Cell signaling in aging and apoptosis

Alterations in apoptotic potential, due to perturbations in cell signaling cascades, could underlie age-related organ-specific cellular degeneration and death. While increased apoptosis could lead to cell loss, as in neuronal degeneration, loss of apoptosis competence might well result in the loss of phenotypic fidelity of somatic cells, which could explain to some extent, the age-related increase in cancer incidence. Results from our laboratory indicate that after subjecting young and old rats to genotoxic stress in the form of methyl methanesulfonate (MMS), an apoptotic response is quickly mounted in the liver of the young animals but virtually absent in the same organ of old animals (Nature Med. 8 (2002) 3). To address the possible molecular signaling defect(s) responsible for the age-related dysfunction of apoptosis in response to MMS, mitogen-activated protein kinases (MAPKs), extracellular signal-regulated kinases (ERKs), c-Jun NH(2)-terminal kinases (JNKs) and p38 MAPKs, were evaluated in the liver of young and old rats after MMS treatment. The results demonstrated distinct age-specific patterns of MMS-induced MAPKs activation, suggesting that the balance between cell survival and apoptosis after genotoxic stress may be impaired during aging. These results are discussed in terms of the relative importance in aging of biological redundancy, a concept put forward by the late Bernard Strehler, and cellular fidelity.     

缺血/再灌注损伤时丝裂原活化蛋白激酶信号转导通路的变化

丝裂原活化蛋白激酶 (ｍｉｔｏｇｅｎ -ａｃｔｉｖａｔｅｄｐｒｏｔｅｉｎｋｉｎａｓｅｓ,ＭＡＰＫｓ)是一类丝 /苏氨酸蛋白激酶 ,是公认与细胞增殖、分化或凋亡调控密切相关的细胞内信号转导酶类 ,到目前为止 ,在哺乳类动物细胞中 ,已经发现ＭＡＰＫｓ家族具有ＥＲＫｓ(ｅｘｔｒａｃｅｌｌｕｌａｒｓｉｇｎａｌ-ｒｅｇｕｌａｔｅｄｋｉｎａｓｅｓ)、ＪＮＫｓ/ＳＡＰＫｓ(ｃ -ＪｕｎＮＨ2 -ｔｅｒ ｍｉｎａｌｋｉｎａｓｅｓ/ｓｔｒｅｓｓ -ａｃｔｉｖａｔｅｄｐｒｏｔｅｉｎｋｉｎａｓｅｓ)、ｐ38ＭＡＰＫ等不同亚类 ,其信号途径上游的信号…     

Diosgenin, a plant steroid, induces apoptosis in COX-2 deficient K562 cells with activation of the p38 MAP kinase signalling and inhibition of NF-kappaB binding

Diosgenin is a steroidal sapogenin with antitumor properties. We previously showed that diosgenin induced apoptosis in human erythroleukemia (HEL) cells. In order to elucidate the mechanism of its apoptotic activity, we investigated the effect of diosgenin on nuclear factor-kappaB (NF-kappaB) binding and on three groups of human mitogen-activated protein kinases (MAPKs) in relation to diosgenin-induced apoptosis in different erythroleukemia cell lines (K562 and HEL). Our results showed that diosgenin decreased DNA binding of NF-kappaB in K562 and HEL cells after 48-h diosgenin treatment. This inhibition of NF-kappaB binding was correlated with strong apoptosis in both erythroleukemia cell lines. Diosgenin-induced apoptosis was associated with cyclo-oxygenase-2 (COX-2) up-regulation in HEL cells but not in K562 cells which are COX-2 deficient. Furthermore, diosgenin inhibited extracellular signal-regulated kinase (ERK) activation only in HEL cells. However, diosgenin activated p38 MAPK in both cell lines and activated c-jun NH2-terminal kinases (JNKs) only in HEL cells. Pre-treatment with a selective p38 inhibitor inhibited diosgenin-induced DNA fragmentation in K562 cells. For the first time, our results suggest that inhibition of NF-kappaB nuclear binding and p38 MAPK activation are involved in the diosgenin-mediated signal cascades in K562 cells for inducing/regulating DNA fragmentation.     

Specific activities of individual c-Jun N-terminal kinases in the brain

The c-Jun N-terminal kinases (JNKs) are multifunctional molecules which, on the one hand, regulate various processes in brain development, repair and memory formation. On the other hand, JNKs are potent effectors of neuronal death and neuroinflammation. This review summarizes recent findings on individual JNK functions in the nervous system under pathophysiological conditions and on their regulation by upstream kinases, phosphatases and formation of context-dependent signalosomes. By focusing on different aspects of JNK signaling, it becomes increasingly obvious that the JNK cascade is intricately regulated and intensely dependent on the availability and functionality of its single components and their intracellular localization. Our review also emphasizes, that JNKs are indispensable for neuronal cell death as well as many physiological functions in the brain. Finally, we discuss pharmacological strategies which target pathological JNK activities without affecting their physiological functions.     

Secreted beta-amyloid precursor protein activates microglia via JNK and p38-MAPK

Reactive microglia are thought to play a role in the pathogenesis of Alzheimer's disease (AD) and are localized to the senile plaques that are associated with cognitive decline. The beta-amyloid precursor protein (betaAPP) is over-expressed in the dystrophic neurites near such plaques, and secreted forms of betaAPP (sAPPalpha) activate inflammatory responses in microglia. To characterize the mechanisms by which sAPPalpha activates microglia, we assayed its effects on MAP kinases, including c-Jun N-terminal kinases (JNK), extracellular signal-regulated protein kinases (ERK), and p38-MAPK. sAPPalpha was found to rapidly activate JNKs, ERKs and p38-MAPK in a dose-dependent manner. The JNK inhibitor SP600125 and the p38 inhibitor SB203580 independently reduced both nitrite accumulation and induction of inflammatory nitric oxide synthase (iNOS). By contrast, inhibition of the ERK pathway with U0126 did not appreciably affect either outcome measure. These findings suggest that sAPP activates the ERK, JNK and p38 classes of MAP kinases but that only JNK and p38-MAPK are critical for activation of microglia by sAPPalpha, a process that compromises neuronal function and survival.     

Differential modulation of MAP kinases by zinc deficiency in IMR-32 cells: role of H(2)O(2)

The influence of zinc deficiency on the modulation of the mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase (ERK1/2), p38, and c-Jun N-terminal kinase (JNK) was studied. Using human IMR-32 cells as a model of neuronal cells, the role of oxidants on MAPKs and activator protein-1 (AP-1) activation in zinc deficiency was investigated, characterizing the participation of these events in the triggering of apoptosis. Relative to controls, cells incubated in media with low zinc concentrations showed increased cell oxidants and hydrogen peroxide (H(2)O(2)) release, increased JNK and p38 activation, high nuclear AP-1-DNA binding activity, and AP-1-dependent gene expression. Catalase addition to the media prevented the increase of cellular oxidants and inhibited JNK, p38, and AP-1 activation. Low levels of ERK1/2 phosphorylation were observed in the zinc-deficient cells in association with a reduction in cell proliferation. Catalase treatment did not prevent the above events nor the increased rate of apoptosis in the zinc-deficient cells. It is first demonstrated that a decrease in cellular zinc triggers H(2)O(2)-independent, as well as H(2)O(2)-dependent effects on MAPKs. Zinc deficiency-induced increases in cellular H(2)O(2) can trigger the activation of JNK and p38, leading to AP-1 activation, events that are not involved in zinc deficiency-induced apoptosis.     

TNF and MAP kinase signalling pathways

The binding of tumour necrosis factor α (TNFα) to cell surface receptors engages multiple signal transduction pathways, including three groups of mitogen-activated protein (MAP) kinases: extracellular-signal-regulated kinases (ERKs); the cJun NH₂-terminal kinases (JNKs); and the p38 MAP kinases. These MAP kinase signalling pathways induce a secondary response by increasing the expression of several inflammatory cytokines (including TNFα) that contribute to the biological activity of TNFα. MAP kinases therefore function both upstream and down-stream of signalling by TNFα receptors. Here we review mechanisms that mediate these actions of MAP kinases during the response to TNFα.     

Mitogen-activated protein kinases and apoptosis in PIN

 Mitogen-activated protein (MAP) kinases are key elements of the signalling systems needed to transduce different extracellular messages into cellular responses. At least three parallel MAP kinase pathways have been identified: one, stimulated by serum and growth factors to activate extracellular signal-regulated protein kinases (ERKs) by dual tyrosine and threonine phosphorylation, triggers cell proliferation or differentiation; the other two, induced by a variety of cellular stresses to activate c-jun N-terminal kinases (JNKs) and reactivating kinase (p38/RK), result in growth arrest and induction of apoptosis. Mitogen-activated protein kinase phosphatases (MKPs) inactivate MAP kinases through dephosphorylation and, thus, can modulate the MAP kinase pathways. Expression of JNK-1, ERK-1, p38/RK and MKP-1 proteins was investigated by immunohistochemistry and expression of MKP-1 mRNA by in situ hybridisation in 50 cases of high-grade prostatic intraepithelial neoplasia (PIN), thought to represent the precursor of prostate cancer. The frequency of apoptotic cells was also determined in these cases. Overexpression of the three MAP kinases and MKP-1 mRNA was found in all cases of high-grade PIN compared with normal prostate. Immunoreactivity for MKP-1 protein was found to be as intense as in normal glands in 30% and weaker in 56% of the PIN cases. Fourteen per cent of PIN cases did not stain with MKP-1 antibody. The proportion of apoptosis was significantly higher (P < 0.008) in PIN lesions that did not express MKP-1 protein than in those that did. These results are consistent with our previous demonstration of preferential inhibition of the apoptosis-related kinases by MKP-1 and further support the contention that MKP-1, even in PIN, may shift the balance existing between cell proliferation and death. When expressed, it may inhibiting those pathways that lead to apoptosis. Received: 27 August 1997 / Accepted: 29 December 1997     

Effect of inhibition of extracellular signal-regulated kinase 1 and 2 pathway on apoptosis and bcl-2 expression in Helicobacter pylori-infected AGS cells

Helicobacter pylori induces activation of mitogen-activated protein kinases (MAPKs). However, its effect on H. pylori-induced apoptosis has not been evaluated. Thus, we examined whether H. pylori-induced extracellular signal-regulated kinase 1 and 2 (ERK1/2) and p38 MAPK activation affects gastric epithelial cell apoptosis and bcl-2 family gene expression, especially in relation to the cagA status of an H. pylori strain. In flow cytometric and oligonucleosome-bound DNA enzyme-linked immunosorbent assay analyses, infection with cagA(+) H. pylori strains induced gastric cancer cell apoptosis in AGS cells more prominently than infection with cagA mutants. Activation of ERK1/2 and p38 MAPKs was also more prominent in cagA(+) strains. Pretreatment with a MEK inhibitor (PD98059) inhibited ERK1/2 activation and increased H. pylori-induced apoptosis significantly. This increased apoptosis was accompanied by decreased antiapoptotic bcl-2 mRNA expression among bcl-2-related genes (bcl-2, bax, bak, mcl-1, and bcl-X(L/S)), and the effect was also more prominent in the cagA(+) strains. However, the alteration of bcl-2 gene expression was not accompanied by protein level changes. Inhibition of p38 using specific inhibitor SB203580 decreased H. pylori-induced apoptosis but resulted in little alteration of bcl-2-related gene expression. In conclusion, H. pylori-induced ERK1/2 activation, especially by the cagA(+) H. pylori strain, may play a protective role against gastric epithelial cell apoptosis partially through maintenance of bcl-2 gene expression.     

p38β MAPK affords cytoprotection against oxidative stress-induced astrocyte apoptosis via induction of αB-crystallin and its anti-apoptotic function

The activation of p38 mitogen-activated protein kinases (MAPKs) has been implicated in many cellular processes, such as, inflammation, cell death, and survival. In mammals, four distinct genes encode the four known members of p38 MAPKs, p38α, p38β, p38γ, and p38δ. Despite the fact that p38α and p38β MAPKs share over 75% homology sequences, they have distinct, perhaps even opposite roles under stress conditions. In our previous report, we showed that p38β MAPK is induced in activated astrocytes in the penumbra of the postischemic brain, wherein it was co-localized with αB-crystallin and MAPKAPK-2. To investigate the functional significance of p38β MAPK in astrocytes, a C6 astroglioma cell line stably over-expressing p38β MAPK was generated. In these cells, hydrogen peroxide-induced apoptosis was reduced to 44.3% of that obtained from normal C6 cells. Interestingly, we found that expression of a small heat shock protein, αB-crystallin, was significantly increased in these cells, but that the expressions of HSP27 and HSP70 were not. Repression of αB-crystallin expression by αB-crystallin siRNA transfection suppressed the protective effect and recovered caspase 3 activity, indicating that αB-crystallin induction plays a crucial role in the protection against H₂O₂-induced apoptosis observed in p38β-overexpressing C6 astroglioma cells. We found that the binding between αB-crystallin and partially processed caspase-3 (a p24 intermediate) was significantly increased in p38β-overexpressing cells, which might result in suppression of caspase 3 activity in these cells. These results indicate that p38β confers protection against H₂O₂-induced astrocytes apoptosis by inducing a small heat shock protein, αB-crystallin, which inhibits caspase-3 activation.     

Possible pathophysiological roles of mitogen-activated protein kinases (MAPKs) in endometriosis

PROBLEM: Endometriosis accompanies local inflammatory reactions in the peritoneal cavity. We examined the phosphorylation of mitogen-activated protein kinases (MAPKs), i.e. extracellular signal-regulated kinase (ERK), p38 MAPK (p38) and c-Jun N-terminal kinase (JNK) in endometriotic stromal cells, and their possible pathophysiological roles in endometriosis in relation to proinflammatory substances. METHOD OF STUDY: Endometriotic stromal cells were isolated from endometriomas and were cultured for the experiments. Phosphorylation of MAPKs in endometriotic stromal cells treated with interleukin (IL)-1beta, tumor necrosis factor (TNF)alpha and H(2)O(2) were examined by Western blot analysis. Effects of PD98059, SB202190 and SP600125 (inhibitors of ERK, p38 and JNK, respectively) on IL-1beta-induced secretion of IL-6 and IL-8, and on IL-1beta-induced expression of cyclo-oxygenase-2 (COX-2) in endometriotic cells were studied. In addition, eutopic endometrial tissues were collected, and the phosphorylation rate of p38 in eutopic endometrial tissues and endometriotic tissues were determined. RESULTS: IL-1beta, TNFalpha and H(2)O(2) stimulated the phosphorylation of ERK, p38 and JNK, while the total amounts of proteins of the respective MAPKs were virtually the same compared with those in the unstimulated controls. Both SB202190 and SP600125 suppressed IL-1beta-induced secretion of IL-6 and IL-8, and PD98059 suppressed IL-1beta-induced secretion of IL-8. Both SB202190 and PD98059 suppressed IL-1beta-induced expression of COX-2 in endometriotic cells. The p38 phosphorylation rates in the endometriotic tissues were significantly higher than those in the eutopic endometrial tissues of the same patients. CONCLUSIONS: Given the current theory that inflammatory changes are involved in the progression of endometriosis, MAPKs could play as pivotal intracellular signal transducers in endometriotic cells, and thus have a pathophysiological role in the disease.     

Regulation of proliferation/apoptosis equilibrium by mitogen-activated protein kinases in normal, hyperplastic, and carcinomatous human prostate

This study investigate the expression of the mitogen-activated protein kinases (MAPKs) in normal prostate, benign prostatic hyperplasia (BPH), and prostatic cancer (PC), and also the possible relationship between the activity of these MAPKs and the apoptosis/proliferation index. Immunochemical techniques were carried out using 2 mouse monoclonal antibodies against human extracellular signal-regulated protein kinase (ERK) and Jun N-terminal kinase (JNK), and 1 goat polyclonal antibody against mouse p38. To compare the results obtained in the 3 specimens, the average percentages of both epithelial and stromal immunostained cells were calculated on immunostained sections. For each of the 3 kinases studied, the percentage of immunostained stromal cells did not change with prostatic alterations. For both ERK and p38, the percentage of immunostained epithelial cells increased significantly in BPH and even more so in PC. For JNK, the percentage of immunostained epithelial cells increased significantly only in PC. These results suggest that ERK could be involved in the elevated proliferation indexes reported in BPH and PC, whereas p38 might contribute to the increased apoptotic index reported in PC. The most probable action of JNK in PC would be cell proliferation stimulation. Overexpression of MAPKs, involved in the development of prostatic hyperplasia and neoplasia, might be secondary to the overexpression of several growth factors.     

Cationic liposomes induce apoptosis through p38 MAP kinase-caspase-8-Bid pathway in macrophage-like RAW264.7 cells

We have demonstrated that cationic liposomes composed of stearylamine (SA-liposomes) induce apoptosis in a variety of cells, but the mechanism responsible for the cellular death is not clear. In this paper, we investigated the signaling pathways implicated in SA-liposome-induced apoptosis in the macrophage-like cell line RAW264.7. Treatment with SA-liposomes caused the activation of mitogen-activated protein kinases (MAPKs), especially p38 and c-jun N-terminal kinase, and apoptosis was only inhibited upon the addition of a specific inhibitor for p38. N-acetylcysteine, a scavenger of reactive oxygen species (ROS), effectively inhibited the activation of p38 and cellular death, indicating that the activation induced by ROS is an initial step in the process of apoptosis triggered by SA-liposomes. Caspase-8 was activated by p38, and caspase-8-dependent cleavage of Bid was also observed. No down-regulation of bcl-2 expression, and no cleavage of Bax protein were observed. Taken together, our results suggest that apoptosis of RAW264.7 by SA-liposomes was mediated by the MAPK p38 and a caspase-8-dependent Bid-cleavage pathway. Moreover, we found that ROS can contribute intimately to the SA-liposome-induced cell death in RAW264.7.     

The MAPK-activated kinase Rsk controls an acute Toll-like receptor signaling response in dendritic cells and is activated through two distinct pathways

Most dendritic cell (DC) responses to Toll-like receptor (TLR) ligands depend on the activation of mitogen-activated protein kinases (MAPKs), but the contributions of the many MAPK-activated kinases (MKs) that act 'downstream' of the MAPKs Erk and p38 are not known. Here we sought to determine which MKs are required for acute TLR-driven, MAPK-dependent DC endocytic responses. Two specific and structurally different inhibitors of the MK Rsk suppressed TLR-induced endocytosis, thus defining in DCs a specific requirement for MKs in TLR responses. In addition, we identify in DCs a previously unknown configuration of the MAPK system whereby Rsk is activated not only by Erk but also by p38 through the intermediates MK2 and MK3. Thus, in DCs, p38 contributes to the activation of all known MK families.     

Role of MAP kinase-dependent apoptotic pathway in innate immune responses and viral infection

Mitogen-activated protein (MAP) kinase cascades are multifunctional signalling networks that influence cell growth, differentiation, apoptosis and cellular responses to stress. Apoptosis signal-regulating kinase 1 (ASK1) is a MAP kinase kinase kinase that triggers apoptogenic kinase cascade leading to the phosphorylation/activation of c-Jun N-terminal kinases (JNK) and p38-MAP kinase, which are responsible to induce apoptotic cell death. This pathway plays a pivotal role in the transduction of signals from different apoptotic stimuli. Recently, it has become evident that ASK1 and its downstream pathway are employed in the transduction of signals from Toll-like receptors (TLR) - multistep processes that interfere with different intracellular signalling pathways. TLR are the key proteins that allow mammals to detect pathogens and mediate innate immune responses. In addition, ASK1 and its downstream pathway play a target role in the regulation of apoptosis in some cases of viral infection - AIDS, influenza, hepatitis C and others. In the present review, we summarize current knowledge about the role of ASK1 and its downstream pathway in innate immune responses and viral infection.     

Cytotoxicity of tubeimoside I in human choriocarcinoma JEG-3 cells by induction of cytochrome c release and apoptosis via the mitochondrial-related signaling pathway

Mitochondria play important roles in the intrinsic pathways that trigger apoptosis. Anticancer chemotherapies eliminate cancer cells mainly through the induction of apoptosis. In the present study, we investigated the mechanism of the cytotoxic effects of tubeimoside I (TBMS1) on the human choriocarcinoma cell line (JEG-3). Choriocarcinoma is one of the most common malignant tumors in the reproductive system. TBMS1, a triterpenoid saponin, isolated from the tubers of Bolbostemma paniculatum (Maxim) Franquet (Cucurbitaceae), showed potent antitumor effects. However, the potential roles of TBMS1 in the treatment of choriocarcinoma remain unknown. In the present study, we examined the effects of TBMS1 on JEG-3 cells. TBMS1 displayed strong growth inhibitory effects on JEG-3 cell growth. In addition, TBMS1 treatment with TBMS1 led to marked cell apoptosis, significant cell cycle arrest at G2 phase and decrease in mitochondrial transmembrane potential (ΔΨm). Cytochrome c was released from the mitochondria and caspase-3 expression was enhanced. Furthermore, TBMS1 induced the up-regulation of Bcl-2 associated X protein (Bax) expression, down-regulation of Bcl-2 expression, inhibition of nuclear factor-κ-B (NF-κB) function and impacted the phosphorylation of p38 mitogen-activated protein kinase (p38/MAPK), extracellular signal-regulated kinases (ERK)1/2 and protein kinase B (Akt). Taken together, our findings suggest that TBMS1 is an efficient apoptosis-inducing agent for choriocarcinoma cells, which exerts its effects, at least partially, by the induction of mitochondrial dysfunction and regulation of the p38/MAPK, ERK1/2 and PI3K/Akt signaling pathways.