Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.24 (mitogen-activated protein kinase)
 95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mixed lineage kinase-3 (MLK-3) is a 97 kDa serine/threonine kinase with multiple interaction domains, including a Cdc42 binding motif, but unknown function. Cdc42 and the related small GTP binding protein Rac1 can activate the SAPK/JNK and p38/RK stress-responsive kinase cascades, suggesting that MLK-3 may have a role in upstream regulation of these pathways. In support of this role, we demonstrate that MLK-3 can specifically activate the SAPK/JNK and p38/RK pathways, but has no effect on the activation of ERKs. Immunoprecipitated MLK-3 catalyzed the phosphorylation of SEK1 in vitro, and co-transfected MLK-3 induced phosphorylation of SEK1 and MKK3 at sites required for activation, suggesting direct regulation of these protein kinases. Furthermore, interactions between MLK-3 and SEK and MLK-3 and MKK6 were observed in co-precipitation experiments. Finally, kinase-dead mutants of MLK-3 blocked activation of the SAPK pathway by a newly identified mammalian analog of Ste20, germinal center kinase, but not by MEKK, suggesting that MLK-3 functions to activate the SAPK/JNK and p38/RK cascades in response to stimuli transduced by Ste20-like kinases.
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PMID:MLK-3 activates the SAPK/JNK and p38/RK pathways via SEK1 and MKK3/6. 900 78

c-Jun N-terminal kinases/stress-activated protein kinases (JNKs/SAPKs) are mitogen-activated protein kinase (MAPK)-related protein kinases that are involved in several cellular events, including growth, differentiation, and apoptosis. Mixed lineage kinases (MLKs) form a family of protein kinases sharing two leucine zipper-like motifs and a kinase domain whose primary structure is similar to both the tyrosine-specific and the serine/threonine-specific kinase classes. We have reported that a member of the MLK family, MUK/DLK/ZPK, can activate JNK/SAPK in vivo, and here we show that another member of the MLK family, MST/MLK2, activates JNK/SAPK. Both MUK/DLK/ZPK and MST/MLK2 cause a slight activation of p38/Mpk2 when overexpressed in COS-1 cells, whereas MST/MLK2, but not MUK/DLK/ZPK, activates extracellular response kinase (ERK) to a certain degree. The activity of SEK1/MKK4/JNKK, a MAPK kinase class protein kinase designated as a direct activator of JNK/SAPK, is also induced by MUK/DLK/ZPK or MST/MLK2 overexpression. Furthermore, recombinant MST/MLK2 produced in bacteria directly phosphorylates and activates SEK1/MKK4/JNKK in vitro, showing that MST/MLK2 acts like a MAPK kinase kinase. Taken together, these results suggest that MLK family members are MAPK kinase kinases preferentially acting on the JNK/SAPK pathway.
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PMID:MST/MLK2, a member of the mixed lineage kinase family, directly phosphorylates and activates SEK1, an activator of c-Jun N-terminal kinase/stress-activated protein kinase. 918 38

Mixed lineage kinases (MLKs) are MAPKKK members that activate JNK and reportedly lead to cell death. However, the agonist(s) that regulate MLK activity remain unknown. Here, we demonstrate ceramide as the activator of Drosophila MLK (dMLK) and identify ceramide and TNF-alpha as agonists of mammalian MLK3. dMLK and MLK3 are activated by a ceramide analog and bacterial sphingomyelinase in vivo, whereas a low nanomolar concentration of natural ceramide activates them in vitro. Specific inhibition of dMLK and MLK3 significantly attenuates activation of JNK by ceramide in vivo without affecting ceramide-induced p38 or ERK activation. In addition, TNF-alpha also activates MLK3 and evidently leads to JNK activation in vivo. Thus, the ceramide serves as a common agonist of dMLK and MLK3, and MLK3 contributes to JNK activation induced by TNF-alpha.
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PMID:Activation of the Drosophila MLK by ceramide reveals TNF-alpha and ceramide as agonists of mammalian MLK3. 1250 27

Mixed lineage kinases (MLKs) belong to the family of mitogen activated protein kinase kinase kinase (MAPKKK) and cause neuronal cell death mediated through c-Jun, N-terminal kinase (JNK) pathway. Recently, genetic studies in Drosophila revealed the presence of an MLK termed slipper (slpr). However, its biochemical features like physiological substrate, role in different MAPK pathways and developmental and tissue-specific expression pattern were not reported. Here, we report cDNA cloning, expression analysis and biochemical characterization of a Drosophila mixed lineage kinase (dMLK) that is also known as slipper. The protein structure analysis of dMLK/slipper revealed, in addition to the conserved domains, a stretch of glutamine in the amino terminus and an asparagine-threonine stretch at the carboxy-terminus. In situ hybridization and reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed that dMLK is expressed in early embryonic stages, adult brain and thorax. Ectopic expression of dMLK either in Drosophila S2 or in mammalian HEK293 cells leads to activation of JNK, p38 and extracellular signal regulated kinase (ERK) pathways. Further, dMLK directly phosphorylates Hep, dMKK4 and also their mammalian counterparts, MKK7 and SEK1, in an in vitro kinase assay. Taken together, our results provide for the first time a comprehensive expression profile and new biochemical insight of dMLK/slipper.
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PMID:Drosophila mixed lineage kinase/slipper, a missing biochemical link in Drosophila JNK signaling. 1267 57

Mixed lineage kinases (MLKs) are a family of serine/threonine kinases that function in the SAPK signaling cascade. MLKs activate JNK/SAPK in vivo by directly phosphorylating and activating the JNK kinase SEK-1 (MKK4 and -7). Importantly, the MLK member MLK3/SPRK has been shown recently to be a direct target of ceramide and tumor necrosis factor-alpha (TNF-alpha) and to mediate the TNF-alpha and ceramide-induced JNK activation in Jurkat cells. 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. Surprisingly, this induction of MEK phosphorylation does not result in ERK activation in vivo. Rather, in cells expressing active MLK3, ERK becomes resistant to activation by growth factors and mitogens. This restriction in ERK activation requires MLK3 kinase activity, is independent of Raf activation, and is reversed by JNK pathway inhibition either at the level of SEK-1, JNK, or Jun. These results demonstrate that sustained JNK activation uncouples ERK activation from MEK in a manner requiring Jun-mediated gene transcription. This in turn points to the existence of a negative cross-talk relationship between the stress-activated JNK pathway and the mitogen-activated ERK pathway. Thus, our findings imply that some of the biological functions of JNK activators, such as TNF-alpha and ceramide, may be attributed to their ability to block cell responses to growth and survival factors acting through the ERK/MAPK pathway.
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PMID:Cross-talk between JNK/SAPK and ERK/MAPK pathways: sustained activation of JNK blocks ERK activation by mitogenic factors. 1273 96

Mixed lineage kinase 7 (MLK7) is a MAPKKK with enriched expression in heart and skeletal muscle that functions to activate JNK and p38. The MLKs have several conserved domains, including a leucine zipper that in other family members mediates oligomerization critical for catalytic activity and JNK activation. Nested C-terminal deletion mutants of MLK7 from 436 to 286 as well as a mutant lacking only the leucine zipper (delLZ) were generated to determine the role of these domains in catalytic activity and JNK activation. Specific activity of MLK7366 was 75% full length while 436, 322, and delLZ retained approximately 25% and 286, 4% of the full-length catalytic function, demonstrating that the leucine zipper, while not absolutely necessary for catalytic activity, is required to reach full catalytic function of the enzyme. Co-transfection studies of JNK with the MLK7 mutants demonstrated full JNK activation with MLK7, 436, and delLZ, marginal activation for 1-400 or 1-366, and no activation for 1-322, demonstrating that the leucine zipper is not required for JNK activation and that sequence contained in C-terminal residue 322-436 is necessary for full pathway activation by MLK7.
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PMID:Effect of C-terminal truncations on MLK7 catalytic activity and JNK activation. 1452 31

The ERK group of mitogen-activated protein kinases (MAPKs) is essential for cell proliferation stimulated by mitogens, oncogenic ras and raf (ref. 1). All MAPKs are activated by MAP3K/MEK/MAPK core pathways and the Raf proto-oncoproteins, especially B-Raf, are ERK-specific MAP3Ks (refs 1-3). 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). Here we report that silencing of mlk3 by RNAi suppressed mitogen and cytokine activation not only of JNK but of ERK and p38 as well. Silencing mlk3 also blocked mitogen-stimulated phosphorylation of B-Raf at Thr 598 and Ser 601, a step required for B-Raf activation. Furthermore, silencing mlk3 prevented serum-stimulated cell proliferation and the proliferation of tumour cells bearing either oncogenic Ki-Ras or loss-of-function neurofibromatosis-1 (NF1) or NF2 mutations. The proliferation of tumour cells containing activating B-raf or raf-1 mutations was unaffected by silencing mlk3. Our results define an unexpected role for MLK3 in mitogen regulation of B-Raf, ERK and cell proliferation.
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PMID:MLK3 is required for mitogen activation of B-Raf, ERK and cell proliferation. 1530 91

Inflammatory conversion of murine astrocytes correlates with the activation of various MAPK, and inhibition of terminal MAPKs like JNK or p38 dampens the inflammatory reaction. Mixed lineage kinases (MLKs), a family of MAPK kinase kinases, may therefore be involved in astrocyte inflammation. In this study, we explored the effect of the MLK inhibitors CEP-1347 and CEP-11004 on the activation of murine astrocytes by either TNF plus IL-1 or by a complete cytokine mix containing additional IFN-gamma. The compounds blocked NO-, PG-, and IL-6 release with a median inhibitory concentration of approximately 100 nM. This activity correlated with a block of the JNK and the p38 pathways activated in complete cytokine mix-treated astrocytes. Although CEP-1347 did not affect the activation of NF-kappaB, it blocked the expression of cyclooxygenase-2 and inducible NO synthase at the transcriptional level. Quantitative transcript profiling of 17 inflammation-linked genes revealed a specific modulation pattern of astrocyte activation by MLK inhibition, for instance, characterized by up-regulation of the anti-stress factors inhibitor of apoptosis protein-2 and activated transcription factor 4, no effect on manganese superoxide dismutase and caspase-11, and down-regulation of major inflammatory players like TNF, GM-CSF, urokinase-type plasminogen activator, and IL-6. In conclusion, MLK inhibitors like CEP-1347 are highly potent astrocyte immune modulators with a novel spectrum of activity.
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PMID:Specific modulation of astrocyte inflammation by inhibition of mixed lineage kinases with CEP-1347. 1529 95

Mixed lineage kinase 7 (MLK7) is a recently identified mitogen-activated protein kinase kinase kinase with enriched expression in skeletal muscle and heart. When over-expressed in cardiac myocytes, MLK7 activates both the p38 and c-Jun N-terminal kinase (JNK) stress-activated pathways and induces a cellular phenotype characteristic of cardiac hypertrophy, including a fetal gene expression pattern and increased protein synthesis. We sought to determine the effect of MLK7 on cardiac function in vivo by generating transgenic (Tg) mice with cardiac restricted over-expression of the enzyme. The mice were viable and demonstrated no visible signs of distress at rest. Microscopic examination of the hearts showed myocardial fibrosis and hypertrophy. Hemodynamic analysis of the Tg mice revealed impaired systolic function and significant diastolic dysfunction. Furthermore, significant mortality was observed in MLK7 Tg mice following 24-48 h of isoproterenol administration. Isoproterenol activation of JNK and p38, but not extracellular signal-regulated kinase, was significantly greater in the MLK7 Tg mice compared to littermate controls. These data indicate that MLK7 is an important signal transducer in cardiac compensation. Simultaneous activation of JNK and p38 by MLK7 may contribute to cardiac decompensation during the periods of acute cardiac stress.
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PMID:Transgenic mice with cardiac-specific over-expression of MLK7 have increased mortality when exposed to chronic beta-adrenergic stimulation. 1535 Aug 44

The extracellular signal-regulated kinase (ERK) group of MAPKs is essential for cell proliferation, including that stimulated by mitogens, oncogenic ras and raf. The Raf kinases (especially B-Raf) are ERK-specific, mitogen-activated MAP3Ks. Mixed lineage kinase-3 (MLK3) is a MAP3K previously thought to be a selective regulator of the JNK group of MAPKs. Surprisingly, we found that silencing of mlk3 by RNAi suppresses mitogen and cytokine activation not only of JNK but of ERK and p38 as well. Silencing mlk3 also blocks mitogen-stimulated phosphorylation of B-Raf at Thr598 and Ser601-a step required for B-Raf activation. Finally, silencing mlk3 prevents serum-stimulated cell proliferation and the proliferation of tumor cells bearing either oncogenic Ki-Ras or loss of function neurofibromatosis-1 (NF1) or NF2 mutations. The proliferation of tumor cells with activating mutations in B-raf or raf-1 are unaffected by silencing mlk3. These results define a new role for MLK3 in B-Raf activation, ERK signaling and cell proliferation. Accordingly, targeting MLK3 could be beneficial to the treatment of tumors with activated receptor tyrosine kinase or ras mutations, and to the treatment of NF1 or NF2 tumors.
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PMID:A novel role for mixed lineage kinase 3 (MLK3) in B-Raf activation and cell proliferation. 1546 51


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