not affect the response to LPS (26). However, even in this murine model, treatment with herbimycin was effective in preventing TNF-␣ release showing the involvement of an Src-like kinase other than Hck, Fgr, and Lyn in the LPS signaling pathway (26). Little is known on the role played by the Src-like kinases in the activation process of iDCs.…”