Expression and function of mixed lineage kinases in dendritic cells

Abstract

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.

Discovery, Synthesis, and Characterization of an Orally Bioavailable, Brain Penetrant Inhibitor of Mixed Lineage Kinase 3

“…4,5,6 MLK3 (MAP3K11) is the most widely expressed MLK family member, 4,5,6 and is expressed in neurons 7 (as well as other cell types). 8 At the cellular level, MLK3 is activated by stress, including reactive oxygen species, ceramide, and TNFα. 10,11 At the molecular level, it is activated by Cdc42 and Rac, which interact with MLK3, and can cause it to dimerize via a leucine zipper interface, resulting in autophosphorylation at Thr277 and Ser281 within the protein activation loop, and enzyme activation.…”

Mixed Lineage Kinase Phosphorylates Transcription Factor E47 and Inhibits TrkB Expression to Link Neuronal Death and Survival Pathways

“…Here we show that MLK2 kinase, whose activity has been involved in the regulation of JNK pathway (17,39), represses TrkB promoter activity by phosphorylating E47 in a JNK-independent manner. In particular, we show that phosphorylation of Ser/ Thr residues within the LH motif of the AD2 activation domain inhibits E47 as a transcriptional activator of TrkB.…”

“…Purified E47-TAP complexes were analyzed by nano-liquid chromatography coupled to nano-electrospray ionization and tandem mass spectrometry analysis. One of the identified peptides specifically present in the N-terminal E47-TAP pulldown was matched to MLK2, one of the mixed lineage kinases that had been initially identified as signaling effectors in the nervous system (17,38,39). To confirm and analyze further the interaction between E47 and MLK2, HEK293T cells were transfected with fulllength E47 and different FLAG-tagged MLK2 constructs (Fig.…”

Adjunctive and long-acting nanoformulated antiretroviral therapies for HIV-associated neurocognitive disorders

“…Thus, MLK3 likely plays an important role in inflammation and immunity. Consistent with this, MLK3 is expressed in dendritic cells [13, 14] and regulates CD3/CD28-mediated signaling events in T cells [49]. …”

“…1), and also regulate the other two major MAPK pathways, p38 and extracellular signal-regulated kinase (ERK) [9–11]. MLK3 (aka MAP3K11) is the most widely expressed MLK family member [9–11] and is known to be expressed in neurons [12], dendritic cells [13, 14], and many other cell types. At the cellular level, MLK3 is activated by cellular/metabolic stress, including reactive oxygen species, ceramide and TNF-α [15, 16].…”