Requirement for p38alpha in erythropoietin expression: a role for stress kinases in erythropoiesis

The relationship mammalian p38 with human health and its homolog Hog1 in response to environmental stresses in Saccharomyces cerevisiae

The mammalian p38 MAPK pathway plays a vital role in transducing extracellular environmental stresses into numerous intracellular biological processes. The p38 MAPK have been linked to a variety of cellular processes including inflammation, cell cycle, apoptosis, development and tumorigenesis in specific cell types. The p38 MAPK pathway has been implicated in the development of many human diseases and become a target for treatment of cancer. Although MAPK p38 pathway has been extensively studied, many questions still await clarification. More comprehensive understanding of the MAPK p38 pathway will provide new possibilities for the treatment of human diseases. Hog1 in S. cerevisiae is the conserved homolog of p38 in mammalian cells and the HOG MAPK signaling pathway in S. cerevisiae has been extensively studied. The deep understanding of HOG MAPK signaling pathway will help provide clues for clarifying the p38 signaling pathway, thereby furthering our understanding of the relationship between p38 and disease. In this review, we elaborate the functions of p38 and the relationship between p38 and human disease. while also analyzing how Hog1 regulates cellular processes in response to environmental stresses. 1, p38 in response to various stresses in mammalian cells.2, The functions of mammalian p38 in human health.3, Hog1 as conserved homolog of p38 in response to environmental stresses in Saccharomyces cerevisiae. 1, p38 in response to various stresses in mammalian cells. 2, The functions of mammalian p38 in human health. 3, Hog1 as conserved homolog of p38 in response to environmental stresses in S. cerevisiae.

Differential Modulation of the Phosphoproteome by the MAP Kinases Isoforms p38α and p38β

The p38 members of the mitogen-activated protein kinases (MAPKs) family mediate various cellular responses to stress conditions, inflammatory signals, and differentiation factors. They are constitutively active in chronic inflammatory diseases and some cancers. The differences between their transient effects in response to signals and the chronic effect in diseases are not known. The family is composed of four isoforms, of which p38α seems to be abnormally activated in diseases. p38α and p38β are almost identical in sequence, structure, and biochemical and pharmacological properties, and the specific unique effects of each of them, if any, have not yet been revealed. This study aimed to reveal the specific effects induced by p38α and p38β, both when transiently activated in response to stress and when chronically active. This was achieved via large-scale proteomics and phosphoproteomics analyses using stable isotope labeling of two experimental systems: one, mouse embryonic fibroblasts (MEFs) deficient in each of these p38 kinases and harboring either an empty vector or vectors expressing p38αWT, p38βWT, or intrinsically active variants of these MAPKs; second, induction of transient stress by exposure of MEFs, p38α-/-, and p38β-/- MEFs to anisomycin. Significant differences in the repertoire of the proteome and phosphoproteome between cells expressing active p38α and p38β suggest distinct roles for each kinase. Interestingly, in both cases, the constitutive activation induced adaptations of the cells to the chronic activity so that known substrates of p38 were downregulated. Within the dramatic effect of p38s on the proteome and phosphoproteome, some interesting affected phosphorylation sites were those found in cancer-associated p53 and Hspb1 (HSP27) proteins and in cytoskeleton-associated proteins. Among these, was the stronger direct phosphorylation by p38α of p53-Ser309, which was validated on the Ser315 in human p53. In summary, this study sheds new light on the differences between chronic and transient p38α and p38β signaling and on the specific targets of these two kinases.

Qiangguyin inhibited fat accumulation in OVX mice through the p38 MAPK signaling pathway to achieve anti-osteoporosis effects

Postmenopausal osteoporosis (PMOP) is a common bone disease characterized by decreased bone density and increased bone fragility due to decreased estrogen levels. Qiangguyin (QGY) is transformed from the famous traditional Chinese medicine BuShen Invigorating Blood Decoction. In this study, we used QGY to treat PMOP. We observed that QGY significantly reduced fat accumulation in the chondro-osseous junction. However, its specific mechanism of action remains unclear. To determine the specific molecular mechanism of QGY, we explored the pharmacological mechanism by which QGY reduces fat accumulation in the chondro-osseous junction through network pharmacological analysis. The active components and targets related to PMOP and QGY were screened from different databases, forming a composition-target-disease network. Next, a comprehensive analysis platform including protein-protein interaction (PPI) network, Gene Ontology (GO) enrichment analysis, and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis were established. The results revealed that QGY inhibits adipogenic differentiation by activating the mitogen-activated protein kinase (MAPK) signaling pathway, thus reducing the accumulation of fat in the chondro-osseous junction. For further verification. In vitro and in vivo experiments were carried out. Our data showed that QGY significantly reversed the high expression of fatty acid binding protein 4 (FABP4) and peroxisome proliferator-activated receptor γ (PPARγ). Further, QGY prevents fat accumulation by inhibiting the expression of p38. In summary, the results of this study suggested that QGY-induced phenotypic changes are related to the activation of the p38 MAPK signaling pathway.

Erythrocyte mitogen-activated protein kinases mediate hemolytic events under osmotic and oxidative stress and in hemolytic diseases

p38 MAPKs are key regulators of cellular adaptation to various stress stimuli, however, their role in mediating erythrocyte cell death and hemolysis is largely unknown. We hypothesized that activation of erythrocyte p38 MAPK is a common event in the stimulation of hemolysis, and that inhibition of p38 MAPK pathways could mitigate hemolysis in hemoglobinopathies. We exposed human erythrocytes to diamide-induced oxidative stress or to hypoosmotic shock in the presence or absence of p38 MAPK inhibitors (SCIO469, SB203580, CMPD1) and used immunoblotting to determine MAPK activity and to identify possible downstream effectors of p38 MAPK. We also evaluated the impact of p38 MAPK inhibitors on stress-induced hemolysis or hypoxia-induced sickling in erythrocytes from mouse models of sickle cell disease. We found that human erythrocytes express conventional MAPKs (MKK3, p38 MAPK, MAPKAPK2) and identified differential MAPK activation pathways in each stress condition. Specifically, p38 MAPK inhibition in diamide-treated erythrocytes was associated with decreased phosphorylation of Src tyrosine kinases and Band 3 protein. Conversely, hypoosmotic shock induced MAPKAPK2 and RSK2 phosphorylation, which was inhibited by SCIO469 or CMPD1. Relevant to hemoglobinopathies, sickle cell disease was associated with increased erythrocyte MKK3, p38 MAPK, and MAPKAPK2 expression and phosphorylation as compared with erythrocytes from healthy individuals. Furthermore, p38 MAPK inhibition was associated with decreased hemolysis in response to diamide treatments or osmotic shock, and with decreased erythrocyte sickling under experimental hypoxia. These findings provided insights into MAPK-mediated signaling pathways that regulate erythrocyte function and hemolysis in response to extracellular stressors or human diseases.

Concurrent Zrsr2 mutation and Tet2 loss promote myelodysplastic neoplasm in mice

RNA splicing and epigenetic gene mutations are the most frequent genetic lesions found in patients with myelodysplastic neoplasm (MDS). About 25% of patients present concomitant mutations in such pathways, suggesting a cooperative role in MDS pathogenesis. Importantly, mutations in the splicing factor ZRSR2 frequently associate with alterations in the epigenetic regulator TET2. However, the impact of these concurrent mutations in hematopoiesis and MDS remains unclear. Using CRISPR/Cas9 genetically engineered mice, we demonstrate that Zrsr2^m/mTet2^-/- promote MDS with reduced penetrance. Animals presented peripheral blood cytopenia, splenomegaly, extramedullary hematopoiesis, and multi-lineage dysplasia, signs consistent with MDS. We identified a myelo-erythroid differentiation block accompanied by an expansion of LT-HSC and MPP2 progenitors. Transplanted animals presented a similar phenotype, thus indicating that alterations were cell-autonomous. Whole-transcriptome analysis in HSPC revealed key alterations in ribosome, inflammation, and migration/motility processes. Moreover, we found the MAPK pathway as the most affected target by mRNA aberrant splicing. Collectively, this study shows that concomitant Zrsr2 mutation and Tet2 loss are sufficient to initiate MDS in mice. Understanding this mechanistic interplay will be crucial for the identification of novel therapeutic targets in the spliceosome/epigenetic MDS subgroup.

The Role of PI3K/AKT and MAPK Signaling Pathways in Erythropoietin Signalization

Erythropoietin (EPO) is a glycoprotein cytokine known for its pleiotropic effects on various types of cells and tissues. EPO and its receptor EPOR trigger signaling cascades JAK2/STAT5, MAPK, and PI3K/AKT that are interconnected and irreplaceable for cell survival. In this article, we describe the role of the MAPK and PI3K/AKT signaling pathways during red blood cell formation as well as in non-hematopoietic tissues and tumor cells. Although the central framework of these pathways is similar for most of cell types, there are some stage-specific, tissue, and cell-lineage differences. We summarize the current state of research in this field, highlight the novel members of EPO-induced PI3K and MAPK signaling, and in this respect also the differences between erythroid and non-erythroid cells.

Expression of a constitutively active p38α mutant in mice causes early death, anemia, and accumulation of immunosuppressive cells

The MAP kinase p38α is associated with numerous processes in eukaryotes, and its elevated activity is a prominent feature of inflammatory diseases, allergies, and aging. Since p38α is a nodal component of a complex signaling network, it is difficult to reveal exactly how p38α contributes to disparate outcomes. Identification of p38α -specific effects requires activation of p38α per se in vivo. We generated a transgenic mouse model that meets this requirement by allowing inducible and reversible expression of an intrinsically active p38α molecule (p38αD176A+F327S ). p38α's activation across all murine tissues resulted in a significant loss of body weight and death of about 40% of the mice within 17 weeks of activation, although most tissues were unaffected. Flow cytometric analysis of the lungs and bronchoalveolar lavage fluid detected an accumulation of 'debris' within the airways, suggesting impaired clearance. It also revealed increased numbers of alternatively activated alveolar macrophages and myeloid-derived suppressor cells within the lung, pointing at suppression and resolution of inflammation. Blood count suggested that mice expressing p38αD176A+F327S suffer from hemolytic anemia. Flow cytometry of bone marrow revealed a reduced number of hematopoietic stem cells and abnormalities in the erythroid lineage. Unexpectedly, p38α's substrate MAPKAPK2, mitogen-activated protein kinase-activated protein kinase 2 was downregulated in mice expressing p38αD176A+F327S , suggesting that constitutive activity of p38α may impose pathological phenotypes by downregulating downstream components, perhaps via a feedback inhibition mechanism. In summary, this new mouse model shows that induced p38α activity per se is hazardous to mouse vitality and welfare, although pathological parameters are apparent only in blood count, bone marrow, and lungs.

MAPK14 over-expression is a transcriptomic feature of polycythemia vera and correlates with adverse clinical outcomes

Background

The transcriptomic signature has not been fully elucidated in PV, as well as mRNA markers for clinical variables (thrombosis, leukemic transformation, survival, etc.). We attempted to reveal and validate crucial co-expression modules and marker mRNAs correlating with polycythemia vera (PV) by weighted gene co-expression network analysis (WGCNA).

Material and methods

The GSE57793/26014/61629 datasets were downloaded from Gene Expression Omnibus (GEO) database and integrated into one fused dataset. By R software and ‘WGCNA’ package, the PV-specific co-expression module was identified, the pathway enrichment profile of which was obtained by over-representation analysis (ORA). Protein–protein interaction (PPI) network and hub gene analysis identified MAPK14 as our target gene. Then the distribution of MAPK14 expression in different disease/mutation types, were depicted based on external independent datasets. Genome-scale correlation analysis revealed the association of MAPK14 and JAK/STAT family genes. Then gene set enrichment analysis (GSEA) was performed to detect the activated and suppressed pathways associating with MAPK14 expression. Moreover, GSE47018 dataset was utilized to compare clinical variables (thrombosis, leukemic transformation, survival, etc.) between MAPK14-high and MAPK14-low groups.

Results

An integrated dataset including 177 samples (83 PV, 35 ET, 17 PMF and 42 normal donors) were inputted into WGCNA. The ‘tan’ module was identified as the PV-specific module (R² = 0.56, p = 8e−16), the genes of which were dominantly enriched in pro-inflammatory pathways (Toll-like receptor (TLR)/TNF signaling, etc.). MAPK14 is identified as the top hub gene in PV-related PPI network with the highest betweenness. External datasets validated that the MAPK14 expression was significantly higher in PV than that of essential thrombocytosis (ET)/primary myelofibrosis (PMF) patients and normal donors. JAK2 homozygous mutation carriers have higher level of MAPK14 than that of other mutation types. The expression of JAK/STAT family genes significantly correlated with MAPK14, which also contributed to the activation of oxidated phosphorylation, interferon-alpha (IFNα) response and PI3K-Akt-mTOR signaling, etc. Moreover, MAPK14-high group have more adverse clinical outcomes (splenectomy, thrombosis, disease aggressiveness) and inferior survival than MAPK14-low group.

Conclusion

MAPK14 over-expression was identified as a transcriptomic feature of PV, which was also related to inferior clinical outcomes. The results provided novel insights for biomarkers and therapeutic targets for PV.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-02913-3.

ZRSR1 cooperates with ZRSR2 in regulating splicing of U12-type introns in murine hematopoietic cells

Recurrent loss-of-function mutations of spliceosome gene, ZRSR2, occur in myelodysplastic syndromes (MDS). Mutation/loss of ZRSR2 in human myeloid cells primarily causes impaired splicing of the U12-type introns. In order to further investigate the role of this splice factor in RNA splicing and hematopoietic development, we generated mice lacking ZRSR2. Unexpectedly, Zrsr2-deficient mice developed normal hematopoiesis with no abnormalities in myeloid differentiation evident in either young or ≥1-year old knockout mice. Repopulation ability of Zrsr2-deficient hematopoietic stem cells was also unaffected in both competitive and non-competitive reconstitution assays. Myeloid progenitors lacking ZRSR2 exhibited mis-splicing of U12-type introns, however, this phenotype was moderate compared to the ZRSR2-deficient human cells. Our investigations revealed that a closely related homolog, Zrsr1, expressed in the murine hematopoietic cells, but not in human cells contributes to splicing of U12-type introns. Depletion of Zrsr1 in Zrsr2 KO myeloid cells exacerbated retention of the U12-type introns, thus highlighting a collective role of ZRSR1 and ZRSR2 in murine U12-spliceosome. We also demonstrate that aberrant retention of U12-type introns of MAPK9 and MAPK14 leads to their reduced protein expression. Overall, our findings highlight that both ZRSR1 and ZRSR2 are functional components of the murine U12-spliceosome, and depletion of both proteins is required to accurately model ZRSR2-mutant MDS in mice.

Myonectin inhibits adipogenesis in 3T3-L1 preadipocytes by regulating p38 MAPK pathway

In current times, obesity is a major health problem closely associated with metabolic disease such as diabetes, dyslipidemia, and cardiovascular disease. The direct cause of obesity is known as an abnormal increase in fat cell size and the adipocyte pool. Hyperplasia, the increase in number of adipocytes, results from adipogenesis in which preadipocytes differentiate into mature adipocytes. Adipogenesis is regulated by local and systemic cues that alter transduction pathways and subsequent control of adipogenic transcription factors. Therefore, the regulation of adipogenesis is an important target for preventing obesity. Myonectin, a member of the CTRP family, is a type of myokine released by skeletal muscle cells. Although several studies have shown that myonectin is associated with lipid metabolism, the role of myonectin during adipogenesis is not known. Here, we demonstrate the role of myonectin during adipocyte differentiation of 3T3-L1 cells. We found that myonectin inhibits the adipogenesis of 3T3-L1 preadipocytes with a reduction in the expression of adipogenic transcription factors such as C/EBPα, β and PPARγ. Furthermore, we show that myonectin has an inhibitory effect on adipogenesis through the regulation of the p38 MAPK pathway and CHOP. These findings suggest that myonectin may be a novel therapeutic target for the prevention of obesity.

Tumor Immune Evasion Induced by Dysregulation of Erythroid Progenitor Cells Development

Cancer cells harness normal cells to facilitate tumor growth and metastasis. Within this complex network of interactions, the establishment and maintenance of immune evasion mechanisms are crucial for cancer progression. The escape from the immune surveillance results from multiple independent mechanisms. Recent studies revealed that besides well-described myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs) or regulatory T-cells (Tregs), erythroid progenitor cells (EPCs) play an important role in the regulation of immune response and tumor progression. EPCs are immature erythroid cells that differentiate into oxygen-transporting red blood cells. They expand in the extramedullary sites, including the spleen, as well as infiltrate tumors. EPCs in cancer produce reactive oxygen species (ROS), transforming growth factor β (TGF-β), interleukin-10 (IL-10) and express programmed death-ligand 1 (PD-L1) and potently suppress T-cells. Thus, EPCs regulate antitumor, antiviral, and antimicrobial immunity, leading to immune suppression. Moreover, EPCs promote tumor growth by the secretion of growth factors, including artemin. The expansion of EPCs in cancer is an effect of the dysregulation of erythropoiesis, leading to the differentiation arrest and enrichment of early-stage EPCs. Therefore, anemia treatment, targeting ineffective erythropoiesis, and the promotion of EPC differentiation are promising strategies to reduce cancer-induced immunosuppression and the tumor-promoting effects of EPCs.

The relation between mitogen activated protein kinase (MAPK) pathway and different genes expression in patients with beta Thalassemia

BACKGROUND

β-thalassemia is an inherited hemoglobinopathy resulting in quantitative changes in the β-globin chain. Understanding the molecular basis of that disorder requires studying the expression of genes controlling the pathways that affect the erythropoietic homeostasis especially the MAPK pathway. The MAPKs are a family of serine/threonine kinases that play an essential role in connecting cell-surface receptors to DNA in the nucleus of the cell.

AIM

to study the effect of expression of GNAI2, DUSP5 and ARRB1 genes on MAPK signaling pathway in pediatric patients with beta thalassemia.

METHODS

Forty children with beta thalassemia major (TM), forty children with beta thalassemia intermedia (TI) and forty age and gender matched healthy controls were enrolled in this study. Detection of GNAI2, DUSP5 and ARRB1 mRNA expression was done by real time polymerase chain reaction (RT-PCR).

RESULTS

revealed increased expression of ARRB1 (Arrestin Beta 1) gene, and decreased expression of both GNAI2 (Guanine nucleotide-binding protein G (i) subunit alpha-2) and DUSP5 (Dual specificity protein phosphatase 5) genes in both patient groups than control groups respectively.

CONCLUSIONS

Change in the rate of expression of ARRB1, GNAI2 and DUSP5 may have a role in the pathogenesis of abnormal hematopoiesis in cases of β thalassemia through affecting the MAPK pathway.

Ribosomal stress-surveillance: three pathways is a magic number

Cells rely on stress response pathways to uphold cellular homeostasis and limit the negative effects of harmful environmental stimuli. The stress- and mitogen-activated protein (MAP) kinases, p38 and JNK, are at the nexus of numerous stress responses, among these the ribotoxic stress response (RSR). Ribosomal impairment is detrimental to cell function as it disrupts protein synthesis, increase inflammatory signaling and, if unresolved, lead to cell death. In this review, we offer a general overview of the three main translation surveillance pathways; the RSR, Ribosome-associated Quality Control (RQC) and the Integrated Stress Response (ISR). We highlight recent advances made in defining activation mechanisms for these pathways and discuss their commonalities and differences. Finally, we reflect on the physiological role of the RSR and consider the therapeutic potential of targeting the sensing kinase ZAKα for treatment of ribotoxin exposure.

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.

Neuronal deficiency of p38α-MAPK ameliorates symptoms and pathology of APP or Tau-transgenic Alzheimer's mouse models

Alzheimer's disease (AD) is the leading cause of dementia with very limited therapeutic options. Amyloid β (Aβ) and phosphorylated Tau (p-Tau) are key pathogenic molecules in AD. P38α-MAPK is specifically activated in AD lesion sites. However, its effects on AD pathogenesis, especially on p-Tau-associated brain pathology, and the underlying molecular mechanisms remain unclear. We mated human APP-transgenic mice and human P301S Tau-transgenic mice with mapk14-floxed and neuron-specific Cre-knock-in mice. We observed that deletion of p38α-MAPK specifically in neurons improves the cognitive function of both 9-month-old APP and Tau-transgenic AD mice, which is associated with decreased Aβ and p-Tau load in the brain. We further used next-generation sequencing to analyze the gene transcription in brains of p38α-MAPK deficient and wild-type APP-transgenic mice, which indicated that deletion of p38α-MAPK regulates the transcription of calcium homeostasis-related genes, especially downregulates the expression of grin2a, a gene encoding NMDAR subunit NR2A. Cell culture experiments further verified that deletion of p38α-MAPK inhibits NMDA-triggered calcium influx and neuronal apoptosis. Our systemic studies of AD pathogenic mechanisms using both APP- and Tau-transgenic mice suggested that deletion of neuronal p38α-MAPK attenuates AD-associated brain pathology and protects neurons in AD pathogenesis. This study supports p38α-MAPK as a novel target for AD therapy.

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.

Thermal Bioprinting Causes Ample Alterations of Expression of LUCAT1, IL6, CCL26, and NRN1L Genes and Massive Phosphorylation of Critical Oncogenic Drug Resistance Pathways in Breast Cancer Cells

Bioprinting technology merges engineering and biological fields and together, they possess a great translational potential, which can tremendously impact the future of regenerative medicine and drug discovery. However, the molecular effects elicited by thermal inkjet bioprinting in breast cancer cells remains elusive. Previous studies have suggested that bioprinting can be used to model tissues for drug discovery and pharmacology. We report viability, apoptosis, phosphorylation, and RNA sequence analysis of bioprinted MCF7 breast cancer cells at separate timepoints post-bioprinting. An Annexin A5-FITC apoptosis stain was used in combination with flow cytometry at 2 and 24 h post-bioprinting. Antibody arrays using a Human phospho-MAPK array kit was performed 24 h post-bioprinting. RNA sequence analysis was conducted in samples collected at 2, 7, and 24 h post-bioprinting. The post-bioprinting cell viability averages were 77 and 76% at 24 h and 48 h, with 31 and 64% apoptotic cells at 2 and 24 h after bioprinting. A total of 21 kinases were phosphorylated in the bioprinted cells and 9 were phosphorylated in the manually seeded controls. The RNA seq analysis in the bioprinted cells identified a total of 12,235 genes, of which 9.7% were significantly differentially expressed. Using a ±2-fold change as the cutoff, 266 upregulated and 206 downregulated genes were observed in the bioprinted cells, with the following 5 genes uniquely expressed NRN1L, LUCAT1, IL6, CCL26, and LOC401585. This suggests that thermal inkjet bioprinting is stimulating large scale gene alterations that could potentially be utilized for drug discovery. Moreover, bioprinting activates key pathways implicated in drug resistance, cell motility, proliferation, survival, and differentiation.

Hepatospecific ablation of p38α MAPK governs liver regeneration through modulation of inflammatory response to CCl4-induced acute injury

Mammalian p38α MAPK (Mitogen-Activated Protein Kinase) transduces a variety of extracellular signals that regulate cellular processes, such as inflammation, differentiation, proliferation or apoptosis. In the liver, depending of the physiopathological context, p38α acts as a negative regulator of hepatocyte proliferation as well as a promotor of inflammatory processes. However, its function during an acute injury, in adult liver, remains uncharacterized. In this study, using mice that are deficient in p38α specifically in mature hepatocytes, we unexpectedly found that lack of p38α protected against acute injury induced by CCl₄ compound. We demonstrated that the hepatoprotective effect alleviated ROS accumulation and shaped the inflammatory response to promote efficient tissue repair. Mechanistically, we provided strong evidence that Ccl2/Ccl5 chemokines were crucial for a proper hepatoprotective response observed secondary to p38α ablation. Indeed, antibody blockade of Ccl2/Ccl5 was sufficient to abrogate hepatoprotection through a concomitant decrease of both inflammatory cells recruitment and antioxidative response that result ultimately in higher liver damages. Our findings suggest that targeting p38α expression and consequently orientating immune response may represent an attractive approach to favor tissue recovery after acute liver injury.

MAPK p38alpha Kinase Influences Haematopoiesis in Embryonic Stem Cells

The activation of p38alpha kinase mediates cell response to various extracellular factors including many interleukins and growth factors important for haematopoiesis. The role of p38alpha kinase was previously analysed in particular haematopoietic cells. In this study and for the first time, the role of p38alpha kinase in haematopoiesis was studied using a model of continuous haematopoietic development in pluripotent embryonic stem cells in vitro. The expression of transcripts associated with haematopoiesis and the potential for the formation of specific haematopoietic cell colonies were compared between wild-type and mutant p38alpha gene-depleted cells. The absence of p38alpha kinase led to the inhibition of hemangioblast formation during the first step of haematopoiesis. Later, during differentiation, due to the lack of p38alpha kinase, erythrocyte maturation was impaired. Mutant p38α−/− cells also exhibited decreased potential with respect to the expansion of granulocyte colony-forming units. This effect was reversed in the absence of erythropoietin as shown by colony-forming unit assay in media for colony-forming unit granulocytes/macrophages. p38alpha kinase thus plays an important role in the differentiation of common myeloid precursor cells into granulocyte lineages.

A network pharmacology approach to investigate the blood enriching mechanism of Danggui buxue Decoction

ETHNOPHARMACOLOGICAL RELEVANCE

Danggui buxue Decoction (DBD) has been frequently used to treat with blood deficiency, which consisted of Danggui (DG) and Huangqi (HQ) at a ratio of 1:5. Accumulating evidence showed that blood deficiency in traditional Chinese medicine (TCM) was similar to anemia in modern medicine.

AIM OF THE STUDY

The purpose of this study was to explore its therapeutic mechanism of with network pharmacology approach.

MATERIALS AND METHODS

We explored the chemical compounds of DBD and used compound ADME screening to identify the potential compounds. Targets for the therapeutic actions of DBD were obtained from the PharmMapper, Swiss, SEA and STITCH. GO analysis and pathway enrichment analysis was performed using the DAVID webserver. Cytoscape was used to visualize the compound-target-pathway network for DBD. The pharmacodynamics and crucial targets were also validated.

RESULTS

Thirty-six potential active components in DBD and 49 targets which the active components acted on were identified. 47 KEGG pathways which DBD acted on were also come to light. And then, according to KEGG pathway annotation analysis, only 16 pathways seemed to be related to the blood nourishing effect of DBD, such as PI3K-AKT pathway, and so on. Only 32 targets participated in these 16 pathways and they were acted on by 29 of the 36 active compounds. Whole pharmacodynamic experiments showed that DBD had significant effects to blood loss rats. Furthermore, DBD could promote the up-regulation of hematopoietic and immune related targets and the down-regulation of inflammatory related targets. Significantly, with the results of effective rate, molecular docking and experimental validation, we predicted astragaloside IV in HQ, senkyunolide A and senkyunolide K in DG might be the major contributing compounds to DBD's blood enriching effect.

CONCLUSION

In this study, a systematical network pharmacology approach was built. Our results provided a basis for the future study of senkyunolide A and senkyunolide K as the blood enriching compounds in DBD. Furthermore, combined network pharmacology with validation experimental results, the nourishing blood effect of DBD might be manifested by the dual mechanism of enhancing immunity and promoting hematopoiesis.

MAPK and PI3K signaling: At the crossroads of neural crest development

Receptor tyrosine kinase-mediated growth factor signaling is essential for proper formation and development of the neural crest. The many ligands and receptors implicated in these processes signal through relatively few downstream pathways, frequently converging on the MAPK and PI3K pathways. Despite decades of study, there is still considerable uncertainty about where and when these signaling pathways are required and how they elicit particular responses. This review summarizes our current understanding of growth factor-induced MAPK and PI3K signaling in the neural crest.

Induction of functional erythropoietin and erythropoietin receptor gene expression by gamma-aminobutyric acid and piperine in kidney epithelial cells

AIMS

The aim of this study was to evaluate gamma-aminobutyric acid (GABA)- and piperine-induced erythropoietin (EPO) and EPO-receptor expression.

MATERIALS AND METHODS

The effect of GABA and piperine on cell viability was examined using kidney epithelial cells. Expression levels of EPO and EPO-R mRNA and protein were evaluated in response to GABA and piperine treatments. GABA- and piperine-mediated activation of the mitogen-activated protein kinase (MAPK) signaling pathway was investigated. Additionally, EPO function was evaluated using conditioned media containing EPO. The GABA receptor type involved in this process was identified.

KEY FINDINGS

Messenger RNA and protein expression levels of EPO and EPO-R significantly increased in response to treatment with GABA, piperine, or the combination of both, compared with control. GABA plus piperine synergistically enhanced EPO and EPO-R expression through p38 and c-Jun N-terminal kinase (JNK) MAPK signaling pathways, but not through the extracellular signal-regulated kinase (ERK) MAPK pathway. SB203580 and SP600125 (p38 and JNK pathway inhibitors, respectively) attenuated GABA plus piperine-induced EPO and EPO-R expression. Treatment of macrophages with EPO-containing conditioned media induced mRNA expression of interleukin (IL)-10 and nuclear factor (NF)-κB due to the interaction between EPO and EPO-R. Interestingly, GABA-induced EPO and EPO-R expression was mediated through GABA_A, not GABA_B, receptor activation.

SIGNIFICANCE

These findings demonstrate that GABA plus piperine-mediated p38 and JNK MAPK activation increases EPO and EPO-R expression, resulting in up-regulation of IL-10 and NF-κB.

P38α/JNK signaling restrains erythropoiesis by suppressing Ezh2-mediated epigenetic silencing of Bim

While erythropoietin (EPO) constitutes the major treatment for anemia, a range of anemic disorders remain resistant to EPO treatment. The need for alternative therapeutic strategies requires the identification of mechanisms that physiologically restrain erythropoiesis. Here we show that P38α restrains erythropoiesis in mouse and human erythroblasts independently of EPO by integrating apoptotic signals during recovery from anemia. P38α deficiency promotes JNK activation through increased expression of Map3k4 via a negative feedback mechanism. JNK prevents Cdk1-mediated phosphorylation and subsequent degradation by Smurf2 of the epigenetic silencer Ezh2. Stabilized Ezh2 silences Bim expression and protects erythroblasts from apoptosis. Thus, we identify P38α/JNK signaling as a molecular brake modulating erythropoiesis through epigenetic silencing of Bim. We propose that inhibition of P38α, by enhancing erythropoiesis in an EPO-independent fashion, may provide an alternative strategy for the treatment of anemia.

Erythropoietin (EPO) stimulates erythropoiesis and is commonly used to treat anemia. Here Hu et al. find that P38α/JNK signaling restrains erythropoiesis independently of EPO by regulating epigenetic silencing of the proapoptotic protein Bim, and thus identify putative targets for the treatment of anemic disorders resistant to EPO.

Stress-Activated Protein Kinases in Spinal Cord Injury: Focus on Roles of p38

Spinal cord injury (SCI) consists of three phases-acute, secondary, and chronic damages-and limiting the development of secondary damage possibly improves functional recovery after SCI. A major component of the secondary phase of SCI is regarded as inflammation-triggered events: induction of cytokines, edema, microglial activation, apoptosis of cells including oligodendrocytes and neurons, demyelination, formation of the astrocytic scar, and so on. Two major stress-activated protein kinases (SAPKs)-c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK)-are activated in various types of cells in response to cellular stresses such as apoptotic stimuli and inflammatory waves. In animal models of SCI, inhibition of either JNK or p38 has been shown to promote neuroprotection-associated functional recovery. Here, we provide an overview on the roles of SAPKs in SCI and, in particular, the pathological role of p38 will be discussed as a promising target for therapeutic intervention in SCI.

p38γ and p38δ Are Involved in T Lymphocyte Development

p38 mitogen-activated protein kinase (MAPK) signal transduction pathways are essential regulators of the immune response. Particularly, p38γ and p38δ regulate many immune cell functions such as cytokine production, migration, or T cell activation; however, their involvement in immune cell development is largely unknown. Here, we analysed the role of p38 MAPK isoforms p38γ and p38δ in T cell differentiation in the thymus and in lymph nodes, using mice deficient in p38γ, p38δ, or in both. We found that the T cell differentiation program in the thymus was affected at different stages in p38γ-, p38δ-, and p38γ/δ-deficient mice, and also peripheral T cell homaeostasis was compromised. Particularly, p38δ deletion affects different stages of early CD4⁻CD8⁻ double-negative thymocyte development, whereas lack of p38γ favours thymocyte positive selection from CD4⁺CD8⁺ double-positive to CD4⁺ or CD8⁺ single-positive cells. Our results identify unreported functions for p38γ and p38δ in T cells.

Stressed-Out HSCs Turn Up p38α and Purine to Proliferate

Changes in cellular metabolism drive hematopoietic stem cell (HSC) behavior during homeostasis, although whether they control HSC behavior during stress conditions is unclear. In this issue of Cell Stem Cell, Karigane et al. (2016) identify a p38α-dependent pathway that alters purine metabolism in HSCs during stress hematopoiesis, promoting hematopoietic recovery.

p38MAPK builds a hyaluronan cancer niche to drive lung tumorigenesis

Brichkina et al. show that lung cancer growth depends on short-distance cues produced by the cancer niche and identify fibroblast-specific hyaluronan synthesis at the center of p38-driven tumorigenesis. This in turn regulates early stromal fibroblast activation, the conversion to carcinoma-associated fibroblasts (CAFs), and cancer cell proliferation.

Expansion of neoplastic lesions generates the initial signal that instigates the creation of a tumor niche. Nontransformed cell types within the microenvironment continuously coevolve with tumor cells to promote tumorigenesis. Here, we identify p38MAPK as a key component of human lung cancer, and specifically stromal interactomes, which provides an early, protumorigenic signal in the tissue microenvironment. We found that lung cancer growth depends on short-distance cues produced by the cancer niche in a p38-dependent manner. We identified fibroblast-specific hyaluronan synthesis at the center of p38-driven tumorigenesis, which regulates early stromal fibroblast activation, the conversion to carcinoma-associated fibroblasts (CAFs), and cancer cell proliferation. Systemic down-regulation of p38MAPK signaling in a knock-in model with substitution of activating Tyr182 to phenylalanine or conditional ablation of p38 in fibroblasts has a significant tumor-suppressive effect on K-ras lung tumorigenesis. Furthermore, both Kras-driven mouse lung tumors and orthotopically grown primary human lung cancers show a significant sensitivity to both a chemical p38 inhibitor and an over-the-counter inhibitor of hyaluronan synthesis. We propose that p38MAPK–hyaluronan-dependent reprogramming of the tumor microenvironment plays a critical role in driving lung tumorigenesis, while blocking this process could have far-reaching therapeutic implications.

P38 MAPK Signaling Pathway Mediates Angiotensin II-Induced miR143/145 Gene Cluster Downregulation during Aortic Dissection Formation

BACKGROUND

We endeavored to prove that angiotensin II (Ang II) regulates both the expression of micro-RNA143/145 (miR143/145) and differentiation of vascular smooth muscle cells (VSMCs) during the formation of aortic dissection (AD). We also studied the contribution of p38 mitogen-activated protein kinase (MAPK) signaling pathway toward this process.

METHODS

Ascending aortic tissues were harvested from the patients with AD and organ donors. Tissues were immunostained with labeled antibodies targeting p38 MAPK, phospho-p38 MAPK, alpha-smooth muscle actin (α-SMA), and osteopontin (OPN). Next, we treated mouse aortic VSMCs with different regimens of Ang II (duration and dosages) in vitro and determined expression levels of miR143/145 and VSMC phenotype marker proteins (α-SMA and OPN) by quantitative polymerase chain reaction and/or western blotting. SB203580 was used to inhibit the p38 MAPK signaling pathway. Finally, the VSMC phenotype was validated by immunofluorescence microscopy.

RESULTS

Expression of phospho-p38 MAPK was significantly greater in the AD tissue. Ang II induced the phenotypic switching of VSMCs along with the downregulation of an miR143/145 gene cluster. Expression of OPN and phospho-p38 was significantly increased in VSMCs treated with 0.1 μM Ang II for 12 hr. Furthermore, the expression of miR143 and miR145 was downregulated by Ang II treatment. When the p38 MAPK signaling pathway was blocked by pretreatment with an SB203580 inhibitor, the expression of miR143, miR145, and VSMC phenotypic markers was not affected by Ang II. Immunohistochemical staining of aortic tissues donated by AD patients and healthy donors showed that the expression of α-SMA decreased in pathological tissue, while the OPN increased and the arrangement of the smooth muscle cells of the media was dysregulated, which we verified in vitro.

CONCLUSIONS

Ang II could regulate the expression of miR143/145 gene cluster and the phenotypic switching of VSMCs via the p38 MAPK signaling pathway. This may play an important role in the pathogenesis of AD.

MAP kinase p38 is a novel target of CacyBP/SIP phosphatase

Mitogen-activated protein (MAP) kinases are important players in cellular signaling pathways. Recently, it has been shown that CacyBP/SIP serves as a phosphatase for one of the MAP kinases, ERK1/2. Through dephosphorylation of this kinase CacyBP/SIP modulates the transcriptional activity of Elk-1 and the activity of the CREB-BDNF pathway. In this work, using NB2a cell lysate and recombinant proteins, we show that CacyBP/SIP binds and dephosphorylates another member of the MAP kinase family, p38. Analysis of recombinant full-length CacyBP/SIP and its three major domains, N-terminal, middle CS and C-terminal SGS, indicates that the middle CS domain is responsible for p38 dephosphorylation. Moreover, we show that CacyBP/SIP might be implicated in response to oxidative stress. Dephosphorylation of phospho-p38 by CacyBP/SIP in NB2a cells treated with hydrogen peroxide is much more effective than in control ones. In conclusion, involvement of CacyBP/SIP in the regulation of p38 kinase activity, in addition to that of ERK1/2, might point to the function of CacyBP/SIP in pro-survival and pro-apoptotic pathways.

Genetic and Pharmacological Inhibition of p38α Improves Locomotor Recovery after Spinal Cord Injury

One of the mitogen-activated protein kinases, p38α plays a crucial role in various inflammatory diseases and apoptosis of various types of cells. In this study, we investigated the pathophysiological roles of p38α in spinal cord injury (SCI), using a mouse model. Lateral hemisection at T9 of the SC was performed in wild type (WT) and p38α^+/- mice (p38α^-/- showed embryonic lethality). p38α^+/- mice showed a better functional recovery from SCI-associated paralyzed hindlimbs compared to WT mice at 7 days post-injury (dpi), which remained until 28 dpi (an end time point of monitoring the behavior). In histopathological analysis at 28 dpi, there was more axonal regeneration with remyelination on the caudal side of the lesion epicenter in p38α^+/- mice than in WT mice. At 7 dpi, infiltration of inflammatory cells into the lesion and expression of cytokines in the lesion were reduced in p38α^+/- mice compared with WT mice. At the same time point, the number of apoptotic oligodendrocytes in the white matter at the caudal boarder of the lesion of p38α^+/- mice was lower than that of WT mice. At 14 dpi, more neural and oligodendrocyte precursor cells in the gray matter and white matter, respectively, were observed around the lesion epicenter of p38α^+/- mice compared with the case of WT mice. At the same time point, astrocytic scar formation was less apparent in p38α^+/- than in WT mice, while compaction of inflammatory immune cells associated with the wound contraction was more apparent in p38α^+/- than in WT mice. Furthermore, we verified the effectiveness of oral administration of SB239063, a p38α inhibitor on the hindlimb locomotor recovery after SCI. These results suggest that p38α deeply contributes to the pathogenesis of SCI and that inhibition of p38α is a beneficial strategy to recovery from SCI.

Protein abundance of AKT and ERK pathway components governs cell type-specific regulation of proliferation

Signaling through the AKT and ERK pathways controls cell proliferation. However, the integrated regulation of this multistep process, involving signal processing, cell growth and cell cycle progression, is poorly understood. Here, we study different hematopoietic cell types, in which AKT and ERK signaling is triggered by erythropoietin (Epo). Although these cell types share the molecular network topology for pro‐proliferative Epo signaling, they exhibit distinct proliferative responses. Iterating quantitative experiments and mathematical modeling, we identify two molecular sources for cell type‐specific proliferation. First, cell type‐specific protein abundance patterns cause differential signal flow along the AKT and ERK pathways. Second, downstream regulators of both pathways have differential effects on proliferation, suggesting that protein synthesis is rate‐limiting for faster cycling cells while slower cell cycles are controlled at the G1‐S progression. The integrated mathematical model of Epo‐driven proliferation explains cell type‐specific effects of targeted AKT and ERK inhibitors and faithfully predicts, based on the protein abundance, anti‐proliferative effects of inhibitors in primary human erythroid progenitor cells. Our findings suggest that the effectiveness of targeted cancer therapy might become predictable from protein abundance.

Pivotal Role of Mitogen-Activated Protein Kinase-Activated Protein Kinase 2 in Inflammatory Pulmonary Diseases

Mitogen-activated protein kinase (MAPK)-activated protein kinase (MK2) is exclusively regulated by p38 MAPK in vivo. Upon activation of p38 MAPK, MK2 binds with p38 MAPK, leading to phosphorylation of TTP, Hsp27, Akt, and Cdc25 that are involved in regulation of various essential cellular functions. In this review, we discuss current knowledge about molecular mechanisms of MK2 in regulation of TNF-α production, NADPH oxidase activation, neutrophil migration, and DNA-damage-induced cell cycle arrest which are involved in the molecular pathogenesis of acute lung injury, pulmonary fibrosis, and non-small-cell lung cancer. Collectively current and emerging new information indicate that developing MK2 inhibitors and blocking MK2-mediated signal pathways are potential therapeutic strategies for treatment of inflammatory and fibrotic lung diseases and lung cancer.

Pterostilbene protects against myocardial ischemia/reperfusion injury via suppressing oxidative/nitrative stress and inflammatory response

Recent studies have shown that pterostilbene (Pte) confers protection against myocardial ischemia/reperfusion injury. The oxidative/nitrative stress and inflammation induce injury after myocardial ischemia/reperfusion. The present study was designed to evaluate whether treatment with Pte attenuates oxidative/nitrative stress and inflammation in myocardial ischemia/reperfusion (MI/R). Rats were subjected to 30min of myocardial ischemia and 3h of reperfusion, and the rats were administered with vehicle or Pte. The results showed that Pte (10mg/kg) dramatically improved cardiac function and reduced myocardial infarction and myocardial apoptosis following MI/R. As an indicator of oxidative/nitrative stress, myocardial ONOO^- content was markedly reduced after Pte treatment. And, Pte led to a dramatic decrease in superoxide generation and malondialdehyde (MDA) content and a dramatic increase in superoxide dismutase (SOD) activity. In addition, Pte treatment significantly reduced p38 MAPK activation and the expression of iNOS and gp91^phox and increased phosphorylated eNOS expression. Pte treatment dramatically decreased myocardial TNF-α, and IL-1β levels and myeloperoxidase (MPO) activity. Furthermore, ONOO^- suppression by either Pte or uric acid (UA), an ONOO^- scavenger, reduced myocardial injury. In conclusion, Pte exerts a protective effect against MI/R injury by suppressing oxidative/nitrative stress. These results provide evidence that Pte might be a therapeutic approach for the treatment of MI/R injury.

Intracellular Staphylococcus aureus eludes selective autophagy by activating a host cell kinase

Autophagy, a catabolic pathway of lysosomal degradation, acts not only as an efficient recycle and survival mechanism during cellular stress, but also as an anti-infective machinery. The human pathogen Staphylococcus aureus (S. aureus) was originally considered solely as an extracellular bacterium, but is now recognized additionally to invade host cells, which might be crucial for persistence. However, the intracellular fate of S. aureus is incompletely understood. Here, we show for the first time induction of selective autophagy by S. aureus infection, its escape from autophagosomes and proliferation in the cytoplasm using live cell imaging. After invasion, S. aureus becomes ubiquitinated and recognized by receptor proteins such as SQSTM1/p62 leading to phagophore recruitment. Yet, S. aureus evades phagophores and prevents further degradation by a MAPK14/p38α MAP kinase-mediated blockade of autophagy. Our study demonstrates a novel bacterial strategy to block autophagy and secure survival inside the host cell.

ASK1: a new therapeutic target for kidney disease

Stress-induced activation of p38 MAPK and JNK signaling is a feature of both acute and chronic kidney disease and is associated with disease progression. Inhibitors of p38 MAPK or JNK activation provide protection against inflammation and fibrosis in animal models of kidney disease; however, clinical trials of p38 MAPK and JNK inhibitors in other diseases (rheumatoid arthritis and pulmonary fibrosis) have been disappointing. Apoptosis signal-regulating kinase 1 (ASK1) acts as an upstream regulator for the activation of p38 MAPK and JNK in kidney disease. Mice lacking the Ask1 gene are healthy with normal homeostatic functions and are protected from acute kidney injury induced by ischemia-reperfusion and from renal interstitial fibrosis induced by ureteric obstruction. Recent studies have shown that a selective ASK1 inhibitor substantially reduced renal p38 MAPK activation and halted the progression of nephropathy in diabetic mice, and this has led to a current clinical trial of an ASK1 inhibitor in patients with stage 3 or 4 diabetic kidney disease. This review explores the rationale for targeting ASK1 in kidney disease and the therapeutic potential of ASK1 inhibitors based on current experimental evidence.

Attenuation of p38α MAPK stress response signaling delays the in vivo aging of skeletal muscle myofibers and progenitor cells

Functional competence and self-renewal of mammalian skeletal muscle myofibers and progenitor cells declines with age. Progression of the muscle aging phenotype involves the decline of juvenile protective factors i.e., proteins whose beneficial functions translate directly to the quality of life, and self-renewal of progenitor cells. These characteristics occur simultaneously with the age-associated increase of p38α stress response signaling. This suggests that the maintenance of low levels of p38α activity of juvenile tissues may delay or attenuate aging. We used the dominant negative haploinsufficient p38α mouse (DN-p38α^AF/+) to demonstrate that in vivo attenuation of p38α activity in the gastrocnemius of the aged mutant delays age-associated processes that include: a) the decline of the juvenile protective factors, BubR1, aldehyde dehydrogenase 1A (ALDH1A1), and aldehyde dehydrogenase 2 (ALDH2); b) attenuated expression of p16^Ink4a and p19^Arf tumor suppressor genes of the Cdkn2a locus; c) decreased levels of hydroxynonenal protein adducts, expression of COX2 and iNOS; d) decline of the senescent progenitor cell pool level and d) the loss of gastrocnemius muscle mass. We propose that elevated P-p38α activity promotes skeletal muscle aging and that the homeostasis of p38α impacts the maintenance of a beneficial healthspan.

First comprehensive structural and biophysical analysis of MAPK13 inhibitors targeting DFG-in and DFG-out binding modes

BACKGROUND

P38 MAP kinases are centrally involved in mediating extracellular signaling in various diseases. While much attention has previously been focused on the ubiquitously expressed family member MAPK14 (p38α), recent studies indicate that family members such as MAPK13 (p38δ) display a more selective cellular and tissue expression and might therefore represent a specific kinase to target in certain diseases.

METHODS

To facilitate the design of potent and specific inhibitors, we present here the structural, biophysical, and functional characterization of two new MAPK13-inhibitor complexes, as well as the first comprehensive structural, biophysical, and functional analysis of MAPK13 complexes with four different inhibitor compounds of greatly varying potency.

RESULTS

These inhibitors display IC50 values either in the nanomolar range or micromolar range (>800-fold range). The nanomolar inhibitors exhibit much longer ligand-enzyme complex half-lives compared to the micromolar inhibitors as measured by biolayer interferometry. Crystal structures of the MAPK13 inhibitor complexes reveal that the nanomolar inhibitors engage MAPK13 in the DFG-out binding mode, while the micromolar inhibitors are in the DFG-in mode. Detailed structural and computational docking analyses suggest that this difference in binding mode engagement is driven by conformational restraints imposed by the chemical structure of the inhibitors, and may be fortified by an additional hydrogen bond to MAPK13 in the nanomolar inhibitors.

CONCLUSIONS

These studies provide a structural basis for understanding the differences in potency exhibited by these inhibitors.

GENERAL SIGNIFICANCE

They also provide the groundwork for future studies to improve specificity, potency, pharmacodynamics, and pharmacokinetic properties.

Redundancy in the World of MAP Kinases: All for One

The protein kinases ERK1 and ERK2 are the effector components of the prototypical ERK1/2 mitogen-activated protein (MAP) kinase pathway. This signaling pathway regulates cell proliferation, differentiation and survival, and is essential for embryonic development and cellular homeostasis. ERK1 and ERK2 homologs share similar biochemical properties but whether they exert specific physiological functions or act redundantly has been a matter of controversy. However, recent studies now provide compelling evidence in support of functionally redundant roles of ERK1 and ERK2 in embryonic development and physiology. In this review, we present a critical assessment of the evidence for the functional specificity or redundancy of MAP kinase isoforms. We focus on the ERK1/ERK2 pathway but also discuss the case of JNK and p38 isoforms.

p38α Activates Purine Metabolism to Initiate Hematopoietic Stem/Progenitor Cell Cycling in Response to Stress

Hematopoietic stem cells (HSCs) maintain quiescence by activating specific metabolic pathways, including glycolysis. We do not yet have a clear understanding of how this metabolic activity changes during stress hematopoiesis, such as bone marrow transplantation. Here, we report a critical role for the p38MAPK family isoform p38α in initiating hematopoietic stem and progenitor cell (HSPC) proliferation during stress hematopoiesis in mice. We found that p38MAPK is immediately phosphorylated in HSPCs after a hematological stress, preceding increased HSPC cycling. Conditional deletion of p38α led to defective recovery from hematological stress and a delay in initiation of HSPC proliferation. Mechanistically, p38α signaling increases expression of inosine-5'-monophosphate dehydrogenase 2 in HSPCs, leading to altered levels of amino acids and purine-related metabolites and changes in cell-cycle progression in vitro and in vivo. Our studies have therefore uncovered a p38α-mediated pathway that alters HSPC metabolism to respond to stress and promote recovery.

p38γ and p38δ reprogram liver metabolism by modulating neutrophil infiltration

Non-alcoholic fatty liver disease (NAFLD) is a major health problem and the main cause of liver disease in Western countries. Although NAFLD is strongly associated with obesity and insulin resistance, its pathogenesis remains poorly understood. The disease begins with an excessive accumulation of triglycerides in the liver, which stimulates an inflammatory response. Alternative p38 mitogen-activated kinases (p38γ and p38δ) have been shown to contribute to inflammation in different diseases. Here we demonstrate that p38δ is elevated in livers of obese patients with NAFLD and that mice lacking p38γ/δ in myeloid cells are resistant to diet-induced fatty liver, hepatic triglyceride accumulation and glucose intolerance. This protective effect is due to defective migration of p38γ/δ-deficient neutrophils to the damaged liver. We further show that neutrophil infiltration in wild-type mice contributes to steatosis development by means of inflammation and liver metabolic changes. Therefore, p38γ and p38δ in myeloid cells provide a potential target for NAFLD therapy.

p38 MAP kinases in the heart

p38 kinases are members of the mitogen-activated protein kinases (MAPK) with established contribution to a wide range of signaling pathways and different biological processes. The prototypic p38 MAPK, p38α was originally identified as an essential signaling kinase for inflammatory cytokine production Extensive studies have now revealed that p38s have critical roles in many different tissues far beyond immune regulation and inflammatory responses. In this review, we will focus on the structure and molecular biology of p38s, and their specific roles in heart, especially regarding myocyte proliferation, apoptosis, and hypertrophic responses.

p38γ MAPK is required for inflammation-associated colon tumorigenesis

Chronic inflammation has long been considered to causatively link to colon cancer development. However, signal transduction pathways involved remain largely unidentified. Here, we report that p38γ mitogen-activated protein kinase mediates inflammatory signaling to promote colon tumorigenesis. Inflammation activates p38γ in mouse colon tissues and intestinal epithelial cell-specific p38γ knockout (KO) attenuates colitis and inhibits pro-inflammatory cytokine expression. Significantly, p38γ KO inhibits tumorigenesis in a colitis-associated mouse model. The specific p38γ pharmacological inhibitor pirfenidone also suppresses pro-inflammatory cytokine expression and colon tumorigenesis. The tumor-promoting activity of epithelial p38γ was further demonstrated by xenograft studies. In addition, p38γ is required for β-catenin/Wnt activities and p38γ stimulates Wnt transcription by phosphorylating β-catenin at Ser605. These results show that p38γ activation links inflammation and colon tumorigenesis. Targeting p38γ may be a novel strategy for colon cancer prevention and treatment.

p38α controls self-renewal and fate decision of neurosphere-forming cells in adult hippocampus

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Neural stem cells (NSC) from the adult hippocampus easily lose their activity in vitro.

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Inhibition of p38α enables successful long-term culture of adult hippocampus NSC.

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Inhibition of p38α can maintain a high neurogenic capacity for NSC.

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Neurogenic competence-related microRNAs are upregulated in NSC by p38α inhibition.

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In vitro expanded NSC by p38α inhibition are beneficial against brain damage.

Neural stem cells (NSC) from the adult hippocampus easily lose their activity in vitro. Efficient in vitro expansion of adult hippocampus-derived NSC is important for generation of tools for research and cell therapy. Here, we show that a single copy disruption or pharmacological inhibition of p38α enables successful long-term neurosphere culture of adult mouse hippocampal cells. Expanded neurospheres with high proliferative activity differentiated into the three neuronal lineages under differentiating conditions. Thus, inhibition of p38α can maintain adult hippocampal NSC activity in vitro.

Identification of signalling cascades involved in red blood cell shrinkage and vesiculation

Even though red blood cell (RBC) vesiculation is a well-documented phenomenon, notably in the context of RBC aging and blood transfusion, the exact signalling pathways and kinases involved in this process remain largely unknown. We have established a screening method for RBC vesicle shedding using the Ca²⁺ ionophore ionomycin which is a rapid and efficient method to promote vesiculation. In order to identify novel pathways stimulating vesiculation in RBC, we screened two libraries: the Library of Pharmacologically Active Compounds (LOPAC) and the Selleckchem Kinase Inhibitor Library for their effects on RBC from healthy donors. We investigated compounds triggering vesiculation and compounds inhibiting vesiculation induced by ionomycin. We identified 12 LOPAC compounds, nine kinase inhibitors and one kinase activator which induced RBC shrinkage and vesiculation. Thus, we discovered several novel pathways involved in vesiculation including G protein-coupled receptor (GPCR) signalling, the phosphoinositide 3-kinase (PI3K)–Akt (protein kinase B) pathway, the Jak–STAT (Janus kinase–signal transducer and activator of transcription) pathway and the Raf–MEK (mitogen-activated protein kinase kinase)–ERK (extracellular signal-regulated kinase) pathway. Moreover, we demonstrated a link between casein kinase 2 (CK2) and RBC shrinkage via regulation of the Gardos channel activity. In addition, our data showed that inhibition of several kinases with unknown functions in mature RBC, including Alk (anaplastic lymphoma kinase) kinase and vascular endothelial growth factor receptor 2 (VEGFR-2), induced RBC shrinkage and vesiculation.

After screening two libraries of small bioactive molecules and kinase inhibitors, we identified several signalling pathways to be involved in red blood cell (RBC) shrinkage and vesiculation. These include the Jak (Janus kinase)–STAT (signal transducer and activator of transcription) pathway, phosphoinositide 3-kinase (PI3K)–Akt pathway, the Raf–MEK (mitogen-activated protein kinase kinase)–ERK (extracellular signal-regulated kinase) pathway and GPCR (G protein-coupled receptor) signalling.

MAPK phosphatase 7 regulates T cell differentiation via inhibiting ERK-mediated IL-2 expression

Members of the MAPK phosphatase (MKP) protein family play critical roles in immune responses through differential regulation of MAPK activation. In this study, we show that MKP7, also known as dual-specificity phosphatase 16, was required for CD4(+) T cell responses in vivo. Mkp7(-/-) CD4(+) T cells exhibited enhanced ERK and JNK activation, and produced increased amount of IL-2 compared with Mkp7(+/+) cells upon activation. Mkp7(-/-) CD4(+) T cells were selectively defective in Th17 differentiation in vitro, which was rescued by blocking IL-2 or inhibition of ERK activation. Furthermore, mice carrying Mkp7(-/-) T cells were deficient in generation of Th17 and T follicular helper cells in vivo, and were resistant to autoimmune experimental encephalomyelitis. Our results thus demonstrate an essential role of MKP7 in effector T cell function.