RESUMO
Transforming growth factor ß (TGF-ß)-activated kinase 1 (TAK1) is a key regulator in the signals transduced by proinflammatory cytokines and Toll-like receptors (TLRs). The regulatory mechanism of TAK1 in response to various tissue types and stimuli remains incompletely understood. Here, we show that ribosomal S6 kinase 1 (S6K1) negatively regulates TLR-mediated signals by inhibiting TAK1 activity. S6K1 overexpression causes a marked reduction in NF-κB and AP-1 activity induced by stimulation of TLR2 or TLR4. In contrast, S6K1(-/-) and S6K1 knockdown cells display enhanced production of inflammatory cytokines. Moreover, S6K1(-/-) mice exhibit decreased survival in response to challenge with lipopolysaccharide (LPS). We found that S6K1 inhibits TAK1 kinase activity by interfering with the interaction between TAK1 and TAB1, which is a key regulator protein for TAK1 catalytic function. Upon stimulation with TLR ligands, S6K1 deficiency causes a marked increase in TAK1 kinase activity that in turn induces a substantial enhancement of NF-κB-dependent gene expression, indicating that S6K1 is negatively involved in the TLR signaling pathway by the inhibition of TAK1 activity. Our findings contribute to understanding the molecular pathogenesis of the impaired immune responses seen in type 2 diabetes, where S6K1 plays a key role both in driving insulin resistance and modulating TLR signaling.
Assuntos
MAP Quinase Quinase Quinases/metabolismo , Proteínas Quinases S6 Ribossômicas 70-kDa/metabolismo , Transdução de Sinais , Receptor 2 Toll-Like/metabolismo , Receptor 4 Toll-Like/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Western Blotting , Linhagem Celular , Linhagem Celular Tumoral , Feminino , Perfilação da Expressão Gênica , Células HEK293 , Humanos , Lipopolissacarídeos/farmacologia , MAP Quinase Quinase Quinases/genética , Masculino , Camundongos , Camundongos da Linhagem 129 , Camundongos Endogâmicos C57BL , Camundongos Knockout , NF-kappa B/metabolismo , Análise de Sequência com Séries de Oligonucleotídeos , Ligação Proteica/efeitos dos fármacos , Proteínas Quinases S6 Ribossômicas 70-kDa/genética , Proteínas Quinases S6 Ribossômicas 90-kDa/genética , Proteínas Quinases S6 Ribossômicas 90-kDa/metabolismo , Receptor 2 Toll-Like/agonistas , Receptor 2 Toll-Like/genética , Receptor 4 Toll-Like/agonistas , Receptor 4 Toll-Like/genéticaRESUMO
Salt-inducible kinases (SIKs) are a family of related serine-threonine kinases and are involved in controlling various metabolisms such as liver glucose homeostasis, hepatic lipogenesis, steroidogenesis, and adipogenesis. Here we investigated the regulatory role of SIK proteins in Toll-like receptor 4 (TLR4)-mediated signaling. Overexpression of SIK1 and SIK3, but not SIK2, significantly inhibited nuclear factor-κB activity in response to lipopolysaccharide stimulation and affected the expression of proinflammatory cytokines. In contrast, both SIK1(KD) and SIK3(KD) Raw 264.7 cells exhibit dramatic elevations of nuclear factor-κB activation and activations of downstream signaling molecules, such as TGF-ß-activated kinase 1, p38, and c-Jun N-terminal kinase, in response to TLR4 stimulation, indicating that SIK1 and SIK3 are negatively involved in the TLR4-mediated signaling. Through biochemical studies, we found that SIK1 and SIK3 interact with TGF-ß-activated kinase 1-binding protein 2 (TAB2), and interrupt the functional complex of TAB2-TNF receptor-associated factor 6 (TRAF6). Interestingly, the molecular interruption is induced to suppress the ubiquitination of TRAF6 in response to TLR4 stimulation. These result suggest that SIK1 and SIK3 negatively regulate TLR4-mediated signaling through the interruption of TAB2-TRAF6 complex and thereby the inhibition of ubiquitination of TRAF6. The present findings can be useful for a better understanding of multilevel interactions between the metabolic and immune systems.
