Purification and activation of recombinant p38 isoforms alpha, beta, gamma, and delta

Isoform-specific optical activation of kinase function reveals p38-ERK signaling crosstalk

Evolution has diversified the mammalian proteome by the generation of protein isoforms that originate from identical genes, e.g., through alternative gene splicing or post-translational modifications, or very similar genes found in gene families. Protein isoforms can have either overlapping or unique functions and traditional chemical, biochemical, and genetic techniques are often limited in their ability to differentiate between isoforms due to their high similarity. This is particularly true in the context of highly dynamic cell signaling cascades, which often require acute spatiotemporal perturbation to assess mechanistic details. To that end, we describe a method for the selective perturbation of the individual protein isoforms of the mitogen-activated protein kinase (MAPK) p38. The genetic installation of a photocaging group at a conserved active site lysine enables the precise light-controlled initiation of kinase signaling, followed by investigation of downstream events. Through optical control, we have identified a novel point of crosstalk between two major signaling cascades: the p38/MAPK pathway and the extracellular signal-regulated kinase (ERK)/MAPK pathway. Specifically, using the photoactivated p38 isoforms, we have found the p38γ and p38δ variants to be positive regulators of the ERK signaling cascade, while confirming the p38α and p38β variants as negative regulators.

Alternative Splicing of MAPKs in the Regulation of Signaling Specificity

The mitogen-activated protein kinase (MAPK) cascades transmit signals from extracellular stimuli to a variety of distinct cellular processes. The MAPKKs in each cascade specifically phosphorylate and activate their cognate MAPKs, indicating that this step funnels various signals into a seemingly linear pathway. Still, the effects of these cascades vary significantly, depending on the identity of the extracellular signals, which gives rise to proper outcomes. Therefore, it is clear that the specificity of the signals transmitted through the cascades is tightly regulated in order to secure the desired cell fate. Indeed, many regulatory components or processes that extend the specificity of the cascades have been identified. Here, we focus on a less discussed mechanism, that is, the role of distinct components in each tier of the cascade in extending the signaling specificity. We cover the role of distinct genes, and the alternatively spliced isoforms of MAPKKs and MAPKs, in the signaling specificity. The alternatively spliced MEK1b and ERK1c, which form an independent signaling route, are used as the main example. Unlike MEK1/2 and ERK1/2, this route’s functions are limited, including mainly the regulation of mitotic Golgi fragmentation. The unique roles of the alternatively spliced isoforms indicate that these components play an essential role in determining the proper cell fate in response to distinct stimulations.

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.

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.

Regulation of c-Jun NH2-Terminal Kinase for Islet Transplantation

Islet transplantation has been demonstrated to provide superior glycemic control with reduced glucose lability and hypoglycemic events compared with standard insulin therapy. However, the insulin independence rate after islet transplantation from one donor pancreas has remained low. The low frequency of islet grafting is dependent on poor islet recovery from donors and early islet loss during the first hours following grafting. The reduction in islet mass during pancreas preservation, islet isolation, and islet transplantation leads to β-cell death by apoptosis and the prerecruitment of intracellular death signaling pathways, such as c-Jun NH₂-terminal kinase (JNK), which is one of the stress groups of mitogen-activated protein kinases (MAPKs). In this review, we show some of the most recent contributions to the advancement of knowledge of the JNK pathway and several possibilities for the treatment of diabetes using JNK inhibitors.

Metabolic benefits of inhibition of p38α in white adipose tissue in obesity

p38 has long been known as a central mediator of protein kinase A (PKA) signaling in brown adipocytes, which positively regulate the transcription of uncoupling protein 1 (UCP-1). However, the physiological role of p38 in adipose tissues, especially the white adipose tissue (WAT), is largely unknown. Here, we show that mice lacking p38α in adipose tissues display a lean phenotype, improved metabolism, and resistance to diet-induced obesity. Surprisingly, ablation of p38α causes minimal effects on brown adipose tissue (BAT) in adult mice, as evident from undetectable changes in UCP-1 expression, mitochondrial function, body temperature (BT), and energy expenditure. In contrast, genetic ablation of p38α in adipose tissues not only markedly facilitates the browning in WAT upon cold stress but also prevents diet-induced obesity. Consistently, pharmaceutical inhibition of p38α remarkably enhances the browning of WAT and has metabolic benefits. Furthermore, our data suggest that p38α deficiency promotes white-to-beige adipocyte reprogramming in a cell-autonomous manner. Mechanistically, inhibition of p38α stimulates the UCP-1 transcription through PKA and its downstream cAMP-response element binding protein (CREB), which form a positive feedback loop that functions to reinforce the white-to-beige phenotypic switch during cold exposure. Together, our study reveals that inhibition of p38α is able to promote WAT browning and confer metabolic benefits. Our study also indicates that p38α in WAT represents an exciting pharmacological target to combat obesity and metabolic diseases.

The functional brown adipose tissue (BAT) identified in human adults consists of not only classic brown adipocytes but also brown-like adipocytes (beige adipocytes), both of which are important for energy homeostasis. Due to the same ability to convert fat into heat as brown adipocytes, beige adipocytes have been considered as a novel pharmacological target to combat obesity. Growing evidence suggests that promoting the development and formation of beige adipocytes in white adipose tissue (WAT), also called the browning of WAT, is able to prevent diet-induced obesity and improve metabolism in rodents. Thus, understanding the molecular basis for the regulation of browning in WAT may help us to develop new strategies to counteract obesity and metabolic diseases. In this study, adipocyte-specific p38α knockout (Fp38αKO) mice are generated that display a lean phenotype, improved metabolism, and resistance to diet-induced obesity. Interestingly, we found that adipocyte p38α deficiency facilitates the browning in WAT. Then, we show that pharmaceutical inhibition of p38α enhances the browning in WAT and has metabolic benefits. We propose that inhibiting p38α in WAT, possibly combined with cold exposure, could constitute an exciting pharmacological target to combat obesity and metabolic diseases.

Differential expression of p38 MAPK α, β, γ, δ isoforms in nucleus pulposus modulates macrophage polarization in intervertebral disc degeneration

P38MAPK mediates cytokine induced inflammation in nucleus pulposus (NP) cells and involves in multiple cellular processes which are related to intervertebral disc degeneration (IDD). The aim of this study was to investigate the expression, activation and function of p38 MAPK isoforms (α,β, γ and δ) in degenerative NP and the effect of p38 activation in NP cells on macrophage polarization. P38 α, β and δ isoforms are preferential expressed, whereas the p38γ isoform is absent in human NP tissue. LV-sh-p38α, sh-p38β transfection in NP cells significantly decreased the ADAMTS-4,-5, MMP-13,CCL3 expression and restored collagen-II and aggrecan expression upon IL-1β stimulation. As compared with p38α and p38β, p38δ exhibited an opposite effect on ADAMTS-4,-5, MMP-13 and aggrecan expression in NP cells. Furthermore, the production of GM-CSF and IFNγ which were trigged by p38α or p38β in NP cells induced macrophage polarization into M1 phenotype. Our finding indicates that p38 MAPK α, β and δ isoform are predominantly expressed and activated in IDD. P38 positive NP cells modulate macrophage polarization through the production of GM-CSF and IFNγ. Hence, Our study suggests that selectively targeting p38 isoforms could ameliorate the inflammation in IDD and regard IDD progression.

Selective inhibition of ATPase activity during contraction alters the activation of p38 MAP kinase isoforms in skeletal muscle

Muscle contractions strongly activate p38 MAP kinases, but the precise contraction-associated sarcoplasmic event(s) (e.g., force production, energetic demands, and/or calcium cycling) that activate these kinases are still unclear. We tested the hypothesis that during contraction the phosphorylation of p38 isoforms is sensitive to the increase in ATP demand relative to ATP supply. Energetic demands were inhibited using N-benzyl-p-toluene sulphonamide (BTS, type II actomyosin) and cyclopiazonic acid (CPA, SERCA). Extensor digitorum longus muscles from Swiss Webster mice were incubated in Ringer's solution (37°C) with or without inhibitors and then stimulated at 10 Hz for 15 min. Muscles were immediately freeze-clamped for metabolite and Western blot analysis. BTS and BTS + CPA treatment decreased force production by 85%, as measured by the tension time integral, while CPA alone potentiated force by 310%. In control muscles, contractions resulted in a 73% loss of ATP content and a concomitant sevenfold increase in IMP content, a measure of sustained energetic imbalance. BTS or CPA treatment lessened the loss of ATP, but BTS + CPA treatment completely eliminated the energetic imbalance since ATP and IMP levels were nearly equal to those of non-stimulated muscles. The independent inhibition of cytosolic ATPase activities had no effect on contraction-induced p38 MAPK phosphorylation, but combined treatment prevented the increase in phosphorylation of the γ isoform while the α/β isoforms unaffected. These observations suggest that an energetic signal may trigger phosphorylation of the p38γ isoform and also may explain how contractions differentially activate signaling pathways.

Characterization of the regulatory mechanisms of activating transcription factor 3 by hypertrophic stimuli in rat cardiomyocytes

Aims

Activating transcription factor 3 (ATF3) is a stress-activated immediate early gene suggested to have both detrimental and cardioprotective role in the heart. Here we studied the mechanisms of ATF3 activation by hypertrophic stimuli and ATF3 downstream targets in rat cardiomyocytes.

Methods and Results

When neonatal rat cardiomyocytes were exposed to endothelin-1 (ET-1, 100 nM) and mechanical stretching in vitro, maximal increase in ATF3 expression occurred at 1 hour. Inhibition of extracellular signal-regulated kinase (ERK) by PD98059 decreased ET-1– and stretch–induced increase of ATF3 protein but not ATF3 mRNA levels, whereas protein kinase A (PKA) inhibitor H89 attenuated both ATF3 mRNA transcription and protein expression in response to ET-1 and stretch. To characterize further the regulatory mechanisms upstream of ATF3, p38 mitogen-activated protein kinase (MAPK) signaling was investigated using a gain-of-function approach. Adenoviral overexpression of p38α, but not p38β, increased ATF3 mRNA and protein levels as well as DNA binding activity. To investigate the role of ATF3 in hypertrophic process, we overexpressed ATF3 by adenovirus-mediated gene transfer. In vitro, ATF3 gene delivery attenuated the mRNA transcription of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1), and enhanced nuclear factor-κB (NF-κB) and Nkx-2.5 DNA binding activities. Reduced PAI-1 expression was also detected in vivo in adult rat heart by direct intramyocardial adenovirus-mediated ATF3 gene delivery.

Conclusions

These data demonstrate that ATF3 activation by ET-1 and mechanical stretch is partly mediated through ERK and cAMP-PKA pathways, whereas p38 MAPK pathway is involved in ATF3 activation exclusively through p38α isoform. ATF3 activation caused induction of modulators of the inflammatory response NF-κB and Nkx-2.5, as well as attenuation of pro-fibrotic and pro-inflammatory proteins IL-6 and PAI-1, suggesting cardioprotective role for ATF3 in the heart.

Regulation of the JNK3 signaling pathway during islet isolation: JNK3 and c-fos as new markers of islet quality for transplantation

Stress conditions generated throughout pancreatic islet processing initiate the activation of pro-inflammatory pathways and beta-cell destruction. Our goal is to identify relevant and preferably beta-specific markers to assess the activation of beta-cell stress and apoptotic mechanisms, and therefore the general quality of the islet preparation prior to transplantation. Protein expression and activation were analyzed by Western blotting and kinase assays. ATP measurements were performed by a luminescence-based assay. Oxygen consumption rate (OCR) was measured based on standard protocols using fiber optic sensors. Total RNA was used for gene expression analyzes. Our results indicate that pancreas digestion initiates a potent stress response in the islets by activating two stress kinases, c-Jun N-terminal Kinase (JNK) and p38. JNK1 protein levels remained unchanged between different islet preparations and following culture. In contrast, levels of JNK3 increased after islet culture, but varied markedly, with a subset of preparations bearing low JNK3 expression. The observed changes in JNK3 protein content strongly correlated with OCR measurements as determined by the Spearman's rank correlation coefficient rho in the matching islet samples, while inversely correlating with c-fos mRNA expression . In conclusion, pancreas digestion recruits JNK and p38 kinases that are known to participate to beta-cell apoptosis. Concomitantly, the islet isolation alters JNK3 and c-fos expression, both strongly correlating with OCR. Thus, a comparative analysis of JNK3 and c-fos expression before and after culture may provide for novel markers to assess islet quality prior to transplantation. JNK3 has the advantage over all other proposed markers to be islet-specific, and thus to provide for a marker independent of non-beta cell contamination.

Functional roles of p38 mitogen-activated protein kinase in macrophage-mediated inflammatory responses

Inflammation is a natural host defensive process that is largely regulated by macrophages during the innate immune response. Mitogen-activated protein kinases (MAPKs) are proline-directed serine and threonine protein kinases that regulate many physiological and pathophysiological cell responses. p38 MAPKs are key MAPKs involved in the production of inflammatory mediators, including tumor necrosis factor-α (TNF-α) and cyclooxygenase-2 (COX-2). p38 MAPK signaling plays an essential role in regulating cellular processes, especially inflammation. In this paper, we summarize the characteristics of p38 signaling in macrophage-mediated inflammation. In addition, we discuss the potential of using inhibitors targeting p38 expression in macrophages to treat inflammatory diseases.

Optimizing intramuscular adaptations to aerobic exercise: effects of carbohydrate restriction and protein supplementation on mitochondrial biogenesis

Mitochondrial biogenesis is a critical metabolic adaptation to aerobic exercise training that results in enhanced mitochondrial size, content, number, and activity. Recent evidence has shown that dietary manipulation can further enhance mitochondrial adaptations to aerobic exercise training, which may delay skeletal muscle fatigue and enhance exercise performance. Specifically, studies have demonstrated that combining carbohydrate restriction (endogenous and exogenous) with a single bout of aerobic exercise potentiates the beneficial effects of exercise on markers of mitochondrial biogenesis. Additionally, studies have demonstrated that high-quality protein supplementation enhances anabolic skeletal muscle intracellular signaling and mitochondrial protein synthesis following a single bout of aerobic exercise. Mitochondrial biogenesis is stimulated by complex intracellular signaling pathways that appear to be primarily regulated by 5'AMP-activated protein kinase and p38 mitogen-activated protein kinase mediated through proliferator-activated γ receptor co-activator 1 α activation, resulting in increased mitochondrial DNA expression and enhanced skeletal muscle oxidative capacity. However, the mechanisms by which concomitant carbohydrate restriction and dietary protein supplementation modulates mitochondrial adaptations to aerobic exercise training remains unclear. This review summarizes intracellular regulation of mitochondrial biogenesis and the effects of carbohydrate restriction and protein supplementation on mitochondrial adaptations to aerobic exercise.

p27 suppresses cyclooxygenase-2 expression by inhibiting p38β and p38δ-mediated CREB phosphorylation upon arsenite exposure

p27 is a cyclin-dependent kinase (CDK) inhibitor that suppresses a cell's transition from G0 to S phase, therefore acting as a tumor suppressor. Our most recent studies demonstrate that upon arsenite exposure, p27 suppresses Hsp27 and Hsp70 expressions through the JNK2/c-Jun- and HSF-1-dependent pathways, suggesting a novel molecular mechanism underlying the tumor suppressive function of p27 in a CDK-independent manner. We found that p27-deficiency (p27-/-) resulted in the elevation of cyclooxygenase-2 (COX-2) expression at transcriptional level, whereas the introduction of p27 brought back COX-2 expression to a level similar to that of p27+/+ cells, suggesting that p27 exhibits an inhibitory effect on COX-2 expression. Further studies identified that p27 inhibition of COX-2 expression was specifically due to phosphorylation of transcription factor cAMP response element binding (CREB) phosphorylation mediated by p38β and p38δ. These results demonstrate a novel mechanism underlying tumor suppression effect of p27 and will contribute to the understanding of the overall mechanism of p27 tumor suppression in a CDK-independent manner.

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.

The role of a Brugia malayi p38 MAP kinase ortholog (Bm-MPK1) in parasite anti-oxidative stress responses

Filariasis, caused by thread-like nematode worms, affects millions of individuals throughout the tropics and is a major cause of acute and chronic morbidity. Filarial nematodes effectively evade host immunological responses and are long lived within their hosts. Recently an emphasis has been placed on enzymatic and non-enzymatic anti-oxidant systems which counteract the generation of reactive oxygen species (ROS) by macrophages and granulocytes, a first line of defense against parasites. We have characterized an anti-oxidant pathway in the filarial parasite Brugia malayi related to the evolutionarily conserved human mitogen-activated p38 protein kinase and the Caenorhabditis elegans PMK-1 protein kinase stress pathways. We have expressed a recombinant p38/PMK-1 ortholog from B. malayi (Bm-MPK1) and have successfully activated the kinase with mammalian upstream kinases. In addition, we have demonstrated inhibition of Bm-MPK1 activity using a panel of known p38 inhibitors. Using the potent and highly selective allosteric p38 inhibitor, BIRB796, we have implicated Bm-MPK1 in a pathway which offers B. malayi protection from the effects of ROS. Our results, for the first time, describe a stress-activated protein kinase pathway within the filarial parasite B. malayi which plays a role in protecting the parasite from ROS. Inhibition of this pathway may have therapeutic benefit in treating filariasis by increasing the sensitivity of filarial parasites to ROS and other reactive intermediates.

Effect of pressure overload-induced hypertrophy on the expression and localization of p38 MAP kinase isoforms in the mouse heart

p38 mitogen-activated protein kinases (MAPKs) are serine/threonine specific protein kinases that respond to cellular stress and regulate a broad range of cellular activities. There are four major isoforms of p38 MAPK: alpha, beta, gamma, and delta. To date, the prominent isoform in heart has been thought to be p38alpha. We examined the expression of each p38 isoform at both the mRNA and protein level in murine heart. mRNA for all four p38 isoforms was detected. p38gamma and p38delta were expressed at protein levels comparable to p38alpha and 38beta, respectively. In the early phase of pressure-overload hypertrophy (1-7 days after constriction of the transverse aorta), the abundance of p38beta, p38gamma and p38delta mRNA increased; however, no corresponding changes were detected at the protein level. Confocal immunofluorescence studies revealed p38alpha and p38gamma in both the cytoplasm and nucleus. In the established phase of hypertrophy induced by chronic pressure overload (7-28 days after constriction of the transverse aorta), p38gamma immunoreactivity accumulated in the nucleus whereas the distribution of p38alpha remained unaffected. Hence, both p38alpha and p38gamma are prominent p38 isoforms in heart and p38gamma may play a role in mediating the changes in gene expression associated with cardiac remodeling during pressure-overload hypertrophy.

p38 MAP kinase inhibits neutrophil development through phosphorylation of C/EBPalpha on serine 21

Many extracellular stimuli regulate growth, survival, and differentiation responses through activation of the dual specificity mitogen activated protein kinase (MAPK) kinase three (MKK3) and its downstream effector p38 MAPK. Using CD34+ hematopoietic progenitor cells, here we describe a novel role for MKK3-p38MAPK in the regulation of myelopoiesis. Inhibition of p38MAPK utilizing the pharmacological inhibitor SB203580, enhanced neutrophil development ex vivo, but conversely reduced eosinophil differentiation. In contrast, constitutive activation of MKK3 dramatically inhibited neutrophil differentiation. Transplantation of beta2-microglobulin(-/-) nonobese diabetic/severe combined immune deficient (NOD/SCID) mice with CD34+ cells ectopically expressing constitutively active MKK3 resulted in reduced neutrophil differentiation in vivo, whereas eosinophil development was enhanced. Inhibitory phosphorylation of CCAAT/enhancer binding protein alpha (C/EBPalpha) on serine 21 was induced upon activation of p38MAPK. Moreover, ectopic expression of a non-phosphorylatable C/EBPalpha mutant was sufficient to abrogate MKK3-induced inhibition of neutrophil development. Furthermore, treatment of CD34+ progenitors from patients with severe congenital neutropenia with SB203580 restored neutrophil development. These results establish a novel role for MKK3-p38MAPK in the regulation of lineage choices during myelopoiesis through modulation of C/EBPalpha activity. This signaling module may thus provide an important therapeutic target in the treatment of bone marrow failure.

Role of MAPK kinase 6 in arthritis: distinct mechanism of action in inflammation and cytokine expression

Development of p38alpha inhibitors for rheumatoid arthritis has been hindered by toxicity and limited efficacy. Therefore, we evaluated whether MKK6, an upstream kinase that regulates multiple p38 isoforms, might be an alternative therapeutic target in inflammatory arthritis. Wild-type (WT), MKK6(-/-), and MKK3(-/-) mice were administered K/BxN serum to induce arthritis. Articular expression of activated kinases and cytokines was determined by Western blot, qPCR, ELISA, and multiplex analysis. Immunoprecipitation and confocal microscopy experiments were performed to determine the subcellular location of MKK6, P-p38, and MAPKAPK2 (MK2). Arthritis scores were significantly lower in MKK6(-/-) mice compared with WT mice. Joint destruction and osteoclast differentiation were lower in MKK6(-/-), as were articular IL-6 and matrix metalloproteinase-3 expression. Phospho-p38 levels were modestly decreased in the joints of arthritic MKK6(-/-) mice compared with WT but were significantly higher than MKK3(-/-) mice. P-MK2 was low in MKK6(-/-) and MKK3(-/-) mice. Uncoupled p38 and MK2 activation was also observed in cultured, MKK6(-/-) FLS and confirmed using kinase assays. Immunoprecipitation assays and confocal microscopy showed that P-p38 and MK2 colocalized in activated WT but not MKK6(-/-) FLS. Distinct patterns of cytokine production were observed in MKK6(-/-) and MKK3(-/-) cells. MKK6 deficiency suppresses inflammatory arthritis and joint destruction, suggesting it might be a therapeutic target for inflammation. Although MKK3 and MKK6 activate the p38 pathway, they regulate distinct subsets of proinflammatory cytokines. MKK6 appears mainly to facilitate p38 and MK2 colocalization in the nucleus rather than to phosphorylate p38.

The p38 mitogen-activated protein kinase (MAPK) pathway in rheumatoid arthritis

Chronic inflammatory processes are based on a sustained and tightly regulated communication network among different cells types. This network comprises extracellular mediators such as cytokines, chemokines and matrix-degrading proteases, which orchestrate the participation of cells in the chronic inflammatory process. The mirrors of this outside communication world are intracellular transcription factor pathways, which shuttle information about inflammatory stimuli to the cell nucleus. This review examines the function of one key signal transduction pathway of inflammation--the p38 mitogen-activated protein kinases (p38MAPK). The signalling pathway is considered as crucial for the induction and maintenance of chronic inflammation, and its components thus emerge as interesting molecular targets of small molecule inhibitors for controlling inflammation. This review not only summarises the current knowledge of activation, regulation and function of the p38MAPK pathway but also examines the role of this pathway in clinical disease. It gives an overview of current evidence of p38MAPK activation in inflammatory arthritis and elaborates the key molecular determinants which contribute to p38MAPK activation in joint disease.

Activation of c-Jun NH2-terminal kinase during islet isolation

Pancreatic islet transplantation has been remarkably improved by the Edmonton protocol; however, it is not easy to achieve insulin independence after islet transplantation from one donor pancreas. The islet isolation procedure itself destroys cellular and noncellular components of the pancreas that probably play a role in supporting islet survival. Further islet transplantation exposes cells to a variety of stressful stimuli such as proinflammatory cytokines. The reduction in islet mass immediately after isolation and transplantation implicates beta cell death by apoptosis and the prerecruitment of intracellular death signalling pathways. The c-Jun NH2-terminal kinases (JNKs) are classic stress-activated protein kinases and many cellular stresses have been shown to stimulate JNK activation. JNK in the pancreas is activated during brain death, pancreas procurement, and organ preservation, and its activity is progressively increased during the isolation procedure. Moreover, JNK activity in the transplanted liver after islet transplantation increases markedly within 24 hrs. Use of the JNK inhibitor in pancreas preservation, islet culture, and/or islet transplantation prevents islet apoptosis and improves islet graft function. These findings suggest that the control of JNK activation is important for pancreatic islet transplantation.

p38α and p38δ mitogen-activated protein kinase isoforms regulate invasion and growth of head and neck squamous carcinoma cells

Recent studies indicate that the specificity of p38 mitogen-activated protein kinase (MAPK)-mediated cellular stress responses is determined by the expression pattern of the distinct p38 isoforms. Here, we have analysed the function of distinct p38 isoforms in the growth and invasion of head and neck squamous cell carcinomas (HNSCCs). Activation of p38 MAPK by arsenite resulted in inactivation of the ERK1,2 signaling pathway by dephosphorylation of MEK1,2 in primary human epidermal keratinocytes (HEKs), whereas in HNSCC cells this p38-mediated inhibition of the ERK1,2 pathway was absent. Quantitation of p38 pathway component mRNA expression in HNSCC cell lines (n=42) compared to HEKs (n=8) revealed that p38alpha and p38delta isoforms are predominantly expressed in both cell types and that MKK3 is the primary upstream activator expressed. Inhibition of endogenous p38alpha or p38delta activity by adenoviral delivery of corresponding dominant-negative p38 isoforms potently reduced MMP-13 and MMP-1 expressions, and suppressed the invasion of HNSCC cells through collagen. Dominant-negative p38alpha and p38delta inhibited squamous cell carcinoma (SCC) cell proliferation and inhibition of p38alpha activity also compromised survival of SCC cells. p38alpha and p38delta were predominantly expressed in HNSCCs (n=24) and nonneoplastic epithelium in vivo (n=6), with MKK3 being the primary upstream activator. Activation and expression of p38alpha and p38delta by tumor cells was detected in HNSCCs in vivo (n=16). Adenoviral expression of dominant-negative p38alpha or p38delta in cutaneous SCC cells potently inhibited their implantation in skin of severe combined immunodeficiency mice and growth of xenografts in vivo. Our results indicate that p38alpha and p38delta specifically promote the malignant phenotype of SCC cells by regulating cell survival, proliferation and invasion, suggesting these p38 MAPK isoforms as potential therapeutic targets in HNSCCs.

Activation of c-Jun NH2-terminal kinase (JNK) pathway during islet transplantation and prevention of islet graft loss by intraportal injection of JNK inhibitor

AIMS/HYPOTHESIS

Although application of the Edmonton protocol has markedly improved the outcome for pancreatic islet transplantation, the insulin independence rate after islet transplantation from one donor pancreas has remained low. During the isolation process and subsequent clinical transplantation, islets are subjected to severe adverse conditions that impair survival and ultimately contribute to graft failure. The aim of this study was to map the c-Jun NH2-terminal kinase (JNK) pathway that mediates islet loss during islet transplantation and to clarify whether intraportal injection with JNK inhibitor during islet transplantation can prevent islet graft loss.

METHODS

We measured JNK activity in the liver, fat and muscle of diabetic mice and in the liver immediately after islet transplantation. We examined the effect of intraportal injection of JNK inhibitory peptide at islet transplantation.

RESULTS

JNK activity became progressively higher at least until 24 h after transplantation. The cell-permeable peptide of JNK inhibitor was delivered not only in the liver but also in other insulin target organs, preventing JNK activation in the liver at least until 24 h after transplantation and reducing JNK activity in these insulin target organs. Moreover, the peptide inhibitor prevented islet graft loss immediately after transplantation and improved islet transplant outcome.

CONCLUSIONS/INTERPRETATION

These findings suggest that control of the JNK pathway is extremely important in islet transplantation and that intraportal injection of JNK inhibitor during islet transplantation (addition of JNK inhibitor to transplant media) could prevent the impairment of islet cells, leading to improved outcome for pancreatic islet transplantation.

Intrinsically active variants of all human p38 isoforms

The p38 mitogen-activated protein kinases are activated in response to various extracellular signals in eukaryotic cells and play a critical role in the cellular responses to these signals. The four mammalian isoforms (p38alpha, p38beta, p38gamma, and p38delta) are coexpressed and coactivated in the same cells. The exact role of each p38 isoform has not been entirely identified, in part due to the inability to activate each member individually. This could be resolved by the use of intrinsically active mutants. Based on previous studies on yeast p38/Hog1 [Bell M, Capone R, Pashtan I, Levitzki A & Engelberg D (2001) J Biol Chem276, 25351-2538] and human p38alpha[Diskin R, Askari N, Capone R, Engelberg D & Livnah O (2004) J Biol Chem279, 47040-47049] we have generated intrinsically active p38beta, p38gamma and p38delta mutants. In addition, we have identified a new activating mutation site in p38alpha. Most of the activating mutations are located in the L16 loop, in which conformational changes were shown to induce activation. We show that these changes impose substantial autophosphorylation activity, providing a mechanistic explanation for the intrinsic activity of the mutants. The new active variants maintain specificity towards substrates and inhibitors similar to that of the parental wild-type proteins, and are phosphorylated by mitogen-activated protein kinase kinase 6, their upstream activator. Thus, we have completed the development of a series of intrinsically active mutants of all p38 isoforms. These active variants could now become powerful tools for the elucidating the activation mechanism and specific biological roles of each p38 isoform.

Regulation of calnexin sub-cellular localization modulates endoplasmic reticulum stress-induced apoptosis in MCF-7 cells

The endoplasmic reticulum (ER) is the cellular compartment where proteins enter the secretory pathway, undergo post-translational modifications and acquire a correct conformation. If these functions are chronically altered, specific ER stress signals are triggered to promote cell death through the intrinsic apoptotic pathway. Here, we show that tunicamycin causes significant alteration of calnexin sub-cellular distribution in MCF-7 cells. Interestingly, this correlates with the absence of both tunicamycin-induced calnexin phosphorylation as well as tunicamycin-induced cell death. Under these conditions, calnexin-associated Bap31, an ER integral membrane protein, is subjected to a caspase-8 cleavage pattern within a specific sub-compartment of the ER. These results suggest that MCF-7 resistance to ER stress-induced apoptosis is partially mediated by the expression level of calnexin which in turn controls its sub-cellular localization, and its association with Bap31. These data may delineate a resistance mechanism to the ER stress-induced intrinsic apoptotic pathway.

PP2Cδ (Ppm1d, WIP1), an endogenous inhibitor of p38 MAPK, is regulated along WithTrp53 andCdkn2a following p38 MAPK inhibition during mouse preimplantation development

Preimplantation embryos utilize mitogen-activated protein kinase signaling (MAPK) pathways to relay signals from the external environment to prepare appropriate responses and adaptations to a changing milieu. It is therefore important to investigate how MAPK pathways are regulated during preimplantation development. This study was conducted to investigate whether PP2Cdelta (Ppm1d, WIP1) is expressed during mouse preimplantation development and to determine the influences of p38 MAPK inhibition on expression of Trp53 (p53), Ppm1d, (WIP1), and Cdkn2a (p16) during mouse preimplantation development. Our results indicate that Trp53, Ppm1d, and Cdkn2a mRNAs and TRP53 and PP2Cdelta proteins are expressed throughout mouse preimplantation development. Treatment of 2-cell embryos with SB220025 (potent inhibitor of p38 MAPK alpha/beta/MAPK 14/11) significantly increased Trp53, Ppm1d and Cdkn2a and Mapk14 mRNA levels at 12 and 24 hr. Treatment of 8-cell embryos with SB220025 for 12 hr increased Trp53, Ppm1d, and Cdkn2a mRNA levels, but not Mapk14 mRNA levels. Treatment of 8-cell embryos for 24 hr increased Trp53, and Ppm1d mRNA levels, but decreased Cdkn2a and Mapk14 mRNA levels. Therefore, blockade of p38 MAPK activity is associated with embryo stage specific influences on Trp53, Ppm1d, Cdkn2a, and Mapk14 expression during mouse preimplantation development. These results define downstream targets of p38 MAPK during preimplantation development and indicate that the p38 MAPK pathway regulates Trp53, Ppm1d, and Cdkn2a expression. This study increases our understanding of the mechanisms controlling preimplantation development and of the interactions between preimplantation embryos and their culture environments.

Differential tissue expression and activation of p38 MAPK alpha, beta, gamma, and delta isoforms in rheumatoid arthritis

OBJECTIVE

Activation of p38 MAPK is a key signaling step in chronic inflammation. Inhibition of p38 MAPK is considered to be a promising future strategy to control inflammatory diseases, but studies of compounds to inhibit this kinase have so far been limited to investigation of their side effects. We undertook the present study to investigate which specific molecule, among 4 different isoforms of p38 MAPK (alpha, beta, gamma, and delta), is predominantly expressed and activated in inflammation. Such knowledge could allow more specific targeting of p38 MAPK in inflammatory disease.

METHODS

Studies were performed on inflamed tissue from patients with rheumatoid arthritis, as a prototype of inflammatory disease. The expression and activation of the alpha, beta, gamma, and delta isoforms of p38 MAPK were examined by immunoblotting, immunoprecipitation, and immunohistochemistry.

RESULTS

Immunoblot analysis revealed that alpha and gamma were the predominantly expressed p38 MAPK isoforms, whereas the other 2 isoforms were less frequently present. By immunohistochemistry, the expression of all p38 MAPK isoforms was localized to the synovial lining layer as well as to blood vessels. Colabeling with cell-specific markers revealed that macrophages expressed the alpha and gamma isoforms, synovial fibroblasts the beta and gamma isoforms, and granulocytes the delta isoform, whereas T lymphocytes were rarely positive for any p38 MAPK isoform. Double-labeling with isoform-specific antibody and pan-p38 antibody against the phosphorylated form of p38 MAPK showed activation of the alpha and gamma isoforms. Occasional activation of the beta isoform was also noted in the synovial lining and the endothelium, whereas the delta isoform, although expressed in pericytes around blood vessels, was not phosphorylated. This phosphorylation pattern was confirmed in immunoprecipitation studies in which activated p38 MAPK from synovial tissue extracts was identified as p38 MAPKalpha and -gamma but not p38 MAPKbeta or -delta.

CONCLUSION

These data show that the alpha and gamma isoforms of p38 MAPK dominate in chronic inflammation. Effective strategies to inhibit p38 MAPK should therefore aim to specifically target either or both of these isoforms.

MAP kinases p38 and JNK are activated by the steroid hormone 1alpha,25(OH)2-vitamin D3 in the C2C12 muscle cell line

In chick skeletal muscle cell primary cultures, we previously demonstrated that 1alpha,25(OH)2-vitamin D3 [1alpha,25(OH)2D3], the hormonally active form of vitamin D, increases the phosphorylation and activity of the extracellular signal-regulated mitogen-activated protein (MAP) kinase isoforms ERK1 and ERK2, their subsequent translocation to the nucleus and involvement in DNA synthesis stimulation. In this study, we show that other members of the MAP kinase superfamily are also activated by the hormone. Using the muscle cell line C2C12 we found that 1alpha,25(OH)2D3 within 1 min phosphorylates and increases the activity of p38 MAPK. The immediately upstream mitogen-activated protein kinase kinases 3/6 (MKK3/MKK6) were also phosphorylated by the hormone suggesting their participation in p38 activation. 1Alpha,25(OH)2D3 was able to dephosphorylate/activate the ubiquitous cytosolic tyrosine kinase c-Src in C2C12 cells and studies with specific inhibitors imply that Src participates in hormone induced-p38 activation. Of relevance, 1alpha,25(OH)2D3 induced in the C2C12 line the stimulation of mitogen-activated protein kinase activating protein kinase 2 (MAPKAP-kinase 2) and subsequent phosphorylation of heat shock protein 27 (HSP27) in a p38 kinase activation-dependent manner. Treatment with the p38 inhibitor, SB203580, blocked p38 phosphorylation caused by the hormone and inhibited the phosphorylation of its downstrean substrates. 1Alpha,25(OH)2D3 also promotes the phosphorylation of c-jun N-terminal protein kinases (JNK 1/2), the response is fast (0.5-1 min) and maximal phosphorylation of the enzyme is observed at physiological doses of 1alpha,25(OH)2D3 (1 nM). The relative contribution of ERK-1/2, p38, and JNK-1/2 and their interrelationships in hormonal regulation of muscle cell proliferation and differentiation remain to be established.

Role of MKK3 and p38 MAPK in cytokine-induced death of insulin-producing cells

The aim of the present investigation was to elucidate further the importance of p38 MAPK (mitogen-activated protein kinase) in nitric oxide- and cytokine-induced beta-cell death. For this purpose, isolated human islets were treated with d-siRNA (diced small interfering RNA) and then exposed to the nitric oxide donor DETA/NONOate [2,2'-(hydroxynitrosohydrazono)bis-ethanamine]. We observed that cells treated with p38alpha-specific d-siRNA, but not with d-siRNA targeting GL3 (a firefly luciferase siRNA plasmid) or PKCdelta (protein kinase Cdelta), were protected against nitric oxide-induced death. This was paralleled by an increased level of Bcl-XL (B-cell leukaemia/lymphoma-X long). For an in-depth study of the mechanisms of p38 activation, MKK3 (MAPK kinase 3), MKK6 and their dominant-negative mutants were overexpressed in insulin-producing RIN-5AH cells. In transient transfections, MKK3 overexpression resulted in increased p38 phosphorylation, whereas in stable MKK3-overexpressing RIN-5AH clones, the protein levels of p38 and JNK (c-Jun N-terminal kinase) were decreased, resulting in unaffected phospho-p38 levels. In addition, a long-term MKK3 overexpression did not affect cell death rates in response to the cytokines interleukin-1beta and interferon-gamma, whereas a short-term MKK3 expression resulted in increased cytokine-induced RIN-5AH cell death. The MKK3-potentiating effect on cytokine-induced cell death was abolished by a nitric oxide synthase inhibitor, and MKK3-stimulated p38 phosphorylation was enhanced by inhibitors of phosphatases. Finally, as the dominant-negative mutant of MKK3 did not affect cytokine-induced p38 phosphorylation, and as wild-type MKK3 did not influence p38 autophosphorylation, it may be that p38 is activated by MKK3/6-independent pathways in response to cytokines and nitric oxide. In addition, it is likely that a long-term increase in p38 activity is counteracted by both a decreased expression of the p38, JNK and p42 genes as well as an increased dephosphorylation of p38.

Blocking Stress Signaling Pathways with Cell Permeable Peptides

Cells are continuously adapting to changes in their environment by activating extracellular stimuli-dependent signal transduction cascades. These cascades, or signaling pathways, culminate both in changes in genes expression and in the functional regulation of pre-existing proteins. The Mitogen-Activated Protein Kinases (MAPKs) constitute a structurally related class of signaling proteins whose distinctive feature is their ability to directly phosphorylate, and thereby modulate, the activity of the transcription factors that are targets of the initial stimuli. The specificity of activation of MAPK signaling modules is determined, at least for an important part, by the specificity of the protein-protein contacts that are required for the propagation of the signal. We will discuss how we may interfere with MAPK signaling by using short cell-permeable peptides able to block, through a competitive mechanisms, relevant protein-protein contacts, and their effects on signaling and cell function.

Mechanisms of liver fibrosis

Liver fibrosis represents a significant health problem worldwide of which no acceptable therapy exists. The most characteristic feature of liver fibrosis is excess deposition of type I collagen. A great deal of research has been performed to understand the molecular mechanisms responsible for the development of liver fibrosis. The activated hepatic stellate cell (HSC) is the primary cell type responsible for the excess production of collagen. Following a fibrogenic stimulus, HSCs change from a quiescent to an activated, collagen-producing cell. Numerous changes in gene expression are associated with HSC activation including the induction of several intracellular signaling cascades, which help maintain the activated phenotype and control the fibrogenic and proliferative state of the cell. Detailed analyses in understanding the molecular basis of collagen gene regulation have revealed a complex process offering the opportunity for multiple potential therapeutic strategies. However, further research is still needed to gain a better understanding of HSC activation and how this cell maintains its fibrogenic nature. In this review we describe many of the molecular events that occur following HSC activation and collagen gene regulation that contribute to the fibrogenic nature of these cells and provide a review of therapeutic strategies to treat this disease.

Improved expression, purification, and crystallization of p38alpha MAP kinase

p38alpha mitogen-activated protein (MAP) kinase is widely expressed in many mammalian tissues and is activated as a part of signal transduction cascades that respond to inflammatory stimuli. The activation of p38 is known to trigger various biological effects, including cell death, differentiation, and proliferation. The central role played by p38alpha in cellular signaling events, including those that control a wide range of inflammatory and autoimmune diseases, makes it an attractive drug target. To develop optimized small molecule therapeutics targeting p38alpha, different techniques must be employed for the detailed biochemical, biophysical, and structural characterization of the interactions of p38alpha with lead compounds. These methods typically require large quantities of highly purified p38alpha protein. We describe here an improved expression and purification method for recombinant p38alpha production that reproducibly yields over 70 mg of highly purified protein per liter of shake flask bacterial culture. This yield is significantly higher than that previously reported for p38alpha production in Escherichia coli. We achieved a significant increase in soluble p38alpha protein expression by using the genetically modified E. coli strain BL21 DE3 Rosetta, which is optimized for expression of eukaryotic proteins with codons rarely used in E. coli. The p38alpha protein was purified to near homogeneity using a simple two-step procedure including nickel-chelating Sepharose chromatography followed by anion-exchange chromatography using MonoQ resin. Purified p38alpha was characterized using the standard commercially available small molecule inhibitor SB-203580. The binding association and dissociation rate constants determined by Biacore are in excellent agreement with previously reported values. The purified p38alpha protein was efficiently activated by MKK6 kinase to yield phosphorylated p38alpha. Purified p38alpha protein was also successfully crystallized, producing crystals diffracting to 1.9 angstroms, exceeding the highest resolution for p38alpha reported in the Protein DataBank. The simplicity and efficiency of this approach should prove useful for many laboratories that are interested in production of p38alpha for biochemical and biophysical studies and structure-based drug design.

Following in vitro activation of mitogen-activated protein kinases by mass spectrometry and tryptic peptide analysis: purifying fully activated p38 mitogen-activated protein kinase α

p38 mitogen-activated protein kinase alpha (MAPKalpha) belongs to the MAPK subfamily, which plays a pivotal role in cell signal transduction, where it mediates responses to cell stresses and, to a lesser extent, growth factors. Although its cellular function has been under intense scrutiny since its initial discovery, little progress has been made in understanding its kinetic mechanism. A contributory factor has been the lack of a fast and rigorous method for the purification of activated p38 MAPKalpha in sufficient quantity and purity for biophysical studies. Here we present a method for the preparation of milligram quantities of activated p38 MAPKalpha, specifically phosphorylated on Thr180 and Tyr182. Purification of the inactive (unphosphorylated) p38 MAPKalpha is facilitated by an N-terminal hexahistidine tag. Removal of this tag from His6-p38 MAPKalpha, prior to its activation, is essential to ensure preparation of high yields of homogeneous, dually phosphorylated enzyme. Activation is achieved on incubation with a glutathione S-transferase (GST) fusion of the constitutively active mutant of the upstream activator, MKK6b (GST-MKK6b S207E T211E), in the presence of MgATP2-. Notably, we show that specific formation of activated p38 MAPKalpha can be quantified by following the formation of the bis-phosphorylated tryptic peptide, 173-HTDDEMT*GY*VATR-186, using [gamma-32P]adenosine triphosphate (ATP) as the phosphate source and reverse-phase high-performance liquid chromatography (HPLC) to separate the phosphopeptides. This approach offers the only means to specifically determine both stoichiometry and specificity of p38 MAPKalpha phosphorylation.

Intracellular stress signaling pathways activated during human islet preparation and following acute cytokine exposure

Pancreatic islet transplantation may successfully restore normoglycemia in type 1 diabetic patients. However, successful grafting requires transplantation of a sufficient number of islets, usually requiring two or more donors. During the isolation process and following clinical transplantation, islets are subjected to severe adverse conditions that impair survival and ultimately contribute to graft failure. Here, we have mapped the major intracellular stress-signaling pathways that may mediate human islet loss during isolation and following cytokine attack. We found that the isolation procedure potently recruits two pathways consisting of |mitogen-activated protein kinase kinase (MKK)7 --> Jun NH(2)-terminal kinase (JNK)/p38 --> c-fos| and the |nuclear factor-kappaB (NF-kappaB) --> iNOS| module. Cytokines activate the |NF-kappaB --> iNOS| and |MKK4/MKK3/6 --> JNK/p38| pathways without recruitment of c-fos. Culturing the islets for 48 h after isolation allows for the activated pathways to return to background levels, with expression of MKK7 becoming undetectable. These data indicate that isolation and cytokines recruit different death pathways. Therefore, strategies might be rationally developed to avoid possible synergistic activation of these pathways in mediating islet loss during isolation and following grafting.

Inhibition of human immunodeficiency virus type 1 replication by Z-100, an immunomodulator extracted from human-type tubercle bacilli, in macrophages

Z-100 is an arabinomannan extracted from Mycobacterium tuberculosis that has various immunomodulatory activities, such as the induction of interleukin 12, interferon gamma (IFN-gamma) and beta-chemokines. The effects of Z-100 on human immunodeficiency virus type 1 (HIV-1) replication in human monocyte-derived macrophages (MDMs) are investigated in this paper. In MDMs, Z-100 markedly suppressed the replication of not only macrophage-tropic (M-tropic) HIV-1 strain (HIV-1JR-CSF), but also HIV-1 pseudotypes that possessed amphotropic Moloney murine leukemia virus or vesicular stomatitis virus G envelopes. Z-100 was found to inhibit HIV-1 expression, even when added 24 h after infection. In addition, it substantially inhibited the expression of the pNL43lucDeltaenv vector (in which the env gene is defective and the nef gene is replaced with the firefly luciferase gene) when this vector was transfected directly into MDMs. These findings suggest that Z-100 inhibits virus replication, mainly at HIV-1 transcription. However, Z-100 also downregulated expression of the cell surface receptors CD4 and CCR5 in MDMs, suggesting some inhibitory effect on HIV-1 entry. Further experiments revealed that Z-100 induced IFN-beta production in these cells, resulting in induction of the 16-kDa CCAAT/enhancer binding protein (C/EBP) beta transcription factor that represses HIV-1 long terminal repeat transcription. These effects were alleviated by SB 203580, a specific inhibitor of p38 mitogen-activated protein kinases (MAPK), indicating that the p38 MAPK signalling pathway was involved in Z-100-induced repression of HIV-1 replication in MDMs. These findings suggest that Z-100 might be a useful immunomodulator for control of HIV-1 infection.

Differentiation stage-specific activation of p38 mitogen-activated protein kinase isoforms in primary human erythroid cells

p38alpha, p38beta, p38gamma, and p38delta are four isoforms of p38 mitogen-activated protein (MAP) kinase (MAPK) involved in multiple cellular functions such as cell proliferation, differentiation, apoptosis, and inflammation response. In the present study, we examined the mRNA expression pattern of each of the four isoforms during erythroid differentiation of primary erythroid progenitors. We show that p38alpha and p38gamma transcripts are expressed in early hematopoietic progenitors as well as in late differentiating erythroblasts, whereas p38delta mRNA is only expressed and active during the terminal phase of erythroid differentiation. On the other hand, p38beta is minimally expressed in early CD34(+) hematopoietic progenitors but not expressed in lineage-committed erythroid progenitors. We also determined the phosphorylation/activation of p38alpha, MAPK kinase 3/6, and MAPKAP-2 in response to erythropoietin and stem cell factor. We found that phosphorylation of p38alpha, MAPK kinase kinase 3/6 and MAPKAP-2 occurs only upon growth factor withdrawal in primary erythroid progenitors. Moreover, our data indicate that activation of p38alpha does not induce apoptosis or promote proliferation of erythroid progenitors. On the other hand, under steady-state culture conditions, both p38alpha and p38delta isoforms are increasingly phosphorylated activated in the terminal phase of differentiation. This increased phosphorylation/activity was accompanied by up-regulation of heat shock protein 27 phosphorylation. Finally, we demonstrate that tumor necrosis factor alpha, an inflammatory cytokine that is modulated by p38alpha, is expressed by differentiating erythroblasts and inhibition of p38alpha or tumor necrosis factor alpha results in reduction in differentiation. Taken together, our data demonstrate that both p38alpha and delta isoforms function to promote the late-stage differentiation of primary erythroid progenitors and are likely to be involved in functions related to erythrocyte membrane remodeling and enucleation.

Lipopolysaccharide induces CYP2E1 in astrocytes through MAP kinase kinase-3 and C/EBPbeta and -delta

Cytochrome P450 2E1 (CYP2E1) is highly inducible in a subset of astrocytes in vivo following ischemic or mechanical injury and in vitro by lipopolysaccharide (LPS) or interleukin-1beta. We have studied the mechanism of induction, and found that transcriptional activation of CYP2E1 occurred within 3 h, and CYP2E1 dependent catalytic activity was induced more than 4-fold within 5 h. The induction was sensitive to several tyrosine kinase inhibitors, and was further modulated by inhibitors of p38 MAP kinase. MAP kinase kinase-3 (MKK3) was phosphorylated in response to LPS, and expression of constitutively active MKK3, but not the MAP kinase kinases MEKK1 or MKK1, activated CYP2E1. Transcriptional activation was mediated through a C/EBPbeta and -delta binding element situated at -486/-474, and appeared to involve activation of prebound factors as well as recruitment of newly synthesized C/EBPbeta and -delta. It is thus suggested that LPS induces MKK3 activation in astrocytes, which in turn stimulates a C/EBPbeta and -delta binding element to mediate transcriptional activation of CYP2E1.

Integrated transcriptome analysis of the cellular mechanisms associated with Ha-ras-dependent malignant transformation of the human breast epithelial MCF7 cell line

To understand the cellular mechanisms of malignant transformation induced by constitutive activation of the ras oncogene (Ha-ras), we used a subtractive hybridization method (VGID) together with an integrative analytical procedure based upon literature databases in the form of extensive interaction graphs. We found 166 over- and under-expressed genes which, in the human MCF7-ras breast epithelial cell line, are involved in the different aspects of tumoral transformation such as defined signaling pathways, cellular growth, protection against apoptosis, extracellular matrix and cytoskeleton remodeling. Integrative analysis led to the construction of a physiological model defining cross-talk and signaling pathway alterations which explicitly suggested mechanisms directly involved in tumor progression. The model further suggested points and means of intervention which could induce cell death in Ha-ras-transformed cells specifically. These hypotheses were directly tested in vitro and found to be largely correct, hence indicating that these new analytical and technological approaches allow the discovery of pathology-associated cellular mechanisms and physiologically defined targets leading to phenotype-specific pharmacological interventions.

Review article: mitogen-activated protein kinases in chronic intestinal inflammation - targeting ancient pathways to treat modern diseases

Conventional treatment of chronic inflammatory disorders, including inflammatory bowel diseases, employs broad-range anti-inflammatory drugs. In order to reduce the side-effects and increase the efficacy of treatment, several strategies have been developed in the last decade to interfere with intercellular and intracellular inflammatory signalling processes. The highly conserved mitogen-activated protein kinase pathways regulate most cellular processes, particularly defence mechanisms such as stress reactions and inflammation. In this review, we provide an overview of the current knowledge of the specificity and interconnection of mitogen-activated protein kinase pathways, their functions in the gut immune system and published and ongoing studies on the role of mitogen-activated protein kinases in inflammatory bowel disease. The development of mitogen-activated protein kinase inhibitors and their use for the therapy of inflammatory disorders is a paradigm of the successful bridging of the gap between basic research and clinical practice.

Regulation of C2C12 myogenic terminal differentiation by MKK3/p38alpha pathway

The signal transduction pathways connecting cell surface receptors to the activation of muscle-specific promoters and leading to myogenesis are still largely unknown. Recently, a contribution of the p38 mitogen-activated protein kinase (MAPK) pathway to this process was evoked through the use of pharmacological inhibitors. We used several mutants of the kinases composing this pathway to modulate the activity of the muscle-specific myosin light chain and myogenin promoters in C2C12 cells by transient transfections. In addition, we show for the first time, using a stable C2C12 cell line expressing a dominant-negative form of the p38 activator MAPK kinase (MKK)3, that a functional p38 MAPK pathway is indeed required for terminal muscle cell differentiation. The most obvious phenotype of this cell line, besides the inhibition of the activation of p38, is its inability to undergo terminal differentiation. This phenotype is accompanied by a drastic inhibition of cell cycle and myogenesis markers such as p21, p27, MyoD, and troponin T, as well as a profound disorganization of the cytoskeleton.

Mitogen-activated protein kinase p38 defines the common senescence-signalling pathway

BACKGROUND

Cellular senescence is a state of irreversible growth arrest shown by normal cells, and has been most extensively studied in replicative senescence caused by telomere shortening. Several conditions, including oncogenic Ras over-expression and inappropriate culture conditions, also induce senescence without telomere shortening. However, it remains unclear how a common set of senescence phenotypes is indistinguishably induced in various types of senescence.

RESULTS

We demonstrate that p38 mitogen-activated protein kinase (MAPK) plays important causative roles in senescent cells following telomere shortening, Ras-Raf activation, oxidative stress or inappropriate culture conditions. By monitoring the kinetics of p38 activation, we suggest that p38 is activated not directly by the initial stimuli, but in response to unidentified cellular conditions caused by these stimuli. Importantly, this p38-activating condition appears to be defined quantitatively as a sum of continuous and low-level stresses, and remains even after the initial stimuli are withdrawn, which may explain the well-known irreversible nature of cellular senescence. We also show that papilloma virus E7 abolishes the p38-induced growth arrest but not other senescence-associated phenotypes, indicating the differential role of pRb in the downstream of p38.

CONCLUSION

These results indicate that p38 comprises the senescence-executing pathway in response to diverse stimuli.

p38 MAPK mediates acid-induced transcription of PEPCK in LLC-PK(1)-FBPase(+) cells

LLC-PK(1)-FBPase(+) cells are a gluconeogenic and pH-responsive renal proximal tubule-like cell line. On incubation with acidic medium (pH 6.9), LLC-PK(1)-FBPase(+) cells exhibit an increased rate of ammonia production as well as increases in glutaminase and phosphoenolpyruvate carboxykinase (PEPCK) mRNA levels and enzyme activities. The increase in PEPCK mRNA is due to an enhanced rate of transcription that is initiated in response to intracellular acidosis. The involvement of known MAPK activities (ERK1/2, SAPK/JNK, p38) in the associated signal transduction pathway was examined by determining the effects of specific MAPK activators and inhibitors on basal and acid-induced PEPCK mRNA levels. Transfer of LLC-PK(1)-FBPase(+) cultures to acidic medium resulted in specific phosphorylation, and thus activation, of p38 and of activating transcription factor-2 (ATF-2), respectively. Anisomycin (AI), a strong p38 activator, increased PEPCK mRNA to levels comparable to those observed with acid stimulation. AI also induced a time-dependent phosphorylation of p38 and ATF-2. SB-203580, a specific p38 inhibitor, blocked both acid- and AI-induced PEPCK mRNA levels. Western blot analyses revealed that the SB-203580-sensitive p38alpha isoform is strongly expressed. The octanucleotide sequence of the cAMP-response element-1 site of the PEPCK promotor is a perfect match to the consensus element for binding ATF-2. The specificity of ATF-2 binding was proven by ELISA. We conclude that the SB-203580-sensitive p38alpha-ATF-2 signaling pathway is a likely mediator of the pH-responsive induction of PEPCK mRNA levels in renal LLC-PK(1)-FBPase(+) cells.

The effect of aging on p38 signaling pathway activity in the mouse liver and in response to ROS generated by 3-nitropropionic acid

Since mitochondrial dysfunction is a major source of oxidative stress in aged tissues, we asked whether the basal activities of stress response signaling pathway(s) are indicative of oxidative stress in aged tissues. To address this issue we asked whether: (a). aging affects the basal activity of the p38 MAPK stress signaling pathway; (b). the p38 MAPK pathway is activated by 3-nitropropionic acid (3-NPA), an inhibitor of complex II (succinic dehydrogenase) and generator of reactive oxygen species (ROS); (c). aging affects the response of the p38 alpha signaling pathway to 3-NPA. Our studies have shown that the basal kinase activities of p38 alpha, its upstream activator, MKK3, and its downstream substrate, ATF-2, are elevated in livers of aged C57BL/6 male mice and that these kinase activities, which are induced by 3-NPA in young livers, do not occur in aged livers. Furthermore, although aging does not affect their protein pool levels there are specific increases in phosphorylation of threonine residues in the p38 alpha and ATF-2 catalytic sites that might account for the increased basal level kinase activities in the aged livers. Our studies suggest that failure to respond to 3-NPA may be a factor in the susceptibility of aged tissue to oxidative damage, and support our hypothesis that aged tissues (especially liver) develop a state of chronic stress even in the absence of a challenge.

Activation of p38 alpha MAPK enhances collagenase-1 (matrix metalloproteinase (MMP)-1) and stromelysin-1 (MMP-3) expression by mRNA stabilization

Here, we have examined the role of distinct MAPK pathways in the regulation of collagenase-1 (matrix metalloproteinase (MMP)-1) and stromelysin-1 (MMP-3) expression by human skin fibroblasts. Tumor necrosis factor-alpha rapidly and transiently activated ERK1/2 and JNK in fibroblasts, whereas the activation of p38 MAPK was more persistent. Inhibition of p38 activity by SB203580 markedly (by 80-90%) inhibited induction of MMP-1 and MMP-3 expression by tumor necrosis factor-alpha, whereas blocking the activation of ERK1/2 by PD98059 had no effect. Activation of endogenous ERK1/2 by adenovirus-mediated transfer of constitutively active MEK1 resulted in potent induction of MMP-1 and MMP-3 expression. Activation of endogenous or adenovirally expressed p38 alpha by adenovirally delivered constitutively active MKK3b and MKK6b also enhanced MMP-1 and MMP-3 expression and augmented the up-regulatory effect of ERK1/2 activation on the expression of these MMPs. Activation of ERK1/2 resulted in induction of c-jun, junB, and c-fos expression, whereas activation of p38 alone had no effect. In contrast, activation of p38 alpha resulted in marked stabilization of MMP-1 and MMP-3 mRNAs. These results identify two distinct and complementary signaling mechanisms mediating induction of MMP-1 and MMP-3 expression in dermal fibroblasts: AP-1-dependent transcriptional activation via the ERK1/2 pathway and AP-1-independent enhancement via p38 alpha MAPK by mRNA stabilization. It is conceivable that both modes of action play an important role in controlling the proteolytic phenotype of fibroblasts, e.g. in wound repair and tumor invasion.

Modulation of human cytomegalovirus immediate-early gene enhancer by mitogen-activated protein kinase kinase kinase-1

The immediate-early (IE) promoter of human cytomegalovirus (HCMV) constitutes a primary genetic switch, which determines the progression of viral infection. Earlier reports by others have shown mitogen-activated protein kinase kinase kinase-1 (MEKK1) to be able to up-regulate HCMV-IE promoter through downstream mitogen-activated protein kinase (MAPK) pathways. However, we noticed that the activation of the HCMV-IE promoter by constitutively active MEKK1 (MEKK1-TRU) might not be through the MAPK pathways. Using a HCMV-IE enhancer/promoter (- 522 to + 72) driving a luciferase reporter, we demonstrated that the downstream MAPK activation actually repressed the up-regulation of the promoter by MEKK1 in CHO-K1 and human 293 cells. We further found that the up-regulation of HCMV-IE promoter by MEKK1 could be in great extent suppressed by over-expression of IkappaBalpha. Deletion of the NFkappaB/rel sites in the HCMV-IE enhancer region by mutagenesis proportionally reduced the transcriptional activation by MEKK1-TRU, whereas deletion of the ATF/CREB binding sites or cyclic AMP response elements (CRE) had no effects. Furthermore, the NFkappaB/rel deletion mutant also showed repression on the basic transcription activity of the HCMV-IE promoter. Our results indicate that the NFkappaB/rel sites are not only responsible for the modulation of HCMV-IE enhancer activity by MEKK1 but also control the basic transcription activity of the HCMV-IE promoter. On the other hand, the four consensus CRE sites were found to have no function in the activation of the promoter by MEKK1.

The proto-oncoprotein Brx activates estrogen receptor beta by a p38 mitogen-activated protein kinase pathway

The estrogen receptors (ERs) are ligand-inducible transcription factors that play key roles in the control of growth and differentiation in reproductive tissues. We showed that the novel Dbl family proto-oncoprotein Brx enhances ligand-dependent activity of ERalpha via a Cdc42-dependent pathway. Brx also significantly enhances ligand-dependent activity of ERbeta. This enhancement is not affected by inhibition of p44/42 mitogen-activated protein kinase (MAPK) activation by PD98059. However, addition of the p38 MAPK inhibitor SB202190 abrogates the enhancement of ERbeta activity by Brx, showing that p38 MAPK activity is required for the enhancement of ERbeta function by Brx. In COS-7 cells, transfection of Brx leads to activation of endogenous p38 MAPK activity. Co-expression of the beta2 isoform of human p38 MAPK and a constitutively active form of the p38 MAPK kinase MKK6 (MKK6-EE) synergistically augments ligand-dependent activity of ERbeta. Our findings suggest that p38 MAPKs may be important regulators of ERbeta activity.

Chronic exposure of human mesangial cells to high glucose environments activates the p38 MAPK pathway

BACKGROUND

High glucose (HG) environments activate several protein kinase pathways in mesangial cells, including the mitogen-activated protein kinase (MAPK) pathway, ERK. The p38 MAPK pathway is activated by events that occur in the setting of diabetes, such as protein kinase C (PKC) up-regulation and cellular stresses (osmotic stress and redox changes). Substrates of activated p38 MAPK include transcription factors that are involved in the microvascular complications of diabetes. This current study investigated the mechanisms of HG-mediated activation of p38 MAPK in cultured human mesangial cells (HMCs) and the effects of p38 MAPK activation on the transcription factor activator protein-1 (AP-1).

METHODS

HMCs were cultured in 5 mmol/L D-glucose [normal glucose (NG)] or 30 mmol/L D-glucose (HG) for seven days. Cells were also treated with HG for brief periods of time (0.5 to 4 hours) to assess the acute effects of HG on p38 MAPK. Using Western blotting of HMC lysates, changes in the tyrosine and threonine phosphorylation of p38 MAPK were measured. The kinase activity of immunoprecipitated p38 MAPK was determined by an in vitro assay that measured the phosphorylation and activation of MAPKAP kinase-2, an intermediary signaling protein downstream of p38 MAPK. To investigate the role of osmotic stress in HG activation of p38 MAPK, cells were acutely treated with mannitol (25 to 250 mOsm/L x 5 to 60 min) or were grown seven days in media supplemented with mannitol at concentrations iso-osmotic to HG media. To investigate the role of PKC in HG-mediated p38 MAPK activation, HMCs were treated with the PKC inhibitors GF 109203X, Ro 32-0432, or rottlerin during the last several hours of HG treatment. HG conditioned cells were also treated with the antioxidants L-N-acetylcysteine (L-NAC) or diphenyliodonium (DPI) prior to harvest. To determine a functional significance of HG-mediated p38 MAPK activation, the DNA binding of the transcription factor complex AP-1 was measured by electrophoretic mobility shift assay.

RESULTS

The p38 MAPK pathway was not activated by the acute addition of HG to the HMCs. However, activation of p38 MAPK in HMCs grown seven days in HG was demonstrated by increased tyrosine and threonine phosphorylation of p38 MAPK proteins and increased kinase activity of immunoprecipitated p38 MAPK. As assessed by a kinase assay, p38 MAPK activity in cells grown in HG for seven days exceeded that of NG cells by more than 250%. This difference was not due to differences in the amount of p38 MAPK protein between the treatment groups. Acute osmotic activation of p38 MAPK occurred at extremely high mannitol concentrations (250 mOsm/L) that exceeded the osmotic stress of acute HG. Furthermore, in cells grown for seven days in mannitol at concentrations similar to HG, p38 MAPK activity was similar to control values. Phorbol ester (PMA) treatment stimulated a twofold increase in p38 MAPK activity. The addition of GFX or Ro 32-0432 to HG cells, at concentrations that inhibited PMA activation of p38 MAPK, did not inhibit the glucose-mediated p38 MAPK activation. Rottlerin, a PKC delta inhibitor, also failed to reverse the HG-mediated p38 MAPK activation. Treatment of HG cells with L-NAC or DPI inhibited the HG-mediated p38 MAPK phosphorylation. As we have previously shown, DNA binding of the transcription factor complex AP-1 was increased in HG cells. This binding was reversed by treatment of the HG cells with the p38 MAPK inhibitor SB 203580.

CONCLUSIONS

Chronic exposure of HMC to HG concentrations activates the p38 MAPK pathway. This activation appears to be independent of changes in the amount of total p38 MAPK produced by the cells, independent of chronic osmotic stress and independent of PKC activation. The reversal of p38 MAPK by L-NAC and DPI suggests the glucose-mediated p38 MAPK activation may occur via reactive oxygen species. The activity of AP-1, a transcription factor complex that regulates several genes involved in diabetic nephropathy, is reversed when the p38 MAPK pathway is inhibited. These findings suggest the p38 MAPK pathway may be an important pathway involved in diabetic complications.

Developmental variability in expression and regulation of inducible nitric oxide synthase in rat intestine

Inducible nitric oxide synthase (iNOS) may be a key mediator of intestinal injury, which varies with developmental age. One member of the mitogen-activated protein kinase (MAPK) family, p38, is involved in the lipopolysaccharide (LPS)-mediated iNOS induction. The involvement of p38 MAPK in basal and LPS-induced iNOS expression was examined in the rat intestine at two developmental ages. Neonatal (4 days postnatal) and adolescent (15 days postnatal) rats were injected with LPS (5 microg/g ip), a selective p38 inhibitor (SB 203580), or both. Tissue was removed after 4 h and 6 h for mRNA and protein analysis. iNOS mRNA and protein were markedly upregulated in the adolescent female following LPS exposure, whereas males had an attenuated response. Neonates had a minimal response. SB 203580 suppressed LPS-induced iNOS mRNA and protein in the ileum, more so in females than in males. Adolescent ileal p38 activation was constitutively high and nonresponsive to LPS. Basal and post-LPS p38 phosphorylation was low in neonatal ileum. We conclude that ileal iNOS expression is developmentally regulated and influenced by gender and that p38 is permissive for LPS effect. The developmental regulation of p38 may contribute to age-dependent variations of intestinal injury.

MEK6 regulates human involucrin gene expression via a p38alpha - and p38delta -dependent mechanism

A signaling cascade that includes protein kinase C (PKC), Ras, and MEKK1 regulates involucrin (hINV) gene expression in epidermal keratinocytes (Efimova, T., LaCelle, P., Welter, J. F., and Eckert, R. L. (1998) J. Biol. Chem. 273, 24387-24395 and Efimova, T., and Eckert, R. L. (2000) J. Biol. Chem. 275, 1601-1607). Because signal transfer downstream of MEKK1 may involve several MAPK kinases (MEKs), it is important to evaluate the regulatory role of each MEK isoform. In the present study we evaluate the role of MEK6 in transmitting this signal. Constitutively active MEK6 (caMEK6) increases hINV promoter activity and increases endogenous hINV levels. The caMEK6-dependent increase in gene expression is inhibited by the p38 MAPK inhibitor, SB203580, and is associated with a marked increase in p38alpha MAPK activity; JNK and ERK kinases are not activated. In addition, hINV gene expression is inhibited by dominant-negative p38alpha and increased when caMEK6 and p38alpha are co-expressed. caMEK6 also activates p38delta, but p38delta inhibits the caMEK6-dependent activation. These results suggest that MEK6 increases hINV gene expression by regulating the balance between activation of p38alpha, which increases gene expression, and p38delta, which decreases gene expression.

Mitogen-activated protein kinase signal transduction in skeletal muscle: effects of exercise and muscle contraction

Exercise has numerous growth and metabolic effects in skeletal muscle, including changes in glycogen metabolism, glucose and amino acid uptake, protein synthesis and gene transcription. However, the mechanism(s) by which exercise regulates intracellular signal transduction to the transcriptional machinery in the nucleus, thus modulating gene expression, is largely unknown. This review will provide insight on potential intracellular signalling mechanisms by which muscle contraction/exercise leads to changes in gene expression. Mitogen-activated protein kinase (MAPK) cascades are associated with increased transcriptional activity. The MAPK family members can be separated into distinct parallel pathways including the extracellular signal-regulated kinase (ERK) 1/2, the stress-activated protein kinase cascades (SAPK1/JNK and SAPK2/p38) and the extracellular signal-regulated kinase 5 (ERK5). Acute exercise elicits signal transduction via MAPK cascades in direct response to muscle contraction. Thus, MAPK pathways appear to be potential physiological mechanisms involved in the exercise-induced regulation of gene expression in skeletal muscle.