MEKK2 is required for T-cell receptor signals in JNK activation and interleukin-2 gene expression

MicroRNAs in Hepatocellular Carcinoma Pathogenesis: Insights into Mechanisms and Therapeutic Opportunities

Hepatocellular carcinoma (HCC) presents a significant global health burden, with alarming statistics revealing its rising incidence and high mortality rates. Despite advances in medical care, HCC treatment remains challenging due to late-stage diagnosis, limited effective therapeutic options, tumor heterogeneity, and drug resistance. MicroRNAs (miRNAs) have attracted substantial attention as key regulators of HCC pathogenesis. These small non-coding RNA molecules play pivotal roles in modulating gene expression, implicated in various cellular processes relevant to cancer development. Understanding the intricate network of miRNA-mediated molecular pathways in HCC is essential for unraveling the complex mechanisms underlying hepatocarcinogenesis and developing novel therapeutic approaches. This manuscript aims to provide a comprehensive review of recent experimental and clinical discoveries regarding the complex role of miRNAs in influencing the key hallmarks of HCC, as well as their promising clinical utility as potential therapeutic targets.

A systems and computational biology perspective on advancing CAR therapy

In the recent decades, chimeric antigen receptor (CAR) therapy signaled a new revolutionary approach to cancer treatment. This method seeks to engineer immune cells expressing an artificially designed receptor, which would endue those cells with the ability to recognize and eliminate tumor cells. While some CAR therapies received FDA approval and others are subject to clinical trials, many aspects of their workings remain elusive. Techniques of systems and computational biology have been frequently employed to explain the operating principles of CAR therapy and suggest further design improvements. In this review, we sought to provide a comprehensive account of those efforts. Specifically, we discuss various computational models of CAR therapy ranging in scale from organismal to molecular. Then, we describe the molecular and functional properties of costimulatory domains frequently incorporated in CAR structure. Finally, we describe the signaling cascades by which those costimulatory domains elicit cellular response against the target. We hope that this comprehensive summary of computational and experimental studies will further motivate the use of systems approaches in advancing CAR therapy.

MicroRNA-181a restricts human γδ T cell differentiation by targeting Map3k2 and Notch2

γδ T cells are a conserved population of lymphocytes that contributes to anti-tumor responses through its overt type 1 inflammatory and cytotoxic properties. We have previously shown that human γδ T cells acquire this profile upon stimulation with IL-2 or IL-15, in a differentiation process dependent on MAPK/ERK signaling. Here, we identify microRNA-181a as a key modulator of human γδ T cell differentiation. We observe that miR-181a is highly expressed in patients with prostate cancer and that this pattern associates with lower expression of NKG2D, a critical mediator of cancer surveillance. Interestingly, miR-181a expression negatively correlates with an activated type 1 effector profile obtained from in vitro differentiated γδ T cells and miR-181a overexpression restricts their levels of NKG2D and TNF-α. Upon in silico analysis, we identify two miR-181a candidate targets, Map3k2 and Notch2, which we validate via overexpression coupled with luciferase assays. These results reveal a novel role for miR-181a as critical regulator of human γδ T cell differentiation and highlight its potential for manipulation of γδ T cells in next-generation immunotherapies.

The Effect and Mechanism of lncRNA NR2F1-As1/miR-493-5p/MAP3K2 Axis in the Progression of Gastric Cancer

Background

LncRNA NR2F1-AS1 has been identified as an oncogene in some human tumors, such as breast cancer, nonsmall cell lung cancer, and esophageal squamous cell carcinoma. Nonetheless, whether NR2F1-AS1 is involved in the progression of gastric cancer (GC) remains unknown.

Methods

The expression patterns of NR2F1-AS1, MAP3K2, and miR-493-5p in GC tissues and cells were detected by RT-qPCR. The protein expression of MAP3K2 was assessed by the Western blotting assay. The MTT assay and flow cytometry were performed to measure cell proliferation and cell apoptosis in GC cells. The transwell assay was adopted to assess cell migration in GC cells. The relationship between NR2F1-AS1, MAP3K2, and miR-493-5p was verified by a dual-luciferase reporter assay.

Results

The increased NR2F1-AS1 and MAP3K2 expressions were discovered in GC tissues and cells compared with control groups. Knockdown of NR2F1-AS1 and MAP3K2 dramatically suppressed cell proliferation and migration, while it enhanced cell apoptosis in GC cells. In addition, NR2F1-AS1 was found to be a sponge of miR-493-5p, and MAP3K2 was a downstream gene of miR-493-5p. Moreover, the expression of MAP3K2 was notably reduced by miR-493-5p, and NR2F1-AS1 counteracted the inhibition of miR-493-5p.

Conclusion

Thus, NR2F1-AS1 was verified to regulate GC cell progression by sponging miR-493-5p to upregulate MAP3K2 expression.

Allicin regulates Treg/Th17 balance in mice with collagen-induced arthritis by increasing the expression of MEKK2 protein

To study the role of Allicin in regulating Treg/Th17 ratio in splenic lymphocyte by increasing the expression of MEKK2 protein in MAPK signaling pathway, and to explore the mechanism of immune response in mice with collagen-induced arthritis (CIA). Mouse CIA model was induced by chicken collagen type II, and experimental mice were randomly divided into NC group, Model group, and Allicin group. HE staining was used to compare the degree of joint pathological damage in mice of each group, and Masson staining to observe the proliferation of collagen tissue in each group. Flow cytometry detected Treg/Th17 ratio in splenic lymphocytes. Furthermore, RT-PCR and WB were used to detect the mRNA and protein expression of related transcription factors and inflammatory factors Foxp3, ROR-γt, and IL-17A, as well as MEK2 protein expression in splenic lymphocytes. The results showed that Allicin treatment could reduce the severity of arthritis and the proliferation of collagen fibers on the surface of cartilage and bone joints in CIA mice. Compared with NC group, Treg decreased and Th17 increased in spleen lymphocyte of Model group (p < .01); after Allicin treatment, Treg increased while Th17 decreased significantly (p < .01). Meanwhile, MEKK2 protein expression in spleen lymphocyte of Model group decreased compared to that in NC group (p < .01), and MEK2 protein expression increased significantly after Allicin treatment (p < .01). To sum up, the present study suggests that MEKK2 protein plays an important role in the pathogenesis of CIA model. In terms of mechanism, Allicin may play a therapeutic role in rheumatoid arthritis (RA) by increasing the expression of MEKK2 protein and affecting Treg/Th17 ratio.

MEKK2 mediates aberrant ERK activation in neurofibromatosis type I

Neurofibromatosis type I (NF1) is characterized by prominent skeletal manifestations caused by NF1 loss. While inhibitors of the ERK activating kinases MEK1/2 are promising as a means to treat NF1, the broad blockade of the ERK pathway produced by this strategy is potentially associated with therapy limiting toxicities. Here, we have sought targets offering a more narrow inhibition of ERK activation downstream of NF1 loss in the skeleton, finding that MEKK2 is a novel component of a noncanonical ERK pathway in osteoblasts that mediates aberrant ERK activation after NF1 loss. Accordingly, despite mice with conditional deletion of Nf1 in mature osteoblasts (Nf1^fl/fl;Dmp1-Cre) and Mekk2^−/− each displaying skeletal defects, Nf1^fl/fl;Mekk2^−/−;Dmp1-Cre mice show an amelioration of NF1-associated phenotypes. We also provide proof-of-principle that FDA-approved inhibitors with activity against MEKK2 can ameliorate NF1 skeletal pathology. Thus, MEKK2 functions as a MAP3K in the ERK pathway in osteoblasts, offering a potential new therapeutic strategy for the treatment of NF1.

Neurofibromatosis type I (NF1) is characterized by prominent skeletal abnormalities mediated in part by aberrant ERK pathway activation due to NF1 loss-of-function. Here, the authors report the MEKK2 is a key mediator of this aberrant ERK activation and that MEKK2 inhibitors, including ponatinib, ameliorate skeletal defects in a mouse model of NF1.

The Global Phosphorylation Landscape of SARS-CoV-2 Infection

The causative agent of the coronavirus disease 2019 (COVID-19) pandemic, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has infected millions and killed hundreds of thousands of people worldwide, highlighting an urgent need to develop antiviral therapies. Here we present a quantitative mass spectrometry-based phosphoproteomics survey of SARS-CoV-2 infection in Vero E6 cells, revealing dramatic rewiring of phosphorylation on host and viral proteins. SARS-CoV-2 infection promoted casein kinase II (CK2) and p38 MAPK activation, production of diverse cytokines, and shutdown of mitotic kinases, resulting in cell cycle arrest. Infection also stimulated a marked induction of CK2-containing filopodial protrusions possessing budding viral particles. Eighty-seven drugs and compounds were identified by mapping global phosphorylation profiles to dysregulated kinases and pathways. We found pharmacologic inhibition of the p38, CK2, CDK, AXL, and PIKFYVE kinases to possess antiviral efficacy, representing potential COVID-19 therapies.

Role of Ginkgolides in the Inflammatory Immune Response of Neurological Diseases: A Review of Current Literatures

The inflammatory immune response (IIR) is a physiological or excessive systemic response, induced by inflammatory immune cells according to changes in the internal and external environments. An excessive IIR is the pathological basis for the generation and development of neurological diseases. Ginkgolides are one of the important medicinal ingredients in Ginkgo biloba. Many studies have verified that ginkgolides have anti-platelet-activating, anti-apoptotic, anti-oxidative, neurotrophic, and neuroimmunomodulatory effects. Inflammatory immunomodulation is mediated by inhibition of the mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signaling pathways. They also inhibit the platelet-activating factor (PAF)-mediated signal transduction to attenuate the inflammatory response. Herein, we reviewed the studies on the roles of ginkgolides in inflammatory immunomodulation and suggested its potential role in novel treatments for neurological diseases.

MAP3K2 augments Th1 cell differentiation via IL-18 to promote T cell-mediated colitis

T cell-mediated immunity in the intestine is stringently controlled to ensure proper immunity against pathogenic microbes and to prevent autoimmunity, a known cause of inflammatory bowel disease. However, precisely how T cells regulate intestine immunity remains to be fully understood. In this study, we found that mitogen-activated protein kinase kinase kinase 2 (MAP3K2) is required for the CD4⁺ T cell-mediated inflammation in the intestine. Using a T cell transfer colitis model, we found that MAP3K2-deficient naïve CD4 T cells had a dramatically reduced ability to induce colitis compared to wild type T cells. In addition, significantly fewer IFN-γ- but more IL-17A-producing CD4⁺ T cells in the intestines of mice receiving MAP3K2-deficient T cells than in those from mice receiving wild type T cells was observed. Interestingly, under well-defined in vitro differentiation conditions, MAP3K2-deficient naïve T cells were not impaired in their ability to differentiate into Th1, Th17 and Treg. Furthermore, the MAP3K2-regulated colitis severity was mediated by Th1 but not Th17 cells in the intestine. At the molecular level, we showed that MAP3K2-mediated Th1 cell differentiation in the intestine was regulated by IL-18 and required specific JNK activation. Together, our study reveals a novel regulatory role of MAP3K2 in intestinal T cell immunity via the IL-18-MAP3K2-JNK axis and may provide a novel target for intervention in T cell-mediated colitis.

Mitogen-Activated Protein Kinase Inhibitors and T-Cell-Dependent Immunotherapy in Cancer

Mitogen-activated protein kinase (MAPK) signaling networks serve to regulate a wide range of physiologic and cancer-associated cell processes. For instance, a variety of oncogenic mutations often lead to hyperactivation of MAPK signaling, thereby enhancing tumor cell proliferation and disease progression. As such, several components of the MAPK signaling network have been proposed as viable targets for cancer therapy. However, the contributions of MAPK signaling extend well beyond the tumor cells, and several MAPK effectors have been identified as key mediators of the tumor microenvironment (TME), particularly with respect to the local immune infiltrate. In fact, a blockade of various MAPK signals has been suggested to fundamentally alter the interaction between tumor cells and T lymphocytes and have been suggested a potential adjuvant to immune checkpoint inhibition in the clinic. Therefore, in this review article, we discuss the various mechanisms through which MAPK family members contribute to T-cell biology, as well as circumstances in which MAPK inhibition may potentiate or limit cancer immunotherapy.

Acute myeloid leukemia-induced T-cell suppression can be reversed by inhibition of the MAPK pathway

Acute myeloid leukemia (AML) remains difficult to treat due to mutational heterogeneity and the development of resistance to therapy. Targeted agents, such as MEK inhibitors, may be incorporated into treatment; however, the impact of MEK inhibitors on the immune microenvironment in AML is not well understood. A greater understanding of the implications of MEK inhibition on immune responses may lead to a greater understanding of immune evasion and more rational combinations with immunotherapies. This study describes the impact of trametinib on both T cells and AML blast cells by using an immunosuppressive mouse model of AML and primary patient samples. We also used a large AML database of functional drug screens to understand characteristics of trametinib-sensitive samples. In the mouse model, trametinib increased T-cell viability and restored T-cell proliferation. Importantly, we report greater proliferation in the CD8+CD44+ effector subpopulation and impaired activation of CD8+CD62L+ naive cells. Transcriptome analysis revealed that trametinib-sensitive samples have an inflammatory gene expression profile, and we also observed increased programmed cell death ligand 1 (PD-L1) expression on trametinib-sensitive samples. Finally, we found that trametinib consistently reduced PD-L1 and PD-L2 expression in a dose-dependent manner on the myeloid population. Altogether, our data present greater insight into the impact of trametinib on the immune microenvironment and characteristics of trametinib-sensitive patient samples.

IL-17R-EGFR axis links wound healing to tumorigenesis in Lrig1+ stem cells

This study provides mechanistic insight into how IL-17 receptor adopts EGFR to activate ERK5 axis in Lrig1⁺ stem cells for their proliferation and migration during wounding healing and tumorigenesis.

Lrig1 marks a distinct population of stem cells restricted to the upper pilosebaceous unit in normal epidermis. Here we report that IL-17A–mediated activation of EGFR plays a critical role in the expansion and migration of Lrig1⁺ stem cells and their progenies in response to wounding, thereby promoting wound healing and skin tumorigenesis. Lrig1-specific deletion of the IL-17R adaptor Act1 or EGFR in mice impairs wound healing and reduces tumor formation. Mechanistically, IL-17R recruits EGFR for IL-17A–mediated signaling in Lrig1⁺ stem cells. While TRAF4, enriched in Lrig1⁺ stem cells, tethers IL-17RA and EGFR, Act1 recruits c-Src for IL-17A–induced EGFR transactivation and downstream activation of ERK5, which promotes the expansion and migration of Lrig1⁺ stem cells. This study demonstrates that IL-17A activates the IL-17R–EGFR axis in Lrig1⁺ stem cells linking wound healing to tumorigenesis.

The MAPK hypothesis: immune-regulatory effects of MAPK-pathway genetic dysregulations and implications for breast cancer immunotherapy

With the advent of checkpoint inhibition, immunotherapy has revolutionized the clinical management of several cancers, but has demonstrated limited efficacy in mammary carcinoma. Transcriptomic profiling of cancer samples defined distinct immunophenotypic categories characterized by different prognostic and predictive connotations. In breast cancer, genomic alterations leading to the dysregulation of mitogen-activated protein kinase (MAPK) pathways have been linked to an immune-silent phenotype associated with poor outcome and treatment resistance. These aberrations include mutations of MAP3K1 and MAP2K4, amplification of KRAS, BRAF, and RAF1, and truncations of NF1. Anticancer therapies targeting MAPK signaling by BRAF and MEK inhibitors have demonstrated clear immunologic effects. These off-target properties could be exploited to convert the immune-silent tumor phenotype into an immune-active one. Preclinical evidence supports that MAPK-pathway inhibition can dramatically increase the efficacy of immunotherapy. In this review, we provide a detailed overview of the immunomodulatory impact of MAPK-pathway blockade through BRAF and MEK inhibitions. While BRAF inhibition might be relevant in melanoma only, MEK inhibition is potentially applicable to a wide range of tumors. Context-dependent similarities and differences of MAPK modulation will be dissected, in light of the complexity of the MAPK pathways. Therapeutic strategies combining the favorable effects of MAPK-oriented interventions on the tumor microenvironment while maintaining T-cell function will be presented. Finally, we will discuss recent studies highlighting the rationale for the implementation of MAPK-interference approaches in combination with checkpoint inhibitors and immune agonists in breast cancer.

MiR-17-5p and miR-20a promote chicken cell proliferation at least in part by upregulation of c-Myc via MAP3K2 targeting

The miR-17-92 cluster has been well studied in mammals but less extensively studied in birds. Here, we demonstrated that miR-17-92 cluster overexpression promoted the proliferation of DF1 cells and immortalized chicken preadipocytes (ICPA-1), and miR-17-5p and miR-20a, members of the miR-17-92 cluster, targeted MAP3K2. Further analysis showed that MAP3K2 overexpression reduced the proliferation of DF1 and ICPA-1 cells and attenuated the promotive effect of the miR-17-92 cluster on cell proliferation. Downstream gene expression analysis of the MAPK signalling pathway showed that MAP3K2 overexpression decreased c-Myc expression; in contrast, MAP3K2 knockdown using RNA interference and miR-17-92 cluster overexpression increased c-Myc expression. Furthermore, c-Myc overexpression promoted miR-17-92 cluster expression and DF1 cell proliferation. Taken together, these data indicated that miR-17-92 promotes chicken cell proliferation at least in part by the upregulation of c-Myc via targeting MAP3K2, and the miR-17-92 cluster, c-Myc and E2F1 form a complex regulatory network in chicken cell proliferation.

Prospects for combining targeted and conventional cancer therapy with immunotherapy

Over the past 25 years, research in cancer therapeutics has largely focused on two distinct lines of enquiry. In one approach, efforts to understand the underlying cell-autonomous, genetic drivers of tumorigenesis have led to the development of clinically important targeted agents that result in profound, but often not durable, tumour responses in genetically defined patient populations. In the second parallel approach, exploration of the mechanisms of protective tumour immunity has provided several therapeutic strategies - most notably the 'immune checkpoint' antibodies that reverse the negative regulators of T cell function - that accomplish durable clinical responses in subsets of patients with various tumour types. The integration of these potentially complementary research fields provides new opportunities to improve cancer treatments. Targeted and immune-based therapies have already transformed the standard-of-care for several malignancies. However, additional insights into the effects of targeted therapies, along with conventional chemotherapy and radiation therapy, on the induction of antitumour immunity will help to advance the design of combination strategies that increase the rate of complete and durable clinical response in patients.

MicroRNA-186 suppresses cell proliferation and metastasis through targeting MAP3K2 in non-small cell lung cancer

MicroRNAs are a class of small endogenous non-coding RNAs that play crucial roles in the initiation and progression of human cancers. miR-186 was found decreased in various human malignancies and function as a tumor suppressor. However, the regulating mechanism of miR-186 in growth and metastasis of human non-small cell lung cancer (NSCLC) is still poorly understood. We investigated the role of miR-186 in the growth and metastasis of human NSCLC. In the present study, we found that miR-186 was significantly decreased in lung cancer tissues and cells. Furthermore, overexpression of miR-186 suppressed lung cancer cell proliferation, migration and invasion, and induced cell apoptosis. Moreover, we found that confirmed mitogen-activated protein kinase kinase kinase 2 (MAP3K2) protein was increased in lung cancer tissues and confirmed that MAP3K2 is a target gene of miR-186. In addition, knockdown of MAP3K2 by RNA interference inhibited lung cancer cell proliferation, migration and invasion, and promoted cell apoptosis in vitro. Furthermore, we observed tthat the overexpression of MAP3K2 partially reversed the inhibitory effect of miR-186 on the proliferation and metastasis of A549 and HCC827 cell lines. Taken together, our data indicated that miR-186 regulates lung cancer growth and metastasis through suppressing MAP3K2 expression, at least partly. Therefore, miR-186-MAP3K2 may represent a new and useful potential clinical treatment and diagnosis target for NSCLC.

miRNA-106a directly targeting RARB associates with the expression of Na(+)/I(-) symporter in thyroid cancer by regulating MAPK signaling pathway

BACKGROUND

Serum miRNAs profiles between papillary thyroid carcinoma (PTC) patients with non-(131)I and (131)I-avid lung metastases are differentially expressed. These miRNAs have to be further validated and the role of these miRNAs in the molecular function level of thyroid cancer cell lines has not been investigated.

METHODS

Expression levels of six identified miRNAs were assessed via quantitative real-time PCR (qRT-PCR) in the serum of eligible patients. Dual-luciferase reporter assay was used to determine the potential target of miR-106a. Cell viability and apoptosis were evaluated by MTT assay and flow cytometry analysis, respectively. The change of gene expression was detected by qRT-PCR and western blotting analysis. In vitro iodine uptake assay was conducted by a γ-counter.

RESULTS

Compared to PTC patients with (131)I-avid lung metastases, miR-106a was up-regulated in the serum of patients with non-(131)I-avid lung metastases. The results of dual-luciferase reporter assay demonstrated that miR-106a directly targeted retinoic acid receptor beta (RARB) 3'-UTR. miR-106a-RARB promoted viability of thyroid cancer cells by regulating MEKK2-ERK1/2 and MEKK2-ERK5 pathway. miR-106a-RARB inhibited apoptosis of thyroid cancer cells by regulating ASK1-p38 pathway. Moreover, miR-106a-RARB could regulate the expression of sodium iodide symporter, TSH receptor and alter the iodine uptake function of thyroid cancer cells.

CONCLUSIONS

miRNA-106a, directly targeting RARB, associates with the viability, apoptosis, differentiation and the iodine uptake function of thyroid cancer cell lines by regulating MAPK signaling pathway in vitro. These findings in the present study may provide new strategies for the diagnosis and treatment in radioiodine-refractory differentiated thyroid carcinoma.

MAP Kinase Inhibition Promotes T Cell and Anti-tumor Activity in Combination with PD-L1 Checkpoint Blockade

Targeted inhibition of mitogen-activated protein kinase (MAPK) kinase (MEK) can induce regression of tumors bearing activating mutations in the Ras pathway but rarely leads to tumor eradication. Although combining MEK inhibition with T-cell-directed immunotherapy might lead to more durable efficacy, T cell responses are themselves at least partially dependent on MEK activity. We show here that MEK inhibition did profoundly block naive CD8(+) T cell priming in tumor-bearing mice, but actually increased the number of effector-phenotype antigen-specific CD8(+) T cells within the tumor. MEK inhibition protected tumor-infiltrating CD8(+) T cells from death driven by chronic TCR stimulation while sparing cytotoxic activity. Combining MEK inhibition with anti-programmed death-ligand 1 (PD-L1) resulted in synergistic and durable tumor regression even where either agent alone was only modestly effective. Thus, despite the central importance of the MAP kinase pathway in some aspects of T cell function, MEK-targeted agents can be compatible with T-cell-dependent immunotherapy.

Overexpression of MEKK2 is associated with colorectal carcinogenesis

Mitogen-activated protein kinase kinase kinase 2 (MEKK2) is an important upstream mediator of the extracellular signal-regulated kinase 5 signaling cascade that is essential for a number of cellular functions, including mitogenesis, differentiation and oncogenic transformation. Using western blotting to examine MEKK2 expression in 16 cases of primary colorectal cancer (CRC) lesions with paired normal mucosa, it was identified that MEKK2 is highly expressed in CRC lesions compared with that of the normal mucosa. Immunohistochemistry of 24 normal mucosa, 24 adenoma and 96 adenocarcinoma colorectal specimens indicated that the expression of MEKK2 was significantly increased in the adenoma and carcinoma specimens compared with that of the normal mucosa cases (P<0.0001 for both). However, no significant differences were detected in MEKK2 expression between the carcinoma and adenoma specimens (P=0.85). Similarly, no correlations were identified between MEKK2 expression and clinicopathological features, including gender, age, body mass index, histological differentiation, depth of invasion, lymph node metastasis, UICC stage and K-ras mutations (P>0.05). The present study demonstrated that MEKK2 functions as a promotive factor in CRC.

MEKK2 kinase association with 14-3-3 protein regulates activation of c-Jun N-terminal kinase

MEKK2 (MAP/ERK kinase kinase-2) is a serine/threonine kinase that belongs to the MEKK/STE11 family of MAP kinase kinase kinases (MAP(3)Ks). MEKK2 integrates stress and mitogenic signals to the activation of NF-κB, JNK1/2, p38, and ERK5 pathways. We have found that MEKK2 is regulated through a phosphorylation-dependent association with 14-3-3, a group of adapters that modulate dimerization and association between proteins. We found that MEKK2 was phosphorylated at Thr-283, which resulted in decreased activation loop phosphorylation at Ser-519 and consequently reduced activity. Mechanistically, we found that MEKK2 associated with inactive MEKK2 in the absence of 14-3-3 binding, which led to trans-autophosphorylation of Ser-519. Enforced binding with 14-3-3 reduced Ser-519 trans-autophosphorylation. Expression of T283A MEKK2 within a MEKK2(-/-) background enhanced stress-activated c-Jun N-terminal kinase activity while elevating IL-6 expression, but also reduced ERK activation with a corresponding reduced proliferation rate. These results indicate that Thr-283 phosphorylation is an important regulatory mechanism for MEKK2 activation.

Applying ligands profiling using multiple extended electron distribution based field templates and feature trees similarity searching in the discovery of new generation of urea-based antineoplastic kinase inhibitors

This study provides a comprehensive computational procedure for the discovery of novel urea-based antineoplastic kinase inhibitors while focusing on diversification of both chemotype and selectivity pattern. It presents a systematic structural analysis of the different binding motifs of urea-based kinase inhibitors and the corresponding configurations of the kinase enzymes. The computational model depends on simultaneous application of two protocols. The first protocol applies multiple consecutive validated virtual screening filters including SMARTS, support vector-machine model (ROC = 0.98), Bayesian model (ROC = 0.86) and structure-based pharmacophore filters based on urea-based kinase inhibitors complexes retrieved from literature. This is followed by hits profiling against different extended electron distribution (XED) based field templates representing different kinase targets. The second protocol enables cancericidal activity verification by using the algorithm of feature trees (Ftrees) similarity searching against NCI database. Being a proof-of-concept study, this combined procedure was experimentally validated by its utilization in developing a novel series of urea-based derivatives of strong anticancer activity. This new series is based on 3-benzylbenzo[d]thiazol-2(3H)-one scaffold which has interesting chemical feasibility and wide diversification capability. Antineoplastic activity of this series was assayed in vitro against NCI 60 tumor-cell lines showing very strong inhibition of GI₅₀ as low as 0.9 uM. Additionally, its mechanism was unleashed using KINEX™ protein kinase microarray-based small molecule inhibitor profiling platform and cell cycle analysis showing a peculiar selectivity pattern against Zap70, c-src, Mink1, csk and MeKK2 kinases. Interestingly, it showed activity on syk kinase confirming the recent studies finding of the high activity of diphenyl urea containing compounds against this kinase. Allover, the new series, which is based on a new kinase scaffold with interesting chemical diversification capabilities, showed that it exhibits its “emergent” properties by perturbing multiple unexplored kinase pathways.

MicroRNA-520b inhibits growth of hepatoma cells by targeting MEKK2 and cyclin D1

Growing evidence indicates that the deregulation of microRNAs (miRNAs) contributes to the tumorigenesis. We previously revealed that microRNA-520b (miR-520b) was involved in the complement attack and migration of breast cancer cells. In this report, we show that miR-520b is an important miRNA in the development of hepatocellular carcinoma (HCC). Our data showed that the expression levels of miR-520b were significantly reduced in clinical HCC tissues and hepatoma cell lines. We observed that the introduction of miR-520b dramatically suppressed the growth of hepatoma cells by colony formation assays, 5-ethynyl-2-deoxyuridine (EdU) incorporation assays and 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Moreover, ectopic expression of miR-520b was able to inhibit the growth of hepatoma cells in nude mice. Further studies revealed that the mitogen-activated protein kinase kinase kinase 2 (MEKK2) and cyclin D1 were two of direct target genes of miR-520b. Silencing of MEKK2 or cyclin D1 was able to inhibit the growth of hepatoma cells in vitro and in vivo, which is consistent with the effect of miR-520b overexpression on the growth of hepatoma cells. In addition, miR-520b significantly decreased the phosphorylation levels of c-Jun N-terminal kinase (p-JNK, a downstream effector of MEKK2) or retinoblastoma (p-Rb, a downstream effector of cyclin D1). In conclusion, miR-520b is able to inhibit the growth of hepatoma cells by targeting MEKK2 or cyclin D1 in vitro and in vivo. Our findings provide new insights into the role of miR-520b in the development of HCC, and implicate the potential application of miR-520b in cancer therapy.

Hepatitis B virus X protein promotes hepatoma cell proliferation via upregulation of MEKK2

AIM

To investigate the mechanism underlying the increase of hepatoma cell proliferation by hepatitis B virus X protein (HBx).

METHODS

HepG2, H7402 and HepG2.2.15 cells, which constitutively replicated hepatitis B virus were used. The effects of HBx on hepatoma cell proliferation were examined using 5-ethynyl-2-deoxyuridine (EdU) incorporation assay and MTT assay. The expression level of MEKK2 was measured using RT-PCR, Western blot and luciferase reporter gene assay. The activity of activator protein 1 (AP-1) was detected using luciferase reporter gene assay. The phosphorylation levels of JNK and c-Jun were measured using Western blot. The expression levels of HBx and MEKK2 in 11 clinical hepatocellular carcinoma (HCC) tissues were measured using real time PCR and Western blot. In addition, the expression of MEKK2 in 95 clinical HCC tissues was examined using immunohistochemistry.

RESULTS

HBx significantly enhanced HepG2-X cell proliferation. In HepG2-X, H7402-X and HepG2.2.15 cells, the expression level of MEKK2 was remarkably increased. In HepG2.2.15 cells, HBx was found to activate JNK and AP-1, which were the downstream effectors of MEKK2 in HepG2-X and HepG2.2.15 cells. In 11 clinical HCC tissues, both HBx and MEKK2 expression levels were remarkably increased, as compared to those in the corresponding peritumor tissues. In 95 clinical HCC tissues, the rate of detection of MEKK2 was 85.3%.

CONCLUSION

HBx promotes hepatoma cell proliferation via upregulating MEKK2, which may be involved in hepatocarcinogenesis.

CHIP-dependent termination of MEKK2 regulates temporal ERK activation required for proper hyperosmotic response

The extracellular signal-regulated kinase (ERK) pathway is an important signalling pathway that regulates a large number of cellular processes, including proliferation, differentiation and gene expression. Hyperosmotic stress activates the ERK pathway, whereas little is known about the regulatory mechanisms and physiological functions of ERK activation in hyperosmotic response. Here, we show that MAPK/ERK kinase kinase 2 (MEKK2), a member of the MAPKKK family, mediated the specific and transient activation of ERK, which was required for the induction of aquaporin 1 (AQP1) and AQP5 gene expression in response to hyperosmotic stress. Moreover, we identified the E3 ubiquitin ligase carboxyl terminus of Hsc70-interacting protein (CHIP) as a binding partner of MEKK2. Depletion of CHIP by small-interference RNA or gene targeting attenuated the degradation of MEKK2 and prolonged the ERK activity. Interestingly, hyperosmolality-induced gene expression of AQP1 and AQP5 was suppressed by CHIP depletion and was reversed by inhibition of the prolonged phase of ERK activity. These findings show that transient activation of the ERK pathway, which depends not only on MEKK2 activation, but also on CHIP-dependent MEKK2 degradation, is crucial for proper gene expression in hyperosmotic stress response.

Integrative genome analysis reveals an oncomir/oncogene cluster regulating glioblastoma survivorship

Using a multidimensional genomic data set on glioblastoma from The Cancer Genome Atlas, we identified hsa-miR-26a as a cooperating component of a frequently occurring amplicon that also contains CDK4 and CENTG1, two oncogenes that regulate the RB1 and PI3 kinase/AKT pathways, respectively. By integrating DNA copy number, mRNA, microRNA, and DNA methylation data, we identified functionally relevant targets of miR-26a in glioblastoma, including PTEN, RB1, and MAP3K2/MEKK2. We demonstrate that miR-26a alone can transform cells and it promotes glioblastoma cell growth in vitro and in the mouse brain by decreasing PTEN, RB1, and MAP3K2/MEKK2 protein expression, thereby increasing AKT activation, promoting proliferation, and decreasing c-JUN N-terminal kinase-dependent apoptosis. Overexpression of miR-26a in PTEN-competent and PTEN-deficient glioblastoma cells promoted tumor growth in vivo, and it further increased growth in cells overexpressing CDK4 or CENTG1. Importantly, glioblastoma patients harboring this amplification displayed markedly decreased survival. Thus, hsa-miR-26a, CDK4, and CENTG1 comprise a functionally integrated oncomir/oncogene DNA cluster that promotes aggressiveness in human cancers by cooperatively targeting the RB1, PI3K/AKT, and JNK pathways.

Regulation of NF-kappaB-dependent T cell activation and development by MEKK3

The serine/threonine kinase MEKK3, also known as mitogen-activated protein kinase kinase kinase 3, is a critical activator of the transcription factor NF-kappaB in innate immunity. However, the physiological function of MEKK3 in adaptive immunity is unclear. Here we report that following TCR signaling, MEKK3 positively regulated the kinase, IkappaB kinase, leading to NF-kappaB activation. T cells lacking MEKK3 were defective in TCR-induced and cytokine-induced responses. Furthermore, T cell-specific deletion of MEKK3 resulted in reduced numbers of thymocytes and peripheral T cells. Thus, our results provide genetic evidence that MEKK3 plays a crucial role in adaptive immunity.

XIAP regulates bi-phasic NF-kappaB induction involving physical interaction and ubiquitination of MEKK2

The transcription factor NF-kappaB is transiently activated by a wide variety of stress signals, including pro-inflammatory mediators, and regulates the expression of genes with e.g., immune, inflammatory, and anti-apoptotic functions. The strength and kinetics of its induction, as well as its ultimate down-regulation is subject to multiple levels of regulation. One such regulatory protein is X chromosome-linked inhibitor of apoptosis (XIAP) that, besides its anti-apoptotic properties, has been shown to enhance NF-kappaB activity, however, the underlying molecular mechanism has remained elusive. We show here that following TNFalpha stimulation XIAP regulates a second wave of NF-kappaB activation. XIAP interacts with and ubiquitinates MEKK2, a kinase that has previously been associated with bi-phasic NF-kappaB activation. We conclude that, through interaction with MEKK2, XIAP functions in an ubiquitin ligase dependent manner to evoke a second wave of NF-kappaB activation, resulting in the modulation of NF-kappaB target gene expression.

Regulation of the JNK pathway by TGF-beta activated kinase 1 in rheumatoid arthritis synoviocytes

c-Jun N-terminal kinase (JNK) contributes to metalloproteinase (MMP) gene expression and joint destruction in inflammatory arthritis. It is phosphorylated by at least two upstream kinases, the mitogen-activated protein kinase kinases (MEK) MKK4 and MKK7, which are, in turn, phosphorylated by MEK kinases (MEKKs). However, the MEKKs that are most relevant to JNK activation in synoviocytes have not been determined. These studies were designed to assess the hierarchy of upstream MEKKs, MEKK1, MEKK2, MEKK3, and transforming growth factor-β activated kinase (TAK)1, in rheumatoid arthritis (RA). Using either small interfering RNA (siRNA) knockdown or knockout fibroblast-like synoviocytes (FLSs), MEKK1, MEKK2, or MEKK3 deficiency (either alone or in combination) had no effect on IL-1β-stimulated phospho-JNK (P-JNK) induction or MMP expression. However, TAK1 deficiency significantly decreased P-JNK, P-MKK4 and P-MKK7 induction compared with scrambled control. TAK1 knockdown did not affect p38 activation. Kinase assays showed that TAK1 siRNA significantly suppressed JNK kinase function. In addition, MKK4 and MKK7 kinase activity were significantly decreased in TAK1 deficient FLSs. Electrophoretic mobility shift assays demonstrated a significant decrease in IL-1β induced AP-1 activation due to TAK1 knockdown. Quantitative PCR showed that TAK1 deficiency significantly decreased IL-1β-induced MMP3 gene expression and IL-6 protein expression. These results show that TAK1 is a critical pathway for IL-1β-induced activation of JNK and JNK-regulated gene expression in FLSs. In contrast to other cell lineages, MEKK1, MEKK2, and MEKK3 did not contribute to JNK phosphorylation in FLSs. The data identify TAK1 as a pivotal upstream kinase and potential therapeutic target to modulate synoviocyte activation in RA.

Negative regulation of MEKK1/2 signaling by serine-threonine kinase 38 (STK38)

Mitogen-activated protein kinases (MAPKs) are activated through the kinase cascades of MAPK, MAPK kinase (MAPKK) and MAPKK kinase (MAPKKK). MAPKKKs phosphorylate and activate their downstream MAPKKs, which in turn phosphorylate and activate their downstream MAPKs. MAPKKK proteins relay upstream signals through the MAPK cascades to induce cellular responses. However, the molecular mechanisms by which given MAPKKKs are regulated remain largely unknown. Here, we found that serine-threonine protein kinase 38, STK38, physically interacts with the MAPKKKs MEKK1 and MEKK2 (MEKK1/2). The carboxy terminus, including the catalytic domain, but not the amino terminus of MEKK1/2 was necessary for the interaction with STK38. STK38 inhibited MEKK1/2 activation without preventing MEKK1/2 binding to its substrate, SEK1. Importantly, STK38 suppressed the autophosphorylation of MEKK2 without interfering with MEKK2 dimer formation, and converted MEKK2 from its phosphorylated to its nonphosphorylated form. The negative regulation of MEKK1/2 was not due to its phosphorylation by STK38. On the other hand, stk38 short hairpin RNA enhanced sorbitol-induced activation of MEKK2 and phosphorylation of the downstream MAPKKs, MKK3/6. Taken together, our results indicate that STK38 negatively regulates the activation of MEKK1/2 by direct interaction with the catalytic domain of MEKK1/2, suggesting a novel mechanism of MEKK1/2 regulation.

Inhibition of tumour necrosis factor-? secretion from EpiDermTMtissues by a novel small molecule, UTL-5d

BACKGROUND

UTL-5d [N-(4-chlorophenyl)-3-carboxyamidyl-5-methylisoxazole] is a small-molecule tumour necrosis factor (TNF)-alpha modulator being investigated for its potential in several immune-mediated diseases, including psoriasis.

OBJECTIVES

We aimed to determine whether UTL-5d represents a potential antipsoriasis agent.

METHODS

Firstly, a keratinocyte cell-based study was used to study the inhibition of TNF-alpha and gene suppression by UTL-5d in vitro. Secondly, a multilayered human epidermis tissue model, consisting of normal human-derived epidermal keratinocytes, was used to study the dose-dependent reduction of TNF-alpha by UTL-5d as well as the feasibility of using UTL-5d in a lotion formulation.

RESULTS

The cell-based study showed that UTL-5d significantly reduced TNF-alpha secretion from keratinocytes (68% reduction at 17 mug mL(-1)) and suppressed JAK3 and MAP3K2 genes by 70% and 40%, respectively. In the human epidermis tissue model, reduction of TNF-alpha by UTL-5d appeared to be dose dependent (8.35-33.4 microg mL(-1)); UTL-5d also reduced cell death induced by ultraviolet (UV) B. Tissues treated by UTL-5d in a preliminary lotion formulation showed significant reduction of TNF-alpha induced by UVB.

CONCLUSIONS

Our results indicate that UTL-5d may be worthy of further investigation for its potential as a topical agent for psoriasis.

Activation of transcription factors by extracellular nucleotides in immune and related cell types

Extracellular nucleotides, acting through P2 receptors, can regulate gene expression via intracellular signaling pathways that control the activity of transcription factors. Relatively little is known about the activation of transcription factors by nucleotides in immune cells. The NF-kappaB family of transcription factors is critical for many immune and inflammatory responses. Nucleotides released from damaged or stressed cells can act alone through certain P2 receptors to alter NF-kappaB activity or they can enhance responses induced by pathogen-associated molecules such as LPS. Nucleotides have also been shown to regulate the activity of other transcription factors (AP-1, NFAT, CREB and STAT) in immune and related cell types. Here, we provide an overview of transcription factors shown to be activated by nucleotides in immune cells, and describe what is known about their mechanisms of activation and potential functions. Furthermore, we propose areas for future work in this new and expanding field.

MEKK3 is essential for lipopolysaccharide-induced interleukin-6 and granulocyte-macrophage colony-stimulating factor production in macrophages

Mitogen-activated protein/ERK kinase kinase 3 (MEKK3) is a Ser/Thr protein kinase belonging to the MEKK/STE11 subgroup of the MAP3K family. Recently, we found that MEKK3 plays a critical role in interleukin-1 (IL-1) receptor and Toll-like receptor 4 signalling using established primary mouse embryonic fibroblast (MEF) cell lines. However, the function of MEKK3 in immune cells has not been studied because germ-line MEKK3 knockout mice are embryonically lethal between embryonic days 10 and 11. In this study, we used small interference RNA to the mouse Mekk3 gene to specifically knock down MEKK3 expression in the macrophage line Raw264.7. We found that the lipopolysaccharide-induced IL-6 and granulocyte-macrophage colony-stimulating factor (GM-CSF) production was dramatically decreased in MEKK3 knockdown cells whereas the tumour necrosis factor-alpha and IL-1beta production were not affected. We also observed that the ERK1/2, p38 and JNK MAPK induction in MEKK3 knockdown cells were moderately inhibited within the first 60 min of stimulation, while the ERK and p38 were more severely inhibited after 2-4 hr of stimulation. Degradation of IkappaBalpha was also partially blocked in MEKK3 knockdown cells. Notably, the impairment in IL-6 and GM-CSF production in the MEKK3 knockdown cells was restored by reintroducing a human Mekk3 cDNA that could not be targeted by mouse Mekk3-siRNAs. In conclusion, this study showed that MEKK3 is a crucial and specific regulator of the proinflammatory cytokines IL-6 and GM-CSF in macrophages and provided a novel method for investigating MEKK3 function in other immune cells.

Brain-derived Neurotrophic Factor Activates ERK5 in Cortical Neurons via a Rap1-MEKK2 Signaling Cascade

The extracellular signal-regulated kinase 5 (ERK5) is activated in neurons of the central nervous system by neurotrophins including brain-derived neurotrophic factor (BDNF). Although MEK5 is known to mediate BDNF stimulation of ERK5 in central nervous system neurons, other upstream signaling components have not been identified. Here, we report that BDNF induces a sustained activation of ERK5 in rat cortical neurons and activates Rap1, a small GTPase, as well as MEKK2, a MEK5 kinase. Our data indicate that activation of Rap1 or MEKK2 is sufficient to stimulate ERK5, whereas inhibition of either Rap1 or MEKK2 attenuates BDNF activation of ERK5. Furthermore, BDNF stimulation of MEKK2 is regulated by Rap1. Our evidence also indicates that Ras and MEKK3, a MEK5 kinase in non-neuronal cells, do not play a significant role in BDNF activation of ERK5. This study identifies Rap1 and MEKK2 as critical upstream signaling molecules mediating BDNF stimulation of ERK5 in central nervous system neurons.

Identification of MEKK2/3 serine phosphorylation site targeted by the Toll-like receptor and stress pathways

Members of the mitogen-activated protein kinase kinase kinase (MAP3K) family are crucial for the Toll-like receptor (TLR) signaling and cellular stress responses. However, the molecular mechanisms underlying the TLR- and cellular stress-mediated MAP3K activation remain largely unknown. In this study, we identified a key regulatory phosphorylation site, serine 519 and serine 526, in MAP3K MEKK2 and MEKK3, respectively. Mutation of this serine to an alanine severely impaired MEKK2/3 activation. We generated an anti-p-MEKK2/3 antibody and used this antibody to demonstrate that lipopolysaccharide induced MEKK2 and MEKK3 phosphorylation on their regulatory serine. We found that the serine phosphorylation was crucial for TLR-induced interleukin 6 production and this process is regulated by TRAF6, a key adaptor molecule for the TLR pathway. We further demonstrated that many, but not all, MAPK agonists induced the regulatory serine phosphorylation, suggesting an involvement of different MAP3Ks in activation of the MAPK cascades leading to different cellular responses. In conclusion, this study reveals a novel molecular mechanism for MEKK2/3 activation by the TLR and cellular stress pathways.

TAK1-mediated transcriptional activation of CD28-responsive element and AP-1-binding site within the IL-2 promoter in Jurkat T cells

We focused on the functional involvement of transforming growth factor-beta-activated kinase 1 (TAK1) in transcriptional regulation of interleukin-2 (IL-2) in T cells. Costimulation of Jurkat cells with 12-O-tetradecanoylphorbol-13-acetate and A23187 leads to a rapid phosphorylation of TAK1 and TAK1-binding protein 1 (TAB1), critical for TAK1 activation. A specific inhibitor of TAK1 blocked production of IL-2. In addition, overexpression of TAK1 and TAB1 induced secretion of IL-2. CD28-responsive element/activator protein-1-binding site (RE/AP) within the IL-2 promoter was a functional target for TAK1. The RE/AP-driven transcription was regulated by TAK1-mediated activation of the c-Jun NH2-terminal kinase, p38 and IkappaB kinase. These results indicate that TAK1 plays a critical role in T cell activation by controlling production of IL-2.

Mip1, an MEKK2-interacting protein, controls MEKK2 dimerization and activation

Mitogen-activated protein kinase (MAPK) cascades are central components of the intracellular signaling networks used by eukaryotic cells to respond to a wide spectrum of extracellular stimuli. An MAPK is activated by an MAPK kinase, which in turn is activated by an MAPK kinase kinase (MAP3K). However, little is known about the molecular aspects of the regulation and activation of large numbers of MAP3Ks that are crucial in relaying upstream receptor-mediated signals through the MAPK cascades to induce various physiological responses. In this study, we identified a novel MEKK2-interacting protein, Mip1, that regulates MEKK2 dimerization and activation by forming a complex with inactive and nonphosphorylated MEKK2. In particular, Mip1 prevented MEKK2 activation by blocking MEKK2 dimer formation, which in turn blocked JNKK2, c-Jun N-terminal kinase 1 (JNK1), extracellular signal-regulated kinase 5, and AP-1 reporter gene activation by MEKK2. Furthermore, we found that the endogenous Mip1-MEKK2 complex was dissociated transiently following epidermal growth factor stimulation. In contrast, the knockdown of Mip1 expression by siRNA augmented the MEKK2-mediated JNK and AP-1 reporter activation. Together, our data suggest a novel model for MEKK2 regulation and activation.

Ubiquitin ligase Smurf1 controls osteoblast activity and bone homeostasis by targeting MEKK2 for degradation

Bone is constantly resorbed and formed throughout life by coordinated actions of osteoclasts and osteoblasts. Here we show that Smurf1, a HECT domain ubiquitin ligase, has a specific physiological role in suppressing the osteogenic activity of osteoblasts. Smurf1-deficient mice are born normal but exhibit an age-dependent increase of bone mass. The cause of this increase can be traced to enhanced activities of osteoblasts, which become sensitized to bone morphogenesis protein (BMP) in the absence of Smurf1. However, loss of Smurf1 does not affect the canonical Smad-mediated intracellular TGFbeta or BMP signaling; instead, it leads to accumulation of phosphorylated MEKK2 and activation of the downstream JNK signaling cascade. We demonstrate that Smurf1 physically interacts with MEKK2 and promotes the ubiquitination and turnover of MEKK2. These results indicate that Smurf1 negatively regulates osteoblast activity and response to BMP through controlling MEKK2 degradation.

Dimerization through the Catalytic Domain Is Essential for MEKK2 Activation

Mitogen-activated protein kinase (MAPK) cascades are the central components of the intracellular signaling networks that eukaryotic cells use to respond to a wide spectrum of extracellular stimuli. MAPKs are activated through a module consisting of a MAPK, a MAPK kinase (MKK), and a MKK kinase (MAP3K). Because of its unique position in the MAPK module, a MAP3K is crucial in relaying the upstream receptor-mediated signals through the MAPK cascades to induce physiological responses. Yet, the underlying molecular mechanism of MAP3K regulation and activation remains largely unknown. In this study, we demonstrated that MAP3K MEKK2 activation requires dimerization. We mapped the MEKK2 dimerization motif in its catalytic domain and showed that the NH2-terminal region is not required for MEKK2 dimer formation. We also found that the inactive, non-phosphorylated MEKK2 formed significantly more dimers than the phosphorylated and, hence, active MEKK2. Moreover, prevention of MEKK2 dimer formation inhibited MEKK2-mediated JNK activation. Using a chemical-induced dimerization system, we further demonstrated that MEKK2 dimer formation in vivo augmented MEKK2-dependent JNK activation and JNK/AP-1 reporter gene transcription. Together, these results suggest a novel mechanism underlying MEKK2 regulation and activation.

The signaling pathways in tissue morphogenesis: a lesson from mice with eye-open at birth phenotype

Tissue morphogenesis during development is regulated by growth factors and cytokines, and is characterized by constant remodeling of extracellular matrix in response to signaling molecules. MEK kinase 1 (MEKK1) is a mitogen-activated protein kinase (MAPK) kinase kinase originally identified as an upstream activator for several MAPK pathways. During mouse embryogenesis, MEKK1 controls cell shape changes and formation of actin stress fibers that are required for sealing epidermis in the embryos in a process known as eyelid closure. MEKK1-null mice display eye-open at birth (EOB), a phenotype found also in mice impaired in activin, a subgroup of the transforming growth factor beta (TGFbeta) family, or in epidermal growth factor receptor (EGFR) or its ligand TGFalpha, or in transcription factor c-Jun. Molecular analyses have revealed at least two signaling mechanisms in the control of eyelid closure. One is originated from the activins and is transduced through MEKK1, leading to transcription-independent actin stress fiber formation and transcription-dependent keratinocyte migration. Another is the TGFalpha/EGFR signal that is transduced through a MEKK1-independent pathway to the activation of the ERK MAPK, which also leads to keratinocyte migration. c-Jun might serve as a connection between the two pathways. As embryonic eyelid closure is a specific morphogenetic process that is easily detectable, genetic mutant mice with EOB will be ideal models to understand the signaling mechanisms in the control of epithelial cell migration and the morphogenetic process of epithelial sheet movement.

Regulation of c-Jun N-Terminal Kinase by MEKK-2 and Mitogen-Activated Protein Kinase Kinase Kinases in Rheumatoid Arthritis

The mitogen-activated protein kinase (MAPK) c-Jun N-terminal kinase (JNK) is a critical regulator of collagenase-1 production in rheumatoid arthritis (RA). The MAPKs are regulated by upstream kinases, including MAPK kinases (MAPKKs) and MAPK kinase kinases (MAP3Ks). The present study was designed to evaluate the expression and regulation of the JNK pathway by MAP3K in arthritis. RT-PCR studies of MAP3K gene expression in RA and osteoarthritis synovial tissue demonstrated mitogen-activated protein kinase/ERK kinase kinase (MEKK) 1, MEKK2, apoptosis-signal regulating kinase-1, TGF-beta activated kinase 1 (TAK1) gene expression while only trace amounts of MEKK3, MEKK4, and MLK3 mRNA were detected. Western blot analysis demonstrated immunoreactive MEKK2, TAK1, and trace amounts of MEKK3 but not MEKK1 or apoptosis-signal regulating kinase-1. Analysis of MAP3K mRNA in cultured fibroblast-like synoviocytes (FLS) showed that all of the MAP3Ks examined were expressed. Western blot analysis of FLS demonstrated that MEKK1, MEKK2, and TAK1 were readily detectable and were subsequently the focus of functional studies. In vitro kinase assays using MEKK2 immunoprecipitates demonstrated that IL-1 increased MEKK2-mediated phosphorylation of the key MAPKKs that activate JNK (MAPK kinase (MKK)4 and MKK7). Furthermore, MEKK2 immunoprecipitates activated c-Jun in an IL-1 dependent manner and this activity was inhibited by the selective JNK inhibitor SP600125. Of interest, MEKK1 immunoprecipitates from IL-1-stimulated FLS appeared to activate c-Jun through the JNK pathway and TAK1 activation of c-Jun was dependent on JNK, ERK, and p38. These data indicate that MEKK2 is a potent activator of the JNK pathway in FLS and that signal complexes including MEKK2, MKK4, MKK7, and/or JNK are potential therapeutic targets in RA.

IL-2 and IL-10 production by human CD4+T cells is differentially regulated by p38: mode of stimulation-dependent regulation of IL-2

Antigenic stimulation of T cells initiates a complex series of intracellular signaling pathways that target and activate different cytokine genes. The participation of mitogen-activated protein kinases (MAPKs) in these processes has not been studied thoroughly and in some instances conflicting results have been reported. Here we have examined the role of p38 MAPK on IL-2 and IL-10 production following activation of human CD4+ T cells or of the leukemic cell line Hut-78, with either plate-bound anti-CD3 in the presence or absence of soluble anti-CD28 (plCD3, plCD3/sCD28), or with cross-linked anti-CD3 and anti-CD28 (crsCD3+CD28), or with PMA plus ionomycin. Pharmacological inhibition of the p38 pathway with either SB203580, SB202190, or SKF86002 strongly downregulated IL-10 production by T cells stimulated with any of the above treatments. In contrast the effect of p38 inhibition on IL-2 was stimulus dependent. Thus, p38 inhibition strongly upregulated IL-2 production (up to 10-fold) in the plCD3- and plCD3/sCD28-stimulated cultures while it had minimal or no effect in the other two stimulation protocols. Intracellular and mRNA levels of IL-2 and IL-10 were also upregulated and downregulated, respectively, by p38 inhibitors in the plCD3/sCD28-stimulated CD4+ T cells. Also, the induction of IL-2 and the parallel suppression of IL-10 by p38 inhibitors were independent of the balance between these two cytokines, as demonstrated by the addition of exogenous IL-10 or blocking anti-IL-10 antibody in CD4+ and Hut-78 cell cultures. These results show that p38 acts as a molecular switch that changes the balance between IL-2 and IL-10. This is especially important considering the opposing role of these cytokines in peripheral immune tolerance.

Differential regulation of interleukin 1 receptor and Toll-like receptor signaling by MEKK3

Interleukin 1 receptor (IL-1R) and Toll-like receptors (TLRs) induce inflammatory genes through the complex of MyD88, IL-1R-associated protein kinase (IRAK) and tumor necrosis factor receptor-associated factor 6 (TRAF6), which is believed to function 'upstream' of the cascades of IkappaB kinase (IKK) and nuclear factor-kappaB (NF-kappaB); extracellular signal-regulated protein kinase (ERK); c-Jun N-terminal kinase (JNK); and p38 mitogen-activated protein kinase (MAPK). Here we show that MAPK-ERK kinase kinase (MEKK3) is an essential signal transducer of the MyD88-IRAK-TRAF6 complex in IL-1R-TLR4 signaling. MEKK3 forms a complex with TRAF6 in response to IL-1 and lipopolysaccharide (LPS) but not CpG, and is required for IL-1R- and TLR4-induced IL-6 production. Furthermore, MEKK3 is crucial for IL-1- and LPS-induced activation of NF-kappaB and JNK-p38 but not ERK, indicating that MAPKs are differentially activated during IL-1R-TLR4 signaling. These data demonstrate that MEKK3 is crucial for IL-1R and TLR4 signaling through the IKK-NF-kappaB and JNK-p38 MAPK pathways.*Note: In the version of this article originally published online, the third author's name was incorrect. The correct author name should be Yong Lin. This error has been corrected for the HTML and print versions of this article.

Translation inhibitors sensitize prostate cancer cells to apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) by activating c-Jun N-terminal kinase

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in several human tumors both in vitro and in vivo, however, some tumors remain resistant for poorly understood reasons. Using a quantitative DNA fragmentation assay for apoptosis, we have shown that human prostate cancer cells are resistant to a wide range of TRAIL doses up to 500 ng/ml. However, translation inhibitors, such as anisomycin, cycloheximide, emetine, harringtonine, and puromycin, unlike several transcription inhibitors, significantly sensitized PC3-neomycin (PC3-neo) cells to TRAIL-induced apoptosis. These effects were inhibited in PC3 cells engineered to express bcl2 (PC3-bcl2). Translation inhibitors led to activation of c-Jun N-terminal kinase (JNK), which plays a role in this sensitization process because inhibition of JNK activation resulted in protection against TRAIL plus translation inhibitor-induced apoptosis. JNK activation may be required for this process, but it is not sufficient because activation of JNK using an MEKK2 expression vector did not mimic the sensitizing effect of translation inhibitors. Other stress-activated protein kinases, such as ERK and p38, play an insignificant role in determining the apoptotic sensitivity. We conclude that activation of JNK is required for sensitization of PC3 cells to TRAIL-induced apoptosis by translation inhibitors in cells that are otherwise TRAIL-resistant. However, in addition to JNK activation, other aspects of translation inhibition such as the suppressed activity of apoptosis-inhibitory proteins or activation of other signal transduction pathways must also be involved.

Mutations in protein kinase subdomain X differentially affect MEKK2 and MEKK1 activity

MAPK/ERK kinase kinase 2 (MEKK2) is a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family of protein kinases. MAP3Ks are components of a three-tiered protein kinase pathway in which a MAP3K phosphorylates and activates a mitogen-activated protein kinase kinase (MAP2K), which in turn activates a mitogen-activated protein kinase (MAPK). We have previously identified residues within protein kinase subdomain X in the MAP3K, MEKK1, that are critical for its interaction with the MAP2K, MKK4, and MEKK1-induced MKK4 activation. We report here that kinase subdomain X also plays a critical role in MEKK2 activity. Select point mutations in subdomain X impair MEKK2 phosphorylation of the MAP2Ks, MKK7 and MEK5, abolish MEKK2-induced activation of the MAPKs, JNK1 and ERK5, and diminish MEKK2-dependent activation of an AP-1 reporter gene. Interestingly, the spectrum of mutations in subdomain X of MEKK2 that affects its activity is overlapping with but not identical to those that have effects on MEKK1. Thus, mutations in subdomain X differentially affect MEKK2 and MEKK1.

MEK kinase 2 and the adaptor protein Lad regulate extracellular signal-regulated kinase 5 activation by epidermal growth factor via Src

Lad is an SH2 domain-containing adaptor protein that binds MEK kinase 2 (MEKK2), a mitogen-activated protein kinase (MAPK) kinase kinase for the extracellular signal-regulated kinase 5 (ERK5) and JNK pathways. Lad and MEKK2 are in a complex in resting cells. Antisense knockdown of Lad expression and targeted gene disruption of MEKK2 expression results in loss of epidermal growth factor (EGF) and stress stimuli-induced activation of ERK5. Activation of MEKK2 and the ERK5 pathway by EGF and stress stimuli is dependent on Src kinase activity. The Lad-binding motif is encoded within amino acids 228 to 282 in the N terminus of MEKK2, and expression of this motif blocks Lad-MEKK2 interaction, resulting in inhibition of Src-dependent activation of MEKK2 and ERK5. JNK activation by EGF is similarly inhibited by loss of Lad or MEKK2 expression and by blocking the interaction of MEKK2 and Lad. Our studies demonstrate that Src kinase activity is required for ERK5 activation in response to EGF, MEKK2 expression is required for ERK5 activation by Src, Lad and MEKK2 association is required for Src activation of ERK5, and EGF and Src stimulation of ERK5-regulated MEF2-dependent promoter activity requires a functional Lad-MEKK2 signaling complex.

Signaling through P2X7 receptor in human T cells involves p56lck, MAP kinases, and transcription factors AP-1 and NF-kappa B

ATP-gated ion channel P2X receptors are expressed on the surface of most immune cells and can trigger multiple cellular responses, such as membrane permeabilization, cytokine production, and cell proliferation or apoptosis. Despite broad distribution and pleiotropic activities, signaling pathways downstream of these ionotropic receptors are still poorly understood. Here, we describe intracellular signaling events in Jurkat cells treated with millimolar concentrations of extracellular ATP. Within minutes, ATP treatment resulted in the phosphorylation and activation of p56(lck) kinase, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase but not p38 kinase. These effects were wholly dependent upon the presence of extracellular Ca(2+) ions in the culture medium. Nevertheless, calmodulin antagonist calmidazolium and CaM kinase inhibitor KN-93 both had no effect on the activation of p56(lck) and ERK, whereas a pretreatment of Jurkat cells with MAP kinase kinase inhibitor P098059 was able to abrogate phosphorylation of ERK. Further, expression of c-Jun and c-Fos proteins and activator protein (AP-1) DNA binding activity were enhanced in a time-dependent manner. In contrast, DNA binding activity of NF-kappa B was reduced. ATP failed to stimulate the phosphorylation of ERK and c-Jun N-terminal kinase and activation of AP-1 in the p56(lck)-deficient isogenic T cell line JCaM1, suggesting a critical role for p56(lck) kinase in downstream signaling. Regarding the biological significance of the ATP-induced signaling events we show that although extracellular ATP was able to stimulate proliferation of both Jurkat and JCaM1 cells, an increase in interleukin-2 transcription was observed only in Jurkat cells. The nucleotide selectivity and pharmacological profile data supported the evidence that the ATP-induced effects in Jurkat cells were mediated through the P2X7 receptor. Taken together, these results demonstrate the ability of extracellular ATP to activate multiple downstream signaling events in a human T-lymphoblastoid cell line.

Disruption of Mekk2 in mice reveals an unexpected role for MEKK2 in modulating T-cell receptor signal transduction

MEKK2 is a member of the mitogen-activated protein kinase (MAPK) kinase kinase gene family involved in regulating multiple MAPK signaling pathways. To elucidate the in vivo function of MEKK2, we generated mice carrying a targeted mutation in the Mekk2 locus. Mekk2(-/-) mice are viable and fertile. Major subsets of thymic and spleen T cells in Mekk2-deficient mice were indistinguishable from those in wild-type mice. B-cell development appeared to proceed similarly in the bone marrow of Mekk2-deficient and wild-type mice. However, Mekk2(-/-) T-cell proliferation was augmented in response to anti-CD3 monoclonal antibody (MAb) stimulation, and these T cells produced more interleukin 2 and gamma interferon than did the wild-type T cells, suggesting that MEKK2 may be involved in controlling the strength of T-cell receptor (TCR) signaling. Consistently, Mekk2(-/-) thymocytes were more susceptible than wild-type thymocytes to anti-CD3 MAb-induced cell death. Furthermore, TCR-mediated c-Jun N-terminal kinase activation was not blocked but moderately enhanced in Mekk2(-/-) T cells. Neither extracellular signal-regulated kinase nor p38 MAPK activation was affected in Mekk2(-/-) T cells. In conclusion, we found that MEKK2 may be required for controlling the strength of TCR/CD3 signaling.