Tpl2 Ablation Leads to Hypercytokinemia and Excessive Cellular Infiltration to the Lungs During Late Stages of Influenza Infection

Tumor progression locus 2 (Tpl2) is a serine-threonine kinase known to promote inflammation in response to various pathogen-associated molecular patterns (PAMPs), inflammatory cytokines and G-protein-coupled receptors and consequently aids in host resistance to pathogens. We have recently shown that Tpl2-/- mice succumb to infection with a low-pathogenicity strain of influenza (x31, H3N2) by an unknown mechanism. In this study, we sought to characterize the cytokine and immune cell profile of influenza-infected Tpl2-/- mice to gain insight into its host protective effects. Although Tpl2-/- mice display modestly impaired viral control, no virus was observed in the lungs of Tpl2-/- mice on the day of peak morbidity and mortality suggesting that morbidity is not due to virus cytopathic effects but rather to an overactive antiviral immune response. Indeed, increased levels of interferon-β (IFN-β), the IFN-inducible monocyte chemoattractant protein-1 (MCP-1, CCL2), Macrophage inflammatory protein 1 alpha (MIP-1α; CCL3), MIP-1β (CCL4), RANTES (CCL5), IP-10 (CXCL10) and Interferon-γ (IFN-γ) was observed in the lungs of influenza-infected Tpl2-/- mice at 7 days post infection (dpi). Elevated cytokine and chemokines were accompanied by increased infiltration of the lungs with inflammatory monocytes and neutrophils. Additionally, we noted that increased IFN-β correlated with increased CCL2, CXCL1 and nitric oxide synthase (NOS2) expression in the lungs, which has been associated with severe influenza infections. Bone marrow chimeras with Tpl2 ablation localized to radioresistant cells confirmed that Tpl2 functions, at least in part, within radioresistant cells to limit pro-inflammatory response to viral infection. Collectively, this study suggests that Tpl2 tempers inflammation during influenza infection by constraining the production of interferons and chemokines which are known to promote the recruitment of detrimental inflammatory monocytes and neutrophils.

Tpl2 kinase regulates inflammation but not tumorigenesis in mice

Tumor progression locus 2 (Tpl2, gene name MAP3K8), a mitogen-activated protein kinase, is widely expressed in immune and non-immune cells to integrate tumor necrosis factor (TNF), toll-like receptors (TLRs), and interleukin-1 (IL1) receptor signaling to regulate inflammatory response. Given its central role in inflammatory response, Tpl2 is an attractive small molecule drug target. However, the role of Tpl2 as an oncogene or tumor suppressor gene remains controversial, and its function outside immune cells is not understood. We therefore utilized a Tpl2 kinase dead (Tpl2-KD) mouse model in an 18-month aging study to further elucidate Tpl2 effects on lifespan and chronic disease. Histopathological studies revealed the incidence and severity of spontaneous tumors and non-neoplastic lesions were comparable between wild type and Tpl2-KD mice. The only finding was that male Tpl2-KD mice had higher bodyweight and an increased incidence of liver steatosis, suggesting a sex-specific role for Tpl2 in hepatic lipid metabolism. In conclusion, loss of Tpl2 kinase activity did not lead to increased tumorigenesis over aging in mice but affected likely alterations in lipid metabolism in male animals.

Ribosome Collisions Trigger General Stress Responses to Regulate Cell Fate

Problems arising during translation of mRNAs lead to ribosome stalling and collisions that trigger a series of quality control events. However, the global cellular response to ribosome collisions has not been explored. Here, we uncover a function for ribosome collisions in signal transduction. Using translation elongation inhibitors and general cellular stress conditions, including amino acid starvation and UV irradiation, we show that ribosome collisions activate the stress-activated protein kinase (SAPK) and GCN2-mediated stress response pathways. We show that the MAPKKK ZAK functions as the sentinel for ribosome collisions and is required for immediate early activation of both SAPK (p38/JNK) and GCN2 signaling pathways. Selective ribosome profiling and biochemistry demonstrate that although ZAK generally associates with elongating ribosomes on polysomal mRNAs, it specifically auto-phosphorylates on the minimal unit of colliding ribosomes, the disome. Together, these results provide molecular insights into how perturbation of translational homeostasis regulates cell fate.

MLK3 silence induces cervical cancer cell apoptosis via the Notch-1/autophagy network

Mixed-lineage kinase 3 (MLK3), the mitogen-activated protein kinase kinase kinase (MAP3K), has been recognized as a player in tumorigenesis and oncogenic signalling, yet its detailed functions and signalling in cervical cancer have not been fully elucidated. Here, we identify that cervical cancer cells display higher mRNA and protein levels of MLK3 than normal cervical epithelial squamous cells. In HeLa and SiHa cell, MLK3 knockdown using siRNA remarkably suppressed cell survival and promoted cell apoptosis, with increased expression of the apoptosis-related protein Bax and reduced Bcl-2. Moreover, MLK3 knockdown promoted cell autophagy, demonstrated by increased ratio of autophagy-related proteins LC3II/LC3I and decreased p62 expression in MLK3 depletion cells. Furthermore, MLK3 knockdown remarkably abolished Notch-1 expression in cervical cancer cells. By co-treating Hela cells with MLK3 specific siRNA and pcDNA3.1-Notch-1 overexpression plasmid or autophagy inhibitor 3-MA, we found that MLK3 played its role in cervical cancer cells via the Notch-1/autophagy network. Our results demonstrate the importance of MLK3 in cervical cancer progression via modulating the Notch-1/autophagy network, and suggest that MLK3 is a promising therapeutic target for cervical cancer.

ABIN-2, of the TPL-2 Signaling Complex, Modulates Mammalian Inflammation

Mammalian TPL-2 kinase (MAP3K8) mediates Toll-like receptor activation of ERK1/2 and p38α MAP kinases and is critical for regulating immune responses to pathogens. TPL-2 also has an important adaptor function, maintaining stability of associated ABIN-2 ubiquitin-binding protein. Consequently, phenotypes detected in Map3k8^-/- mice can be caused by lack of TPL-2, ABIN-2, or both proteins. Recent studies show that increased inflammation of Map3k8^-/- mice in allergic airway inflammation and colitis results from reduced ABIN-2 signaling, rather than blocked TPL-2 signaling. However, Map3k8^-/- mice have been employed extensively to evaluate the potential of TPL-2 as an anti-inflammatory drug target. We posit that Map3k8^D270A/D270A mice, expressing catalytically inactive TPL-2 and physiologic ABIN-2, should be used to evaluate the potential effects of TPL-2 inhibitors in disease.

Tpl2 Promotes Innate Cell Recruitment and Effector T Cell Differentiation To Limit Citrobacter rodentium Burden and Dissemination

Tumor progression locus 2 (Tpl2) is a serine-threonine kinase that regulates Th1 differentiation, secretion of the inflammatory cytokine gamma interferon (IFN-γ), and host defense against the intracellular pathogens Toxoplasma gondii, Listeria monocytogenes, and Mycobacterium tuberculosis However, relatively little is known about the contribution of Tpl2 to Th17 differentiation and immune cell function during infection with an extracellular pathogen. The goal of this study was to determine whether Tpl2 influences the immune response generated to the extracellular bacterium Citrobacter rodentium, which induces a mixed Th1 and Th17 response. During peak infection with C. rodentium, Tpl2-/- mice experienced greater bacterial burdens with evidence of dissemination to the liver and spleen but ultimately cleared the bacteria within 3 weeks postinfection, similar to the findings for wild-type mice. Tpl2-/- mice also recruited fewer neutrophils and monocytes to the colon during peak infection, which correlated with increased bacterial burdens. In mixed bone marrow chimeras, Tpl2 was shown to play a T cell-intrinsic role in promoting both IFN-γ and interleukin-17A production during infection with C. rodentium However, upon CD4 T cell transfer into Rag-/- mice, Tpl2-/- CD4 T cells were as protective as wild-type CD4 T cells against the dissemination of bacteria and mortality. These data indicate that the enhanced bacterial burdens in Tpl2-/- mice are not caused primarily by impairments in CD4 T cell function but result from defects in innate immune cell recruitment and function.

Severe Dermatitis Associated with Spontaneous Staphylococcus xylosus Infection in Rag-/-Tpl2-/- Mice

Staphylococcus xylosus is a commensal bacterium found on the skin and mucosal surfaces of SPF mice. S. xylosus is rarely pathogenic, most often causing skin lesions and dermatitis in immunocompromised mice, particularly those with impaired NADPH oxidase function. Here we report spontaneous infection with S. xylosus in Rag1-/-Tpl2-/- mice. Infection was characterized by the presence of alopecia, crusts, and scaly skin. S. xylosus was detected in the feces, skin, lymph nodes, and lungs of Rag1-/-Tpl2-/- mice and led to mortality or euthanasia due to humane endpoints. C57BL/6 mice were culture-positive for S. xylosus on the skin, and Rag1-/- and Tpl2-/- mice were culture-positive on the skin and occasionally in the feces. However, S. xylosus did not cause clinical symptoms in C57BL/6, Rag1-/-, or Tpl2-/- mice. Compared with those in Rag1-/- mice, relative concentrations of circulating monocytes, but not neutrophils or lymphocytes, were increased in Rag1-/-Tpl2-/- mice, consistent with their increased incidence of clinical symptoms. Overall, this case study suggests a novel role for Tpl2 in T-cell-independent host resistance to the otherwise commensal organism S. xylosus.

A Novel Zak Knockout Mouse with a Defective Ribotoxic Stress Response

Ricin activates the proinflammatory ribotoxic stress response through the mitogen activated protein 3 kinase (MAP3K) ZAK, resulting in activation of mitogen activated protein kinases (MAPKs) p38 and JNK1/2. We had a novel zak−/− mouse generated to study the role of ZAK signaling in vivo during ricin intoxication. To characterize this murine strain, we intoxicated zak−/− and zak+/+ bone marrow–derived murine macrophages with ricin, measured p38 and JNK1/2 activation by Western blot, and measured zak, c-jun, and cxcl-1 expression by qRT-PCR. To determine whether zak−/− mice differed from wild-type mice in their in vivo response to ricin, we performed oral ricin intoxication experiments with zak+/+ and zak−/− mice, using blinded histopathology scoring of duodenal tissue sections to determine differences in tissue damage. Unlike macrophages derived from zak+/+ mice, those derived from the novel zak−/− strain fail to activate p38 and JNK1/2 and have decreased c-jun and cxcl-1 expression following ricin intoxication. Furthermore, compared with zak+/+ mice, zak−/− mice have decreased duodenal damage following in vivo ricin challenge. zak−/− mice demonstrate a distinct ribotoxic stress–associated phenotype in response to ricin and therefore provide a new animal model for in vivo studies of ZAK signaling.

Fibroblast Growth Factor 21 Mediates Glycemic Regulation by Hepatic JNK

The cJun NH2-terminal kinase (JNK)-signaling pathway is implicated in metabolic syndrome, including dysregulated blood glucose concentration and insulin resistance. Fibroblast growth factor 21 (FGF21) is a target of the hepatic JNK-signaling pathway and may contribute to the regulation of glycemia. To test the role of FGF21, we established mice with selective ablation of the Fgf21 gene in hepatocytes. FGF21 deficiency in the liver caused marked loss of FGF21 protein circulating in the blood. Moreover, the protective effects of hepatic JNK deficiency to suppress metabolic syndrome in high-fat diet-fed mice were not observed in mice with hepatocyte-specific FGF21 deficiency, including reduced blood glucose concentration and reduced intolerance to glucose and insulin. Furthermore, we show that JNK contributes to the regulation of hepatic FGF21 expression during fasting/feeding cycles. These data demonstrate that the hepatokine FGF21 is a key mediator of JNK-regulated metabolic syndrome.

Conditional Deletion of TAK1 in T Cells Reveals a Pivotal Role of TCRαβ+ Intraepithelial Lymphocytes in Preventing Lymphopenia-Associated Colitis

The kinase TAK is required for the development of conventional and regulatory T cells. We previously reported that mice with conditional deletion of TAK1 in T cells (Lck-cre:TAK1fl/fl mice) exhibited severe T lymphopenia, and were nevertheless predisposed to spontaneous colitis with unknown etiology. Here we focused on the immunopathological mechanism in colitic Lck-cre:TAK1fl/fl mice. We found that 'leaky' CD4+ T cells retaining TAK1 acquired inflammatory phenotypes that contribute to disease onset in Lck-cre:TAK1fl/fl mice. Furthermore, the gut microbiota-triggered signaling was also a key event leading to the pathogenesis. We discovered that Lck-cre:TAK1fl/fl mice were almost completely devoid of TCRαβ+CD8α+ intestinal intraepithelial lymphocytes (IELs) and this was largely due to the developmental defect of the thymic precursors by TAK1 deficiency. Remarkably, transfer of TCRαβ+CD8α+ IELs from wild-type mice ameliorated colitis in Lck-cre:TAK1fl/fl mice. Taken together, our current study highlighted the emerging role of TAK1 in configuring the gut-specialized T cell subset, which regulates mucosal homeostasis under lymphopenic conditions.

Mouse models of liver cancer

Hepatocellular carcinoma (HCC) is the sixth most common cancer worldwide, and the third leading cause of cancer mortality. The great majority of patients are not eligible for curative therapies, and therapeutic approaches for advanced disease show only limited efficacy. Difficulties to treat HCC are due to the heterogenous genetic alterations of HCC, profound alterations in the hepatic microenvironment, and incomplete understanding of HCC biology. Mouse models of HCC will be helpful to improve our understanding of HCC biology, the contributions of the specific pathways and genetic alterations to carcinogenesis. In addition, mouse models of HCC may contribute to elucidate the role of the tumor microenvironment, and serve as models for preclinical studies. As no single mouse model is appropriate to study all of the above, we discuss key features and limitations of commonly used models. Furthermore, we provide detailed protocols for select models, in which HCC is induced genetically, chemically or by transplantation of tumor cells.

Mixed-lineage kinase 3 deficiency promotes neointima formation through increased activation of the RhoA pathway in vascular smooth muscle cells

OBJECTIVE

Mitogen-activated protein kinase pathways play an important role in neointima formation secondary to vascular injury, in part by promoting proliferation of vascular smooth muscle cells (VSMC). Mixed-lineage kinase 3 (MLK3) is a mitogen-activated protein kinase kinase kinase that activates multiple mitogen-activated protein kinase pathways and has been implicated in regulating proliferation in several cell types. However, the role of MLK3 in VSMC proliferation and neointima formation is unknown. The aim of this study was to determine the function of MLK3 in the development of neointimal hyperplasia and to elucidate the underlying mechanisms.

APPROACH AND RESULTS

Neointima formation was analyzed after endothelial denudation of carotid arteries from wild-type and MLK3-deficient mice. MLK3 deficiency promoted injury-induced neointima formation and increased proliferation of primary VSMC derived from aortas isolated from MLK3-deficient mice compared with wild-type mice. Furthermore, MLK3 deficiency increased the activation of p63Rho guanine nucleotide exchange factor, RhoA, and Rho kinase in VSMC, a pathway known to promote neointimal hyperplasia, and reconstitution of MLK3 expression attenuated Rho kinase activation. Furthermore, cJun NH2-terminal kinase activation was decreased in MLK3-deficient VSMC, and proliferation of wild-type but not MLK3 knockout cells treated with a cJun NH2-terminal kinase inhibitor was attenuated.

CONCLUSIONS

We demonstrate that MLK3 limits RhoA activation and injury-induced neointima formation by binding to and inhibiting the activation of p63Rho guanine nucleotide exchange factor, a RhoA activator. In MLK3-deficient cells, activation of p63Rho guanine nucleotide exchange factor proceeds in an unchecked manner, leading to a net increase in RhoA pathway activation. Reconstitution of MLK3 expression restores MLK3/p63Rho guanine nucleotide exchange factor interaction, which is attenuated by feedback from activated cJun NH2-terminal kinase.

TAK1-mediated autophagy and fatty acid oxidation prevent hepatosteatosis and tumorigenesis

The MAP kinase kinase kinase TGFβ-activated kinase 1 (TAK1) is activated by TLRs, IL-1, TNF, and TGFβ and in turn activates IKK-NF-κB and JNK, which regulate cell survival, growth, tumorigenesis, and metabolism. TAK1 signaling also upregulates AMPK activity and autophagy. Here, we investigated TAK1-dependent regulation of autophagy, lipid metabolism, and tumorigenesis in the liver. Fasted mice with hepatocyte-specific deletion of Tak1 exhibited severe hepatosteatosis with increased mTORC1 activity and suppression of autophagy compared with their WT counterparts. TAK1-deficient hepatocytes exhibited suppressed AMPK activity and autophagy in response to starvation or metformin treatment; however, ectopic activation of AMPK restored autophagy in these cells. Peroxisome proliferator-activated receptor α (PPARα) target genes and β-oxidation, which regulate hepatic lipid degradation, were also suppressed in hepatocytes lacking TAK1. Due to suppression of autophagy and β-oxidation, a high-fat diet challenge aggravated steatohepatitis in mice with hepatocyte-specific deletion of Tak1. Notably, inhibition of mTORC1 restored autophagy and PPARα target gene expression in TAK1-deficient livers, indicating that TAK1 acts upstream of mTORC1. mTORC1 inhibition also suppressed spontaneous liver fibrosis and hepatocarcinogenesis in animals with hepatocyte-specific deletion of Tak1. These data indicate that TAK1 regulates hepatic lipid metabolism and tumorigenesis via the AMPK/mTORC1 axis, affecting both autophagy and PPARα activity.

TAK1 (MAP3K7) signaling regulates hematopoietic stem cells through TNF-dependent and -independent mechanisms

A cytokine/stress signaling kinase Tak1 (Map3k7) deficiency is known to impair hematopoietic progenitor cells. However, the role of TAK1 signaling in the stem cell function of the hematopoietic system is not yet well defined. Here we characterized hematopoietic stem cells (HSCs) harboring deletion of Tak1 and its activators, Tak1 binding proteins 1 and 2 (Tab1 and Tab2) using a competitive transplantation assay in a mouse model. Tak1 single or Tab1/Tab2 double deletions completely eliminated the reconstitution activity of HSCs, whereas Tab1 or Tab2 single deletion did not cause any abnormality. Tak1 single or Tab1/Tab2 double deficient lineage-negative, Sca-1⁺, c-Kit⁺ (LSK) cells did not proliferate and underwent cell death. We found that Tnfr1 deficiency restored the reconstitution activity of Tak1 deficient bone marrow cells for 6–18 weeks. However, the reconstitution activity of Tak1- and Tnfr1-double deficient bone marrow cells declined over the long term, and the number of phenotypically identified long-term hematopoietic stem cells were diminished. Our results indicate that TAB1- or TAB2-dependent activation of TAK1 is required for maintenance of the hematopoietic system through two mechanisms: one is prevention of TNF-dependent cell death and the other is TNF-independent maintenance of long-term HSC.

Tumor progression locus 2 (Tpl2) deficiency does not protect against obesity-induced metabolic disease

Obesity is associated with a state of chronic low grade inflammation that plays an important role in the development of insulin resistance. Tumor progression locus 2 (Tpl2) is a serine/threonine mitogen activated protein kinase kinase kinase (MAP3K) involved in regulating responses to specific inflammatory stimuli. Here we have used mice lacking Tpl2 to examine its role in obesity-associated insulin resistance. Wild type (wt) and tpl2(-/-) mice accumulated comparable amounts of fat and lean mass when fed either a standard chow diet or two different high fat (HF) diets containing either 42% or 59% of energy content derived from fat. No differences in glucose tolerance were observed between wt and tpl2(-/-) mice on any of these diets. Insulin tolerance was similar on both standard chow and 42% HF diets, but was slightly impaired in tpl2(-/-) mice fed the 59% HFD. While gene expression markers of macrophage recruitment and inflammation were increased in the white adipose tissue of HF fed mice compared with standard chow fed mice, no differences were observed between wt and tpl2(-/-) mice. Finally, a HF diet did not increase Tpl2 expression nor did it activate Extracellular Signal-Regulated Kinase 1/2 (ERK1/2), the MAPK downstream of Tpl2. These findings argue that Tpl2 does not play a non-redundant role in obesity-associated metabolic dysfunction.

Myeloid TAKI [corrected] acts as a negative regulator of the LPS response and mediates resistance to endotoxemia

TGFβ-activated kinase 1 (TAK1), a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family, is considered a key intermediate in a multitude of innate immune signaling pathways. Yet, the specific role of TAK1 in the myeloid compartment during inflammatory challenges has not been revealed. To address this question, we generated myeloid-specific kinase-dead TAK1 mutant mice. TAK1 deficiency in macrophages results in impaired NF-κB and JNK activation upon stimulation with lipopolysaccharide (LPS). Moreover, TAK1-deficient macrophages and neutrophils show an enhanced inflammatory cytokine profile in response to LPS stimulation. Myeloid-specific TAK1 deficiency in mice leads to increased levels of circulating IL-1β, TNF and reduced IL-10 after LPS challenge and sensitizes them to LPS-induced endotoxemia. These results highlight an antiinflammatory role for myeloid TAK1, which is essential for balanced innate immune responses and host survival during endotoxemia.

MLK3 regulates bone development downstream of the faciogenital dysplasia protein FGD1 in mice

Mutations in human FYVE, RhoGEF, and PH domain-containing 1 (FGD1) cause faciogenital dysplasia (FGDY; also known as Aarskog syndrome), an X-linked disorder that affects multiple skeletal structures. FGD1 encodes a guanine nucleotide exchange factor (GEF) that specifically activates the Rho GTPase CDC42. However, the mechanisms by which mutations in FGD1 affect skeletal development are unknown. Here, we describe what we believe to be a novel signaling pathway in osteoblasts initiated by FGD1 that involves the MAP3K mixed-lineage kinase 3 (MLK3). We observed that MLK3 functions downstream of FGD1 to regulate ERK and p38 MAPK, which in turn phosphorylate and activate the master regulator of osteoblast differentiation, Runx2. Mutations in FGD1 found in individuals with FGDY ablated its ability to activate MLK3. Consistent with our description of this pathway and the phenotype of patients with FGD1 mutations, mice with a targeted deletion of Mlk3 displayed multiple skeletal defects, including dental abnormalities, deficient calvarial mineralization, and reduced bone mass. Furthermore, mice with knockin of a mutant Mlk3 allele that is resistant to activation by FGD1/CDC42 displayed similar skeletal defects, demonstrating that activation of MLK3 specifically by FGD1/CDC42 is important for skeletal mineralization. Thus, our results provide a putative biochemical mechanism for the skeletal defects in human FGDY and suggest that modulating MAPK signaling may benefit these patients.

Ablation of mixed lineage kinase 3 (Mlk3) does not inhibit ototoxicity induced by acoustic trauma or aminoglycoside exposure

Jun N-terminal kinase (JNK) is activated in cochlear hair cells following acoustic trauma or exposure to aminoglycoside antibiotics. Blockade of JNK activation using mixed lineage kinase (MLK) inhibitors prevents hearing loss and hair cell death following these stresses. Since current pharmacologic inhibitors of MLKs block multiple members of this kinase family, we examined the contribution of the major neuronal family member (MLK3) to stress-induced ototoxicity, usingMlk3(-/-) mice. Immunohistochemical staining revealed that MLK3 is expressed in cochlear hair cells of C57/BL6 mice (but not in Mlk3(-/-) animals). After exposure to acoustic trauma there was no significant difference in DPOAE and ABR values betweenMlk3(-/-) and wild-type mice at 48 h following exposure or 2 weeks later. Susceptibility of hair cells to aminoglycoside toxicity was tested by exposing explanted utricles to gentamicin. Gentamicin-induced hair cell death was equivalent in utricles from wild-type and Mlk3(-/-) mice. Blockade of JNK activation with the pharmacologic inhibitor SP600125 attenuated cell death in utricles from both wild-type and Mlk3(-/-) mice. These data show that MLK3 ablation does not protect against hair cell death following acoustic trauma or exposure to aminoglycoside antibiotics, suggesting that MLK3 is not the major upstream regulator of JNK-mediated hair cell death following these stresses. Rather, other MLK family members such as MLK1, which is also expressed in cochlea, may have a previously unappreciated role in noise- and aminoglycoside-induced ototoxicity.

Mixed Lineage Kinase 3 deficiency delays viral clearance in the lung and is associated with diminished influenza-induced cytopathic effect in infected cells

Influenza virus leads to acute respiratory disease resulting in seasonal epidemics and periodic pandemics. Little is known about the signaling events that regulate host defense to influenza. One particular pathway, the c-Jun amino-terminal kinase (JNK) cascade is activated following influenza infection and blocking JNK leads to enhanced viral replication. We hypothesize that Mixed Lineage Kinase 3 (MLK3), an upstream regulator of JNK, is involved in the host response to influenza. To test this, wild-type and MLK3-/- mice were infected with pathogenic strain of influenza A virus, A/PR/8/34 (PR8). Although, cellular and humoral immune responses were similar between wild-type and MLK3-/- hosts, the viral load in the lungs was comparatively higher in MLK3-/- mice at day 8 post-infection. Consistent with this, MLK3-/- murine lung fibroblast and epithelial cells had prolonged survival and increased virion production following infection compared to wild-type. These findings support a role for MLK3 in viral production during influenza infection.

Intestinal epithelial-derived TAK1 signaling is essential for cytoprotection against chemical-induced colitis

Background

We have previously reported that intestinal epithelium-specific TAK1 deleted mice exhibit severe inflammation and mortality at postnatal day 1 due to TNF-induced epithelial cell death. Although deletion of TNF receptor 1 (TNFR1) can largely rescue those neonatal phenotypes, mice harboring double deletion of TNF receptor 1 (TNFR1) and intestinal epithelium-specific deletion of TAK1 (TNFR1KO/TAK1^IEKO) still occasionally show increased inflammation. This indicates that TAK1 is important for TNF-independent regulation of intestinal integrity.

Methodology/Principal Findings

In this study, we investigated the TNF-independent role of TAK1 in the intestinal epithelium. Because the inflammatory conditions were sporadically developed in the double mutant TNFR1KO/TAK1^IEKO mice, we hypothesize that epithelial TAK1 signaling is important for preventing stress-induced barrier dysfunction. To test this hypothesis, the TNFR1KO/TAK1^IEKO mice were subjected to acute colitis by administration of dextran sulfate sodium (DSS). We found that loss of TAK1 significantly augments DSS-induced experimental colitis. DSS induced weight loss, intestinal damages and inflammatory markers in TNFR1KO/TAK1^IEKO mice at higher levels compared to the TNFR1KO control mice. Apoptosis was strongly induced and epithelial cell proliferation was decreased in the TAK1-deficient intestinal epithelium upon DSS exposure. These suggest that epithelial-derived TAK1 signaling is important for cytoprotection and repair against injury. Finally, we showed that TAK1 is essential for interleukin 1- and bacterial components-induced expression of cytoprotective factors such as interleukin 6 and cycloxygenase 2.

Conclusions

Homeostatic cytokines and microbes-induced intestinal epithelial TAK1 signaling regulates cytoprotective factors and cell proliferation, which is pivotal for protecting the intestinal epithelium against injury.

Mechanism of action of A-769662, a valuable tool for activation of AMP-activated protein kinase

We have studied the mechanism of A-769662, a new activator of AMP-activated protein kinase (AMPK). Unlike other pharmacological activators, it directly activates native rat AMPK by mimicking both effects of AMP, i.e. allosteric activation and inhibition of dephosphorylation. We found that it has no effect on the isolated alpha subunit kinase domain, with or without the associated autoinhibitory domain, or on interaction of glycogen with the beta subunit glycogen-binding domain. Although it mimics actions of AMP, it has no effect on binding of AMP to the isolated Bateman domains of the gamma subunit. The addition of A-769662 to mouse embryonic fibroblasts or primary mouse hepatocytes stimulates phosphorylation of acetyl-CoA carboxylase (ACC), effects that are completely abolished in AMPK-alpha1(-/-)alpha2(-/-) cells but not in TAK1(-/-) mouse embryonic fibroblasts. Phosphorylation of AMPK and ACC in response to A-769662 is also abolished in isolated mouse skeletal muscle lacking LKB1, a major upstream kinase for AMPK in this tissue. However, in HeLa cells, which lack LKB1 but express the alternate upstream kinase calmodulin-dependent protein kinase kinase-beta, phosphorylation of AMPK and ACC in response to A-769662 still occurs. These results show that in intact cells, the effects of A-769662 are independent of the upstream kinase utilized. We propose that this direct and specific AMPK activator will be a valuable experimental tool to understand the physiological roles of AMPK.

Tumor progression locus-2 is a critical regulator of pancreatic and lung inflammation during acute pancreatitis

Pancreatic and lung inflammation during acute pancreatitis is a poorly understood, but clinically important, phenomenon. The proto-oncogene Tpl2 (tumor progression locus-2) has recently been shown to have important immunomodulatory effects on some inflammatory processes, but its importance to pancreatitis has not been previously examined. Our studies were designed to (a) define the effects of Tpl2 on pancreatic and lung inflammation during pancreatitis and (b) identify mechanisms and cell types responsible for those effects. We examined pancreatitis-associated Tpl2 effects in wild type and Tpl2(-/-) mice subjected to either secretagogue-induced or bile salt-induced pancreatitis. To determine the myeloid or non-myeloid lineage of cells responsible for the Tpl2 effects, we used Tpl2(-/-) chimeric mice generated by lethal irradiation followed by bone marrow transplantation. Mechanisms responsible for the effects of Tpl2 ablation on caerulein-induced proinflammatory events were evaluated under in vivo and in vitro conditions using the techniques of electrophoretic mobility shift assay, immunoblot analysis, and quantitative reverse transcription-PCR. We found that Tpl2 ablation markedly reduced pancreatic and lung inflammation in these two dissimilar models of pancreatitis, but it did not alter pancreatic injury/necrosis in either model. The reduction in caerulein-induced pancreatic inflammation is dependent upon Tpl2 ablation in non-myeloid cells and is associated with both in vivo and in vitro inhibition of MEK, JNK, and AP-1 activation and the expression of MCP-1, MIP-2, and interleukin-6. Non-myeloid cell expression of Tpl2 regulates pancreatic inflammation during pancreatitis by mediating proinflammatory signals and the generation of neutrophil chemoattracting factors.

TAK1 is indispensable for development of T cells and prevention of colitis by the generation of regulatory T cells

Transforming growth factor (TGF)-beta-activating kinase 1 (TAK1) is critical for Toll-like receptor- and tumor necrosis factor-mediated cellular responses. In B cells, TAK1 is essential for the activation of mitogen-activated protein kinases (MAPKs), but not nuclear factor-kappaB (NF-kappaB), in antigen receptor signaling. In this study, we generate T cell-specific TAK1-deficient (Lck(Cre/(+))Tak1(flox/flox)) mice and show that TAK1 is indispensable for the maintenance of peripheral CD4 and CD8 T cells. In thymocytes, TAK1 is essential for TCR-mediated activation of both NF-kappaB and MAPKs. Additionally, Lck(Cre/(+))Tak1(flox/flox) mice developed colitis as they aged. In these mice, accumulations of activated/memory T cells as well as B cells were observed. Development of regulatory T (Treg) cells in thymus was abrogated in Lck(Cre/(+))Tak1(flox/flox) mice, suggesting that the loss of Treg cells is the cause of the disease. Together, the results show that TAK1, by controlling the generation of central Treg cells, is important for preventing spontaneously developing colitis.

Transforming growth factor-beta-activated kinase 1 is essential for differentiation and the prevention of apoptosis in epidermis

Transforming growth factor-beta-activated kinase 1 (TAK1) is a member of the mitogen-activated protein (MAP) kinase family and is an upstream signaling molecule of nuclear factor-kappaB (NF-kappaB). Given that NF-kappaB regulates keratinocyte differentiation and apoptosis, TAK1 may be essential for epidermal functions. To test this, we generated keratinocyte-specific TAK1-deficient mice from Map3k7(flox/flox) mice and K5-Cre mice. The keratinocyte-specific TAK1-deficient mice were macroscopically indistinguishable from their littermates until postnatal day 2 or 3, when the skin started to roughen and wrinkle. This phenotype progressed, and the mice died by postnatal day 7. Histological analysis showed thickening of the epidermis with foci of keratinocyte apoptosis and intra-epidermal micro-abscesses. Immunohistochemical analysis showed that the suprabasal keratinocytes of the TAK1-deficient epidermis expressed keratin 5 and keratin 14, which are normally confined to the basal layer. The expression of keratin 1, keratin 10, and loricrin, which are markers for the suprabasal and late phase differentiation of the epidermis, was absent from the TAK1-deficient epidermis. Furthermore, the TAK1-deficient epidermis expressed keratin 16 and had an increased number of Ki67-positive cells. These data indicate that TAK1 deficiency in keratinocytes results in abnormal differentiation, increased proliferation, and apoptosis in the epidermis. However, the keratinocytes from the TAK1-deficient epidermis induced keratin 1 in suspension culture, indicating that the TAK1-deficient keratinocytes retain the ability to differentiate. Moreover, the removal of TAK1 from cultured keratinocytes of Map3k7(flox/flox) mice resulted in apoptosis, indicating that TAK1 is essential for preventing apoptosis. In conclusion, TAK1 is essential in the regulation of keratinocyte growth, differentiation, and apoptosis.

The TGFβ activated kinase TAK1 regulates vascular development in vivo

TGFβ activated kinase 1 (TAK1) is a MAPKKK that in cell culture systems has been shown to act downstream of a variety of signaling molecules,including TGFβ. Its role during vertebrate development, however, has not been examined by true loss-of-function studies. In this report, we describe the phenotype of mouse embryos in which the Tak1 gene has been inactivated by a genetrap insertion. Tak1 mutant embryos exhibit defects in the developing vasculature of the embryo proper and yolk sac. These defects include dilation and misbranching of vessels, as well as an absence of vascular smooth muscle. The phenotype of Tak1 mutant embryos is strikingly similar to that exhibited by loss-of-function mutations in the TGFβ type I receptor Alk1 and the type III receptor endoglin,suggesting that TAK1 may be a major effector of TGFβ signals during vascular development. Consistent with this view, we find that in zebrafish,morpholinos to TAK1 and ALK1 synergize to enhance the Alk1 vascular phenotype. Moreover, we show that overexpression of TAK1 is able to rescue the vascular defect produced by morpholino knockdown of ALK1. Taken together,these results suggest that TAK1 is probably an important downstream component of the TGFβ signal transduction pathway that regulates vertebrate vascular development. In addition, as heterozygosity for mutations in endoglin and ALK1 lead to the human syndromes known as hereditary hemorrhagic telangiectasia 1 and 2, respectively, our results raise the possibility that mutations in human TAK1 might contribute to this disease.

Diverse Toll-like receptors utilize Tpl2 to activate extracellular signal-regulated kinase (ERK) in hemopoietic cells

Engaging mammalian Toll-like receptors (TLRs) activate both the NF-kappaB and mitogen-activated protein kinase signaling pathways. Here we establish that mitogen-activated protein 3 kinase Tpl2, levels of which are markedly reduced in nfkb1(-/-) cells, is required for extracellular signal-regulated kinase (ERK) activation in bone marrow-derived macrophages and B cells stimulated with diverse TLR ligands. Despite rescuing TLR-dependent ERK activation in nfkb1(-/-) bone marrow-derived macrophages by using an estrogen receptor-regulated version of the mitogen-activated protein 3 kinase, c-Raf (Raf:ER), CpG or LPS induction of IL-10 was only partially restored in nfkb1(-/-) cells expressing Raf:ER, a finding consistent with NF-kappaB1 regulating IL-10 by a combination of ERK-independent and -dependent mechanisms. Collectively, our findings indicate that the Tpl2/MEK/ERK signaling module is a master regulator of ERK-dependent gene expression downstream of TLRs in different hemopoietic cells.

The tyrosine kinase Syk regulates TPL2 activation signals

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

Essential function for the kinase TAK1 in innate and adaptive immune responses

Transforming growth factor-beta-activated kinase 1 (TAK1) has been linked to interleukin 1 receptor and tumor necrosis factor receptor signaling. Here we generated mouse strains with conditional expression of a Map3k7 allele encoding part of TAK1. TAK1-deficient embryonic fibroblasts demonstrated loss of responses to interleukin 1beta and tumor necrosis factor. Studies of mice with B cell-specific TAK1 deficiency showed that TAK1 was indispensable for cellular responses to Toll-like receptor ligands, CD40 and B cell receptor crosslinking. In addition, antigen-induced immune responses were considerably impaired in mice with B cell-specific TAK1 deficiency. TAK1-deficient cells failed to activate transcription factor NF-kappaB and mitogen-activated protein kinases in response to interleukin 1beta, tumor necrosis factor and Toll-like receptor ligands. However, TAK1-deficient B cells were able to activate NF-kappaB but not the kinase Jnk in response to B cell receptor stimulation. These results collectively indicate that TAK1 is key in the cellular response to a variety of stimuli.

A serine/threonine kinase, Cot/Tpl2, modulates bacterial DNA-induced IL-12 production and Th cell differentiation

A serine/threonine protein kinase, Cot/Tpl2, is indispensable for extracellular signal-regulated kinase (ERK) activation and production of TNF-alpha and PGE2 in LPS-stimulated macrophages. We show here that Cot/Tpl2 is also activated by other Toll-like receptor (TLR) ligands. Bacterial DNA rich in the dinucleotide CG (CpG-DNA), unlike LPS or synthetic lipopeptide, activated ERK in a Cot/Tpl2-independent manner. Peritoneal macrophages and bone marrow-derived DCs from Cot/Tpl2-/- mice produced significantly more IL-12 in response to CpG-DNA than those from WT mice. Enhanced IL-12 production in Cot/Tpl2-/- macrophages is, at least partly, regulated at the transcriptional level, and the elevated IL-12 mRNA level in Cot/Tpl2-/- macrophages is accompanied by decreased amounts of IL-12 repressors, such as c-musculoaponeurotic fibrosarcoma (c-Maf) and GATA sequence in the IL-12 promoter-binding protein (GA-12-binding protein; GAP-12) in the nucleus. Consistently, Cot/Tpl2-/- mice showed Th1-skewed antigen-specific immune responses upon OVA immunization and Leishmania major infection in vivo. These results indicate that Cot/Tpl2 is an important negative regulator of Th1-type adaptive immunity, that it achieves this regulation by inhibiting IL-12 production from accessory cells, and that it might be a potential target molecule in CpG-DNA-guided vaccination.

Targeted deletion of apoptosis signal-regulating kinase 1 attenuates left ventricular remodeling

Left ventricular remodeling that occurs after myocardial infarction (MI) and pressure overload is generally accepted as a determinant of the clinical course of heart failure. The molecular mechanism of this process, however, remains to be elucidated. Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase kinase kinase that plays an important role in stress-induced apoptosis. We used ASK1 knockout mice (ASK-/-) to test the hypothesis that ASK1 is involved in development of left ventricular remodeling. ASK-/- hearts showed no morphological or histological defects. Echocardiography and cardiac catheterization revealed normal global structure and function. Left ventricular structural and functional remodeling were determined 4 weeks after coronary artery ligation or thoracic transverse aortic constriction (TAC). ASK-/- had significantly smaller increases in left ventricular end-diastolic and end-systolic ventricular dimensions and smaller decreases in fractional shortening in both experimental models compared with WT mice. The number of terminal deoxynucleotidyl transferase biotin-dUDP nick end-labeling-positive myocytes after MI or TAC was decreased in ASK-/- compared with that in WT mice. Overexpression of a constitutively active mutant of ASK1 induced apoptosis in isolated rat neonatal cardiomyocytes, whereas neonatal ASK-/- cardiomyocytes were resistant to H2O2-induced apoptosis. An in vitro kinase assay showed increased ASK1 activity in heart after MI or TAC in WT mice. Thus, ASK1 plays an important role in regulating left ventricular remodeling by promoting apoptosis.

Activation of Apoptosis Signal-Regulating Kinase 1 in Injured Artery and Its Critical Role in Neointimal Hyperplasia

Background— Apoptosis signal-regulating kinase 1 (ASK1), recently identified as one of the mitogen-activated protein kinase kinase kinases, is activated by various extracellular stimuli and involved in a variety of cellular function. Therefore, we first examined the role of ASK1 in vascular remodeling.

Methods and Results— We used rat balloon injury model and cultured vascular smooth muscle cells (VSMCs). Arterial ASK1 activity was rapidly and dramatically increased after balloon injury. To specifically inhibit endogenous ASK1 activation, dominant-negative mutant of ASK1 (DN-ASK1) was transfected into rat carotid artery before balloon injury. Gene transfer of DN-ASK1 significantly prevented neointimal formation at 14 days after injury. Bromodeoxyuridine labeling index at 7 days after injury showed that DN-ASK1 remarkably suppressed VSMC proliferation in both the intima and the media. We also examined the role of ASK1 in cultured rat VSMCs. Infection with DN-ASK1 significantly attenuated serum-induced VSMC proliferation and migration. We also compared neointimal formation after cuff placement around the femoral artery between mice deficient in ASK1 (ASK1 −/− mice) and wild-type (WT) mice. Neointimal formation at 28 days after cuff injury in ASK1 −/− mice was significantly attenuated compared with WT mice. Furthermore, we compared the proliferation and migration of VSMCs isolated from ASK1 −/− mice with WT mice. Both proliferation and migration of VSMCs from ASK1 −/− mice were significantly attenuated compared with VSMCs from WT mice.

Conclusions— ASK1 activation plays the key role in vascular intimal hyperplasia. ASK1 may provide the basis for the development of new therapeutic strategy for vascular diseases.

Apoptosis Signal-Regulating Kinase 1 Plays a Pivotal Role in Angiotensin II–Induced Cardiac Hypertrophy and Remodeling

Multiple lines of evidence establish that angiotensin II (Ang II) induces not only hypertension but also directly contributes to cardiac diseases. Apoptosis signal-regulating kinase 1 (ASK1), one of mitogen-activated protein kinase kinase kinases, plays a key role in stress-induced cellular responses. However, nothing is known about the role of ASK1 in cardiac hypertrophy and remodeling in vivo. In this study, by using mice deficient in ASK1 (ASK1 −/− mice), we investigated the role of ASK1 in cardiac hypertrophy and remodeling induced by Ang II. Left ventricular (LV) ASK1 was activated by Ang II infusion in wild-type mice, which was mediated by angiotensin II type 1 receptor and superoxide. Although Ang II-induced hypertensive effect was comparable to wild-type and ASK1 −/− mice, LV ASK1 activation by Ang II was not detectable in ASK1 −/− mice, and p38 and c-Jun N-terminal kinase (JNK) activation was lesser in ASK −/− mice than in wild-type mice. Elevation of blood pressure by continuous Ang II infusion was comparable between ASK1 −/− and wild-type mice. However, Ang II–induced cardiac hypertrophy and remodeling, including cardiomyocyte hypertrophy, cardiac hypertrophy–related mRNA upregulation, cardiomyocyte apoptosis, interstitial fibrosis, coronary arterial remodeling, and collagen gene upregulation, was significantly attenuated in ASK1 −/− mice compared with wild-type mice. These results provided the first in vivo evidence that ASK1 is the critical signaling molecule for Ang II–induced cardiac hypertrophy and remodeling. Thus, ASK1 is proposed to be a potential therapeutic target for cardiac diseases.

The in vitro production and characterization of neutrophils from embryonic stem cells

An embryonic stem (ES) cell/OP9 coculture system for the effective production of functional neutrophils is described. A 3-step differentiation strategy was developed that uses liquid culture, enabling reliable and abundant production of neutrophils at high purity without the need of sorting for isolation of mature neutrophils. Use of the OP9 stromal cell line significantly enhances the number, percentage, and duration of differentiated neutrophils produced from embryonic stem cells. Effective and sustained differentiation of ES cells into neutrophils provides a useful model system for studying neutrophil differentiation and function and the factors that regulate them. Morphologic and functional evaluation of these ES-derived neutrophils indicates that large numbers of mature neutrophils can be produced from pluripotent ES cells in vitro. Specifically, their morphology, ability to produce superoxides, flux calcium, undergo chemotaxis in response to macrophage inflammatory protein 2 (MIP-2), stain for the granulocyte-specific marker-specific chloroacetate esterase, and contain the neutrophil-specific markers Gr-1 and the mouse neutrophil-specific antigen indicates that they are comparable with purified mouse bone marrow neutrophils. They also express gelatinase and lactoferrin granule proteins. During the differentiation of these ES-derived neutrophils, regional areas of neutrophil production can be identified that have been designated as neutrophil generating regions (NGRs).

MEKK2 gene disruption causes loss of cytokine production in response to IgE and c-Kit ligand stimulation of ES cell-derived mast cells

Ligation of the high-affinity IgE receptor (FcepsilonRI) or of c-Kit stimulates cytokine production in mast cells. We show that MEK kinase 2 (MEKK2), a MAPK kinase kinase (MAP3K) that regulates the JNK and ERK5 pathways, is required for cytokine production in embryonic stem (ES) cell-derived mast cells (ESMC). Targeted disruption of the MEKK2 or MEKK1 gene was used to abolish expression of the respective kinases in ESMC. Transcription of specific cytokines in response to IgE or c-Kit ligand was markedly reduced in MEKK2(-/-) ESMC relative to wild-type ESMC. Cytokine production in MEKK1(-/-) ESMC was similar to that of wild-type ESMC, demonstrating the specificity of MEKK2 in signaling cytokine gene regulation. MEKK2(-/-) ESMC also lost receptor-mediated stimulation of JNK. In contrast, JNK activation in response to UV irradiation was normal, showing that MEKK2 is required for receptor signaling but not for cellular stress responses. MEKK2 is the first MAP3K shown to be required for mast cell tyrosine kinase receptor signaling controlling cytokine gene expression.

MEKK1 suppresses oxidative stress-induced apoptosis of embryonic stem cell-derived cardiac myocytes

A combination of in vitro embryonic stem (ES) cell differentiation and targeted gene disruption has defined complex regulatory events underlying oxidative stress-induced cardiac apoptosis, a model of postischemic reperfusion injury of myocardium. ES cell-derived cardiac myocytes (ESCM) having targeted disruption of the MEKK1 gene were extremely sensitive, relative to wild-type ESCM, to hydrogen peroxide-induced apoptosis. In response to oxidative stress, MEKK1-/- ESCM failed to activate c-Jun kinase (JNK) but did activate p38 kinase similar to that observed in wild-type ESCM. The increased apoptosis was mediated through enhanced tumor necrosis factor alpha production, a response that was positively and negatively regulated by p38 and the MEKK1-JNK pathway, respectively. Thus, MEKK1 functions in the survival of cardiac myocytes by inhibiting the production of a proapoptotic cytokine. MEKK1 regulation of the JNK pathway is a critical response for the protection against oxidative stress-induced apoptosis in cardiac myocytes.