MK2 Activity Research Articles

Increased Activity of MAPKAPK2 within Mesenchymal Cells as a Target for Inflammation-Associated Fibrosis in Crohn's Disease.

Mesenchymal stromal cells are suggested to play a critical role in Crohn's disease [CD]-associated fibrosis. MAPKAPK2 [MK2] has emerged as a potential therapeutic target to reduce inflammation in CD. However, the cell-specific pattern of phospho-MK2 activation and its role in CD-associated fibrosis are unknown. The objectives of this study were to evaluate cell-specific changes in MK2 activity between predominantly inflammatory CD vs CD with fibrotic complications and define the role of stromal cell-specific MK2 activation in CD-associated fibrosis. CD tissue, CD tissue-derived mesenchymal stromal cells known as myo-/fibroblasts [CD-MFs], and fibroblast-specific MK2 conditional knockout [KO] mice were used. In the inflamed area of predominantly inflammatory CD, high MK2 activity was equally distributed between mesenchymal and haematopoietic cells. By contrast, in CD with fibrotic complications, high MK2 activity was mostly associated with mesenchymal stromal cells. Using ex vivo CD tissue explants and an IL-10KO murine colitis model, we demonstrated that pro-fibrotic responses are significantly reduced by treatment with the MK2 inhibitor PF-3644022. Inhibition of MK2 activity in primary cultures of CD-MFs significantly reduced basal and TGF-β1-induced profibrotic responses. Using fibroblast-specific MK2 knockout mice in chronic dextran saline sulphate colitis, we demonstrated that fibroblast intrinsic MK2 signalling is among the key processes involved in the chronic inflammation-induced profibrotic responses. Our data suggest that activation of MK2 within fibroblasts contributes to the chronic inflammation-induced fibrosis in CD and that targeting MK2 has potential for the development of novel therapeutic approaches for fibrosis in CD.

BRD4‐MK2 signaling: target for Crohn’s Disease‐associated fibrosis

IntroductionFibrosis is the major complication of Crohn’s disease (CD). No targeted therapies are currently available to revert CD‐associated fibrosis. While inflammatory mechanisms in CD have been extensively investigated, understanding the pathogenesis of fibrosis is relatively limited. Mesenchymal cells are the major effectors in profibrotic processes in CD. A dramatic increase in α‐SMA expressing subsets of mesenchymal cells, also known as myofibroblasts (MF), is among the main hallmarks of profibrotic changes in CD. Mitogen‐activated protein kinase‐activated protein kinase 2 (MK2) is involved in the increase of α‐SMAexpression by MFs. Along with an increase in MK2 activity in CD we also observed an increase in the bromodomain‐containing Protein 4 (BRD4), an important epigenetic reader. BRD4 is critical for the expression of enhancer‐mediated profibrotic genes and, thus, is a potential novel regulator of MK2. However, the presence of mechanistic link between BRD4 and MK2 activity with respect to profibrotic activation of MFs in CD is unknown. Herein, we tested hypothesis that BRD4 mediated increase in MK2 activity is critical to the profibrotic reprogramming of MFs in CD and this pathway has potential for novel anti‐fibrotic therapy.MethodsHuman normal (N)‐ and CD‐derived MFs were analyzed using RNAseq, cytokine/chemokine multiplex array, FACS, and immunofluorescent microscopy. The T cell transfer murine colitis model relevant to CD was also used in this study.ResultsAn Increase in BRD4 and MK2 expression was observed in primary human CD‐ when compared to N‐MFs and were associated with the expression of the profibrotic genes including Col1α2, α‐SMA, TNC, Fn1, and TGF‐β1. Inhibition of MK2 activity in CD‐MFs with the MK2 specific inhibitor PF‐3644022 and murine MK2 KO MFs showed significantly reduced basal and TGF‐β1‐induced profibrotic gene expression. Use of the BRD4 specific inhibitor ZL0454 significantly reduced MK2 mRNA expression in CD‐MFs Additionally, ex vivo treatment of the CD tissues with ZL0454 also abrogated MK2 expression. Therapeutic use of the BRD4 inhibitor ZL0454 (10 mg/kg, daily for 10 days) in T cell transfer murine colitis significantly decreased MK2 expression and downstream profibrotic responses as measured by collagen deposition and expression of fibrosis‐related genes.ConclusionsOur data suggests that BRD4 positively regulates MK2 expression in CD. Further, BRD4‐MK2 signaling is critical to profibrotic activation of mesenchymal cells in CD and is a potential therapeutic target to reverse CD‐associated fibrosis.

ACTIVATION OF MK2 IN CROHN’S DISEASE-ASSOCIATED FIBROSIS: NEW TARGET FOR ANTI-FIBROTIC THERAPY

Abstract INTRODUCTION Fibrosis is the major aggressive complication of Crohn’s disease (CD), causing intestinal obstruction. No targeted therapies are currently available to revert CD-associated fibrosis. While inflammatory mechanisms in CD have been extensively investigated, understanding the pathogenesis of fibrosis is relatively limited. Mesenchymal cells are believed to be the major effectors in profibrotic processes in CD. There is a dramatic increase in α-SMA expressing subsets of mesenchymal cells, also known as myofibroblasts (MF), and this is considered to be among the main hallmarks of profibrotic changes in CD. Thus, targeting the profibrotic reprogramming/increase of α-SMA+ MFs and/or fibrosis-driving signaling could lead to the development of novel anti-fibrotic approaches in CD. Mitogen-activated protein kinase-activated protein kinase 2 (MK2) is a downstream substrate of p38 and is known to regulate pro-inflammatory cytokines. Moreover, MK2 is a regulator of downstream signaling in the profibrotic non-canonical TGF-β1/p38 pathway. However, the role of MK2 in CD-associated fibrosis and profibrotic reprogramming of MFs is not known. We hypothesize that hyperactivation of MK2 is critical to the profibrotic reprogramming of MF in CD and has potential as an anti-fibrotic therapeutic target. METHODS Human normal- and CD-derived MFs were analyzed using RNAseq, cytokine/chemokine multiplex array, FACS, and confocal microscopy. Chronic IL-10 KO colitis murine models relevant to CD were used in this study. RESULTS Increased expression of MK2 within α-SMA+ mesenchymal cells was observed in stricturing CD. Ex vivo treatment of the CD tissues with MK2 inhibitor PF-3644022 (10 μM) abrogated MK2 activity and decreased expression of fibrosis-related genes. An increase in MK2 activity within intestinal MFs was observed in vivo in IL-10KO murine colitis. Therapeutic use of the MK2 inhibitor PF-3644022 (0.2 mg/kg, daily for 10 days) in vivo significantly decreased the degree of intestinal fibrosis as measured by collagen deposition and reduced the expression of fibrosis-related genes. When compared to the WT murine-derived MFs, MK2-/- MFs showed low basal and TGF-β1 induced levels of pro-fibrotic genes expression in vitro. Using primary human MFs, we found that MK2 activity was associated with hallmark profibrotic genes in CD-MFs. Inhibition of MK2 activity with PF-3644022 reduced TGF-β1-induced overexpression of Col1α2, α-SMA, TNC, Fn1, and TGF-β1 genes. Profibrotic responses in MFs through SMAD2/3 and p38, but not MAPK signaling were mediated by MK2. CONCLUSIONS Our data provide evidence that activation of MK2 drives profibrotic reprogramming of mesenchymal cells in CD and it may be an attractive therapeutic target for the development of novel targeted strategies against CD-associated fibrosis.

Differential regulation of cytokine and chemokine expression by MK2 and MK3 in airway smooth muscle cells

BackgroundAirway smooth muscle (ASM) contributes to local inflammation and plays an immunomodulatory role in airway diseases. This is partially regulated by p38 mitogen-activated protein kinase (MAPK), which further activates two closely related isoforms of the MAPK-activated protein kinases (MKs), MK2 and MK3. The MKs have similar substrate specificities but less is known about differences in their functional responses. This study was undertaken to identify differential downstream inflammatory targets of MK2 and MK3 signaling and assess cross-talk between the MAPK pathway and NF-κB signaling relevant to ASM function. MethodsWild-type and kinase-deficient MK2 (MK2WT, MK2KR) and MK3 (MK3WT, MK33A) were expressed in human ASM cells stimulated for 20 h with 10 ng/ml each interleukin (IL)-1β, tumor necrosis factor (TNF)-α and interferon (IFN)-γ. Inflammatory mediator secretion was assessed by Luminex assays and ELISA. Signaling pathway activation was monitored by Western blotting. ResultsExpression of these MKs and stimulation with 10 ng/ml IL-1β, TNFα and IFNγ for 20 h did not affect secretion of multiple cytokines including IL-4, IL-5, IL-13 and monocyte chemotactic protein (MCP)-1/CCL2 but did differentially affect the secretion of regulated upon activation, normal T cell expressed and secreted (RANTES)/CCL5, IL-6 and granulocyte macrophage-colony stimulating factor (GM-CSF). RANTES/CCL5 secretion was decreased by MK2WT or MK3WT and stimulated by inhibition of MK2 or MK3 activity with expression of the kinase-deficient enzymes MK2KR or MK33A. IL-6 and GM-CSF secretion was decreased by inhibition of MK2 activity with MK2KR and while MK3WT had no effect, the kinase-deficient MK33A further decreased secretion of these mediators. Cross-talk of the MKs with other signaling pathways was investigated by examining NF-κB activation, which was inhibited by expression of MK3 but not affected by MK2. ConclusionsThese results suggest an inhibitory role for MK2 and MK3 activity in RANTES/CCL5 secretion and cross-talk of MK3 with NF-κB to regulate IL-6 and GM-CSF. These findings differentiate MK2 and MK3 function in ASM cells and provide insight that may enable selective targeting of MKs in ASM to modulate local inflammation in airway disease.

PAR1 and p38 MAPK Regulation of Endothelial Pro‐Inflammatory Responses

Endothelial cells line the lumen of blood vessels and create a semi‐permeable barrier that is disrupted during vascular inflammation resulting in increased permeability, tissue edema, and subsequent organ failure. Endothelial dysfunction also results in cytokine production and leukocyte recruitment. However, the molecular mechanisms behind this pro‐inflammatory state remains to be elucidated. Protease‐activated receptor‐1 (PAR1) is a G protein‐coupled receptor for the coagulant protease thrombin and mediates hemostasis, thrombosis, and inflammatory response to vascular injury. However, the distinct mechanism of how endothelial PAR1 promotes vascular pro‐inflammatory responses represents a major gap in knowledge. We recently discovered that thrombin activation of PAR1 stimulates p38 MAPK activation through a non‐canonical pathway mediated by TAB1 to promote endothelial permeability. PAR1‐induced p38 activation has been linked to vascular barrier disruption; however, the mechanism as to how p38 may be integrated into major signaling pathways that promote pro‐inflammatory responses is not known. We found that thrombin‐stimulated p38 signals independent of the classic g‐protein pathways of RhoA activation and MLC phosphorylation to induce endothelial barrier permeability. Instead, thrombin‐stimulated p38 appears to be signaling through phosphorylation of the MK2 and HSP27. We further show MK2 activity is PAR1 and p38 dependent and regulates differential phosphorylation of its direct substrate, HSP27. Additionally we show HSP27 activity is p38 and PAR1‐dependent. The p38‐MK2‐HSP27 signaling pathway also appears to modulate HUVEC monolayer permeability. These studies show thrombin‐induced p38 signals through MK2 and HSP27 cascade to regulate endothelial barrier permeability.Support or Funding InformationT32 Pharmocological Sciences Training Grant (NIGMS T32 GM007752) (C. Rada) NIH NIGM R01 GM116597 (J. Trejo)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

MK2 Kinase Activity Is Required To Restore Intestinal Homeostasis After Damage

BACKGROUND: IBD is a group of diseases that have no cure and are always progressive, thus the discovery and development of new therapies is an active field of research. Biological agents have stood as a great breakthrough for improvement of patients' life quality, but only 10-30% respond to biologics and around 50% or initial responders acquire resistance over time. MAP kinase p38/MK2 pathway has been on the spot as targetable option for IBD treatment, as a master regulator of pro-inflammatory cytokines. Particularly MK2 inhibitors for clinical use are in process of development, as p38 inhibition led to unacceptable side effects when tested clinically. METHODS: Inflammation associated intestinal damage was induced in MK2 whole body KO, tissue-specific KO or each corresponding MK2 wt controls by administration of 2.5% DSS in the drinking water for 5 days, and then were allowed to recover in fresh water for an additional 4 days. Samples for pathology, protein and quantitative immunophenotyping were collected at several time points during this treatment. RESULTS: Using this mouse model of intestinal injury and inflammation, we have shown that MK2 activity is indeed required for intestinal recovery after damage; in particular, MK2 is required for neutrophil recruitment after initial damage and B and T regulatory cell recruitment in the recovery phase. Using a series of tissue-specific KO of MK2 we could identify MK2 activity in the myeloid compartment as key for restoring intestinal homeostasis after damage. CONCLUSION(S): MK2 activity is required to restore intestinal homeostasis after inflammation-induced damage.

The MAPK-Activated Kinase MK2 Attenuates Dendritic Cell–Mediated Th1 Differentiation and Autoimmune Encephalomyelitis

Dendritic cell (DC)-mediated inflammation induced via TLRs is promoted by MAPK-activated protein kinase (MK)-2, a substrate of p38 MAPK. In this study we show an opposing role of MK2, by which it consolidates immune regulatory functions in DCs through modulation of p38, ERK1/2-MAPK, and STAT3 signaling. During primary TLR/p38 signaling, MK2 mediates the inhibition of p38 activation and positively cross-regulates ERK1/2 activity, leading to a reduction of IL-12 and IL-1α/β secretion. Consequently, MK2 impairs secondary autocrine IL-1α signaling in DCs, which further decreases the IL-1α/p38 but increases the anti-inflammatory IL-10/STAT3 signaling route. Therefore, the blockade of MK2 activity enables human and murine DCs to strengthen proinflammatory effector mechanisms by promoting IL-1α-mediated Th1 effector functions in vitro. Furthermore, MK2-deficient DCs trigger Th1 differentiation and Ag-specific cytotoxicity in vivo. Finally, wild-type mice immunized with LPS in the presence of an MK2 inhibitor strongly accumulate Th1 cells in their lymph nodes. These observations correlate with a severe clinical course in DC-specific MK2 knockout mice compared with wild-type littermates upon induction of experimental autoimmune encephalitis. Our data suggest that MK2 exerts a profound anti-inflammatory effect that prevents DCs from prolonging excessive Th1 effector T cell functions and autoimmunity.

A Synergistic Interaction between Chk1- and MK2 Inhibitors in KRAS-Mutant Cancer

KRAS is one of the most frequently mutated oncogenes in human cancer. Despite substantial efforts, no clinically applicable strategy has yet been developed to effectively treat KRAS-mutant tumors. Here, we perform a cell-line-based screen and identify strong synergistic interactions between cell-cycle checkpoint-abrogating Chk1- and MK2 inhibitors, specifically in KRAS- and BRAF-driven cells. Mechanistically, we show that KRAS-mutant cancer displays intrinsic genotoxic stress, leading to tonic Chk1- and MK2 activity. We demonstrate that simultaneous Chk1- and MK2 inhibition leads to mitotic catastrophe in KRAS-mutant cells. This actionable synergistic interaction is validated using xenograft models, as well as distinct Kras- or Braf-driven autochthonous murine cancer models. Lastly, we show that combined checkpoint inhibition induces apoptotic cell death in KRAS- or BRAF-mutant tumor cells directly isolated from patients. These results strongly recommend simultaneous Chk1- and MK2 inhibition as a therapeutic strategy for the treatment of KRAS- or BRAF-driven cancers.

HSP27 phosphorylation protects against endothelial barrier dysfunction under burn serum challenge

F-actin rearrangement is an early event in burn-induced endothelial barrier dysfunction. HSP27, a target of p38 MAPK/MK2 pathway, plays an important role in actin dynamics through phosphorylation. The question of whether HSP27 participates in burn-related endothelial barrier dysfunction has not been identified yet. Here, we showed that burn serum induced a temporal appearance of central F-actin stress fibers followed by a formation of irregular dense peripheral F-actin in pulmonary endothelial monolayer, concomitant with a transient increase of HSP27 phosphorylation that conflicted with the persistent activation of p38 MAPK/MK2 unexpectedly. The appearance of F-actin stress fibers and transient increase of HSP27 phosphorylation occurred prior to the burn serum-induced endothelial hyperpermeability. Overexpressing phospho-mimicking HSP27 (HSP27(Asp)) reversed the burn serum-induced peripheral F-actin rearrangement with the augmentation of central F-actin stress fibers, and more importantly, attenuated the burn serum-induced endothelial hyperpermeability; such effects were not observed by HSP27(Ala), a non-phosphorylated mutant of HSP27. HSP27(Asp) overexpression also rendered the monolayer more resistant to barrier disruption caused by Cytochalasin D, a chemical reagent that depolymerizes F-actin specifically. Further study showed that phosphatases and sumoylation-inhibited MK2 activity contributed to the blunting of HSP27 phosphorylation during the burn serum-induced endothelial hyperpermeability. Our study identifies HSP27 phosphorylation as a protective response against burn serum-induced endothelial barrier dysfunction, and suggests that targeting HSP27 wound be a promising therapeutic strategy in ameliorating burn-induced lung edema and shock development.

Novel Therapeutic Targets in Neuroinflammation and Neuropathic Pain.

There is abounding evidence that neuroinflammation plays a major role in the pathogenesis of neurodegeneration and neuropathic pain. Chemokine-induced recruitment of peripheral immune cells is a central feature in inflammatory neurodegenerative disorders. Immune cells, glial cells and neurons constitute an integral network that coordinates the immune response by releasing inflammatory mediators that in turn modulate inflammation, neurodegeneration and the signal transduction of pain, via interaction with neurotransmitters and their receptors. The chemokine monocyte chemoattractant protein-1/ chemokine (C-C motif) ligand (MCP-1/CCL2) and its receptor C-C chemokine receptor (CCR2) play a major role in mediating neuroinflammation and targeting CCL2/CCR2 represents a promising strategy to limit neuroinflammation-induced neuropathy. In addition, the CCL2/CCR2 axis is also involved in mediating the pain response. Key cellular signaling events such as phosphorylation and subsequent activation of mitogen activated protein kinase (MAPK) p38 and its substrate MAPK-activated protein MAPKAP Kinase (MK) MK-2, regulate neuroinflammation, neuronal survival and synaptic activity. Further, MAPKs such as extracellular signal-regulated kinases (ERK), c-jun N-terminal kinase (JNK) and p38 play vital roles in mediating the pain signaling cascade and contribute to the maintenance of peripheral and central neuronal sensitization associated with chronic pain. This review outlines the rationale for developing therapeutic strategies against CCL2/CCR2 and MAPK signaling networks, identifying them as novel therapeutic targets for limiting neuroinflammation and neuropathic pain.

Damage-induced DNA replication stalling relies on MAPK-activated protein kinase 2 activity

DNA damage can obstruct replication forks, resulting in replicative stress. By siRNA screening, we identified kinases involved in the accumulation of phosphohistone 2AX (γH2AX) upon UV irradiation-induced replication stress. Surprisingly, the strongest reduction of phosphohistone 2AX followed knockdown of the MAP kinase-activated protein kinase 2 (MK2), a kinase currently implicated in p38 stress signaling and G2 arrest. Depletion or inhibition of MK2 also protected cells from DNA damage-induced cell death, and mice deficient for MK2 displayed decreased apoptosis in the skin upon UV irradiation. Moreover, MK2 activity was required for damage response, accumulation of ssDNA, and decreased survival when cells were treated with the nucleoside analogue gemcitabine or when the checkpoint kinase Chk1 was antagonized. By using DNA fiber assays, we found that MK2 inhibition or knockdown rescued DNA replication impaired by gemcitabine or by Chk1 inhibition. This rescue strictly depended on translesion DNA polymerases. In conclusion, instead of being an unavoidable consequence of DNA damage, alterations of replication speed and origin firing depend on MK2-mediated signaling.

Inhibition of MK2 shows promise for preventing postoperative ileus in mice

BackgroundPostoperative ileus (POI) is a common iatrogenic complication caused by physical disturbances to the bowel during abdominal surgery. Inflammation contributes to the development of POI and leads to impaired intestinal motility. Mitogen-activated protein kinase-activated protein kinase 2 (MK2) plays an essential role in inflammation and is an established drug target for many inflammatory diseases. We evaluated the role of MK2 in POI and investigated whether MK2 inhibition will alleviate POI. Materials and methodsOne group of mice were sham operated as controls. In another two groups, POI was induced by intestinal manipulation, and in one of the groups, MK2 inhibitor was administered 1 h before intestinal manipulation. The bowel tissues were collected and analyzed using real-time reverse-transcriptase polymerase chain reaction, immunoblot, whole-mount histochemistry, immunofluorescence in muscularis, and functional analyses. ResultsBowel manipulation resulted in an upregulation of MK2 activation. Preoperative treatment with an MK2 inhibitor reduced the proinflammatory gene expression induced by intestinal manipulation, such as macrophage inflammatory protein-1α, tumor necrosis factor-α, interleukin-6, interleukin-1β, intercellular adhesion molecule-1, and monocyte chemotactic protein-1. MK2 inhibitor administration significantly reduced the number of myeloperoxidase-positive polymorphonuclear neutrophils, mast cells, and monocyte-derived macrophages that infiltrated the muscularis and prevented the surgically induced reduction in bowel smooth muscle contractility and gastrointestinal transit ability. ConclusionsMK2 mediated the cellular inflammatory responses within the intestinal muscularis in a mouse model of POI. Inhibition of MK2 activity reduced recruitment of immune cells to the intestinal muscularis, preventing loss of intestine smooth muscle contractility. These findings suggest MK2 inhibition is a promising potential target for preventing POI.

The effect of small-molecule inhibition of MAPKAPK2 on cell ageing phenotypes of fibroblasts from human Werner syndrome

Fibroblasts derived from the progeroid Werner syndrome (WS) show reduced replicative lifespan and a “stressed” morphology, both phenotypes being alleviated by using the p38 MAP kinase inhibitor SB203580. Because p38 is a major hub for the control of stress-signalling pathways we were interested in examining the possible role for downstream kinases in order to refine our understanding of the role of p38 signalling in regulation of WS cell growth. To this end we treated WS and normal fibroblasts with MK2 inhibitors to determine whether MK2 inhibition would affect either the growth or morphology of WS cells. The first inhibitor, 7,8-dihydroxy-2,4-diamino-3-cyanobenzopyranopyridine (inhibitor 2), resulted in inhibition of WS cell growth and had no effect on morphology, effects that occurred below the level needed to inhibit MK2 and thus suggestive of inhibitor toxicity. The second inhibitor, 2-(2-quinolin-3-ylpyridin-4-yl)-1,5,6,7-tetrahydro-4H-pyrrolo-[3,2-c]pyridin-4-one (CMPD16), resulted in a significant extension of WS fibroblast replicative capacity compared to normal cells. In addition, CMPD16 reverted the WS cellular morphology to that seen in normal dermal fibroblasts. These data suggest that MK2 activity plays a substantial role in proliferation control in WS cells. CMPD16 was not as effective in cellular lifespan extension as SB203580, however, suggesting that, although MK2 is a downstream kinase involved in cell cycle arrest, other p38 targets may play a role. Alternatively, as CMPD16 is toxic to cell growth at levels just above those that extend lifespan, it is possible that the therapeutic window is too small. However, as CMPD16 does show significant effects in WS fibroblasts, this acts as proof-of-principle for the efforts to design and synthesise improved MK2 inhibitors. As MK2 is involved in inflammatory processes and inflammation plays a major role in WS phenotypes, these data suggest MK2 as a potential therapeutic target for the treatment of Werner syndrome.

MAPK-Activated Protein Kinase 2 Contributes to Clostridium difficile-Associated Inflammation

Clostridium difficile infection (CDI) results in toxin-induced epithelial injury and marked intestinal inflammation. Fecal markers of intestinal inflammation correlate with CDI disease severity, but regulation of the inflammatory response is poorly understood. Previous studies demonstrated that C. difficile toxin TcdA activates p38 kinase in tissue culture cells and mouse ilium, resulting in interleukin-8 (IL-8) release. Here, we investigated the role of phosphorylated mitogen-activated protein kinase (MAPK)-activated protein kinase (MK2 kinase, pMK2), a key mediator of p38-dependent inflammation, in CDI. Exposure of cultured intestinal epithelial cells to the C. difficile toxins TcdA and TcdB resulted in p38-dependent MK2 activation. Toxin-induced IL-8 and GROα release required MK2 activity. We found that p38 and MK2 are activated in response to other actin-disrupting agents, suggesting that toxin-induced cytoskeleton disruption is the trigger for kinase-dependent cytokine response. Phosphorylated MK2 was detected in the intestines of C. difficile-infected hamsters and mice, demonstrating for the first time that the pathway is activated in infected animals. Furthermore, we found that elevated pMK2 correlated with the presence of toxigenic C. difficile among 100 patient stool samples submitted for C. difficile testing. In conclusion, we find that MK2 kinase is activated by TcdA and TcdB and regulates the expression of proinflammatory cytokines. Activation of p38-MK2 in infected animals and humans suggests that this pathway is a key driver of intestinal inflammation in patients with CDI.

Characterization of hsp27 kinases activated by elevated aortic pressure in heart

Chronic hemodynamic overload results in left ventricular hypertrophy, fibroblast proliferation, and interstitial fibrosis. The small heat shock protein hsp27 has been shown to be cardioprotective and this requires a phosphorylatable form of this protein. To further understand the regulation of hsp27 in heart in response to stress, we investigated the ability of elevated aortic pressure to activate hsp27-kinase activities. Isolated hearts were subjected to retrograde perfusion and then snap frozen. Hsp27-kinase activity was measured in vitro as hsp27 phosphorylation. Immune complex assays revealed that MK2 activity was low in non-perfused hearts and increased following crystalline perfusion at 60 or 120 mmHg. Hsp27-kinase activities were further studied following ion-exchange chromatography. Anion exchange chromatography on Mono Q revealed 2 peaks (b and c) of hsp27-kinase activity. A third peak a was detected upon chromatography of the Mono Q flow-through fractions on the cation exchange resin, Mono S. The hsp27-kinase activity underlying peaks a and c increased as perfusion pressure was increased from 40 to 120 mmHg. In contrast, peak b increased over pressures 60-100 mmHg but was decreased at 120 mmHg. Peaks a, b, and c contained MK2 immunoreactivity, whereas MK3 and MK5 immunoreactivity was detected in peak a. p38 MAPK and phospho-p38 MAPK were also detected in peaks b and c but absent from peak a. Hsp27-kinase activity in peaks b and c (120 mmHg) eluted from a Superose 12 gel filtration column with an apparent molecular mass of 50 kDa. Hence, peaks b and c were not a result of MK2 forming complexes. In-gel hsp27-kinase assays revealed a single 49-kDa renaturable hsp27-kinase activity in peaks b and c at 60 mmHg, whereas several hsp27-kinases (p43, p49, p54, p66) were detected in peaks b and c from hearts perfused at 120 mmHg. Thus, multiple hsp27-kinases were activated in response to elevated aortic pressure in isolated, perfused rat hearts and hence may be implicated in regulating the cardioprotective effects of hsp27 and thus may represent targets for cardioprotective therapy.

Abstract P188: Suppression of MK2 Signaling Protects Against Pressure Overload-Induced Cardiac Dysfunction

p38 mitogen-activated protein kinases (MAPKs) regulate a broad range of cellular activities but have been implicated in the pathogenesis of cardiovascular diseases. The mechanisms whereby p38 exerts divergent effects are unknown. Current p38 inhibitors both produce serious side effects and loose efficacy with chronic use. Hence, a better understanding of the downstream targets of p38, i.e. MAPK-activated protein kinases (MKs), is essential. We hypothesized that inhibition of MK2 activity (MK2-/-) during chronic pressure overload is cardioprotective. Twelve-week-old MK2-/- and littermate control (MK2+/+) mice were subjected to transverse aortic constriction (2 wks, n=8). MK2-/- mice showed a ∼20% reduced increase in heart weight-to-tibia length ratio (Fig A) despite similar increases in mean blood pressure and ANP expression. Compared to controls, banded MK2-/- hearts also showed preserved left ventricular: (i) fractional shortening, (ii) ejection fraction (preserved at 72.5 ± 2.2% after banding for MK2-/- but decreased from 67.9 ± 3.6% to 58.8 ± 3.4% in MK2+/+, p<0.05, Fig B), and (iii) diastolic function evidenced by the ratio of transmitral and myocardial early diastolic velocities (E/Em preserved after banding in MK2-/- but increased by 78.8 ± 11.1% in MK2+/+, p<0.01). MK2 deficiency did not reduce interstitial fibrosis. For equivalent respiration rates, mitochondria from MK2-/- hearts showed a significant decrease in Ca2+-sensitivity for mitochondrial permeability transition pore opening (p<0.05, Fig C). Overall, these results suggest that MK2 mediates part of the detrimental remodeling evoked by chronic pressure overload-induced activation of p38.

Cell-penetrating peptides can confer biological function: Regulation of inflammatory cytokines in human monocytes by MK2 inhibitor peptides

Cell-penetrating peptides have been used as a method of delivering biologically active peptide for over two decades. In this paper, we covalently attached four different cell-penetrating peptides to a peptide that inhibits a kinase important in inflammation, mitogen-activated protein kinase activated protein kinase 2 (MAPKAP2 or MK2). We evaluated the specificity, toxicity, and functionality of these therapeutics in an in vitro model of inflammation using THP-1 monocytes. When treated with the MK2 peptide inhibitors, activated THP-1 human monocytes challenged with lipopolysaccharide (LPS) showed a decrease in TNF-α and IL-6 excretion without apparent toxicity. In addition, western blot analysis revealed decreases in the phosphorylation of heat shock protein 27 (HSP27), a downstream substrate of MK2. These results suggested that our peptides inhibited MK2 activity in vitro and should be investigated further as a potential therapeutic for applications involving inflammation. Furthermore, our results suggested that cell-penetrating peptides can be bioactive.

Peptide Inhibitors of MK2 Show Promise for Inhibition of Abdominal Adhesions

Abdominal adhesions are a common side effect of surgical procedures with complications including infertility, chronic pain, and bowel obstruction, which may lead to the need for surgical lyses of the adhesions. Mitogen-activated protein kinase-activated protein kinase 2 (MK2) has been implicated in several diseases, involving inflammation and fibrosis. Thus, the development of a cell-penetrating peptide (CPP) that modulates MK2 activity may confer therapeutic benefit after abdominal surgery in general and more specifically after bowel anastomosis. This study evaluated the function of a CPP inhibitor of MK2 in human mesothelial cells and in a rat bowel anastomosis model. To determine IC50 and basic specificity, kinase inhibition was performed using a radiometric assay. Enzyme-linked immunoassay (ELISA) was used to evaluate interleukin-6 (IL-6) expression in response to IL-1β and tumor necrosis factor-α (TNF-α) stimulation in vitro to validate MK2 kinase inhibition. Following bowel anastomosis (10 rats for each control and treatment at 4 and 10 d), the rats were evaluated for weight loss, normal healing (colonic burst strength and hydroxyproline content at the anastomosis), and number and density of adhesions. The IC50 of the MK2 inhibitor peptide (22 μM) was similar to that of the nonspecific small molecule rottlerin (IC50 = 5 μM). The MK2 inhibitor peptide was effective at suppressing IL-1β and TNF-α stimulated IL-6 expression in mesothelial cells. In vivo, the MK2 inhibitor peptide was effective at suppressing both the density and number of adhesions formed as a result of bowel an anastamosis. Importantly, the peptide had no negative effect on normal healing. In conclusion, the peptide inhibitor of MK2, MMI-0100, has the potential to significantly reduce inflammation through suppression of inflammatory cytokine expression and showed promise as a therapeutic for abdominal adhesions.

DNA Damage Activates a Spatially Distinct Late Cytoplasmic Cell-Cycle Checkpoint Network Controlled by MK2-Mediated RNA Stabilization

Following genotoxic stress, cells activate a complex kinase-based signaling network to arrest the cell cycle and initiate DNA repair. p53-defective tumor cells rewire their checkpoint response and become dependent on the p38/MK2 pathway for survival after DNA damage, despite a functional ATR-Chk1 pathway. We used functional genetics to dissect the contributions of Chk1 and MK2 to checkpoint control. We show that nuclear Chk1 activity is essential to establish a G(2)/M checkpoint, while cytoplasmic MK2 activity is critical for prolonged checkpoint maintenance through a process of posttranscriptional mRNA stabilization. Following DNA damage, the p38/MK2 complex relocalizes from nucleus to cytoplasm where MK2 phosphorylates hnRNPA0, to stabilize Gadd45α mRNA, while p38 phosphorylates and releases the translational inhibitor TIAR. In addition, MK2 phosphorylates PARN, blocking Gadd45α mRNA degradation. Gadd45α functions within a positive feedback loop, sustaining the MK2-dependent cytoplasmic sequestration of Cdc25B/C to block mitotic entry in the presence of unrepaired DNA damage. Our findings demonstrate a critical role for the MK2 pathway in the posttranscriptional regulation of gene expression as part of the DNA damage response in cancer cells.

Mitogen‐activated protein kinase activated protein kinase 2 (MK2) participates in p38 MAPK regulated control of oligodendrocyte differentiation

The p38 mitogen-activated protein kinases (p38 MAPKs) are a family of kinases that regulate a number of cellular functions including cell migration, proliferation, and differentiation. We have previously reported a role for p38 MAPK in the regulation of oligodendrocyte (OLG) differentiation and Schwann cell myelination. Here, we extend our previous findings by showing that a p38 substrate, mitogen-activated protein kinase activated protein kinase 2 (MK2) is a downstream element of the p38 signaling pathway responsible for effecting OLG differentiation. Inhibition of MK2 activity in oligodendrocyte progenitors (OLPs) using CMPD1 [4-(2'-fluorobiphenyl-4-yl)-N-(4-hydroxyphenyl)-butyramide] blocked the activation of MK2 and resulted in decreased accumulation of myelin-differentiation markers, including myelin-associated glycoprotein (MAG) and myelin basic protein (MBP). We corroborated these findings using a small-interfering RNA to MK2, which decreased the myelin-specific lipid galactosylceramide and MAG. Treatment of cultures with CMPD1 decreased the steady state levels of mRNA encoding myelin transcription factor 1 (Myt1), MAG, MBP, and Opalin, a transmembrane sialylglycoprotein expressed in oligodendrocytes. In contrast, increases were observed in the mRNA levels of OLG transcriptional repressors, including transcription factor 4 (Tcf4), Notch1, and inhibitor of differentiation 2 (Id2). Furthermore, we found that the predominantly expressed isoform of p38 in OLGs, p38alpha, and MK2 can form coimmunoprecipitable complexes in OLPs and OLGs. Our results demonstrate that the p38-MK2 pathway is a component of the signaling cascade regulating OLG differentiation.