SP600125, an anthrapyrazolone inhibitor of Jun N-terminal kinase

Activation of mitogen-activated protein kinase pathways during the death of PC12 cells is dependent on the state of differentiation

PC12 cells that are differentiated with NGF and cAMP become totally dependent on these factors for their survival, unlike those that are differentiated with NGF alone. We have asked whether the MAP Kinases, ERKs, JNKs and p38s play a role in the cell death induced by withdrawal of trophic factors on NGF- and NGF/cAMP-differentiated PC12 cells. By Western-blot analyses with antibodies directed against the activated forms of these kinases, we show that when the trophic factors were withdrawn, ERK phosphorylation was reduced to very low levels within 1 h in both cases. Changes in the other enzymes were observed only in the NGF/cAMP-differentiated cells, in which the JNK phosphorylation increased about 160% by 6 h and that of p38 increased linearly to at least 18-fold throughout the cell death process. The increases in p38 and JNK phosphorylation were implicated in the death of the cells, since the p38 inhibitor PD169316 and the JNK inhibitor SP600125 were protective. These results demonstrate that the state of differentiation of PC12 cells, a model for the differentiation of sympathetic neurons, determines their vulnerability to cell death by modifying the state of phosphorylation and the regulation of specific kinases implicated in signal transduction pathways that are responsible for the survival or the death of these cells.

Identification of a novel Bcl-xL phosphorylation site regulating the sensitivity of taxol- or 2-methoxyestradiol-induced apoptosis

Bcl-xL, a close homolog of Bcl2, is an important regulator of apoptosis and is overexpressed in human cancer. Phosphorylation of Bcl-xL can be induced by microtubule-damaging drugs such as taxol or 2-methoxyestradiol (2-ME). By site-directed mutagenesis studies, we have identified that serine 62 is the necessary site for taxol- or 2-ME-induced Bcl-xL phosphorylation in prostate cancer cells. Further studies with the inhibitor of Jun kinase (JNK) and phosphorylation null mutant of Bcl-xL reveal the augmentative role of JNK-mediated Bcl-xL phosphorylation in apoptosis of prostate cancer cells. In summary, our studies suggest that the phosphorylation of Bcl-xL by stress response kinase signaling might oppose the anti-apoptotic function of Bcl-xL to permit prostate cancer cells to die by apoptosis.

Modulation of insulin-stimulated degradation of human insulin receptor substrate-1 by Serine 312 phosphorylation

Ser/Thr phosphorylation of insulin receptor substrate-1 (IRS-1) is a negative regulator of insulin signaling. One potential mechanism for this is that Ser/Thr phosphorylation decreases the ability of IRS-1 to be tyrosine-phosphorylated by the insulin receptor. An additional mechanism for modulating insulin signaling is via the down-regulation of IRS-1 protein levels. Insulin-induced degradation of IRS-1 has been well documented, both in cells as well as in patients with diabetes. Ser/Thr phosphorylation of IRS-1 correlates with IRS-1 degradation, yet the details of how this occurs are still unknown. In the present study we have examined the potential role of different signaling cascades in the insulin-induced degradation of IRS-1. First, we found that inhibitors of the phosphatidylinositol 3-kinase and mammalian target of rapamycin block the degradation. Second, knockout cells lacking one of the key effectors of this cascade, the phosphoinositide-dependent kinase-1, were found to be deficient in the insulin-stimulated degradation of IRS-1. Conversely, overexpression of this enzyme potentiated insulin-stimulated IRS-1 degradation. Third, concurrent with the decrease in IRS-1 degradation, the inhibitors of the phosphatidylinositol 3-kinase and mammalian target of rapamycin also blocked the insulin-stimulated increase in Ser(312) phosphorylation. Most important, an IRS-1 mutant in which Ser(312) was changed to alanine was found to be resistant to insulin-stimulated IRS-1 degradation. Finally, an inhibitor of c-Jun N-terminal kinase, SP600125, at 10 microm did not block IRS-1 degradation and IRS-1 Ser(312) phosphorylation yet completely blocked insulin-stimulated c-Jun phosphorylation. Further, insulin-stimulated c-Jun phosphorylation was not blocked by inhibitors of the phosphatidylinositol 3-kinase and mammalian target of rapamycin, indicating that c-Jun N-terminal kinase is unlikely to be the kinase phosphorylating IRS-1 Ser(312) in response to insulin. In summary, our results indicate that the insulin-stimulated degradation of IRS-1 via the phosphatidylinositol 3-kinase pathway is in part dependent upon the Ser(312) phosphorylation of IRS-1.

Grape seed extract inhibits EGF-induced and constitutively active mitogenic signaling but activates JNK in human prostate carcinoma DU145 cells: possible role in antiproliferation and apoptosis

A loss of functional androgen receptor and an enhanced expression of growth factor receptors and associated ligands are causal genetic events in prostate cancer (PCA) progression. These genetic alterations lead to an epigenetic mechanism where a feedback autocrine loop between membrane receptor and ligand (e.g. EGFR-TGFalpha) results in a constitutive activation of MAPK-Elk1-AP1-mediated mitogenic signaling in human PCA at an advanced and androgen-independent stage. We rationalized that inhibiting these epigenetic events could be useful in controlling advanced PCA growth. Recently, we found that grape seed extract (GSE), a dietary supplement rich in flavonoid procyanidins, inhibits advanced and androgen-independent human PCA DU145 cell growth in culture and nude mice. Here, we performed detailed mechanistic studies to define the effect of GSE on EGFR-Shc-MAPK-Elk1-AP1-mediated mitogenic signaling in DU145 cells. Pretreatment of serum-starved cells with GSE resulted in 70% to almost complete inhibition of EGF-induced EGFR activation and 50% to complete inhibition of Shc activation, which corroborated with a comparable decrease in EGF-induced Shc binding to EGFR. Conversely, EGF-induced ERK1/2 phosphorylation was inhibited only by lower doses of GSE; in fact, higher doses showed an increase. Additional studies showed that GSE alone causes a dose- and time-dependent increase in ERK1/2 phosphorylation in starved DU145 cells that is inhibited by an MEK1 inhibitor PD98059. Independent of this increase in ERK1/2 phosphorylation, GSE showed a strong inhibition of ERK1/2 kinase activity to Elk1 in both cellular and cell-free systems. GSE treatment of cells also inhibited both EGF-induced and constitutively active Elk1 phosphorylation and AP1 activation. GSE treatment also showed DNA synthesis inhibition in starved and EGF-stimulated cells as well as loss of cell viability and apoptotic death that was further increased by adding MEK1 inhibitor. Since GSE strongly induced apoptosis independent of its affect on an increase in phospho-ERK1/2, we hypothesized that apoptotic effect of GSE could be by other mechanism(s) including its effect on stress-associated MAPK, the JNK. Indeed, GSE-treated cells showed a strong and sustained increase in phospho-JNK1/JNK2 levels, JNK activity and phospho-cJun levels. An inhibition of GSE-induced JNK activation by a novel JNK inhibitor SP600125 resulted in a significant reversal of GSE-induced apoptotic death suggesting the involvement of JNK activation by GSE in its apoptosis response. Together, these results suggest that anticancer effects of GSE in PCA be mediated via impairment of EGFR-ERK1/2-Elk1-AP1-mediated mitogenic signaling and activation of JNK causing growth inhibition and apoptosis, respectively.

Suppression of Ras-stimulated transformation by the JNK signal transduction pathway

The c-Jun NH(2)-terminal kinase (JNK) phosphorylates and activates members of the activator protein-1 (AP-1) group of transcription factors and is implicated in oncogenic transformation. To examine the role of JNK, we investigated the effect of JNK deficiency on Ras-stimulated transformation. We demonstrate that although JNK does play a role in transformation in vitro, JNK is not required for tumor development in vivo. Importantly, the loss of JNK expression resulted in substantial increases in the number and growth of tumor nodules in vivo. Complementation assays demonstrated that this phenotype was caused by JNK deficiency. These data demonstrate that, in contrast to expectations, the normal function of JNK may be to suppress tumor development in vivo. This conclusion is consistent with the presence in human tumors of loss-of-function mutations in the JNK pathway.

Subcellular localization of Photofrin determines the death phenotype of human epidermoid carcinoma A431 cells triggered by photodynamic therapy: when plasma membranes are the main targets

Photodynamic therapy (PDT) is a kind of photochemo-therapeutic treatment that exerts its effect mainly through the induction of cell death. Distinct types of cell death may be elicited by different PDT regimes. In this study, the mechanisms involved in the death of human epidermoid carcinoma A431 cells triggered by PDT with Photofrin (a clinically approved photosensitizer) were characterized. Photofrin distributes dynamically in A431 cells; the plasma membranes and Golgi complex are the main target sites of Photofrin after a brief (3 h) and prolonged (24 h) incubation, respectively. Cells with differentially localized Photofrin displayed distinct death phenotypes in response to PDT. The effects of PDT on cells with plasma membrane-localized Photofrin were further studied in details. Cells stopped proliferating post PDT at Photofrin dose >7 micro g/ml, and at higher dose (28 micro g/ml) plasma membrane disruption and cell swelling were observed immediately after PDT. Dramatic alterations of several important signaling events were detected in A431 cells post Photofrin-PDT, including (i) immediate formation of reactive oxygen species (ROS), (ii) rapid activation of c-Jun N-terminal kinase, (iii) delayed activation of caspase-3 and cleavage of polyADP-ribose polymerase and p21-activated kinase 2, and (iv) loss of mitochondrial membrane potential. Intriguingly, the characteristics of typical apoptosis such as phosphatidylserine externalization and DNA fragmentation were not detected in the cell death process caused by this PDT regime. In conclusion, our results show that when plasma membranes are the main targets, Photofrin-PDT can lead to instant ROS formation and subsequent activation of downstream signaling events similar to those elicited by many apoptotic stimuli, but the damage of plasma membranes renders the death phenotype more necrosis like.

Modulation of vascular smooth muscle cell alignment by cyclic strain is dependent on reactive oxygen species and P38 mitogen-activated protein kinase

PURPOSE

The aim of this study was to investigate the molecular targets of reactive oxygen species (ROS) and to determine whether cyclic strain induces smooth muscle cell (SMC) alignment via the ROS system. We assessed stretch-induced nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase activation and the redox sensitivity of cyclic strain-stimulated activation of the mitogen-activated protein kinase (MAPK) family.

METHODS

SMCs were seeded on flexible collagen I-coated plates and exposed to cyclic strain. NAD(P)H oxidase activation was measured with lucigenin-enhanced chemiluminescent detection of superoxide. Activation of MAPK was detected by determining phosphorylation of extracellular signal-regulated protein kinase (ERK1/2), c-jun N-terminal kinase (JNK1/2), and p38 MAPK with immunoblotting. In other experiments, SMCs were exposed to diphenylene iodonium (DPI), an NAD(P)H inhibitor, 30 minutes before stretch. MAPK activation and cell orientation were then assessed.

RESULTS

Cyclic strain elicits a rapid increase in intracellular NADH/NADPH oxidase in SMCs. There was also a rapid and robust phosphorylation of ERK1/2, JNK1/2, and p38 MAPK. Cyclic strain-induced intracellular NAD(P)H generation was almost completely blocked with DPI. DPI also inhibited the strain-induced phosphorylation of ERK1/2, JNK1/2, and p38 MAPK. Both the p38 MAPK specific inhibitor, SB 202190, and DPI blocked cyclic strain-induced cell alignment, but PD98059, an ERK1/2-specific inhibitor, and SP600125, an anthrazolone inhibitor of JNK, did not.

CONCLUSION

Our results provide evidence that p38 MAPK is a critical component of the oxidant stress ROS-sensitive signaling pathway and plays a crucial role in vascular alignment induced by cyclic stain.

Toll-like receptor-4 (TLR4) signaling augments chemokine-induced neutrophil migration by modulating cell surface expression of chemokine receptors

Polymorphonuclear leukocytes (PMNs) are critical effector cells of the innate immune system that protect the host by migrating to inflammatory sites and killing pathogenic microbes. We addressed the role of chemokine receptor desensitization induced by G-protein-coupled receptor kinases (GRKs) in the feedback control of PMN migration. We show that the chemokine macrophage inflammatory protein-2 (MIP-2) induces GRK2 and GRK5 expression in PMNs through phosphoinositide-3-kinase (PI3K)-gamma signaling. We also show that lipopolysaccharide (LPS)-activated signaling through the Toll-like receptor (TLR)-4 pathway transcriptionally downregulates the expression of GRK2 and GRK5 in response to MIP-2. The reduced expression of GRKs lowers chemokine receptor desensitization and markedly augments the PMN migratory response. These data indicate that TLR4 modulation of PMN surface chemokine receptor expression subsequent to the downregulation of GRK2 and GRK5 expression is a critical determinant of PMN migration.

Type 2 deiodinase expression is stimulated by growth factors in human vascular smooth muscle cells

Type 2 deiodinase (D2) catalyzes the conversion of the prohormone T4 to the biologically active T3. D2 is expressed in human aortic smooth muscle cells (hASMCs). In this study, we demonstrated that the D2 mRNA and activity in hASMCs were up-regulated by platelet-derived growth factor-BB (PDGF-BB) and basic fibroblast growth factor (bFGF). The induction of D2 mRNA by PDGF-BB and bFGF was dependent on de novo RNA and protein synthesis. PD98059, a specific inhibitor of the upstream kinase that activates extracellular signal-regulated kinase (ERK), significantly suppressed the induction by both PDGF-BB and bFGF. SB203580, a specific inhibitor of p38 mitogen-activated protein (MAP) kinase, and SP600125, a specific inhibitor of c-Jun N-terminal kinase (JNK), also reduced the induction by both PDGF-BB and bFGF. These results suggest that both PDGF-BB and bFGF induce D2 expression at least partly via ERK pathway. The p38 MAP kinase and JNK pathways may also be involved in the induction.

Molecular mechanisms mediating antimyeloma activity of proteasome inhibitor PS-341

We have recently shown that proteasome inhibitor PS-341 induces apoptosis in drug-resistant multiple myeloma (MM) cells, inhibits binding of MM cells in the bone marrow microenvironment, and inhibits cytokines mediating MM cell growth, survival, drug resistance, and migration in vitro. PS-341 also inhibits human MM cell growth and prolongs survival in a SCID mouse model. Importantly, PS-341 has achieved remarkable clinical responses in patients with refractory relapsed MM. We here demonstrate molecular mechanisms whereby PS-341 mediates anti-MM activity by inducing p53 and MDM2 protein expression; inducing the phosphorylation (Ser15) of p53 protein; activating c-Jun NH(2)-terminal kinase (JNK), caspase-8, and caspase-3; and cleaving the DNA protein kinase catalytic subunit, ATM, and MDM2. Inhibition of JNK activity abrogates PS-341-induced MM cell death. These studies identify molecular targets of PS-341 and provide the rationale for the development of second-generation, more targeted therapies.

Beta-adrenergic receptor-stimulated apoptosis in cardiac myocytes is mediated by reactive oxygen species/c-Jun NH2-terminal kinase-dependent activation of the mitochondrial pathway

Stimulation of beta-adrenergic receptors (betaARs) causes apoptosis in adult rat ventricular myocytes (ARVMs). The role of reactive oxygen species (ROS) in mediating betaAR-stimulated apoptosis is not known. Stimulation of betaARs with norepinephrine (10 micromol/L) in the presence of prazosin (100 nmol/L) for 24 hours increased the number of apoptotic myocytes as determined by TUNEL staining by 3.6- fold. The superoxide dismutase/catalase mimetics Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride (MnTMPyP; 10 micromol/L) and Euk-134 decreased betaAR-stimulated apoptosis by 89+/-6% and 76+/-10%, respectively. Infection with an adenovirus expressing catalase decreased betaAR-stimulated apoptosis by 82+/-15%. The mitochondrial permeability transition pore inhibitor bongkrekic acid (50 micromol/L) decreased betaAR-stimulated apoptosis by 76+/-8%, and the caspase inhibitor zVAD-fmk (25 micromol/L) decreased betaAR-stimulated apoptosis by 62+/-11%. betaAR-stimulated cytochrome c release was inhibited by MnTMPyP. betaAR stimulation caused c-Jun NH2-terminal kinase (JNK) activation, which was abolished by MnTMPyP. Transfection with an adenovirus expressing dominant-negative JNK inhibited betaAR-stimulated apoptosis by 81+/-12%, and the JNK inhibitor SP600125 inhibited both betaAR-stimulated apoptosis and cytochrome c release. Thus, betaAR-stimulated apoptosis in ARVMs involves ROS/JNK-dependent activation of the mitochondrial death pathway.

Critical role of c-Jun N-terminal protein kinase activation in troglitazone-induced apoptosis of human HepG2 hepatoma cells

The peroxisome proliferator-activated receptor agonist troglitazone (TRO) was used for treatment of non-insulin-dependent diabetes until its removal from the market because of its severe hepatotoxicity. However, the mechanism for its hepatotoxicity is still poorly understood. In this study, we investigated whether TRO caused cell death by altering signaling pathways associated with cell damage and survival in human hepatoma cells. Our data reveal that TRO caused time- and concentration-dependent apoptosis of HepG2 and Chang liver human hepatoma cells, as evidenced by DNA fragmentation and staining with Hoechst 33342. In contrast, 50 or 100 microM rosiglitazone, a structural analog of TRO, did not cause apoptosis in these hepatoma cells. TRO activated both c-Jun N-terminal protein kinase (JNK) and p38 kinase about 5-fold between 0.5 and 8 h before they returned to control levels at 16 h in HepG2 cells. In contrast, TRO failed to activate the extracellular signal-regulated kinase. Furthermore, TRO increased the levels of proapoptotic proteins, Bad, Bax, release of cytochrome c, and cleavage of Bid in a time-dependent manner. The antiapoptotic Bcl-2 protein level decreased in hepatoma cells treated with TRO. Pretreatment of hepatoma cells with a selective JNK inhibitor, anthra[1,9-cd]pyrazol-6(2H)-one (SP600125), significantly reduced the rate of TRO-induced cell death, whereas 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole (SB203580), an inhibitor of p38 kinase, had little effect on apoptosis. Pretreatment with SP600125 also prevented JNK activation and c-Jun phosphorylation. In addition, rosiglitazone, which is not as toxic to hepatoma cells as TRO, did not stimulate JNK activity. Transfection of cDNA for the dominant-negative mutant JNK-KR (Lys-->Arg) or SEK1-KR (Lys-->Arg), an immediate upstream kinase of JNK, significantly reduced TRO-induced JNK activation and cell death rate. Furthermore, SP600125 pretreatment effectively prevented the TRO-mediated changes in Bad, Bax, Bid cleavage, and cytochrome c release. These data strongly suggest that hepatotoxic TRO causes apoptosis by activating the JNK-dependent cell death pathway accompanied by increased Bid cleavage and elevation of proapoptotic proteins.

Involvement of c-Jun N-terminal kinase in amyloid precursor protein-mediated neuronal cell death

Amyloid precursor protein (APP), the precursor of Abeta, has been shown to function as a cell surface receptor that mediates neuronal cell death by anti-APP antibody. The c-Jun N-terminal kinase (JNK) can mediate various neurotoxic signals, including Abeta neurotoxicity. However, the relationship of APP-mediated neurotoxicity to JNK is not clear, partly because APP cytotoxicity is Abeta independent. Here we examined whether JNK is involved in APP-mediated neuronal cell death and found that: (i) neuronal cell death by antibody-bound APP was inhibited by dominant-negative JNK, JIP-1b and SP600125, the specific inhibitor of JNK, but not by SB203580 or PD98059; (ii) constitutively active (ca) JNK caused neuronal cell death and (iii) the pharmacological profile of caJNK-mediated cell death closely coincided with that of APP-mediated cell death. Pertussis toxin (PTX) suppressed APP-mediated cell death but not caJNK-induced cell death, which was suppressed by Humanin, a newly identified neuroprotective factor which inhibits APP-mediated cytotoxicity. In the presence of PTX, the PTX-resistant mutant of Galphao, but not that of Galphai, recovered the cytotoxic action of APP. These findings demonstrate that JNK is involved in APP-mediated neuronal cell death as a downstream signal transducer of Go.

Potentiation of protein kinase C zeta activity by 15-deoxy-delta(12,14)-prostaglandin J(2) induces an imbalance between mitogen-activated protein kinases and NF-kappa B that promotes apoptosis in macrophages

Activation of the macrophage cell line RAW 264.7 with lipopolysaccharide (LPS) transiently activates protein kinase C zeta (PKC zeta) and Jun N-terminal kinase (JNK) through a phosphoinositide-3-kinase (PI3-kinase)-dependent pathway. Incubation of LPS-treated cells with the cyclopentenone 15-deoxy-Delta(12,14)-prostaglandin J(2) (15dPGJ(2)) promoted a sustained activation of PKC zeta and JNK and inhibited I kappa B kinase (IKK) and NF-kappa B activity. Accordingly, 15dPGJ(2) induced an imbalance between JNK and IKK activities by increasing the former signaling pathway and inhibiting the latter signaling pathway. Under these conditions, apoptosis was significantly enhanced; this response was very dependent on PKC zeta and JNK activation. The effect of 15dPGJ(2) on PKC zeta activity observed in LPS-activated macrophages was not dependent on a direct action of this prostaglandin on the enzyme but was due to the activation of a step upstream of PI3-kinase. Moreover, LPS promoted the redistribution of activated PKC zeta from the cytosol to the nucleus, a process that was enhanced by treatment of the cells with 15dPGJ(2) that favored a persistent and broader distribution of PKC zeta in the nucleus. These results indicate that 15dPGJ(2) and other cyclopentenone prostaglandins, through the sustained activation of PKC zeta, might contribute significantly to the process of resolution of inflammation by promoting apoptosis of activated macrophages.

Herpes simplex virus type 1-induced encephalitis has an apoptotic component associated with activation of c-Jun N-terminal kinase

Herpes simplex virus type 1 (HSV-1) triggered apoptosis in hippocampal cultures, as determined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) and immunohistochemistry with antibody specific for the large fragment of activated caspase 3. The levels of phosphorylated (activated) c-Jun N-terminal kinase (JNK) were also increased in HSV-1-infected hippocampal cultures as were the levels of activated c-Jun, its target. JNK activation was involved in HSV-1-induced apoptosis as evidenced by apoptosis inhibition with the JNK inhibitor SP600125. HSV-2 activated the mitogen-activated protein kinase/extracellular regulated protein kinase (MEK/ERK) survival pathway and did not trigger apoptosis in hippocampal cultures. The MEK specific inhibitor U0126 inhibited ERK activation and caused a significant increase in the percent TUNEL(+) cells in HSV-2-infected cultures, indicating that the failure of HSV-2 to trigger apoptosis is due to its ability to activate the MEK/ERK survival pathway. JNK was also activated in brain tissues from patients with HSV-associated acute focal encephalitis (HSE) that were positive for HSV-1 antigen. JNK activation correlated with apoptosis, as determined by immunohistochemistry with antibody to activated caspase 3 or cleaved poly (ADP-ribose) polymerase (PARP). The data suggest that HSE has an apoptotic component that may contribute to disease pathogenesis.

Inhibition of hippocampal Jun N-terminal kinase enhances short-term memory but blocks long-term memory formation and retrieval of an inhibitory avoidance task

Learning initiates a series of plastic events the occurrence of which are required for the storage of information related to the training experience. Several lines of evidence indicate that, in the rat hippocampus, different members of the family of mitogen-activated protein kinases (MAPK) play a key role in the onset of such plastic events. Using SP600125, the newly developed inhibitor of the MAPK c-Jun amino-terminal kinase (JNK), we show a direct involvement of this protein kinase in mnemonic processes. The intra-CA1 infusion of SP600125, at a dose that in naïve animals significantly reduced the phosphorylation levels of c-Jun without affecting the activity of ERK1/2 or p38 MAPK, enhanced short-term memory (STM) but blocked long-term memory (LTM) formation and retrieval of an inhibitory avoidance learning task. No action of this drug on locomotor/exploratory activity or general anxiety state could be detected. The significance of these results is discussed in the context of others describing the independence of LTM from STM.

Characterization of JNK-like protein derived from a mosquito cell line, C6/36

When Western blot analysis of heat-killed bacteria- and lipopolysaccharide (LPS)-treated Aedes albopictus mosquito cell line C6/36 was performed using antiphospholyrated c-Jun amino-terminal kinase (JNK) antibodies, approximately 46 kDa protein was clearly detected with a peak around 30 min. After the C6/36 cells were incubated at 45 degrees C in order to induce apoptosis, the 46 kDa protein continued to be detected for at least 3 h. The internalization of fluorescein-labelled bacteria was inhibited by a JNK-specific inhibitor SP600125, suggesting that phagocytosis involves the JNK signalling pathway in mosquito cells. Based on these results, we found one candidate for the nucleotide sequence of JNK (Ae-JNK) from the C6/36 cells. This study is the first report regarding the mitogen-activated protein kinase (MAPK) of mosquito.

Paclitaxel induces inactivation of p70 S6 kinase and phosphorylation of Thr421 and Ser424 via multiple signaling pathways in mitosis

The 70 kDa ribosomal S6 kinase (p70S6K) is important for cell growth and survival. Activation of p70S6K requires sequential phosphorylation of multiple serine and threonine sites often triggered by growth factors and hormones. Here, we report that paclitaxel, a microtubule-damaging agent, induces phosphorylation of p70S6K at threonine 421 and serine 424 (T421/S424) in a concentration- and time-dependent manner in multiple breast and ovarian cancer cell lines demonstrated by a T421/S424 phospho-p70S6K antibody. Phosphoamino-acid analysis and Western blot analysis by serine-/threonine-specific antibodies further confirms that both serine and threonine residues are phosphorylated in p70S6K following treatment with paclitaxel. Paclitaxel-induced p70S6K(T421/S424) phosphorylation requires both de novo RNA and protein synthesis via multiple signaling pathways including ERK1/2 MAP kinase, JNK, PKC, Ca(++), PI3K, and mammalian target of rapamycin (mTOR). Despite phosphorylation of p70S6K(T421/S424), paclitaxel inactivates this kinase in a concentration- and time-dependent manner as illustrated by in vitro kinase assay. Inhibitors of mTOR, PI3K, and Ca(++) impair p70S6K activity, whereas inhibitors of JNK and PKC stimulate p70S6K activity. Inhibition of PKC and JNK prevents paclitaxel-induced p70S6K inactivation. Moreover, the paclitaxel-induced phosphorylation and low activity of p70S6K mainly occurs during mitosis. In summary, paclitaxel is able to induce p70S6K(T421/S424) phosphorylation and decrease its activity in mitotic cells via multiple signaling pathways. Our data suggest that paclitaxel-induced p70S6K(T421/S424) phosphorylation and kinase inactivation are differentially regulated. Our data also indicate that paclitaxel may exert its antitumor effect, at least in part, via inhibition of p70S6K.

Ajoene-induced cell death in human promyeloleukemic cells does not require JNK but is amplified by the inhibition of ERK

Treatment of human promyeloleukemic HL-60 cells with the experimental antileukemic drug ajoene induces the activation of the mitogen-activated protein kinases (MAPKs) c-Jun NH(2)-terminal kinase (JNK), p38 and extracellular signal-regulated kinases (ERK) 1/2 as well as the survival kinase Akt. JNK activation occurred in HL-60/neo, HL-60/bcl-x(L), and in HL-60 cells pretreated with the pan-caspase inhibitor zVAD-fmk, indicating that JNK activation is not dependent on ajoene-induced mitochondria perturbation and subsequent caspase activation. Cells overexpressing a dominant-negative JNK showed no altered sensitivity towards ajoene suggesting that the activation of JNK is not necessary for ajoene-induced cell death. Inhibition of p38 MAPK by SB 203580 had no influence on ajoene-mediated apoptosis. In contrast, inhibition of ERK1/2 vastly enhanced ajoene-induced cell death. The survival kinase Akt, in contrast, did not participate in ajoene-induced death signaling as shown by the use of the phosphatidylinositol-3-kinase inhibitor wortmannin. Thus in contrast to the previous findings regarding stress-induced cell death, ajoene-mediated activation of JNK and p38 has no impact on ajoene-induced apoptosis in HL-60 cells. Blockade of ERK1/2 but not Akt pathways leads to sensitization of cells against ajoene-mediated apoptosis supporting the view that inhibition of ERK1/2 is a valuable strategy to increase the sensitivity of promyeloleukemic cells towards ajoene.

NS-398 and piroxicam suppress UVB-induced activator protein 1 activity by mechanisms independent of cyclooxygenase-2

Cyclooxygenases (COX) are rate-limiting enzymes that catalyze the conversion of arachidonic acid to prostaglandins, which are involved in many physiological and pathophysiological responses. COX-2, one of two isoforms of COX, was recently found to play an important role in carcinogenesis in many cell and tissue types. COX-2 inhibitors, which belong to the family of nonsteroidal anti-inflammatory drugs, are believed to be effective in many biological activities such as tumor chemoprevention because of their inhibition of COX-2. However, in the present study we found that both piroxicam, a general COX inhibitor, and NS-398, a COX-2 selective inhibitor, effectively suppressed the activation of transcription factor activator protein 1 (AP-1) induced by ultraviolet B (UVB) or 12-O-tetradecanoylphorbol-13-acetate in mouse epidermal JB6 cells. These COX-2 inhibitors could also inhibit 12-O-tetradecanoylphorbol-13-acetate-induced cell transformation. UVB significantly increased AP-1 activity in Cox-2(-/-) fibroblasts transfected with an AP-1 luciferase reporter gene, and this increase was blocked by NS-389 or piroxicam. In JB6, Cox-2(-/-), or wild-type Cox-2(+/+) cells, both NS-398 and piroxicam inhibited UVB-induced phosphorylation of c-Jun NH(2)-terminal kinases, the kinases that activate the AP-1/c-Jun complex. Based on our results, we propose that the inhibition of AP-1 activity by COX-2 inhibitors NS-398 or piroxicam may occur by a mechanism that is independent of COX-2.

Salicylic acid reverses phorbol 12-myristate-13-acetate (PMA)- and tumor necrosis factor alpha (TNFalpha)-induced insulin receptor substrate 1 (IRS1) serine 307 phosphorylation and insulin resistance in human embryonic kidney 293 (HEK293) cells

Salicylates, including aspirin, have been shown to improve insulin sensitivity both in human and animal models. Although it has been suggested that salicylates sensitize insulin action by inhibiting IkappaB kinase beta (IKKbeta), the detailed mechanisms remain unclear. Protein kinase C isoforms and tumor necrosis factor alpha (TNFalpha) signaling pathways are well described mediators of insulin resistance; they are implicated in the activation of IKKbeta and the subsequent inhibition of proximal insulin signaling via insulin receptor substrate 1 (IRS1) and Akt. This study investigated the effect of salicylic acid on phorbol 12-myristate 13-acetate (PMA)- and TNFalpha-induced insulin resistance in a human embryonic kidney 293 (HEK293) cell line stably expressing recombinant human IRS1. The results showed that both PMA and TNFalpha inhibited insulin-induced Akt phosphorylation and promoted IRS1 phosphorylation on Ser-307. Salicylic acid pretreatment completely reversed the effects of PMA and TNFalpha on both Akt and IRS1. Whereas PMA activated protein kinase C isoforms and IKKbeta, TNFalpha activated neither. On the other hand, both PMA and TNFalpha activated the c-Jun N-terminal kinase (JNK), which has been reported to directly phosphorylate IRS1 Ser-307. SP600125, a JNK inhibitor, prevented PMA and TNFalpha-induced IRS1 Ser-307 phosphorylation. Finally, salicylic acid inhibited JNK activation induced by both PMA and TNFalpha. Taken together, these observations suggest that salicylic acid can reverse the inhibitory effects of TNFalpha on insulin signaling via an IKKbeta-independent mechanism(s), potentially involving the inhibition of JNK activation. The role of JNK in salicylic acid-mediated insulin sensitization, however, requires further validation because the JNK inhibitor SP600125 appears to have other nonspecific activity in addition to inhibiting JNK activity.

Novel agents for the prevention of breast cancer: targeting transcription factors and signal transduction pathways

Transformation of breast cells occurs through loss or mutation of tumor suppressor genes, or activation or amplification of oncogenes, leading to deregulation of signal transduction pathways, abnormal amplification of growth signals, and aberrant expression of genes that ultimately transform the cells into invasive cancer. The goal of cancer preventive therapy, or "chemoprevention," is to eliminate premalignant cells or to block the progression of normal cells into cancer. Multiple alterations in signal pathways and transcription factors are observed in mammary gland tumorigenesis. In particular, estrogen receptor (ER) deregulation plays a critical role in breast cancer development and progress, and targeting ER with selective ER modulators (SERMs) has achieved significant reduction of breast cancer incidence in women at high risk for breast cancer. However, not all breast cancer is prevented by SERMs, because 30-40% of the tumors are ER-negative. Other receptors for retinoids, vitamin D analogs and peroxisome proliferator-activiator, along with transcription factors such as AP-1, NF-kappaB, and STATs (signal transducers and activators of transcription) affect breast tumorigenesis. This is also true for the signal transduction pathways, for example cyclooxygenase 2 (Cox-2), HER2/neu, mitogen-activated protein kinase (MAPK), and PI3K/Akt. Therefore, proteins in pathways that are altered during the process of mammary tumorigenesis may be promising targets of future chemopreventive drugs. Many newly-developed synthetic or natural compounds/agents are now under testing in preclinical studies and clinical trials. Receptor selective retinoids, receptor tyrosine kinase inhibitors (TKIs), SERMs, Cox-2 inhibitors, and others are some of the promising novel agents for the prevention of breast cancer. The chemopreventive activity of these agents and other novel signal transduction inhibitors are discussed in this chapter.

The herpes simplex virus type 2 R1 protein kinase (ICP10 PK) functions as a dominant regulator of apoptosis in hippocampal neurons involving activation of the ERK survival pathway and upregulation of the antiapoptotic protein Bag-1

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) can trigger or block apoptosis in a cell type-dependent manner. We have recently shown that the protein kinase activity of the large subunit of the HSV-2 ribonucleotide reductase (R1) protein (ICP10 PK) blocks apoptosis in cultured hippocampal neurons by activating the extracellular signal-regulated kinase (ERK) survival pathway (Perkins et al., J. Virol. 76:1435-1449, 2002). The present studies were designed to better elucidate the mechanism of ICP10 PK-induced neuroprotection and determine whether HSV-1 has similar activity. The data indicate that apoptosis inhibition by ICP10 PK involves a c-Raf-1-dependent mechanism and induction of the antiapoptotic protein Bag-1 by the activated ERK survival pathway. Also associated with neuroprotection by ICP10 PK are increased activation/stability of the transcription factor CREB and stabilization of the antiapoptotic protein Bcl-2. HSV-1 and the ICP10 PK-deleted HSV-2 mutant ICP10DeltaPK activate JNK, c-Jun, and ATF-2, induce the proapoptotic protein BAD, and trigger apoptosis in hippocampal neurons. c-Jun activation and apoptosis are inhibited in hippocampal cultures infected with HSV-1 in the presence of the JNK inhibitor SP600125, suggesting that JNK/c-Jun activation is required for HSV-1-induced apoptosis. Ectopically delivered ICP10 PK (but not its PK-negative mutant p139) inhibits apoptosis triggered by HSV-1 or ICP10DeltaPK. Collectively, the data indicate that ICP10 PK-induced activation of the ERK survival pathway results in Bag-1 upregulation and overrides the proapoptotic JNK/c-Jun signal induced by other viral proteins.

Oxidant-mediated mitochondrial injury in eosinophil apoptosis: enhancement by glucocorticoids and inhibition by granulocyte-macrophage colony-stimulating factor

The mainstay of asthma therapy, glucocorticosteroids (GCs) have among their therapeutic effects the inhibition of inflammatory cytokine production and induction of eosinophil apoptosis. In the absence of prosurvival cytokines (e.g., GM-CSF), eosinophils appear to be short-lived, undergoing apoptosis over 96 h in vitro. In a dose-dependent manner, GC further enhances apoptosis, while prosurvival cytokines inhibit apoptosis and antagonize the effect of GC. The mechanisms of eosinophil apoptosis, its enhancement by GC, and antagonism of GC by GM-CSF are not well-understood. As demonstrated in this study, baseline apoptosis of eosinophils resulted from oxidant-mediated mitochondrial injury that was significantly enhanced by GC. Mitochondrial injury was detected by early and progressive loss of mitochondrial membrane potential and the antioxidant protein, Mn superoxide dismutase (SOD). Also observed was the activation/translocation of the proapoptotic protein, Bax, to mitochondria. Underscoring the role of oxidants was the inhibition of mitochondrial changes and apoptosis with culture in hypoxia, or pretreatment with a flavoprotein inhibitor or a SOD mimic. GCs demonstrated early (40 min) and late (16 h) activation of proapoptotic c-Jun NH2-terminal kinase (JNK) and decreased the antiapoptotic protein X-linked inhibitor of apoptosis, a recently demonstrated inhibitor of JNK activation. Similarly, inhibition of JNK prevented GC-enhanced mitochondrial injury and apoptosis. Importantly, GM-CSF prevented GC-induced loss of X-linked inhibitor of apoptosis protein, late activation of JNK, and mitochondrial injury even in the face of unchanged oxidant production, loss of MnSOD, and early JNK activation. These data demonstrate that oxidant-induced mitochondrial injury is pivotal in eosinophil apoptosis, and is enhanced by GC-induced prolonged JNK activation that is in turn inhibited by GM-CSF.

A new identity for MLK3 as an NIMA-related, cell cycle-regulated kinase that is localized near centrosomes and influences microtubule organization

Although conserved counterparts for most proteins involved in the G(2)/M transition of the cell cycle have been found in all eukaryotes, a notable exception is the essential but functionally enigmatic fungal kinase NIMA. While a number of vertebrate kinases have been identified with catalytic domain homology to NIMA, none of these resemble NIMA within its extensive noncatalytic region, a region critical for NIMA function in Aspergillus nidulans. We used a bioinformatics approach to search for proteins with homology to the noncatalytic region of NIMA and identified mixed lineage kinase 3 (MLK3). MLK3 has been proposed to serve as a component in MAP kinase cascades, particularly those resulting in the activation of the c-Jun N-terminal kinase (JNK). Here we describe the first in-depth study of endogenous MLK3 and report that, like NIMA, MLK3 phosphorylation and activity are enhanced during G(2)/M, whereas JNK remains inactive. Coincident with the G(2)/M transition, a period marked by dramatic reorganization of the cytoplasmic microtubule network, endogenous MLK3 transiently disperses away from the centrosome and centrosomal-proximal sites where it is localized during interphase. Furthermore, when overexpressed, MLK3, like NIMA, localizes to the centrosomal region, induces profound disruption of cytoplasmic microtubules and a nuclear distortion phenotype that differs from mitotic chromosome condensation. Cellular depletion of MLK3 protein using siRNA technology results in an increased sensitivity to the microtubule-stabilizing agent taxol. Our studies suggest a new role for MLK3, separable from its function in the JNK pathway, that may contribute to promoting microtubule instability, a hallmark of M phase entry.

ATF1 phosphorylation by the ERK MAPK pathway is required for epidermal growth factor-induced c-jun expression

Epidermal growth factor induction of c-jun expression requires ATF1 and MEF2 sites in the c-jun promoter. We find that activation of the c-jun promoter through the ATF1 site requires phosphorylation of ATF1 at serine 63. A serine 63 to alanine mutation of ATF1 acts to block epidermal growth factor (EGF) induction of a transfected c-jun gene. ATF1 can be phosphorylated by mitogen- and stress-activated protein kinase 1 (MSK1), which is activated by EGF and ERK1/2. Kinase-dead MSK1 mutants blocked EGF induction of a transfected c-jun gene suggesting that MSK1 or a similar family member is required for induced c-jun expression. Use of the MEK1 inhibitor U0126 and dominant negative MEK1 further showed that MSK1 activation and c-jun induction require the ERK pathway. In contrast, a JNK inhibitor blocked EGF induction of c-jun expression but not ATF1 phosphorylation. These results show that the two MAPK pathways, ERK and JNK, are required for EGF-induced c-jun expression and that the ERK pathway acts through downstream phosphorylation of ATF1.

Oxidation-triggered c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein (MAP) kinase pathways for apoptosis in human leukaemic cells stimulated by epigallocatechin-3-gallate (EGCG): a distinct pathway from those of chemically induced and receptor-mediated apoptosis

We investigated intracellular signalling pathways for apoptosis induced by epigallocatechin-3-gallate (EGCG) as compared with those induced by a toxic chemical substance (etoposide, VP16) or the death receptor ligand [tumour necrosis factor (TNF)]. EGCG as well as VP16 and TNF induced activation of two apoptosis-regulating mitogen-activated protein (MAP) kinases, namely c-Jun N-terminal kinase (JNK) and p38 MAP kinase, in both human leukaemic U937 and OCI-AML1a cells. In U937 cells, the apoptosis and activation of caspases-3 and -9 induced by EGCG but not VP16 and TNF were inhibited with SB203580, a specific inhibitor of p38, while those induced by EGCG and VP16 but not TNF were inhibited with SB202190, a rather broad inhibitor of JNK and p38. In contrast, the EGCG-induced apoptosis in OCI-AML1a cells was resistant to SB203580 but not to SB202190. Unlike TNF, EGCG did not induce the activation of nuclear factor-kappaB but rather induced the primary activation of caspase-9. N -Acetyl-L-cysteine (NAC) almost completely abolished apoptosis induced by EGCG under conditions in which the apoptosis induced by VP16 or TNF was not affected. The JNK/p38 activation by EGCG was also potently inhibited by NAC, whereas those by VP16 and TNF were either not or only minimally affected by NAC. In addition, dithiothreitol also suppressed both apoptosis and JNK/p38 activation by EGCG, and EGCG-induced activation of MAP kinase kinase (MKK) 3/6, MKK4 and apoptosis-regulating kinase 1 (ASK1) was suppressed by NAC. Dominant negative ASK1, MKK6, MKK4 and JNK1 potently inhibited EGCG-induced cell death. EGCG induced an intracellular increase in reactive oxygen species and GSSG, both of which were also inhibited by NAC, and the decreased synthesis of glutathione rendered the cell susceptible to EGCG-induced apoptosis. Taken together these results strongly suggest that EGCG executed apoptotic cell death via an ASK1, MKK and JNK/p38 cascade which is triggered by NAC-sensitive intracellular oxidative events in a manner distinct from chemically induced or receptor-mediated apoptosis.

Serine phosphorylation of insulin receptor substrate 1 by inhibitor kappa B kinase complex

Insulin resistance contributes importantly to the pathophysiology of type 2 diabetes mellitus. One mechanism mediating insulin resistance may involve the phosphorylation of serine residues in insulin receptor substrate-1 (IRS-1), leading to impairment in the ability of IRS-1 to activate downstream phosphatidylinositol 3-kinase-dependent pathways. Insulin-resistant states and serine phosphorylation of IRS-1 are associated with the activation of the inhibitor kappaB kinase (IKK) complex. However, the precise molecular mechanisms by which IKK may contribute to the development of insulin resistance are not well understood. In this study, using phosphospecific antibodies against rat IRS-1 phosphorylated at Ser(307) (equivalent to Ser(312) in human IRS-1), we observed serine phosphorylation of IRS-1 in response to TNF-alpha or calyculin A treatment that paralleled surrogate markers for IKK activation. The phosphorylation of human IRS-1 at Ser(312) in response to tumor necrosis factor-alpha was significantly reduced in cells pretreated with the IKK inhibitor 15 deoxy-prostaglandin J(2) as well as in cells derived from IKK knock-out mice. We observed interactions between endogenous IRS-1 and IKK in intact cells using a co-immunoprecipitation approach. Moreover, this interaction between IRS-1 and IKK in the basal state was reduced upon IKK activation and increased serine phosphorylation of IRS-1. Data from in vitro kinase assays using recombinant IRS-1 as a substrate were consistent with the ability of IRS-1 to function as a direct substrate for IKK with multiple serine phosphorylation sites in addition to Ser(312). Taken together, our data suggest that IRS-1 is a novel direct substrate for IKK and that phosphorylation of IRS-1 at Ser(312) (and other sites) by IKK may contribute to the insulin resistance mediated by activation of inflammatory pathways.

The p65/RelA subunit of NF-kappaB suppresses the sustained, antiapoptotic activity of Jun kinase induced by tumor necrosis factor

Tumor necrosis factor (TNF) signaling through the TNF receptors involves the recruitment of key signaling factors, leading to the activation of both the transcription factor NF-kappaB and the stress-activated Jun kinase (JNK). In most cells, TNF signaling leads to a rapid and transient increase in JNK activity. However, we show that TNF treatment leads to the sustained activation of JNK in cells that are null for the p65/RelA subunit of NF-kappaB as well as in cells expressing the super-repressor form of IkappaB. In addition, the data indicate that the ability of p65/RelA to regulate gene expression is required to suppress the persistent activation of JNK. Interestingly, this suppression occurs upstream of JNK, within the signal transduction cascade leading to JNK activation, without affecting the stress-activated kinase p38. Since NF-kappaB has previously been shown to be involved in the suppression of TNF-induced apoptosis, we were interested in determining the role of deregulated JNK activity, induced by the loss of NF-kappaB, in controlling the cell death response. Through the use of different approaches for inhibition of JNK, we show that the suppression of JNK activity in cells that lack active NF-kappaB enhances the apoptotic response to TNF. These data suggest that the activity of JNK in cells blocked for NF-kappaB function provides an antiapoptotic signal and explains, at least partly, why a significant number of NF-kappaB null cells remain viable following TNF treatment.

Rough lipopolysaccharide from Brucella abortus and Escherichia coli differentially activates the same mitogen-activated protein kinase signaling pathways for tumor necrosis factor alpha in RAW 264.7 macrophage-like cells

The intracellular, gram-negative pathogen Brucella abortus establishes chronic infections in host macrophages while downregulating cytokines such as tumor necrosis factor alpha (TNF-alpha). When producing TNF-alpha, Brucella abortus rough lipopolysaccharide (LPS) activates the same mitogen-activated protein kinase signaling pathways (ERK and JNK) as Escherichia coli LPS, but Brucella LPS is a much less potent agonist.

A central role for JNK in obesity and insulin resistance

Obesity is closely associated with insulin resistance and establishes the leading risk factor for type 2 diabetes mellitus, yet the molecular mechanisms of this association are poorly understood. The c-Jun amino-terminal kinases (JNKs) can interfere with insulin action in cultured cells and are activated by inflammatory cytokines and free fatty acids, molecules that have been implicated in the development of type 2 diabetes. Here we show that JNK activity is abnormally elevated in obesity. Furthermore, an absence of JNK1 results in decreased adiposity, significantly improved insulin sensitivity and enhanced insulin receptor signalling capacity in two different models of mouse obesity. Thus, JNK is a crucial mediator of obesity and insulin resistance and a potential target for therapeutics.

Differential regulation of CD44 expression by lipopolysaccharide (LPS) and TNF-alpha in human monocytic cells: distinct involvement of c-Jun N-terminal kinase in LPS-induced CD44 expression

Alterations in the regulation of CD44 expression play a critical role in modulating cell adhesion, migration, and inflammation. LPS, a bacterial cell wall component, regulates CD44 expression and may modulate CD44-mediated biological effects in monocytic cells during inflammation and immune responses. In this study, we show that in normal human monocytes, LPS and LPS-induced cytokines IL-10 and TNF-alpha enhance CD44 expression. To delineate the mechanism underlying LPS-induced CD44 expression, we investigated the role of the mitogen-activated protein kinases (MAPKs), p38, p42/44 extracellular signal-regulated kinase, and c-Jun N-terminal kinase (JNK) by using their specific inhibitors. We demonstrate the involvement, at least in part, of p38 MAPK in TNF-alpha-induced CD44 expression in both monocytes and promonocytic THP-1 cells. However, neither p38 nor p42/44 MAPKs were involved in IL-10-induced CD44 expression in monocytes. To further dissect the TNF-alpha and LPS-induced signaling pathways regulating CD44 expression independent of IL-10-mediated effects, we used IL-10 refractory THP-1 cells as a model system. Herein, we show that CD44 expression induced by the LPS-mediated pathway predominantly involved JNK activation. This conclusion was based on results derived by transfection of THP-1 cells with a dominant-negative mutant of stress-activated protein/extracellular signal-regulated kinase kinase 1, and by exposure of cells to JNK inhibitors dexamethasone and SP600125. All these treatments prevented CD44 induction in LPS-stimulated, but not in TNF-alpha-stimulated, THP-1 cells. Furthermore, we show that CD44 induction may involve JNK-dependent early growth response gene activation in LPS-stimulated monocytic cells. Taken together, these results suggest a predominant role of JNK in LPS-induced CD44 expression in monocytic cells.

Up-regulation of c-jun mRNA in cardiac myocytes requires the extracellular signal-regulated kinase cascade, but c-Jun N-terminal kinases are required for efficient up-regulation of c-Jun protein

Cardiac hypertrophy, an important adaptational response, is associated with up-regulation of the immediate early gene, c- jun, which encodes the c-Jun transcription factor. c-Jun may feed back to up-regulate its own transcription and, since the c-Jun N-terminal kinase (JNK) family of mitogen-activated protein kinases (MAPKs) phosphorylate c-Jun(Ser-63/73) to increase its transactivating activity, JNKs are thought to be the principal factors involved in c- jun up-regulation. Hypertrophy in primary cultures of cardiac myocytes is induced by endothelin-1, phenylephrine or PMA, probably through activation of one or more of the MAPK family. These three agonists increased c- jun mRNA with the rank order of potency of PMA approximately endothelin-1>phenylephrine. Up-regulation of c- jun mRNA by endothelin-1 was attenuated by inhibitors of protein kinase C (GF109203X) and the extracellular signal-regulated kinase (ERK) cascade (PD98059 or U0126), but not by inhibitors of the JNK (SP600125) or p38-MAPK (SB203580) cascades. Hyperosmotic shock (0.5 M sorbitol) powerfully activates JNKs, but did not increase c- jun mRNA. These data suggest that ERKs, rather than JNKs, are required for c- jun up-regulation. However, endothelin-1 and phenylephrine induced greater up-regulation of c-Jun protein than PMA and phosphorylation of c-Jun(Ser-63/73) correlated with the level of c-Jun protein. Up-regulation of c-Jun protein by endothelin-1 was attenuated by inhibitors of protein kinase C and the ERK cascade, probably correlating with a primary input of ERKs into transcription. In addition, SP600125 inhibited the phosphorylation of c-Jun(Ser-63/73), attenuated the increase in c-Jun protein induced by endothelin-1 and increased the rate of c-Jun degradation. Thus whereas ERKs are the principal MAPKs required for c- jun transcription, JNKs are necessary to stabilize c-Jun for efficient up-regulation of the protein.

Nocodazole-induced p53-dependent c-Jun N-terminal kinase activation reduces apoptosis in human colon carcinoma HCT116 cells

Microtubule-interfering agents are widely used in cancer chemotherapy, and prognostic results vary significantly from tumor to tumor, depending on the p53 status. In preliminary experiments, we compared the expression and phosphorylation profiles of more than 100 protein kinases and protein phosphatases in human colorectal carcinoma cell line HCT116 between p53+/+ and p53-/- cells in response to short term nocodazole treatment through application of Kinetworks immunoblotting screens. Among the proteins tracked, the regulation of the phosphorylation of c-Jun N-terminal kinase (JNK)1/2 at Thr-183/Tyr-185 was the major difference between p53+/+ and p53-/- cells. With the loss of the p53 gene, the levels of phosphorylation of Ser-63 of c-Jun and Thr-183/Tyr-185 of JNK1/2 in p53-/- cells did not increase as markedly as in p53+/+ cells in response to a 1-h treatment with nocodazole or other microtubule-disrupting drugs such as vinblastine and colchicine. Similar observations were also made in MCF-7 and A549 tumor cells, which were rendered p53-deficient by E6 oncoprotein expression. However, arsenate-induced JNK activation in p53-/- cells was preserved. Inhibition of p53 expression by its antisense oligonucleotide also attenuated nocodazole-induced JNK activation in p53+/+ cells. Surprisingly, cotransfection of p53+/+ cells with dominant negative mutants of JNK isoforms and treatment of p53+/+ cells with the JNK inhibitor SP600125 actually further enhanced apoptosis in p53+/+ cells by up to 2-fold in response to nocodazole. These findings indicate that inhibition of p53-mediated JNK1/2 activity in certain tumor cells could serve to enhance the apoptosis-inducing actions of cancer chemotherapeutic agents that disrupt mitotic spindle function.

From extracellular to intracellular targets, inhibiting MAP kinases in treatment of Crohn's disease

In recent years the emphasis in finding new therapeutic options for chronic inflammatory diseases has been on targeting extracellular mediators of inflammation. A range of tools has become available to interfere with signaling by cytokines and their receptors. As our understanding of the intracellular pathways that mediate inflammatory signals expands, new therapeutic targets within the inflammatory cells come into sight. In this review we will discuss possible intracellular targets for treatment in Crohn's disease, a chronic relapsing inflammatory disease of the gut. Despite the encouraging results with anti-TNF antibodies in patients with Crohn's disease, our current treatment options are still insufficient and warrant novel treatment strategies. The mitogen-activated protein kinase (MAPK) family of signal transduction proteins is an important intracellular mediator of inflammation, and recently a MAPK inhibitor was successfully used in patients with Crohn's disease. We will discuss our current understanding of the molecular pathophysiology of Crohn's disease and also novel therapies that specifically target members of the MAPK pathway.

Differential cytostatic and apoptotic effects of ecteinascidin-743 in cancer cells. Transcription-dependent cell cycle arrest and transcription-independent JNK and mitochondrial mediated apoptosis

We have found that ecteinascidin-743 (ET-743) inhibited cell proliferation at 1-10 ng/ml, leading to S and G(2)/M arrest and subsequent apoptosis, and induced early apoptosis without previous cell cycle arrest at 10-100 ng/ml in cancer cells. ET-743-mediated apoptosis, did not involve Fas/CD95. ET-743 induced c-Jun NH(2)-terminal kinase (JNK) and caspase-3 activation, and JNK and caspase inhibition prevented ET-743-induced apoptosis. ET-743 failed to promote apoptosis in caspase-3-deficient MCF-7 cells, further implicating caspase-3 in its proapoptotic action. Overexpression of bcl-2 by gene transfer abrogated ET-743-induced apoptosis, but cells underwent cell cycle arrest. ET-743 triggered cytochrome c release from mitochondria that was inhibited by Bcl-2 overexpression. Inhibition of transcription or protein synthesis did not prevent ET-743-induced apoptosis, but abrogated ET-743-induced cell cycle arrest. Microarray analyses revealed changes in the expression of a small number of cell cycle-related genes (p21, GADD45A, cyclin G2, MCM5, and histones) that suggested their putative involvement in ET-743-induced cell cycle arrest. These data indicate that ET-743 is a very potent anticancer drug showing dose-dependent cytostatic and proapoptotic effects through activation of two different signaling pathways, namely a transcription-dependent pathway leading to cell cycle arrest and a transcription-independent route leading to rapid apoptosis that involves mitochondria, JNK, and caspase-3.

Glutathione in defense and signaling: lessons from a small thiol

The mechanisms of thiol metabolism and chemistry have particular relevance to both cellular defenses against toxicant exposure and to redox signaling. Here, we will focus on glutathione (GSH), the major endogenous low- molecular-weight nonprotein thiol synthesized de novo in mammalian cells. The major pathways for GSH metabolism in defense of the cell are reduction of hydroperoxides by glutathione peroxidases (GSHPx) and some peroxiredoxins, which yield glutathione disulfide (GSSG), and conjugation reactions catalyzed by glutathione-S-transferases. GSSG can be reduced to GSH by glutathione reductase, but glutathione conjugates are excreted from cells. The exoenzyme gamma-glutamyltranspeptidase (GGT) removes the glutamate from extracellular GSH, producing cysteinyl-glycine from which a dipeptidase then generates cysteine, an amino acid often limiting for de novo GSH synthesis. Synthesis of GSH from the constituent amino acids occurs in two regulated, enzymatically catalyzed steps. The signaling pathways leading to activation of the transcription factors that regulate these genes are a current area of intense investigation. The elucidation of the signaling for GSH biosynthesis in human bronchial epithelial cells in response to 4-hydroxynonenal (4HNE), an end product of lipid peroxidation, will be used as an example. GSH also participates in redox signaling through the removal of H(2)O(2), which has the properties of a second messenger, and by reversing the formation of sulfenic acid, a moiety formed by reaction of critical cysteine residues in signaling proteins with H(2)O(2). Disruption of GSH metabolism will therefore have major a impact upon function of cells in terms of both defense and normal physiology.

JNK phosphorylation and activation of BAD couples the stress-activated signaling pathway to the cell death machinery

The c-Jun N-terminal kinase (JNK) signaling pathway plays a critical role in mediating apoptosis in the developing and mature organism. The JNK signaling pathway is thought to induce apoptosis via transcription-dependent and transcription-independent mechanisms that remain to be elucidated. In this study, we report a novel mechanism by which the JNK signaling pathway directly activates a component of the cell death machinery. We have found that JNK catalyzes the phosphorylation of the BH3-only protein BAD at the distinct site of serine 128 in vitro. Activation of the JNK signaling pathway induces the BAD serine 128 phosphorylation in vivo, including in primary granule neurons of the developing rat cerebellum. The JNK-induced BAD serine 128 phosphorylation promotes the apoptotic effect of BAD in primary neurons by antagonizing the ability of growth factors to inhibit BAD-mediated apoptosis. These findings indicate that BAD is a novel substrate of JNK that links the stress-activated signaling pathway to the cell death machinery.

Signaling pathways and late-onset gene induction associated with renal mesangial cell hypertrophy

In chronic diseases such as diabetes mellitus, continuous stress stimuli trigger a persistent, self-reinforcing reprogramming of cellular function and gene expression that culminates in the pathological state. Late-onset, stable changes in gene expression hold the key to understanding the molecular basis of chronic diseases. Renal failure is a common, but poorly understood complication of diabetes. Diabetic nephropathy begins with mesangial cell hypertrophy and hyperplasia, combined with excess matrix deposition. The vasoactive peptide endothelin promotes the mesangial cell hypertophy characteristic of diabetic nephropathy. In this study, we examined the signaling pathways and changes in gene expression required for endothelin-induced mesangial cell hypertrophy. Transcriptional profiling identified seven genes induced with slow kinetics by endothelin. Of these, p8, which encodes a small basic helix-loop-helix protein, was most strongly and stably induced. p8 is also induced in diabetic kidney. Mesangial cell hypertrophy and p8 induction both require activation of the ERK, JNK/SAPK and PI-3-K pathways. Small interfering RNA (siRNA)-mediated RNA interference indicates that p8 is required for endothelin-induced hypertrophy. Thus, p8 is a novel marker for diabetic renal hypertrophy.

Relationship of Mcl-1 isoforms, ratio p21WAF1/cyclin A, and Jun kinase phosphorylation to apoptosis in human breast carcinomas

Full length Mcl-1 is an anti-apoptotic protein consisting of two closely migrating 42/40kDa species. We now investigated the relationship of these isoforms to the expression of cell cycle stimulatory (cyclin A) and inhibitory (p21WAF1) proteins and to the induction of apoptosis in wt p53 MCF-7 and mutant p53 SKBR3 human breast carcinomas. The latter cells exhibited lower 42kDa Mcl-1, higher expression of cyclin A relative to that of p21WAF1, and apoptosis in response to okadaic acid, a phosphatase 1/2A inhibitor. The proteasome inhibitor MG-115 selectively increased expression of the 40kDa Mcl-1 isoform and induced p21WAF1, but also promoted preferential apoptosis in SKBR3 cells. Neither okadaic acid nor MG-115 caused comparable effects in MCF-7 cells. However, vanadate or acetyl furanonaphthoquinone induced the 40kDa Mcl-1 and greater Jun kinase (JNK) phosphorylation without apoptosis-associated PARP fragmentation in MCF-7 cells. Our data suggest that the higher susceptibility of SKBR3 cells to undergo apoptosis may be partly due to their greater proliferative potential (cyclin A), low expression of the anti-apoptotic 42kDa Mcl-1 isoform, and suboptimal JNK activation in response to stress.

c-Jun N-terminal kinase activation mediates downregulation of connexin43 in cardiomyocytes

Loss of gap junctions and impaired intercellular communication are characteristic features of pathological remodeling in heart failure as a result of stress or injury, yet the underlying regulatory mechanism has not been identified. Here, we report that in cultured myocytes, rapid loss of the gap junction protein connexin43 (Cx43) occurs in conjunction with the activation of c-Jun N-terminal kinase (JNK), a stress-activated protein kinase, on stress stimulation. To investigate the specific role of JNK activation in the regulation of connexin in cardiomyocytes, an activated mutant of mitogen-activated protein kinase kinase 7 (mutant D), a JNK-specific upstream activator, was expressed in myocytes by adenovirus-mediated gene transfer. JNK activation in infected cardiomyocytes resulted in significant reduction of Cx43 expression at both mRNA and protein levels and impaired cell-cell communication. To evaluate the role of JNK in the regulation of Cx43 expression and gap junction structure in vivo, a Cre-LoxP-mediated gene-switch system was used to establish a transgenic animal model with targeted activation of JNK in ventricular myocardium. The transgenic hearts exhibited significant downregulation of Cx43 expression and loss of gap junctions in myocardium that may contribute to the cardiac dysfunction and premature death phenotype. Our report represents the first evidence, both in vitro and in vivo, implicating JNK as an important mediator of stress-induced Cx43 downregulation and impaired intercellular communication in the failing heart.

Formation of caspase-3 complexes and fragmentation of caspase-12 during anisomycin-induced apoptosis in AKR-2B cells without aggregation of Apaf-1

Treatment of AKR-2B fibroblasts with anisomycin (10 microM) led to a rapid disintegration of the cells (t1/2 = 5 h) which was complete after 24 h. Cell death was associated with typical hallmarks of apoptosis like membrane blebbing, exposure of phophatidylserine on the cell surface, nuclear condensation and specific cleavage of rRNA. However, there was no dissipation of the mitochondrial potential and no intranucleosomal fragmentation. By affinity labeling with YVK(-bio)D.aomk in combination with immunostaining against activated caspase-3 analyzed by 2-D gel electrophoresis it was shown that caspase-3 is the dominant executioner caspase. Gel filtration experiments of cytosolic extract analyzed by Western blotting revealed the formation of high-molecular-weight complexes of caspase-3 (600 kDa and 250 kDa, respectively), but there was no complex formation of Apaf-1. Anisomycin treatment led to a strong activation of the stress kinases p38 kinases and the jun kinases, that was not sufficient for the activation of caspase-3 which required much higher concentrations. By using the selective inhibitors SB 203580 for p38 kinases and SP 600125 for c-jun kinases, respectively, it is shown that activation of these kinases is not necessary for cell death induced by anisomycin in AKR-2B cells. Furthermore, we disclose the activation of caspase-12 in AKR-2B cells following the addition of anisomycin. Caspase-12 zymogen present as a cytosolic complex (> 600 kDa) is activated by anisomycin leading to an uncomplexed cleaved enzyme. Since anisomycin treatment did neither lead to stress of the endoplasmic reticulum nor to a breakdown of intracellular Ca(2+)-stores, alternative pathways involved in the activation of caspases are discussed.

Macrophage apoptosis by anthrax lethal factor through p38 MAP kinase inhibition

The bacterium Bacillus anthracis causes the death of macrophages, which may allow it to avoid detection by the innate immune system. We found that B. anthracis lethal factor (LF) selectively induces apoptosis of activated macrophages by cleaving the amino-terminal extension of mitogen-activated protein kinase (MAPK) kinases (MKKs) that activate p38 MAPKs. Because macrophages that are deficient in transcription factor nuclear factor kappaB (NF-kappaB) are also sensitive to activation-induced death and p38 is required for expression of certain NF-kappaB target genes, p38 is probably essential for synergistic induction of those NF-kappaB target genes that prevent apoptosis of activated macrophages. This dismantling of the p38 MAPK module represents a strategy used by B. anthracis to paralyze host innate immunity.

Activation of the mitochondrial caspase cascade in the absence of protein synthesis does not require c-Jun N-terminal kinase

Prolonged activation of the c-Jun N-terminal kinase (JNK) has been suggested as a signal for apoptosis in response to a wide variety of stimuli. Using three cytocidal RNA or protein synthesis inhibitors (actinomycin D, anisomycin, and emetine), the potential role of JNK in activation of the mitochondrial apoptotic cascade was investigated in A549-S cells. Protein synthesis inhibition per se was not the cause of cell death as cycloheximide induced only growth arrest. All the cytocidal inhibitors induced cytochrome c release and caspases 9 activation within hours, but only anisomycin caused persistent JNK activation. Although, the JNK inhibitor, SP600125, inhibited JNK-dependent anisomycin-induced c-Jun phosphorylation, it was ineffective in preventing anisomycin-induced caspase activation and cell death. Thus, all three lethal macromolecule synthesis inhibitors can activate the mitochondrial apoptotic machinery independent of JNK activation, demonstrating that the mitochondrial apoptotic pathway can be activated independently of the JNK pathway in the absence of protein synthesis.

Cellular glutathione and thiols metabolism

Low molecular weight thiol-containing compounds have an essential role in many biochemical and pharmacological reactions due to the ease with each they are oxidized, and the rapidity with which they can be regenerated. Thioredoxin and glutathione (GSH) are two of the major small molecular weight thiol-containing compounds synthesized de novo in mammalian cells that participate in those functions. Understanding the mechanisms of thiol metabolism has special relevance to understanding the cell's defense against toxicant exposure and as the focal point in redox signaling. This commentary will, however, focus on GSH consumption and synthesis, and the role of thiols in signaling. The chemical reactions of GSH, including conjugation reactions mediated by glutathione S-transferases (GST) and oxidation reactions mediated by glutathione peroxidases will be described. The regulation of GSH synthesis will be illustrated from a compilation of studies designed to understand the various levels at which enzymatic GSH biosynthesis is controlled, and the signaling pathways that mediate them. The response of the cell to 4-hydroxynonenal (4HNE), a reactive aldehyde produced physiologically in response to inflammation and various air pollutants, will be explored in detail. Finally, the direct role of thiols as signaling molecules will be addressed, with particular attention given to "redox state." It is our aim that this commentary will lead the reader to appreciate that studies investigating the signaling for and regulation of thiol metabolism must never be generalized, and that perturbations in any of step of thiol metabolism may have etiological roles in genetically, virally, and environmentally borne pathologies.

Ras and Rap control AMPA receptor trafficking during synaptic plasticity

Recent studies show that AMPA receptor (-R) trafficking is important in synaptic plasticity. However, the signaling controlling this trafficking is poorly understood. Small GTPases have diverse neuronal functions and their perturbation is responsible for several mental disorders. Here, we examine the small GTPases Ras and Rap in the postsynaptic signaling underlying synaptic plasticity. We show that Ras relays the NMDA-R and CaMKII signaling that drives synaptic delivery of AMPA-Rs during long-term potentiation. In contrast, Rap mediates NMDA-R-dependent removal of synaptic AMPA-Rs that occurs during long-term depression. Ras and Rap exert their effects on AMPA-Rs that contain different subunit composition. Thus, Ras and Rap, whose activity can be controlled by postsynaptic enzymes, serve as independent regulators for potentiating and depressing central synapses.