Characterization of the structure and function of the fourth member of p38 group mitogen-activated protein kinases, p38delta

Conformational bias imposed by source microseeds results in structural ambiguity

The p38 MAP kinase pathway is an essential component of numerous cellular signalling networks which are usually activated in response to extracellular environmental stress conditions. In addition to the canonical activation, several alternative activation pathways have been identified for p38; one of these, in which p38 is initially phosphorylated on Tyr323 and consequently autoactivated, is exclusive to T cells and is induced by TCR activation. Intrinsically active and inactive mutants at position 323 have been developed in order to evaluate the structural changes that occur upon TCR-induced activation. In order to promote crystal growth, cross streak-seeding techniques were utilized. This technique has gained popularity in promoting crystal growth when spontaneous nucleation induces critical defects or is being entirely hindered. The crystal characteristics of some mutants were highly similar to those of the wild-type source seeds (form A). In contrast, other mutants crystallized spontaneously with a different space group and molecular packing (form B). One of the active mutants (Y323T) crystallized in both crystal forms, displaying different packing characteristics and significant differences in molecular conformation that were clearly dictated by the source seeds. This implies that the source seeds used in cross streak-seeding could, in some cases, impose bias on the structural outcome of the studied molecule. Such incidents could occur when the conformational freedom permits crystal packing while not reflecting the authentic structure.

Phosphorylation of Raptor by p38beta participates in arsenite-induced mammalian target of rapamycin complex 1 (mTORC1) activation

Cell growth is influenced by environmental stress. Mammalian target of rapamycin (mTOR), the central regulator of cell growth, can be positively or negatively regulated by various stresses through different mechanisms. The p38 MAP kinase pathway is essential in cellular stress responses. Activation of MK2, a downstream kinase of p38α, enhances mTOR complex 1 (mTORC1) activity by preventing TSC2 from inhibiting mTOR activation. The p38β-PRAK cascade targets Rheb to inhibit mTORC1 activity upon glucose depletion. Here we show the activation of p38β participates in activation of mTOR complex 1 (mTORC1) induced by arsenite but not insulin, nutrients, anisomycin, or H(2)O(2). Arsenite treatment of cells activates p38β and induces interaction between p38β and Raptor, a regulatory component of mTORC1, resulting in phosphorylation of Raptor on Ser(863) and Ser(771). The phosphorylation of Raptor on these sites enhances mTORC1 activity, and contributes largely to arsenite-induced mTORC1 activation. Our results shown here and in previous work demonstrate that the p38 pathway can regulate different components of the mTORC1 pathway, and that p38β can target different substrates to either positively or negatively regulate mTORC1 activation when a cell encounters different environmental stresses.

Rac1/osmosensing scaffold for MEKK3 contributes via phospholipase C-gamma1 to activation of the osmoprotective transcription factor NFAT5

Separate reports that hypertonicity activates p38 via a Rac1-OSM-MEKK3-MKK3-p38 pathway and that p38α contributes to activation of TonEBP/OREBP led us to the hypothesis that Rac1 might activate TonEBP/OREBP via p38. The present studies examine that possibility. High NaCl is hypertonic. We find that siRNA knockdown of Rac1 reduces high NaCl-induced increase of TonEBP/OREBP transcriptional activity (by reducing its transactivating activity but not its nuclear localization). Similarly, siRNA knockdown of osmosensing scaffold for MEKK3 (OSM) also reduces high NaCl-dependent TonEBP/OREBP transcriptional and transactivating activities. Simultaneous siRNA knockdown of Rac1 and OSM is not additive in reduction of TonEBP/OREBP transcriptional activity, indicating a common pathway. However, siRNA knockdown of MKK3 does not reduce TonEBP/OREBP transcriptional activity, although siRNA knockdown of MKK6 does. Nevertheless, the effect of Rac1 on TonEBP/OREBP is also independent of MKK6 because it occurs in MKK6-null cells. Furthermore, we find that siRNA knockdown of Rac1 or OSM actually increases activity (phosphorylation) of p38, rather than decreasing it, as previously reported. Thus, the effect of Rac1 on TonEBP/OREBP is independent of p38. We find instead that phospholipase C-γ1 (PLC-γ1) is involved. When transfected into PLC-γ1-null mouse embryonic fibroblast cells, catalytically active Rac1 does not increase TonEBP/OREBP transcriptional activity unless PLC-γ1 is reconstituted. Similarly, dominant-negative Rac1 also does not inhibit TonEBP/OREBP in PLC-γ1-null cells unless PLC-γ1 is reconstituted. We conclude that Rac1/OSM supports TonEBP/OREBP activity and that this activity is mediated via PLC-γ1, not p38.

Distinct regulation of B-type natriuretic peptide transcription by p38 MAPK isoforms

Persistent controversy underlies the functional roles of specific p38 MAPK isoforms in cardiac biology and regulation of hypertrophy-associated genes. Here we show that adenoviral gene transfer of p38β but not p38α increased B-type natriuretic peptide (BNP) mRNA levels in vitro as well as atrial natriuretic peptide mRNA levels both in vitro and in vivo. Overexpression of p38α, in turn, augmented the expression fibrosis-related genes connective tissue growth factor, basic fibroblast growth factor and matrix metalloproteinase-9 both in vitro and in vivo. p38β-induced BNP transcription was diminished by mutation of GATA-4 binding site, whereas overexpression of MKK6b, an upstream regulator of p38α and p38β, activated BNP transcription through both GATA-4 and AP-1. Overexpression of MKK3, upstream regulator of p38α, induced BNP transcription independently from AP-1 and GATA-4. These data provide new evidence for diversity in downstream targets and functional roles of p38 pathway kinases in regulation of hypertrophy-associated cardiac genes.

Inactivation of Rheb by PRAK-mediated phosphorylation is essential for energy-depletion-induced suppression of mTORC1

Cell growth can be suppressed by stressful environments, but the role of stress pathways in this process is largely unknown. Here we show that a cascade of p38β mitogen-activated protein kinase (MAPK) and p38-regulated/activated kinase (PRAK) plays a role in energy-starvation-induced suppression of mammalian target of rapamycin (mTOR), and that energy starvation activates the p38β-PRAK cascade. Depletion of p38β or PRAK diminishes the suppression of mTOR complex 1 (mTORC1) and reduction of cell size induced by energy starvation. We show that p38β-PRAK operates independently of the known mTORC1 inactivation pathways--phosphorylation of tuberous sclerosis protein 2 (TSC2) and Raptor by AMP-activated protein kinase (AMPK)--and surprisingly, that PRAK directly regulates Ras homologue enriched in brain (Rheb), a key component of the mTORC1 pathway, by phosphorylation. Phosphorylation of Rheb at Ser 130 by PRAK impairs the nucleotide-binding ability of Rheb and inhibits Rheb-mediated mTORC1 activation. The direct regulation of Rheb by PRAK integrates a stress pathway with the mTORC1 pathway in response to energy depletion.

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.

p38 MAPK activation is downstream of the loss of intercellular adhesion in pemphigus vulgaris

Pemphigus vulgaris (PV) is a potentially fatal blistering disease characterized by autoantibodies against the desmosomal adhesion protein desmoglein (Dsg) 3. Whether autoantibody steric hindrance or signaling through pathways such as p38 MAPK is primary in disease pathogenesis is controversial. PV mAbs that cause endocytosis of Dsg3 but do not dissociate keratinocytes because of compensatory adhesion by Dsg1 do not activate p38. The same mAbs plus exfoliative toxin to inactivate Dsg1 but not exfoliative toxin alone activate p38, suggesting that p38 activation is secondary to loss of adhesion. Mice with epidermal p38α deficiency blister after passive transfer of PV mAbs; however, acantholytic cells retain cell surface Dsg3 compared with wild-type mice. In cultured keratinocytes, p38 knockdown prevents loss of desmosomal Dsg3 by PV mAbs, and exogenous p38 activation causes internalization of Dsg3, desmocollin 3, and desmoplakin. p38α MAPK is therefore not required for the loss of intercellular adhesion in PV, but may function downstream to augment blistering via Dsg3 endocytosis. Treatments aimed at increasing keratinocyte adhesion could be used in conjunction with immunosuppressive agents, potentially leading to safer and more effective combination therapy regimens.

p38gamma mitogen-activated protein kinase suppresses chondrocyte production of MMP-13 in response to catabolic stimulation

OBJECTIVE

The signaling protein p38 mitogen-activated protein kinase is required for inflammatory signaling in chondrocytes that regulates matrix metalloproteinase (MMP) production. We sought to determine the role of specific p38 isoforms in chondrocyte catabolic signaling in response to IL-1beta and fibronectin fragments (Fn-f).

METHODS

Human articular chondrocytes isolated from normal ankle cartilage from tissue donors or from osteoarthritic knee cartilage obtained during knee replacement were stimulated with IL-1beta or Fn-f, with or without pretreatment with p38 inhibitors (SB203580 or BIRB796) or growth factors (IGF-1 and OP-1). p38 isoform phosphorylation was measured by antibody array and immunoblotting. MMP-13 expression was measured by real-time polymerase chain reaction (PCR), enzyme-linked immunosorbent assay (ELISA), and immunoblotting. Chondrocytes were transfected with plasmids expressing constitutively active (CA) p38gamma or with adenovirus expressing dominant negative (DN) p38gamma.

RESULTS

Stimulation of chondrocytes with either IL-1beta or Fn-f led to enhanced phosphorylation of p38alpha and p38gamma, with little phosphorylation of p38beta or p38delta isoforms. p38alpha localized to the nucleus and p38gamma to the cytosol. Inhibition of both p38alpha and p38gamma with BIRB796 resulted in less inhibition of MMP-13 production in response to IL-1beta or FN-f than did inhibition of only p38alpha with SB203580. Transfection with CA p38gamma resulted in decreased MMP-13 production while transduction with DN p38gamma resulted in increased MMP-13 production. IGF-1 and OP-1 pretreatment inhibited p38alpha phosphorylation but not p38gamma phosphorylation.

CONCLUSIONS

p38gamma is activated by catabolic stimulation of human articular chondrocytes, but interestingly suppresses MMP-13 production. Treatments that increase p38gamma activation may be of therapeutic benefit in reducing chondrocyte production of MMP-13.

Oestrogen prevents cardiomyocyte apoptosis by suppressing p38α-mediated activation of p53 and by down-regulating p53 inhibition on p38β

AIMS

we have previously shown that 17-β-estradiol (E2) protects cardiomyocytes exposed to simulated ischaemia-reperfusion (I/R) by differentially regulating pro-apoptotic p38α mitogen-activated protein kinase (p38α MAPK) and pro-survival p38β. However, little is known about how E2 modulation of these kinases alters apoptotic signalling. An attractive downstream target is p53, a well-known mediator of apoptosis and a substrate of p38α MAPK. The aim of this study was to determine whether the cytoprotective actions of oestrogen involve regulation of p53 via cardiac p38 MAPKs.

METHODS AND RESULTS

cultured rat cardiomyocytes underwent hypoxia followed by reoxygenation (H/R) to simulate I/R. We found that inhibiting p53 significantly reduced apoptosis. Phosphorylation of p53 at serine 15 [p-p53(S15)] increased after H/R in a p38α MAPK- and reactive oxygen species (ROS)-dependent manner. E2 at 10 nM effectively inhibited p-p53(S15) and mitochondrial translocation of p53. Blocking p53 led to augmented p38β activity and attenuated ROS, suggesting suppression of this antioxidant kinase by p53. The use of a specific agonist for each oestrogen receptor (ER) isoform, ERα and ERβ, demonstrated that both isoforms participate in preventing cell death by inhibiting p53 in the mitochondria-centred apoptotic processes.

CONCLUSION

our results demonstrate that during H/R stress, cardiomyocytes undergo p53-dependent apoptosis following phosphorylation of p53 by p38α MAPK, leading to p38β suppression. E2 protects cardiomyocytes by inhibiting p38α-p53 signalling in apoptosis.

Mechanisms and functions of p38 MAPK signalling

The p38 MAPK (mitogen-activated protein kinase) signalling pathway allows cells to interpret a wide range of external signals and respond appropriately by generating a plethora of different biological effects. The diversity and specificity in cellular outcomes is achieved with an apparently simple linear architecture of the pathway, consisting of a core of three protein kinases acting sequentially. In the present review, we dissect the molecular mechanisms underlying p38 MAPK functions, with special emphasis on the activation and regulation of the core kinases, the interplay with other signalling pathways and the nature of p38 MAPK substrates as a source of functional diversity. Finally, we discuss how genetic mouse models are facilitating the identification of physiological functions for p38 MAPKs, which may impinge on their eventual use as therapeutic targets.

Alcohol withdrawal and brain injuries: beyond classical mechanisms

Unmanaged sudden withdrawal from the excessive consumption of alcohol (ethanol) adversely alters neuronal integrity in vulnerable brain regions such as the cerebellum, hippocampus, or cortex. In addition to well known hyperexcitatory neurotransmissions, ethanol withdrawal (EW) provokes the intense generation of reactive oxygen species (ROS) and the activation of stress-responding protein kinases, which are the focus of this review article. EW also inflicts mitochondrial membranes/membrane potential, perturbs redox balance, and suppresses mitochondrial enzymes, all of which impair a fundamental function of mitochondria. Moreover, EW acts as an age-provoking stressor. The vulnerable age to EW stress is not necessarily the oldest age and varies depending upon the target molecule of EW. A major female sex steroid, 17β-estradiol (E2), interferes with the EW-induced alteration of oxidative signaling pathways and thereby protects neurons, mitochondria, and behaviors. The current review attempts to provide integrated information at the levels of oxidative signaling mechanisms by which EW provokes brain injuries and E2 protects against it.

The degree of p70 S6k and S6 phosphorylation in human skeletal muscle in response to resistance exercise depends on the training volume

Regular performance of resistance exercise induces an increase in skeletal muscle mass, however, the molecular mechanisms underlying this effect are not yet fully understood. The purpose of the present investigation was to examine acute changes in molecular signalling in response to resistance exercise involving different training volumes. Eight untrained male subjects carried out one, three and five sets of 6 repetition maximum (RM) in leg press exercise in a random order. Muscle biopsies were taken from the vastus lateralis both prior to and 30 min after each training session and the effect on protein signalling was studied. Phosphorylation of Akt was not altered significantly after any of the training protocols, whereas that of the mammalian target of rapamycin was enhanced to a similar extent by training at all three volumes. The phosphorylation of p70S6 kinase (p70(S6k)) was elevated threefold after 3 × 6 RM and sixfold after 5 × 6 RM, while the phosphorylation of S6 was increased 30- and 55-fold following the 3 × 6 RM and 5 × 6 RM exercises, respectively. Moreover, the level of the phosphorylated form of the gamma isoform of p38 MAPK was enhanced three to fourfold following each of the three protocols, whereas phosphorylation of ERK1/2 was unchanged 30 min following exercise. These findings indicate that when exercise is performed in a fasted state, the increase in phosphorylation of signalling molecules such as p70(S6k) and the S6 ribosomal protein in human muscle depends on the exercise volume.

The binding of actin to p38 MAPK and inhibiting its kinase activity in vitro

p38 MAP kinase mediates a signal pathway that is involved in many physiological and pathological processes such as inflammation, cellular stress, apoptosis, cell cycle and growth, ischemia/re-perfusion, and myocardium hypertrophy. To determine the molecular and regulative mechanism of p38 signal pathway, we used in vitro binding methods to screen the proteins that interact with p38. Here we report two proteins from mouse macrophage RAW264.7 strain treated with lipopolysaccharide (LPS) or ultraviolet radiation (UV), binding directly to p38. One of them is beta-actin identified by peptide mass spectrum and ProFound program. Actin can inhibit the autophosphorylation of p38 and the phosphorylation of ATF by p38. It suggests that the binding of actin to p38 in vitro may represent a negative feedback to the kinase activity of p38, which leads to the regulation of p38 pathway and cellular function.

p38γ regulates UV-induced checkpoint signaling and repair of UV-induced DNA damage

In eukaryotic cells, DNA damage triggers activation of checkpoint signaling pathways that coordinate cell cycle arrest and repair of damaged DNA. These DNA damage responses serve to maintain genome stability and prevent accumulation of genetic mutations and development of cancer. The p38 MAPK was previously implicated in cellular responses to several types of DNA damage. However, the role of each of the four p38 isoforms and the mechanism for their involvement in DNA damage responses remained poorly understood. In this study, we demonstrate that p38γ, but not the other p38 isoforms, contributes to the survival of UV-treated cells. Deletion of p38γ sensitizes cells to UV exposure, accompanied by prolonged S phase cell cycle arrest and increased rate of apoptosis. Further investigation reveal that p38γ is essential for the optimal activation of the checkpoint signaling caused by UV, and for the efficient repair of UV-induced DNA damage. These findings have established a novel role of p38γ in UV-induced DNA damage responses, and suggested that p38γ contributes to the ability of cells to cope with UV exposure by regulating the checkpoint signaling pathways and the repair of damaged DNA.

Molecular distinction between physiological and pathological cardiac hypertrophy: experimental findings and therapeutic strategies

Cardiac hypertrophy can be defined as an increase in heart mass. Pathological cardiac hypertrophy (heart growth that occurs in settings of disease, e.g. hypertension) is a key risk factor for heart failure. Pathological hypertrophy is associated with increased interstitial fibrosis, cell death and cardiac dysfunction. In contrast, physiological cardiac hypertrophy (heart growth that occurs in response to chronic exercise training, i.e. the 'athlete's heart') is reversible and is characterized by normal cardiac morphology (i.e. no fibrosis or apoptosis) and normal or enhanced cardiac function. Given that there are clear functional, structural, metabolic and molecular differences between pathological and physiological hypertrophy, a key question in cardiovascular medicine is whether mechanisms responsible for enhancing function of the athlete's heart can be exploited to benefit patients with pathological hypertrophy and heart failure. This review summarizes key experimental findings that have contributed to our understanding of pathological and physiological heart growth. In particular, we focus on signaling pathways that play a causal role in the development of pathological and physiological hypertrophy. We discuss molecular mechanisms associated with features of cardiac hypertrophy, including protein synthesis, sarcomeric organization, fibrosis, cell death and energy metabolism and provide a summary of profiling studies that have examined genes, microRNAs and proteins that are differentially expressed in models of pathological and physiological hypertrophy. How gender and sex hormones affect cardiac hypertrophy is also discussed. Finally, we explore how knowledge of molecular mechanisms underlying pathological and physiological hypertrophy may influence therapeutic strategies for the treatment of cardiovascular disease and heart failure.

Cyclic AMP stimulates Mrp2 translocation by activating p38{alpha} MAPK in hepatic cells

Cyclic AMP (cAMP) induces translocation of multidrug resistant protein 2 (Mrp2) to the canalicular membrane and activates p38 MAPK in rat hepatocytes. In this study, we tested the hypothesis that cAMP-induced Mrp2 translocation may be mediated via p38 MAPK. Studies were conducted in rat hepatocytes and in a human hepatoma cell line, HuH-7. In rat hepatocytes, cAMP increased Mrp2 translocation and p38 MAPK activity. These effects of cAMP were inhibited by SB203580, an inhibitor of p38 MAPK. Wortmannin, a specific inhibitor of phosphoinositide-3-kinase (PI3K), did not inhibit cAMP induced activation of p38 MAPK, indicating PI3K-independent activation of p38 MAPK by cAMP. To further define the role of p38 MAPK, molecular approaches were used to up- or downregulate p38 MAPK activity in HuH-7 cells using constitutively active (CA) and dominant-negative (DN) MAPK kinase 3 and 6 (MKK3/6). MKK3/6 are upstream kinases responsible for the activation of p38 MAPK. Cells transfected with CAMKK6 showed increased p38 MAPK activity and MRP2 translocation compared with empty vector. cAMP-induced activation of p38 MAPK was inhibited in cells transfected with DNMKK3/6 and DNMKK3, but not with DNMKK6. DNMKK3/6 and DNMKK3 also inhibited cAMP-induced MRP2 translocation. cAMP selectively activated p38alpha MAPK in HuH-7 cells. Knockdown of p38alpha MAPK by short heterodimer RNA resulted in decreased level of p38 MAPK and failure of cAMP to stimulate MRP2 translocation. Taken together, these results suggest that cAMP-induced MRP2 translocation in hepatic cells is mediated via PI3K-independent and MKK3-mediated activation of p38alpha MAPK.

Ethanol withdrawal acts as an age-specific stressor to activate cerebellar p38 kinase

We investigated whether protein kinase p38 plays a role in the brain-aging changes associated with repeated ethanol withdrawal (EW). Ovariectomized young, middle-age and older rats, with or without 17β-estradiol (E2) implantation, received a 90-day ethanol with repeated withdrawal. They were tested for active pP38 expression in cerebellar Purkinje neurons and whole-cerebellar lysates using immunohistochemistry and enzyme-linked immunosorbent assay, respectively. They were also tested for the Rotarod task to determine the behavioral manifestation of cerebellar neuronal stress and for reactive oxygen species (ROS) and mitochondrial protein carbonyls to determine oxidative mechanisms. Middle-age EW rats showed higher levels of pP38-positive Purkinje neurons/cerebellar lysates, which coincided with increased mitochondrial protein oxidation than other diet/age groups. Exacerbated motor deficit due to age-EW combination also began at the middle-age. In comparison, ROS contents peaked in older EW rats. E2 treatment mitigated each of the EW effects to a different extent. Collectively, pP38 may mediate the brain-aging changes associated with pro-oxidant EW at vulnerable ages and in vulnerable neurons in a manner protected by estrogen.

Activation of p38 and determination of its activity

The p38 mitogen-activated protein kinase (MAPK) pathway plays an important role in cellular responses to inflammatory stimuli and environmental stresses. Extracellular stimuli activate kinases upstream of p38, such as MKK3 and MKK6, which subsequently phosphorylate p38. p38 then participates in numerous biological processes by phosphorylating its downstream substrates. Here, our methodology mainly highlights how endogenous or exogenous p38 can be activated and its upstream kinases and downstream substrates identified.

Astrocytes express Mxi2, a splice isoform of p38MAPK

Mitogen-activated protein kinases (MAPKs) are a superfamily of cytoplasmic serine/threonine kinases that transduce many types of extracellular stimuli into cellular responses. p38MAPK is a member of this family with its active form in a diphosphorylated state (p38MAPKdiP). Two strong anti-p38MAPKdiP immunoreactive bands (apparent molecular weight 38 and 34 kDa) were detected by Western blotting in cultured astrocytes. Using a specific antibody and employing immunoprecipitation procedures and SELDI-TOF analysis, the 34 kDa band was found to correspond to Mxi2, a splice variant of p38MAPK; cultured astrocytes therefore express Mxi2. Separate protein extractions of different subcellular fractions, and fluorescent immunovisualisation employing confocal microscopy, showed Mxi2 to have a non-nuclear, cytosolic distribution in the studied cells. ERK1/2, protein whose intracellular distribution is influenced by Mxi2, showed the same cytoplasmic pattern than Mxi2.

Differential activation of p38MAPK isoforms by MKK6 and MKK3

All four members of the mammalian p38 mitogen-activated protein kinase (MAPK) family (p38alpha, p38beta, p38gamma and p38delta) are activated by dual phosphorylation in the TGY motif in the activation loop. This phosphorylation is mediated by three kinases, MKK3, MKK6 and MKK4, at least in vitro. The role of these MKK in the activation of p38alpha has been demonstrated in studies using fibroblasts that lack MKK3 and/or MKK6. Nonetheless, the physiological upstream activators of the other p38MAPK isoforms have not yet been reported using MKK knockout cells. In this study, we examined p38beta, gamma and delta activation by MKK3 and MKK6, in cells lacking MKK3, MKK6 or both. We show that MKK3 and MKK6 are both essential for the activation of p38gamma and p38beta induced by environmental stress, whereas MKK6 is the major p38gamma activator in response to TNFalpha. In contrast, p38delta activation by ultraviolet radiation, hyperosmotic shock, anisomycin or by TNFalpha is mediated by MKK3. Moreover, in response to osmotic stress, MKK3 and MKK6 are crucial in regulating the phosphorylation of the p38gamma substrate hDlg and its activity as scaffold protein. These data indicate that activation of distinct p38MAPK isoforms is regulated by the selective and synchronized action of two kinases, MKK3 and MKK6, in response to cell stress.

p38 MAPK links oxidative stress to autophagy-related gene expression in cachectic muscle wasting

Oxidative stress is a primary trigger of cachectic muscle wasting, but the signaling pathway(s) that links it to the muscle wasting processes remains to be defined. Here, we report that activation of p38 mitogen-activated protein kinase (MAPK) (phosphorylation) and increased oxidative stress (trans-4-hydroxy-2-nonenal protein modification) in skeletal muscle occur as early as 8 h after lipopolysaccharide (1 mg/kg) and 24 h after dexamethasone (25 mg/kg) injection (intraperitoneal) in mice, concurrent with upregulation of autophagy-related genes, Atg6, Atg7, and Atg12. Treating cultured C2C12 myotubes with oxidant hydrogen peroxide (4 h) resulted in increased p38 phosphorylation and reduced FoxO3 phosphorylation along with induced Atg7 mRNA expression without activation of NF-kappaB or FoxO3a transcriptional activities. Furthermore, inhibition of p38alpha/beta by SB202190 blocked hydrogen peroxide-induced atrophy with diminished upregulation of Atg7 and atrogenes [muscle atrophy F-box protein (MAFbx/Atrogin-1), muscle ring finger protein 1 (MuRF-1), and Nedd4]. These findings provide direct evidence for p38alpha/beta MAPK in mediating oxidative stress-induced autophagy-related genes, suggesting that p38alpha/beta MAPK regulates both the ubiquitin-proteasome and the autophagy-lysosome systems in muscle wasting.

The role of ATF-2 family transcription factors in adipocyte differentiation: antiobesity effects of p38 inhibitors

ATF-2 is a member of the ATF/CREB family of transcription factors and is activated by stress-activated protein kinases, such as p38. To analyze the physiological role of ATF-2 family transcription factors, we have generated mice with mutations in Atf-2 and Cre-bpa, an Atf-2-related gene. The trans-heterozygotes of both mutants were lean and had reduced white adipose tissue (WAT). ATF-2 and CRE-BPa were required for bone morphogenetic protein 2 (BMP-2)-and p38-dependent induction of peroxisome proliferator-activated receptor gamma2 (PPARgamma2), a key transcription factor mediating adipocyte differentiation. Since stored fat supplies have been recognized as a possible target for antiobesity treatments, we tested whether inhibition of the p38-ATF-2 pathway suppresses adipocyte differentiation and leads to reduced WAT by treating mice with a p38 inhibitor for long periods of time. High-fat diet (HFD)-induced obesity was significantly reduced in mice fed the p38 inhibitor. Furthermore, the p38 inhibitor alleviated HFD-induced insulin resistance. In p38 inhibitor-treated mice, macrophage infiltration into WAT was reduced and the tumor necrosis factor alpha (TNF-alpha) levels were lower than control mice. Thus, p38 inhibitors may provide a novel antiobesity treatment.

Nemo-like kinase, an essential effector of anterior formation, functions downstream of p38 mitogen-activated protein kinase

Nemo-like kinase (NLK) is known to function as a mitogen-activated protein kinase (MAPK)-like kinase. However, the upstream molecules and molecular mechanisms that regulate NLK activity remain unclear. In the present study, we identified p38 MAPK as an upstream kinase and activator of NLK. p38 regulates the function of NLK via phosphorylation, and this modification can be abrogated by depletion of endogenous p38. In Xenopus laevis embryos, depletion of either p38beta or NLK by antisense morpholino oligonucleotides results in a severe defect in anterior development and impaired expression of endogenous anterior markers. It is notable that morphants of Xenopus p38alpha, another isoform of the p38 MAPK family, exhibited no obvious defects in anterior development. Defects in head formation or in the expression of anterior marker genes caused by suppression of endogenous p38beta expression could be rescued by expression of wild-type NLK but not by expression of mutant NLK lacking the p38beta phosphorylation site. In contrast, defects in head formation or in the expression of anterior marker genes caused by suppression of endogenous NLK expression could not be rescued by expression of p38. These results provide the first evidence that p38 specifically regulates NLK function, which is required for anterior formation in Xenopus development.

p38 Mitogen-activated protein kinase and hematologic malignancies

CONTEXT

p38 mitogen-activated protein kinase (MAPK) signaling has been implicated in responses ranging from apoptosis to cell cycle, induction of expression of cytokine genes, and differentiation. This plethora of activators conveys the complexity of the p38 pathway. This complexity is further complicated by the observation that the downstream effects of p38 MAPK activation may be different depending on types of stimuli, cell types, and various p38 MAPK isoforms involved.

OBJECTIVE

This review focuses on the recent advancement of the p38 MAPK isoforms as well as the roles of p38 MAPK in hematologic malignancies.

DATA SOURCES

Review of pertinent published literature and work in our laboratory.

CONCLUSIONS

In some hematologic malignancies, activation of p38 plays a key role in promoting or inhibiting proliferation and also in increasing resistance to chemotherapeutic agents. The importance of different p38 isoforms in various cellular functions has been acknowledged recently. Further understanding of these isoforms will allow the design of more specific inhibitors to target particular isoforms to maximize the treatment effect and minimize the side effects for treating hematopoietic malignancies.

P38 mitogen activated protein kinase expression and regulation by interleukin-4 in human B cell non-Hodgkin lymphomas

The prevalence and regulation of p38 mitogen activated protein kinase (MAPK) expression in human lymphomas have not been extensively studied. In order to elucidate the role of p38 MAPK in lymphomagenesis, we examined the expression of native and phosphorylated p38 (p-p38) MAPK in cell lines derived from human hematopoietic neoplasms including B cell lymphoma-derived cell lines using Western blot analysis. The p-p38 MAPK protein was also analyzed in 30 B cell non-Hodgkin lymphoma (NHL) tissue biopsies by immunohistochemistry. Our results show that the expression of p38 MAPK was up-regulated in most of the cell lines as compared with peripheral blood lymphocytes, while the expression of p-p38 MAPK was more variable. A subset of B cell NHL biopsies showed increased expression of p-p38 MAPK relative to reactive germinal center cells. Interleukin-4 (IL-4) induced a dose-dependent increase in the expression of p-p38 MAPK (1.6- to 2.8-fold) in cell lines derived from activated B cell-like diffuse large B cell lymphoma (DLBCL) but not those from germinal center-like DLBCL. No change was seen in native p38 MAPK. The in vitro kinase activity of p38 MAPK, however, was induced (1.6- to 3.2-fold) in all five cell lines by IL-4. Quantitative fluorescent RT-PCR demonstrated that all four isoforms of p38 MAPK gene were expressed in the lymphoma cell lines, with p38γ and p38β isoforms being predominant. IL-4 stimulation increased the expression of β, γ, and δ isoforms but not α isoform in two cell lines. In conclusion, there is constitutive expression and activation of p38 MAPK in a large number of B-lymphoma-derived cell lines and primary lymphoma tissues, supportive of its role in lymphomagenesis. The differential IL-4 regulation of p38 MAPK expression in cell lines derived from DLBCL may relate to the cellular origin of these neoplasms.

Studies of chirality effect of 4-(phenylamino)-pyrrolo[2,1-f][1,2,4]triazine on p38alpha by molecular dynamics simulations and free energy calculations

4-(Phenylamino)-pyrrolo[2,1-f][1,2,4]triazines have been discovered as inhibitors of p38alpha. Experimental assays have proven that the configuration of alpha-Me-benzyl connected with amide at C6 is essential for the binding affinity. The S-configured inhibitor (11j) displays 80 times more potency than the R-configured one (11k). Here we investigated the mechanism how different configurations influence the binding affinity using molecular dynamics simulations, free energy calculations and free energy decomposition analysis. We found that the van der Waals interactions play the most important role in differentiating the activities between 11j and 11k with p38alpha. The difference of the van der Waals interactions is primarily determined by two residues, LEU108 and LEU167. Consequently stabilization of pyrrolo[2,1-f][1,2,4]triazine ring is important for the activities of inhibitors. Meanwhile we observed that the different configuration of the alpha-Me-benzyl group leads to the difference of binding between 11j and 11k. In conclusion, our work shows that it is feasible to analyze the chirality effect of inhibitors with different configurations by molecular dynamics simulations and free energy calculations, and provides useful information for drug design.

p38(MAPK): stress responses from molecular mechanisms to therapeutics

The p38(MAPK) protein kinases affect a variety of intracellular responses, with well-recognized roles in inflammation, cell-cycle regulation, cell death, development, differentiation, senescence and tumorigenesis. In this review, we examine the regulatory and effector components of this pathway, focusing on their emerging roles in biological processes involved in different pathologies. We summarize how this pathway has been exploited for the development of therapeutics and discuss the potential obstacles of targeting this promiscuous protein kinase pathway for the treatment of different diseases. Furthermore, we discuss how the p38(MAPK) pathway might be best exploited for the development of more effective therapeutics with minimal side effects in a range of specific disease settings.

Advances in hepatic barrier function and injury

Hepatic barrier is a very important structure to protect hepar, and also considerable to protect liver's function. It can prevent endotoxin and virus from entering hepar to damage hepatocyte. The primary aim of this review is to introduce the research status of hepatic barrier and analyze its function and structure. We also introduce several kinds of factors that can induce the failure of the barrier's structure and function and some countermeasures that can resist this factors.

Kinases that control the cell cycle in response to DNA damage: Chk1, Chk2, and MK2

In response to DNA damage eukaryotic cells activate cell cycle checkpoints -- complex kinase signaling networks that prevent further progression through the cell cycle. Parallel to implementing a cell cycle arrest, checkpoint signaling also mediates the recruitment of DNA repair pathways. If the extent of damage exceeds repair capacity, additional signaling cascades are activated to ensure elimination of these damaged cells. The DNA damage response has traditionally been divided into two major kinase branches. The ATM/Chk2 module is activated after DNA double strand breaks and the ATR/Chk1 pathway responds primarily to DNA single strand breaks or bulky lesions. Both pathways converge on Cdc25, a positive regulator of cell cycle progression, which is inhibited by Chk1-mediated or Chk2-mediated phosphorylation. Recently a third effector kinase complex consisting of p38MAPK and MK2 has emerged. This pathway is activated downstream of ATM and ATR in response to DNA damage. MK2 has been shown to share substrate homology with both Chk1 and Chk2. Here we will discuss recent advances in our understanding of the eukaryotic DNA damage response with emphasis on the Chk1, Chk2, and the newly emerged effector kinases p38MAPK and MK2.

Acid beta-glucosidase 1 counteracts p38delta-dependent induction of interleukin-6: possible role for ceramide as an anti-inflammatory lipid

Activation of protein kinase C (PKC) by the phorbol ester (phorbol 12-myristate 13-acetate) induces ceramide formation through the salvage pathway involving, in part, acid beta-glucosidase 1 (GBA1), which cleaves glucosylceramide to ceramide. Here, we examine the role of the GBA1-ceramide pathway, in regulating a pro-inflammatory pathway initiated by PKC and leading to activation of p38 and induction of interleukin 6 (IL-6). Inhibition of ceramide formation by fumonisin B1 or down-regulation of PKCdelta potentiated PMA-induced activation of p38 in human breast cancer MCF-7 cells. Similarly, knockdown of GBA1 by small interfering RNAs or pharmacological inhibition of GBA1 promoted further activation of p38 after PMA treatment, implicating the GBA1-ceramide pathway in the termination of p38 activation. Knockdown of GBA1 also evoked the hyperproduction of IL-6 in response to 4beta phorbol 12-myristate 13-acetate. On the other hand, increasing cellular ceramide with cell-permeable ceramide treatment resulted in attenuation of the IL-6 response. Importantly, silencing the delta isoform of the p38 family significantly attenuated the hyperproduction of IL-6. Reciprocally, p38delta overexpression induced IL-6 biosynthesis. Thus, the GBA1-ceramide pathway is suggested to play an important role in terminating p38delta activation responsible for IL-6 biosynthesis. Furthermore, the p38delta isoform was identified as a novel and predominant target of ceramide signaling as well as a regulator of IL-6 biosynthesis.

p38alpha and p38gamma mediate oncogenic ras-induced senescence through differential mechanisms

Oncogene-induced senescence is a tumor-suppressive defense mechanism triggered upon activation of certain oncogenes in normal cells. Recently, the senescence response to oncogene activation has been shown to act as a bona fide barrier to cancer development in vivo. Multiple previous studies have implicated the importance of the p38 MAPK pathway in oncogene-induced senescence. However, the contribution of each of the four p38 isoforms (encoded by different genes) to senescence induction is unclear. In the current study, we demonstrated that p38alpha and p38gamma, but not p38beta, play an essential role in oncogenic ras-induced senescence. Both p38alpha and p38gamma are expressed in primary human fibroblasts and are activated upon transduction of oncogenic ras. Small hairpin RNA-mediated silencing of p38alpha or p38gamma expression abrogated ras-induced senescence, whereas constitutive activation of p38alpha and p38gamma caused premature senescence. Furthermore, upon activation by oncogenic ras, p38gamma stimulated the transcriptional activity of p53 by phosphorylating p53 at Ser(33), suggesting that the ability of p38gamma to mediate senescence is at least partly achieved through p53. However, p38alpha contributed to ras-inducted senescence via a p53-indepdendent mechanism in cells by mediating ras-induced expression of p16(INK4A), another key senescence effector. These findings have identified p38alpha and p38gamma as essential components of the signaling pathway that regulates the tumor-suppressing senescence response, providing insights into the molecular mechanisms underlying the differential involvement of the p38 isoforms in senescence induction.

Regulation of PKD by the MAPK p38delta in insulin secretion and glucose homeostasis

Dysfunction and loss of insulin-producing pancreatic beta cells represent hallmarks of diabetes mellitus. Here, we show that mice lacking the mitogen-activated protein kinase (MAPK) p38delta display improved glucose tolerance due to enhanced insulin secretion from pancreatic beta cells. Deletion of p38delta results in pronounced activation of protein kinase D (PKD), the latter of which we have identified as a pivotal regulator of stimulated insulin exocytosis. p38delta catalyzes an inhibitory phosphorylation of PKD1, thereby attenuating stimulated insulin secretion. In addition, p38delta null mice are protected against high-fat-feeding-induced insulin resistance and oxidative stress-mediated beta cell failure. Inhibition of PKD1 reverses enhanced insulin secretion from p38delta-deficient islets and glucose tolerance in p38delta null mice as well as their susceptibility to oxidative stress. In conclusion, the p38delta-PKD pathway integrates regulation of the insulin secretory capacity and survival of pancreatic beta cells, pointing to a pivotal role for this pathway in the development of overt diabetes mellitus.

Effects of a MAPK p38 inhibitor on lung function and airway inflammation in equine recurrent airway obstruction

REASONS FOR PERFORMING STUDY

It has been suggested that many of the beneficial effects of corticosteroids are mediated through mitogen-activated protein kinase (MAPK) p38 inhibition.

OBJECTIVE

To investigate the efficacy of the MAPK p38 inhibitor compound MRL-EQ1 to either prevent (Phase 1) or treat (Phase 2) recurrent airway obstruction (RAO) in horses.

METHODS

MRL-EQ1 was administered i.v. at a dosage of 0.75-1.5 mg/kg bwt q. 12 h. In Phase 1, susceptible horses in clinical remission were divided into 2 groups (n = 5/group), based on historical values of respiratory mechanics. All horses were entered in the study in pairs (one control, one treated horse) and exposed to the same environmental challenge (stabling, mouldy hay and dusty conditions). The treatment group received MRL-EQ1 for 14 days while the control horses were untreated during the same period. In Phase 2, affected horses were ranked by severity of respiratory dysfunction and split randomly into either dexamethasone or MRL-EQ1 treatment groups (n = 5/group). Bronchoalveolar lavage fluid, respiratory mechanic measurements, MRL-EQ1 plasma concentration and tumour necrosis factor (TNF) whole blood activity were evaluated sequentially.

RESULTS

In Phase 1, MRL-EQ1 did not prevent the occurrence of clinical signs and pulmonary inflammation. However, treatment was associated with a reduction in severity and a delay in the onset of signs and a reduction in pulmonary neutrophilia. In Phase 2, plasma concentrations achieved resulted in ex vivo suppression of lipopolysaccharide-induced TNF production in equine blood. MRL-EQ1 did not improve airway inflammation or lung function and was associated in a dose dependent manner with behavioural (depression, excitability) and blood changes (neutrophilia, increased serum muscle enzyme concentrations).

CONCLUSIONS

Inhibition of p38 in the horse was partially effective in reducing clinical signs and airway inflammation when administered prior to, but not during clinical exacerbation in RAO.

POTENTIAL RELEVANCE

Inhibitors of p38 MAPK with a better toxicity profile may be effective in the prevention or treatment of RAO.

Selective p38α mitogen-activated protein kinase inhibitor attenuates lung inflammation and fibrosis in IL-13 transgenic mouse model of asthma

p38 Mitogen-activated protein kinase (MAPK) plays a critical role in the activation of inflammatory cells. We investigated the anti-inflammatory effects of a p38α-selective MAPK inhibitor (SD-282) in a mouse transgenic (CC10:IL-13) asthma model. The CC-10-driven over-expression of IL-13 in the mouse lung/airway has been shown to result in a remarkable phenotype recatitulating many features of asthma and characterized by eosinophilic and mononuclear inflammation, with airway epithelial cell hypertrophy, mucus cell metaplasia, the hyperproduction of neutral and acidic mucus, the deposition of Charcot–Leyden-like crystal, and airway sub-epitheilial fibrosis. Here we show how activated p38 MAPK can be observed in the lungs at the onset of asthma ie, around 8 weeks of age in both female and male mice. We also show that administration of a p38α MAPK selective inhibitor, SD-282 at 30 or 90 mg/kg, twice a day for a period of four weeks beginning at the onset of asthma, significantly reduced the inflammation (p < 0.001); hyperplasia of airway epithelium (p < 0.05); goblet cell metaplasia and mucus hypersecretion (p < 0.001) and reduced lung remodeling and fibrosis (p < 0.01), alleviating the severity of lung damage as measured by a composite score (p < 0.05). Furthermore, SD-282 significantly reduced activated p38 MAPK in the lymphocytes and epithelial cells (p < 0.001). Simultaneously, identical studies were conducted with an anti-fibrotic TGFβR1 kinase inhibitor (SD-208) which demonstrated anti-fibrotic but not anti-inflammatory properties. These findings suggest that the p38α-selective MAPK inhibitor may have dual therapeutic potential in attenuating both the inflammatory component and the fibrotic component of asthma and other Th2-polarized inflammatory lung diseases.

An autocrine VEGF/VEGFR2 and p38 signaling loop confers resistance to 4-hydroxytamoxifen in MCF-7 breast cancer cells

Tamoxifen, a partial estrogen receptor antagonist, is part of the standard treatment of both primary and advanced breast cancers. However, significant proportions of breast cancers are either de novo resistant or develop tamoxifen resistance during the course of treatment through mechanisms which have been only partly characterized. We have previously found that high vascular endothelial growth factor (VEGF) or VEGF receptor 2 (VEGFR2) expression and concomitant high p38 mitogen-activated protein kinase activity within breast cancers predict a poor outcome for tamoxifen-treated patients. Here, we have molecularly dissected how VEGF/VEGFR2 and p38 are linked, and contribute to tamoxifen resistance within breast cancer using a MCF-7 BC cell model with different 4-hydroxytamoxifen (4-OHT) responsiveness. We report that MCF-7 breast cancer cell lines with tamoxifen resistance have increased secretion of VEGF and increased signaling through VEGFR2 compared with parental MCF-7 cells. 4-OHT treatment caused the ablation of VEGF secretion in parental MCF-7 cells, whereas in the tamoxifen-resistant subline, a VEGF/VEGFR2 signaling loop was still evident upon treatment. Increased basal levels of total and phosphorylated p38 were observed in tamoxifen-resistant cells. Pharmacologic inhibition of p38 reduced the proliferation of both tamoxifen-responsive and tamoxifen-resistant cells and showed an additive growth-inhibitory effect in combination with 4-OHT. A connection between VEGF/VEGFR2 and p38 signaling was identified by VEGF and VEGFR2 knockdown, which equally reduced both the total and the active forms of p38 in tamoxifen-resistant cells. Taken together, our results suggest that decreased sensitivity to 4-OHT is caused by a death-protecting VEGF/VEGFR2 and p38 growth factor loop in breast cancer cells. Inhibition of these signaling pathways may be beneficial to overcome tamoxifen resistance.

Cumulating researches on the relationship between P38 MAPK signaling pathway and gastric carcinoma

The cascade reaction of mitogen-activated protein kinases (MAPKs) is one of the vital intracellular signal transduction systems, participating in many physiological progressions, such as cell growth, proliferation, differentiation and apoptosis. P38 is a member of MAPKs, mediating many cell reactions induced by stress, inflammatory cytokines or bacterial products and playing a key role in the regulation of cell cycle. For different cell lines of gastric carcinoma, P38 has different functions. The same phenomenon can be seen when the cells are presented under different stimulus. P38 pathway may be one candidate target of cancer therapy.

p38beta2-mediated phosphorylation and sumoylation of ATF7 are mutually exclusive

The ubiquitous activating transcription factor (ATF) 7 binds as a homodimer to the cAMP response element/TPA response element motifs present in the promoters of its target genes. ATF7 is homologous to ATF2 and heterodimerizes with Jun or Fos proteins, modulating their DNA-binding specificities. We previously demonstrated that TAF12, a component of the TFIID general transcription factor, mediates ATF7 transcriptional activity through direct interactions between the two proteins. By contrast, ATF7, but not ATF2, is modified in vivo by sumoylation, which restricts its subcellular localization, thereby inhibiting its transcriptional activity. In the present study, we dissect the mechanism of this functional switch. We characterized the multisite phosphorylation of the ATF7 activation domain and identified one of the involved kinase, p38beta2 mitogen-activated protein kinase. In addition, we show that epidermal growth factor treatment results in a two-step modification mechanism of ATF7 activation domain. The Thr53 residue is phosphorylated first by a presently unknown kinase, allowing p38beta2 mitogen-activated protein kinase to modify the Thr51 residue, excluding the sumoylation of ATF7 protein. The resulting activation of transcription is related to an increased association of TAF12 with this phosphorylated form of ATF7. Our data therefore conclusively establish that sumoylation and phosphorylation of ATF7 are two antagonistic posttranslational modifications.

The kinase p38 alpha serves cell type-specific inflammatory functions in skin injury and coordinates pro- and anti-inflammatory gene expression

The mitogen-activated protein kinase p38 mediates cellular responses to injurious stress and immune signaling. Among the many p38 isoforms, p38 alpha is the most widely expressed in adult tissues and can be targeted by various pharmacological inhibitors. Here we investigated how p38 alpha activation is linked to cell type-specific outputs in mouse models of cutaneous inflammation. We found that both myeloid and epithelial p38 elicit inflammatory responses, yet p38 alpha signaling in each cell type served distinct inflammatory functions and varied depending on the mode of skin irritation. In addition, myeloid p38 alpha limited acute inflammation via activation of anti-inflammatory gene expression dependent on mitogen- and stress-activated kinases. Our results suggest a dual function for p38 alpha in the regulation of inflammation and show mixed potential for its inhibition as a therapeutic strategy.

Are MAP kinases drug targets? Yes, but difficult ones

Pharmaceutical companies are facing an increasing interest in new target identification and validation. In particular, extensive efforts are being made in the field of protein kinase inhibitors research and development, and the past ten years of effort in this field have altered our perception of the potential of kinases as drug targets. Therefore, in the drug discovery process, the selection of relevant, susceptible protein kinase targets combined with searches for leads and candidates have become a crucial approach. The success of recent launches of protein kinase inhibitors (Gleevec, Imatinib, Sutent, Iressa, Nexavar, Sprycel) gave another push to this field. Numerous other kinase inhibitors are currently undergoing clinical trials or clinical development. Some questions are nevertheless unanswered, mostly related to the great number of known kinases in the human genome, to their similarity with each other, to the existence of functionally redundant kinases for specific pathways, and also because the connection between particular pathways and diseases is not always clear. The review is leading the reader through a panoramic view of protein kinase inhibition with a major focus on MAPK, successful examples and clinical candidates.

H2S-induced pancreatic acinar cell apoptosis is mediated via JNK and p38 MAP kinase

Treatment of pancreatic acinar cells by hydrogen sulphide has been shown to induce apoptosis. However, a potential role of mitogen-activated protein kinases (MAPKs) in this apoptotic pathway remains unknown. The present study examined the role of MAPKs in H(2)S-induced apoptosis in mouse pancreatic acinar cells. Pancreatic acinar cells were treated with 10 microM NaHS (a donor of H(2)S) for 3 hrs. For the evaluation of the role of MAPKs, PD98059, SP600125 and SB203580 were used as MAPKs inhibitors for ERK1/2, JNK1/2 and p38 MAPK, respectively. We observed activation of ERK1/2, JNK1/2 and p38 when pancreatic acini were exposed to H(2)S. Moreover, H(2)S-induced ERK1/2, JNK1/2 and p38 activation were blocked by pre-treatment with their corresponding inhibitor in a dose-dependent manner. H(2)S-induced apoptosis led to an increase in caspase 3 activity and this activity was attenuated when caspase 3 inhibitor were used. Also, the cleavage of caspase 3 correlated with that of poly-(ADP-ribose)-polymerase (PARP) cleavage. H(2)S treatment induced the release of cytochrome c, smac from mitochondria into the cytoplasm, translocation of Bax into mitochondria and decreased the protein level of Bcl-2. Inhibition of ERK1/2 using PD98059 caused further enhancement of apoptosis as evidenced by annexin V staining, while SP600125 and SB203580 abrogated H(2)S-induced apoptosis. Taken together, the data suggest that activation of ERKs promotes cell survival, whereas activation of JNKs and p38 MAP kinase leads to H(2)S-induced apoptosis.