Disease relevance of MAP3K11

• We show that the activation of ERK and the proliferation of human schwannoma cells bearing a loss-of-function mutation in the neurofibromatosis 2 (NF2) gene require MLK3 [1].
• A survey of human cell lines revealed high levels of MLK3 in breast cancer cells [2].
• Mixed lineage kinase 3 (MLK3)-activated p38 MAP kinase mediates transforming growth factor-beta-induced apoptosis in hepatoma cells [3].
• Inhibition of mixed lineage kinase 3 prevents HIV-1 Tat-mediated neurotoxicity and monocyte activation [4].
• Genome-wide expression changes induced by HTLV-1 Tax: evidence for MLK-3 mixed lineage kinase involvement in Tax-mediated NF-kappaB activation [5].

High impact information on MAP3K11

• In addition, TNF-alpha also activates MLK3 and evidently leads to JNK activation in vivo [6].
• Mixed lineage kinase-3 (MLK3) is a MAP3K that was thought to be a cytokine-activated, and comparatively selective, regulator of the JNK group of MAPKs (refs 1, 4-6) [7].
• The proliferation of tumour cells containing activating B-raf or raf-1 mutations was unaffected by silencing mlk3 [7].
• Silencing mlk3 also blocked mitogen-stimulated phosphorylation of B-Raf at Thr 598 and Ser 601, a step required for B-Raf activation [7].
• Our results define an unexpected role for MLK3 in mitogen regulation of B-Raf, ERK and cell proliferation [7].

Chemical compound and disease context of MAP3K11

• To learn more about MLK3 regulation and its signaling pathways in breast cancer cells, we engineered the estrogen-responsive human breast cancer cell line, MCF-7, to stably, inducibly express FLAG epitope-tagged MLK3 [2].
• N-Acetylcysteine inhibit the translocation of mixed lineage kinase-3 from cytosol to plasma membrane during transient brain ischemia in rat hippocampus [8].

Biological context of MAP3K11

• The interaction domain maps to the C-terminal half of MLK3 (amino acids 511-847), and this region also contains a putative AKT phosphorylation consensus sequence [9].
• MLK3 and its family members have been implicated in JNK-mediated apoptosis [2].
• Thus, these data provide the first direct link between MLK3-mediated cell death and its regulation by a cell survival signaling protein, AKT1 [9].
• Further experiments demonstrate that MLK3 associates with Hsp90/p50(cdc37) through its catalytic domain in an activity-independent manner [2].
• Negative regulation of mixed lineage kinase 3 by protein kinase B/AKT leads to cell survival [9].

Anatomical context of MAP3K11

• Here we report that MLK3 can phosphorylate and activate MEK-1 directly in vitro and also can induce MEK phosphorylation on its activation sites in vivo in COS-7 cells [10].
• Mixed lineage kinase 3 inhibits phorbol myristoyl acetate-induced DNA synthesis but not osteopontin expression in rat mesangial cells [11].
• Accordingly, endogenous MLK3 was phosphorylated and activated by T-cell costimulation but not by treatment of cells with tumor necrosis factor alpha or interleukin-1 [12].
• A new identity for MLK3 as an NIMA-related, cell cycle-regulated kinase that is localized near centrosomes and influences microtubule organization [13].
• We show herein that Cdc42, in a prenylation-dependent manner, targets MLK3 from a perinuclear region to membranes, including the plasma membrane [14].

Associations of MAP3K11 with chemical compounds

• AKT phosphorylates MLK3 on serine 674 both in vitro and in vivo [9].
• In this study, we substituted a proposed stabilizing leucine residue in the zipper domain with a helix-disrupting proline to abrogate zipper-mediated SPRK oligomerization [15].
• Upon treatment of MCF-7 cells with geldanamycin, an ansamycin antibiotic that inhibits Hsp90 function, MLK3 levels decrease dramatically [2].
• Endogenous JNK, MKK7, and MLK3 kinase activities in HepG2 cells are significantly attenuated by insulin treatment, whereas the phosphatidylinositol 3-kinase inhibitors LY294002 and wortmannin reversed the effect [9].
• Mutation of this sole proline abrogates SH3 binding and increases MLK3 catalytic activity [16].

Physical interactions of MAP3K11

• We show that endogenous MLK3 complexes with Hsp90 and p50(cdc37) [2].
• Thus we propose a model in which GTP-bound Cdc42/Rac binds MLK3 and disrupts SH3-mediated autoinhibition leading to dimerization and activation loop autophosphorylation [14].
• In addition, we show that Akt activation results in the disassembly of the plenty of SH3s (POSH)-MLK3-Rac1 signaling complex and down-regulation of the activation of MLK3/c-Jun N-terminal kinase (JNK) pathway [17].

Enzymatic interactions of MAP3K11

• MLK3 directly phosphorylated and thus activated IkappaB kinase alpha (IKKalpha) and IKKbeta, revealing its function as an IkappaB kinase kinase (IKKK) [12].
• Herein we provide evidence that MLK3 can be phosphorylated by JNK in vitro and in vivo [18].
• This mechanism involves activation of protein tyrosine kinases (PTK) that phosphorylate IkappaBalpha with peak phosphorylation occurring after 30 min of reoxygenation [19].

Regulatory relationships of MAP3K11

• Furthermore, the expression of activated AKT1 inhibits MLK3-mediated cell death in a manner dependent on serine 674 phosphorylation [9].
• We demonstrate that constitutively activated Cdc42 fully activates this monomeric SPRK mutant in terms of both autophosphorylation and histone phosphorylation activity and induces the same in vivo phosphorylation pattern as wild type SPRK [15].
• Targeting of this partially active MLK3 to membranes likely results in additional phosphorylation events that fully activate MLK3 and its ability to maximally signal through the JNK pathway [14].

Other interactions of MAP3K11

• Finally, MLK3-mediated JNK activation is inhibited by AKT1 [9].
• Instead, MLK3 is a component of the B-Raf/Raf-1 complex and is required for maintenance of the integrity of this complex [1].
• In mesangial cells stably expressing MLK 3, the PMA-induced increase in [3H]-thymidine incorporation was significantly reduced (> 50%) [11].
• Mixed-lineage kinase 3 delivers CD3/CD28-derived signals into the IkappaB kinase complex [12].
• Cdc42 induces activation loop phosphorylation and membrane targeting of mixed lineage kinase 3 [14].

Analytical, diagnostic and therapeutic context of MAP3K11

• Endogenous MLK 3 expression was demonstrated in SH-SY5Y cells through protein levels and RT-PCR [20].
• Using both co-immunoprecipitation and nonreducing SDS-polyacrylamide gel electrophoresis, we demonstrated that MLK-3 forms disulfide bridged homo-dimers and that the LZs motif is sufficient for MLK-3 homodimerization [21].
• Using a site-directed mutagenesis approach, we show that SPRK contains a functional Cdc42/Rac interactive binding motif that is required for SPRKs association with and activation by Cdc42 [22].
• The gene encoding MLK-3 has been mapped using fluorescence in situ hybridization to human chromosome 11 q13.1-13.3, a region frequently altered in human malignancies [23].
• Following resolution by PGC chromatography, MALDI-MS in conjunction with alkaline phosphatase treatment identified Ser(555), Ser(556), Ser(724), and Ser(727) as sites of phosphorylation on MLK3 [24].

References