Genetic analysis of specific and redundant roles for p38alpha and p38beta MAPKs during mouse development

Regulating effect of miR-132-3p on the changes of MAPK pathway in rat brains and SH-SY5Y cells exposed to excessive fluoride by targeting expression of MAPK1

BACKGROUND

Although the changes of mitogen-activated protein kinase (MAPK) pathway in the central nervous system (CNS) induced by excessive fluoride has been confirmed by our previous findings, the underlying mechanism(s) of the action remains unclear. Here, we investigate the possibility that microRNAs (miRNAs) are involved in the aspect.

METHODS

As a model of chronic fluorosis, SD rats received different concentrations of fluoride in their drinking water for 3 or 6 months and SH-SY5Y cells were exposed to fluoride. Literature reviews and bioinformatics analyses were used to predict and real-time PCR to measure the expression of 12 miRNAs; an algorithm-based approach was applied to identify multiply potential target-genes and pathways; the dual-luciferase reporter system to detect the association of miR-132-3p with MAPK1; and fluorescence in situ hybridization to detect miR-132-3p localization. The miR-132-3p inhibitor or mimics or MAPK1 silencing RNA were transfected into cultured cells. Expression of protein components of the MAPK pathway was assessed by immunofluorescence or Western blotting.

RESULTS

In the rat hippocampus exposed with high fluoride, ten miRNAs were down-regulated and two up-regulated. Among these, miR-132-3p expression was down-regulated to the greatest extent and MAPK1 level (selected from the 220 genes predicted) was corelated with the alteration of miR-132-3p. Furthermore, miR-132-3p level was declined, whereas the protein levels MAPK pathway components were increased in the rat brains and SH-SY5Y cells exposed to high fluoride. MiR-132-3p up-regulated MAPK1 by binding directly to its 3'-untranslated region. Obviously, miR-132-3p mimics or MAPK1 silencing RNA attenuated the elevated expressions of the proteins components of the MAPK pathway induced by fluorosis in SH-SY5Y cells, whereas an inhibitor of miR-132-3p just played the opposite effect.

CONCLUSION

MiR-132-3p appears to modulate the changes of MAPK signaling pathway in the CNS associated with chronic fluorosis.

Tracheal agenesis versus tracheal atresia: anatomical conditions, pathomechanisms and causes with a possible link to a novel MAPK11 variant in one case

BACKGROUND

In this study we aimed to describe the morphological and pathogenetic differences between tracheal agenesis and tracheal atresia, which are not clearly distinguished from each other in the literature, and to contribute thereby to the understanding and management of these conditions. Both tracheal agenesis and tracheal atresia represent rare disorders of still unknown aetiology that cannot be detected by prenatal ultrasound. If the affected foetuses survive until birth these conditions result in respiratory failure and in futile attempts to rescue the infant's life.

RESULTS

Autopsies and genetic analyses, including singleton or trio exome sequencing, were performed on five neonates/foetuses with tracheal agenesis and three foetuses with tracheal atresia. Tracheal agenesis was characterized by absence of the sublaryngeal trachea and presence of a bronchooesophageal fistula and by pulmonary isomerism and occurred as an isolated malformation complex or as part of a VACTERL association. Special findings were an additional so-called 'pig bronchus' and a first case of tracheal agenesis with sirenomelia. Tracheal atresia presenting with partial obliteration of its lumen and persistence of a fibromuscular streak resulted in CHAOS. This condition was associated with normal lung lobulation and single, non-VACTERL type malformations. Trio ES revealed a novel variant of MAPK11 in one tracheal agenesis case. Its involvement in tracheooesophageal malformation is herein discussed, but remains hypothetical.

CONCLUSION

Tracheal agenesis and tracheal atresia represent different disease entities in terms of morphology, pathogenesis and accompanying anomalies due to a primary developmental and secondary disruptive possibly vascular disturbance, respectively.

Function and inhibition of P38 MAP kinase signaling: Targeting multiple inflammation diseases

Inflammation is a natural host defense mechanism that protects the body from pathogenic microorganisms. A growing body of research suggests that inflammation is a key factor in triggering other diseases (lung injury, rheumatoid arthritis, etc.). However, there is no consensus on the complex mechanism of inflammatory response, which may include enzyme activation, mediator release, and tissue repair. In recent years, p38 MAPK, a member of the MAPKs family, has attracted much attention as a central target for the treatment of inflammatory diseases. However, many p38 MAPK inhibitors attempting to obtain marketing approval have failed at the clinical trial stage due to selectivity and/or toxicity issues. In this paper, we discuss the mechanism of p38 MAPK in regulating inflammatory response and its key role in major inflammatory diseases and summarize the synthetic or natural products targeting p38 MAPK to improve the inflammatory response in the last five years, which will provide ideas for the development of novel clinical anti-inflammatory drugs based on p38 MAPK inhibitors.

Anthracycline cardiotoxicity is exacerbated by global p38β genetic ablation in a sexually dimorphic manner but unaltered by cardiomyocyte-specific p38α loss

Severe cardiotoxic effects limit the efficacy of doxorubicin (DOX) as a chemotherapeutic agent. Activation of intracellular stress signaling networks, including p38 mitogen-activated protein kinase (MAPK), has been implicated in DOX-induced cardiotoxicity (DIC). However, the roles of the individual p38 isoforms in DIC remain incompletely elucidated. We recently reported that global p38δ deletion protected female but not male mice from DIC, whereas global p38γ deletion did not significantly modulate it. Here we studied the in vivo roles of p38α and p38β in acute DIC. Male and female mice with cardiomyocyte-specific deletion of p38α or global deletion of p38β and their wild-type counterparts were injected with DOX. Survival and health were tracked for 10 days postinjection. Cardiac function was assessed by echocardiography and electrocardiography and fibrosis by Picrosirius red staining. Expression and activation of signaling proteins and inflammatory markers were measured by Western blot, phosphorylation array, and chemokine/cytokine array. Global p38β deletion significantly aggravated DIC and worsened cardiac electrical and mechanical function deterioration in female mice. Mechanistically, DIC in p38β-null female mice correlated with increased autophagy, sustained hyperactivation of proapoptotic JNK signaling, as well as remodeling of a myocardial inflammatory environment. In contrast, cardiomyocyte-specific deletion of p38α improved survival of DOX30-treated male mice 5 days posttreatment but did not influence cardiac function in DOX-treated male or female mice. Our data highlight the sex- and isoform-specific roles of p38α and p38β MAPKs in DOX-induced cardiac injury and suggest a novel in vivo function of p38β in protecting female mice from DIC.NEW & NOTEWORTHY We show that p38α and p38β have distinct in vivo functions in a murine model of acute DIC. Specifically, although conditional cardiomyocyte-specific p38α deletion exhibited mild cardioprotective effects in male mice, p38β deletion exacerbated the DOX cardiotoxicity in female mice. Our findings caution against employing pyridinyl imidazole inhibitors that target both p38α and p38β isoforms as a cardioprotective strategy against DIC. Such an approach could have undesirable sex-dependent effects, including attenuating p38β-dependent cardioprotection in females.

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.

Synthesis and Preclinical Positron Emission Tomography Imaging of the p38 MAPK Inhibitor [11C]Talmapimod: Effects of Drug Efflux and Sex Differences

Stress-activated kinases are targets of interest in neurodegenerative disease due to their involvement in inflammatory signaling and synaptic dysfunction. The p38α kinase has shown clinical and preclinical promise as a druggable target in several neurodegenerative conditions. We report the radiosynthesis and evaluation of the first positron emission tomography (PET) radiotracer for imaging MAPK p38α/β through radiolabeling of the inhibitor talmapimod (SCIO-469) with carbon-11. [¹¹C]Talmapimod was reliably synthesized by carbon-11 methylation with non-decay corrected radiochemical yields of 3.1 ± 0.7%, molar activities of 38.9 ± 13 GBq/μmol, and >95% radiochemical purity (n = 20). Preclinical PET imaging in rodents revealed a low baseline brain uptake and retention with standardized uptake values (SUV) of ∼0.2 over 90 min; however, pretreatment with the P-glycoprotein (P-gp) drug efflux transporter inhibitor elacridar enabled [¹¹C]talmapimod to pass the blood-brain barrier (>1.0 SUV) with distinct sex differences in washout kinetics. Blocking studies with a structurally dissimilar p38α/β inhibitor, neflamapimod (VX-745), and displacement imaging studies with talmapimod were attempted in elacridar-pretreated rodents, but neither compound displaced radiotracer uptake in the brain of either sex. Ex vivo radiometabolite analysis revealed substantial differences in the composition of radioactive species present in blood plasma but not in brain homogenates at 40 min post radiotracer injection. Digital autoradiography in fresh-frozen rodent brain tissue confirmed that the radiotracer signal was largely non-displaceable in vitro, where self-blocking and blocking with neflamapimod marginally decreased the total signal by 12.9 ± 8.8% and 2.66 ± 2.1% in C57bl/6 healthy controls and 29.3 ± 2.7% and 26.7 ± 12% in Tg2576 rodent brains, respectively. An MDCK-MDR1 assay suggests that talmapimod is likely to suffer from drug efflux in humans as well as rodents. Future efforts should focus on radiolabeling p38 inhibitors from other structural classes to avoid P-gp efflux and non-displaceable binding.

Roles of p38 MAPK signalling in intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is a common degenerative disease mediated by multiple factors. Because of its complex aetiology and pathology, no specific molecular mechanisms have yet been identified and no definitive treatments are currently available for IVDD. p38 mitogen-activated protein kinase (MAPK) signalling, part of the serine and threonine (Ser/Thr) protein kinases family, is associated with the progression of IVDD, by mediating the inflammatory response, increasing extracellular matrix (ECM) degradation, promoting cell apoptosis and senescence and suppressing cell proliferation and autophagy. Meanwhile, the inhibition of p38 MAPK signalling has a significant effect on IVDD treatment. In this review, we first summarize the regulation of p38 MAPK signalling and then highlight the changes in the expression of p38 MAPK signalling and their impact on pathological process of IVDD. Moreover, we discuss the current applications and future prospects of p38 MAPK as a therapeutic target for IVDD treatment.

P38 MAPK and Radiotherapy: Foes or Friends?

Over the last 30 years, the study of the cellular response to ionizing radiation (IR) has increased exponentially. Among the various signaling pathways affected by IR, p38 MAPK has been shown to be activated both in vitro and in vivo, with involvement in key processes triggered by IR-mediated genotoxic insult, such as the cell cycle, apoptosis or senescence. However, we do not yet have a definitive clue about the role of p38 MAPK in terms of radioresistance/sensitivity and its potential use to improve current radiotherapy. In this review, we summarize the current knowledge on this family of MAPKs in response to IR as well as in different aspects related to radiotherapy, such as their role in the control of REDOX, fibrosis, and in the radiosensitizing effect of several compounds.

Synthesis and Biological Activity of a VHL-Based PROTAC Specific for p38α

We report a series of small molecule proteolysis-targeting chimeras (PROTACs) that target the protein kinase p38α for degradation. These PROTACs are based on a ligand of the VHL E3 ubiquitin ligase, which is linked to an ATP competitive inhibitor of p38α. We provide evidence that these compounds can induce the specific degradation of p38α, but not p38β and other related kinases, at nanomolar concentrations in several mammalian cell lines. We also show that the p38α-specific PROTACs are soluble in aqueous solutions and therefore suitable for their administration to mice. Systemic administration of the PROTACs induces p38α degradation only in the liver, probably due to the PROTAC becoming inactivated in that organ, but upon local administration the PROTACs induce p38α degradation in mammary tumors. Our compounds provide an alternative to traditional chemical inhibitors for targeting p38α signaling in cultured cells and in vivo.

MKK6 deficiency promotes cardiac dysfunction through MKK3-p38γ/δ-mTOR hyperactivation

Stress-activated p38 kinases control a plethora of functions, and their dysregulation has been linked to the development of steatosis, obesity, immune disorders, and cancer. Therefore, they have been identified as potential targets for novel therapeutic strategies. There are four p38 family members (p38α, p38β, p38γ, and p38δ) that are activated by MKK3 and MKK6. Here, we demonstrate that lack of MKK6 reduces the lifespan in mice. Longitudinal study of cardiac function in MKK6 KO mice showed that young mice develop cardiac hypertrophy which progresses to cardiac dilatation and fibrosis with age. Mechanistically, lack of MKK6 blunts p38α activation while causing MKK3-p38γ/δ hyperphosphorylation and increased mammalian target of rapamycin (mTOR) signaling, resulting in cardiac hypertrophy. Cardiac hypertrophy in MKK6 KO mice is reverted by knocking out either p38γ or p38δ or by inhibiting the mTOR pathway with rapamycin. In conclusion, we have identified a key role for the MKK3/6-p38γ/δ pathway in the development of cardiac hypertrophy, which has important implications for the clinical use of p38α inhibitors in the long-term treatment since they might result in cardiotoxicity.

Role of p38 MAP kinase in cancer stem cells and metastasis

Therapeutic resistance and metastatic progression are responsible for the majority of cancer mortalities. In particular, the development of resistance is a significant barrier to the efficacy of cancer treatments such as chemotherapy, radiotherapy, targeted therapies, and immunotherapies. Cancer stem cells (CSCs) underlie treatment resistance and metastasis. p38 mitogen-activated protein kinase (p38 MAPK) is downstream of several CSC-specific signaling pathways, and it plays an important role in CSC development and maintenance and contributes to metastasis and chemoresistance. Therefore, the development of therapeutic approaches targeting p38 can sensitize tumors to chemotherapy and prevent metastatic progression.

Developments of CRBN-based PROTACs as potential therapeutic agents

Protease-targeted chimeras (PROTACs) are a new technology that is receiving much attention in the treatment of diseases. The mechanism is to inhibit protein function by hijacking the ubiquitin E3 ligase for protein degradation. Heterogeneous bifunctional PROTACs contain a ligand for recruiting E3 ligase, a linker, and another ligand to bind to the target protein for degradation. A variety of small-molecule PROTACs (CRBN, VHL, IAPs, MDM2, DCAF15, DCAF16, and RNF114-based PROTACs) have been identified so far. In particular, CRBN-based PROTACs (e.g., ARV-110 and ARV-471) have received more attention for their promising therapeutic intervention. To date, CRBN-based PRTOACs have been extensively explored worldwide and have excelled not only in cancer diseases but also in cardiovascular diseases, immune diseases, neurodegenerative diseases, and viral infections. In this review, we will provide a comprehensive update on the latest research progress in CRBN-based PRTOACs area. Following the criteria, such as disease area and drug target class, we will present the degradants in alphabetical order by target. We also provide our own perspective on the future prospects and potential challenges facing PROTACs.

Mitogen-activated protein kinase-activated protein kinase-2 (MK2) and its role in cell survival, inflammatory signaling, and migration in promoting cancer

Cancer and the immune system share an intimate relationship. Chronic inflammation increases the risk of cancer occurrence and can also drive inflammatory mediators into the tumor microenvironment enhancing tumor growth and survival. The p38 MAPK pathway is activated both acutely and chronically by stress, inflammatory chemokines, chronic inflammatory conditions, and cancer. These properties have led to extensive efforts to find effective drugs targeting p38, which have been unsuccessful. The immediate downstream serine/threonine kinase and substrate of p38 MAPK, mitogen-activated-protein-kinase-activated-protein-kinase-2 (MK2) protects cells against stressors by regulating the DNA damage response, transcription, protein and messenger RNA stability, and motility. The phosphorylation of downstream substrates by MK2 increases inflammatory cytokine production, drives an immune response, and contributes to wound healing. By binding directly to p38 MAPK, MK2 is responsible for the export of p38 MAPK from the nucleus which gives MK2 properties that make it unique among the large number of p38 MAPK substrates. Many of the substrates of both p38 MAPK and MK2 are separated between the cytosol and nucleus and interfering with MK2 and altering this intracellular translocation has implications for the actions of both p38 MAPK and MK2. The inhibition of MK2 has shown promise in combination with both chemotherapy and radiotherapy as a method for controlling cancer growth and metastasis in a variety of cancers. Whereas the current data are encouraging the field requires the development of selective and well tolerated drugs to target MK2 and a better understanding of its effects for effective clinical use.

Impact of environmental toxicants on p38- and ERK-MAPK signaling pathways in the central nervous system

There are several candidate signalling pathways that mediate the response of the central nervous system (CNS) cells to environmental toxins. However, much is still to be learned on how these pathways modulate neurotoxicity. The mitogen-activated protein kinases (MAPKs) signalling pathways, which include the extracellular signal-regulated protein kinase (ERK) and the p38-MAPK, are potentially key pathways to regulate CNS responses to environmental toxins. The pathways play leading roles in the transmission of extracellular signals into the cell nucleus, leading to cell differentiation, cell growth, and apoptosis, to name a few. Moreover, exposure to environmental toxins induces p38- and ERK-MAPK activation, which leads to oxidative stress, inflammation, and apoptosis in the CNS. Here, we provide a concise review of the recent evidence demonstrating the role of p38- and ERK-MAPK signaling pathways and their downstream targets in the CNS following exposure to environmental toxicants such as metals, organophosphorus and persistent organic pollutants.

p38β - MAPK11 and its role in female cancers

Background

The p38MAPK family of Mitogen Activated Protein Kinases are a group of signalling molecules involved in cell growth, survival, proliferation and differentiation. The widely studied p38α isoform is ubiquitously expressed and is implicated in a number of cancer pathologies, as are p38γ and p38δ. However, the mechanistic role of the isoform, p38β, remains fairly elusive. Recent studies suggest a possible role of p38β in both breast and endometrial cancer with research suggesting involvement in bone metastasis and cancer cell survival. Female tissue specific cancers such as breast, endometrial, uterine and ovary account for over 3,000,000 cancer related incidents annually; advancements in therapeutics and treatment however require a deeper understanding of the molecular aetiology associated with these diseases. This study provides an overview of the MAPK signalling molecule p38β (MAPK11) in female cancers using an in-silico approach.

Methods

A detailed gene expression and methylation analysis was performed using datasets from cBioportal, CanSar and MEXPRESS. Breast, Uterine Endometrial, Cervical, Ovarian and Uterine Carcinosarcoma TCGA cancer datasets were used and analysed.

Results

Data using cBioportal and CanSAR suggest that expression of p38β is lower in cancers: BRCA, UCEC, UCS, CESC and OV compared to normal tissue. Methylation data from SMART and MEXPRESS indicate significant probe level variation of CpG island methylation status of the gene MAPK11. Analysis of the genes’ two CpG islands shows that the gene was hypermethylated in the CpG1 with increased methylation seen in BRCA, CESC and UCEC cancer data sets with a slight increase of expression recorded in cancer samples. CpG2 exhibited hypomethylation with no significant difference between samples and high levels of expression. Further analysis from MEXPRESS revealed no significance between probe methylation and altered levels of expression. In addition, no difference in the expression of BRCA oestrogen/progesterone/HER2 status was seen.

Conclusion

This data provides an overview of the expression of p38β in female tissue specific cancers, showing a decrease in expression of the gene in BRCA, UCEC, CESC, UCS and OV, increasing the understanding of p38β MAPK expression and offering insight for future in-vitro investigation and therapeutic application.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13048-021-00834-9.

A Special View of What Was Almost Forgotten: p38δ MAPK

The p38δ mitogen-activated protein kinase is an important signal transduction enzyme. p38δ has recently emerged as a drug target due to its tissue-specific expression patterns and its critical roles in regulation of cellular processes related to cancer and inflammatory diseases, such as cell proliferation, cell migration, apoptosis, and inflammatory responses. However, potent and specific p38δ inhibitors have not been defined so far. Moreover, in cancer disease, p38δ appears to act as a tumor suppressor or tumor promoter according to cancer and cell type studied. In this review, we outline the current understanding of p38δ roles in each cancer type, to define whether it is possible to delineate new cancer therapies based on small-molecule p38δ inhibitors. We also highlight recent advances made in the design of molecules with potential to inhibit p38 isoforms and discuss structural approaches to guide the search for p38δ inhibitors.

Diversity and versatility of p38 kinase signalling in health and disease

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

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

The role of stress kinases in metabolic disease

Obesity is a health condition that has reached pandemic levels and is implicated in the development and progression of type 2 diabetes mellitus, cancer and heart failure. A key characteristic of obesity is the activation of stress-activated protein kinases (SAPKs), such as the p38 and JNK stress kinases, in several organs, including adipose tissue, liver, skeletal muscle, immune organs and the central nervous system. The correct timing, intensity and duration of SAPK activation contributes to cellular metabolic adaptation. By contrast, uncontrolled SAPK activation has been proposed to contribute to the complications of obesity. The stress kinase signalling pathways have therefore been identified as potential targets for the development of novel therapeutic approaches for metabolic syndrome. The past few decades have seen intense research efforts to determine how these kinases are regulated in a cell-specific manner and to define their contribution to the development of obesity and insulin resistance. Several studies have uncovered new and unexpected functions of the non-classical members of both pathways. Here, we provide an overview of the role of SAPKs in metabolic control and highlight important discoveries in the field.

p38β and Cancer: The Beginning of the Road

The p38 mitogen-activated protein kinase (MAPK) signaling pathway is implicated in cancer biology and has been widely studied over the past two decades as a potential therapeutic target. Most of the biological and pathological implications of p38MAPK signaling are often associated with p38α (MAPK14). Recently, several members of the p38 family, including p38γ and p38δ, have been shown to play a crucial role in several pathologies including cancer. However, the specific role of p38β (MAPK11) in cancer is still elusive, and further investigation is needed. Here, we summarize what is currently known about the role of p38β in different types of tumors and its putative implication in cancer therapy. All evidence suggests that p38β might be a key player in cancer development, and could be an important therapeutic target in several pathologies, including cancer.

p38 MAPK Pathway in the Heart: New Insights in Health and Disease

The p38 mitogen-activated kinase (MAPK) family controls cell adaptation to stress stimuli. p38 function has been studied in depth in relation to cardiac development and function. The first isoform demonstrated to play an important role in cardiac development was p38α; however, all p38 family members are now known to collaborate in different aspects of cardiomyocyte differentiation and growth. p38 family members have been proposed to have protective and deleterious actions in the stressed myocardium, with the outcome of their action in part dependent on the model system under study and the identity of the activated p38 family member. Most studies to date have been performed with inhibitors that are not isoform-specific, and, consequently, knowledge remains very limited about how the different p38s control cardiac physiology and respond to cardiac stress. In this review, we summarize the current understanding of the role of the p38 pathway in cardiac physiology and discuss recent advances in the field.

Functions of p38 MAP Kinases in the Central Nervous System

Mitogen-activated protein (MAP) kinases are a central component in signaling networks in a multitude of mammalian cell types. This review covers recent advances on specific functions of p38 MAP kinases in cells of the central nervous system. Unique and specific functions of the four mammalian p38 kinases are found in all major cell types in the brain. Mechanisms of p38 activation and downstream phosphorylation substrates in these different contexts are outlined and how they contribute to functions of p38 in physiological and under disease conditions. Results in different model organisms demonstrated that p38 kinases are involved in cognitive functions, including functions related to anxiety, addiction behavior, neurotoxicity, neurodegeneration, and decision making. Finally, the role of p38 kinases in psychiatric and neurological conditions and the current progress on therapeutic inhibitors targeting p38 kinases are covered and implicate p38 kinases in a multitude of CNS-related physiological and disease states.

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.

Optimal linker length for small molecule PROTACs that selectively target p38α and p38β for degradation

We report the design of hetero-bifunctional small molecules that selectively target p38α and p38β for degradation. These proteolysis targeted chimeras (PROTACs) are based on an ATP competitive inhibitor of p38α and p38β, which is linked to thalidomide analogues to recruit the Cereblon E3 ubiquitin ligase complex. Compound synthesis was facilitated by the use of a copper catalyzed "click" reaction. We show that optimization of the linker length and composition is crucial for the degradation-inducing activity of these PROTACs. We provide evidence that these chemical compounds can induce degradation of p38α and p38β but no other related kinases at nanomolar concentrations in several mammalian cell lines. Accordingly, the PROTACs inhibit stress and cytokine-induced p38α signaling. Our compounds contribute to understanding the development of PROTACs, and provide a useful tool to investigate functions of the p38 MAPK pathway and its involvement in diseases.

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.

A new regulatory mechanism of protein phosphatase 2A activity via SET in acute myeloid leukemia

Acute myeloid leukemia (AML) is an aggressive hematologic malignancy. Although novel emerging drugs are available, the overall prognosis remains poor and new therapeutic approaches are required. PP2A phosphatase is a key regulator of cell homeostasis and is recurrently inactivated in AML. The anticancer activity of several PP2A-activating drugs (e.g., FTY720) depends on their interaction with the SET oncoprotein, an endogenous PP2A inhibitor that is overexpressed in 30% of AML cases. Elucidation of SET regulatory mechanisms may therefore provide novel targeted therapies for SET-overexpressing AMLs. Here, we show that upregulation of protein kinase p38β is a common event in AML. We provide evidence that p38β potentiates SET-mediated PP2A inactivation by two mechanisms: facilitating SET cytoplasmic translocation through CK2 phosphorylation, and directly binding to and stabilizing the SET protein. We demonstrate the importance of this new regulatory mechanism in primary AML cells from patients and in zebrafish xenograft models. Accordingly, combination of the CK2 inhibitor CX-4945, which retains SET in the nucleus, and FTY720, which disrupts the SET-PP2A binding in the cytoplasm, significantly reduces the viability and migration of AML cells. In conclusion, we show that the p38β/CK2/SET axis represents a new potential therapeutic pathway in AML patients with SET-dependent PP2A inactivation.

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.

YY1 and HDAC9c transcriptionally regulate p38-mediated mesenchymal stem cell differentiation into osteoblasts

Mesenchymal stem cells (MSCs) have a high self-renewal potential and can differentiate into various types of cells, including adipocytes, osteoblasts, and chondrocytes. Previously, we reported that the enhancer of zeste homolog 2 (EZH2), the catalytic component of the Polycomb-repressive complex 2, and HDAC9c mediate the osteogenesis and adipogenesis of MSCs. In the current study, we identify the role of p38 in osteogenic differentiation from a MAPK antibody array screen and investigate the mechanisms underlying its transcriptional regulation. Our data show that YY1, a ubiquitously expressed transcription factor, and HDAC9c coordinate p38 transcriptional activity to promote its expression to facilitate the osteogenic potential of MSCs. Our results show that p38 mediates osteogenic differentiation, and this has significant implications in bone-related diseases, bone tissue engineering, and regenerative medicine.

Regulation of Mammary Luminal Cell Fate and Tumorigenesis by p38α

Mammary stem and progenitor cells are essential for mammary gland homeostasis and are also candidates for cells of origin of mammary tumors. Here, we have investigated the function of the protein kinase p38α in the mammary gland using mice that delete this protein in the luminal epithelial cells. We show that p38α regulates the fate of luminal progenitor cells through modulation of the transcription factor RUNX1, an important controller of the estrogen receptor-positive cell lineage. We also provide evidence that the regulation of RUNX1 by p38α probably involves the kinase MSK1, which phosphorylates histone H3 at the RUNX1 promoter. Moreover, using a mouse model for breast cancer initiated by luminal cells, we show that p38α downregulation in mammary epithelial cells reduces tumor burden, which correlates with decreased numbers of tumor-initiating cells. Collectively, our results define a key role for p38α in luminal progenitor cell fate that affects mammary tumor formation.

•

Luminal progenitor cell fate in the mammary gland is regulated by p38α

•

p38α controls the ER transcriptional program by modulating RUNX1

•

p38α regulates H3 phosphorylation at the RUNX1 promoter through the kinase MSK1

•

p38α promotes mammary tumorigenesis by maintaining luminal tumor-initiating cells

The Regulatory Roles of Mitogen-Activated Protein Kinase (MAPK) Pathways in Health and Diabetes: Lessons Learned from the Pancreatic β-Cell

BACKGROUND

Glucose-stimulated insulin secretion (GSIS) from the pancreatic β-cell involves several intracellular metabolic events which lead to the translocation of insulin granules towards the membrane for fusion and release. It is well established that loss of β-cell function and decreased GSIS underlie the pathogenesis of diabetes. Evidence from several laboratories, including our own, demonstrated requisite roles of Rac1 and phagocyte-like NADPH oxidase (Nox2)-derived reactive oxygen species (ROS) in optimal function of the pancreatic β-cell, including GSIS. However, it is becoming increasingly clear that prolonged exposure of β-cells to hyperglycemic conditions, leads to sustained activation of Rac1-Nox2 signaling axis culminating in excessive generation of intracellular ROS (oxidative stress) and β-cell dysregulation and demise. Such "cytotoxic" effects of ROS appear to be mediated via the stress-activated protein kinases/mitogen-activated protein kinases (SAPK/MAPK) signaling pathways.

OBJECTIVE

This review discusses our current understanding of regulation and functions of the conventional MAPKs, namely, ERK1/2, JNK1/2 and p38MAPK.

CONCLUSION

The MAPK pathways are activated in the presence of various stress stimuli including intracellular ROS, via distinct signaling cascades. Once activated, MAPKs participate in specific intracellular signaling processes via interaction with several downstream kinases including the MAPKactivated protein kinases (MAPKAPKs) and transcription factors including c-jun and p53. We have provided an overview of existing evidence in the islet β-cell on the regulatory roles of these MAPKs in mediating cellular responses to alterations in intracellularly generated ROS, which is mediated by the Rac1-Nox2 signaling module. Additionally, we enlisted recent patents developed to improve β-cell function in diabetes and novel pharmacological agents that target oxidative stress and MAPK pathways.

p38α regulates cytokine-induced IFNγ secretion via the Mnk1/eIF4E pathway in Th1 cells

The p38 mitogen-activated protein kinase (MAPK) pathway is involved in the regulation of immune and inflammatory processes. We used p38α-conditional, p38β-deficient and p38α/β double-null mouse models to address the role of these two p38 MAPK in CD4⁺ T cells, and found that p38α deficiency causes these cells to hyperproliferate. Our studies indicate that both p38α and p38β are dispensable for T helper cell type 1 (Th1) differentiation but, by controlling interferon (IFN)γ and tumor necrosis factor (TNF)α production, are critical for normal Th1 effector function. We found that both p38α and p38β modulate T-cell receptor-induced IFNγ and TNFα production, whereas only p38α regulates cytokine-induced IFNγ production. The lack of p38α and p38β did not affect transcription and mRNA stability of Ifng. However, the absence of p38α in Th1 cells resulted in a decreased MNK1 phosphorylation after cytokine activation, and MNK1 inhibition blocked IFNγ production. Our results indicate that p38α regulates IFNγ secretion through the activation of the MNK1/eIF4E pathway of translation initiation and identify specific functions for p38α and p38β in T-cell proliferation.

Loss of Functionally Redundant p38 Isoforms in T Cells Enhances Regulatory T Cell Induction

The evolutionarily conserved protein kinase p38 mediates innate resistance to environmental stress and microbial infection. Four p38 isoforms exist in mammals and may have been co-opted for new roles in adaptive immunity. Murine T cells deficient in p38α, the ubiquitously expressed p38 isoform, showed no readily apparent cell-autonomous defects while expressing elevated amounts of another isoform, p38β. Mice with T cells simultaneously lacking p38α and p38β displayed lymphoid atrophy and elevated Foxp3⁺ regulatory T cell frequencies. Double deficiency of p38α and p38β in naïve CD4⁺ T cells resulted in an attenuation of MAPK-activated protein kinase (MK)-dependent mTOR signaling after T cell receptor engagement, and enhanced their differentiation into regulatory T cells under appropriate inducing conditions. Pharmacological inhibition of the p38-MK-mTOR signaling module produced similar effects, revealing potential for therapeutic applications.

Estrogen Protects the Female Heart from Ischemia/Reperfusion Injury through Manganese Superoxide Dismutase Phosphorylation by Mitochondrial p38β at Threonine 79 and Serine 106

A collective body of evidence indicates that estrogen protects the heart from myocardial ischemia/reperfusion (I/R) injury, but the underlying mechanism remains incompletely understood. We have previously delineated a novel mechanism of how 17β-estradiol (E2) protects cultured neonatal rat cardiomyocytes from hypoxia/reoxygenation (H/R) by identifying a functionally active mitochondrial pool of p38β and E2-driven upregulation of manganese superoxide dismutase (MnSOD) activity via p38β, leading to the suppression of reactive oxygen species (ROS) and apoptosis. Here we investigate these cytoprotective actions of E2 in vivo. Left coronary artery ligation and reperfusion was used to produce I/R injury in ovariectomized (OVX) female mice and in estrogen receptor (ER) null female mice. E2 treatment in OVX mice reduced the left ventricular infarct size accompanied by increased activity of mitochondrial p38β and MnSOD. I/R-induced infarct size in ERα knockout (ERKO), ERβ knockout (BERKO) and ERα and β double knockout (DERKO) female mice was larger than that in wild type (WT) mice, with little difference among ERKO, BERKO, and DERKO. Loss of both ERα and ERβ led to reduced activity of mitochondrial p38β and MnSOD at baseline and after I/R. The physical interaction between mitochondrial p38β and MnSOD in the heart was detected by co-immunoprecipitation (co-IP). Threonine 79 (T79) and serine 106 (S106) of MnSOD were identified to be phosphorylated by p38β in kinase assays. Overexpression of WT MnSOD in cardiomyocytes reduced ROS generation during H/R, while point mutation of T79 and S106 of MnSOD to alanine abolished its antioxidative function. We conclude that the protective effects of E2 and ER against cardiac I/R injury involve the regulation of MnSOD via posttranslational modification of the dismutase by p38β.

p38 MAP kinase is required for Wnt3a-mediated osterix expression independently of Wnt-LRP5/6-GSK3β signaling axis in dental follicle cells

Wnt3a is a secreted glycoprotein that activates the glycogen synthase kinase-3β (GSK3β)/β-catenin signaling pathway through low-density-lipoprotein receptor-related protein (LRP)5/6 co-receptors. Wnt3a has been implicated in periodontal development and homeostasis, as well as in cementum formation. Recently, we have reported that Wnt3a increases alkaline phosphatase expression through the induction of osterix (Osx) expression in dental follicle cells, a precursor of cementoblasts. However, the molecular mechanism by which Wnt3a induces Osx expression is still unknown. In this study, we show that Wnt3a-induced Osx expression was inhibited in the presence of p38 mitogen-activated protein kinase (MAPK) inhibitors (SB203580 and SB202190) at gene and protein levels, as assessed by real-time PCR and immunocytohistochemistry, respectively. Pretreatment of cells with Dickkopf-1, a potent canonical Wnt antagonist binding to LRP5/6 co-receptors, did not influence Wnt3a-mediated p38 MAPK phosphorylation, suggesting that Wnt3a activates p38 MAPK through LRP5/6-independent signaling. On the other hand, pretreatment with p38 MAPK inhibitors had no effects on the phosphorylated status of GSK3β and β-catenin as well as β-catenin nuclear translocation, but inhibited Wnt3a-mediated β-catenin transcriptional activity. These findings suggest that p38 MAPK modulates canonical Wnt signaling at the β-catenin transcriptional level without any crosstalk with the Wnt3a-mediated LRP5/6-GSK3β signaling axis and subsequent β-catenin nuclear translocation. These findings expand our knowledge of the mechanisms controlling periodontal development and regeneration.

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.

p38 MAPK Signaling in Osteoblast Differentiation

The skeleton is a highly dynamic tissue whose structure relies on the balance between bone deposition and resorption. This equilibrium, which depends on osteoblast and osteoclast functions, is controlled by multiple factors that can be modulated post-translationally. Some of the modulators are Mitogen-activated kinases (MAPKs), whose role has been studied in vivo and in vitro. p38-MAPK modifies the transactivation ability of some key transcription factors in chondrocytes, osteoblasts and osteoclasts, which affects their differentiation and function. Several commercially available inhibitors have helped to determine p38 action on these processes. Although it is frequently mentioned in the literature, this chemical approach is not always as accurate as it should be. Conditional knockouts are a useful genetic tool that could unravel the role of p38 in shaping the skeleton. In this review, we will summarize the state of the art on p38 activity during osteoblast differentiation and function, and emphasize the triggers of this MAPK.

TAK1 determines susceptibility to endoplasmic reticulum stress and leptin resistance in the hypothalamus

Sustained endoplasmic reticulum (ER) stress disrupts normal cellular homeostasis and leads to the development of many types of human diseases, including metabolic disorders. TAK1 (also known as MAP3K7) is a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family and is activated by a diverse set of inflammatory stimuli. Here, we demonstrate that TAK1 regulates ER stress and metabolic signaling through modulation of lipid biogenesis. We found that deletion of Tak1 increased ER volume and facilitated ER-stress tolerance in cultured cells, which was mediated by upregulation of sterol-regulatory-element-binding protein (SREBP)-dependent lipogenesis. In the in vivo setting, central nervous system (CNS)-specific Tak1 deletion upregulated SREBP-target lipogenic genes and blocked ER stress in the hypothalamus. Furthermore, CNS-specific Tak1 deletion prevented ER-stress-induced hypothalamic leptin resistance and hyperphagic obesity under a high-fat diet (HFD). Thus, TAK1 is a crucial regulator of ER stress in vivo, which could be a target for alleviation of ER stress and its associated disease conditions.

p38γ and δ promote heart hypertrophy by targeting the mTOR-inhibitory protein DEPTOR for degradation

Disrupted organ growth leads to disease development. Hypertrophy underlies postnatal heart growth and is triggered after stress, but the molecular mechanisms involved in these processes are largely unknown. Here we show that cardiac activation of p38γ and p38δ increases during postnatal development and by hypertrophy-inducing stimuli. p38γ/δ promote cardiac hypertrophy by phosphorylating the mTORC1 and mTORC2 inhibitor DEPTOR, which leads to its degradation and mTOR activation. Hearts from mice lacking one or both kinases are below normal size, have high levels of DEPTOR, low activity of the mTOR pathway and reduced protein synthesis. The phenotype of p38γ/δ^−/− mice is reverted by overactivation of mTOR with amino acids, shRNA-mediated knockdown of Deptor, or cardiomyocyte overexpression of active p38γ and p38δ. Moreover, in WT mice, heart weight is reduced by cardiac overexpression of DEPTOR. Our results demonstrate that p38γ/δ control heart growth by modulating mTOR pathway through DEPTOR phosphorylation and subsequent degradation.

mTOR signalling pathway is a critical regulator of cardiac hypertrophy. Here the authors show that two kinases, p38γ and p38δ, control heart growth by promoting mTOR activity via phosphorylation and consequent proteasome degradation of mTOR inhibitor DEPTOR, extending our knowledge of cardiac hypertrophy regulation.

The Stress Kinase p38α as a Target for Cancer Therapy

p38α is a ubiquitous protein kinase strongly activated by stress signals, inflammatory cytokines, and many other stimuli, which has been implicated in the modulation of multiple cellular processes. There is good evidence in the literature that p38α plays an important tumor-suppressor role by interfering with malignant cell transformation. This is mainly based on the ability of the p38α pathway to regulate tissue homeostasis by integrating signals that balance cell proliferation and differentiation or induce apoptosis. However, recent reports have also illustrated protumorigenic functions for p38α. Thus, p38α signaling may facilitate the survival and proliferation of tumor cells contributing to the progression of some tumor types. In addition, p38α activation helps tumor cells to survive chemotherapeutic treatments. In all these cases, the inhibition of p38α has a potential therapeutic interest. Further elucidation of the context-dependent functions of p38α signaling in tumoral processes is of obvious importance for the use of inhibitors of this pathway in cancer therapy.

Roles of p38α mitogen-activated protein kinase in mouse models of inflammatory diseases and cancer

The p38α mitogen‐activated protein kinase pathway not only regulates the production of inflammatory mediators, but also controls processes related to tissue homeostasis, such as cell proliferation, differentiation and survival, which are often disrupted during malignant transformation. The versatility of this signaling pathway allows for the regulation of many specific functions depending on the cell type and context. Here, we discuss mouse models that have been used to identify in vivo functions of p38α signaling in the pathogenesis of inflammatory diseases and cancer. Experiments using genetically modified mice and pharmacological inhibitors support that targeting the p38α pathway could be therapeutically useful for some inflammatory diseases and tumor types.

MAP Kinase Cascades in Antigen Receptor Signaling and Physiology

Mitogen-activated protein kinases (MAPKs) play roles in a cell type and context-dependent manner to convert extracellular stimuli to a variety of cellular responses, thereby directing cells to proliferation, differentiation, survival, apoptosis, and migration. Studies of genetically engineered mice or chemical inhibitors specific to each MAPK signaling pathway revealed that MAPKs have various, but non-redundant physiologically important roles among different families. MAPK cascades are obviously integrated in the B cell receptor signaling pathways as critical components to drive B cell-mediated immunity.

The formation of proximal and distal definitive endoderm populations in culture requires p38 MAPK activity

Endoderm formation in the mammal is a complex process with two lineages forming during the first weeks of development, the primitive (or extraembryonic) endoderm, which is specified in the blastocyst, and the definitive endoderm that forms later, at gastrulation, as one of the germ layers of the embryo proper. Fate mapping evidence suggests that the definitive endoderm arises as two waves, which potentially reflect two distinct cell populations. Early primitive ectoderm-like (EPL) cell differentiation has been used successfully to identify and characterise mechanisms regulating molecular gastrulation and lineage choice during differentiation. The roles of the p38 MAPK family in the formation of definitive endoderm were investigated using EPL cells and chemical inhibitors of p38 MAPK activity. These approaches define a role for p38 MAPK activity in the formation of the primitive streak and a second role in the formation of the definitive endoderm. Characterisation of the definitive endoderm populations formed from EPL cells demonstrates the formation of two distinct populations, defined by gene expression and ontogeny, that were analogous to the proximal and distal definitive endoderm populations of the embryo. Formation of the proximal definitive endoderm was found to require p38 MAPK activity and is correlated with molecular gastrulation, defined by the expression of brachyury (T). Distal definitive endoderm formation also requires p38 MAPK activity but can form when T expression is inhibited. Understanding lineage complexity will be a prerequisite for the generation of endoderm derivatives for commercial and clinical use.

Mitochondrial p38β and manganese superoxide dismutase interaction mediated by estrogen in cardiomyocytes

Aims

While etiology behind the observed acceleration of ischemic heart disease in postmenopausal women is poorly understood, collective scientific data suggest cardioprotective effects of the endogenous female sex hormone, estrogen. We have previously shown that 17β-estradiol (E2) protects cardiomyocytes exposed to hypoxia-reoxygenation (H/R) by inhibiting p38α - p53 signaling in apoptosis and activating pro-survival p38β mitogen activated protein kinase (p38β MAPK), leading to suppression of reactive oxygen species (ROS) post H/R. However, little is known about the mechanism behind the antioxidant actions of E2-dependent p38β. The aim of this study is to determine whether the cytoprotection by estrogen involves regulation of manganese superoxide dismutase (MnSOD), a major mitochondrial ROS scavenging enzyme, via cardiac p38β.

Methods and Results

We identified mitochondrial p38β by immunocytochemistry and by immunoblotting in mitochondria isolated from neonatal cardiomyocytes of Sprague-Dawley rats. E2 facilitated the mitochondrial localization of the active form of the kinase, phosphorylated p38β (p-p38β). E2 also reduced the H/R-induced mitochondrial membrane potential decline, augmented the MnSOD activity and suppressed anion superoxide generation, while the dismutase protein expression remained unaltered. Co-immunoprecipitation studies showed physical association between MnSOD and p38β. p38β phosphorylated MnSOD in an E2-dependent manner in in-vitro kinase assays.

Conclusion

This work demonstrates for the first time a mitochondrial pool of active p38β and E2-mediated phosphorylation of MnSOD by the kinase. The results shed light on the mechanism behind the cytoprotective actions of E2 in cardiomyocytes under oxidative stress.

Inhibition of p38 MAPK sensitizes tumour cells to cisplatin-induced apoptosis mediated by reactive oxygen species and JNK

The p38 MAPK pathway is an important regulator of many cellular responses. It is well established that p38 MAPK signalling negatively regulates epithelial cell transformation, but enhanced p38 MAPK activity has been also correlated with bad clinical prognosis in some tumour types. Here, we provide genetic and pharmacological evidence showing that p38 MAPK inhibition cooperates with the chemotherapeutic agent cisplatin to kill tumour cells. We show that p38 MAPK inhibition results in ROS upregulation, which in turn activates the JNK pathway via inactivation of phosphatases, sensitizing human tumour cells to cisplatin-induced apoptosis. Using a mouse model for breast cancer, we confirm that inhibition of p38 MAPK cooperates with cisplatin treatment to reduce tumour size and malignancy in vivo. Taken together, our results illustrate a new function of p38 MAPK that helps tumour cells to survive chemotherapeutic drug treatments, and reveal that the combination of p38 MAPK inhibitors with cisplatin can be potentially exploited for cancer therapy.

Mitogen-activated protein kinase pathways in osteoblasts

Mitogen-activated protein kinases (MAPKs) are ancient signal transducers well characterized as mediators of inflammation and neoplastic transformation. Recent work has expanded our understanding of their developmental functions, particularly in the regulation of bone mass via control of osteoblast differentiation. Here, we review the functions of MAPK pathways in osteoblasts, including a consideration of MAPK substrates. In particular, MAPKs function to regulate the key transcriptional mediators of osteoblast differentiation, with ERK and p38 MAPKs phosphorylating RUNX2, the master regulator of osteoblast differentiation. ERK also activates RSK2, which in turn phosphorylates ATF4, a transcriptional regulator of late-stage osteoblast synthetic functions. The MAP3Ks and MAP2Ks upstream of MAPKs have also been investigated, and significant differences have been found in the wiring of MAPK pathways in osteoblasts relative to other tissues. Thus, the investigation of MAPKs in osteoblasts has both revealed critical mechanisms for the maintenance of bone mass and added to our understanding of how the individual components of MAPK pathways function in concert in a complex in vivo system.

Met acts through Abl to regulate p53 transcriptional outcomes and cell survival in the developing liver

BACKGROUND & AIMS

Genetic studies indicate that distinct signaling modulators are each necessary but not individually sufficient for embryonic hepatocyte survival in vivo. Nevertheless, how signaling players are interconnected into functional circuits and how they coordinate the balance of cell survival and death in developing livers are still major unresolved issues. In the present study, we examined the modulation of the p53 pathway by HGF/Met in embryonic livers.

METHODS

We combined pharmacological and genetic approaches to biochemically and functionally evaluate p53 pathway modulation in primary embryonic hepatocytes and in developing livers. RT-PCR arrays were applied to investigate the selectivity of p53 transcriptional response triggered by Met.

RESULTS

Met recruits p53 to regulate the liver developmental program, by qualitatively modulating its transcriptional properties: turning on the Mdm2 survival gene, while keeping death and cell-cycle arrest genes Pmaip1 and p21 silent. We investigated the mechanism leading to p53 regulation by Met and found that Abl and p38MAPK are required for p53 phosphorylation on S(389), Mdm2 upregulation, and hepatocyte survival. Alteration of this signaling mechanism switches p53 properties, leading to p53-dependent cell death in embryonic livers. RT-PCR array studies affirmed the ability of the Met-Abl-p53 axis to modulate the expression of distinct genes that can be regulated by p53.

CONCLUSIONS

A signaling circuit involving Abl and p38MAPK is required downstream of Met for the survival of embryonic hepatocytes, via qualitative regulation of the p53 transcriptional response, by switching its proapoptotic into survival properties.

p38α mitogen-activated protein kinase depletion and repression of signal transduction to translation machinery by miR-124 and -128 in neurons

The p38α to p38δ mitogen-activated protein kinases (MAPKs) are central regulatory nodes coordinating acute stress and inflammatory responses. Their activation leads to rapid adjustment of protein synthesis, for instance translational induction of proinflammatory cytokines. The only known direct link of p38 to translation machinery is the MAPK signal-integrating kinase Mnk. Only p38α and p38β transcripts are ubiquitously expressed. These mRNAs encode highly conserved proteins that equally phosphorylate recombinant Mnk1 in vitro. We discovered that expression of the p38α protein, but not the p38β isoform, is suppressed in the brain. This is due to p38α depletion by two neuron-selective microRNAs (miRNAs), miR-124 and -128. Suppression of p38α protein was reversed by miR-124/-128 antisense oligonucleotides in primary explant neuronal cultures. Targeted p38α depletion reduced Mnk1 activation, which cannot be compensated by p38β. Our research shows that p38α alone controls acute stress and cytokine signaling from p38 MAPK to translation machinery. This regulatory axis is greatly diminished in neurons, which may insulate brain physiology and function from p38α-Mnk1-mediated signaling.

Gadd45γ and Map3k4 interactions regulate mouse testis determination via p38 MAPK-mediated control of Sry expression

Loss of the kinase MAP3K4 causes mouse embryonic gonadal sex reversal due to reduced expression of the testis-determining gene, Sry. However, because of widespread expression of MAP3K4, the cellular basis of this misregulation was unclear. Here, we show that mice lacking Gadd45γ also exhibit XY gonadal sex reversal caused by disruption to Sry expression. Gadd45γ is expressed in a dynamic fashion in somatic cells of the developing gonads from 10.5 days postcoitum (dpc) to 12.5 dpc. Gadd45γ and Map3k4 genetically interact during sex determination, and transgenic overexpression of Map3k4 rescues gonadal defects in Gadd45γ-deficient embryos. Sex reversal in both mutants is associated with reduced phosphorylation of p38 MAPK and GATA4. In addition, embryos lacking both p38α and p38β also exhibit XY gonadal sex reversal. Taken together, our data suggest a requirement for GADD45γ in promoting MAP3K4-mediated activation of p38 MAPK signaling in embryonic gonadal somatic cells for testis determination in the mouse.

Genetic evidence for critical roles of P38α protein in regulating mast cell differentiation and chemotaxis through distinct mechanisms

Mast cells mediate a range of immune responses. However, the mechanisms that contribute to their development remain poorly understood. Here, using a P38α conditional knockout system, we provide evidence to suggest that P38α plays critical roles in regulating mast cell differentiation and migration via distinct mechanisms. Induced deletion of P38α in bone marrow cells retards the maturation of mast cells in part by inhibiting the activation of cAMP response element-binding protein and expression of microphthalmia-associated transcription factor, which encourages the generation of basophils over mast cells. In fully differentiated mast cells, absence of P38α inhibits stem cell factor-induced activation of Akt and ERK, which is associated with reduced chemotaxis. In vivo, conditional deletion of P38α results in reduced numbers of mast cells in certain tissues and a failure to reconstitute these cells in W(sh) mice transplanted with P38α(-/-) Lin(-)c-kit(+)Sca-1(+) (LKS(+)) cells. Our findings suggest that P38α plays a dual role in mast cell development by regulating IL-3-induced differentiation of mast cell progenitor cells as well as by regulating stem cell factor-induced migration of fully differentiated mast cells.