The human cot proto-oncogene encodes two protein serine/threonine kinases with different transforming activities by alternative initiation of translation

Severe fever with thrombocytopenia syndrome phlebovirus non-structural protein activates TPL2 signalling pathway for viral immunopathogenesis

Severe fever with thrombocytopenia syndrome phlebovirus (SFTSV), listed in the World Health Organization Prioritized Pathogens, is an emerging phlebovirus with a high fatality^1-4. Owing to the lack of therapies and vaccines^5,6, there is a pressing need to understand SFTSV pathogenesis. SFSTV non-structural protein (NSs) has been shown to block type I interferon induction^7-11 and facilitate disease progression^12,13. Here, we report that SFTSV-NSs targets the tumour progression locus 2 (TPL2)-A20-binding inhibitor of NF-κB activation 2 (ABIN2)-p105 complex to induce the expression of interleukin-10 (IL-10) for viral pathogenesis. Using a combination of reverse genetics, a TPL2 kinase inhibitor and Tpl2^-/- mice showed that NSs interacted with ABIN2 and promoted TPL2 complex formation and signalling activity, resulting in the marked upregulation of Il10 expression. Whereas SFTSV infection of wild-type mice led to rapid weight loss and death, Tpl2^-/- mice or Il10^-/- mice survived an infection. Furthermore, SFTSV-NSs P₁₀₂A and SFTSV-NSs K₂₁₁R that lost the ability to induce TPL2 signalling and IL-10 production showed drastically reduced pathogenesis. Remarkably, the exogenous administration of recombinant IL-10 effectively rescued the attenuated pathogenic activity of SFTSV-NSs P₁₀₂A, resulting in a lethal infection. Our study demonstrates that SFTSV-NSs targets the TPL2 signalling pathway to induce immune-suppressive IL-10 cytokine production as a means to dampen the host defence and promote viral pathogenesis.

The role of hybrid ubiquitin chains in the MyD88 and other innate immune signalling pathways

The adaptor protein MyD88 is required for signal transmission by toll-like receptors and receptors of the interleukin-1 family of cytokines. MyD88 signalling triggers the formation of Lys63-linked and Met1-linked ubiquitin (K63-Ub, M1-Ub) chains within minutes. The K63-Ub chains, which are formed by the E3 ubiquitin ligases TRAF6, Pellino1 and Pellino2, activate TAK1, the master kinase that switches on mitogen-activated protein (MAP) kinase cascades and initiates activation of the canonical IκB kinase (IKK) complex. The M1-Ub chains, which are formed by the linear ubiquitin chain assembly complex (LUBAC), bind to the NEMO (NF-κB essential modulator) component of the IKK complex and are required for TAK1 to activate IKKs, but not MAP kinases. An essential E3 ligase-independent role of TRAF6 is to recruit LUBAC into the MyD88 signalling complex, where it recognises preformed K63-Ub chains attached to protein components of these complexes, such as IRAK1 (IL-1 receptor-associated kinase), producing ubiquitin chains containing both types of linkage, termed K63/M1-Ub hybrids. The formation of K63/M1-Ub hybrids, which is a feature of several innate immune signalling pathways, permits the co-recruitment of proteins that interact with either K63-Ub or M1-Ub chains. Two likely roles for K63/M1-Ub hybrids are to facilitate the TAK1-dependent activation of the IKK complex and to prevent the hyperactivation of these kinases by recruiting A20 and A20-binding inhibitor of NF-κB1 (ABIN1). These proteins restrict activation of the TAK1 and IKK complexes, probably by competing with them for binding to K63/M1-Ub hybrids. The formation of K63/M1-Ub hybrids may also regulate the rate at which the ubiquitin linkages in these chains are hydrolysed. The IKK-catalysed phosphorylation of some of its substrates permits their recognition by the E3 ligase SCF^βTRCP, leading to their Lys48-linked ubiquitylation and proteasomal degradation. Innate immune signalling is therefore controlled by the formation and destruction of three different types of ubiquitin linkage.

COT phosphorylates prolyl-isomerase Pin1 to promote tumorigenesis in breast cancer

Pin1, a conserved eukaryotic Peptidyl-prolyl cis/trans isomerase, has profound effects on numerous key-signaling molecules, and its deregulation contributes to disease, particularly cancer. Although Pin1-mediated prolyl isomerization is an essential and novel regulatory mechanism for protein phosphorylation, little is known about the upstream signaling pathway(s) that regulates Pin1 activity. Here, we identify MAP3K-related serine-threonine kinase (the gene encoding COT/Tpl2) as a kinase responsible for phosphorylation of Pin1 Ser16. COT interacts with and phosphorylates Pin1 on Ser16. Consequently, Pin1 Ser16 phosphorylation by COT increases cyclin D1 abundance and enhances tumorigenecity of MCF7 cells. In contrast, depletion of COT in MCF7 cells leads to downregulation of Pin1 Ser16 phosphorylation, which subsequently decrease cyclin D1 levels, inhibiting tumorigenecity of MCF7 cells. In a xenograft model, treatment of TKI, a COT inhibitor, and Juglone, a Pin1 inhibitor, abrogates tumor growth. In human breast cancer patients, immunohistochemical staining shows that Pin1 pSer16 levels are positively correlated with COT levels, providing strong evidence for an essential role of the COT/Pin1 axis in conveying oncogenic signals to promote aggressiveness in human breast cancer.

Tumor progression locus 2-dependent oxidative burst drives phosphorylation of extracellular signal-regulated kinase during TLR3 and 9 signaling

Signal transduction via NFκB and MAP kinase cascades is a universal response initiated upon pathogen recognition by Toll-like receptors (TLRs). How activation of these divergent signaling pathways is integrated to dictate distinct immune responses to diverse pathogens is still incompletely understood. Herein, contrary to current perception, we demonstrate that a signaling pathway defined by the inhibitor of κB kinase β (IKKβ), MAP3 kinase tumor progression locus 2 (Tpl2/MAP3K8), and MAP kinase ERK is differentially activated by TLRs. TLRs 2, 4, and 7 directly activate this inflammatory axis, inducing immediate ERK phosphorylation and early TNFα secretion. In addition to TLR adaptor proteins, IKKβ-Tpl2-ERK activation by TLR4 is regulated by the TLR4 co-receptor CD14 and the tyrosine kinase Syk. Signals from TLRs 3 and 9 do not initiate early activation of IKKβ-Tpl2-ERK pathway but instead induce delayed, NADPH-oxidase-dependent ERK phosphorylation and TNFα secretion via autocrine reactive oxygen species signaling. Unexpectedly, Tpl2 is an essential regulator of ROS production during TLR signaling. Overall, our study reveals distinct mechanisms activating a common inflammatory signaling cascade and delineates differences in MyD88-dependent signaling between endosomal TLRs 7 and 9. These findings further confirm the importance of Tpl2 in innate host defense mechanisms and also enhance our understanding of how the immune system tailors pathogen-specific gene expression patterns.

IκB kinase-induced interaction of TPL-2 kinase with 14-3-3 is essential for Toll-like receptor activation of ERK-1 and -2 MAP kinases

The MEK-1/2 kinase TPL-2 is critical for Toll-like receptor activation of the ERK-1/2 MAP kinase pathway during inflammatory responses, but it can transform cells following C-terminal truncation. IκB kinase (IKK) complex phosphorylation of the TPL-2 C terminus regulates full-length TPL-2 activation of ERK-1/2 by a mechanism that has remained obscure. Here, we show that TPL-2 Ser-400 phosphorylation by IKK and TPL-2 Ser-443 autophosphorylation cooperated to trigger TPL-2 association with 14-3-3. Recruitment of 14-3-3 to the phosphorylated C terminus stimulated TPL-2 MEK-1 kinase activity, which was essential for TPL-2 activation of ERK-1/2. The binding of 14-3-3 to TPL-2 was also indispensible for lipopolysaccharide-induced production of tumor necrosis factor by macrophages, which is regulated by TPL-2 independently of ERK-1/2 activation. Our data identify a key step in the activation of TPL-2 signaling and provide a mechanistic insight into how C-terminal deletion triggers the oncogenic potential of TPL-2 by rendering its kinase activity independent of 14-3-3 binding.

TPL2 signalling: from Toll-like receptors-mediated ERK1/ERK2 activation to Cystic Fibrosis lung disease

Cystic Fibrosis (CF) is the most common lethal genetic recessive disorder, with a carrier frequency of 1 in 27 among North American Caucasians. Mitogen-activated protein kinases (MAPKs) and pro-inflammatory cytokines have crucial functions in the innate immune response of epithelial cells. They determine the inflammation status and the host response to pathogenic infections. However, in CF, bacterial-driven inflammation leads to tissue destruction, reduction in lung function and mortality. Recognition of invading pathogens is mediated in part by Toll-like receptors (TLR) activation of intracellular signalling cascade leading to cytokines' synthesis. The protein kinase Tumour Progression Locus 2 (TPL2) is a key molecule in relaying inflammatory stimuli to ERK1/ERK2 MAPKs. In this review, we summarized the recent findings on TPL2 signalling and how TPL2 can contribute to the excessive inflammation found in CF. Pharmacologically targeting this kinase could have a significant benefit for CF patients dealing with chronic bacterial infections such as Pseudomonas aeruginosa. This article is part of a Directed Issue entitled: Cystic Fibrosis: From o-mics to cell biology, physiology, and therapeutic advances.

IκB kinase 2 regulates TPL-2 activation of extracellular signal-regulated kinases 1 and 2 by direct phosphorylation of TPL-2 serine 400

Tumor progression locus 2 (TPL-2) functions as a MEK-1/2 kinase, which is essential for Toll-like receptor 4 (TLR4) activation of extracellular signal-regulated kinase 1 and 2 (ERK-1/2) mitogen-activated protein (MAP) kinases in lipopolysaccharide (LPS)-stimulated macrophages and for inducing the production of the proinflammatory cytokines tumor necrosis factor and interleukin-1β. In unstimulated cells, association of TPL-2 with NF-κB1 p105 prevents TPL-2 phosphorylation of MEK-1/2. LPS stimulation of TPL-2 MEK-1/2 kinase activity requires TPL-2 release from p105. This is triggered by IκB kinase 2 (IKK-2) phosphorylation of the p105 PEST region, which promotes p105 ubiquitination and degradation by the proteasome. LPS activation of ERK-1/2 additionally requires transphosphorylation of TPL-2 on serine 400 in its C terminus, which controls TPL-2 signaling to ERK-1/2 independently of p105. However, the identity of the protein kinase responsible for TPL-2 serine 400 phosphorylation remained unknown. In the present study, we show that TPL-2 serine 400 phosphorylation is mediated by IKK2. The IKK complex therefore regulates two of the key regulatory steps required for TPL-2 activation of ERK-1/2, underlining the close linkage of ERK-1/2 MAP kinase activation to upregulation of NF-κB-dependent transcription.

Coordinate regulation of TPL-2 and NF-κB signaling in macrophages by NF-κB1 p105

The role of IκB kinase (IKK)-induced proteolysis of NF-κB1 p105 in innate immune signaling was investigated using macrophages from Nfkb1(SSAA/SSAA) mice, in which the IKK target serines on p105 are mutated to alanines. We found that the IKK/p105 signaling pathway was essential for TPL-2 kinase activation of extracellular signal-regulated kinase (ERK) mitogen-activate protein (MAP) kinase and modulated the activation of NF-κB. The Nfkb1(SSAA) mutation prevented the agonist-induced release of TPL-2 from its inhibitor p105, which blocked activation of ERK by lipopolysaccharide (LPS), tumor necrosis factor (TNF), CpG, tripalmitoyl-Cys-Ser-Lys (Pam(3)CSK), poly(I · C), flagellin, and R848. The Nfkb1(SSAA) mutation also prevented LPS-induced processing of p105 to p50 and reduced p50 levels, in addition to decreasing the nuclear translocation of RelA and cRel. Reduced p50 in Nfkb1(SSAA/SSAA) macrophages significantly decreased LPS induction of the IκBζ-regulated Il6 and Csf2 genes. LPS upregulation of Il12a and Il12b mRNAs was also impaired although specific blockade of TPL-2 signaling increased expression of these genes at late time points. Activation of TPL-2/ERK signaling by IKK-induced p105 proteolysis, therefore, induced a negative feedback loop to downregulate NF-κB-dependent expression of the proinflammatory cytokine interleukin-12 (IL-12). Unexpectedly, TPL-2 promoted soluble TNF production independently of IKK-induced p105 phosphorylation and its ability to activate ERK, which has important implications for the development of anti-inflammatory drugs targeting TPL-2.

Bleomycin-induced lung injury in mice investigated by MRI: model assessment for target analysis

Magnetic resonance imaging (MRI) has been used to follow the course of bleomycin-induced lung injury in mice and to investigate two knockout mouse lines with the aim of providing potential therapeutic targets. Bleomycin (0.25 mg/kg) was administered intranasally six times, once a day. MRI was carried out on spontaneously breathing animals up to day 70 after bleomycin. Neither cardiac nor respiratory gating was applied during image acquisition. A long lasting response following bleomycin has been detected by MRI in the lungs of male C57BL/6 mice. Histology showed that, from day 14-70 after bleomycin, fibrosis was the predominant component of the injury. Female C57BL/6 mice displayed a smaller response than males. Bleomycin-induced injury was significantly more pronounced in C57BL/6 than in Balb/C mice. MRI and histology demonstrated a protection against bleomycin insult in female heterozygous and male homozygous cancer Osaka thyroid kinase knockout animals. In contrast, no protection was seen in cadherin-11 knockout animals. In summary, MRI can quantify, in spontaneously breathing mice, bleomycin-induced lung injury. With the ability for repetitive measurements in the same animal, the technique is attractive for in vivo target analysis and compound profiling in this murine model.

Regulation and function of TPL-2, an IκB kinase-regulated MAP kinase kinase kinase

The IκB kinase (IKK) complex plays a well-documented role in innate and adaptive immunity. This function has been widely attributed to its role as the central activator of the NF-κB family of transcription factors. However, another important consequence of IKK activation is the regulation of TPL-2, a MEK kinase that is required for activation of ERK-1/2 MAP kinases in myeloid cells following Toll-like receptor and TNF receptor stimulation. In unstimulated cells, TPL-2 is stoichiometrically complexed with the NF-κB inhibitory protein NF-κB1 p105, which blocks TPL-2 access to its substrate MEK, and the ubiquitin-binding protein ABIN-2 (A20-binding inhibitor of NF-κB 2), both of which are required to maintain TPL-2 protein stability. Following agonist stimulation, the IKK complex phosphorylates p105, triggering its K48-linked ubiquitination and degradation by the proteasome. This releases TPL-2 from p105-mediated inhibition, facilitating activation of MEK, in addition to modulating NF-κB activation by liberating associated Rel subunits for translocation into the nucleus. IKK-induced proteolysis of p105, therefore, can directly regulate both NF-κB and ERK MAP kinase activation via NF-κB1 p105. TPL-2 is critical for production of the proinflammatory cytokine TNF during inflammatory responses. Consequently, there has been considerable interest in the pharmaceutical industry to develop selective TPL-2 inhibitors as drugs for the treatment of TNF-dependent inflammatory diseases, such as rheumatoid arthritis and inflammatory bowel disease. This review summarizes our current understanding of the regulation of TPL-2 signaling function, and also the complex positive and negative roles of TPL-2 in immune and inflammatory responses.

Inhibition of Cot1/Tlp2 oncogene in AML cells reduces ERK5 activation and up-regulates p27Kip1 concomitant with enhancement of differentiation and cell cycle arrest induced by silibinin and 1,25-dihydroxyvitamin D(3)

Acute myelogenous leukemia (AML) is a disease characterized by dysregulated cell proliferation associated with impaired cell differentiation, and current treatment regimens rarely save the patient. Thus, new mechanism-based approaches are needed to improve prognosis of this disease. We have investigated in preclinical studies the potential anti-leukemia use of the plant-derived polyphenol Silibinin (SIL) in combination with 1,25-dihydroxyvitamin D3 (1,25D). Although most of the leukemic blasts ex vivo responded by differentiation to treatment with this combination, the reasons for the absence of SIL-1,25D synergy in some cases were unclear. Here we report that failure of SIL to enhance the action of 1,25D is likely due to the SIL-induced increase in the activity of differentiation-antagonizing cell components, such as ERK5. This kinase is under the control of Cot1/Tlp2, and inhibition of Cot1 activity by a specific pharmacological inhibitor 4-(3-chloro-4-fluorophenylamino)-6-(pyridin-3-yl-methylamino-3-cyano-[1-7]-naphthyridine, or by Cot1 siRNA, increases the differentiation by SIL/1,25D combinations. Conversely, over-expression of a Cot1 construct increases the cellular levels of P-ERK5, and SIL/1,25D-induced differentiation and cell cycle arrest are diminished. It appears that reduction in ERK5 activity by inhibition of Cot1 allows SIL to augment the expression of 1,25D-induced differentiation promoting factors and cell cycle regulators such as p27 (Kip1) , which leads to cell cycle arrest. This study shows that in some cell contexts SIL/1,25D can promote expression of both differentiation-promoting and differentiation-inhibiting genes, and that the latter can be neutralized by a highly specific pharmacological inhibitor, suggesting a potential for supplementing treatment of AML with this combination of agents.

Tpl2 kinase is upregulated in adipose tissue in obesity and may mediate interleukin-1beta and tumor necrosis factor-{alpha} effects on extracellular signal-regulated kinase activation and lipolysis

OBJECTIVE

Activation of extracellular signal-regulated kinase-(ERK)-1/2 by cytokines in adipocytes is involved in the alterations of adipose tissue functions participating in insulin resistance. This study aims at identifying proteins regulating ERK1/2 activity, specifically in response to inflammatory cytokines, to provide new insights into mechanisms leading to abnormal adipose tissue function.

RESEARCH DESIGN AND METHODS

Kinase activities were inhibited with pharmacological inhibitors or siRNA. Lipolysis was monitored through glycerol production. Gene expression in adipocytes and adipose tissue of obese mice and subjects was measured by real-time PCR.

RESULTS

IkappaB kinase-(IKK)-beta inhibition prevented mitogen-activated protein (MAP) kinase kinase (MEK)/ERK1/2 activation in response to interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha but not insulin in 3T3-L1 and human adipocytes, suggesting that IKKbeta regulated a MAP kinase kinase kinase (MAP3K) involved in ERK1/2 activation induced by inflammatory cytokines. We show that the MAP3K8 called Tpl2 was expressed in adipocytes and that IL-1beta and TNF-alpha activated Tpl2 and regulated its expression through an IKKbeta pathway. Pharmacological inhibition or silencing of Tpl2 prevented MEK/ERK1/2 activation by these cytokines but not by insulin, demonstrating its involvement in ERK1/2 activation specifically in response to inflammatory stimuli. Importantly, Tpl2 was implicated in cytokine-induced lipolysis and in insulin receptor substrate-1 serine phosphorylation. Tpl2 mRNA expression was upregulated in adipose tissue of obese mice and patients and correlated with TNF-alpha expression.

CONCLUSIONS

Tpl2 is selectively involved in inflammatory cytokine-induced ERK1/2 activation in adipocytes and is implicated in their deleterious effects on adipocyte functions. The deregulated expression of Tpl2 in adipose tissue suggests that Tpl2 may be a new actor in adipose tissue dysfunction in obesity.

IRAK1-independent pathways required for the interleukin-1-stimulated activation of the Tpl2 catalytic subunit and its dissociation from ABIN2

The protein kinase Tpl2 (tumour progression locus 2) is activated by LPS (lipopolysaccharide), TNFalpha (tumour necrosis factor alpha) and IL (interleukin)-1. Activation of the native Tpl2 complex by these agonists requires the IKKbeta {IkappaB [inhibitor of NF-kappaB (nuclear factor kappaB)] kinase beta}-catalysed phosphorylation of the p105/NF-kappaB1 subunit and is accompanied by the release of the catalytic subunit from both p105/NF-kappaB1 and another subunit ABIN2 (A20-binding inhibitor of NF-kappaB 2). In the present study we report that IL-1 activates the transfected Tpl2 catalytic subunit in an HEK (human embryonic kidney)-293 cell line that stably expresses the IL-1R (IL-1 receptor), but does not express the protein kinase IRAK1 (IL-1R-associated kinase). In these cells IL-1 does not activate IKKbeta or induce the phosphorylation of p105/NF-kappaB1, and nor does the IKKbeta inhibitor PS1145 prevent the IL-1-induced activation of transfected Tpl2. However, the IL-1-stimulated activation of transfected Tpl2 in IRAK1-null cells or activation of the endogenous Tpl2 complex in IRAK1-expressing cells is suppressed by the protein kinase inhibitor PP2 by a mechanism that does not involve inhibition of Src family protein tyrosine kinases. The IL-1-stimulated activation of transfected Tpl2 is accompanied by its phosphorylation at Thr290 and Ser400 and by enhanced phosphorylation of Ser62, which we demonstrate are autophosphorylation events catalysed by Tpl2 itself. We further show that IL-1 triggers the dissociation of Tpl2 from co-transfected ABIN2 in IRAK1-null IL-1R cells, which is not suppressed by PP2 or by the inhibition of Tpl2 or IKKbeta. These studies identify two new signalling events involved in activation of the native Tpl2 complex by IL-1. First, the IRAK1-, IKKbeta- and PP2-independent dissociation of Tpl2 from ABIN2; secondly, the IRAK1- and IKKbeta-independent, but PP2-sensitive, activation of the Tpl2 catalytic subunit.

Identification of a selective thieno[2,3-c]pyridine inhibitor of COT kinase and TNF-alpha production

COT (Tpl2 in mice) is a serine/threonine MAP3 kinase that regulates production of TNF-alpha and other pro-inflammatory cytokines such as IL-1beta via the ERK/MAP kinase pathway. As TNF-alpha and IL-1beta are clinically validated targets for therapeutic intervention in rheumatoid arthritis (RA), blocking COT provides a potential avenue for amelioration of disease. Herein we describe identification of a cellular active selective small molecule inhibitor of COT kinase.

BCL11B enhances TCR/CD28-triggered NF-kappaB activation through up-regulation of Cot kinase gene expression in T-lymphocytes

BCL11B is a transcriptional regulator with an important role in T-cell development and leukaemogenesis. We demonstrated recently that BCL11B controls expression from the IL (interleukin)-2 promoter through direct binding to the US1 (upstream site 1). In the present study, we provide evidence that BCL11B also participates in the activation of IL-2 gene expression by enhancing NF-kappaB (nuclear factor kappaB) activity in the context of TCR (T-cell receptor)/CD28-triggered T-cell activation. Enhanced NF-kappaB activation is not a consequence of BCL11B binding to the NF-kappaB response elements or association with the NF-kappaB-DNA complexes, but rather the result of higher translocation of NF-kappaB to the nucleus caused by enhanced degradation of IkappaB (inhibitor of NF-kappaB). The enhanced IkappaB degradation in cells with increased levels of BCL11B was specific for T-cells activated through the TCR, but not for cells activated through TNFalpha (tumour necrosis factor alpha) or UV light, and was caused by increased activity of IkappaB kinase, as indicated by its increase in phosphorylation. As BCL11B is a transcription factor, we investigated whether the expression of genes upstream of IkappaB kinase in the TCR/CD28 signalling pathway was affected by increased BCL11B expression, and found that Cot (cancer Osaka thyroid oncogene) kinase mRNA levels were elevated. Cot kinase is known to promote enhanced IkappaB kinase activity, which results in the phosphorylation and degradation of IkappaB and activation of NF-kappaB. The implied involvement of Cot kinase in BCL11B-mediated NF-kappaB activation in response to TCR activation is supported by the fact that a Cot kinase dominant-negative mutant or Cot kinase siRNA (small interfering RNA) knockdown blocked BCL11B-mediated NF-kappaB activation. In support of our observations, in the present study we report that BCL11B enhances the expression of several other NF-kappaB target genes, in addition to IL-2. In addition, we provide evidence that BCL11B associates with intron 2 of the Cot kinase gene to regulate its expression.

Prostaglandin E receptor type 4-associated protein interacts directly with NF-kappaB1 and attenuates macrophage activation

Macrophage activation participates pivotally in the pathophysiology of chronic inflammatory diseases, including atherosclerosis. Through the receptor EP4, prostaglandin E(2) (PGE(2)) exerts an anti-inflammatory action in macrophages, suppressing stimulus-induced expression of certain proinflammatory genes, including chemokines. We recently identified a novel EP4 receptor-associated protein (EPRAP), whose function in PGE(2)-mediated anti-inflammation remains undefined. Here we demonstrate that PGE(2) pretreatment selectively inhibits lipopolysaccharide (LPS)-induced nuclear factor kappaB1 (NF-kappaB1) p105 phosphorylation and degradation in mouse bone marrow-derived macrophages through EP4-dependent mechanisms. Similarly, directed EPRAP expression in RAW264.7 cells suppresses LPS-induced p105 phosphorylation and degradation, and subsequent activation of mitogen-activated protein kinase kinase 1/2. Forced expression of EPRAP also inhibits NF-kappaB activation induced by various proinflammatory stimuli in a concentration-dependent manner. In co-transfected cells, EPRAP, which contains multiple ankyrin repeat motifs, directly interacts with NF-kappaB1 p105/p50 and forms a complex with EP4. In EP4-overexpressing cells, PGE(2) enhances the protective action of EPRAP against stimulus-induced p105 phosphorylation, whereas EPRAP silencing in RAW264.7 cells impairs the inhibitory effect of PGE(2)-EP4 signaling on LPS-induced p105 phosphorylation. Additionally, EPRAP knockdown as well as deficiency of NF-kappaB1 in macrophages attenuates the inhibitory effect of PGE(2) on LPS-induced MIP-1beta production. Thus, PGE(2)-EP4 signaling augments NF-kappaB1 p105 protein stability through EPRAP after proinflammatory stimulation, limiting macrophage activation.

Phosphorylation of TPL-2 on serine 400 is essential for lipopolysaccharide activation of extracellular signal-regulated kinase in macrophages

Tumor progression locus 2 (TPL-2) kinase is essential for Toll-like receptor 4 activation of the mitogen-activated protein kinase extracellular signal-regulated kinase (ERK) and for upregulation of the inflammatory cytokine tumor necrosis factor (TNF) in lipopolysaccharide (LPS)-stimulated macrophages. LPS activation of ERK requires TPL-2 release from associated NF-kappaB1 p105, which blocks TPL-2 access to its substrate, the ERK kinase MEK. Here we demonstrate that TPL-2 activity is also regulated independently of p105, since LPS stimulation was still needed for TPL-2-dependent activation of ERK in Nfkb1(-/-) macrophages. In wild-type macrophages, LPS induced the rapid phosphorylation of serine (S) 400 in the TPL-2 C-terminal tail. Mutation of this conserved residue to alanine (A) blocked the ability of retrovirally expressed TPL-2 to induce the activation of ERK in LPS-stimulated Nfkb1(-/-) macrophages. TPL-2(S400A) expression also failed to reconstitute LPS activation of ERK and induction of TNF in Map3k8(-/-) macrophages, which lack endogenous TPL-2. Consistently, the S400A mutation was found to block LPS stimulation of TPL-2 MEK kinase activity. Thus, induction of TPL-2 MEK kinase activity by LPS stimulation of macrophages requires TPL-2 phosphorylation on S400, in addition to its release from NF-kappaB1 p105. Oncogenic C-terminal truncations of TPL-2 that remove S400 could promote its transforming potential by eliminating this critical control step.

Epigenetic regulation of microRNA-370 by interleukin-6 in malignant human cholangiocytes

Interleukin-6 (IL-6) is overexpressed and contributes to tumor cell growth in cholangiocarcinoma. Enforced IL-6 production can alter the expression of specific microRNAs (miRNAs) involved in tumor growth, and moreover can modulate expression of methylation-dependent genes. Thus, we assessed the methylation-dependent regulation of miRNA expression in human malignant cholangiocytes stably transfected to overexpress IL-6. The expression of the methyltransferases DNA methyltransferase enzyme-1 and HASJ4442 was increased by IL-6 overexpression, but was decreased by the methylation inhibitor 5-aza-2'-deoxycytidine (5-aza-CdR). Expression profiling identified seven miRNAs that were significantly downregulated by IL-6 overexpression (<0.4-fold) and upregulated (>2-fold) by 5-aza-CdR. One of these, miR-370, is embedded in a CpG island. Although 5-aza-CdR increased miR-370 expression by 2.1-fold in malignant cells, the expression in nonmalignant cells was unchanged. The oncogene mitogen-activated protein kinase kinase kinase 8 (MAP3K8) was identified as a target of miR-370, and its expression was decreased by 5-aza-CdR in cholangiocarcinoma cells. Overexpression of IL-6 reduced miR-370 expression and reinstated MAP3K8 expression in vitro as well as in tumor cell xenografts in vivo. Thus, IL-6 may contribute to tumor growth by modulation of expression of selected miRNAs, such as miR-370. These studies define a mechanism by which inflammation-associated cytokines can epigenetically modulate gene expression and directly contribute to tumor biology.

ABIN-2 is required for optimal activation of Erk MAP kinase in innate immune responses

The TPL-2 MEK kinase is essential for activation of the Erk MAP kinase pathway during innate immune responses. TPL-2 is found in complex with ABIN-2 (A20-binding inhibitor of NF-kappaB 2). Here, using antigen-presenting cells from ABIN-2-deficient mice, we show that ABIN-2 was required for optimal activation of Erk induced by receptors that signal via TPL-2, including Toll-like receptor 4 and tumor necrosis factor receptor 1 in macrophages, and CD40 in B cells. ABIN-2 was necessary for the maintenance of TPL-2 protein stability. In contrast, ABIN-2 deficiency did not affect agonist-induced regulation of transcription factor NF-kappaB. Stimulation of ABIN-2-deficient macrophages via Toll-like receptor 4 showed that different thresholds of Erk signaling were required for optimal induction of tumor necrosis factor and interleukin 1beta. Thus, ABIN-2 acts to positively regulate the Erk signaling potential by stabilizing TPL-2.

cDNA microarray analysis of isogenic paclitaxel- and doxorubicin-resistant breast tumor cell lines reveals distinct drug-specific genetic signatures of resistance

cDNA microarray analysis is a highly useful tool for the classification of tumors and for prediction of patient prognosis to specific cancers based on this classification. However, to date, there is little evidence that microarray approaches can be used to reliably predict patient response to specific chemotherapy drugs or regimens. This is likely due to an inability to differentiate between genes affecting patient prognosis and genes that play a role in response to specific drugs. Thus, it would be highly useful to identify genes whose expression correlates with tumor cell sensitivity to specific chemotherapy agents in a drug-specific manner. Using cDNA microarray analysis of wildtype MCF-7 breast tumor cells and isogenic paclitaxel-resistant (MCF-7(TAX)) or doxorubicin-resistant (MCF-7(DOX)) derivative cell lines, we have uncovered drug-specific changes in gene expression that accompany the establishment of paclitaxel or doxorubicin resistance. These changes in gene expression were confirmed by quantitative reverse transcription polymerase chain reaction and immunoblotting experiments, with a confirmation rate of approximately 91-95%. The genes identified may prove highly useful for prediction of response to paclitaxel or doxorubicin in patients with breast cancer. To our knowledge this is the first report of drug-specific genetic signatures of resistance to paclitaxel or doxorubicin, based on a comparison of gene expression between isogenic wildtype and drug-resistant tumor cell lines. Moreover, this study provides significant insight into the wide variety of mechanisms through which resistance to these agents may be acquired in breast cancer.

Comparative analysis of various in vitro COT kinase assay formats and their applications in inhibitor identification and characterization

Cancer osaka thyroid (COT) is a member of the mitogen-activated protein kinase kinase kinase family of enzymes and plays a pivotal role in tumor necrosis factor-alpha production in macrophages. Consequently, COT is considered to be a promising target for antiinflammatory drug discovery. We describe here the development of in vitro COT assays in several formats and the advantages and disadvantages of each. A cascade assay requires very small amounts of enzyme and can provide a useful tool for high-throughput screening, but it is not desirable for compound mechanistic studies due to complicated kinetics. Direct assays are superior to cascade assays and are suitable for both compound screening and mechanistic studies. Among the direct assays, the homogeneous time-resolved fluorescence (HTRF) format is preferred over the radiometric format due to the robustness, throughput, and ease of use of the HTRF format. When the physiological protein substrate MEK1 (MAP/Erk kinase 1) was used to determine inhibitor potencies, false positives were observed due to compound interference by binding to MEK1. Using a MEK1 peptide substrate, these false positives were eliminated. In addition, we describe a simple method to study the ATP competitiveness of compounds. The knowledge gained through our studies with COT, and the methods described for our assays and compound mechanistic studies, can be readily applied to other kinase targets.

Purification and kinetic characterization of recombinant human mitogen-activated protein kinase kinase kinase COT and the complexes with its cellular partner NF-kappa B1 p105

Cancer osaka thyroid (COT), a human MAP 3 K, is essential for lipopolysaccharide activation of the Erk MAPK cascade in macrophages. COT 30--467 is insoluble, whereas low levels of COT 30--397 can be expressed, but this protein is unstable. However, both COT 30--467 and COT 30--397 are expressed in a soluble and stable form when produced in complex with the C-terminal half of p105. The k(cat) of COT 30--397 is reduced approximately 47--fold in the COT 30--467/p105 Delta N complex. COT prefers Mn(2+) to Mg(2+) as the ATP metal cofactor, exhibiting an unusually high ATP K(m) in the presence of Mg(2+). When using Mn(2+) as the cofactor, the ATP K(m) is reduced to a level typical of most kinases. In contrast, the binding affinity of COT for its other substrate MEK is cofactor independent. Our results using purified proteins indicate that p105 binding improves COT solubility and stability while down-regulating kinase activity, consistent with cellular data showing that p105 functions as an inhibitor of COT.

Phosphorylation at Thr-290 regulates Tpl2 binding to NF-kappaB1/p105 and Tpl2 activation and degradation by lipopolysaccharide

The serine-threonine protein kinase encoded by the Tpl2 protooncogene transduces Toll-like and death receptor signals in a variety of cell types and plays an important role in innate immunity and inflammation. Differential translational initiation of the Tpl2 mRNA gives rise to 58-kDa (p58) and 52-kDa (p52) isoforms. In unstimulated cells, both isoforms are stabilized and inactivated by stoichiometric binding to NF-kappaB1/p105. After lipopolysaccharide or TNF-alpha stimulation, p58 is released from p105 preferentially relative to p52. The released p58 is active but unstable and undergoes rapid degradation via the proteasome. Recent studies revealed that Tpl2 undergoes phosphorylation at Thr-290 and that phosphorylation at this site is required for activation. Here, we present evidence showing that it is the p58 isoform that is preferentially phosphorylated at Thr-290 and that phosphorylation is more efficient when p58 is complexed to p52. Because p58 is preferentially released from p105 after stimulation, we examined whether Tpl2 phosphorylation at this site controls the dissociation of the two proteins in response to external signals and the subsequent events leading to the activation of Tpl2. The results showed that lipopolysaccharide-induced Tpl2 phosphorylation at Thr-290 in macrophages promotes the release of Tpl2 from p105, contributes to the enzymatic activation of the Tpl2 kinase, and is required for the degradation of Tpl2 via the proteasome.

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.

Mutational activation of the MAP3K8 protooncogene in lung cancer

The MAP3K8 protooncogene (Cot/Tpl-2) activates the MAP kinase, SAP kinase, and NF-kappaB signaling pathways. MAP3K8 mutations occur in the rat homologue, but activating mutations have yet to be identified in primary human tumors. We have identified MAP3K8 as a transforming gene from a human lung adenocarcinoma and characterized a 3' end mutation in the cDNA. In addition, we confirmed that the mutation occurs in the original lung tumor, and we screened a series of lung cancer cell lines to determine whether the MAP3K8 mutation is a common occurrence in lung tumorigenesis. The oncogene was isolated and identified with the NIH3T3 nude mouse tumorigenicity assay and cDNA library screening. The gene was analyzed by polymerase chain reaction (PCR), single-strand conformational polymorphism (SSCP), and 3'RACE for mutations. The mutation was localized to MAP3K8 exon 8 and confirmed in the primary tumor DNA. Both wild-type and mutant MAP3K8 cDNAs transformed NIH3T3 cells, but the transforming activity of the mutant was much greater than that of the wild type. PCR-SSCP screening of cell line cDNAs identified one silent polymorphism in cell line SK-LU-1. Although we were unable to find additional activating mutations, these data support a role for MAP3K8 activity in cellular transformation, but suggest that mutational activation of the gene is a rare event in lung cancer.

Genetic complementation of cytokine signaling identifies central role of kinases in hematopoietic cell proliferation

Molecular evidence suggests a multistep process in the development of acute leukemia. Since inappropriate activation of cytokine signaling cascades is a recurring theme in human leukemia, we performed expression screens to identify genes that transform cytokine-dependent cells. Using retroviral cDNA libraries derived from peripheral blood mononuclear cells of patients with myeloproliferative disorders, we isolated numerous genes that genetically complement cytokine requirements for proliferation of BaF/3 and TF-1 cells. The majority of recovered genes represent members of the kinase family, including several previously linked to leukemogenesis. Our unbiased screen highlights the central role of kinase activation in hematopoietic cell proliferation and identifies a number of potential leukemic oncoproteins.

NF-kappaB1 p105 negatively regulates TPL-2 MEK kinase activity

Activation of the oncogenic potential of the MEK kinase TPL-2 (Cot) requires deletion of its C terminus. This mutation also weakens the interaction of TPL-2 with NF-kappaB1 p105 in vitro, although it is unclear whether this is important for the activation of TPL-2 oncogenicity. It is demonstrated here that TPL-2 stability in vivo relies on its high-affinity, stoichiometric association with NF-kappaB1 p105. Formation of this complex occurs as a result of two distinct interactions. The TPL-2 C terminus binds to a region encompassing residues 497 to 534 of p105, whereas the TPL-2 kinase domain interacts with the p105 death domain. Binding to the p105 death domain inhibits TPL-2 MEK kinase activity in vitro, and this inhibition is significantly augmented by concomitant interaction of the TPL-2 C terminus with p105. In cotransfected cells, both interactions are required for inhibition of TPL-2 MEK kinase activity and, consequently, the catalytic activity of a C-terminally truncated oncogenic mutant of TPL-2 is not affected by p105. Thus, in addition to its role as a precursor for p50 and cytoplasmic inhibitor of NF-kappaB, p105 is a negative regulator of TPL-2. Insensitivity of C-terminally truncated TPL-2 to this regulatory mechanism is likely to contribute to its ability to transform cells.

Microarray analysis of lipopolysaccharide-treated human neutrophils

Neutrophils respond to infection by degranulation, release of reactive oxygen intermediates, and secretion of chemokines and cytokines; however, activation of neutrophil transcriptional machinery has been little appreciated. Recent findings suggest that gene expression may represent an additional neutrophil function after exposure to lipopolysaccharide (LPS). We performed microarray gene expression analysis of 4,608 mostly nonredundant genes on LPS-stimulated human neutrophils. Analysis of three donors indicated some variability but also a high degree of reproducibility in gene expression. Twenty-eight verifiable, distinct genes were induced by 4 h of LPS treatment, and 13 genes were repressed. Genes other than cytokines and chemokines are regulated; interestingly, genes involved in cell growth regulation and survival, transcriptional regulation, and interferon response are among those induced, whereas genes involved in cytoskeletal regulation are predominantly repressed. In addition, we identified monocyte chemoattractant protein-1 as a novel LPS-regulated chemokine in neutrophils. Included in these lists are five clones with no defined function. These data suggest molecular mechanisms by which neutrophils respond to infection and indicate that the transcriptional potential of neutrophils is greater than previously thought.

T lymphocytes constitutively produce an interferonlike cytokine limitin characterized as a heat- and acid-stable and heparin-binding glycoprotein

Several reports have described "multifunctional" eukaryotic mRNAs producing more than one protein through alternative translational initiation at multiple AUG codons. There are 2 such codons in the 5' region of our recently cloned limitin gene where 2 open reading frames overlap by 34 nucleotides. The deduced protein translated from the first ATG contains 33 amino acids, lacks a signal peptide, and has no obvious effects on the transfected 293T cells. We found that the second ATG is more effective as a translational initiation site than the first ATG and yields a secreted protein of 182 amino acids with the same activity as products made with full-length limitin cDNA. Immunohistochemical and reverse transcription-polymerase chain reaction analysis revealed that the longer limitin protein is produced by mature T lymphocytes in spleen and thymus as well as by bronchial epithelial and salivary duct cells in healthy mice. Properties of recombinant limitin were determined, revealing it to be a serologically distinct, heat- and acid-stable, heparin-binding glycoprotein with the potential for dimerization. Although the longer limitin protein is structurally and characteristically related to type I interferons, its production is uniquely regulated by translation as well as transcription.

Use of cDNA microarrays to analyze dioxin-induced changes in human liver gene expression

One mechanism by which cells adapt to environmental changes is by altering gene expression. Here, we have used cDNA microarrays to identify genes whose expression is altered by exposure to the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The goal of our study was to enhance our understanding of toxicity mediated through the pathway by which TCDD stimulates gene expression. To model this toxicity response, we exposed human hepatoma (HepG2) cells to TCDD (10 nM for 18 h) and analyzed mRNA by two-color fluorescent hybridization to cDNA sequences immobilized on glass microscope slides (2.5 x 7.5 cm) covering a surface area of 2.25 cm(2). We analyzed approximately one-third of the genes expressed in HepG2 cells and found that TCDD up- or down-regulates 112 genes two-fold or more. Most changes are relatively subtle (two- to four-fold). We verified the regulation of protooncogene cot, XMP, and human enhancer of filamentation-1 (HEF1), genes involved in cellular proliferation, as well as metallothionein, plasminogen activator inhibitor (PAI1), and HM74, genes involved in cellular signaling and regeneration. To characterize the response in more detail, we performed time-course, dose-dependence studies, and cycloheximide experiments. We observed direct and indirect responses to TCDD implying that adaptation to TCDD (and other related environmental stimuli) is substantially more complex than we previously realized.

Cot kinase induces cyclooxygenase-2 expression in T cells through activation of the nuclear factor of activated T cells

Cyclooxygenase-2 (COX-2) is induced in human T lymphocytes upon T cell receptor triggering. Here we report that Cot kinase, a mitogen-activated protein kinase kinase kinase involved in T cell activation, up-regulates COX-2 gene expression in Jurkat T cells. Induction of COX-2 promoter activity by Cot kinase occurred mainly through activation of the nuclear factor of activated T cells (NFAT). Mutation of the distal (-105/-97) and proximal (-76/-61) NFAT response elements in the COX-2 promoter abolished the activation induced by Cot kinase. Even more, coexpression of a dominant negative version of NFAT inhibited Cot kinase-mediated COX-2 promoter activation, whereas cotransfection of a constitutively active version of the calcium-dependent phosphatase calcineurin synergizes with Cot kinase in the up-regulation of COX-2 promoter-driven transcription. Strikingly, Cot kinase increased transactivation mediated by a GAL4-NFAT fusion protein containing the N-terminal transactivation domain of NFATp. In contrast to phorbol ester plus calcium ionophore A23187, Cot kinase increases both COX-2 promoter activity and NFAT-mediated transactivation in a cyclosporin A-independent manner. These data indicate that Cot kinase up-regulates COX-2 promoter-driven transcription through the NFAT response elements, being the Cot kinase-induced NFAT-dependent transactivation presumably implicated in this up-regulation.

Identification of an internal gene to the human Galectin-3 gene with two different overlapping reading frames that do not encode Galectin-3

We previously reported that alternative transcripts were initiated within the second intron of the human Galectin-3 gene (LGALS3). We now demonstrate that these transcripts arise from an internal gene embedded within LGALS3 and named galig (Galectin-3 internal gene). Tissue-specific expression of galig was assayed by screening of several human tissues. Contrary to LGALS3, galig appears to be tightly regulated and principally activated in leukocytes from peripheral blood. Cloning and characterization of galig transcripts revealed that they contain two out-of-frame overlapping open-reading frames (ORFs). Transfection of expression vectors encoding enhanced green fluorescent protein (EGFP) chimeras indicated that both ORFs could be translated in proteins unrelated to Galectin-3. The ORF1 polypeptide targets EGFP to cytosol and nucleus whereas ORF2 targets EGFP to mitochondria. These results revealed the exceptional genetic organization of the LGALS3 locus.

COT kinase proto-oncogene expression in T cells: implication of the JNK/SAPK signal transduction pathway in COT promoter activation

COT/Tpl-2 proto-oncogene encodes a serine/threonine kinase implicated in cellular activation. In this study we have identified the human COT gene promoter region and three different human COT transcripts. These transcripts, with the same initiation site, display heterogeneity in their 5' untranslated regions and in their subcellular localization. Activation of Jurkat T cells with either calcium ionophore or alphaCD3 and a phorbol ester increases the levels of the different COT transcripts. Analysis of the 5' flanking region of the human COT gene reveals a unique transcription initiation site and a TATA element 20 nucleotides upstream. Transient expression of COT promoter constructs containing a reporter gene indicates that the transcriptional activity of the 5' flanking region of the COT gene is regulated by T cell-activating signals. Cotransfection of a dominant negative version of SEK-2 abolishes the inducible transcriptional activity of COT promoter, indicating that the inducible expression of the COT gene by T cell activating signals is mediated by the JNK/SAPK signal transduction pathway. All these data indicate stringent regulation of COT kinase proto-oncogene expression.

Cot protooncoprotein activates the dual specificity kinases MEK-1 and SEK-1 and induces differentiation of PC12 cells

Mitogenic signals initiated at the plasma membrane are transmitted to the nucleus through an intricate signalling network. We identified the protooncoprotein Cot as a new component of mitogenic signalling cascades, which activates both the classic cytoplasmic cascade and the SAPK stress pathway. Wildtype and activated Cot phosphorylate and activate MEK-1 and SEK-1 in vitro. These findings are consistent with the sequence homology between Cot and the rat gene Tpl-2. Expression of oncogenic Cot in 293, NIH3T3 and PC12 cells leads to in vivo phosphorylation of endogenous c-Jun and Erk-1/2 suggesting that the serine/threonine kinase Cot functions beside c-Raf-1 and Mos as a direct activator of MEK-1. Furthermore, we have examined the biological effects of Cot on the phenotype of fibroblastic and neuronal cells. In order to test a potential c-Raf-1 dependency of Cot transformation, the effect of oncogenic Cot on Raf revertant CHP25 cells was determined. Cot could restore the transformed phenotype indicating that Cot transformation is not dependent on active c-Raf-1 and that Cot is not a target for the putative Raf inhibitor, which is presumably active in the revertant cell line. Expression of oncogenic versions of Raf as well as v-Mos leads to differentiation of PC12 cells. Cot also induces neurite outgrowth of PC12 cells. These data are consistent with the role of Cot in the classic mitogenic cascade and suggest that the simultaneously activated JNK/SAPK stress pathway has no antagonistic effects in this context.

TPL-2 kinase regulates the proteolysis of the NF-kappaB-inhibitory protein NF-kappaB1 p105

The transcription factor NF-kappaB is composed of homodimeric and heterodimeric complexes of Rel/NF-kappaB-family polypeptides, which include Rel-A, c-Rel, Rel-B, NF-kappaB/p50 and NF-kappaB2/p52 . The NF-kappaB1 gene encodes a larger precursor protein, p105, from which p50 is produced constitutively by proteasome-mediated removal of the p105 carboxy terminus. The p105 precursor also acts as an NFkappaB-inhibitory protein, retaining associated p50, c-Rel and Rel-A proteins in the cytoplasm through its carboxy terminus. Following cell stimulation by agonists, p105 is proteolysed more rapidly and released Rel subunits translocate into the nucleus. Here we show that TPL-2 , which is homologous to MAP-kinase-kinase kinases in its catalytic domain, forms a complex with the carboxy terminus of p105. TPL-2 was originally identified, in a carboxy-terminal-deleted form, as an oncoprotein in rats and is more than 90% identical to the human oncoprotein COT. Expression of TPL-2 results in phosphorylation and increased degradation of p105 while maintaining p50 production. This releases associated Rel subunits or p50-Rel heterodimers to generate active nuclear NF-kappaB. Furthermore, kinase-inactive TPL-2 blocks the degradation of p105 induced by tumour-necrosis factor-alpha. TPL-2 is therefore a component of a new signalling pathway that controls proteolysis of NF-kappaB1 p105.

Mitogen-activated protein kinase: conservation of a three-kinase module from yeast to human

Mitogen-activated protein kinases (MAPK) are serine-threonine protein kinases that are activated by diverse stimuli ranging from cytokines, growth factors, neurotransmitters, hormones, cellular stress, and cell adherence. Mitogen-activated protein kinases are expressed in all eukaryotic cells. The basic assembly of MAPK pathways is a three-component module conserved from yeast to humans. The MAPK module includes three kinases that establish a sequential activation pathway comprising a MAPK kinase kinase (MKKK), MAPK kinase (MKK), and MAPK. Currently, there have been 14 MKKK, 7 MKK, and 12 MAPK identified in mammalian cells. The mammalian MAPK can be subdivided into five families: MAPKerk1/2, MAPKp38, MAPKjnk, MAPKerk3/4, and MAPKerk5. Each MAPK family has distinct biological functions. In Saccharomyces cerevisiae, there are five MAPK pathways involved in mating, cell wall remodelling, nutrient deprivation, and responses to stress stimuli such as osmolarity changes. Component members of the yeast pathways have conserved counterparts in mammalian cells. The number of different MKKK in MAPK modules allows for the diversity of inputs capable of activating MAPK pathways. In this review, we define all known MAPK module kinases from yeast to humans, what is known about their regulation, defined MAPK substrates, and the function of MAPK in cell physiology.

Characterization of a Low Molecular Weight Isoform of IL-1 Receptor Antagonist

IL-1R antagonist (IL-1Ra) exists in two well-characterized forms, 17-kDa secretory IL-1Ra (sIL-1Ra) and 18-kDa intracellular IL-1Ra (icIL-1Ra), that arise by alternative transcription of the same IL-1Ra gene. A third, lower molecular mass form (∼16 kDa) was detected by immunoblot within lysates of a variety of cells, including human monocytes and myelomonocytic cell lines. The 16-kDa isoform was designated icIL-1RaII, and the previously established 18-kDa form was designated icIL-1RaI. Intracellular IL-1RaII bound type I IL-1R up to fivefold less avidly than did sIL-1Ra and icIL-1RaI. Microsequencing of cyanogen bromide fragments of purified icIL-1RaII provided evidence consistent with initiation of protein translation at the second start site in either IL-1Ra mRNA. The results of site-directed mutation experiments established that icIL-1RaII could be derived by alternative translation initiation. In vitro transcription and translation of intact sIL-1Ra cDNA in rabbit reticulocyte lysates led to both pro-sIL-1Ra and icIL-1RaII proteins, whereas transcription and translation of icIL-1RaI cDNA produced both icIL-1RaI and icIL-1RaII proteins. Mutation of the first 5′ ATG in sIL-1Ra cDNA led to translation of only icIL-1RaII, while only sIL-1Ra was observed after mutation of the second ATG. These results indicate that icIL-1RaII is a third member of the IL-1Ra family and is a 16-kDa, 143-amino acid intracellular protein derived by alternative translation initiation from either sIL-1Ra mRNA or icIL-1Ra mRNA. The role in biology of either intracellular form of IL-1Ra remains unknown.

Cot kinase activates tumor necrosis factor-alpha gene expression in a cyclosporin A-resistant manner

Cot kinase is a protein serine/threonine kinase, classified as a mitogen-activated protein kinase kinase kinase, implicated in T lymphocyte activation. Here we show that an increase in Cot kinase expression promotes tumor necrosis factor-alpha (TNF-alpha) production in Jurkat T cells stimulated by soluble anti-CD3 or by low concentrations of phorbol 12,13-dibutyrate (PDBu) and calcium ionophore. Overexpression of Cot kinase in Jurkat cells activates TNF-alpha gene expression. Cot kinase promotes TNF-alpha promoter activation to a similar extent as calcium ionophore and PDBu or soluble anti-CD28 and PDBu. Neither phorbol esters nor calcium ionophore can replace Cot kinase on TNF-alpha promoter-driven transcription. Expression of a dominant negative form of Cot kinase inhibits TNF-alpha promoter activation induced by stimulation with either calcium ionophore and PDBu, soluble anti-CD28 and PDBu, or soluble anti-CD3 and PDBu. TNF-alpha promoter-driven transcription by Cot kinase is partially mediated by MAPK/ERK kinase and is cyclosporin A-resistant. Cot kinase increases at least the AP-1 and AP-2 response elements. These data indicate that Cot kinase plays a critical role in TNF-alpha production.

Identification of the cells expressing cot proto-oncogene mRNA

The cell types expressing cot proto-oncogene mRNA were identified by in situ hybridization (ISH) histochemistry. Among a variety of adult mouse tissues examined, four types of glandular cells expressing cot gene were identified: (1) granular duct cells in the submandibular and sublingual glands; (2) serous cells in the parotid gland; (3) peptic (chief) cells in gastric glands; and (4) goblet cells in colonic glands. Investigation of the developmentally regulated expression of cot mRNA using tissues of 14-day and 18-day embryos, newborn and weanling mice showed that cot gene is expressed only in morphologically differentiated and functionally activated cells of these four types. No other types of cells showing ISH signals were observed. Based on these results, cot gene expressions in cultured cells of colonic adenocarcinomas and gastric adenocarcinomas were examined. SW 480 and WiDr cells showed high expression of this gene and so should be useful for functional analysis of Cot kinase. The expression patterns of cot gene in tumor tissues of the parotid gland, and gastric and colonic glands were investigated. Two of the tissues overexpressed this gene markedly, suggesting that overproduction of Cot kinase may be one cause of their transformation.