p38γ MAPK Is Essential for Aerobic Glycolysis and Pancreatic Tumorigenesis.

KRAS is mutated in most pancreatic ductal adenocarcinomas (PDAC) and yet remains undruggable. Here, we report that p38γ MAPK, which promotes PDAC tumorigenesis by linking KRAS signaling and aerobic glycolysis (also called the Warburg effect), is a novel therapeutic target. p38γ interacted with a glycolytic activator PFKFB3 that was dependent on mutated KRAS. KRAS transformation and overexpression of p38γ increased expression of PFKFB3 and glucose transporter GLUT2, conversely, silencing mutant KRAS, and p38γ decreased PFKFB3 and GLUT2 expression. p38γ phosphorylated PFKFB3 at S467, stabilized PFKFB3, and promoted their interaction with GLUT2. Pancreatic knockout of p38γ decreased p-PFKFB3/PFKFB3/GLUT2 protein levels, reduced aerobic glycolysis, and inhibited PDAC tumorigenesis in KPC mice. PFKFB3 and GLUT2 depended on p38γ to stimulate glycolysis and PDAC growth and p38γ required PFKFB3/S467 to promote these activities. A p38γ inhibitor cooperated with a PFKFB3 inhibitor to blunt aerobic glycolysis and PDAC growth, which was dependent on p38γ. Moreover, overexpression of p38γ, p-PFKFB3, PFKFB3, and GLUT2 in PDAC predicted poor clinical prognosis. These results indicate that p38γ links KRAS oncogene signaling and aerobic glycolysis to promote pancreatic tumorigenesis through PFKFB3 and GLUT2, and that p38γ and PFKFB3 may be targeted for therapeutic intervention in PDAC. SIGNIFICANCE: These findings show that p38γ links KRAS oncogene signaling and the Warburg effect through PFKBF3 and Glut2 to promote pancreatic tumorigenesis, which can be disrupted via inhibition of p38γ and PFKFB3.

Phenotype-Based Screens with Conformation-Specific Inhibitors Reveal p38 Gamma and Delta as Targets for HCC Polypharmacology.

The approved kinase inhibitors for hepatocellular carcinoma (HCC) are not matched to specific mutations within tumors. This has presented a daunting challenge; without a clear target or mechanism, no straightforward path has existed to guide the development of improved therapies for HCC. Here, we combine phenotypic screens with a class of conformation-specific kinase inhibitors termed type II to identify a multikinase inhibitor, AD80, with antitumoral activity across a variety of HCC preclinical models, including mouse xenografts. Mass spectrometry profiling found a number of kinases as putative targets for AD80, including several receptor and cytoplasmic protein kinases. Among these, we found p38 gamma and delta as direct targets of AD80. Notably, a closely related analog of AD80 lacking p38δ/γ activity, but retaining several other off-target kinases, lost significant activity in several HCC models. Moreover, forced and sustained MKK6 → p38→ATF2 signaling led to a significant reduction of AD80 activity within HCC cell lines. Together with HCC survival data in The Cancer Genome Atlas and RNA-seq analysis, we suggest p38 delta and gamma as therapeutic targets in HCC and an "AD80 inhibition signature" as identifying those patients with best clinical outcomes.

p38γ is essential for cell cycle progression and liver tumorigenesis.

The cell cycle is a tightly regulated process that is controlled by the conserved cyclin-dependent kinase (CDK)-cyclin protein complex1. However, control of the G0-to-G1 transition is not completely understood. Here we demonstrate that p38 MAPK gamma (p38γ) acts as a CDK-like kinase and thus cooperates with CDKs, regulating entry into the cell cycle. p38γ shares high sequence homology, inhibition sensitivity and substrate specificity with CDK family members. In mouse hepatocytes, p38γ induces proliferation after partial hepatectomy by promoting the phosphorylation of retinoblastoma tumour suppressor protein at known CDK target residues. Lack of p38γ or treatment with the p38γ inhibitor pirfenidone protects against the chemically induced formation of liver tumours. Furthermore, biopsies of human hepatocellular carcinoma show high expression of p38γ, suggesting that p38γ could be a therapeutic target in the treatment of this disease.

Multi-Kinase Inhibitor with Anti-p38γ Activity in Cutaneous T-Cell Lymphoma.

Current cutaneous T-cell lymphoma (CTCL) therapies are marked by an abbreviated response, subsequent drug resistance, and poor prognosis for patients with advanced disease. An understanding of molecular regulators involved in CTCL is needed to develop effective targeted therapies. One candidate regulator is p38γ, a mitogen-activated protein kinase crucial for malignant T-cell activity and growth. p38γ gene expression is selectively increased in CTCL patient samples and cell lines but not in healthy T cells. In addition, gene silencing of p38γ reduced CTCL cell viability, showing a key role in CTCL pathogenesis. Screening p38γ inhibitors is critical for understanding the mechanism of CTCL tumorigenesis and developing therapeutic applications. We prioritized a potent p38γ inhibitor (F7, also known as PIK75) through a high-throughput kinase inhibitor screen. At nanomolar concentrations, PIK75, a multiple kinase inhibitor, selectively killed CD4+ malignant CTCL cells but spared healthy CD4+ cells; induced significant reduction of tumor size in mouse xenografts; and effectively inhibited p38γ enzymatic activity and phosphorylation of its substrate, DLGH1, in CTCL cells and mouse xenografts. Here, we report that PIK75 has a potential clinical application to serve as a scaffold molecule for the development of a more selective p38γ inhibitor.

p38 MAPK regulates the Wnt inhibitor Dickkopf-1 in osteotropic prostate cancer cells.

The Wnt inhibitor Dickkopf-1 (DKK-1) has been associated with the occurrence of bone metastases in osteotropic prostate cancer by inhibiting osteoblastogenesis. P38 mitogen-activated protein kinase (MAPK) activity is also dysregulated in advanced prostate cancer. However, the impact of p38 MAPK signaling on DKK-1 remains unknown. Inhibition of p38 MAPK signaling in osteolytic PC3 cells by small molecule inhibitors (doramapimod, LY2228820 and SB202190) suppressed DKK-1 expression, whereas activation of p38 MAPK by anisomycin increased DKK-1. Further dissection by targeting individual p38 MAPK isoforms with siRNA revealed a stronger role for MAPK11 than MAPK14 and MAPK12 in the regulation of DKK-1. Moreover, prostate cancer cells with a predominantly osteolytic phenotype produced sufficient amounts of DKK-1 to inhibit Wnt3a-induced osteoblastic differentiation in C2C12 cells. This inhibition was blocked directly by neutralizing DKK-1 using a specific antibody and also indirectly by blocking p38 MAPK. Furthermore, tissue expression in human prostate cancer revealed a correlation between p38 MAPK and DKK-1 expression with higher expression in tumor compared with normal tissues. These results reveal that p38 MAPK regulates DKK-1 in prostate cancer and may present a potential target in osteolytic prostate cancers.

p38γ MAPK Is a Therapeutic Target for Triple-Negative Breast Cancer by Stimulation of Cancer Stem-Like Cell Expansion.

Triple-negative breast cancer (TNBC) is highly progressive and lacks established therapeutic targets. p38γ mitogen-activated protein kinase (MAPK) (gene name: MAPK12) is overexpressed in TNBC but how overexpressed p38γ contributes to TNBC remains unknown. Here, we show that p38γ activation promotes TNBC development and progression by stimulating cancer stem-like cell (CSC) expansion and may serve as a novel therapeutic target. p38γ silencing in TNBC cells reduces mammosphere formation and decreases expression levels of CSC drivers including Nanog, Oct3/4, and Sox2. Moreover, p38γ MAPK-forced expression alone is sufficient to stimulate CSC expansion and to induce epithelial cell transformation in vitro and in vivo. Furthermore, p38γ depends on its activity to stimulate CSC expansion and breast cancer progression, indicating a therapeutic opportunity by application of its pharmacological inhibitor. Indeed, the non-toxic p38γ specific pharmacological inhibitor pirfenidone selectively inhibits TNBC growth in vitro and/or in vivo and significantly decreases the CSC population. Mechanistically, p38γ stimulates Nanog transcription through c-Jun/AP-1 via a multi-protein complex formation. These results together demonstrate that p38γ can drive TNBC development and progression and may be a novel therapeutic target for TNBC by stimulating CSC expansion. Inhibiting p38γ activity with pirfenidone may be a novel strategy for the treatment of TNBC.

Protective effects of extendin­4 on hypoxia/reoxygenation­induced injury in H9c2 cells.

Glucagon-like peptide-1 (GLP-1) analogues are likely to exert cardioprotective effects via balancing the energy metabolism in cardiomyocytes following ischemic or hypoxic insults. The present study aimed to explore the protective effects and mechanism of exendin-4, a GLP-1 analogue, on cardiomyocyte glucose uptake using an in vitro model of hypoxia/reoxygenation (H/R) of H9c2 cardiomyocyte cells. Pre-treatment with exendin-4 (200 nM) prior to H/R increased the cell viability, decreased cell apoptosis, enhanced cardiomyocyte glucose uptake and increased the production of adenosine triphosphate. Exendin-4 also decreased the levels of lactate dehydrogenase and creatine kinase-MB in the culture medium. Furthermore, the activity of carnitine palmitoyltransferase-1 in the H9c2 cells was decreased, while the activity of phosphofructokinase-1 was increased following exendin-4 treatment. Moreover, pre-treatment with exendin-4 increased the expression of p38 mitogen-activated protein kinase (p38MAPK) γ and translocation of glucose transporter-1 in H9c2 cells subjected to H/R. However, these effects were attenuated by the p38MAPK inhibitors BIRB796 and SB203580. The results suggested that exendin-4 exerted significant cardioprotective effects against H/R-induced cell injury and restored the metabolic imbalance of cardiomyocytes by activating the p38MAPK signaling pathway in the H9c2 cell model. Importantly, p38MAPKγ, one subunit of p38MAPK, may have the most important function in this process. The results of the present study may be helpful in the development of novel drugs to treat patients with coronary heart disease.

Loss-of-function RNAi screens in breast cancer cells identify AURKB, PLK1, PIK3R1, MAPK12, PRKD2, and PTK6 as sensitizing targets of rapamycin activity.

The use of molecularly targeted drugs as single agents has shown limited utility in many tumor types, largely due to the complex and redundant nature of oncogenic signaling networks. Targeting of the PI3K/AKT/mTOR pathway through inhibition of mTOR in combination with aromatase inhibitors has seen success in particular sub-types of breast cancer and there is a need to identify additional synergistic combinations to maximize the clinical potential of mTOR inhibitors. We have used loss-of-function RNAi screens of the mTOR inhibitor rapamycin to identify sensitizers of mTOR inhibition. RNAi screens conducted in combination with rapamycin in multiple breast cancer cell lines identified six genes, AURKB, PLK1, PIK3R1, MAPK12, PRKD2, and PTK6 that when silenced, each enhanced the sensitivity of multiple breast cancer lines to rapamycin. Using selective pharmacological agents we confirmed that inhibition of AURKB or PLK1 synergizes with rapamycin. Compound-associated gene expression data suggested histone deacetylation (HDAC) inhibition as a strategy for reducing the expression of several of the rapamycin-sensitizing genes, and we tested and validated this using the HDAC inhibitor entinostat in vitro and in vivo. Our findings indicate new approaches for enhancing the efficacy of rapamycin including the use of combining its application with HDAC inhibition.

Phosphorylation and stabilization of topoisomerase IIα protein by p38γ mitogen-activated protein kinase sensitize breast cancer cells to its poisons.

Cancer drugs suppress tumor cell growth by inhibiting specific cellular targets. However, most drugs also activate several cellular nonspecific stress pathways, and the implications of these off-target effects are mostly unknown. Here, we report that p38γ, but not p38α, MAPK is specifically activated by treatment of breast cancer cells with topoisomerase II (Topo II) drugs, whereas paclitaxel (Taxol) does not have this effect. The activated p38γ in turn phosphorylates and stabilizes Topo IIα protein, and this enhances the growth inhibition by Topo II drugs. Moreover, p38γ activity was shown to be necessary and sufficient for Topo IIα expression, the drug-p38γ-Topo IIα axis is only detected in intrinsically sensitive but not resistant cells, and p38γ is co-overexpressed with Topo IIα protein in primary breast cancers. These results reveal a new paradigm in which p38γ actively regulates the drug-Topo IIα signal transduction, and this may be exploited to increase the therapeutic activity of Topo II drugs.

How can 1 + 1 = 3? ß2-adrenergic and glucocorticoid receptor agonist synergism in obstructive airway diseases.

For a long time it was believed that ß(2)-adrenergic receptor agonists used in the treatment of obstructive airway diseases worked primarily on airway smooth muscle cells, causing relaxation, whereas glucocorticoids primarily improved airway function via their anti-inflammatory action, indicating that their clinical synergism occurred at the organism rather than the cellular level. However, it is now becoming clear that both drug classes can affect airway function at multiple levels, including an integrated effect on several cell types. This article summarizes data on the molecular interaction between the two receptor systems, particularly with relevance to phenomena of ß(2)-adrenergic receptor desensitization and glucocorticoid insensitivity in the airways. These molecular interactions may contribute to the observed clinical synergism between both drug classes in the treatment of obstructive airway diseases.

p38 mitogen-activated protein kinase-γ inhibition by long-acting ß2 adrenergic agonists reversed steroid insensitivity in severe asthma.

Corticosteroid insensitivity (CI) is a major barrier to treating severe asthma. Despite intensive research, the molecular mechanism of CI remains uncertain. The aim of this study was to determine abnormality in corticosteroid action in severe asthma and to identify the molecular mechanism of the long-acting ß(2)-adrenergic agonists (LABAs) formoterol and salmeterol on restoration of corticosteroid sensitivity in severe asthma in vitro. Peripheral blood mononuclear cells (PBMCs) were obtained from 16 subjects with severe corticosteroid-insensitive asthma, 6 subjects with mild corticosteroid-sensitive asthma, and 11 healthy volunteers. Corticosteroid (dexamethasone) sensitivity was determined on tumor necrosis factor-α (TNF-α)-induced interleukin (IL)-8 production. Glucocorticoid receptor (GR) phosphorylation and kinase phosphorylation were evaluated by immunoprecipitation-Western blotting analysis and kinase phosphorylation array in IL-2/IL-4-treated corticosteroid insensitive model in PBMCs. In vitro corticosteroid sensitivity on TNF-α-induced IL-8 production was significantly lower in patients with severe asthma than in healthy volunteers and patients with mild asthma. This CI seen in severe asthma was associated with reduced GR nuclear translocation and with hyperphosphorylation of GR, which were reversed by LABAs. In IL-2/IL-4-treated PBMCs, LABAs inhibited phosphorylation of Jun-NH(2)-terminal kinase and p38 mitogen-activated protein kinase-γ (p38MAPK-γ) as well as GR. In addition, cells with p38MAPK-γ knockdown by RNA interference did not develop CI in the presence of IL-2/IL-4. Furthermore, p38MAPK-γ protein expression was up-regulated in PBMCs from some patients with severe asthma. In conclusion, p38 MAPK-γ activation impairs corticosteroid action and p38 MAPK-γ inhibition by LABAs has potential for the treatment of severe asthma.

Isoforms of p38MAPK gamma and delta contribute to differentiation of human AML cells induced by 1,25-dihydroxyvitamin D3.

Inhibition of p38MAPK alpha/beta is known to enhance 1,25-dihydroxyvitamin (1,25D)-induced monocytic differentiation, but the detailed mechanism of this effect was not clear. We now show that the enhancement of differentiation becomes apparent with slow kinetics (12-24 h). Interestingly, the inhibition of p38MAPK alpha/beta by their selective inhibitor SB202190 (SB) leads to an upregulated expression of p38MAPK isoforms gamma and delta in 1,25D-treated AML cells, in cell lines and in primary culture. Although the expression and activating phosphorylations of p38MAPK alpha are also increased by an exposure of the cells to SB, its kinase activity is blocked by SB, as shown by reduced levels of phosphorylated Hsp27, a downstream target of p38MAPK alpha. A positive role of p38MAPKs in 1,25D-induced differentiation is shown by the inhibition of differentiation by antisense oligonucleotides to all p38MAPK isoforms. Other principal branches of MAPK pathways showed early (6 h) activation of MEK/ERK by SB, followed by activation of JNK1/2 pathway and enhanced expression and/or activation of PU.1, ATF-2 differentiation-related transcription factors. Taken together with previous reports, the results indicate that 1,25D-induced differentiation is enhanced by the activation of at least three branches of MAPK pathways (ERK1/2; p38MAPK gamma/delta; JNK1/2). This activation may result from the removal of feedback inhibition of an upstream regulator of those pathways, when p38MAPK alpha and beta are inhibited by SB.

Involvement of the p38 mitogen-activated protein kinase alpha, beta, and gamma isoforms in myogenic differentiation.

We and others previously showed that p38 mitogen-activated protein kinase is indispensable for myogenic differentiation. However, it is less clear which of the four p38 isoforms in the mouse genome participates in this process. Using C2C12 myogenic cells as a model, we showed here that p38alpha, beta, and gamma are expressed with distinct expression patterns during differentiation. Knockdown of any of them by small interfering RNA inhibits myogenic differentiation, which suggests that the functions of the three p38 isoforms are not completely redundant. To further elucidate the unique role of each p38 isoform in myogenic differentiation, we individually knocked down one p38 isoform at a time in C2C12 cells, and we compared the whole-genome gene expression profiles by microarrays. We found that some genes are coregulated by all three p38 isoforms, whereas others are uniquely regulated by one particular p38 isoform. Furthermore, several novel p38 target genes (i.e., E2F2, cyclin D3, and WISP1) are found to be required for myogenin expression, which provides a molecular basis to explain why different p38 isoforms are required for myogenic differentiation.

p38alpha antagonizes p38gamma activity through c-Jun-dependent ubiquitin-proteasome pathways in regulating Ras transformation and stress response.

p38 MAPK family consists of four isoform proteins (alpha, beta, gamma, and delta) that are activated by the same stimuli, but the information about how these proteins act together to yield a biological response is missing. Here we show a feed-forward mechanism by which p38alpha may regulate Ras transformation and stress response through depleting its family member p38gamma protein via c-Jun-dependent ubiquitin-proteasome pathways. Analyses of MAPK kinase 6 (MKK6)-p38 fusion proteins showed that constitutively active p38alpha (MKK6-p38alpha) and p38gamma (MKK6-p38gamma) stimulates and inhibits c-Jun phosphorylation respectively, leading to a distinct AP-1 regulation. Depending on cell type and/or stimuli, p38alpha phosphorylation results in either Ras-transformation inhibition or a cell-death escalation that invariably couples with a decrease in p38gamma protein expression. p38gamma, on the other hand, increases Ras-dependent growth or inhibits stress induced cell-death independent of phosphorylation. In cells expressing both proteins, p38alpha phosphorylation decreases p38gamma protein expression, whereas its inhibition increases cellular p38gamma concentrations, indicating an active role of p38alpha phosphorylation in negatively regulating p38gamma protein expression. Mechanistic analyses show that p38alpha requires c-Jun activation to deplete p38gamma proteins by ubiquitin-proteasome pathways. These results suggest that p38alpha may, upon phosphorylation, act as a gatekeeper of the p38 MAPK family to yield a coordinative biological response through disrupting its antagonistic p38gamma family protein.

Inhibitory effect of p38 mitogen-activated protein kinase inhibitors on cytokine release from human macrophages.

BACKGROUND AND PURPOSE: Macrophages release cytokines that may contribute to pulmonary inflammation in conditions such as chronic obstructive pulmonary disease. Thus, inhibition of macrophage cytokine production may have therapeutic benefit. p38 MAPK may regulate cytokine production, therefore, the effect of two p38 MAPK inhibitors, SB239063 and SD-282, on the release of TNF-alpha, GM-CSF and IL-8 from human macrophages was investigated. EXPERIMENTAL APPROACH: Cytokine release was measured by ELISA. Immunoblots and mRNA expression studies were performed to confirm p38 MAPK isoform expression and activity. Macrophages were isolated from lung tissue of current smokers, ex-smokers and emphysema patients and exposed to lipopolysaccharide. These cells then released cytokines in a concentration-dependent manner. KEY RESULTS: SB239063 only inhibited TNF-alpha release (EC50 0.3 +/- 0.1 microM). Disease status had no effect on the efficacy of SB239063. SD-282 inhibited both TNF-alpha and GM-CSF release from macrophages (EC50 6.1 +/- 1.4 nM and 1.8 +/- 0.6 microM respectively) but had no effect on IL-8 release. In contrast, both inhibitors suppressed cytokine production in monocytes. CONCLUSIONS AND IMPLICATIONS: The differential effects of p38 MAPK inhibitors between macrophages and monocytes could not be explained by differences in p38 MAPK isoform expression or activity. However, the stability of TNF-alpha mRNA was significantly increased in macrophages compared to monocytes. These data suggest a differential involvement for p38 MAPK in macrophage cytokine production compared with monocytes. These effects are not due to lack of p38 activation or p38alpha expression in macrophages but may reflect differential effects on the stability of cytokine mRNA.

Outer membrane protein 25-a mitochondrial anchor and inhibitor of stress-activated protein kinase-3.

Stress-activated protein kinase-3 (SAPK3) is unique amongst the mitogen-activated protein kinase (MAPK) family with its C-terminal 5 amino acids directing interaction with the PDZ domain-containing substrates alpha1-Syntrophin and SAP90/PSD95. Here, we identify three additional PDZ domain-containing binding partners, Lin-7C, Scribble, and outer membrane protein 25 (OMP25). This latter protein is localised together with SAPK3 at the mitochondria but it is not a SAPK3 substrate. Instead, OMP25 inhibits SAPK3 activity towards PDZ domain-containing substrates such as alpha1-Syntrophin and substrates without PDZ domains such as the mitochondrial protein Sab. This is a new mechanism for the regulation of SAPK3 and suggests that its intracellular activity should not be solely assessed by its phosphorylation status.

BIRB796 inhibits all p38 MAPK isoforms in vitro and in vivo.

The compound BIRB796 inhibits the stress-activated protein kinases p38alpha and p38beta and is undergoing clinical trials for the treatment of inflammatory diseases. Here we report that BIRB796 also inhibits the activity and the activation of SAPK3/p38gamma. This occurs at higher concentrations of BIRB796 than those that inhibit p38alpha and p38beta and at lower concentrations than those that inhibit the activation of JNK isoforms. We also show that at these concentrations, BIRB796 blocks the stress-induced phosphorylation of the scaffold protein SAP97, further establishing that this is a physiological substrate of SAPK3/p38gamma. Our results demonstrate that BIRB796, in combination with SB203580, a compound that inhibits p38alpha and p38beta, but not the other p38 isoforms, can be used to identify physiological substrates of SAPK3/p38gamma as well as those of p38alpha and p38beta.