MEK5/ERK5 signaling mediates IL-4-induced M2 macrophage differentiation through regulation of c-Myc expression.

Macrophages are highly plastic cells, responding to diverse environmental stimuli to acquire different functional phenotypes. Signaling through MAPKs has been reported to regulate the differentiation of macrophages, but the role of ERK5 in IL-4-mediated M2 macrophage differentiation is still unclear. Here, we showed that the ERK5 signaling pathway plays a critical role in IL-4-induced M2 macrophage differentiation. Pharmacologic inhibition of MEK5, an upstream activator of ERK5, markedly reduced the expression of classical M2 markers, such as Arg-1, Ym-1, and Fizz-1, as well as the production of M2-related chemokines and cytokines, CCL22, CCL17, and IGF-1 in IL-4-stimulated macrophages. Moreover, pharmacologic inhibition of ERK5 also decreased the expression of several M2 markers induced by IL-4. In accordance, myeloid cell-specific Erk5 depletion (Erk5∆mye ), using LysMcre /Erk5f/f mice, confirmed the involvement of ERK5 in IL-4-induced M2 polarization. Mechanistically, the inhibition of ERK5 did not affect STAT3 or STAT6 phosphorylation, suggesting that ERK5 signaling regulates M2 differentiation in a STAT3 and STAT6-independent manner. However, genetic deficiency or pharmacologic inhibition of the MEK5/ERK5 pathway reduced the expression of c-Myc in IL-4-activated macrophages, which is a critical transcription factor involved in M2 differentiation. Our study thus suggests that the MEK5/ERK5 signaling pathway is crucial in IL-4-induced M2 macrophage differentiation through the induction of c-Myc expression.

Lunasin abrogates monocytes to endothelial cells.

The adherence of monocytes to endothelial cells plays a causal role in the early development of atherosclerosis and is driven by several inflammatory stimuli, which includes oxidized low-density lipoprotein (ox-LDL). Lunasin, a natural peptide identified in soybean seeds, soy-derived food products, other grains and herbal plants, has been found to exert numerous biological activities, including anti-inflammatory and antioxidant properties. However, little is known regarding the mechanism of action of lunasin in ox-LDL-induced endothelial inflammation. The results of the present study indicate that lunasin significantly ameliorated ox-LDL-induced adhesion of THP-1 monocytes to the surface of human umbilical vein endothelial cells (HUVECs). Lunasin also suppressed expression of the adhesion molecules VCAM-1 and E-selectin, but not ICAM-1. Notably, the inhibitory mechanism of lunasin is associated with its stimulatory effects on expression of the KLF2 transcriptional factor. In addition, lunasin treatment could reverse the effects of ox-LDL on the expression of eNOS and PAI-1, the direct target genes of KLF2. Mechanistically, it was proven that the MEK5/ERK5 pathway mediates the effects of lunasin on KLF2 expression. Taken together, the results of this study suggest that dietary or supplementary intake of lunasin may have a prophylactic or therapeutic capacity in cardiovascular diseases such as atherosclerosis.

Increased T-cell Infiltration Elicited by Erk5 Deletion in a Pten-Deficient Mouse Model of Prostate Carcinogenesis.

Prostate cancer does not appear to respond to immune checkpoint therapies where T-cell infiltration may be a key limiting factor. Here, we report evidence that ablating the growth regulatory kinase Erk5 can increase T-cell infiltration in an established Pten-deficient mouse model of human prostate cancer. Mice that were doubly mutant in prostate tissue for Pten and Erk5 (prostate DKO) exhibited a markedly increased median survival with reduced tumor size and proliferation compared with control Pten-mutant mice, the latter of which exhibited increased Erk5 mRNA expression. A comparative transcriptomic analysis revealed upregulation in prostate DKO mice of the chemokines Ccl5 and Cxcl10, two potent chemoattractants for T lymphocytes. Consistent with this effect, we observed a relative increase in a predominantly CD4+ T-cell infiltrate in the prostate epithelial and stroma of tumors from DKO mice. Collectively, our results offer a preclinical proof of concept for ERK5 as a target to enhance T-cell infiltrates in prostate cancer, with possible implications for leveraging immune therapy in this disease. Cancer Res; 77(12); 3158-68. ©2017 AACR.

Platelet CD36 promotes thrombosis by activating redox sensor ERK5 in hyperlipidemic conditions.

Atherothrombosis is a process mediated by dysregulated platelet activation that can cause life-threatening complications and is the leading cause of death by cardiovascular disease. Platelet reactivity in hyperlipidemic conditions is enhanced when platelet scavenger receptor CD36 recognizes oxidized lipids in oxidized low-density lipoprotein (oxLDL) particles, a process that induces an overt prothrombotic phenotype. The mechanisms by which CD36 promotes platelet activation and thrombosis remain incompletely defined. In this study, we identify a mechanism for CD36 to promote thrombosis by increasing activation of MAPK extracellular signal-regulated kinase 5 (ERK5), a protein kinase known to be exquisitely sensitive to redox stress, through a signaling pathway requiring Src kinases, NADPH oxidase, superoxide radical anion, and hydrogen peroxide. Pharmacologic inhibitors of ERK5 blunted platelet activation and aggregation in response to oxLDL and targeted genetic deletion of ERK5 in murine platelets prevented oxLDL-induced platelet deposition on immobilized collagen in response to arterial shear. Importantly, in vivo thrombosis experiments after bone marrow transplantation from platelet-specific ERK5 null mice into hyperlipidemic apolipoprotein E null mice showed decreased platelet accumulation and increased thrombosis times compared with mice transplanted with ERK5 expressing control bone marrows. These findings suggest that atherogenic conditions critically regulate platelet CD36 signaling by increasing superoxide radical anion and hydrogen peroxide through a mechanism that promotes activation of MAPK ERK5.

Extracellular signal-regulated kinase 5 promotes acute cellular and systemic inflammation.

Inflammatory critical illness is a syndrome that is characterized by acute inflammation and organ injury, and it is triggered by infections and noninfectious tissue injury, both of which activate innate immune receptors and pathways. Although reports suggest an anti-inflammatory role for the mitogen-activated protein kinase (MAPK) extracellular signal-regulated kinase 5 (ERK5), we previously found that ERK5 mediates proinflammatory responses in primary human cells in response to stimulation of Toll-like receptor 2 (TLR2). We inhibited the kinase activities and reduced the abundances of ERK5 and MEK5, a MAPK kinase directly upstream of ERK5, in primary human vascular endothelial cells and monocytes, and found that ERK5 promoted inflammation induced by a broad range of microbial TLR agonists and by the proinflammatory cytokines interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α). Furthermore, we found that inhibitors of MEK5 or ERK5 reduced the plasma concentrations of proinflammatory cytokines in mice challenged with TLR ligands or heat-killed Staphylococcus aureus, as well as in mice that underwent sterile lung ischemia-reperfusion injury. Finally, we found that inhibition of ERK5 protected endotoxemic mice from death. Together, our studies support a proinflammatory role for ERK5 in primary human endothelial cells and monocytes, and suggest that ERK5 is a potential therapeutic target in diverse disorders that cause inflammatory critical illness.

[Electroacupuncture Intervention Enhances Splenic Natural Killer Cell Activity via Inhibiting Phosphorylation of ERK 5 in the Hypothalamus of Surgically Traumatized Rats].

OBJECTIVE: To observe the effect of electroacupuncture (EA) on cytotoxic activity of splenic natural killer (NK) cells after surgical trauma via extracellular signal-regulated kinase (ERK) 5 pathway in the rats' hypothalamus, so as to explore its mechanism underlying improving immune disorders after surgery. METHODS: Sprague-Dawley rats were randomly divided into the following 6 groups: control, trauma model, EA, sham EA, 4 nmol-BIX 02188 (an inhibitor for ERK 5 catalytic activity) and 20 nmol-BIX 02188 (n = 6 rats per group). The surgical trauma model was established by making a longitudinal incision (6 cm in length) along the median line of the back to expose the spinal column and another longitudinal incision along the abdominal median line. EA (2 Hz/15 Hz, 1 - 2 mA) was applied to bilateral "Zusanli" (ST 36) for 30 min immediately after surgery. For rats of the BIX groups, intra-lateral ventricular microinjection of BIX 02188 (10 µL, 4 nmol or 20 nmol, or saline for control rats) was conducted 30 min before the surgery. The expression level and protein of phosphorylated ERK 5 (p-ERK 5) and corticotropin-releasing factor (CRF) protein were measured by immunohistochemistry and Western blot, respectively. The cytotoxicity of splenic NK cells and the expression of splenic Perforin and Granzyme-B genes were measured by lactate dehydrogenase (LDH) release assay and real-time PCR, respectively. RESULTS: In comparison with the control group, hypothalamic p-ERK 5 immunoactivity, p-ERK 5 protein and CRF protein expression levels were significantly up-regulated in the model group (P<0. 01, P<0. 05), while splenic NK cell cytotoxicity and Perforin mRNA and Granzyme-B mRNA expression levels were notably down-regulated in the model group (P <0. 05, P < 0. 01). Following EA and administration of ERK 5 antagonist, the increased expression levels of p-ERK 5 immunoactivity in the EA group, and p-ERK 5 and CRF proteins in both EA and 20 nmol-BIX 02188 groups were obviously down-regulated (P<0. 05, P<0. 01), without changes in the sham EA and 4 nmol-BIX 02188 groups (P>0. 05) except the increased p-ERK 5 protein in the 4 nmol-BIX 02188 group. In addition, the down-regulated NK cell activity, Perforin mRNA and Granzyme-B mRNA expression levels were significantly reversed in the EA and 20 nmol-BIX 02188 groups (P<0. 05, P<0. 01). No significant differences were found between the EA group and 20 nmol-BIX 02188 group in down-regulating hypothalamic p-ERK 5 and CRF protein expression and up-regulating splenic NK cytotoxicity and Perforin and Granzyme-B gene expression (P>0. 05). CONCLUSION: EA can promote the cytotoxicity of splenic NK cells in surgical trauma rats, which may be closely associated with its functions in down-regulating trauma-induced activation of ERK 5 pathway and production of CRF in the hypothalamus.

Identification of activators of ERK5 transcriptional activity by high-throughput screening and the role of endothelial ERK5 in vasoprotective effects induced by statins and antimalarial agents.

Because ERK5 inhibits endothelial inflammation and dysfunction, activating ERK5 might be a novel approach to protecting vascular endothelial cells (ECs) against various pathological conditions of the blood vessel. We have identified small molecules that protect ECs via ERK5 activation and determined their contribution to preventing cardiac allograft rejection. Using high-throughput screening, we identified certain statins and antimalarial agents including chloroquine, hydroxychloroquine, and quinacrine as strong ERK5 activators. Pitavastatin enhanced ERK5 transcriptional activity and Kruppel-like factor-2 expression in cultured human and bovine ECs, but these effects were abolished by the depletion of ERK5. Chloroquine and hydroxychloroquine upregulated ERK5 kinase activity and inhibited VCAM-1 expression in an ERK5-dependent but MAPK/ERK kinase 5- and Kruppel-like factor 2/4-independent manner. Leukocyte rolling and vascular reactivity were used to evaluate endothelial function in vivo, and we found that EC-specific ERK5 knockout (ERK5-EKO) mice exhibited increased leukocyte rolling and impaired vascular reactivity, which could not be corrected by pitavastatin. The role of endothelial ERK5 in acute cardiac allograft rejection was also examined by heterotopic grafting of the heart obtained from either wild-type or ERK5-EKO mice into allomismatched recipient mice. A robust increase in both inflammatory gene expression and CD45-positive cell infiltration into the graft was observed. These tissue rejection responses were inhibited by pitavastatin in wild-type but not ERK5-EKO hearts. Our study has identified statins and antimalarial drugs as strong ERK5 activators and shown that ERK5 activation is preventive of endothelial inflammation and dysfunction and acute allograft rejection.

Restoration of miR17/20a in solid tumor cells enhances the natural killer cell antitumor activity by targeting Mekk2.

Aberrant microRNA (miRNA) expression has been identified in various human solid cancers. However, whether the levels of miRNA expression in tumor cells have any effect on tumor progression has not been determined. In this proof-of-concept study, the restoration of high-level expression of the miR17-92 cluster of miRNAs reveals its function as a tumor suppressor in murine solid cancer cells. Specifically, genetically engineered expression of higher levels of miR17/20a in the miR17-92 cluster in both murine breast cancer and colon cancer cells triggered natural killer (NK)-cell recognition by inhibiting the expression of MHC class I (H-2D) through the Mekk2-Mek5-Erk5 pathway. Results from the mouse tumor studies were recapitulated using samples of human solid tumors. Together, these data indicate that miR17/20a miRNAs function as tumor suppressors by reprogramming tumor cells for NK cell-mediated cytotoxicity.

Cystamine ameliorates ventricular hypertrophy associated with modulation of IL-6-mediated signaling in lupus-prone mice.

AIMS: The aim of this study is to investigate the protective effects of cystamine on lupus-associated cardiac hypertrophy. MAIN METHODS: Balb/c and lupus-prone NZB/W-F1 mice were individually randomized into sham group (saline, n=16) and cystamine group (n=16). Mice received saline or cystamine (100 mmol in 100 µL saline) by daily intraperitoneal injection for 2 consecutive weeks. Morphological, histological, and biochemical alterations were investigated. KEY FINDINGS: Cystamine decreased both left ventricular (LV) mass and LV mass/tissue-to-blood ratio (TBR) in NZB/W-F1 mice (p<0.05), whereas slight effects were observed in Balb/c mice. Moreover, cystamine reduced levels of atrial natriuretic peptide (ANP), C-reactive protein (CRP), heart type-fatty acid binding protein (h-FABP), creatine kinase-MB (CK-MB) and IL-6 in LV tissues of NZB/W-F1 mice (p<0.05). Additionally, in LV tissues of NZB/W-F1 mice, suppression of hypertrophic signaling mediated by IL-6 in response to administration of cystamine was revealed, including phosphorylation of MEK5, ERK5, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38) (p<0.05). SIGNIFICANCE: Cystamine alleviated LV hypertrophy in NZB/W-F1 mice as a result of decrease in hypertrophic mediators and suppression of IL-6 mediated hypertrophic signaling.

Activity assays for extracellular signal-regulated kinase 5.

Extracellular signal-regulated kinase 5 (ERK5) is also known as big MAPK (BMK1) or MAPK7. ERK5 is 115 kDa in mass and therefore larger than the other MAPKs such as ERK1/2, JNK, and p38. Like other MAPKs, ERK5 is ubiquitously expressed in mammalian cells and is part of a three kinase cascade involving a MAPK kinase (MEK5) and MAPK kinase kinase (primarily MEKK2 and MEKK3). ERK5 is important for proliferative responses to growth factors like epidermal growth factor and stress responses such as hyperosmolarity. Upon stimulation, ERK5 rapidly translocates to the nucleus for the control of transcription. ERK5 is also critical for maintenance of vascular integrity and endothelial cell survival. In this chapter, we define methods used to measure the activation of ERK5 using different biochemical and cell-based assays.

ERK and cell death: ERK location and T cell selection.

The selection of functional T cells is mediated by interactions between the T cell antigen receptor and self-peptide major histocompatibility complex expressed on thymic epithelium. These interactions either lead to survival and development or death. The T cell antigen receptor is an unusual receptor able to signal multiple cell fates. The precise mechanism by which this is achieved has been an area of intense research effort over the years. One model proposes that the differential activation of mitogen-activated protein kinase pathways contributes to this decision. Here, the role of extracellular signal-regulated kinase in promoting or preventing apoptosis during thymic selection is discussed.

Analysis of antibody reactivity in paired cerebrospinal fluid and serum of a relapsing remitting multiple sclerosis patient.

Increasing evidence indicates an involvement of B cells in multiple sclerosis (MS). However, little is known about antigenic targets recognized by antibodies present in blood and cerebrospinal fluid (CSF) of MS patients. This study was therefore aimed at identifying the antigen reactivity of antibodies present in CSF and compares the identified antibody profile with that of the serum of the same patient using cDNA phage display. Selection rounds on paired CSF and serum of this patient identified 13 antigenic targets of which 5 were enriched by serum antibodies and 2 were identified by CSF antibodies. Interestingly, the six remaining antigenic targets were shown to be recognized by both CSF and serum antibodies. These findings point towards both common as well as distinct antibody profiles in CSF and serum of MS patients.

Protein kinase C alpha, betaI, and betaII isozymes regulate cytokine production in mast cells through MEKK2/ERK5-dependent and -independent pathways.

Regulation of MAPK pathways by PKC isoforms was examined in murine bone marrow-derived mast cells (BMMCs). The PKCalpha, betaI, and betaII isoforms showed the most robust activation after FcepsilonR1-mediated stimulation by anti-ovalbumin specific IgE and ovalbumin (IgE-ova). PKCalpha, betaI, and betaII were all involved in activation of JNK, MEKK2, and ERK5, with differential relative contributions of each isoform to specific MAPK pathway components. BMMCs from mice lacking MEKK2 showed reduced production (50-60%) of IL-6, IL-13, and TNF-alpha after stimulation, demonstrating MEKK2-dependent and -independent pathways for cytokine production. Cytokine production was stimulated by over-expression of PKC in cells from MEKK2-deficient and wild-type mice. Activation of ERK5 did not occur in BMMCs lacking MEKK2, indicating that MEKK2-independent cytokine production was also ERK5-independent. Since MAPK modules differentially regulate mast cell functions, including degranulation and cytokine production, it is suggested that specific functions could be targeted by inhibiting specific PKC isoforms.