TRAF-dependent association of protein kinase Tpl2/COT1 (MAP3K8) with CD40

MAP3K8 is a potential therapeutic target in airway epithelial inflammation

BACKGROUND

We have previously discovered clusters of sequentially negative and positive modulators of acute inflammation during cytokine stimulation in epithelial cells and identified potential targets for therapy within these clusters. MAP3K8 is a druggable kinase that we found to be a hub of a principal interaction network. We describe here the results of MAP3K8 knockdown in the A549 lung cancer cell line, the BEAS-2B epithelial cell line and normal human bronchial epithelial (NHBE) cells following IL-1β stimulation. We analysed signalling transduction and global gene expression after IL-1β stimulation with and without MAP3K8 knockdown, quantifying levels of the inflammatory cytokines IL-6, IL-8 and RANTES levels by qPCRs and/or by ELISAs. We also examined potential small molecule inhibitors for MAP3K8 in the same models.

RESULTS

IL-1β significantly and consistently increased MAP3K8 expression after 2 h in A549, BEAS-2B and NHBE cells. Phosphorylation of MAP3K8 occurred at 20 min after IL-1β stimulation and MAP3K8 protein was degraded at 30 min. MAP3K8 knockdown significantly reduced IL-6, IL-8 levels after IL-1β stimulation and yielded a 10-fold enhancement of the anti-inflammatory effects of dexamethasone. Phosphorylation of ERK1/2 (P-ERK1/2) and phosphorylation of SAPK/JNK (P-SAPK/JNK) decreased at 30 min after IL-1β stimulation with MAP3K8 knockdown. The combination of dexamethasone and MAP3K8 knockdown resulted in greater inhibition of phosphorylated ERK1/2 and SAPK/JNK. Nineteen genes including MMP1, MMP3, MMP10, ITGB8, LAMC2 and PLAT (P corrected < 0.01 respectively) demonstrated a distinct altered temporal response to IL-1β following suppression of MAP3K8. However, putative MAP3K8 inhibitors including Tpl2-1, Tpl2-2 and GSK2222867A only showed inhibition of IL-6 and IL-8 production at a high dose.

CONCLUSIONS

These results confirm that MAP3K8 is a key mediator of the early inflammatory response and that it is a potential target in inflammatory diseases. However, current tool compounds do not effectively inhibit its effects.

Functional analyses of TRAF6 gene in Argopecten scallops

The tumor necrosis factor (TNF) receptor-associated factor (TRAF) family has been reported to be involved in many immune pathways. In a previous study, we identified 5 TRAF genes, including TRAF2, 3, 4, 6, and 7, in the bay scallop (Argopecten irradians, Air) and the Peruvian scallop (Argopecten purpuratus, Apu). Since TRAF6 is a key molecular link in the TNF superfamily, we conducted a series of studies targeting the TRAF6 gene in the Air and Apu scallops as well as their hybrid progeny, Aip (Air ♀ × Apu ♂) and Api (Apu ♀ × Air ♂). Subcellular localization assay showed that the Air-, Aip-, and Api-TRAF6 were widely distributed in the cytoplasm of the human embryonic kidney cell line (HEK293T). Additionally, dual-luciferase reporter assay revealed that among TRAF3, TRAF4, and TRAF6, only the overexpression of TRAF6 significantly activated NF-κB activity in the HEK293T cells in a dose-dependent manner. These results suggest a crucial role of TRAF6 in the immune response in Argopecten scallops. To investigate the specific immune mechanism of TRAF6 in Argopecten scallops, we conducted TRAF6 knockdown using RNA interference. Transcriptomic analyses of the TRAF6 RNAi and control groups identified 1194, 2403, and 1099 differentially expressed genes (DEGs) in the Air, Aip, and Api scallops, respectively. KEGG enrichment analyses revealed that these DEGs were primarily enriched in transport and catabolism, amino acid metabolism, peroxisome, lysosome, and phagosome pathways. Expression profiles of 28 key DEGs were confirmed by qRT-PCR assays. The results of this study may provide insights into the immune mechanisms of TRAF in Argopecten scallops and ultimately benefit scallop breeding.

Tumor progression locus 2 (TPL2) in tumor-promoting Inflammation, Tumorigenesis and Tumor Immunity

Over the years, tumor progression locus 2 (TPL2) has been identified as an essential modulator of immune responses that conveys inflammatory signals to downstream effectors, subsequently modulating the generation and function of inflammatory cells. TPL2 is also differentially expressed and activated in several cancers, where it is associated with increased inflammation, malignant transformation, angiogenesis, metastasis, poor prognosis and therapy resistance. However, the relationship between TPL2-driven inflammation, tumorigenesis and tumor immunity has not been addressed. Here, we reconcile the function of TPL2-driven inflammation to oncogenic functions such as inflammation, proliferation, apoptosis resistance, angiogenesis, metastasis, immunosuppression and immune evasion. We also address the controversies reported on TPL2 function in tumor-promoting inflammation and tumorigenesis, and highlight the potential role of the TPL2 adaptor function in regulating the mechanisms leading to pro-tumorigenic inflammation and tumor progression. We discuss the therapeutic implications and limitations of targeting TPL2 for cancer treatment. The ideas presented here provide some new insight into cancer pathophysiology that might contribute to the development of more integrative and specific anti-inflammatory and anti-cancer therapeutics.

A central role of IKK2 and TPL2 in JNK activation and viral B-cell transformation

IκB kinase 2 (IKK2) is well known for its pivotal role as a mediator of the canonical NF-κB pathway, which has important functions in inflammation and immunity, but also in cancer. Here we identify a novel and critical function of IKK2 and its co-factor NEMO in the activation of oncogenic c-Jun N-terminal kinase (JNK) signaling, induced by the latent membrane protein 1 (LMP1) of Epstein-Barr virus (EBV). Independent of its kinase activity, the TGFβ-activated kinase 1 (TAK1) mediates LMP1 signaling complex formation, NEMO ubiquitination and subsequent IKK2 activation. The tumor progression locus 2 (TPL2) kinase is induced by LMP1 via IKK2 and transmits JNK activation signals downstream of IKK2. The IKK2-TPL2-JNK axis is specific for LMP1 and differs from TNFα, Interleukin-1 and CD40 signaling. This pathway mediates essential LMP1 survival signals in EBV-transformed human B cells and post-transplant lymphoma, and thus qualifies as a target for treatment of EBV-induced cancer.

Comprehending the complex connection between PKCbeta, TAK1, and IKK in BCR signaling

The transcription factor nuclear factor-kappaB (NF-kappaB) contributes to many events in the immune system. Characterization of NF-kappaB has facilitated our understanding of immune cell differentiation, survival, proliferation, and effector functions. Intense research continues to elucidate the role of NF-kappaB, which is shared in several receptor signaling pathways, such as Toll-like receptors, the tumor necrosis factor receptor, and antigen receptors. The specificity of cellular responses emanating from stimulation of these receptors is determined by post-translational modification, or 'fine tuning', which regulates spatiotemporal dynamics of downstream signaling. Understanding the fine tuning mechanisms of NF-kappaB activation is crucial for insights into biological regulation and for understanding how cellular signaling pathways are tightly regulated to guide different cell fates. In this review, we focus on recent advances that illuminate the fine tuning mechanisms of NF-kappaB activation by BCR signaling and have increased our comprehension of complex signal systems.

Chemical biology strategy reveals pathway-selective inhibitor of NF-kappaB activation induced by protein kinase C

Dysregulation of NF-kappaB activity contributes to many autoimmune and inflammatory diseases. At least nine pathways for NF-kappaB activation have been identified, most of which converge on the IkappaB kinases (IKKs). Although IKKs represent logical targets for potential drug discovery, chemical inhibitors of IKKs suppress all known NF-kappaB activation pathways and thus lack the selectivity required for safe use. A unique NF-kappaB activation pathway is initiated by protein kinase C (PKC) that is stimulated by antigen receptors and many growth factor receptors. Using a cell-based high-throughput screening (HTS) assay and chemical biology strategy, we identified a 2-aminobenzimidazole compound, CID-2858522, which selectively inhibits the NF-kappaB pathway induced by PKC, operating downstream of PKC but upstream of IKKbeta, without inhibiting other NF-kappaB activation pathways. In human B cells stimulated through surface immunoglobulin, CID-2858522 inhibited NF-kappaB DNA-binding activity and expression of endogenous NF-kappaB-dependent target gene, TRAF1. Altogether, as a selective chemical inhibitor of the NF-kappaB pathway induced by PKC, CID-2858522 serves as a powerful research tool and may reveal new paths toward therapeutically useful NF-kappaB inhibitors.

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.

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.

A CD40 Kozak sequence polymorphism and susceptibility to antibody-mediated autoimmune conditions: the role of CD40 tissue-specific expression

Previously, we and others have demonstrated the association of a C/T single nucleotide polymorphism (SNP), in the Kozak sequence of CD40, with Graves' disease (GD). Here, using an expanded data set of patients, we confirm the association of the CD40 SNP with GD (n=210, P=0.002, odds ratio (OR)=1.8). Subset analysis of patients with persistently elevated thyroid peroxidase (TPO) and/or thyroglobulin (Tg) antibodies (Abs), (TPO/Tg Abs), after treatment (n=126), revealed a significantly stronger association of the SNP with disease (P=5.2 x 10(-5), OR=2.5) than in GD patients who were thyroid antibody-negative. However, the CD40 SNP was not associated with TPO/Tg Abs in healthy individuals. Next, we tested the CD40 SNP for association with Myasthenia Gravis (MG), which, like GD is an antibody-mediated autoimmune condition. Analysis of 81 MG patients found no association of the SNP with disease. Functional studies revealed significant expression of CD40 mRNA and protein in the thyroid (target tissue in GD) but not in skeletal muscle (target tissue in MG). Combined, our genetic and tissue expression data suggest that the CD40 Kozak SNP is specific for thyroid antibody production involved in the etiology of GD. Increased thyroidal expression of CD40 driven by the SNP may contribute to this disease specificity.

Plant and animal pathogen recognition receptors signal through non-RD kinases

Plants and animals mediate early steps of the innate immune response through pathogen recognition receptors (PRRs). PRRs commonly associate with or contain members of a monophyletic group of kinases called the interleukin-1 receptor-associated kinase (IRAK) family that include Drosophila Pelle, human IRAKs, rice XA21 and Arabidopsis FLS2. In mammals, PRRs can also associate with members of the receptor-interacting protein (RIP) kinase family, distant relatives to the IRAK family. Some IRAK and RIP family kinases fall into a small functional class of kinases termed non-RD, many of which do not autophosphorylate the activation loop. We surveyed the yeast, fly, worm, human, Arabidopsis, and rice kinomes (3,723 kinases) and found that despite the small number of non-RD kinases in these genomes (9%-29%), 12 of 15 kinases known or predicted to function in PRR signaling fall into the non-RD class. These data indicate that kinases associated with PRRs can largely be predicted by the lack of a single conserved residue and reveal new potential plant PRR subfamilies.