LIPOPOLYSACCHARIDE (LPS)-INDUCED MACROPHAGE ACTIVATION AND SIGNAL-TRANSDUCTION IN THE ABSENCE OF SRC-FAMILY KINASES HCK, FGR, AND LYN

Lipopolysaccharide (LPS) stimulates immune responses by interacting wi th the membrane receptor CD14 to induce the generation of cytokines su ch as tumor necrosis factor (TNF)-alpha, interleukin (IL)-1, and IL-6. The mechanism by which the LPS signal is transduced from the extracel lular environment to the nuclear compartment is not well defined. Rece ntly, an increasing amount of evidence suggests that protein tyrosine kinases especially the Src-family kinases Hck, Fgr, and Lyn, play impo rtant roles in LPS signaling. To directly address the physiological fu nction of Hck, Fgr and Lyn in LPS signaling, a genetic approach has be en used to generate null mutations of all three kinases in a single mo use strain. hck(-/-)fgr(-/-)lyn(-/-) mice are moderately healthy and f ertile; 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 deriv ed from hck(-/-)fgr(-/-)lyn(-/-) mice, functional analyses indicate th at 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-alpha) are normal or even enhanced in hck(-/-)fgr(-/-)lyn(-/-) ma crophages after LPS stimulation. The development of tumor cell cytotox icity 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-kappa B, are t he same in normal and mutant macrophages after LPS stimulation. The cu rrent study provides direct evidence that three Src-family kinases Hck , Fgr, and Lyn are not obligatory for LPS-initiated signal transductio n.