Apoptosis Signal-regulating Kinase 1 Overexpression Research Articles

Apocynin attenuates diabetic cardiomyopathy by suppressing ASK1-p38/JNK signaling

Diabetic cardiomyopathy (DCM) significantly increased the morbidity of heart failure in diabetic patients. Long-time oxidative stress is an indisputable contributor for DCM development. Apocynin (APO) has been suggested to be a potential drug against oxidative stress. The study aims to find out the effects of APO on DCM and the related mechanisms. Mice were randomly divided into four groups: control (CON), APO, DCM and DCM + APO. Echocardiography analyses, histological analyses, Western blot and RT-PCR were used to explore the roles and mechanisms of APO in DCM. Isolated neonatal rat cardiomyocytes (NRCMs) and cardiac fibroblasts (CFs) were used for further confirming the APO treatment effects in vitro. Deteriorated cardiac function, enlarged cardiomyocytes, excess cardiac fibrosis and significant cardiac oxidative stress were observed in DCM group. However, APO treatment successfully improved cardiac function, decreased cardiac hypertrophy and fibrosis, and depressed oxidative stress. Mechanistically, APO treatment markedly suppressed apoptosis signal regulating kinase 1(ASK1)-p38/c-jun N-terminal kinase (JNK) signaling and reduced apoptosis. It also inhibited NRCM apoptosis and CF activation via depressing ASK1-p38/JNK signaling in vitro. Moreover, adenovirus-mediated ASK1 overexpression completely removed the protection of APO in vitro. In conclusion, APO treatment could effectively attenuate DCM-associated injuries in vivo and protect against high glucose-induced NRCM and CF injuries in vitro via suppressing ASK1-p38/JNK signaling. APO might be a potential ASK1 inhibitor for treating DCM.

Apelin‑36 protects against lipopolysaccharide‑induced acute lung injury by inhibiting the ASK1/MAPK signaling pathway.

Apelin-36 is able to mediate a range of effects on various diseases, and is upregulated in lipopolysaccharide (LPS)-induced acute lung injury (ALI). However, to the best of our knowledge, whether apelin-36 is able to regulate LPS-induced ALI has yet to be investigated. The present study aimed to investigate the role of apelin-36 in LPS-induced ALI, and the putative underlying mechanisms. Rats were assigned to one of four treatment groups: The Control group, apelin-36 group, LPS group and LPS + apelin-36 group. At 4 h after intratracheal instillation of LPS (5 mg/kg), rats were intraperitoneally treated with 10 nmol/kg apelin-36. Subsequently, pathological manifestations and the extent of inflammation and apoptosis of the lung tissues were assessed. Untransfected and apoptosis signal-regulating kinase 1 (ASK1)-overexpressing Beas-2B cells were treated with LPS in the absence or presence of apelin-36, and subsequently the levels of inflammation and apoptosis were assessed. The results obtained showed that the level of apelin-36 was increased in the bronchoalveolar lavage fluid (BALF) of LPS-treated rats. Co-treatment with apelin-36 alleviated LPS-induced lung injury and pulmonary edema, reduced the levels of pro-inflammatory cytokines, including interleukin-6, monocyte chemoattractant protein-1 and tumor necrosis factor-α, in BALF, and inhibited apoptosis in the lung tissues. The presence of apelin-36 also blocked the activation of LPS-induced ASK1, p38, c-Jun N-terminal kinase and extracellular signal-regulated kinase in lung tissues. In vitro studies performed with Beas-2B cells showed that the addition of apelin-36 led to an increase in the cell viability of LPS-induced Beas-2B cells in a concentration-dependent manner. Additionally, co-treatment with 1 µM apelin-36 prevented LPS-induced inflammation and apoptosis. However, overexpression of ASK1 significantly reversed the inhibitory effects of apelin-36 on LPS-induced inflammation and apoptosis. Taken together, the results of the present study demonstrated that apelin-36 was able to protect against LPS-induced lung injury both in vivo and in vitro, and these actions may be dependent on inhibition of the ASK1/mitogen-activated protein kinase signaling pathway.

Liver ASK1 protects from non‐alcoholic fatty liver disease and fibrosis

Non‐alcoholic fatty liver disease (NAFLD) is strongly associated with obesity and may progress to non‐alcoholic steatohepatitis (NASH) and liver fibrosis. The deficit of pharmacological therapies for the latter mainly results from an incomplete understanding of involved pathological mechanisms. Herein, we identify apoptosis signal‐regulating kinase 1 (ASK1) as a suppressor of NASH and fibrosis formation. High‐fat diet‐fed and aged chow‐fed liver‐specific ASK1‐knockout mice develop a higher degree of hepatic steatosis, inflammation, and fibrosis compared to controls. In addition, pharmacological inhibition of ASK1 increased hepatic lipid accumulation in wild‐type mice. In line, liver‐specific ASK1 overexpression protected mice from the development of high‐fat diet‐induced hepatic steatosis and carbon tetrachloride‐induced fibrosis. Mechanistically, ASK1 depletion blunts autophagy, thereby enhancing lipid droplet accumulation and liver fibrosis. In human livers of lean and obese subjects, ASK1 expression correlated negatively with liver fat content and NASH scores, but positively with markers for autophagy. Taken together, ASK1 may be a novel therapeutic target to tackle NAFLD and liver fibrosis.

Apoptosis signal‐regulating kinase‐1 inhibitor as a potent therapeutic drug for the treatment of gastric cancer

Aside from the human epidermal growth factor receptor-2 (HER2)-targeting agent trastuzumab, molecular targeting therapy for gastric cancer (GC) has not been established. We previously reported that apoptosis signal-regulating kinase-1 (ASK1) was upregulated in human GC and that overexpression of ASK1 promoted GC cell proliferation. Here, we investigated the effect of ASK1 inhibitor K811 on GC cells. K811 efficiently prevented cell proliferation in cell lines with high ASK1 expression and in HER2-overexpressing GC cells. Treatment with K811 reduced sizes of xenograft tumors by downregulating proliferation markers. These results indicate that ASK1 inhibition prevents GC cell growth in vitro and in vivo, suggesting that ASK1 inhibitors can be potent therapeutic drugs for GC.

Apoptosis Signal-Regulating Kinase 1–Thioredoxin Complex Dissociation by Capsaicin Causes Pancreatic Tumor Growth Suppression by Inducing Apoptosis

In this study, we evaluated the effect of capsaicin on the interaction of redox-sensitive thioredoxin (Trx)/apoptosis signal-regulating kinase 1 (ASK1) in pancreatic cancer cells. Capsaicin treatment downregulated Trx and increased the phosphorylation (activation) of ASK1 at Thr845 and kinase activity in AsPC-1 and BxPC-3 cells. Capsaicin treatment also activated downstream effector molecules MKK4/7, caspase-9, and caspase-3. Antioxidants tiron or PEG-catalase blocked the activation of ASK1 cascade by capsaicin and protected the cells from apoptosis, indicating the involvement of reactive oxygen species in the activation of ASK1. Our results further revealed that Trx overexpression suppressed the effects of capsaicin, whereas ASK1 overexpression enhanced the apoptosis-inducing effects of capsaicin. β-mercaptoethanol, a reducing agent, blocked capsaicin-mediated activation of ASK1, indicating that Trx-ASK1 complex exists and requires reducing conditions in the cell. On the other hand, the Trx inhibitor (1-chloro-2-4-dinitrobenzene) increased capsaicin-induced ASK1 kinase activity, suggesting that Trx inhibition by capsaicin is essential for ASK1 activation. Oral administration of 5 mg capsaicin/kg body weight substantially suppressed the growth of tumors in xenograft and orthotopic mouse model. Tumors from capsaicin-treated mice showed reduced levels of Trx, increased phosphorylation of ASK1 at Thr845, and cleavage of caspase-3 and poly (ADP-ribose) polymerase. Our results for the first time demonstrated a new perspective that Trx-ASK1 complex can be targeted by capsaicin in pancreatic cancer. Capsaicin reduces Trx expression and dissociates Trx-ASK1 complex resulting in the activation of ASK1 and downstream effectors leading to apoptosis in pancreatic tumor cells in vitro and in vivo.

Abstract 2079: RSK2 mediates anti-anoikis signals by regulating downstream factors through both transcription -independent and -dependent manner in human cancers

Abstract Metastasis is the most dangerous switch during tumor progression, which involves complicated steps of events including anoikis resistance. Anoikis is an anchorage-dependent cell death induced by loss of cell or extracellular matrix attachment. Metastatic tumor cells may escape from anoikis and invade other organs. However, the signaling mechanisms by which invading tumor cells become resistant to the anoikis process remains unclear. We recently reported that continued RSK2 expression contributes to the maintenance of the invasive and metastatic potential of human head and neck squamous cell carcinoma (HNSCC). Further studies revealed that RSK2 signaling is commonly important to protect metastatic human cancer cell lines including 212LN (HNSCC), A549 (lung cancer), and SKBR3 (breast cancer) from anoikis. Stable knockdown of RSK2 did not significantly affect apoptosis induced by control anti-cancer agent cycloheximide, but sensitized various cancer cell lines to detachment-induced anoikis. Phosphor-proteomics based study identified two RSK2 phosphorylation targets, including a newly identified RSK2 substrate, apoptosis signal-regulating kinase 1 (ASK1), and a known target, CREB. Further study revealed that they are involved in RSK2 dependent anti-anoikis signaling. ASK1 is a mitogen-activated protein kinase kinase kinase, and its activity is regulated in various ways, including phosphorylation. Our study showed that RSK2 directly phosphorylates ASK1 at multiple sites, which negatively contribute to ASK1 kinase and pro-apoptotic activity. Knockdown of ASK1 in cells resulted in decreased anoikis, while overexpression of ASK1 sensitized cells to anoikis which suggest that RSK2 phosphorylates and inhibits ASK1 to protect cancer cells from anoikis. CREB is a transcription factor activated by RSK2 whose signaling is implicated in promoting tumor progression and metastasis. We identify RSK2αCREB transcription targets by performing DNA microarray using metastatic HNSCC cells with stable knockdown of RSK2 or CREB. We identified 115 and 45 genes that are down-regulated or up-regulated in both knockdown cells. Among these genes, we identified a group of anti-apoptotic genes down-regulated, and pro-apoptotic genes up-regulated as novel RSK2 and CREB transcription targets. Over-expression of the anti-apoptotic targets or transient knockdown of the pro-apoptotic targets rescued the anoikis induced by RSK2 knockdown and conferred resistance to cells from undergoing anoikis. These data suggest a transcription-dependent mechanism in which RSK2 may in part signal through CREB to provide anti-anoikis signals. These data together suggest that RSK2 provides anti-anoikis signals via ASK1 and CREB in both transcription-independent and -dependent manners, respectively, which may promote cancer cell invasion and tumor metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2079. doi:1538-7445.AM2012-2079

TGF-β-activated Kinase 1 (TAK1) and Apoptosis Signal-regulating Kinase 1 (ASK1) Interact with the Promyogenic Receptor Cdo to Promote Myogenic Differentiation via Activation of p38MAPK Pathway

p38MAPK plays an essential role in the transition of myoblasts to differentiated myotubes through the activation of MyoD family transcription factors. A promyogenic cell surface molecule, Cdo, promotes myogenic differentiation mainly through activation of the p38MAPK pathway. Two MAP3Ks, TAK1 and ASK1, can activate p38MAPK via MKK6 in various cell systems. Moreover TAK1 has been shown to promote myogenic differentiation via p38MAPK activation. In this study, we hypothesized that TAK1 and ASK1 might function as MAP3Ks in Cdo-mediated p38MAPK activation during myoblast differentiation. Both ASK1 and TAK1 were expressed in myoblasts and interacted with the cytoplasmic tail of Cdo and a scaffold protein, JLP. The depletion of TAK1 or ASK1 in C2C12 cells decreased myoblast differentiation, whereas overexpression of TAK1 or ASK1 in C2C12 cells enhanced myotube formation. In agreement with this, overexpression of ASK1 or TAK1 resulted in enhanced p38MAPK activation, and their knockdown inhibited p38MAPK in C2C12 cells. Overexpression of TAK1 or ASK1 in Cdo(-/-) myoblasts and Cdo-depleted C2C12 cells restored p38MAPK activation as well as myotube formation. Furthermore, ASK1 and TAK1 compensated for each other in p38MAPK activation and myoblast differentiation. Taken together, these findings suggest that ASK1 and TAK1 function as MAP3Ks in Cdo-mediated p38MAPK activation to promote myogenic differentiation.

Reciprocal Inhibition between the Transforming Growth Factor-β-activated Kinase 1 (TAK1) and Apoptosis Signal-regulating Kinase 1 (ASK1) Mitogen-activated Protein Kinase Kinase Kinases and Its Suppression by TAK1-binding Protein 2 (TAB2), an Adapter Protein for TAK1

Mitogen-activated protein kinase kinase kinases (MAP3Ks) are activated by a wide spectrum of extracellular stimuli and are involved in various cellular events including proinflammatory and oxidative damage response through activations of two specific transcription factors, nuclear factor κB (NF-κB) and activator protein-1 (AP-1). Although members of the MAP3K family have both overlapping and distinct functions, the inter-regulatory mechanism of MAP3Ks remains largely unknown. In this study we demonstrated that transforming growth factor-β-activated kinase 1 (TAK1)-TAK1-binding protein 1 (TAB1) complex negatively regulates ASK1-mediated signaling, and TAB2 reciprocally regulates TAK1-induced NF-κB and apoptosis signal-regulating kinase 1 (ASK1)-mediated AP-1 activations through the TAK1-TAB2 interaction and the interferences of TAK1-ASK1 interaction. TAK1 interacted with the N or C terminus of ASK1 through the C-terminal TAB2 binding domain of TAK1, with resultant inhibition of ASK1-induced AP-1 activation. Interestingly, the interaction between TAK1 and TAB2 significantly attenuated the ASK1-TAK1 interaction through the competitive interaction with ASK1 to TAK1 and resulted in the activations of TAK1-induced activations of NF-κB and AP-1. More interestingly, H(2)O(2)- and TNF-α-induced apoptosis in TAK1-deficient mouse embryo fibroblast cells were dramatically enhanced by overexpression of ASK1, whereas the apoptosis was markedly inhibited by the overexpression of TAK1. Overall, these results demonstrate that TAK1 and its adapter protein, TAB2, reciprocally regulate both TAK1- and ASK1-mediated signaling pathways to direct the activations of NF-κB and AP-1.

Abstract 3133: Apoptosis signal-regulating kinase 1 and cyclin D1 compose a positive feedback loop contributing to tumor growth in gastric cancer

Abstract Gastric cancer is a common cancer worldwide, associated with a high mortality despite its declining incidence in recent decades. Although the role of H. pylori in causing mucosal effects has been investigated, which molecular signal(s) initiate the program of irreversible transformation remain unclear, and thus molecular targeting therapies for GC have not been well established. Mitogen-activated protein kinase (MAPK) pathways regulate multiple cellular functions and have been demonstrated to be highly active in many types of human cancers, and we have previously reported that c-Jun-N-terminal kinase 1 (JNK1) is important for gastric tumorigenesis. Apoptosis signal-regulating kinase 1 (ASK1) is an upstream MAPK known to be involved in apoptosis, inflammation, and carcinogenesis. In the current study, we investigated the role of ASK1 in the development of gastric cancer. In human gastric cancer specimens, we observed increased ASK1 expression compared to non-tumor epithelium, while we found no difference between colon cancer and non-tumor colon epithelium. Using the chemically induced murine gastric tumorigenesis model, we observed increased tumor ASK1 expression, and ASK1 knockout mice displayed both a lower number and smaller tumor size compared to wild-type mice. In gastric cancer cell lines, immunoprecipitation analysis revealed constitutive ASK1 activation in several cell lines. ASK1 siRNA inhibited cell proliferation through the accumulation of cells in G1 phase of the cell cycle, and reduced cyclin D1 expression in gastric cancer cells, while these effects were uncommon in other cancer cells, suggesting that the ASK1-dependent regulation of the cyclin D1 level and cellular proliferation is specific to gastric cancer. Overexpression of ASK1 induced the transcription of cyclin D1 through AP-1 activation in a kinase-dependent manner. In addition, we found that the expression of ASK1 was elevated following epidermal growth factor (EGF) or Helicobacter pylori (H.pylori) treatment in control cells but not in cyclin D1 silencing cells. Overexpression of cyclin D1 enhanced phosphorylation of Rb, followed by the increase in ASK1 expression. Chromatin immunoprecipitation (ChIP) assay showed that cyclin D1 expression increase E2F1 binding to ASK1 promoter, suggesting that the levels of ASK1 were regulated by cyclin D1 through the Rb-E2F pathway. Exogenous ASK1 induced cyclin D1 expression, followed by an elevated expression of endogenous ASK1. These results indicate an autoregulatory mechanism of ASK1 in the development of gastric cancer. Through targeting this positive feedback loop, ASK1 may present a potential therapeutic target for the treatment of advanced gastric cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3133. doi:10.1158/1538-7445.AM2011-3133

Apoptosis signal-regulating kinase 1 and cyclin D1 compose a positive feedback loop contributing to tumor growth in gastric cancer

Mitogen-activated protein kinase (MAPK) pathways regulate multiple cellular functions and are highly active in many types of human cancers. Apoptosis signal-regulating kinase 1 (ASK1) is an upstream MAPK involved in apoptosis, inflammation, and carcinogenesis. This study investigated the role of ASK1 in the development of gastric cancer. In human gastric cancer specimens, we observed increased ASK1 expression, compared to nontumor epithelium. Using a chemically induced murine gastric tumorigenesis model, we observed increased tumor ASK1 expression, and ASK1 knockout mice had both fewer and smaller tumors than wild-type (WT) mice. ASK1 siRNA inhibited cell proliferation through the accumulation of cells in G1 phase of the cell cycle, and reduced cyclin D1 expression in gastric cancer cells, whereas these effects were uncommon in other cancer cells. ASK1 overexpression induced the transcription of cyclin D1, through AP-1 activation, and ASK1 levels were regulated by cyclin D1, via the Rb-E2F pathway. Exogenous ASK1 induced cyclin D1 expression, followed by elevated expression of endogenous ASK1. These results indicate an autoregulatory mechanism of ASK1 in the development of gastric cancer. Targeting this positive feedback loop, ASK1 may present a potential therapeutic target for the treatment of advanced gastric cancer.

Heat shock transcription factor-1 inhibits H2O2-induced apoptosis via down-regulation of reactive oxygen species in cardiac myocytes

Heat shock transcription factor-1 (HSF1) protects against cardiac diseases such as ischemia/reperfusion injury and myocardial infarction. However, the mechanisms have not yet been fully characterized. In this study, we investigated the effects of reactive oxygen species (ROS) and apoptosis signal-regulating kinase-1 (ASK1) in HSF1-regulated cardiomyocyte protection. Cultured cardiomyocytes of neonatal rats were transfected with HSF1, ASK1 or both of them before exposure to H(2)O(2), and the ROS generation, c-Jun N-terminal kinase (JNK) activity and apoptosis were examined. H(2)O(2) significantly increased intracellular ROS generation and apoptotic cells as expected, and all these cellular events were greatly inhibited by overexpression of HSF1. However, H(2)O(2)-induced increases in JNK phosphorylation and cell apoptosis were largely enhanced by ASK1 overexpression whereas the similar transfection did not affect the ROS generation in the cells. Moreover, inhibition of H(2)O(2)-increased ROS generation, JNK phosphorylation, and cellular apoptosis by overexpression of HSF1 tended to be disappeared, when the cells were co-transfected with ASK1. These results suggest that HSF1 protects cardiomyocytes from apoptosis under oxidative stress via down-regulation of intracellular ROS generation and inhibition of JNK phosphorylation. Although ASK1 itself has no effect on intracellular ROS generation, it may affect the inhibitory effects of HSF1 on ROS generation, JNK activity, and cardiomyocyte injury.

ASK1 Overexpression Accelerates Paraquat-Induced Autophagy via Endoplasmic Reticulum Stress

Apoptosis signal-regulating kinase 1 (ASK1) is activated by various types of stress, including, endoplasmic reticulum (ER) stress. ER stress-induced ASK1 activation could play an important role both in neuronal apoptosis and an autophagic response in the pathogenesis of several neurodegenerative diseases, including Parkinson's disease. The mechanism by which ASK1 executes apoptosis and/or autophagy under ER stress is still unclear. We have addressed this question using SH-SY5Y cells overexpressing wild-type (WT) ASK1. We show an important autophagic response and an acceleration of the paraquat (PQ)-induced autophagy with hallmarks as accumulation of autophagic vacuoles, activation of beclin-1, accumulation of LC3 II, p62 degradation, and mammalian target of rapamycin dephosphorylation. Inhibition of autophagy caused an exacerbation of the apoptosis induced by WT ASK1 overexpression with or without PQ. These data support the idea that the autophagic response could have a protector role. We found also an increase in the phosphorylation of the proteins such as IRE1 and eIF2α in response to both the overexpression of WT ASK1 and pesticide exposure. These data suggest that the WT ASK1 overexpression-induced autophagy is an event that occurs in parallel with ER stress activation. The importance of ER stress in the autophagy induced by ASK1 and/or PQ was confirmed with salubrinal, a selective inhibitor of eIF2α dephosphorylation. In conclusion, we report that PQ induces an early ER stress response that is correlated with the activation of autophagy as a protective response, which is accelerated in cells that overexpress WT ASK1. However, when the toxic stimuli remain, the cell eventually succumbs to apoptosis.

Mechanism of MASH1 induction by ASK1 and ATRA in adult neural progenitors

The molecular mechanisms underlying differentiation and lineage commitment in neural stem cells are just beginning to be understood, however the molecules involved in this process and their functions remain largely unknown. Here we studied the effects and downstream signals of apoptosis signal-regulating kinase 1 (ASK1) together with all-trans retinoic acid (ATRA) on neuronal differentiation in adult hippocampus-derived progenitor (AHP) cells. Following ASK1 over-expression and ATRA treatment in AHPs, a larger number of cells differentiated into neurons and the MASH1 promoter became activated. Analyzing downstream effector molecules of ASK1 or ATRA targeting the MASH1 promoter revealed that the myocyte enhancer factor 2C (MEF2C) mediated ASK1 signalling, while activation of Sp1 was involved in ATRA signalling. Chromatin immunoprecipitation assay on the promoter revealed that ASK1 induced binding of MEF2C and Ca 2+/calmodulin-dependent kinase II to the MASH1 promoter. Taken together, ASK1 and ATRA activate MEF2C and Sp1, respectively, and up-regulate MASH1 protein expression.

Regulation of Apoptosis Signal-regulating Kinase 1 (ASK1) by PolyamineLevels via Protein Phosphatase5

Recent evidence has implicated the protein phosphatase PP5 in a variety of signaling pathways. Whereas several proteins have been identified that interact with PP5 and regulate its activity, a possibility of its regulation by second messengers remains speculative. Activation of PP5 in vitro by polyunsaturated fatty acids (e.g. arachidonic acid) and fatty acyl-CoA esters (e.g. arachidonoyl-CoA) has been reported. We report here that PP5 is strongly inhibited by micromolar concentrations of a natural polyamine spermine. This inhibition was observed both in assays with a low molecular weight substrate p-nitrophenyl phosphate as well as phosphocasein and apoptosis signal-regulating kinase 1 (ASK1), thought to be a physiological substrate of PP5. Furthermore, a decrease in polyamine levels in COS-7 cells induced by alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, led to accelerated dephosphorylation of oxidative stress-activated ASK1. This effect was suppressed by okadaic acid and by siRNA-mediated PP5 depletion, indicating that the effect of polyamine levels on ASK1 dephosphorylation was mediated by PP5. In line with the decreased ASK1 activation, polyamine depletion in COS-7 cells abrogated oxidative stress-induced activation of caspase-3, which executes ASK1-induced apoptosis, as well as caspase-3 activation induced by ASK1 overexpression, but had no effect on basal caspase-3 activity. These results implicate polyamines, emerging intracellular signaling molecules, as potential physiological regulators of PP5. Our findings also suggest a novel mechanism of the anti-apoptotic action of a decrease in polyamine levels via de-inhibition of PP5 and accelerated dephosphorylation and deactivation of ASK1.

ASK1 inhibits astroglial development via p38 mitogen-activated protein kinase and promotes neuronal differentiation in adult hippocampus-derived progenitor cells.

The mechanisms controlling differentiation and lineage specification of neural stem cells are still poorly understood, and many of the molecules involved in this process and their specific functions are yet unknown. We investigated the effect of apoptosis signal-regulating kinase 1 (ASK1) on neural stem cells by infecting adult hippocampus-derived rat progenitors with an adenovirus encoding the constitutively active form of ASK1. Following ASK1 overexpression, a significantly larger number of cells differentiated into neurons and a substantial increase in Mash1 transcription was observed. Moreover, a marked depletion of glial cells was observed, persisting even after additional treatment of ASK1-infected cultures with potent glia inducers such as leukemia inhibitory factor and bone morphogenetic protein. Analysis of the promoter for glial fibrillary acidic protein revealed that ASK1 acts as a potent inhibitor of glial-specific gene transcription. However, the signal transducers and activators of transcription 3 (STAT3)-binding site in the promoter was dispensable, while the activation of p38 mitogen-activated protein kinase was crucial for this effect, suggesting the presence of a novel mechanism for the inhibition of glial differentiation.

Activation of apoptosis signal-regulating kinase 1 by reactive oxygen species through dephosphorylation at serine 967 and 14-3-3 dissociation.

Oxidative stress has been indicated in a variety of pathological processes such as atherosclerosis, diabetes, and neurodegenerative diseases. Understanding how intracellular signaling pathways respond to oxidative insults such as hydrogen peroxide (H(2)O(2)) would have significant therapeutic implications. Recent genetic studies have placed apoptosis signal-regulating kinase 1 (ASK1) in a pivotal position in transmitting H(2)O(2)-initiated signals. How ASK1 is activated by H(2)O(2), though, remains a subject of intense investigation. Here we report a mechanism by which H(2)O(2) induces ASK1 activation through dynamic control of its phosphorylation at serine 967. We found that treatment of COS7 cells with H(2)O(2) triggers dephosphorylation of Ser-967 through an okadaic acid-sensitive phosphatase, resulting in dissociation of the ASK1.14-3-3 complex with concomitant increase of ASK1 catalytic activity and ASK1-mediated activation of JNK and p38 pathways.

ASK1 Inhibits Interleukin-1-induced NF-κB Activity through Disruption of TRAF6-TAK1 Interaction

Apoptosis signal-regulating kinase 1 (ASK1) is a member of the MAPKKK family in the JNK and p38 mitogen-activated protein kinase cascades and critically involved in stress- and cytokine-induced apoptosis. The transcription factor nuclear factor-kappaB (NF-kappaB) is a pivotal regulator of immune and inflammatory responses and exerts anti-apoptotic roles in various cells. Here we show that ASK1 directly interacts with transforming growth factor-beta-activated kinase 1 (TAK1), another MAPKKK that has been identified as a signaling intermediate in the interleukin 1 (IL-1)-induced NF-kappaB pathway as well as the transforming growth factor-beta superfamily-induced JNK/p38 pathway. Overexpression of ASK1 inhibits IL-1-, TRAF6-, or TAK1-induced, but not NF-kappaB-inducing kinase-induced, NF-kappaB activation. ASK1 dissociates TAK1 but not NF-kappaB-inducing kinase from TRAF6. Moreover, IL-1-induced complex formation of endogenous TAK1 and TRAF6 was blocked by ASK1 overexpression. It thus appears that the inhibition of NF-kappaB by ASK1 may result at least in part from the disruption of the TRAF6.TAK1 complex formation in the IL-1 signaling pathway. These results provide a new insight in the mode of action of MAPKKK family members; two distinct MAPKKKs in the same MAP kinase cascades directly interact and exert opposite effects in another signaling pathway, NF-kappaB.