Stress-activated Protein Kinase Cascade Research Articles

Perturbed fatty-acid metabolism is linked to localized chromatin hyperacetylation, increased stress-response gene expression and resistance to oxidative stress.

Oxidative stress is associated with cardiovascular and neurodegenerative diseases, diabetes, cancer, psychiatric disorders and aging. In order to counteract, eliminate and/or adapt to the sources of stress, cells possess elaborate stress-response mechanisms, which also operate at the level of regulating transcription. Interestingly, it is becoming apparent that the metabolic state of the cell and certain metabolites can directly control the epigenetic information and gene expression. In the fission yeast Schizosaccharomyces pombe, the conserved Sty1 stress-activated protein kinase cascade is the main pathway responding to most types of stresses, and regulates the transcription of hundreds of genes via the Atf1 transcription factor. Here we report that fission yeast cells defective in fatty acid synthesis (cbf11, mga2 and ACC/cut6 mutants; FAS inhibition) show increased expression of a subset of stress-response genes. This altered gene expression depends on Sty1-Atf1, the Pap1 transcription factor, and the Gcn5 and Mst1 histone acetyltransferases, is associated with increased acetylation of histone H3 at lysine 9 in the corresponding gene promoters, and results in increased cellular resistance to oxidative stress. We propose that changes in lipid metabolism can regulate the chromatin and transcription of specific stress-response genes, which in turn might help cells to maintain redox homeostasis.

RNA-Seq Reveals the Role of miR-29c in Regulating Inflammation and Oxidative Stress of Bovine Mammary Epithelial Cells.

Healthy mammary gland is essential for milk performance in dairy cows. MicroRNAs (miRNAs) are the key molecules to regulate the steady state of mammary gland in dairy cows. This study investigated the potential role of miR-29c in bovine mammary epithelial cells (bMECs). RNA sequencing (RNA-seq) was used to measure the transcriptome profile of bovine mammary epithelial cells line (MAC-T) transfected with miR-29c inhibitor or negative control (NC) inhibitor, and then differentially expressed genes (DEGs) were screened. The results showed that a total of 42 up-regulated and 27 down-regulated genes were found in the miR-29c inhibitor group compared with the NC inhibitor group. The functional enrichment of the above DEGs indicates that miR-29c is a potential regulator of oxidative stress and inflammatory response in bMECs through multiple genes, such as forkhead box O1 (FOXO1), tumor necrosis factor-alpha (TNF-α), and major histocompatibility complex, class II, DQ alpha 5 (BoLA-DQA5) in the various biological process and signaling pathways of stress-activated mitogen-activated protein kinase (MAPK) cascade, Epstein-Barr virus infection, inflammatory bowel disease, etc. The results imply that miR-29c plays an important role in a steady state of bMECs or cow mammary gland and may be a potential therapeutic target for mastitis in dairy cows.

Regulation of cotton (Gossypiumhirsutum) drought responses by mitogen-activated protein (MAP) kinase cascade-mediated phosphorylation of GhWRKY59.

Drought is a key limiting factor for cotton (Gossypium spp.) production, as more than half of the global cotton supply is grown in regions with high water shortage. However, the underlying mechanism of the response of cotton to drought stress remains elusive. By combining genome-wide transcriptome profiling and a loss-of-function screen using virus-induced gene silencing, we identified Gossypiumhirsutum GhWRKY59 as an important transcription factor that regulates the drought stress response in cotton. Biochemical and genetic analyses revealed a drought stress-activated mitogen-activated protein (MAP) kinase cascade consisting of GhMAP3K15-Mitogen-activated Protein Kinase Kinase 4 (GhMKK4)-Mitogen-activated Protein Kinase 6 (GhMPK6) that directly phosphorylates GhWRKY59 at residue serine 221. Interestingly, GhWRKY59 is required for dehydration-induced expression of GhMAPK3K15, constituting a positive feedback loop of GhWRKY59-regulated MAP kinase activation in response to drought stress. Moreover, GhWRKY59 directly binds to the W-boxes of DEHYDRATION-RESPONSIVE ELEMENT-BINDING PROTEIN 2 (GhDREB2), which encodes a dehydration-inducible transcription factor regulating the plant hormone abscisic acid (ABA)-independent drought response. Our study identified a complete MAP kinase cascade that phosphorylates and activates a key WRKY transcription factor, and elucidated a regulatory module, consisting of GhMAP3K15-GhMKK4-GhMPK6-GhWRKY59-GhDREB2, that is involved in controlling the cotton drought response.

Molecular mechanisms of liver injury and hepatocarcinogenesis: focusing on the role of stress-activated MAPK.

Hepatocellular carcinoma (HCC) is the third most common cause of cancer mortality. Short-term prognosis of patients with HCC has improved recently due to advances in early diagnosis and treatment, but long-term prognosis is still unsatisfactory. Therefore, obtaining a further understanding of the molecular carcinogenic mechanisms and the unique pathogenic biology of HCC is important. The most characteristic process in hepatocarcinogenesis is underlying chronic liver injury, which leads to repeated cycles of hepatocyte death, inflammation, and compensatory proliferation and subsequently provides a mitogenic and mutagenic environment leading to the development of HCC. Recent in vivo studies have shown that the stress-activated mitogen-activated protein kinase (MAPK) cascade converging on c-Jun NH2-terminal kinase (JNK) and p38 plays a central role in these processes, and it has attracted considerable attention as a therapeutic target. However, JNK and p38 have complex functions and a wide range of cellular effects. In addition, crosstalk with each other and the nuclear factor-kappaB pathway further complicate these functions. A full understanding is essential to bring these observations into clinical settings. In this paper, we discuss the latest findings regarding the mechanisms of liver injury and hepatocarcinogenesis focusing on the role of the stress-activated MAPK pathway.

BcAtf1, a global regulator, controls various differentiation processes and phytotoxin production in Botrytis cinerea.

Atf1-homologous basic region leucine zipper (bZIP) transcription factors are known to act downstream of the stress-activated mitogen-activated protein kinase (SAPK) cascade in mammals, as well as in several fungi; they regulate the transcription of genes involved in the general stress response. Functional analyses of BcAtf1 in Botrytis cinerea show that it is also connected to the SAPK BcSak1, as it shares several stress response target genes. However, Δbcatf1 mutants are not hypersensitive to osmotic or oxidative stress, as are Δbcsak1 mutants. Both BcSak1 and BcAtf1 are regulators of differentiation, but their roles in these processes are almost inverse as, in contrast with Δbcsak1, Δbcatf1 mutants are significantly impaired in conidia production and do not differentiate any sclerotia. They show extremely vigorous growth in axenic culture, with a thick layer of aerial hyphae and a marked increase in colonization efficiency on different host plants and tissues. In addition, the sensitivity to cell wall-interfering agents is increased strongly. Microarray analyses demonstrate that the loss of BcAtf1 leads to extensive transcriptional changes: apart from stress response genes, the expression of a broad set of genes, probably involved in primary metabolism, cell wall synthesis and development, is affected by BcAtf1. Unexpectedly, BcAtf1 also controls secondary metabolism: the mutant contains significantly elevated levels of phytotoxins. These data indicate that BcAtf1 controls a diversity of cellular processes and has broad regulatory functions.

KLF4 suppresses HDACi induced caspase activation and the SAPK pathway by targeting p57Kip2

Kruppel-like factor 4 (KLF4) belongs to a family of evolutionarily conserved zinc finger-containing transcription factors. It has been shown to mediate self renewal and pluripotency, regulate adipogenesis and play a critical role in monocyte differentiation. KLF4 is also highly expressed in squamous cell carcinomas and in 70% of all primary human breast cancers, suggesting a putative role for KLF4 as being an oncogene and as an antiapoptotic factor. However, the mechanism of this regulation remains unclear. Here, we show that KLF4 is induced during histone deacetylase inhibitor treatment, and regulates the extrinsic apoptosis pathway by inhibiting caspase cleavage. In addition, KLF4 binds to the p57(Kip2) promoter and transcriptionally upregulates its expression, which in turn inhibits the stress activated protein kinase cascade and c-Jun phosphorylation. Our findings indicate that in cancer cells that express high levels of KLF4 may be refractory to HDACi treatment. Results of our study demonstrate an unexpected antiapoptotic function of KLF4, and suggest an important cell fate determinant following histone deacetylase inhibitor induced apoptosis.

Stress-Activated MAP Kinase Cascades in Cellular Senescence

In response to progressive telomere shortening in successive cell divisions, normal somatic cells withdraw from the cell cycle and exhibit irreversible growth arrest. This state, called cellular senescence, is induced not only by telomere shortening but also by various physico-chemical stressors that induce DNA damage and chromatin disruption as well as by strong mitogenic signals. Because senescent cells never re-enter the cell cycle, cellular senescence appears to prevent malignant transformation of damaged cells and thus contributes to tumor suppression. On the other hand, excess accumulation of senescent cells attenuates the integrity and normal function of tissues, leading to age-related diseases. In addition to the well-established roles of p53 and pRB in cellular senescence, recent evidence suggests that stress-activated mitogen-activated protein kinase (MAPK) cascades that converge on c-Jun N-terminal kinases (JNKs) and p38 MAPKs also play important roles in the regulation of cellular senescence. In this review, we focus on signaling that regulates stress-induced cellular senescence, with special focus on the JNK and p38 MAPK cascades.

Apoptotic cardiomyocyte hypertrophy during sepsis and septic shock results from prolonged exposure to endothelin precursor

Septic shock is a complex cardiovascular dysfunction which leads to regional circulatory alterations and multi-organ dysfunction in humans and animal models. To elucidate the role of stress-activated signaling molecules in the regulation of myocardial dysfunction, we have developed and standardized isolated ventricular myocyte techniques. These techniques allow the assessment of cardiodynamics at cellular (ventricular myocyte) level. These studies are carried out in a well defined model of systemic inflammatory response syndrome following polymicrobial sepsis in the rat. Evidence is provided that sepsis-induced myocardial dysfunction produces indications (signs) of early stages of heart failure. This evidence correlates with upregulation of stress-activated protein kinase cascade. These findings suggest that prolonged exposure to endothelin precursor causes decompensatory hypertrophy in adult rat ventricular myocytes (ARVMs) during sepsis. The decompensatory hypertrophy could, in turn, results in increased cytosolic caspases-3 activity in ARVMs.

Methylglyoxal as a Signal Initiator for Activation of the Stress-activated Protein Kinase Cascade in the Fission Yeast Schizosaccharomyces pombe

Methylglyoxal (MG) is a typical 2-oxoaldehyde derived from glycolysis. We have recently found that MG activates transcription factors such as Yap1 and Msn2, and triggers a Hog1 mitogen-activated protein kinase cascade in Saccharomyces cerevisiae. Regarding the activation of Hog1 by MG, we found that Sln1, an osmosensor possessing histidine kinase activity, functions as a sensor of MG (Maeta, K., Izawa, S., and Inoue, Y. (2005) J. Biol. Chem. 280, 253-260). To gain further insight into the role of MG as a signal initiator, here we analyze the response of Schizosaccharomyces pombe to extracellular MG. Spc1, a stress-activated protein kinase (SAPK), was phosphorylated following the treatment with MG. No phosphorylation was observed in a wis1Delta mutant. The His-to-Asp phosphorelay system consisting of three histidine kinases (Phk1, Phk2, and Phk3), a phosphorelay protein (Spy1), and a response regulator (Mcs4) exists upstream of the Spc1-SAPK pathway. The phosphorylation of Spc1 following MG treatment was observed in phk1Deltaphk2Deltaphk3Delta and spy1Delta cells, but not in mcs4Delta cells. These results suggest that S. pombe has an alternative module(s) that directs the MG signal to the SAPK pathway via Mcs4. Additionally, we found that the transcription factor Pap1 is concentrated in the nucleus in response to MG, independent of the Spc1-SAPK pathway.

Induction of a Ribotoxic Stress Response That Stimulates Stress-Activated Protein Kinases by 13-Deoxytedanolide, an Antitumor Marine Macrolide

13-Deoxytedanolide is a structurally unique macrolide with strong antitumor activity isolated from a marine sponge. Recently, we showed that 13-deoxytedanolide bound to the large subunit of the yeast ribosome and inhibited polypeptide elongation in vitro, but the mechanism by which it exerts antitumor activity is still unknown. Here we show that 13-deoxytedanolide strongly induces plasminogen activator inhibitor 1 (PAI-1) promoter-derived gene expression. 13-Deoxytedanolide, unlike TGF-beta, did not cause apparent nuclear translocation of Smad2/3, but it relocalized the temperature-sensitive mutant of mouse p53 (p53Val153) from the cytoplasm to the nucleus at a nonpermissive temperature, suggesting that 13-deoxytedanolide inhibits protein synthesis. Indeed, the drug inhibited in vivo protein synthesis at low nanomolar concentrations and strongly activated stress-activated protein kinases such as p38 mitogen-activated protein kinase and Jun NH2-terminal protein kinase (JNK). Anisomycin, a well-known inducer of ribotoxic stress that activates both p38 and JNK, also activated PAI-1 gene expression, while other protein synthesis inhibitors that do not activate the kinases failed to do so. PAI-1 gene expression by 13-deoxytedanolide and anisomycin was blocked by SB202190, a specific inhibitor of p38, and SP600125, an inhibitor of both p38 and JNK. 13-Deoxytedanolide and anisomycin caused activation of apoptosis signal-regulating kinase 1, MKK3/MKK6, and SEK1/MKK4, the regulatory kinases upstream of p38 and JNK. These results suggest that 13-deoxytedanolide, like anisomycin, triggers a ribotoxic stress response that activates stress-activated protein kinase cascades, thereby inducing PAI-1 gene expression and apoptosis.

Physiological roles of stress-activated protein kinases in skin

Stress-activated protein kinase (SAPK) cascades control a variety of cellular activities such as survival, differentiation and apoptosis. Recent studies have revealed that SAPKs play important roles in the regulation of homeostasis of skin. This report focuses on SAPK-mediated signal transduction and provides advanced findings on the physiological roles of SAPKs in skin.

Polo kinase links the stress pathway to cell cycle control and tip growth in fission yeast

Stress-activated mitogen-activated protein kinase cascades instigate a range of changes to enable eukaryotic cells to cope with particular insults. In Schizosaccharomyces pombe these responses include the transcription of specific gene sets and inhibition of entry into mitosis. The S. pombe stress response pathway (SRP) also promotes commitment to mitosis in unperturbed cell cycles to allow cells to match their rate of division with nutrient availability. The nature of this SRP function in cell cycle control is unknown. Entry into mitosis is controlled by mitosis-promoting factor (MPF; Cdc2/cyclin B) activity. Inhibitory phosphorylation of Cdc2 by Wee1 kinase inactivates MPF until Cdc25 removes this phosphate to promote mitosis. The balance between Wee1 and Cdc25 activities is influenced by the recruitment of polo kinase (Plo1) to the spindle pole body (SPB). The SPB component Cut12 mediates this recruitment. Hyper-activating mutations in either cut12 or plo1 enable Cdc25-defective cells to enter mitosis. The hyperactive cut12.s11 mutation suppresses cdc25.22, as it promotes recruitment of active Plo1 to interphase SPBs. Here we show that the SRP promotes phosphorylation of Plo1 on Ser 402. In unperturbed cell cycles, SRP-mediated phosphorylation of Ser 402 promotes Plo1 recruitment to SPBs and thus commitment to mitosis. Ser 402 phosphorylation also ensures efficient reinitiation of cell tip growth and cell division during recovery from particular stresses. Thus, phosphorylation of Plo1 Ser 402 not only enables SRP signalling to modulate the timing of mitotic commitment in response to nutrient status in unperturbed cycles, but also promotes the return to normal cell cycle control after stress.

Cellular signaling mechanisms in alcohol-induced liver damage.

Chronic excessive alcohol intake is associated with multiple liver defects ranging from mild steatosis to advanced cirrhosis. However, the mechanisms by which chronic ethanol intake affects liver function remain a matter of intense debate and investigation. The liver is the major site of ethanol metabolism in the body, and a wide range of metabolic alterations is associated with ethanol intake. As a result, the liver is exposed to dramatic changes in redox state, transient hypoxia, episodes of oxidative stress, and the products of ethanol metabolism, such as acetaldehyde, acetate, and fatty acid ethyl esters. Chronic ethanol consumption is associated with increased levels of circulating endotoxins and proinflammatory cytokines that affect liver function. A major source of the increase in circulating proinflammatory cytokines is the Kupffer cells, which are sensitized to generate tumor necrosis factor alpha (TNF-alpha) through multiple mechanisms. In addition, the hepatocytes themselves are more susceptible to external stress. In isolated hepatocytes, this effect of chronic ethanol is evident in a greater sensitivity to proapoptotic challenges and, more specifically, to the cytotoxic actions of TNF-alpha. The mechanism by which hepatocytes are sensitized to external stress remains poorly characterized but may involve defects in mitochondrial function and oxidative defense mechanisms, the activation of death-promoting signaling pathways, and the inactivation of survival pathways. In this article, we emphasize the role of the stress-activated mitogen-activated protein kinase (MAPK) cascades in the onset of cell injury and their regulation by the phosphoinositide-3-kinase/Akt signaling cascade, which appears to function as the central integrating module of the stress-signaling machinery in the cell. We also discuss the complications and challenges of extrapolating these findings to the conditions in vivo and what we can learn from these studies regarding the nature of the liver defects associated with chronic alcohol consumption.

Fission yeast global repressors regulate the specificity of chromatin alteration in response to distinct environmental stresses.

The specific induction of genes in response to distinct environmental stress is vital for all eukaryotes. To study the mechanisms that result in selective gene responses, we examined the role of the fission yeast Tup1 family repressors in chromatin regulation. We found that chromatin structure around a cAMP-responsive element (CRE)-like sequence in ade6-M26 that is bound by Atf1.Pcr1 transcriptional activation was altered in response to osmotic stress but not to heat and oxidative stresses. Such chromatin structure alteration occurred later than the Atf1 phosphorylation but correlated well with stress-induced transcriptional activation at ade6-M26. This chromatin structure alteration required components for the stress-activated protein kinase (SAPK) cascade and both subunits of the M26-binding CREB/ATF-type protein Atf1.Pcr1. Cation stress and glucose starvation selectively caused chromatin structure alteration around CRE-like sequences in cta3(+) and fbp1(+) promoters, respectively, in correlation with transcriptional activation. However, the tup11Delta tup12Delta double deletion mutants lost the selectivity of stress responses of chromatin structure and transcriptional regulation of cta3(+) and fbp1(+). These data indicate that the Tup1-like repressors regulate the chromatin structure to ensure the specificity of gene activation in response to particular stresses. Such a role for these proteins may serve as a paradigm for the regulation of stress response in higher eukaryotes.

Implication of raft microdomains in drug induced apoptosis.

DNA damaging agents such as 1-beta-D-arabinofuranosylcytosine (Ara-C) and daunorubicin (DNR) are widely used in the treatment of acute nonlymphocytic leukemia. These drugs have, of course, been the objects of intense basic research, as well as preclinical and clinical study. Although specific biochemical lesions (DNA damage) have been associated with Ara-C- and DNR-mediated cytotoxicity, the pathways leading to the induction of apoptosis remain ill defined. This standpoint has forced investigators to explore a new concept in cell response to cytotoxic stress: apoptosis signaling. The recent identification of a ceramide (CER) mediated apoptotic signaling pathway triggered by antitumor agents offers a new perspective for the treatment of neoplastic cells. Indeed, these agents have been shown to induce apoptosis through the activation of a sphingomyelinase (SMase) responsible for the hydrolysis of sphingomyelin (SM) and the generation of CER. The latter acts as a potent apoptosis mediator, triggering several downstream signaling pathways among which the stress-activated protein kinase cascade (MEKK1-SEK1-SAP/JNK) plays a critical role in apoptosis induction. However, the spacio-temporal organization of the key early signaling events is unclear. The present review delineates what appears to be a critical factor in apoptosis signaling: sphingomyelin enriched plasma membrane rafts. The apparent topological partitioning between DNA damage and apoptosis signaling (integrated into specialized plasma membrane domains) is discussed.

Immediate-early gene induction by the stresses anisomycin and arsenite in human osteosarcoma cells involves MAPK cascade signaling to Elk-1, CREB and SRF.

Cellular stress activates multiple mitogen-activated protein kinase (MAPK) cascades and immediate-early gene (IEG) transcription. To address how these events are linked, we investigated the endogenous signaling/transcription factor network driving IEG activation by arsenite and anisomycin in the human osteosarcoma cell line HOS/TE-85. Induction of IEG transcription by both stresses corresponded temporally with the phosphorylation of the regulatory factors Elk-1 and cAMP response element-binding protein (CREB), along with activation of the extracellular signal-regulated kinase (ERK), stress-activated protein kinase (SAPK) and p38 MAPK cascades. To assess the role of the different cascades, they were selectively inhibited with PD98059, SP600125 and SB203580, respectively. This implicated all three cascades in Elk-1 phosphorylation after arsenite treatment, whereas ERK and SAPK inhibition diminished this, and IEG mRNA levels, downstream of anisomycin. SB blocked phosphorylation of both serum response factor (SRF) and CREB, and strongly reduced IEG activation by both stresses. Combining PD with SB further reduced arsenite induction of IEG transcription. Thus, all three MAPK cascades mediate anisomycin- and arsenite-induced signaling to IEG promoters in HOS cells through the differential targeting of Elk-1, SRF and CREB.

Involvement of a CCAAT-binding complex in the expression of a nitrogen-starvation-specific gene, isp6+, in Schizosaccharomyces pombe.

The fission yeast gene isp6+ is needed in nitrogen-starvation response but its transcriptional regulation has been unclear. isp6+ was repressed under nutrient conditions, in which cAMP-dependent protein kinase A, the stress-activated protein kinase cascade, and the CCAAT-binding complex were concerned. The CCAAT-binding complex also was involved in the induction of isp6+ during nitrogen starvation.

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.

The parkinsonian neurotoxin, MPP + induces phosphorylated c-Jun in dopaminergric neurons of mesencephalic cultures

The stress-activated protein kinase (SAPK) cascade serves a critical role in the apoptotic death of neuronal cells in response to a variety of cellular stresses. Recent in vitro and in vivo evidence has directly implicated this kinase in the death of dopaminergic nigral neurons in the MPTP model of Parkinson's disease (PD). To assess the involvement of c-Jun, a key transcription factor substrate of SAPK (also known as c-Jun N-terminal kinase, or JNK) in the MPTP-induced death of dopaminergic nigral neurons, we determined the ability of MPP +, the active toxin metabolite of MPTP, to induce the phosphorylated form of c-Jun in dopaminergic neurons in nigral (ventral mesencephalon) cultures. At a dose of MPP + that specifically induces apoptotic changes in nuclear morphology in tyrosine hydroxylase-positive (dopaminergic) cells in these cultures, MPP + induces nuclear phospho-c-Jun immunoreactivity (IR). The peak induction of phospho-c-Jun IR was observed 16 h after beginning MPP + exposure, and preceded the maximal induction of apoptotic nuclear changes by approximately 8 h. These data support an important role for the SAPK/JNK pathway including its c-Jun transcriptional target in the apoptotic death of dopaminergic nigral neurons in the MPTP model of PD.

Regulation of the TAK1 Signaling Pathway by Protein Phosphatase 2C

Protein phosphatase 2C (PP2C) is implicated in the negative regulation of stress-activated protein kinase cascades in yeast and mammalian cells. In this study, we determined the role of PP2Cbeta-1, a major isoform of mammalian PP2C, in the TAK1 signaling pathway, a stress-activated protein kinase cascade that is activated by interleukin-1, transforming growth factor-beta, or stress. Ectopic expression of PP2Cbeta-1 inhibited the TAK1-mediated mitogen-activated protein kinase kinase 4-c-Jun amino-terminal kinase and mitogen-activated protein kinase kinase 6-p38 signaling pathways. In vitro, PP2Cbeta-1 dephosphorylated and inactivated TAK1. Coimmunoprecipitation experiments indicated that PP2Cbeta-1 associates with the central region of TAK1. A phosphatase-negative mutant of PP2Cbeta-1, PP2Cbeta-1 (R/G), acted as a dominant negative mutant, inhibiting dephosphorylation of TAK1 by wild-type PP2Cbeta-1 in vitro. In addition, ectopic expression of PP2Cbeta-1(R/G) enhanced interleukin-1-induced activation of an AP-1 reporter gene. Collectively, these results indicate that PP2Cbeta negatively regulates the TAK1 signaling pathway by direct dephosphorylation of TAK1.