Handley Matthew E, Rasaiyaah Jane, Barnett James, Thakker Manish, Pollara Gabriele, Katz David R, Chain Benjamin M
Department of Immunology and Molecular Pathology, University College London, Windeyer Institute, 46 Cleveland Street, London W1T 4JF, UK.
Int Immunol. 2007 Aug;19(8):923-33. doi: 10.1093/intimm/dxm050. Epub 2007 Aug 13.
Dendritic cells (DCs) sense the presence of conserved microbial structures in their local microenvironment via specific pattern recognition receptors (PRRs). This leads to a programme of changes, which include migration and activation, and enables them to induce adaptive T cell immunity. Mitogen-activated protein kinases (MAPKs) are implicated in this response, but the pathways leading from PRR ligation to MAPK activation, and hence DC activation, are not fully understood. Recent studies in the nervous system have suggested that the mixed lineage kinase (MLK) family of MAPK kinase kinase proteins may be involved as an intermediary step between PRRs and MAPKs. Therefore, in this study, we have used a well-established DC model to explore the role of MLKs in these cells. Messenger RNA for MLKs 2, 3, 4 and DLK and protein for MLKs 2, 3 and DLK are found in DC. DC activation in response to model PRR ligands, such as LPS or poly (I:C), is accompanied by phosphorylation of MLK3. In contrast, another known PRR ligand, zymosan, induces little MLK3 phosphorylation. Inhibition of MLK activity using a pharmacological inhibitor, CEP11004, blocks p38 and Jun N-terminal kinase (JNK) MAPK activation in response to LPS and poly (I:C), but not zymosan. The inhibition is associated with a block in DC activation as measured by cell-surface marker expression and cytokine secretion. Thus, MLKs are expressed in DC, and are implicated in DC activation, and the involvement of MLKs appears to be selective, depending on the nature of the DC stimulus.
树突状细胞（DCs）通过特定的模式识别受体（PRRs）感知其局部微环境中保守的微生物结构。这会引发一系列变化，包括迁移和激活，使其能够诱导适应性T细胞免疫。丝裂原活化蛋白激酶（MAPKs）参与了这一反应，但从PRR连接到MAPK激活进而导致DC激活的途径尚未完全明确。最近在神经系统中的研究表明，MAPK激酶激酶蛋白的混合谱系激酶（MLK）家族可能作为PRRs和MAPKs之间的中间步骤参与其中。因此，在本研究中，我们使用了一个成熟的DC模型来探究MLKs在这些细胞中的作用。在DC中发现了MLKs 2、3、4和DLK的信使RNA以及MLKs 2、3和DLK的蛋白质。DC对模型PRR配体（如LPS或聚肌苷酸胞苷酸（poly (I:C)））的激活伴随着MLK3的磷酸化。相比之下，另一种已知的PRR配体酵母聚糖诱导的MLK3磷酸化很少。使用药理抑制剂CEP11004抑制MLK活性可阻断DC对LPS和聚肌苷酸胞苷酸（poly (I:C)）的反应中p38和Jun N端激酶（JNK）MAPK的激活，但对酵母聚糖无此作用。这种抑制与通过细胞表面标志物表达和细胞因子分泌所测得的DC激活受阻相关。因此，MLKs在DC中表达，并与DC激活有关联，而且MLKs的参与似乎具有选择性，这取决于DC刺激的性质。
