15-Deoxy-Δ12,14-prostaglandin J2 Regulates Endogenous Cot MAPK Kinase Kinase 1 Activity Induced by Lipopolysaccharide

Map3k8 Modulates Monocyte State and Atherogenesis in ApoE-/- Mice

OBJECTIVE

Map3k8 (Cot/Tpl2) activates the MKK1/2-ERK1/2, MAPK pathway downstream from interleukin-1R, tumor necrosis factor-αR, NOD-2R (nucleotide-binding oligomerization domain-like 2R), adiponectinR, and Toll-like receptors. Map3k8 plays a key role in innate and adaptive immunity and influences inflammatory processes by modulating the functions of different cell types. However, its role in atherogenesis remains unknown. In this study, we analyzed the role of this kinase in this pathology.

APPROACH AND RESULTS

We show here that Map3k8 deficiency results in smaller numbers of Ly6C^highCD11c^low and Ly6C^lowCD11c^high monocytes in ApoE^-/- mice fed a high-fat diet (HFD). Map3k8^-/-ApoE^-/- monocytes displayed high rates of apoptosis and reduced amounts of Nr4a1, a transcription factor known to modulate apoptosis in Ly6C^lowCD11c^high monocytes. Map3k8^-/-ApoE^-/- splenocytes and macrophages showed irregular patterns of cytokine and chemokine expression. Map3k8 deficiency altered cell adhesion and migration in vivo and decreased CCR2 expression, a determinant chemokine receptor for monocyte mobilization, on circulating Ly6C^highCD11c^low monocytes. Map3k8^-/-ApoE^-/- mice fed an HFD showed decreased cellular infiltration in the atherosclerotic plaque, with low lipid content. Lesions had similar size after Map3k8^+/+ApoE^-/- bone marrow transplant into Map3k8^-/-ApoE^-/- and Map3k8^+/+ApoE^-/- mice fed an HFD, whereas smaller plaques were observed after the transplantation of bone marrow lacking both ApoE and Map3k8.

CONCLUSIONS

Map3k8 decreases apoptosis of monocytes and enhances CCR2 expression on Ly6C^highCD11c^low monocytes of ApoE^-/- mice fed an HFD. These findings explain the smaller aortic lesions in ApoE^-/- mice with Map3k8^-/-ApoE^-/- bone marrow cells fed an HFD, supporting further studies of Map3k8 as an antiatherosclerotic target.

Anti-inflammatory Activity of Saxifragin via Inhibition of NF-κB Involves Caspase-1 Activation

Saxifragin, the 5-glucoside of the flavonoid quercetin, is found in plants and insects. It has been reported that saxifragin has peroxynitrite-scavenging effects. However, the mechanism of anti-inflammatory effects of saxifragin has not yet been clearly identified. In this study, we investigated the anti-inflammatory effects of saxifragin in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages and animal models of inflammation. We found that saxifragin suppressed the production of nitric oxide (NO) and prostaglandin E2 (PGE2) in LPS-activated RAW 264.7 macrophages by suppressing the level of protein and mRNA expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), respectively. Furthermore, saxifragin inhibited mRNA expression of pro-inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β. We studied the inhibitory effects of saxifragin on the nuclear translocation of nuclear factor (NF)-κB, activation of caspase-1, and phosphorylation of c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Furthermore, pretreatment with saxifragin increased the survival rate of mice with LPS-induced septic death. Collectively, these findings suggest that saxifragin exerts anti-inflammatory activity by inhibiting NF-κB, caspase-1, and mitogen-activated protein kinase (MAPK) activation.

Cot/tpl2 participates in the activation of macrophages by adiponectin

Whereas the main function of APN is to enhance insulin activity, it is also involved in modulating the macrophage phenotype. Here, we demonstrate that at physiological concentrations, APN activates Erk1/2 via the IKKβ-p105/NF-κΒ1-Cot/tpl2 intracellular signal transduction cassette in macrophages. In peritoneal macrophages stimulated with APN, Cot/tpl2 influences the ability to phagocytose beads. However, Cot/tpl2 did not modulate the known capacity of APN to decrease lipid content in peritoneal macrophages in response to treatment with oxLDL or acLDL. A microarray analysis of gene-expression profiles in BMDMs exposed to APN revealed that APN modulated the expression of ∼3300 genes; the most significantly affected biological functions were the inflammatory and the infectious disease responses. qRT-PCR analysis of WT and Cot/tpl2 KO macrophages stimulated with APN for 0, 3, and 18 h revealed that Cot/tpl2 participated in the up-regulation of APN target inflammatory mediators included in the cytokine-cytokine receptor interaction pathway (KEGG ID 4060). In accordance with these data, macrophages stimulated with APN increased secretion of cytokines and chemokines, including IL-1β, IL-1α, TNF-α, IL-10, IL-12, IL-6, and CCL2. Moreover, Cot/tpl2 also played an important role in the production of these inflammatory mediators upon stimulation of macrophages with APN. It has been reported that different types of signals that stimulate TLRs, IL-1R, TNFR, FcγR, and proteinase-activated receptor-1 activate Cot/tpl2. Here, we demonstrate that APN is a new signal that activates the IKKβ-p105/NF-κΒ1-Cot/tpl2-MKK1/2-Erk1/2 axis in macrophages. Furthermore, this signaling cassette modulates the biological functions triggered by APN in macrophages.

Sterile inflammation in acetaminophen-induced liver injury is mediated by Cot/tpl2

Cot/tpl2 (MAP3K8) activates MKK1/2-Erk1/2 following stimulation of the Toll-like/IL-1 receptor superfamily. Here, we investigated the role of Cot/tpl2 in sterile inflammation and drug-induced liver toxicity. Cot/tpl2 KO mice exhibited reduced hepatic injury after acetaminophen challenge, as evidenced by decreased serum levels of both alanine and aspartate aminotransferases, decreased hepatic necrosis, and increased survival relative to Wt mice. Serum levels of both alanine and aspartate aminotransferases were also lower after intraperitoneal injection of acetaminophen in mice expressing an inactive form of Cot/tpl2 compared with Wt mice, suggesting that Cot/tpl2 activity contributes to acetaminophen-induced liver injury. Furthermore, Cot/tpl2 deficiency reduced neutrophil and macrophage infiltration in the liver of mice treated with acetaminophen, as well as their hepatic and systemic levels of IL-1α. Intraperitoneal injection of damage-associated molecular patterns from necrotic hepatocytes also impaired the recruitment of leukocytes and decreased the levels of several cytokines in the peritoneal cavity in Cot/tpl2 KO mice compared with Wt counterparts. Moreover, similar activation profiles of intracellular pathways were observed in Wt macrophages stimulated with Wt or Cot/tpl2 KO damage-associated molecular patterns. However, upon stimulation with damage-associated molecular patterns, the activation of Erk1/2 and JNK was deficient in Cot/tpl2 KO macrophages compared with their Wt counterparts; an effect accompanied by weaker release of several cytokines, including IL-1α, an important component in the development of sterile inflammation. Taken together, these findings indicate that Cot/tpl2 contributes to acetaminophen-induced liver injury, providing some insight into the underlying molecular mechanisms.

Cot/tpl2-MKK1/2-Erk1/2 controls mTORC1-mediated mRNA translation in Toll-like receptor-activated macrophages

Macrophages require rapid fine control of translation to provide an accurate and not self-damaging response to host infection. Cot/tpl2-MKK1/2-Erk1/2 controls 5´TOP and inflammatory mediator–gene encoding mRNA translation in TLR-activated macrophages.

Cot/tpl2 is the only MAP3K that activates MKK1/2-Erk1/2 in Toll-like receptor–activated macrophages. Here we show that Cot/tpl2 regulates RSK, S6 ribosomal protein, and 4E-BP phosphorylation after stimulation of bone marrow–derived macrophages with lipopolysaccharide (LPS), poly I:C, or zymosan. The dissociation of the 4E-BP–eIF4E complex, a key event in the cap-dependent mRNA translation initiation, is dramatically reduced in LPS-stimulated Cot/tpl2-knockout (KO) macrophages versus LPS-stimulated wild-type (Wt) macrophages. Accordingly, after LPS activation, increased cap-dependent translation is observed in Wt macrophages but not in Cot/tpl2 KO macrophages. In agreement with these data, Cot/tpl2 increases the polysomal recruitment of the 5´ TOP eEF1α and eEF2 mRNAs, as well as of inflammatory mediator gene–encoding mRNAs, such as tumor necrosis factor α (TNFα), interleukin-6 (IL-6), and KC in LPS-stimulated macrophages. In addition, Cot/tpl2 deficiency also reduces total TNFα, IL-6, and KC mRNA expression in LPS-stimulated macrophages, which is concomitant with a decrease in their mRNA half-lives. Macrophages require rapid fine control of translation to provide an accurate and not self-damaging response to host infection, and our data show that Cot/tpl2 controls inflammatory mediator gene–encoding mRNA translation in Toll-like receptor–activated macrophages.

Pharmacophore generation and atom-based 3D-QSAR of novel quinoline-3-carbonitrile derivatives as Tpl2 kinase inhibitors

Tumour progression locus-2 (Tpl2) is a serine/threonine kinase, which regulates the expression of tumour necrosis factor α. The article describes the development of a robust pharmacophore model and the investigation of structure-activity relationship analysis of quinoline-3-carbonitrile derivatives reported for Tpl2 kinase inhibition. A five point pharmacophore model (ADRRR) was developed and used to derive a predictive atom-based 3-dimensional quantitative structure activity relationship (3D-QSAR) model. The obtained 3D-QSAR model has an excellent correlation coefficient value (r(2)= 0.96), Fisher ratio (F = 131.9) and exhibited good predictive power (q(2) = 0.79). The QSAR model suggests that the inclusion of hydrophobic substituents will enhance the Tpl2 kinase inhibition. In addition, H-bond donating groups, negative ionic groups and electron withdrawing groups positively contribute to the Tpl2 kinase inhibition. Further, pharmacophoric model was validated by the receiver operating characteristic curve analysis and was employed for virtual screening to identify six potential Tpl2 kinase inhibitors. The findings of this study provide a set of guidelines for designing compounds with better Tpl2 kinase inhibitory potency.

Cot/tpl2 activity is required for TLR-induced activation of the Akt p70 S6k pathway in macrophages: Implications for NO synthase 2 expression

LPS stimulation activates IKK and different MAP kinase pathways, as well as the PI3K-Akt-mTOR-p70 S6k pathway, a negative regulator of these MyD88-dependent intracellular signals. Here, we show that Cot/tpl2, a MAP3K responsible for the activation of the MKK1-Erk1/2, controls P-Ser473 Akt and P-Thr389 p70 S6k phosphorylation in LPS-stimulated macrophages. Analysis of the intracellular signalling in Cot/tpl2 KO macrophages versus WT macrophages reveals lower IκBα recovery and higher phosphorylation of JNK and p38α after 1 h of LPS stimulation. Moreover, Cot/tpl2 deficiency increases LPS-induced NO synthase 2 (NOS2) expression in macrophages. Inhibition of the PI3K pathway abolishes the differences in IκBα and NOS2 expression between Cot/tpl2 KO and WT macrophages following LPS administration. Furthermore, in zymosan- and polyI:C-stimulated macrophages, Cot/tpl2 mediates P-Ser473 Akt phosphorylation, increases IκBα levels and decreases NOS2 expression. In conclusion, these data reveal a novel role for the Cot/tpl2 pathway in mediating TLR activation of the Akt-mTOR-p70 S6k pathway, allowing Cot/tpl2 to fine-control the activation state of other signalling pathways.

Inhibition of tumor progression locus 2 protein kinase decreases lipopolysaccharide-induced tumor necrosis factor alpha production due to the inhibition of the tip-associated protein induction in RAW264.7 cells

The activation of mitogen-activated protein kinases (MAPKs) is critically involved in inflammatory events through mediation of the production of various inflammatory cytokines. The Tpl2 (tumor progression locus 2)-MEK (MAPK/ERK kinase)-ERK (extracellular signal-regulated kinase) signaling pathway plays an essential role in the production of tumor necrosis factor alpha (TNFalpha) in macrophages stimulated with lipopolysaccharide (LPS). Here, we studied the molecular mechanisms of Tpl2-mediated TNFalpha production using a potent Tpl2 kinase inhibitor, 1,7-naphtyridine-3-carbonitrile, and LPS-stimulated RAW264.7 cells. This inhibitor was effective in suppressing the in vitro Tpl2 kinase activity, and caused a significant reduction in TNFalpha production via specific suppression of the phosphorylation of MEK and ERK but not that of p38 and c-Jun N-terminal kinase (JNK). A p38 inhibitor, SB203580, also inhibited the TNFalpha production dose-dependently. Although the TNFalpha mRNA level was not altered by either inhibitor, the Tpl2 inhibitor increased the nuclear TNFalpha mRNA level, while decreasing that in the cytoplasm. Tip-associated protein (TAP), a key molecule in the nucleocytoplasmic transport of TNFalpha mRNA, was up-regulated by LPS, but this increase was impaired by the Tpl2 inhibitor. In all cases, SB203580 was without effect in the presence of LPS. These results suggest that the LPS-induced TNFalpha production via the Tpl2-MEK-ERK signaling pathway is regulated by changing the TAP level at the nucleocytoplasmic transport level. These results improve understanding of TNFalpha regulatory mechanisms and might provide a new therapeutic strategy against inflammatory diseases.

Cot/tpl2 (MAP3K8) mediates myeloperoxidase activity and hypernociception following peripheral inflammation

Cot/tpl2 (also known as MAP3K8) has emerged as a new and potentially interesting therapeutic anti-inflammatory target. Here, we report the first study of Cot/tpl2 involvement in acute peripheral inflammation in vivo. Six hours after an intraplantar injection of zymosan, Cot/tpl2(-/-) mice showed a 47% reduction in myeloperoxidase activity, concomitant with a 46% lower neutrophil recruitment and a 40% decreased luminol-mediated bioluminescence imaging in vivo. Accordingly, Cot/tpl2 deficiency provoked a 25-30% reduction in luminol-mediated bioluminescence and neutrophil recruitment together with a 65% lower macrophage recruitment 4 h following zymosan-induced peritonitis. Significantly impaired levels of G-CSF and GM-CSF and of other cytokines such as TNFα, IL-1β, and IL-6, as well as some chemokines such as MCP-1, MIP-1β, and keratinocyte-derived chemokine, were detected during the acute zymosan-induced intraplantar inflammatory response in Cot/tpl2(-/-) mice. Moreover, Cot/tpl2 deficiency dramatically decreased the production of the hypernociceptive ligand NGF at the inflammatory site during the course of inflammation. Most importantly, Cot/tpl2 deficiency significantly reduced zymosan-induced inflammatory hypernociception in mice, with a most pronounced effect of a 50% decrease compared with wild type (WT) at 24 h following intraplantar injection of zymosan. At this time, Cot/tpl2(-/-) mice showed significantly reduced NGF, TNFα, and prostaglandin E(2) levels compared with WT littermates. In conclusion, our study demonstrates an important role of Cot/tpl2 in the NGF, G-CSF, and GM-CSF production and myeloperoxidase activity in the acute inflammatory response process and its implication in inflammatory hypernociception.

Tpl-2/Cot and COX-2 in breast cancer

BACKGROUND

Breast cancer is the most common cancer in women worldwide and although mortality (129,000/year) stagnates, incidence (370,000/year) is increasing. In addition to histological type, grade, stage, hormonal and c-erbB2 status there is therefore a strong need for new and reliable prognostic and predictive factors.

METHODS AND RESULTS

This minireview focuses on two potential prognostic and predictive candidates Tpl2/Cot and COX-2 and summarise information about them.

CONCLUSION

Tumor progression locus 2 (Tpl2/Cot) is a serine/threonine protein kinase belonging to the family of MAP3 kinases. Activated Tpl2/Cot leads to induction of ERK1/2, JNK, NF-kappaB and p38MAPK pathways. The first study on Tpl2/Cot mRNA in breast cancer showed its increase in 40 % of cases of breast cancer but no available data exist on protein expression. Cyclo-oxygenase 2 (COX-2) is inducible by growth and inflammatory factors and contributes to the development of various tumours. Expression of COX-2 in breast cancer varied from 5-100 % in reviewed papers with significantly higher values in poorly differentiated tumours. Tpl2/Cot and COX-2 have their importance in different intracellular pathways and some of these are involved in cancer development. Briefly, the results from recent studies suggest that Tpl2/Cot and COX-2 could be prognostic factors in breast cancer.

PPARalpha/gamma-Independent Effects of PPARalpha/gamma Ligands on Cysteinyl Leukotriene Production in Mast Cells

Peroxisome proliferator-activated receptor (PPAR) α ligands (Wy-14,643, and fenofibrate) and PPARγ ligands (troglitazone and ciglitazone) inhibit antigen-induced cysteinyl leukotriene production in immunoglobulin E-treated mast cells. The inhibitory effect of these ligands on cysteinyl leukotriene production is quite strong and is almost equivalent to that of the anti-asthma compound zileuton. To develop new aspects for anti-asthma drugs the pharmacological target of these compounds should be clarified. Experiments with bone-marrow-derived mast cells from PPARα knockout mice and pharmacological inhibitors of PPARγ suggest that the inhibitory effects of these ligands are independent of PPARs α and γ. The mechanisms of the PPAR-independent inhibition by these agents on cysteinyl leukotriene production are discussed in this review.

Pharmacologic Inhibition of Tpl2 Blocks Inflammatory Responses in Primary Human Monocytes, Synoviocytes, and Blood

Tumor necrosis factor alpha (TNFalpha) is a pro-inflammatory cytokine that controls the initiation and progression of inflammatory diseases such as rheumatoid arthritis. Tpl2 is a MAPKKK in the MAPK (i.e. ERK) pathway, and the Tpl2-MEK-ERK signaling pathway is activated by the pro-inflammatory mediators TNFalpha, interleukin (IL)-1beta, and bacterial endotoxin (lipopolysaccharide (LPS)). Moreover, Tpl2 is required for TNFalpha expression. Thus, pharmacologic inhibition of Tpl2 should be a valid approach to therapeutic intervention in the pathogenesis of rheumatoid arthritis and other inflammatory diseases in humans. We have developed a series of highly selective and potent Tpl2 inhibitors, and in the present study we have used these inhibitors to demonstrate that the catalytic activity of Tpl2 is required for the LPS-induced activation of MEK and ERK in primary human monocytes. These inhibitors selectively target Tpl2 in these cells, and they block LPS- and IL-1beta-induced TNFalpha production in both primary human monocytes and human blood. In rheumatoid arthritis fibroblast-like synoviocytes these inhibitors block ERK activation, cyclooxygenase-2 expression, and the production of IL-6, IL-8, and prostaglandin E(2), and the matrix metalloproteinases MMP-1 and MMP-3. Taken together, our results show that inhibition of Tpl2 in primary human cell types can decrease the production of TNFalpha and other pro-inflammatory mediators during inflammatory events, and they further support the notion that Tpl2 is an appropriate therapeutic target for rheumatoid arthritis and other human inflammatory diseases.

Interleukin-1 stimulated activation of the COT catalytic subunit through the phosphorylation of Thr290 and Ser62

The protein kinase COT/Tpl2 is activated by interleukin-1 (IL-1), TNFalpha and lipopolysaccharide, and its activation by these agonists involves the IkappaB kinase beta (IKKbeta) catalysed phosphorylation of the p105 regulatory subunit. Here, we show that COT activation also requires catalytic subunit phosphorylation, since IL-1beta induced a 5-10-fold activation of a COT mutant unable to bind p105. Activation was paralleled by the phosphorylation of Thr290 and Ser62 and unaffected by the IKKbeta inhibitor PS1145 at concentrations which prevented the degradation of IkappaBalpha. Mutagenesis experiments indicated that COT activation is initiated by Thr290 phosphorylation catalysed by an IL-1-stimulated protein kinase distinct from IKKbeta, while Ser62 phosphorylation is an autophosphorylation event required for maximal activation.

Vascular protection in brain ischemia

Vascular damage occurring after cerebral ischemia may lead to a worse outcome in patients with ischemic stroke, as it facilitates edema formation and hemorrhagic transformation. There are several phases in the development of vascular injury (acute, subacute and chronic) and different mediators act in each one. Therapeutic options to avoid vascular injury must be focused on acting in each phase. However, even though experimental studies have demonstrated the benefit of therapeutic interventions both in the acute and chronic phases of cerebral ischemia, only the chronic phase offers a therapeutic window sufficiently wide enough to provide vascular protection in clinical practice. Several drugs including erythropoietin and HMG-CoA reductase inhibitors (statins), antihypertensive (angiotensin modulators), antibiotics (minocycline) and antihyperglycemic drugs (thiazolidinediones) have been proved to provide vascular protection in patients with ischemic stroke. Anti-inflammatory, antioxidant, and antiapoptotic actions are responsible for the vascular protective effect related to these drugs.

The tyrosine kinase Syk regulates TPL2 activation signals

Tpl2/Cot is a serine/threonine kinase that plays a key physiological role in the regulation of immune responses to pro-inflammatory stimuli, including tumor necrosis factor-alpha (TNF-alpha). TNF-alpha stimulates the JNK, ERK, and p38 mitogen-activated protein kinases and the NF-kappaB pathway by recruiting RIP1 and TRAF2 to the TNF receptor 1. Here we showed that Tpl2 activation by TNF-alpha signals depends on the integrity of the Tpl2-interacting proteins RIP1 and TRAF2, which are required for the engagement of the ERK mitogen-activated protein kinase pathway. However, neither RIP1 nor TRAF2 overexpression was sufficient to activate Tpl2 and ERK. We also showed that Tpl2 activation by TNF-alpha depends on a tyrosine kinase activity that is detected in TNF-alpha-stimulated cells. Based on both genetic and biochemical evidence, we concluded that in a variety of cell types, Syk is the tyrosine kinase that plays an important role in the activation of Tpl2 upstream of ERK. These data therefore dissect the TNF receptor 1 proximal events that regulate Tpl2 and ERK and highlight a role for RIP1, TRAF2, and Syk in this pathway.

Increased Plasma Levels of 15-Deoxy Δ Prostaglandin J 2 Are Associated With Good Outcome in Acute Atherothrombotic Ischemic Stroke

Background and Purpose— The 15-deoxy Δ prostaglandin J 2 (15-dPGJ 2 ) is an anti-inflammatory prostaglandin that has been proposed to be the endogenous ligand of peroxisome proliferator-activated receptor-γ (PPARγ), a nuclear receptor that can exert potent anti-inflammatory actions by repressing inflammatory genes when activated. It has been suggested that 15-dPGJ 2 could be beneficial in neurological disorders in which inflammation contributes to cell death such as stroke.

Methods— We investigated the relationship between plasma levels of 15-dPGJ 2 and early neurological deterioration (END), infarct volume, and neurologic outcome in 552 patients with an acute stroke admitted within 24 hours after symptoms onset.

Results— Median [quartiles] plasma 15-dPGJ 2 levels on admission were significantly higher in patients than in controls (60.5 [11.2 to 109.4] versus 5.0 [3.8 to 7.2] pg/mL; P <0.0001). Levels of this prostaglandin were also significantly higher in patients with vascular risk factors (history of hypertension or diabetes) and with atherothrombotic infarcts (113.9 [81.6 to 139.7] pg/mL), than in those with lacunar (58.7 [32.7 to 86.2] pg/mL), cardioembolic (12.1 [6.5 to 39.2] pg/mL), or undetermined origin infarcts (11.4 [5.6 to 24.3] pg/mL) ( P <0.0001). In the subgroup of patients with atherothrombotic infarcts, the adjusted odds ratio of END and poor outcome for 1 pg/mL increase in 15-dPGJ 2 were 0.95 (95% CI, 0.94 to 0.97) and 0.97 (95% CI, 0.96 to 0.98), respectively. In a generalized linear model, by 1 U increase in 15-dPGJ 2 , there was a reduction of 0.47 mL (95% CI, 0.32 to 0.63) in the mean estimated infarct volume.

Conclusions— Increased plasma 15-dPGJ 2 concentration is associated with good early and late neurological outcome and smaller infarct volume. These findings suggest a neuroprotective effect of 15-dPGJ 2 in atherothrombotic ischemic stroke.

Lipopolysaccharide activation of the TPL-2/MEK/extracellular signal-regulated kinase mitogen-activated protein kinase cascade is regulated by IkappaB kinase-induced proteolysis of NF-kappaB1 p105

The MEK kinase TPL-2 (also known as Cot) is required for lipopolysaccharide (LPS) activation of the extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase cascade in macrophages and consequent upregulation of genes involved in innate immune responses. In resting cells, TPL-2 forms a stoichiometric complex with NF-kappaB1 p105, which negatively regulates its MEK kinase activity. Here, it is shown that lipopolysaccharide (LPS) stimulation of primary macrophages causes the release of both long and short forms of TPL-2 from p105 and that TPL-2 MEK kinase activity is restricted to this p105-free pool. Activation of TPL-2, MEK, and ERK by LPS is also demonstrated to require proteasome-mediated proteolysis. p105 is known to be proteolysed by the proteasome following stimulus-induced phosphorylation of two serines in its PEST region by the IkappaB kinase (IKK) complex. Expression of a p105 point mutant, which is not susceptible to signal-induced proteolysis, in RAW264.7 macrophages impairs LPS-induced release of TPL-2 from p105 and its subsequent activation of MEK. Furthermore, expression of wild-type but not mutant p105 reconstitutes LPS stimulation of MEK and ERK phosphorylation in primary NF-kappaB1-deficient macrophages. Consistently, pharmacological blockade of IKK inhibits LPS-induced release of TPL-2 from p105 and TPL-2 activation. These data show that IKK-induced p105 proteolysis is essential for LPS activation of TPL-2, thus revealing a novel function of IKK in the regulation of the ERK MAP kinase cascade.

Phosphorylation of threonine 290 in the activation loop of Tpl2/Cot is necessary but not sufficient for kinase activity

Cot/Tpl2/MAP3K8 is a serine/threonine kinase known to activate the ERK, p38, and JNK kinase pathways. Studies of Tpl2 knock-out mice reveal a clear defect in tumor necrosis factor-alpha production, although very little detail is known about its regulation and the signaling events involved. In the present study we demonstrated that phosphorylation of Cot was required for its maximal activity as phosphatase treatment of Cot decreased its kinase activity. The Cot sequence contains a conserved threonine at position 290 in the activation loop of the kinase domain. We found that mutation of this residue to alanine eliminated its ability to activate MEK/ERK and NF-kappaB pathways, whereas a phosphomimetic mutation to aspartic acid could rescue the ability to activate MEK. Thr-290 was also required for robust autophosphorylation of Cot. Antibody generated to phospho-Thr-290-Cot recognized both wild-type and kinase-dead Cot, suggesting that phosphorylation of Thr-290 did not occur through autophosphorylation but via another kinase. We showed that Cot was constitutively phosphorylated at Thr-290 in transfected human embryonic kidney 293T cells as well as human monocytes as this residue was phosphorylated in unstimulated and lipopolysaccharide-stimulated cells to the same degree. Treatment with herbimycin A inhibited Cot activity in the MEK/ERK pathway but did not inhibit phosphorylation at Thr-290. Together these results showed that phosphorylation of Cot at Thr-290 is necessary but not sufficient for full kinase activity in the MEK/ERK pathway.

Inhibition of activator protein 1 activation, vascular endothelial growth factor, and cyclooxygenase-2 expression by 15-deoxy-Delta12,14-prostaglandin J2 in colon carcinoma cells: evidence for a redox-sensitive peroxisome proliferator-activated receptor-gamma-independent mechanism

Cyclooxygenase (COX)-2 and vascular endothelial growth factor (VEGF) are significantly associated with tumor growth and metastasis. Here we show that phorbol ester-mediated induction of VEGF and COX-2 expression in colon carcinoma cells is inhibited by 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)). This cyclopentenone was able to inhibit activator protein1 (AP-1)-dependent transcriptional induction of COX-2 and VEGF promoters induced by phorbol 12-myristate 13-acetate (PMA) or c-Jun overexpression. 15d-PGJ(2) interfered with at least two steps within the signaling pathway leading to AP-1 activation. First, 15d-PGJ(2) impaired AP-1 binding to a consensus DNA sequence. Second, 15d-PGJ(2) selectively inhibited c-Jun NH(2) terminal kinase (JNK) but not extracellular signal-regulated kinase or p38 mitogen-activated protein kinase activation induced by PMA. This led to a decreased ability of JNK to phosphorylate c-Jun and to activate its transactivating activity. Inhibition of AP-1 activation and COX-2 or VEGF transcriptional induction by this cyclopentenone was found to be independent of peroxisome proliferator-activated receptor-gamma (PPARgamma) because it was not affected by either expression of a dominant negative form of PPARgamma or the use of a PPARgamma antagonist. In contrast, we have found that the effects of 15d-PGJ(2) on AP-1 activation may occur through its ability to induce intracellular oxidative stress. The antioxidant N-acetylcysteine significantly reversed the inhibition by 15d-PGJ(2) of AP-1 activity and COX-2 or VEGF transcriptional induction. Together, these findings provide new insight into the antitumoral properties of 15d-PGJ(2) through the inhibition of the induction of AP-1-dependent genes involved in tumor progression, such as COX-2 and VEGF.