Feedback control of the protein kinase TAK1 by SAPK2a/p38alpha

Spatiotemporal control of kinases and the biomolecular tools to trace activity

The delicate balance of cell physiology is implicitly tied to the expression and activation of proteins. Post-translational modifications offer a tool to dynamically switch protein activity on and off to orchestrate a wide range of protein-protein interactions to tune signal transduction during cellular homeostasis and pathological responses. There is a growing acknowledgment that subcellular locations of kinases define the spatial network of potential scaffolds, adaptors, and substrates. These highly ordered and localized biomolecular microdomains confer a spatially distinct bias in the outcomes of kinase activity. Furthermore, they may hold essential clues to the underlying mechanisms that promote disease. Developing tools to dissect the spatiotemporal activation of kinases is critical to reveal these mechanisms and promote the development of spatially targeted kinase inhibitors. Here, we discuss the spatial regulation of kinases, the tools used to detect their activity, and their potential impact on human health.

Analysis of potential TAK1/Map3k7 phosphorylation targets in hypertrophy and cachexia models of skeletal muscle

TGFβ-activated kinase-1 (TAK1) is phosphorylated during both muscle growth and muscle wasting. To understand how this can lead to such opposite effects, we first performed multiplex kinase array of mouse embryonic stem cells with and without stimulation of TAK1 to determine its potential downstream targets. The phosphorylation of these targets was then compared in three different models: hypertrophic longissimus muscle of Texel sheep, tibialis anterior muscle of mice with cancer-induced cachexia and C2C12-derived myofibers, with and without blockade of TAK1 phosphorylation. In both Texel sheep and in cancer-induced cachexia, phosphorylation of both TAK1 and p38 was increased. Whereas p90RSK was increased in Texel sheep but not cachexia and the phosphorylation of HSP27 and total Jnk were increased in cachexia but not Texel. To understand this further, we examined the expression of these proteins in C2C12 cells as they differentiated into myotubes, with and without blockade of TAK1 phosphorylation. In C2C12 cells, decreased phosphorylation of TAK1 leads to reduced phosphorylation of p38, JNK, and HSP27 after 16 h and muscle fiber hypertrophy after 3 days. However, continuous blockade of this pathway leads to muscle fiber failure, suggesting that the timing of TAK1 activation controls the expression of context-dependent targets.

Cyld restrains the hyperactivation of synovial fibroblasts in inflammatory arthritis by regulating the TAK1/IKK2 signaling axis

TNF is a potent cytokine known for its involvement in physiology and pathology. In Rheumatoid Arthritis (RA), persistent TNF signals cause aberrant activation of synovial fibroblasts (SFs), the resident cells crucially involved in the inflammatory and destructive responses of the affected synovial membrane. However, the molecular switches that control the pathogenic activation of SFs remain poorly defined. Cyld is a major component of deubiquitination (DUB) machinery regulating the signaling responses towards survival/inflammation and programmed necrosis that induced by cytokines, growth factors and microbial products. Herein, we follow functional genetic approaches to understand how Cyld affects arthritogenic TNF signaling in SFs. We demonstrate that in spontaneous and induced RA models, SF-Cyld DUB deficiency deteriorates arthritic phenotypes due to increased levels of chemokines, adhesion receptors and bone-degrading enzymes generated by mutant SFs. Mechanistically, Cyld serves to restrict the TNF-induced hyperactivation of SFs by limiting Tak1-mediated signaling, and, therefore, leading to supervised NF-κB and JNK activity. However, Cyld is not critically involved in the regulation of TNF-induced death of SFs. Our results identify SF-Cyld as a regulator of TNF-mediated arthritis and inform the signaling landscape underpinning the SF responses.

Dynamical and combinatorial coding by MAPK p38 and NFκB in the inflammatory response of macrophages

Macrophages sense pathogens and orchestrate specific immune responses. Stimulus specificity is thought to be achieved through combinatorial and dynamical coding by signaling pathways. While NFκB dynamics are known to encode stimulus information, dynamical coding in other signaling pathways and their combinatorial coordination remain unclear. Here, we established live-cell microscopy to investigate how NFκB and p38 dynamics interface in stimulated macrophages. Information theory and machine learning revealed that p38 dynamics distinguish cytokine TNF from pathogen-associated molecular patterns and high doses from low, but contributed little to information-rich NFκB dynamics when both pathways are considered. This suggests that immune response genes benefit from decoding immune signaling dynamics or combinatorics, but not both. We found that the heterogeneity of the two pathways is surprisingly uncorrelated. Mathematical modeling revealed potential sources of uncorrelated heterogeneity in the branched pathway network topology and predicted it to drive gene expression variability. Indeed, genes dependent on both p38 and NFκB showed high scRNAseq variability and bimodality. These results identify combinatorial signaling as a mechanism to restrict NFκB-AND-p38-responsive inflammatory cytokine expression to few cells.

Remodeling tumor-associated macrophage for anti-cancer effects by rational design of irreversible inhibition of mitogen-activated protein kinase-activated protein kinase 2

Mitogen-activated protein kinase-activated protein kinase 2 (MK2) emerges as a pivotal target in developing anti-cancer therapies. The limitations of ATP-competitive inhibitors, due to insufficient potency and selectivity, underscore the urgent need for a covalent irreversible MK2 inhibitor. Our initial analyses of The Cancer Genome Atlas database revealed MK2's overexpression across various cancer types, especially those characterized by inflammation, linking it to poor prognosis and highlighting its significance. Investigating MK2's kinase domain led to the identification of a unique cysteine residue, enabling the creation of targeted covalent inhibitors. Compound 11 was developed, demonstrating robust MK2 inhibition (IC50 = 2.3 nM) and high selectivity. It binds irreversibly to MK2, achieving prolonged signal suppression and reducing pathological inflammatory cytokines in macrophages. Furthermore, compound 11 or MK2 knockdown can inhibit the tumor-promoting macrophage M2 phenotype in vitro and in vivo. In macrophage-rich tumor model, compound 11 notably slowed growth in a dose-dependent manner. These findings support MK2 as a promising anticancer target, especially relevant in cancers fueled by inflammation or dominated by macrophages, and provide compound 11 serving as an invaluable chemical tool for exploring MK2's functions.

Crosstalk with renal proximal tubule cells drives acidosis-induced inflammatory response and dedifferentiation of fibroblasts via p38-singaling

BACKGROUND

Tubulointerstitial kidney disease associated microenvironmental dysregulation, like acidification, inflammation and fibrosis, affects tubule cells and fibroblasts. Micromilieu homeostasis influences intracellular signaling and intercellular crosstalk. Cell-cell communication in turn modulates the interstitial microenvironment. We assessed the impact of acidosis on inflammatory and fibrotic responses in proximal tubule cells and fibroblasts as a function of cellular crosstalk. Furthermore, cellular signaling pathways involved were identified.

METHODS

HK-2 (human proximal tubule) and CCD-1092Sk (human fibroblasts), in mono and coculture, were exposed to acidic or control media for 3 or 48 h. Protein expression of inflammation markers (TNF, TGF-ß and COX-2), dedifferentiation markers (N-cadherin, vinculin, ß-catenin and vimentin), fibrosis markers (collagen III and fibronectin) and phospho- as well as total MAPK levels were determined by western blot. Secreted collagen III and fibronectin were measured by ELISA. The impact of MAPK activation was assessed by pharmacological intervention. In addition, necrosis, apoptosis and epithelial permeability were determined.

RESULTS

Independent of culture conditions, acidosis caused a decrease of COX-2, vimentin and fibronectin expression in proximal tubule cells. Only in monoculture, ß-Catenin expression decreased and collagen III expression increased in tubule cells during acidosis. By contrast, in coculture collagen III protein expression of tubule cells was reduced. In fibroblasts acidosis led to an increase of TNF, COX-2, vimentin, vinculin, N-cadherin protein expression and a decrease of TGF-ß expression exclusively in coculture. In monoculture, expression of COX-2 and fibronectin was reduced. Collagen III expression of fibroblasts was reduced by acidosis independent of culture conditions. In coculture, acidosis enhanced phosphorylation of ERK1/2, JNK1/2 and p38 transiently in proximal tubule cells. In fibroblasts, acidosis enhanced phosphorylation of p38 in a sustained and very strong manner. ERK1/2 and JNK1/2 were not affected in fibroblasts. Inhibition of JNK1/2 and p38 under coculture conditions reduced acidosis-induced changes in fibroblasts significantly.

CONCLUSIONS

Our data show that the crosstalk between proximal tubule cells and fibroblasts is crucial for acidosis-induced dedifferentiation of fibroblasts into an inflammatory phenotype. This dedifferentiation is at least in part mediated by p38 and JNK1/2. Thus, cell-cell communication is essential for the pathophysiological impact of tubulointerstitial acidosis.

MITOGEN-ACTIVATED PROTEIN KINASE3 enhances disease resistance of edr1 mutants by phosphorylating MAPKKK5

Mitogen-activated protein kinase (MAPK/MPK) cascades are key signaling modules that regulate plant immunity. ENHANCED DISEASE RESISTANCE1 (EDR1) encodes a Raf-like MAPK kinase kinase (MAPKKK) that negatively regulates plant defense in Arabidopsis (Arabidopsis thaliana). The enhanced resistance of edr1 requires MAPK KINASE4 (MKK4), MKK5, and MPK3. Although the edr1 mutant displays higher MPK3/6 activation, the mechanism by which plants increase MAPK cascade activation remains elusive. Our previous study showed that MAPKKK5 is phosphorylated at the Ser-90 residue in edr1 mutants. In this study, we demonstrated that the enhanced disease resistance of edr1 required MAPKKK5. Phospho-dead MAPKKK5S90A partially impaired the resistance of edr1, and the expression of phospho-mimetic MAPKKK5S90D in mapkkk5-2 resulted in enhanced resistance to the powdery mildew Golovinomyces cichoracearum strain UCSC1 and the bacterial pathogen Pseudomonas syringae pv. tomato (Pto) strain DC3000. Thus, Ser-90 phosphorylation in MAPKKK5 appears to play a crucial role in disease resistance. However, MAPKKK5-triggered cell death was not suppressed by EDR1. Furthermore, activated MPK3 phosphorylated the N terminus of MAPKKK5, and Ser-90 was one of the phosphorylated sites. Ser-90 phosphorylation increased MAPKKK5 stability, and EDR1 might negatively regulate MAPK cascade activation by suppressing the MPK3-mediated feedback regulation of MAPKKK5. Taken together, these results indicate that MPK3 phosphorylates MAPKKK5 to enhance MAPK cascade activation and disease resistance in edr1 mutants.

The TGFβ→TAK1→LATS→YAP1 Pathway Regulates the Spatiotemporal Dynamics of YAP1

The Hippo kinase cascade functions as a central hub that relays input from the "outside world" of the cell and translates it into specific cellular responses by regulating the activity of Yes-associated protein 1 (YAP1). How Hippo translates input from the extracellular signals into specific intracellular responses remains unclear. Here, we show that transforming growth factor β (TGFβ)-activated TAK1 activates LATS1/2, which then phosphorylates YAP1. Phosphorylated YAP1 (p-YAP1) associates with RUNX3, but not with TEAD4, to form a TGFβ-stimulated restriction (R)-point-associated complex which activates target chromatin loci in the nucleus. Soon after, p-YAP1 is exported to the cytoplasm. Attenuation of TGFβ signaling results in re-localization of unphosphorylated YAP1 to the nucleus, where it forms a YAP1/TEAD4/SMAD3/AP1/p300 complex. The TGFβ-stimulated spatiotemporal dynamics of YAP1 are abrogated in many cancer cells. These results identify a new pathway that integrates TGFβ signals and the Hippo pathway (TGFβ→TAK1→LATS1/2→YAP1 cascade) with a novel dynamic nuclear role for p-YAP1.

ASK1-K716R reduces neuroinflammation and white matter injury via preserving blood-brain barrier integrity after traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is a significant worldwide public health concern that necessitates attention. Apoptosis signal-regulating kinase 1 (ASK1), a key player in various central nervous system (CNS) diseases, has garnered interest for its potential neuroprotective effects against ischemic stroke and epilepsy when deleted. Nonetheless, the specific impact of ASK1 on TBI and its underlying mechanisms remain elusive. Notably, mutation of ATP-binding sites, such as lysine residues, can lead to catalytic inactivation of ASK1. To address these knowledge gaps, we generated transgenic mice harboring a site-specific mutant ASK1 Map3k5-e (K716R), enabling us to assess its effects and elucidate potential underlying mechanisms following TBI.

METHODS

We employed the CRIPR/Cas9 system to generate a transgenic mouse model carrying the ASK1-K716R mutation, aming to investigate the functional implications of this specific mutant. The controlled cortical impact method was utilized to induce TBI. Expression and distribution of ASK1 were detected through Western blotting and immunofluorescence staining, respectively. The ASK1 kinase activity after TBI was detected by a specific ASK1 kinase activity kit. Cerebral microvessels were isolated by gradient centrifugation using dextran. Immunofluorescence staining was performed to evaluate blood-brain barrier (BBB) damage. BBB ultrastructure was visualized using transmission electron microscopy, while the expression levels of endothelial tight junction proteins and ASK1 signaling pathway proteins was detected by Western blotting. To investigate TBI-induced neuroinflammation, we conducted immunofluorescence staining, quantitative real-time polymerase chain reaction (qRT-PCR) and flow cytometry analyses. Additionally, immunofluorescence staining and electrophysiological compound action potentials were conducted to evaluate gray and white matter injury. Finally, sensorimotor function and cognitive function were assessed by a battery of behavioral tests.

RESULTS

The activity of ASK1-K716R was significantly decreased following TBI. Western blotting confirmed that ASK1-K716R effectively inhibited the phosphorylation of ASK1, JNKs, and p38 in response to TBI. Additionally, ASK1-K716R demonstrated a protective function in maintaining BBB integrity by suppressing ASK1/JNKs activity in endothelial cells, thereby reducing the degradation of tight junction proteins following TBI. Besides, ASK1-K716R effectively suppressed the infiltration of peripheral immune cells into the brain parenchyma, decreased the number of proinflammatory-like microglia/macrophages, increased the number of anti-inflammatory-like microglia/macrophages, and downregulated expression of several proinflammatory factors. Furthermore, ASK1-K716R attenuated white matter injury and improved the nerve conduction function of both myelinated and unmyelinated fibers after TBI. Finally, our findings demonstrated that ASK1-K716R exhibited favorable long-term functional and histological outcomes in the aftermath of TBI.

CONCLUSION

ASK1-K716R preserves BBB integrity by inhibiting ASK1/JNKs pathway in endothelial cells, consequently reducing the degradation of tight junction proteins. Additionally, it alleviates early neuroinflammation by inhibiting the infiltration of peripheral immune cells into the brain parenchyma and modulating the polarization of microglia/macrophages. These beneficial effects of ASK1-K716R subsequently result in a reduction in white matter injury and promote the long-term recovery of neurological function following TBI.

Degradation of MK2 with natural compound andrographolide: A new modality for anti-inflammatory therapy

The p38MAPK-MK2 signaling axis functions as an initiator of inflammation. Targeting the p38MAPK-MK2 signaling axis represents a direct therapeutic intervention of inflammatory diseases. We described here a novel role of andrographolide (AG), a small-molecule ent-labdane natural compound, as an inhibitor of p38MAPK-MK2 axis via MK2 degradation. AG was found to bind to the activation loop of MK2, located at the interface of the p38MAPK-MK2 biomolecular complex. This interaction disrupted the complex formation and predisposed MK2 to proteasome-mediated degradation. We showed that AG induced MK2 degradation in a concentration- and time-dependent manner and exerted its anti-inflammatory effects by enhancing the mRNA-destabilizing activity of tristetraprolin, thereby inhibiting pro-inflammatory mediator production (e.g., TNF-α, MCP-1). Administration of AG via intratracheal (i.t.) route to mice induced MK2 downregulation in lung alveolar macrophages, but not lung tissues, and prevented macrophage activation. Our study also demonstrated that the anti-inflammatory effects achieved by AG via MK2 degradation were more durable and sustained than that achieved by the conventional MK2 kinase inhibitors (e.g., PF-3644022). Taken together, our findings illustrated a novel mode of action of AG by modulating the p38MAPK-MK2 signaling axis and would pave the way for the development of a novel class of anti-inflammatory agents targeting MK2 for degradation by harnessing the privileged scaffold of AG.

Tbx5 overexpression in embryoid bodies increases TAK1 expression but does not enhance the differentiation of sinoatrial node cardiomyocytes

Genetic studies place Tbx5 at the apex of the sinoatrial node (SAN) transcriptional program. To understand its role in SAN differentiation, clonal embryonic stem (ES) cell lines were made that conditionally overexpress Tbx5, Tbx3, Tbx18, Shox2, Islet-1, and MAP3k7/TAK1. Cardiac cells differentiated using embryoid bodies (EBs). EBs overexpressing Tbx5, Islet1, and TAK1 beat faster than cardiac cells differentiated from control ES cell lines, suggesting possible roles in SAN differentiation. Tbx5 overexpressing EBs showed increased expression of TAK1, but cardiomyocytes did not differentiate as SAN cells. EBs showed no change in the expression of the SAN transcription factors Shox2 and Islet1 and decreased expression of the SAN channel protein HCN4. EBs constitutively overexpressing TAK1 direct cardiac differentiation to the SAN fate but have reduced phosphorylation of its targets, p38 and Jnk. This opens the possibility that blocking the phosphorylation of TAK1 targets may have the same impact as forced overexpression. To test this, we treated EBs with 5z-7-Oxozeanol (OXO), an inhibitor of TAK1 phosphorylation. Like TAK1 overexpressing cardiac cells, cardiomyocytes differentiated in the presence of OXO beat faster and showed increased expression of SAN genes (Shox2, HCN4, and Islet1). This suggests that activation of the SAN transcriptional network can be accomplished by blocking the phosphorylation of TAK1.

Fluorescence resonance energy transfer (FRET) spatiotemporal mapping of atypical P38 reveals an endosomal and cytosolic spatial bias

Mitogen-activated protein kinase (MAPK) p38 is a central regulator of intracellular signaling, driving physiological and pathological pathways. With over 150 downstream targets, it is predicted that spatial positioning and the availability of cofactors and substrates determines kinase signaling specificity. The subcellular localization of p38 is highly dynamic to facilitate the selective activation of spatially restricted substrates. However, the spatial dynamics of atypical p38 inflammatory signaling are understudied. We utilized subcellular targeted fluorescence resonance energy transfer (FRET) p38 activity biosensors to map the spatial profile of kinase activity. Through comparative analysis of plasma membrane, cytosolic, nuclear, and endosomal compartments, we confirm a characteristic profile of nuclear bias for mitogen-activated kinase kinase 3/6 (MKK3/6) dependent p38 activation. Conversely, atypical p38 activation via thrombin-mediated protease-activated receptor 1 (PAR1) activity led to enhanced p38 activity at the endosome and cytosol, limiting nuclear p38 activity, a profile conserved for prostaglandin E2 activation of p38. Conversely, perturbation of receptor endocytosis led to spatiotemporal switching of thrombin signaling, reducing endosomal and cytosolic p38 activity and increasing nuclear activity. The data presented reveal the spatiotemporal dynamics of p38 activity and provide critical insight into how atypical p38 signaling drives differential signaling responses through spatial sequestration of kinase activity.

Emerging role of TAK1 in the regulation of skeletal muscle mass

Maintenance of skeletal muscle mass and strength throughout life is crucial for heathy living and longevity. Several signaling pathways have been implicated in the regulation of skeletal muscle mass in adults. TGF-β-activated kinase 1 (TAK1) is a key protein, which coordinates the activation of multiple signaling pathways. Recently, it was discovered that TAK1 is essential for the maintenance of skeletal muscle mass and myofiber hypertrophy following mechanical overload. Forced activation of TAK1 in skeletal muscle causes hypertrophy and attenuates denervation-induced muscle atrophy. TAK1-mediated signaling in skeletal muscle promotes protein synthesis, redox homeostasis, mitochondrial health, and integrity of neuromuscular junctions. In this article, we have reviewed the role and potential mechanisms through which TAK1 regulates skeletal muscle mass and growth. We have also proposed future areas of research that could be instrumental in exploring TAK1 as therapeutic target for improving muscle mass in various catabolic conditions and diseases.

RNF207 exacerbates pathological cardiac hypertrophy via post-translational modification of TAB1

AIMS

The heart undergoes pathological remodelling, featured by the hypertrophic growth of cardiomyocytes and increased cardiac fibrosis, under biomechanical stress such as haemodynamic overload. Ring Finger Protein 207 (RNF207) is an E3 ubiquitin ligase that is predominantly expressed in the heart, but its function remains elusive. In this study, we aimed to explore the role of RNF207 in the development of pathological cardiac hypertrophy and dysfunction.

METHODS AND RESULTS

Transverse aortic constriction (TAC) surgery was performed on mice to induce cardiac hypertrophy. Cardiac function and remodelling were evaluated by echocardiography, histological assessment, and molecular analyses. Our data indicated that RNF207 overexpression (OE) exacerbated cardiac hypertrophy, fibrosis, and systolic dysfunction. In contrast, TAC-induced cardiac remodelling was profoundly blunted in RNF207 knockdown (KD) hearts. In line with the in vivo findings, RNF207 OE augmented, whereas RNF207 KD alleviated, phenylephrine-induced cardiomyocyte hypertrophy in vitro. Mechanistically, we demonstrated that RNF207 elicited detrimental effects by promoting K63-linked ubiquitination of TAK1-binding protein 1 (TAB1), which triggered the autophosphorylation of transforming growth factor-β activated kinase 1 (TAK1) and the activation of downstream p38 and c-Jun N-terminal kinase (JNK)1/2 signalling pathways. In the TAB1-KD cardiomyocytes, RNF207-OE-induced cell hypertrophy was significantly attenuated, indicating that RNF207-induced hypertrophy is, at least in part, TAB1-dependent.

CONCLUSIONS

This study demonstrates that RNF207 exacerbates pressure overload-induced cardiac hypertrophy and dysfunction via post-translational modification of TAB1.

Inhibiting O-GlcNAcylation impacts p38 and Erk1/2 signaling and perturbs cardiomyocyte hypertrophy

The dynamic cycling of O-linked GlcNAc (O-GlcNAc) on and off Ser/Thr residues of intracellular proteins, termed O-GlcNAcylation, is mediated by the conserved enzymes O-GlcNAc transferase (OGT) and O-GlcNAcase. O-GlcNAc cycling is important in homeostatic and stress responses, and its perturbation sensitizes the heart to ischemic and other injuries. Despite considerable progress, many molecular pathways impacted by O-GlcNAcylation in the heart remain unclear. The mitogen-activated protein kinase (MAPK) pathway is a central signaling cascade that coordinates developmental, physiological, and pathological responses in the heart. The developmental or adaptive arm of MAPK signaling is primarily mediated by Erk kinases, while the pathophysiologic arm is mediated by p38 and Jnk kinases. Here, we examine whether O-GlcNAcylation affects MAPK signaling in cardiac myocytes, focusing on Erk1/2 and p38 in basal and hypertrophic conditions induced by phenylephrine. Using metabolic labeling of glycans coupled with alkyne-azide "click" chemistry, we found that Erk1/2 and p38 are O-GlcNAcylated. Supporting the regulation of p38 by O-GlcNAcylation, the OGT inhibitor, OSMI-1, triggers the phosphorylation of p38, an event that involves the NOX2-Ask1-MKK3/6 signaling axis and also the noncanonical activator Tab1. Additionally, OGT inhibition blocks the phenylephrine-induced phosphorylation of Erk1/2. Consistent with perturbed MAPK signaling, OSMI-1-treated cardiomyocytes have a blunted hypertrophic response to phenylephrine, decreased expression of cTnT (key component of the contractile apparatus), and increased expression of maladaptive natriuretic factors Anp and Bnp. Collectively, these studies highlight new roles for O-GlcNAcylation in maintaining a balanced activity of Erk1/2 and p38 MAPKs during hypertrophic growth responses in cardiomyocytes.

Long noncoding RNA TARL promotes antibacterial activity and prevents bacterial escape in Miichthys miiuy through suppression of TAK1 downregulation

Noncoding RNA (ncRNA) is an important regulatory factor that plays a major role in innate immunity. However, most studies on ncRNA have focused on mammals, resulting in a knowledge gap on ncRNA in lower vertebrates such as teleost fish. In this study, we identified a new long noncoding RNA (lncRNA), termed TAK1-related lncRNA (TARL), which can play a positive role in the antibacterial immunity of Miichthys miiuy to Vibrio anguillarum and V. harveyi. We also found a novel microRNA miR-2188-3p that could target TAK1 and inhibit the host antibacterial response and promote bacterial escape. We further found that the antibacterial effect inhibited by miR-2188-3p could be reversed with TARL. Moreover, V. anguillarum and V. harveyi are the two most susceptible Gram-negative pathogens of aquaculture fish, and the economic losses caused by these two bacteria are immeasurable every year. This study is the first to report on the ability of lncRNA to prevent the escape of V. anguillarum and V. harveyi in fish through the competing endogenous RNA (ceRNA) mechanism. Our results not only elucidate the ceRNA mechanism of the lncRNA in antibacterial immune responses but also provide new insights into the impact of lncRNA on host immunity and bacterial escape.

TAK1 protein kinase activity is required for TLR signalling and cytokine production in myeloid cells

A conditional knock-in mouse was generated in which the TAK1 catalytic subunit was largely replaced by the kinase-inactive TAK1[D175A] mutant in immune cells. The activation of p38α MAP kinase, c-Jun N-terminal kinases 1 and 2 (JNK1/2) and the canonical IKK complex induced by stimulation with several TLR-activating ligands was reduced in bone marrow-derived macrophages (BMDM) from TAK1[D175A] mice. TLR signalling in TAK1[D175A] BMDM was catalysed by the residual wild-type TAK1 in these cells because it was abolished by either of two structurally unrelated TAK1 inhibitors (NG25 and 5Z-7-oxozeaenol) whose off-target effects do not overlap. The secretion of inflammatory mediators and production of the mRNAs encoding these cytokines induced by TLR ligation was greatly reduced in peritoneal neutrophils or BMDM from TAK1[D175A] mice. The Pam3CSK4- or LPS-stimulated activation of MAP kinases and the canonical IKK complex, as well as cytokine secretion, was also abolished in TAK1 knock-out human THP1 monocytes or macrophages. The results establish that TAK1 protein kinase activity is required for TLR-dependent signalling and cytokine secretion in myeloid cells from mice. We discuss possible reasons why other investigators, studying myeloid mice with a conditional knock-out of TAK1 or a different conditional kinase-inactive knock-in of TAK1, reported TAK1 to be a negative regulator of LPS-signalling and cytokine production in mouse macrophages and neutrophils.

CC-99677, a novel, oral, selective covalent MK2 inhibitor, sustainably reduces pro-inflammatory cytokine production

BACKGROUND

Mitogen-activated protein kinase (MAPK)-activated protein kinase-2 (MK2) is activated downstream of p38 MAPK and regulates stability of mRNAs encoding inflammatory cytokines. CC-99677 is a novel, irreversible, covalent MK2 inhibitor under development for the treatment of ankylosing spondylitis (AS) and other inflammatory diseases. As part of a phase I clinical trial to assess safety and tolerability, we evaluated target engagement, pharmacokinetics, and pharmacodynamics of CC-99677.

METHODS

The MK2 inhibitor CC-99677 was evaluated for its effect on cytokine expression in vitro in peripheral blood mononuclear cells (PBMCs) from healthy donors and patients with a definitive AS diagnosis. A novel in vitro model was developed to compare the potential for tachyphylaxis of CC-99677 and p38 inhibitors in THP-1 cells. The effect of CC-99677 on tristetraprolin (TTP) and cytokine mRNA was assessed in stimulated human monocyte-derived macrophages. In a first-in-human study, thirty-seven healthy volunteers were randomly assigned to daily oral doses of CC-99677 or placebo, and blood was collected at pre-specified time points before and after dosing. CC-99677 concentrations were assessed in the plasma, and CC-99677 binding to MK2 was evaluated in PBMCs. Ex vivo stimulation of the whole blood was conducted from participants in the first-in-human study to assess the pharmacodynamic effects.

RESULTS

In vitro, CC-99677 inhibited tumor necrosis factor (TNF), interleukin (IL)-6, and IL-17 protein production in samples of monocytes and macrophages from AS patients and healthy volunteers via an mRNA-destabilization mechanism. In the in vitro model of tachyphylaxis, CC-99677 showed a differentiated pattern of sustained TNF protein inhibition compared with p38 inhibitors. CC-99677 reduced TTP phosphorylation and accelerated the decay of inflammatory cytokine mRNA in lipopolysaccharide-stimulated macrophages. Administration of CC-99677 to healthy volunteers was safe and well-tolerated, with linear pharmacokinetics and sustained reduction of ex vivo whole blood TNF, IL-6, and chemokine synthesis.

CONCLUSIONS

CC-99677 inhibition of MK2 is a promising approach for the treatment of inflammatory diseases and may overcome the limitations of p38 MAPK inhibition.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03554993 .

GFAT1-linked TAB1 glutamylation sustains p38 MAPK activation and promotes lung cancer cell survival under glucose starvation

Reprogrammed cell metabolism is deemed as one of the hallmarks of cancer. Hexosamine biosynthesis pathway (HBP) acts as an “energy sensor” in cells to regulate metabolic fluxes. Glutamine-fructose-6-phosphate amidotransferase 1 (GFAT1), the rate-limiting enzyme of HBP, is broadly found with elevated expression in human cancers though its exact and concrete role in tumorigenesis still remains unknown and needs further investigation. P38 mitogen-activated protein kinase (MAPK) is an important component of stress-signaling pathway and plays a critical role in cell fate decision, whereas the underlying mechanism of its activation under nutrient stress also remains elusive. In this study, we show that glucose deprivation induces the interaction of GFAT1 with transforming growth factor β-activated kinase 1 binding protein 1 (TAB1) in a TAB1 S438 phosphorylation-dependent manner. Subsequently, the binding of GFAT1 to TAB1 facilitates TTLL5–GFAT1–TAB1 complex formation, and the metabolic activity of GFAT1 for glutamate production further contributes to TTLL5-mediated TAB1 glutamylation. In consequence, TAB1 glutamylation promotes the recruitment of p38α MAPK and thus drives p38 MAPK activation. Physiologically, GFAT1-TAB1-p38 signaling promotes autophagy occurrence and thus protects tumor cell survival under glucose deficiency. Clinical analysis indicates that both GFAT1 and TAB1 S438 phosphorylation levels correlate with the poor prognosis of lung adenocarcinoma patients. These findings altogether uncover an unidentified mechanism underlying p38 MAPK signaling regulation by metabolic enzyme upon nutrient stress and provide theoretical rationality of targeting GFAT1 for cancer treatment.

Small Molecule Signatures of Mice Lacking T-cell p38 Alternate Activation, a Model for Immunosuppression Conditions, after Total-Body Irradiation

Several diagnostic biodosimetry tools have been in development that may aid in radiological/nuclear emergency responses. Of these, correlating changes in non-invasive biofluid small-molecule signatures to tissue damage from ionizing radiation exposure show promise for inclusion in predictive biodosimetry models. Integral to dose reconstruction has been determining how genotypic variation in the general population will affect model performance. Here, we used a mouse model that lacks the T-cell receptor specific alternative p38 pathway [p38αβY323F, double knock-in (DKI) mice] to determine how attenuated autoimmune and inflammatory responses may affect dose reconstruction. We exposed adult male DKI mice (8-10 weeks old) to 2 and 7 Gy in parallel with wild-type mice and assessed perturbations in urine (days 1, 3, 7) and serum (day 1) using a global metabolomics approach. A multidimensional scaling plot showed excellent separation of radiation-exposed groups in wild-type mice with slightly dampened responses in DKI mice. Validated metabolite panels were developed for urine [N6,N6,N6-trimethyllysine (TML), N1-acetylspermidine, spermidine, carnitine, acylcarnitine C21H35NO5, 4-aminohippuric acid] and serum [phenylalanine, glutamine, propionylcarnitine, lysophosphatidylcholine (LysoPC 14:0), LysoPC (22:5)] to determine the area under the receiver operating characteristic curve (AUROC). For both urine and serum, excellent sensitivity and specificity (AUROC > 0.90) was observed for 0 Gy vs. 7 Gy groups irrespective of genotype using identical metabolite panels. Similarly, excellent to fair classification (AUROC > 0.75) was observed for ≤2 Gy vs. 7 Gy mice for both genotypes, however, model performance declined (AUROC < 0.75) between genotypes after irradiation. Overall, these results suggest immunosuppression should not compromise small molecule multiplex panels used in dose reconstruction for biodosimetry.

Identification of a Potent Cytotoxic Pyrazole with Anti-Breast Cancer Activity That Alters Multiple Pathways

In this study, we identified a novel pyrazole-based derivative (P3C) that displayed potent cytotoxicity against 27 human cancer cell lines derived from different tissue origins with 50% cytotoxic concentrations (CC50) in the low micromolar and nanomolar range, particularly in two triple-negative breast cancer (TNBC) cell lines (from 0.25 to 0.49 µM). In vitro assays revealed that P3C induces reactive oxygen species (ROS) accumulation leading to mitochondrial depolarization and caspase-3/7 and -8 activation, suggesting the participation of both the intrinsic and extrinsic apoptotic pathways. P3C caused microtubule disruption, phosphatidylserine externalization, PARP cleavage, DNA fragmentation, and cell cycle arrest on TNBC cells. In addition, P3C triggered dephosphorylation of CREB, p38, ERK, STAT3, and Fyn, and hyperphosphorylation of JNK and NF-kB in TNBC cells, indicating the inactivation of both p38MAPK/STAT3 and ERK1/2/CREB signaling pathways. In support of our in vitro assays, transcriptome analyses of two distinct TNBC cell lines (MDA-MB-231 and MDA-MB-468 cells) treated with P3C revealed 28 genes similarly affected by the treatment implicated in apoptosis, oxidative stress, protein kinase modulation, and microtubule stability.

Pseudophosphatases as Regulators of MAPK Signaling

Mitogen-activated protein kinase (MAPK) signaling pathways are highly conserved regulators of eukaryotic cell function. These enzymes regulate many biological processes, including the cell cycle, apoptosis, differentiation, protein biosynthesis, and oncogenesis; therefore, tight control of the activity of MAPK is critical. Kinases and phosphatases are well established as MAPK activators and inhibitors, respectively. Kinases phosphorylate MAPKs, initiating and controlling the amplitude of the activation. In contrast, MAPK phosphatases (MKPs) dephosphorylate MAPKs, downregulating and controlling the duration of the signal. In addition, within the past decade, pseudoenzymes of these two families, pseudokinases and pseudophosphatases, have emerged as bona fide signaling regulators. This review discusses the role of pseudophosphatases in MAPK signaling, highlighting the function of phosphoserine/threonine/tyrosine-interacting protein (STYX) and TAK1-binding protein (TAB 1) in regulating MAPKs. Finally, a new paradigm is considered for this well-studied cellular pathway, and signal transduction pathways in general.

MK2 degradation as a sensor of signal intensity that controls stress-induced cell fate

Cell survival in response to stress is determined by the coordination of various signaling pathways. The kinase p38α is activated by many stresses, but the intensity and duration of the signal depends on the stimuli. How different p38α-activation dynamics may impact cell life/death decisions is unclear. Here, we show that the p38α-signaling output in response to stress is modulated by the expression levels of the downstream kinase MK2. We demonstrate that p38α forms a complex with MK2 in nonstimulated mammalian cells. Upon pathway activation, p38α phosphorylates MK2, the complex dissociates, and MK2 is degraded. Interestingly, transient p38α activation allows MK2 reexpression, reassembly of the p38α-MK2 complex, and cell survival. In contrast, sustained p38α activation induced by severe stress interferes with p38α-MK2 interaction, resulting in irreversible MK2 loss and cell death. MK2 degradation is mediated by the E3 ubiquitin ligase MDM2, and we identify four lysine residues in MK2 that are directly ubiquitinated by MDM2. Expression of an MK2 mutant that cannot be ubiquitinated by MDM2 enhances the survival of stressed cells. Our results indicate that MK2 reexpression and binding to p38α is critical for cell viability in response to stress and illustrate how particular p38α-activation patterns induced by different signals shape the stress-induced cell fate.

Pathophysiological Roles of Stress-Activated Protein Kinases in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is one of the most symptomatic progressive fibrotic lung diseases, in which patients have an extremely poor prognosis. Therefore, understanding the precise molecular mechanisms underlying pulmonary fibrosis is necessary for the development of new therapeutic options. Stress-activated protein kinases (SAPKs), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (p38) are ubiquitously expressed in various types of cells and activated in response to cellular environmental stresses, including inflammatory and apoptotic stimuli. Type II alveolar epithelial cells, fibroblasts, and macrophages are known to participate in the progression of pulmonary fibrosis. SAPKs can control fibrogenesis by regulating the cellular processes and molecular functions in various types of lung cells (including cells of the epithelium, interstitial connective tissue, blood vessels, and hematopoietic and lymphoid tissue), all aspects of which remain to be elucidated. We recently reported that the stepwise elevation of intrinsic p38 signaling in the lungs is correlated with a worsening severity of bleomycin-induced fibrosis, indicating an importance of this pathway in the progression of pulmonary fibrosis. In addition, a transcriptome analysis of RNA-sequencing data from this unique model demonstrated that several lines of mechanisms are involved in the pathogenesis of pulmonary fibrosis, which provides a basis for further studies. Here, we review the accumulating evidence for the spatial and temporal roles of SAPKs in pulmonary fibrosis.

The inflammatory signalling mediator TAK1 mediates lymphocyte recruitment to lipopolysaccharide-activated murine mesenchymal stem cells through interleukin-6

As a response to pro-inflammatory signals mesenchymal stem cells (MSCs) secrete agents and factors leading to lymphocyte recruitment, counteracting inflammation, and stimulating immunosuppression. On a molecular level, the signalling mediator TGF-β-activated kinase 1 (TAK1) is activated by many pro-inflammatory signals, plays a critical role in inflammation and regulates innate and adaptive immune responses as well. While the role of TAK1 as a signalling factor promoting inflammation is well documented, we also considered a role for TAK1 in anti-inflammatory actions exerted by activated MSCs. We, therefore, investigated the capacity of lipopolysaccharide (LPS)-treated murine MSCs with lentivirally modulated TAK1 expression levels to recruit lymphocytes. TAK1 downregulated by lentiviral vectors expressing TAK1 shRNA in murine MSCs interfered with the capacity of murine MSCs to chemoattract lymphocytes, indeed. Analysing a pool of 84 secreted factors we found that among 26 secreted cytokines/factors TAK1 regulated expression of one cytokine in LPS-activated murine MSCs in particular: interleukin-6 (IL-6). IL-6 in LPS-treated MSCs was responsible for lymphocyte recruitment as substantiated by neutralizing antibodies. Our studies, therefore, suggest that in LPS-treated murine MSCs the inflammatory signalling mediator TAK1 may exert anti-inflammatory properties via IL-6.

Nutrition and PI3K/Akt signaling are required for p38-dependent regeneration

Regeneration after damage requires early signals to trigger the tissue repair machinery. Reactive oxygen species (ROS) act as early signals that are sensed by the MAP3 kinase Ask1, which in turn activates by phosphorylation the MAP kinases p38 and JNK. The sustained or high activation of these kinases can result in apoptosis, whereas short or low activation can promote regeneration. Using the Ask1-dependent regeneration program, we demonstrate in Drosophila wing that PI3K/Akt signaling is necessary for Ask1 to activate p38, but not JNK. In addition, nutrient restriction or mutations that target Ser83 of the Drosophila Ask1 protein, a PI3K/Akt-sensitive residue, block regeneration. However, these effects can be reversed by the ectopic activation of p38, but not of JNK. Our results demonstrate that Ask1 controls the activation of p38 through Ser83, and that the phosphorylation of p38 during regeneration is nutrient sensitive. This mechanism is important for discriminating between p38 and JNK in the cells involved in tissue repair and regenerative growth.

Atypical p38 Signaling, Activation, and Implications for Disease

The mitogen-activated protein kinase (MAPK) p38 is an essential family of kinases, regulating responses to environmental stress and inflammation. There is an ever-increasing plethora of physiological and pathophysiological conditions attributed to p38 activity, ranging from cell division and embryonic development to the control of a multitude of diseases including retinal, cardiovascular, and neurodegenerative diseases, diabetes, and cancer. Despite the decades of intense investigation, a viable therapeutic approach to disrupt p38 signaling remains elusive. A growing body of evidence supports the pathological significance of an understudied atypical p38 signaling pathway. Atypical p38 signaling is driven by a direct interaction between the adaptor protein TAB1 and p38α, driving p38 autophosphorylation independent from the classical MKK3 and MKK6 pathways. Unlike the classical MKK3/6 signaling pathway, atypical signaling is selective for just p38α, and at present has only been characterized during pathophysiological stimulation. Recent studies have linked atypical signaling to dermal and vascular inflammation, myocardial ischemia, cancer metastasis, diabetes, complications during pregnancy, and bacterial and viral infections. Additional studies are required to fully understand how, when, where, and why atypical p38 signaling is induced. Furthermore, the development of selective TAB1-p38 inhibitors represents an exciting new opportunity to selectively inhibit pathological p38 signaling in a wide array of diseases.

Cefoxitin treatment of MRSA leads to a shift in the IL-12/IL-23 production pattern in dendritic cells by a mechanism involving changes in the MAPK signaling

Methicillin resistant Staphylococcus aureus (MRSA) constitute a serious health care problem worldwide. This study addresses the effect of β-lactam treatment on the ability of clinically relevant MRSA strains to induce IL-12 and IL-23. MRSA strains induced a dose-dependent IL-12 response in murine bone-marrow-derived dendritic cells that was dependent on endocytosis and acidic degradation. Facilitated induction of IL-12 (but not of IL-23) called for activation of the MAP kinase JNK, and was suppressed by p38. Compromised peptidoglycan structure in cefoxitin-treated bacteria - as denoted by increased sensitivity to mutanolysin -caused a shift from IL-12 towards IL-23. Moreover, cefoxitin treatment of MRSA led to a p38 MAPK-dependent early up-regulation of Dual Specificity Phosphatase (DUSP)-1. Compared to common MRSA, characteristics associated with a persister phenotype increased intracellular survival and upon cefoxitin treatment, the peptidoglycan was not equally compromised and the cytokine induction still required phagosomal acidification. Together, these data demonstrate that β-lactam treatment changes the MRSA-induced IL-12/IL-23 pattern determined by the activation of JNK and p38. We suggest that accelerated endosomal degradation of the peptidoglycan in cefoxitin-treated MRSA leads to an early expression of DUSP-1 and accordingly, a reduction in the IL-12/IL-23 ratio in dendritic cells. This may influence the clearance of S. aureus.

Stress kinases in the development of liver steatosis and hepatocellular carcinoma

Non-alcoholic fatty liver disease (NAFLD) is an important component of metabolic syndrome and one of the most prevalent liver diseases worldwide. This disorder is closely linked to hepatic insulin resistance, lipotoxicity, and inflammation. Although the mechanisms that cause steatosis and chronic liver injury in NAFLD remain unclear, a key component of this process is the activation of stress-activated kinases (SAPKs), including p38 and JNK in the liver and immune system. This review summarizes findings which indicate that the dysregulation of stress kinases plays a fundamental role in the development of steatosis and are important players in inducing liver fibrosis. To avoid the development of steatohepatitis and liver cancer, SAPK activity must be tightly regulated not only in the hepatocytes but also in other tissues, including cells of the immune system. Possible cellular mechanisms of SAPK actions are discussed.

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Hepatic JNK triggers steatosis and insulin resistance, decreasing lipid oxidation and ketogenesis in HFD-fed mice.

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Decreased liver expression of p38α/β in HFD increases lipogenesis.

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Hepatic p38γ/δ drive insulin resistance and inhibit autophagy, which may lead to steatosis.

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Macrophage p38α/β promote cytokine production and M1 polarization, leading to lipid accumulation in hepatocytes.

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Myeloid p38γ/δ contribute to cytokine production and neutrophil migration, protecting against steatosis, diabetes and NAFLD.

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JNK1 and p38γ induce HCC while p38α blocks it. However, deletion of hepatic JNK1/2 induces cholangiocarcinoma.

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SAPK are potential therapeutic target for metabolic disorders, steatohepatitis and liver cancer.

MK2-Deficient Mice Are Bradycardic and Display Delayed Hypertrophic Remodeling in Response to a Chronic Increase in Afterload

Background

Mitogen‐activated protein kinase–activated protein kinase‐2 (MK2) is a protein serine/threonine kinase activated by p38α/β. Herein, we examine the cardiac phenotype of pan MK2‐null (MK2^−/−) mice.

Methods and Results

Survival curves for male MK2^+/+ and MK2^−/− mice did not differ (Mantel‐Cox test, P=0.580). At 12 weeks of age, MK2^−/− mice exhibited normal systolic function along with signs of possible early diastolic dysfunction; however, aging was not associated with an abnormal reduction in diastolic function. Both R‐R interval and P‐R segment durations were prolonged in MK2‐deficient mice. However, heart rates normalized when isolated hearts were perfused ex vivo in working mode. Ca²⁺ transients evoked by field stimulation or caffeine were similar in ventricular myocytes from MK2^+/+ and MK2^−/− mice. MK2^−/− mice had lower body temperature and an age‐dependent reduction in body weight. mRNA levels of key metabolic genes, including Ppargc1a, Acadm, Lipe, and Ucp3, were increased in hearts from MK2^−/− mice. For equivalent respiration rates, mitochondria from MK2^−/− hearts showed a significant decrease in Ca²⁺ sensitivity to mitochondrial permeability transition pore opening. Eight weeks of pressure overload increased left ventricular mass in MK2^+/+ and MK2^−/− mice; however, after 2 weeks the increase was significant in MK2^+/+ but not MK2^−/− mice. Finally, the pressure overload–induced decrease in systolic function was attenuated in MK2^−/− mice 2 weeks, but not 8 weeks, after constriction of the transverse aorta.

Conclusions

Collectively, these results implicate MK2 in (1) autonomic regulation of heart rate, (2) cardiac mitochondrial function, and (3) the early stages of myocardial remodeling in response to chronic pressure overload.

Pseudomonas aeruginosa induces p38MAP kinase-dependent IL-6 and CXCL8 release from bronchial epithelial cells via a Syk kinase pathway

Pseudomonas aeruginosa (Pa) infection is a major cause of airway inflammation in immunocompromised and cystic fibrosis (CF) patients. Mitogen-activated protein (MAP) and tyrosine kinases are integral to inflammatory responses and are therefore potential targets for novel anti-inflammatory therapies. We have determined the involvement of specific kinases in Pa-induced inflammation. The effects of kinase inhibitors against p38MAPK, MEK 1/2, JNK 1/2, Syk or c-Src, a combination of a p38MAPK with Syk inhibitor, or a novel narrow spectrum kinase inhibitor (NSKI), were evaluated against the release of the proinflammatory cytokine/chemokine, IL-6 and CXCL8 from BEAS-2B and CFBE41o- epithelial cells by Pa. Effects of a Syk inhibitor against phosphorylation of the MAPKs were also evaluated. IL-6 and CXCL8 release by Pa were significantly inhibited by p38MAPK and Syk inhibitors (p<0.05). Phosphorylation of HSP27, but not ERK or JNK, was significantly inhibited by Syk kinase inhibition. A combination of p38MAPK and Syk inhibitors showed synergy against IL-6 and CXCL8 induction and an NSKI completely inhibited IL-6 and CXCL8 at low concentrations. Pa-induced inflammation is dependent on p38MAPK primarily, and Syk partially, which is upstream of p38MAPK. The NSKI suggests that inhibiting specific combinations of kinases is a potent potential therapy for Pa-induced inflammation.

Diversity and versatility of p38 kinase signalling in health and disease

The ability of cells to deal with different types of stressful situations in a precise and coordinated manner is key for survival and involves various signalling networks. Over the past 25 years, p38 kinases — in particular, p38α — have been implicated in the cellular response to stress at many levels. These span from environmental and intracellular stresses, such as hyperosmolarity, oxidative stress or DNA damage, to physiological situations that involve important cellular changes such as differentiation. Given that p38α controls a plethora of functions, dysregulation of this pathway has been linked to diseases such as inflammation, immune disorders or cancer, suggesting the possibility that targeting p38α could be of therapeutic interest. In this Review, we discuss the organization of this signalling pathway focusing on the diversity of p38α substrates, their mechanisms and their links to particular cellular functions. We then address how the different cellular responses can be generated depending on the signal received and the cell type, and highlight the roles of this kinase in human physiology and in pathological contexts.

p38α — the best-characterized member of the p38 kinase family — is a key mediator of cellular stress responses. p38α is activated by a plethora of signals and functions through a multitude of substrates to regulate different cellular behaviours. Understanding context-dependent p38α signalling provides important insights into p38α roles in physiology and pathology.

TAK1-TABs Complex: A Central Signalosome in Inflammatory Responses

Transforming growth factor-β (TGF-β)-activated kinase 1 (TAK1) is a member of the MAPK kinase kinase (MAPKKK) family and has been implicated in the regulation of a wide range of physiological and pathological processes. TAK1 functions through assembling with its binding partners TAK1-binding proteins (TAB1, TAB2, and TAB3) and can be activated by a variety of stimuli such as tumor necrosis factor α (TNFα), interleukin-1β (IL-1β), and toll-like receptor ligands, and they play essential roles in the activation of NF-κB and MAPKs. Numerous studies have demonstrated that post-translational modifications play important roles in properly controlling the activity, stability, and assembly of TAK1-TABs complex according to the indicated cellular environment. This review focuses on the recent advances in TAK1-TABs-mediated signaling and the regulations of TAK1-TABs complex by post-translational modifications.

An overview of mammalian p38 mitogen-activated protein kinases, central regulators of cell stress and receptor signaling

The p38 family is a highly evolutionarily conserved group of mitogen-activated protein kinases (MAPKs) that is involved in and helps co-ordinate cellular responses to nearly all stressful stimuli. This review provides a succinct summary of multiple aspects of the biology, role, and substrates of the mammalian family of p38 kinases. Since p38 activity is implicated in inflammatory and other diseases, we also discuss the clinical implications and pharmaceutical approaches to inhibit p38.

Precision Mapping of O-Linked N-Acetylglucosamine Sites in Proteins Using Ultraviolet Photodissociation Mass Spectrometry

Despite its central importance as a regulator of cellular physiology, identification and precise mapping of O-linked N-acetylglucosamine (O-GlcNAc) post-translational modification (PTM) sites in proteins by mass spectrometry (MS) remains a considerable technical challenge. This is due in part to cleavage of the glycosidic bond occurring prior to the peptide backbone during collisionally activated dissociation (CAD), which leads to generation of characteristic oxocarbenium ions and impairs glycosite localization. Herein, we leverage CAD-induced oxocarbenium ion generation to trigger ultraviolet photodissociation (UVPD), an alternate high-energy deposition method that offers extensive fragmentation of peptides while leaving the glycosite intact. Upon activation using UV laser pulses, efficient photodissociation of glycopeptides is achieved with production of multiple sequence ions that enable robust and precise localization of O-GlcNAc sites. Application of this method to tryptic peptides originating from O-GlcNAcylated proteins TAB1 and Polyhomeotic confirmed previously reported O-GlcNAc sites in TAB1 (S395 and S396) and uncovered new sites within both proteins. We expect this strategy will complement existing MS/MS methods and be broadly useful for mapping O-GlcNAcylated residues of both proteins and proteomes.

A mouse model for functional dissection of TAB1 O-GlcNAcylation

Background: O-GlcNAcylation is a posttranslational modification associated with various physiological and pathophysiological processes including diabetes, cancer, neurodegeneration and inflammation. However, the biological mechanisms underlying the role of specific O-GlcNAc sites and their link to phenotypes remain largely unexplored due to lack of suitable in vivo models. TGF-β activated kinase-1 binding protein-1 (TAB1) is a scaffolding protein required for TGF-β activated kinase-1 (TAK1) mediated signalling. A single O-GlcNAc site has been identified on human TAB1 that modulates TAK1-mediated cytokine release in cells.

Methods: Here, we report the generation of the Tab1 ^S393A mouse model using a constitutive knock-in strategy. The Tab1 ^S393A mice carry a Ser393Ala (S393A) mutation that leads to loss of O-GlcNAcylation site on TAB1.

Results: We did not observe any obvious phenotype in Tab1 ^S393A mice. Loss of O-GlcNAcylation on TAB1 has no consequences on TAB1 protein level or on TAB1-TAK1 interaction.

Conclusions: The homozygous Tab1 ^S393A mice are viable and develop with no obvious abnormalities, providing a powerful tool to further investigate the role of O-GlcNAc on TAB1 in the inflammatory response in the context of a whole organism.

Novel Therapeutic Potential of Mitogen-Activated Protein Kinase Activated Protein Kinase 2 (MK2) in Chronic Airway Inflammatory Disorders

OBJECTIVE

The primary focus of this review is to highlight the current and emerging proinflammatory role of MK2 kinase signaling in p38MAPK pathway and to provide a detailed evaluation on the prospects of MK2 inhibition with special emphasis on the etiology of chronic inflammatory airway diseases, such as asthma, idiopathic pulmonary fibrosis, lung cancer, acute lung injury and acute respiratory distress syndrome.

BACKGROUND

MK2 belongs to serine-threonine kinase family and is activated directly by stress and inflammatory signal through p38MAPK phosphorylation in diverse inflammatory conditions through the Toll-like receptor signaling pathway. MK2 has been thought to be a critical factor involved in the regulation of synthesis and release of pro-inflammatory (TNF-α, IL-6 and IL-1β, etc.) proteins. Targeted inhibition of MK2 kinase has been shown to significantly reduce the production and release of these cytokine molecules. Therefore, MK2 has been identified as an effective strategy (alternative to p38MAPK) to block this pro-inflammatory signaling pathway.

RESULTS

The inhibition of MK2 may lead to similar or better efficacy as that of p38 inhibitors, and interestingly avoids the systemic toxicity shown by the p38 inhibitors. Thus, MK2 has been the focus of intense interdisciplinary research and its specific inhibition can be a novel and potential therapeutic strategy for the treatment of chronic airway inflammatory diseases.

CONCLUSION

Promising advancement in understanding and rigorous exploration of the role of MK2 kinase in inflammatory processes may contribute to the development of newer and safer therapy for the treatment of chronic airway inflammatory diseases in the future.

The p38-interacting protein p38IP suppresses TCR and LPS signaling by targeting TAK1

Negative regulation of immunoreceptor signaling is required for preventing hyperimmune activation and maintaining immune homeostasis. The roles of p38IP in immunoreceptor signaling remain unclear. Here, we show that p38IP suppresses T-cell receptor (TCR)/LPS-activated NF-κB and p38 by targeting TAK1 kinase and that p38IP protein levels are downregulated in human PBMCs from rheumatoid arthritis (RA) patients, inversely correlating with the enhanced activity of NF-κB and p38. Mechanistically, p38IP interacts with TAK1 to disassemble the TAK1-TAB (TAK1-binding protein) complex. p38IP overexpression decreases TCR-induced binding of K63-linked polyubiquitin (polyUb) chains to TAK1 but increases that to TAB2, and p38IP knockdown shows the opposite effects, indicating unanchored K63-linked polyUb chain transfer from TAB2 to TAK1. p38IP dynamically interacts with TAK1 upon stimulation, because of the polyUb chain transfer and the higher binding affinity of TAK1 and p38IP for polyUb-bound TAB2 and TAK1, respectively. Moreover, p38IP scaffolds the deubiquitinase USP4 to deubiquitinate TAK1 once TAK1 is activated. These findings reveal a novel role and the mechanisms of p38IP in controlling TCR/LPS signaling and suggest that p38IP might participate in RA pathogenesis.

TAK1 mediates convergence of cellular signals for death and survival

TGF-β activated kinase 1, a MAPK kinase kinase family serine threonine kinase has been implicated in regulating diverse range of cellular processes that include embryonic development, differentiation, autophagy, apoptosis and cell survival. TAK1 along with its binding partners TAB1, TAB2 and TAB3 displays a complex pattern of regulation that includes serious crosstalk with major signaling pathways including the C-Jun N-terminal kinase (JNK), p38 MAPK, and I-kappa B kinase complex (IKK) involved in establishing cellular commitments for death and survival. This review also highlights how TAK1 orchestrates regulation of energy homeostasis via AMPK and its emerging role in influencing mTORC1 pathway to regulate death or survival in tandem.

Mapping p38α mitogen-activated protein kinase signaling by proximity-dependent labeling

Mitogen-activated protein (MAP) kinase signaling is central to multiple cellular responses and processes. MAP kinase p38α is the best characterized member of the p38 MAP kinase family. Upstream factors and downstream targets of p38α have been identified in the past by conventional methods such as coimmunoprecipitation. However, a complete picture of its interaction partners and substrates in cells is lacking. Here, we employ a proximity-dependent labeling approach using biotinylation tagging to map the interactome of p38α in cultured 293T cells. Fusing the advanced biotin ligase BioID2 to the N-terminus of p38α, we used mass spectrometry to identify 37 biotin-labeled proteins that putatively interact with p38α. Gene ontology analysis confirms known upstream and downstream factors in the p38 MAP kinase cascade (e.g., MKK3, MAPKAPK2, TAB2, and c-jun). We furthermore identify a cluster of zinc finger (ZnF) domain-containing proteins that is significantly enriched among proximity-labeled interactors and is involved in gene transcription and DNA damage response. Fluorescence imaging and coimmunoprecipitation with overexpressed p38α in cells supports an interaction of p38α with ZnF protein XPA, a key factor in the DNA damage response, that is promoted by UV irradiation. These results define an extensive network of interactions of p38α in cells and new direct molecular targets of MAP kinase p38α in gene regulation and the DNA damage response.

The p38 Pathway: From Biology to Cancer Therapy

The p38 MAPK pathway is well known for its role in transducing stress signals from the environment. Many key players and regulatory mechanisms of this signaling cascade have been described to some extent. Nevertheless, p38 participates in a broad range of cellular activities, for many of which detailed molecular pictures are still lacking. Originally described as a tumor-suppressor kinase for its inhibitory role in RAS-dependent transformation, p38 can also function as a tumor promoter, as demonstrated by extensive experimental data. This finding has prompted the development of specific inhibitors that have been used in clinical trials to treat several human malignancies, although without much success to date. However, elucidating critical aspects of p38 biology, such as isoform-specific functions or its apparent dual nature during tumorigenesis, might open up new possibilities for therapy with unexpected potential. In this review, we provide an extensive description of the main biological functions of p38 and focus on recent studies that have addressed its role in cancer. Furthermore, we provide an updated overview of therapeutic strategies targeting p38 in cancer and promising alternatives currently being explored.

Cell-to-Cell Heterogeneity in p38-Mediated Cross-Inhibition of JNK Causes Stochastic Cell Death

The stress-activated protein kinases c-Jun N-terminal kinase (JNK) and p38 are important players in cell-fate decisions in response to environmental stress signals. Crosstalk signaling between JNK and p38 is emerging as an important regulatory mechanism in inflammatory and stress responses. However, it is unknown how this crosstalk affects signaling dynamics, cell-to-cell variation, and cellular responses at the single-cell level. We established a multiplexed live-cell imaging system based on kinase translocation reporters to simultaneously monitor JNK and p38 activities with high specificity and sensitivity at single-cell resolution. Various stresses activated JNK and p38 with various dynamics. In all cases, p38 suppressed JNK activity in a cross-inhibitory manner. We demonstrate that p38 antagonizes JNK through both transcriptional and post-translational mechanisms. This cross-inhibition generates cellular heterogeneity in JNK activity after stress exposure. Our data indicate that this heterogeneity in JNK activity plays a role in fractional killing in response to UV stress.

TAK1/Map3k7 enhances differentiation of cardiogenic endoderm from mouse embryonic stem cells

Specification of the primary heart field in mouse embryos requires signaling from the anterior visceral endoderm (AVE). The nature of these signals is not known. We hypothesized that the TGFβ-activated kinase (TAK1/Map3k7) may act as a cardiogenic factor, based on its expression in heart-inducing endoderm and its requirement for cardiac differentiation of p19 cells. To test this, mouse embryonic stem (ES) cells overexpressing Map3k7 were isolated and differentiated as embryoid bodies (EBs). Map3k7-overexpressing EBs showed increased expression of AVE markers but interestingly, showed little effect on mesoderm formation and had no impact on overall cardiomyocyte formation. To test whether the pronounced expansion of endoderm masks an expansion of cardiac lineages, chimeric EBs were made consisting of Map3k7-overexpressing ES and wild type ES cells harboring a cardiac reporter transgene, MHCα::GFP, allowing cardiac differentiation to be assessed specifically in wild type ES cells. Wild type ES cells co-cultured with Map3k7-overexpressing cells had a 4-fold increase in expression of the cardiac reporter, supporting the hypothesis that Map3k7 increases the formation of cardiogenic endoderm. To further examine the role of Map3k7 in early lineage specification, other endodermal markers were examined. Interestingly, markers that are expressed in both the VE and later in gut development were expanded, whereas transcripts that specifically mark the early definitive (streak-derived) endoderm (DE) were not. To determine if Map3k7 is necessary for endoderm differentiation, EBs were grown in the presence of the Map3k7 specific inhibitor 5Z-7-oxozeaenol. Endoderm differentiation was dramatically decreased in these cells. Western blot analysis showed that known downstream targets of Map3k7 (Jnk, Nemo-like kinase (NLK) and p38 MAPK) were all inhibited. By contrast, transcripts for another TGFβ target, Sonic Hedgehog (Shh) were markedly upregulated, as were transcripts for Gli2 (but not Gli1 and Gli3). Together these data support the hypothesis that Map3k7 governs the formation, or proliferation of cardiogenic endoderm.

The Role of TTP Phosphorylation in the Regulation of Inflammatory Cytokine Production by MK2/3

Tristetraprolin (TTP) is an RNA-binding protein and an essential factor of posttranscriptional repression of cytokine biosynthesis in macrophages. Its activity is temporally inhibited by LPS-induced p38^MAPK/MAPKAPK2/3-mediated phosphorylation, leading to a rapid increase in cytokine expression. We compared TTP expression and cytokine production in mouse bone marrow-derived macrophages of different genotypes: wild type, MAPKAP kinase 2 (MK2) deletion (MK2 knockout [KO]), MK2/3 double deletion (MK2/3 double KO [DKO]), TTP-S52A-S178A (TTPaa) knock-in, as well as combined MK2 KO/TTPaa and MK2/3 DKO/TTPaa. The comparisons reveal that MK2/3 are the only LPS-induced kinases for S52 and S178 of TTP and the role of MK2 and MK3 in the regulation of TNF biosynthesis is not restricted to phosphorylation of TTP at S52/S178 but includes independent processes, which could involve other TTP phosphorylations (such as S316) or other substrates of MK2/3 or p38^MAPK Furthermore, we found differences in the dependence of various cytokines on the cooperation between MK2/3 deletion and TTP mutation ex vivo. In the cecal ligation and puncture model of systemic inflammation, a dramatic decrease of cytokine production in MK2/3 DKO, TTPaa, and DKO/TTPaa mice compared with wild-type animals is observed, thus confirming the role of the MK2/3/TTP signaling axis in cytokine production also in vivo. These findings improve our understanding of this signaling axis and could be of future relevance in the treatment of inflammation.

Molecular characterization and expression of TAK-binding proteins (TAB1-3) in Larimichthys crocea infected by Vibrio parahemolyticus and LPS

TAK1-binding proteins (TABs) are important immune protein involved in various intracellular signalling pathways. Here, TAB1-3 (lcTAB1-3) were characterized from Larimichthys crocea. The predicted 1524 bp coding sequence of lcTAB1 encoded a 507-residue protein, while lcTAB2 (2271 bp) and lcTAB3 (1836 bp) encoded 756 and 611 residue proteins, respectively. Their sequence shared conserved domain structures and functional sites with their orthologs from other species. The expression of lcTAB1-3 were detected in all tested tissues, which were upregulated in spleen, liver and kidney following Vibrio parahemolyticus infection. Immunofluorescence staining revealed that lcTAB1 were localized in cytoplasm, while lcTAB2 and lcTAB3 were in the endsome. Moreover, the NF-κB protein level was obviously upregulated after the co-overexpression of lcTAK1 and lcTABs, higher than that after the overexpression of lcTAK1 or lcTABs alone. Co-immunoprecipitation proved the direct interaction of lcTAB1/lcTAB2/lcTAB3 and lcTAK1. These findings indicated the roles of lcTABs in immune response of Larimichthys crocea.

A mouse model for functional dissection of TAB1 O-GlcNAcylation

Background: O-GlcNAcylation is a posttranslational modification associated with various physiological and pathophysiological processes including diabetes, cancer, neurodegeneration and inflammation. However, the biological mechanisms underlying the role of specific O-GlcNAc sites and their link to phenotypes remain largely unexplored due to lack of suitable in vivo models. TGF-β activated kinase-1 binding protein-1 (TAB1) is a scaffolding protein required for TGF-β activated kinase-1 (TAK1) mediated signalling. A single O-GlcNAc site has been identified on TAB1 that modulates TAK1-mediated cytokine release in cells. Methods: Here, we report the generation of the Tab1S393A mouse model using a constitutive knock-in strategy. The Tab1S393A mice carry a Ser393Ala (S393A) mutation that leads to loss of the single O-GlcNAcylation site on TAB1. Results: We did not observe any obvious phenotype in Tab1S393A mice. Loss of O-GlcNAcylation on TAB1 has no consequences on TAB1 protein level or on TAB1-TAK1 interaction. Conclusions: The homozygous Tab1S393A mice are viable and develop with no obvious abnormalities, providing a powerful tool to further investigate the role of O-GlcNAc on TAB1 in the inflammatory response in the context of a whole organism.

Regulation of tumor angiogenesis and mesenchymal-endothelial transition by p38α through TGF-β and JNK signaling

The formation of new blood vessels is essential for normal development, tissue repair and tumor growth. Here we show that inhibition of the kinase p38α enhances angiogenesis in human and mouse colon tumors. Mesenchymal cells can contribute to tumor angiogenesis by regulating proliferation and migration of endothelial cells. We show that p38α negatively regulates an angiogenic program in mesenchymal stem/stromal cells (MSCs), multipotent progenitors found in perivascular locations. This program includes the acquisition of an endothelial phenotype by MSCs mediated by both TGF-β and JNK, and negatively regulated by p38α. Abrogation of p38α in mesenchymal cells increases tumorigenesis, which correlates with enhanced angiogenesis. Using genetic models, we show that p38α regulates the acquisition of an endothelial-like phenotype by mesenchymal cells in colon tumors and damage tissue. Taken together, our results indicate that p38α in mesenchymal cells restrains a TGF-β-induced angiogenesis program including their ability to transdifferentiate into endothelial cells.

Mesenchymal cells contribute to tumor angiogenesis by regulating proliferation and migration of endothelial cells. Here, the authors show that mesenchymal stem cells also have the ability to acquire an endothelial phenotype upon TGF-β stimulation via the downstream kinase JNK, and that p38α negatively regulates this process.

Black carp TAB1 up-regulates TAK1/IRF7/IFN signaling during the antiviral innate immune activation

TAK1-binding protein 1 (TAB1) forms the protein complex with TAK1 and enhances its kinase activity in human and mammals. To elucidate the role of TAB1 in the innate immunity of teleost sfih, the TAB1 homologue of black carp (Mylopharyngodon piceus) (bcTAB1) has been cloned and characterized in this paper. bcTAB1 is composed of 498 amino acids and contains a typical PP2Cc domain like its mammalian counterpart. The transcription of bcTAB1 gene in vivo and ex vivo varied in response to different stimuli; and the immunofluorescence staining showed that bcTAB1 was distributed in both cytoplasm and nucleus of host cell. The reporter assay showed that neither bcTAB1-expression alone nor co-expression of bcTAB1 and bcTAK1 could activate the transcription of IFN in EPC cells. Accordingly, EPC cells expressing bcTAB1 or co-expressing bcTAB1 and bcTAK1 showed no improved antiviral activity against grass carp reovirus (GCRV) and spring viremia of carp virus (SVCV). However, EPC cells co-expressing bcTAB1, bcTAK1 and bcIRF7 showed fiercely increased IFN-inducing ability in reporter assay and obviously improved antiviral activity in plaque assay compared with EPC cells co-expressing bcTAK1 and bcIRF7. The subsequent co-immunoprecipitation assay identified that bcTAB1 associated with bcTAK1 but not interacted with bcIRF7. Based on our previous finding that bcTAK1 up-regulates bcIRF7-mediated IFN signaling during host innate immune activation, the data generated in this study support the conclusion that bcTAB1 interacts with bcTAK1 and boosts bcTAK1-activated bcIRF7/IFN signaling during host antiviral innate immune response against GCRV and SVCV.

Molecular identification and expression analysis of TAB1 from orange-spotted grouper (Epinephelus coioides)

Transforming growth factor-β activated kinase 1 (TAK1) is a crucial signal transducer in multiple signaling pathways. TAK1 binds TAB1, TAB2, and TAB3, which act as activators and adaptors that specifically regulate the activation of TAK1. To date, the role of TABs is largely unknown in fish. In the present study, a TAB1 cDNA sequence was identified in grouper (Epinephelus coioides), and designated EcTAB1. The full-length open reading frame of EcTAB1 is 1, 521 bp; it encodes 506 amino acids that contains an N-terminal PP2C domain. Many important functional sites in mammalian TAB1 were conserved in TAB1 from grouper and from other fish. Multiple sequence alignment showed that EcTAB1 protein shared high sequence identity with TAB1 of other fish, especially with Stegastes partitus (95% identity). TAB1 was clustered into the same subgroup with other fish TAB1 in the phylogenetic tree. Tissue expression analysis indicated that TAB1 was widely distributed in different tissues. After infection with Cryptocaryon irritans, EcTAB1 expression was up-regulated in the infection site (gills). Besides, EcTAB1 was expressed throughout the grouper spleen (GS) cells and significantly enhanced the activation of NF-κB.

Protein kinase p38α signaling in dendritic cells regulates colon inflammation and tumorigenesis

Dendritic cells (DCs) play pivotal roles in maintaining intestinal homeostasis, but how the DCs regulate diverse immune networks on homeostasis breakdown remains largely unknown. Here, we report that, in response to epithelial barrier disruption, colonic DCs regulate the differentiation of type 1 regulatory T (Tr1) cells through p38α-dependent IL-27 production to initiate an effective immune response. Deletion of p38α in DCs, but not in T cells, led to increased Tr1 and protected mice from dextran sodium sulfate-induced acute colitis and chronic colitis-associated colorectal cancer. We show that higher levels of IL-27 in p38α-deficient colonic cDC1s, but not cDC2s, were responsible for the increase of Tr1 cells. Moreover, p38α-dependent IL-27 enhanced IL-22 secretion from intestinal group 3 innate lymphoid cells and protected epithelial barrier function. In p38α-deficient DCs, the TAK1-MKK4/7-JNK-c-Jun axis was hyperactivated, leading to high IL-27 levels, and inhibition of the JNK-c-Jun axis suppressed IL-27 expression. ChIP assay revealed direct binding of c-Jun to the promoter of Il27p28, which was further enhanced in p38α-deficient DCs. In summary, here we identify a key role for p38α signaling in DCs in regulating intestinal inflammatory response and tumorigenesis, and our finding may provide targets for the treatment of inflammatory intestinal diseases.