RESUMO
The inhibitory signaling of natural killer (NK) cells is crucial in the regulation of innate immune responses. Here we show that the association of KIR2DL1, an inhibitory receptor of NK cells, with beta-arrestin 2 mediated recruitment of the tyrosine phosphatases SHP-1 and SHP-2 to KIR2DL1 and facilitated 'downstream' inhibitory signaling. Consequently, the cytotoxicity of NK cells was higher in beta-arrestin 2-deficient mice but was inhibited in beta-arrestin 2-transgenic mice. Moreover, beta-arrestin 2-deficient mice were less susceptible than wild-type mice to mouse cytomegalovirus infection, an effect that was abolished by depletion of NK cells. Our findings identify a previously unknown mechanism by which the inhibitory signaling in NK cells is regulated.
Assuntos
Arrestinas/farmacologia , Células Matadoras Naturais/efeitos dos fármacos , Células Matadoras Naturais/imunologia , Receptores Imunológicos/imunologia , Transdução de Sinais/imunologia , Animais , Células Cultivadas , Peptídeos e Proteínas de Sinalização Intracelular , Camundongos , Receptores Imunológicos/química , Receptores Imunológicos/genética , Receptores Imunológicos/metabolismo , beta-Arrestina 2 , beta-ArrestinasRESUMO
Mitogen-activated protein (MAP) kinases play a critical role in innate immune responses to microbial infection through eliciting the biosynthesis of proinflammatory cytokines. MAP phosphatases (MKP)-1 is an archetypical member of the dual-specificity phosphatase family that deactivates MAP kinases. Induction of MKP-1 has been implicated in attenuating the lipopolysaccharide (LPS) and Peptidoglycan (PGN) responses, but how the expression of the MKP-1 is regulated is still not fully understood. Here, we show that inhibition of p38 MAP kinase by specific inhibitor SB 203580 or RNA interference (RNAi) markedly reduced the expression of MKP-1 in LPS or PGN-treated macrophages, which is correlated with prolonged activation of p38 and JNK. Depletion of MAPKAP kinase 2 (MK2), a downstream substrate of p38, by RNAi also inhibited the expression of MKP-1. The mRNA level of MKP-1 is not affected by inhibition of p38, but the expression of MKP-1 is inhibited by treatment of cycloheximide. Thus, p38 MAPK plays a critical role in mediating expression of MKP-1 at a post-transcriptional level. Furthermore, inhibition of p38 by SB 203580 prevented the expression of MKP-1 in LPS-tolerized macrophages, restored the activation of MAP kinases after LPS restimulation. These results indicate a critical role of p38-MK2-dependent induction of MKP-1 in innate immune responses.
Assuntos
Proteínas de Ciclo Celular/metabolismo , Retroalimentação Fisiológica , Regulação Enzimológica da Expressão Gênica , Proteínas Imediatamente Precoces/metabolismo , Macrófagos/fisiologia , Fosfoproteínas Fosfatases/metabolismo , Proteínas Tirosina Fosfatases/metabolismo , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismo , Animais , Células Cultivadas , Interações Medicamentosas , Tolerância a Medicamentos , Fosfatase 1 de Especificidade Dupla , Ativação Enzimática , Imidazóis/farmacologia , Peptídeos e Proteínas de Sinalização Intracelular , Lipopolissacarídeos/farmacologia , MAP Quinase Quinase 4/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Modelos Biológicos , Peptidoglicano/farmacologia , Biossíntese de Proteínas , Proteínas Quinases/genética , Proteínas Quinases/metabolismo , Proteína Fosfatase 1 , Proteínas Serina-Treonina Quinases , Piridinas/farmacologia , Interferência de RNA , Transdução de Sinais , Proteínas Quinases p38 Ativadas por Mitógeno/genética , Proteínas Quinases p38 Ativadas por Mitógeno/fisiologiaRESUMO
The TAK1 plays a pivotal role in the innate immune response of Drosophila by controlling the activation of JNK and NF-kappaB. Activation of TAK1 in mammals is mediated by two TAK1-binding proteins, TAB1 and TAB2, but the role of the TAB proteins in the immune response of Drosophila has not yet been established. Here, we report the identification of a TAB2-like protein in Drosophila called dTAB2. dTAB2 can interact with dTAK1, and stimulate the activation of the JNK and NF-kB signaling pathway. Furthermore, we have found that silencing of dTAB2 expression by dsRNAi inhibits JNK activation by peptidoglycans (PGN), but not by NaCl or sorbitol. In addition, suppression of dTAB2 blocked PGN-induced expression of antibacterial peptide genes, a function normally mediated by the activation of NF-kappaB signaling pathway. No significant effect on p38 activation by dTAB2 was found. These results suggest that dTAB2 is specifically required for PGN-induced activation of JNK and NF-kappaB signaling pathways.
Assuntos
Proteínas de Drosophila/fisiologia , Drosophila melanogaster/imunologia , Proteínas Quinases JNK Ativadas por Mitógeno/metabolismo , NF-kappa B/metabolismo , Animais , Células Cultivadas , Proteínas de Drosophila/biossíntese , Proteínas de Drosophila/genética , Drosophila melanogaster/metabolismo , Ativação Enzimática , Imunidade Inata , Proteínas de Insetos/fisiologia , NF-kappa B/farmacologia , Peptidoglicano/farmacologia , Ligação Proteica , Interferência de RNA , Transdução de Sinais , Cloreto de Sódio/farmacologia , Sorbitol/farmacologia , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismoRESUMO
Retinoic acid-inducible gene-I (RIG-I) plays an important role in antiviral response by recognizing double-stranded RNA. Here we demonstrate an unanticipated role of RIG-I in Toll-like receptor (TLR)-stimulated phagocytosis. Stimulation with lipopolysaccharide (LPS), a ligand of TLR4, induced the expression of RIG-I in macrophages. Depletion of RIG-I by RNAi or gene targeting inhibited the LPS-induced phagocytosis of bacteria. Cellular processes involved in phagocytosis, such as small GTPase Cdc42/Rac1 activation, actin polymerization, and actin-regulator Arp2/3 recruitment, were also impaired in RIG-I-deficient macrophages activated by LPS. Moreover, RIG-I(-/-) mice were found to be more susceptible to infection with Escherichia coli as compared to wild-type mice. Thus, the regulatory functions of RIG-I are strikingly broad, including a role not only in antiviral responses but in antibacterial responses as well.