Inhibition of the expression of mitogen-activated protein phosphatase-1 potentiates apoptosis induced by tumor necrosis factor-alpha in rat mesangial cells

Omega-3 Polyunsaturated Fatty Acids and Lung Cancer: nutrition or Pharmacology?

Omega-3 polyunsaturated fatty acid (ω-3 PUFA) supplements for chemoprevention of different types of cancer including lung cancer has been investigated in recent years. ω-3 PUFAs are considered immunonutrients, commonly used in the nutritional therapy of cancer patients. ω-3 PUFAs play essential roles in cell signaling and in cell structure and fluidity of membranes. They participate in the resolution of inflammation and have anti-inflammatory effects. Lung cancer patients suffer complications, such as anorexia-cachexia syndrome, pain and depression. The European Society for Clinical Nutrition and Metabolism (ESPEN) 2017 guidelines for cancer patients only discuss the use of ω-3 PUFAs for cancer-cachexia treatment, leaving aside other cancer-related complications that could potentially be managed by ω-3 PUFAs. This review aims to elucidate whether the effects of ω-3 PUFAs in lung cancer is supplementary, pharmacological or both. In addition, clinical studies, evidence in cell lines and animal models suggest how ω-3 PUFAs induce anticancer effects. ω-3 PUFAs and their metabolites are suggested to modulate pivotal pathways underlying the progression or complications of lung cancer, indicating that this is a promising field to be explored. Further investigation is still required to analyze the benefits of ω-3 PUFAs as supplementation or pharmacological treatment in lung cancer.

Sodium orthovanadate inhibits growth and triggers apoptosis of human anaplastic thyroid carcinoma cells in vitro and in vivo

Vanadium and its compounds exhibit concentration- and time-dependent anticancer effects on various types of tumor; however, the effects of sodium orthovanadate (SOV) on anaplastic thyroid carcinoma (ATC) have not yet been reported. In the present study, the anticancer effects of SOV on ATC were evaluated. In vitro experiments, including cell viability assays, plate colony formation assays, cell cycle analysis and apoptosis analysis were used to study the role of SOV in ATC. Using in vivo experiments, the effects of SOV on the growth and apoptosis of an ATC-xenograft tumor were studied by comparing the SOV-treatment with the control group. The results revealed that treatment of the human ATC cell line 8505C with SOV inhibited cell viability, induced G2/M phase cell cycle arrest, stimulated apoptosis and reduced mitochondrial membrane potential in a concentration-dependent manner. These findings were confirmed in vivo in a nude mouse ATC xenograft model. In conclusion, the present study demonstrated that SOV inhibited human ATC by regulating proliferation, cell cycle progression and apoptosis, thus suggesting that SOV may be considered a novel option for the treatment of ATC.

Dual specificity phosphatase DUSP6 promotes endothelial inflammation through inducible expression of ICAM-1

Tumor necrosis factor (TNF)-α activates a diverse array of signaling pathways in vascular endothelial cells (ECs), leading to the inflammatory phenotype that contributes to the vascular dysfunction and neutrophil emigration in patients with sepsis. To date, it is not well understood what key regulator might coordinate signaling pathways to achieve inflammatory response in TNF-α-stimulated ECs. This study investigated the role of dual specificity phosphatase-6 (DUSP6) in the regulation of endothelial inflammation. Using knockout mice, we found that DUSP6 is important for TNF-α-induced endothelial intercellular adhesion molecule-1 (ICAM-1) expression in aorta and in vein. Moreover, genetic deletion of Dusp6 in pulmonary circulation significantly alleviated the susceptibility of mice to lung injury caused by neutrophil recruitment during experimental sepsis induced by TNF-α or lipopolysaccharide (LPS). The role of DUSP6 was further investigated in primary human umbilical vein endothelial cells (HUVECs). Employing RNAi approach in which endogenous DUSP6 was ablated, we showed a critical function of DUSP6 to facilitate TNF-α-induced ICAM-1 expression and endothelial leukocyte interaction. Interestingly, DUSP6-promoted endothelial inflammation is independent of extracellular signaling-regulated kinase (ERK) signaling. On the other hand, inducible DUSP6 leads to activation of canonical nuclear factor (NF)-κB-mediated transcription of ICAM-1 gene in TNF-α-stimulated human ECs. These results are the first to demonstrate a positive role of DUSP6 in endothelial inflammation-mediated pathological process and the underlying mechanism through which DUSP6 promotes NF-κB signaling in the inflamed ECs. Our findings suggest that manipulation of DUSP6 holds great potential for the treatment of acute inflammatory diseases.

ATF2 contributes to cisplatin resistance in non-small cell lung cancer and celastrol induces cisplatin resensitization through inhibition of JNK/ATF2 pathway

ATF2 is a transcription factor involved in stress and DNA damage. A correlation between ATF2 JNK-mediated activation and resistance to damaging agents has already been reported. The purpose of the present study was to investigate whether ATF2 may have a role in acquired resistance to cisplatin in non-small cell lung cancer (NSCLC). mRNA and protein analysis on matched cancer and corresponding normal tissues from surgically resected NSCLC have been performed. Furthermore, in NSCLC cell lines, ATF2 expression levels were evaluated and correlated to platinum (CDDP) resistance. Celastrol-mediated ATF2/cJUN activity was measured. High expression levels of both ATF2 transcript and proteins were observed in lung cancer specimens (p << 0.01, Log2 (FC) = +4.7). CDDP-resistant NSCLC cell lines expressed high levels of ATF2 protein. By contrast, Celastrol-mediated ATF2/cJUN functional inhibition restored the response to CDDP. Moreover, ATF2 protein activation correlates with worse outcome in advanced CDDP-treated patients. For the first time, it has been shown NSCLC ATF2 upregulation at both mRNA/protein levels in NSCLC. In addition, we reported that in NSCLC cell lines a correlation between ATF2 protein expression and CDDP resistance occurs. Altogether, our results indicate a potential increase in CDDP sensitivity, on Celastrol-mediated ATF2/cJUN inhibition. These data suggest a possible involvement of ATF2 in NSCLC CDDP-resistance.

TNF-α signaling in Fanconi anemia

Tumor necrosis factor-alpha (TNF-α) is a major pro-inflammatory cytokine involved in systemic inflammation and the acute phase reaction. Dysregulation of TNF production has been implicated in a variety of human diseases including Fanconi anemia (FA). FA is a genomic instability syndrome characterized by progressive bone marrow failure and cancer susceptibility. The patients with FA are often found overproducing TNF-α, which may directly affect hematopoietic stem cell (HSC) function by impairing HSC survival, homing and proliferation, or indirectly change the bone marrow microenvironment critical for HSC homeostasis and function, therefore contributing to disease progression in FA. In this brief review, we discuss the link between TNF-α signaling and FA pathway with emphasis on the implication of inflammation in the pathophysiology and abnormal hematopoiesis in FA.

Phase II study of bortezomib and pegylated liposomal doxorubicin in the treatment of metastatic breast cancer

BACKGROUND

Based on preclinical studies and a phase I trial of the combination of bortezomib and pegylated liposomal doxorubicin (PLD), which both showed activity in breast cancer, we conducted a phase II study of this regimen in patients with metastatic breast cancer.

PATIENTS AND METHODS

Patients received bortezomib 1.3 mg/m2 on days 1, 4, 8, and 11 of an every-21-day cycle, along with PLD 30 mg/m2 on day 4. The primary objective was to evaluate the response rate of this combination, while secondary objectives were to obtain further safety data about this combination, to evaluate the time to disease progression (TTP), and to evaluate response by the breast cancer subtype.

RESULTS

One of 12 evaluable patients had a partial response (8%), while 3 (25%) had stable disease. At 26 months follow-up, the median overall survival was 4.3 months (95% CI, 1.2-26.2) and the median TTP was 1.3 months (95% CI, 0.8-14.0 months). The combination was well tolerated, with the most common events including low-grade nausea and vomiting, neutropenia, and neuropathy, and no cardiac toxicity was seen. Of the 7 tumors subtyped, no association was seen between intrinsic subtype or receptor status and response.

CONCLUSION

The combination of PLD and bortezomib was well tolerated but has minimal activity in heavily pretreated unselected metastatic breast cancer.

Regulation of neutrophil-mediated killing of Staphylococcus aureus and chemotaxis by c-jun NH2 terminal kinase

The role of JNK in neutrophil chemotaxis and killing of microbial pathogens remains unclear. Using a recently described cell-permeable peptide inhibitor of the JNK pathway, based on the JBD of JIP-1, coupled to the protein transduction domain of HIV-TAT (TAT-JIP), in association with control peptides, we demonstrate that the JNK pathway plays a major role in regulating human neutrophil chemotaxis and killing of microbial pathogens. Serum-opsonized Staphylococcus aureus elicited JNK activation and c-jun phosphorylation. The activation of the JNK pathway and bactericidal activity were inhibited by the TAT-JIP peptide. The stimulation of oxygen radical generation by S. aureus was dependent on the JNK signaling pathway, as was the phagocytosis of serum-opsonized bacteria. Chemotaxis to activated serum complement but not random migration was inhibited by the TAT-JIP peptide. The findings demonstrate a major role for the JNK signaling pathway in neutrophil-mediated defense against microbial pathogens.

Metabotropic glutamate receptor 5 activation inhibits microglial associated inflammation and neurotoxicity

The Group I metabotropic glutamate receptor 5 (mGluR5) can modulate addiction, pain, and neuronal cell death. Expression of some mGluRs, such as Group II and III mGluRs, has been reported in microglia and may affect their activation. However, the expression and role of mGluR5 in microglia is unclear. Using immunocytochemistry and Western blot, we demonstrate that mGluR5 protein is expressed in primary microglial cultures. Activation of mGluR5 using the selective agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG) significantly reduces microglial activation in response to lipopolysaccharide, as indicated by a reduction in nitric oxide, reactive oxygen species, and TNFalpha production. Microglial induced neurotoxicity is also markedly reduced by CHPG treatment. The anti-inflammatory effects of CHPG are not observed in microglial cultures from mGluR5 knockout mice and are blocked by selective mGluR5 antagonists, suggesting that these actions are mediated by the mGluR5 receptor. Anti-inflammatory actions of mGluR5 activation are attenuated by phospholipase C and protein kinase C inhibitors, as well as by calcium chelators, suggesting that the mGluR5 activation in microglia involves the G(alphaq)-protein signal transduction pathway. These data indicate that microglial mGluR5 may represent a novel target for modulating neuroinflammation, an important component of both acute and chronic neurodegenerative disorders.

Docosahexaenoic acid induces apoptosis in lung cancer cells by increasing MKP-1 and down-regulating p-ERK1/2 and p-p38 expression

Different agents able to modulate apoptosis have been shown to modify the expression of the MAP-kinase-phosphatase-1 (MKP-1). The expression of this phosphatase has been considered a potential positive prognostic factor in lung cancer, and smoke was shown to reduce the levels of MKP-1 in ferret lung. Our aim was to assess whether the n-3 polyunsaturated fatty acid docosahexaenoic acid (DHA), known to inhibit the growth of several cancer cells mainly inducing apoptosis, may exert pro-apoptotic effect in lung cancer cells by modifying MKP-1 expression. We observed that DHA increased MKP-1 protein and mRNA expression and induced apoptosis in different lung cancer cell lines (mink Mv1Lu adenocarcinoma cells, human A549 adenocarcinoma and human BEN squamous carcinoma cells). We inhibited the pro-apoptotic effect of DHA by treating the cells with the phosphatase inhibitor Na(3)VO(4) or by silencing the MKP-1 gene with the specific siRNA. This finding demonstrated that the induction of apoptosis by DHA involved a phosphatase activity, specifically that of MKP-1. DHA reduced also the levels of the phosphorylated MAP-kinases, especially ERK1/2 and p38. Such an effect was not observed when the MKP-1 gene was silenced. Altogether, the data provide evidence that the DHA-induced overexpression of MKP-1 and the resulting decrease of MAP-kinase phosphorylation by DHA may underlie the pro-apoptotic effect of this fatty acid in lung cancer cells. Moreover, they support the hypothesis that DHA may exert chemopreventive action in lung cancer.

Differential expression and oxidation of MKP-1 modulates TNF-alpha gene expression

Monocytic cells are integral in the pathogenesis of inflammatory disorders. We have shown previously that asbestos-induced p38 mitogen-activated protein (MAP) kinase activation and TNF-alpha expression are mediated by H(2)O(2) in blood monocytes. Due to the high expression and activity of catalase and glutathione peroxidase, normal alveolar macrophages do not respond in a manner similar to that of blood monocytes. Since kinase activity is tightly regulated by phosphatases, we hypothesized that the dual specificity phosphatase MAP kinase phosphatase (MKP)-1 regulates p38 activity and TNF-alpha production in alveolar macrophages due to insufficient H(2)O(2) generation in response to asbestos. We found that MKP-1 was highly expressed in alveolar macrophages, while blood monocytes had minimal expression. Inhibition of expression and activity of MKP-1 or overexpression of a catalytic mutant MKP-1 recovered p38 activity in alveolar macrophages. We questioned whether MKP-1 oxidation played a role dictating the contrasting responses of these cells to asbestos exposure, and found that overexpressed wild-type MKP-1 in monocytes was oxidized, while the mutant MKP-1 remained in the reduced form. Monocytes overexpressing either catalase or wild-type MKP-1 had decreased p38 activation and TNF-alpha production, respectively. In addition, TNF-alpha gene expression was regained in alveolar macrophages overexpressing the catalytic mutant MKP-1. These data suggest that MKP-1, through increased expression and lack of oxidation, modulates the inflammatory response in alveolar macrophages exposed to asbestos.

Mitogen-Activated Protein Kinase Phosphatase-1 Is a Mediator of Breast Cancer Chemoresistance

The mitogen-activated protein kinase (MAPK) phosphatase (MKP)-1 is overexpressed in a large proportion of breast cancers, and in some systems interferes with chemotherapy-mediated proapoptotic signaling through c-Jun-NH2-terminal kinase (JNK). We therefore sought to examine whether MKP-1 is a mediator of breast cancer chemoresistance using A1N4-myc human mammary epithelial cells, and BT-474 and MDA-MB-231 breast carcinoma cells. Transient or stable overexpression of MKP-1 reduced caspase activation and DNA fragmentation while enhancing viability in the face of treatment with alkylating agents (mechlorethamine), anthracylines (doxorubicin), and microtubule inhibitors (paclitaxel). This overexpression was associated with suppression of JNK activation, and JNK blockade alone induced similar effects. In contrast, reduction of MKP-1 levels using a small interfering RNA, or its targeted inactivation, enhanced sensitivity to these drugs, and this was associated with increased JNK activity. Pharmacologic reduction of MKP-1 by pretreatment with a novel p38 MAPK inhibitor, SD-282, suppressed MKP-1 activation by mechlorethamine, enhanced active JNK levels, and increased alkylating agent–mediated apoptosis. Combination treatment with doxorubicin and mechlorethamine had similar effects, and the enhanced efficacy of this regimen was abolished by forced overexpression of MKP-1. These results suggest that the clinical efficacy of combinations of alkylating agents and anthracyclines are due to the ability of the latter to target MKP-1. Moreover, they support the hypothesis that MKP-1 is a significant mediator of breast cancer chemoresistance, and provide a rationale for development and translation of other agents targeting MKP-1 into the clinical arena to overcome resistance and induce chemosensitization. [Cancer Res 2007;67(9):4459–66]

Gene-specific recruitment of positive and negative elongation factors during stimulated transcription of the MKP-1 gene in neuroendocrine cells

MAP kinase phosphatase-1 (MKP-1) controls nuclear MAP kinase activity with important consequences on cell growth or apoptosis. MKP-1 transcription is initiated constitutively but elongation is blocked within exon 1. It is unclear how induction of MKP-1 is controlled. Here, we report that the transcriptional elongation factors P-TEFb, DSIF and NELF regulate MKP-1 transcription in the pituitary GH4C1 cell line. Prior to stimulation, DSIF, NELF and RNA polymerase II (pol II) associate with the promoter-proximal region of the MKP-1 gene upstream of the elongation block site. Thyrotropin-releasing hormone (TRH) leads to recruitment of P-TEFb along the whole gene and a marked increase of DSIF and pol II downstream of the elongation block site, whereas NELF remains confined to the promoter-proximal region. 5,6-Dichloro-1-β-d-ribofuranosylbenzimidazole (DRB) an inhibitor of P-TEFb eliminated TRH stimulation of MKP-1 transcription. DRB specifically inhibited TRH-induced recruitment of DSIF and P-TEFb to the MKP-1 gene. Furthermore, DRB treatment eliminated TRH-induced progression along the MKP-1 gene of pol II phosphorylated on Ser-2 of its CTD. These results indicate that P-TEFb is essential for gene-specific stimulated transcriptional elongation in mammalian cells via mechanisms which involve the activation of the DSIF–NELF complex and Ser-2 phosphorylation of pol II.

Prostanoid- and interleukin-1-induced primary genes in cementoblastic cells

BACKGROUND

Cementum is a key component of a functional periodontal organ. However, regenerating lost cementum is difficult and often incomplete. Identifying molecular mediators of cementoblast differentiation and function should lead to better targeted treatment for periodontitis. Prostaglandins increase mineralization of murine cementoblastic OCCM cells and alveolar bone formation, whereas the cytokine interleukin-1 (IL-1) inhibits alveolar bone formation. We hypothesized that differentially induced primary genes in OCCM cells may mediate anabolic and catabolic responses. Our objective was to identify primary genes differentially induced by the synthetic prostanoid fluprostenol and IL-1 in cementoblastic cells.

METHODS

Confluent OCCM cells were pretreated with the protein synthesis inhibitor cycloheximide followed by fluprostenol or IL-1 for 1.5 hours. cDNA generated from each group was used for cDNA subtraction hybridization to identify differentially induced genes. Preferential gene induction was verified by Northern blot analysis.

RESULTS

Thirteen fluprostenol- and seven IL-1-regulated genes were identified. Among the fluprostenol-induced genes was mitogen-activated protein (MAP) kinase phosphatase 1 (MKP1), a negative regulator of MAP kinase signaling. To verify the cDNA subtraction hybridization results, OCCM cells were treated with fluprostenol or prostaglandin F2 (PGF2), and MKP1 mRNA levels were determined. The 0.001 to 1 microM fluprostenol and 0.01 to 1 microM PGF2 significantly induced MKP1 mRNA levels, which peaked at 1 hour of treatment and returned to baseline at 2 hours.

CONCLUSIONS

Fluprostenol enhanced, whereas IL-1 inhibited, OCCM mineralization. Using cDNA subtraction hybridization, we identified primary genes that correlate with the observed anabolic and catabolic responses. These findings further our understanding of cementoblast function and suggest that differentially induced genes may mediate cementum formation and resorption.

Protein kinase Cδ-mediated proteasomal degradation of MAP kinase phosphatase-1 contributes to glutamate-induced neuronal cell death

Mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1) is a dual-specificity phosphatase that is involved in the regulation of cell survival, differentiation and apoptosis through inactivating MAPKs by dephosphorylation. Here, we provide evidence for a role of MKP-1 in the glutamate-induced cell death of HT22 hippocampal cells and primary mouse cortical neurons. We suggest that, during glutamate-induced oxidative stress, protein kinase C (PKC) δ becomes activated and induces sustained activation of extracellular signal-regulated kinase 1/2 (ERK1/2) through a mechanism that involves degradation of MKP-1. Glutamate-induced activation of ERK1/2 was blocked by inhibition of PKCδ, confirming that ERK1/2 is regulated by PKCδ. Prolonged exposure to glutamate caused reduction in the protein level of MKP-1, which correlated with the sustained activation of ERK1/2. Furthermore, knockdown of endogenous MKP-1 by small interfering (si)RNA resulted in pronounced enhancement of ERK1/2 phosphorylation accompanied by increased cytotoxicity under glutamate exposure. In glutamate-treated cells, MKP-1 was polyubiquitylated and proteasome inhibitors markedly blocked the degradation of MKP-1. Moreover, inhibition of glutamate-induced PKCδ activation suppressed the downregulation and ubiquitylation of MKP-1. Taken together, these results demonstrate that activation of PKCδ triggers degradation of MKP-1 through the ubiquitin-proteasome pathway, thereby contributing to persistent activation of ERK1/2 under glutamate-induced oxidative toxicity.

The endocannabinoid anandamide protects neurons during CNS inflammation by induction of MKP-1 in microglial cells

Endocannabinoids are released after brain injury and believed to attenuate neuronal damage by binding to CB(1) receptors and protecting against excitotoxicity. Such excitotoxic brain lesions initially result in primary destruction of brain parenchyma, which attracts macrophages and microglia. These inflammatory cells release toxic cytokines and free radicals, resulting in secondary neuronal damage. In this study, we show that the endocannabinoid system is highly activated during CNS inflammation and that the endocannabinoid anandamide (AEA) protects neurons from inflammatory damage by CB(1/2) receptor-mediated rapid induction of mitogen-activated protein kinase phosphatase-1 (MKP-1) in microglial cells associated with histone H3 phoshorylation of the mkp-1 gene sequence. As a result, AEA-induced rapid MKP-1 expression switches off MAPK signal transduction in microglial cells activated by stimulation of pattern recognition receptors. The release of AEA in injured CNS tissue might therefore represent a new mechanism of neuro-immune communication during CNS injury, which controls and limits immune response after primary CNS damage.

Late activation of stress kinases (SAPK/JNK) by genotoxins requires the DNA repair proteins DNA-PKcs and CSB

Although genotoxic agents are powerful inducers of stress kinases (SAPK/JNK), the contribution of DNA damage itself to this response is unknown. Therefore, SAPK/JNK activation of cells harboring specific defects in DNA damage-recognition mechanisms was studied. Dual phosphorylation of SAPK/JNK by the genotoxin methyl methanesulfonate (MMS) occurred in two waves. The early response (< or = 2 h after exposure) was similar in cells knockout for ATM, PARP, p53, and CSB or defective in DNA-PK(cs) compared with wild-type cells. The late response however (> or = 4 h), was drastically reduced in DNA-PK(cs) and Cockayne's syndrome B (CSB)-deficient cells. Similar results were obtained with human cells lacking DNA-PK(cs) and CSB. Activation of SAPK/JNK by MMS was not affected upon inhibition of base excision repair (BER), indicating base damage itself does not signal to SAPK/JNK. Because SAPK/JNK activation was attenuated in nongrowing cells, DNA replication-dependent processing of lesions, involving DNA-PK(cs) and CSB, appears to be required. DNA-PK(cs) coprecipitates with SEK1/MKK4 and SAPK/JNK, supporting a role of DNA-PK(cs) in SAPK/JNK activation. In this process, Rho GTPases are involved since inhibition of Rho impairs MMS-induced signaling to SAPK/JNK. The data show that sensing of DNA damage by DNA-PK(cs) and CSB causes a delayed SEK1/MKK4-mediated dual phosphorylation of SAPK/JNK.

Osmotic Regulation of MG-132-induced MAP-kinase Phosphatase MKP-1 Expression in H4IIE Rat Hepatoma Cells

BACKGROUND/AIMS

Proteasome inhibitors such as MG-132 are considered as potential therapeutical tools in different clinical settings. The dual specificity MAP-kinase phosphatase MKP-1 plays a role in balancing signals mediating cell death or survival. Here the effect of cell hydration on MG-132-induced MKP-1 expression was investigated in H4IIE rat hepatoma cells.

RESULTS

Hyperosmolarity (405mosmol/l) increased MKP-1 expression by MG-132, which was accompanied by an induction of c-Fos, c-Jun, cJun Ser73 phosphorylation, and AP-1 DNA binding. MKP-1 induction by MG-132 plus hyperosmolarity was sensitive to inhibition of p38(MAPK) and c-Jun-N-terminal kinases (JNKs) but not extracellular signal-regulated kinases Erk-1/Erk-2, and was accompanied by a decline of MAP-kinase activities. Although hyperosmolarity increased overall protein ubiquitination in presence of MG-132, ubiquitination of MKP-1 was found under normo-, but not hyperosmotic conditions. Hyperosmolarity also enabled MG-132 to induce poly-ADP-ribose polymerase (PARP) cleavage which was sensitive to inhibition of p38(MAPK) and JNKs but not Erk-1/Erk-2. PARP cleavage and caspase-3 activation in H4IIE cells treated with hyperosmolarity plus MG-132 was further increased by vanadate, consistent with a contribution of MKP-1 to counterbalance proapoptotic MAP-kinase signals.

CONCLUSION

The findings suggest that among other factors cell hydration critically determines the cellular response to proteasome inhibitors.

DNA damage in transcribed genes induces apoptosis via the JNK pathway and the JNK-phosphatase MKP-1

The nucleotide excision repair (NER) system consists of two sub-pathways, global genome repair (GGR) and transcription-coupled repair (TCR), which exhibit distinct functions in the cellular response to genotoxic stress. Defects in TCR result in prolonged UV light-induced stalling of RNA polymerase II and hypersensitivity to apoptosis induced by UV and certain chemotherapeutic drugs. Here, we show that low doses of UV trigger delayed activation of the stress-induced MAPkinase JNK and its proapoptotic targets c-Jun and ATF-3 in TCR-deficient primary human fibroblasts from Xeroderma Pigmentosum (XP) and Cockayne syndrome (CS) patients. This delayed activation of the JNK pathway is not observed in GGR-deficient TCR-proficient XP cells, is independent of functional p53, and is established through repression of the JNK-phosphatase MKP-1 rather than by activation of the JNK kinases MKK4 and 7. Enzymatic reversal of UV-induced cyclobutane pyrimidine dimers (CPDs) by CPD photolyase abrogated JNK activation, MKP-1 repression, and apoptosis in TCR-deficient XPA cells. Ectopic expression of MKP-1 inhibited DNA-damage-induced JNK activity and apoptosis. These results identify both MKP-1 and JNK as sensors and downstream effectors of persistent DNA damage in transcribed genes and suggest a link between the JNK pathway and UV-induced stalling of RNApol II.

Evaluation of glucocorticoid sensitivity in 697 pre-B acute lymphoblastic leukemia cells after overexpression or silencing of MAP kinase phosphatase-1

PURPOSE

To determine the effect of modulating MAP kinase phosphatase-1 (MKP-1) expression levels on cell death induced by glucocorticoid (GC) or hydroxyurea (HU) treatment in the human pre-B acute lymphoblastic leukemia cell line 697.

METHODS

Stable MKP-1 overexpressing transformants of the 697 pre-B acute lymphoblastic leukemia cell line were created and tested for sensitivity to the GC triamcinolone acetonide (TA) and HU, and compared to a control 697 cell line containing normal MKP-1 expression levels. Small interfering RNAs (siRNAs) were designed to inhibit MKP-1 expression and evaluated for their effect on GC-mediated cell death.

RESULTS

MKP-1 overexpression caused a phenotype of partial resistance to HU-induced apoptosis but not to GC-induced apoptosis. Electroporation of siRNAs effectively silenced MKP-1 expression, and increased sensitivity to TA by 9.6+/-1.9%.

CONCLUSIONS

Because MKP-1 protects certain tumor cells from chemotherapy-induced apoptosis, its inhibition is being considered as a possible strategy for combination cancer therapy. However, this study suggests that while MKP-1 inhibition may improve the efficacy of DNA damaging agents, it may have only limited utility in combination with glucocorticoids.

Essential role for mitogen-activated protein (MAP) kinase phosphatase-1 in stress-responsive MAP kinase and cell survival signaling

Mitogen-activated protein kinase (MAPK) phosphatases (MKPs) constitute a family of 11 dual-specificity phosphatases that inactivate the MAPKs by dephosphorylation. Although the contribution of MAPKs to cell growth and cell death has been examined extensively, it remains unclear whether MKPs play an essential role in the regulation of these processes. To clarify the role of MKP-1, we determined the effects on the MAPKs and cell growth and death in primary fibroblasts derived from mice lacking MKP-1. Here we have shown that MKP-1 is critical for the inactivation of p38 MAPK and JNK following stimulation with serum, anisomycin, and osmotic stress. In addition, MKP-1 was identified as a critical negative regulator of the cAMP-mediated p38 MAPK pathway. MKP-1-deficient mouse embryonic fibroblasts (MEFs) displayed enhanced p38 MAPK activity and cAMP-response element-dependent transcriptional activation in response to forskolin. Surprisingly, MKP-1-deficient fibroblasts exhibited reduced cell growth compared with wild type MEFs as a result of enhanced cell death. The enhanced level of cell death in MKP-1-deficient MEFs was rescued by SB203580, an inhibitor of p38 MAPK. MKP-1-deficient MEFs were also sensitive to anisomycin-induced apoptosis. Collectively, these data demonstrate that MKP-1 promotes cell survival by attenuating stress-responsive MAPK-mediated apoptosis.

Evidence that mitogen-activated protein kinase phosphatase-1 induction by proteasome inhibitors plays an antiapoptotic role

Inhibitors of the proteasome, a multicatalytic proteinase complex responsible for intracellular proteolysis, activate programmed cell death in part through the c-Jun-N-terminal kinase (JNK). Proteasome inhibitors also induce mitogen-activated protein kinase phosphatase-1 (MKP-1), however, which can inactivate JNK, and we therefore considered the hypothesis that MKP-1 induction may be antiapoptotic. Over-expression of MKP-1 in A1N4-myc human mammary epithelial and BT-474 breast carcinoma cells decreased proteasome inhibitor-mediated apoptosis. On the other hand, BT-474 cells stably expressing an MKP-1 small interfering RNA (siMKP-1) and MKP-1 knockout mouse embryo fibroblasts underwent enhanced apoptosis compared with their respective controls. MKP-1-mediated inhibition of apoptosis was associated with decreased phospho-JNK levels, whereas MKP-1 suppression or inactivation enhanced phospho-JNK. Anthracyclines repress MKP-1 transcription, suggesting that they could enhance proteasome inhibitor-mediated apoptosis. Such combinations induced increased cell death in association with enhanced phospho-JNK and decreased MKP-1 levels. Inhibition of JNK signaling decreased the proapoptotic activity of the anthracycline/proteasome inhibitor regimen. Xenograft studies showed the combination was more effective at inducing tumor growth delay, associated with suppression of MKP-1 and enhancement of apoptosis and phospho-JNK. Infection of anthracycline/proteasome inhibitor-treated A1N4-myc cells with Adenoviral-MKP-1 suppressed apoptosis and phospho-JNK. Finally, the anthracycline/proteasome inhibitor regimen activated apoptosis and phospho-JNK to a greater extent in BT-474/siMKP-1 cells than controls. These findings for the first time demonstrate that proteasome inhibitor-mediated induction of MKP-1 is antiapoptotic through inhibition of JNK. Furthermore, they suggest that a proteasome inhibitor/anthracycline regimen holds potential for enhanced antitumor activity in part through repression of MKP-1, supporting clinical evaluation of such combinations.

Expression of mitogen-activated protein kinase phosphatase 1, a negative regulator of the mitogen-activated protein kinases, in rheumatoid arthritis: up-regulation by interleukin-1beta and glucocorticoids

OBJECTIVE

Mitogen-activated protein kinases (MAPKs) are activated by proinflammatory stimuli. MAPK phosphatases (MKPs), in particular MKP-1, have been identified as endogenous negative regulators of MAPK activation. Since MAPKs are known to be important in rheumatoid arthritis (RA) synoviocyte activation, this study assessed the expression, regulation, and function of MKP-1 in RA.

METHODS

MKP-1 expression was measured by Western blotting (WB) and real-time polymerase chain reaction (PCR). RA fibroblast-like synoviocytes (FLS) were treated with interleukin-1beta (IL-1beta), tumor necrosis factor alpha, fetal calf serum, and dexamethasone. Expression of MAPKs in RA FLS was analyzed by WB using phosphospecific antibodies, while IL-6 expression was assessed by real-time PCR.

RESULTS

MKP-1 protein and messenger RNA were detected in cultured RA FLS. IL-1beta rapidly up-regulated MKP-1, coinciding with reciprocal down-regulation of ERK, JNK, and p38 MAPK phosphorylation. Dexamethasone rapidly and sustainably up-regulated MKP-1, and this also coincided with down-regulation of ERK, JNK, and p38 MAPK phosphorylation. In addition, dexamethasone augmented IL-1beta-induced up-regulation of MKP-1, and this was associated with inhibition of ERK, JNK, and p38 MAPK phosphorylation and IL-6 expression. Dexamethasone had no effect on the phosphorylation of upstream kinases such as MEKK-3/6. In the presence of glucocorticoid (GC) receptor antagonist RU 486, the dexamethasone-mediated up-regulation of MKP-1 was impaired. Moreover, inhibition of MKP-1 expression impaired dexamethasone-mediated inhibition of MAPK phosphorylation.

CONCLUSION

This study demonstrates the expression of MKP-1 in RA FLS. Cytokine and GC regulation of MKP-1 may be important in determining the magnitude of the inflammatory response in RA that is mediated via MAPKs. The effects of GCs in RA may be mediated, in part, via GC receptor-dependent up-regulation of MKP-1.

Prologation of c-Jun N-terminal kinase is associated with cell death induced by tumor necrosis factor alpha in human chondrocytes

The aim of this study was to elucidate the role of JNK signaling pathway involved in tumor necrosis factor-alpha (TNF-alpha)-induced death of chondrocytes. Primary chondrocyte cultures were obtained from human knee osteoarthritis cartilages. First passage chondrocytes were treated with TNF-alpha and various potentiators, and cell death was measured with MTT assay. C-Jun N terminal kinase (JNK) activation was investigated with the solid phase kinase assay. Expression of apoptosis-related molecule was assayed with Western blot. Chondrocytes were resistant to TNF-alpha-induced cell death. In contrast, pretreatment with actinomycin D, the phosphatase inhibitor vanadate or MAP kinase phosphatase-1 (MKP-1) inhibitor Ro318220 invariably led to chondrocyte death. While TNF-alpha alone stimulated a single, brief JNK activity, a second JNK peak was observed when the cells were pretreated with actinomycin D. When the cells were pretreated with vanadate or Ro318220, TNF-alpha-induced JNK activation was greatly prolonged, which was associated with the induction of cell death. The expression of Bcl-2 and Mcl-1 decreased significantly in conditions of cell death. In conclusions, our data suggest that chondrocyte death induced by TNF-alpha is associated with sustained JNK activation. This effect may be due to downregulation of TNF-alpha induced phosphatase that inactivates JNK and of Bcl-2 family proteins.

Stimulated initiation of mitogen-activated protein kinase phosphatase-1 (MKP-1) gene transcription involves the synergistic action of multiple cis-acting elements in the proximal promoter

Mitogen-activated protein kinases (MAPKs) are inactivated by a dual specificity phosphatase, MAPK phosphatase-1 (MKP-1). MKP-1 is transcribed as an immediate early response gene (IEG) following various stimuli. In the pituitary cell line GH4C1, MKP-1 gene transcription is strongly induced by thyrotropin-releasing hormone (TRH) as well as by epidermal growth factor (EGF) as a consequence of activated MAPK/extracellular-signal-regulated kinase (ERK) signalling. Intriguingly, reporter gene analysis with the MKP-1 promoter showed strong basal transcription, but only limited induction by TRH and EGF. Site-directed mutagenesis of the reporter construct combined with band-shift and in vivo studies revealed that part of the constitutive activity of the MKP-1 promoter resides in two GC boxes bound by Sp1 and Sp3 transcription factors in the minimal promoter. Basal transcription of transiently transfected luciferase reporter can be initiated by either of the two GC boxes or also by either of the two cAMP/Ca(2+) responsive elements or by the E-box present in the proximal promoter. On the other hand, when analysed by stable transfection, the five responsive elements are acting in synergy to transactivate the MKP-1 proximal promoter. We show in this study that the MKP-1 promoter can function as a constitutive promoter or as a rapid and transient sensor for the activation state of MAPKs/ERKs. This dual mode of transcription initiation may have different consequences for the control of a block to elongation situated in the first exon of the MKP-1 gene, as described previously [Ryser, Tortola, van Haasteren, Muda, Li and Schlegel (2001) J. Biol. Chem. 276, 33319-33327].

Nerve growth factor-dependent survival of CESS B cell line is mediated by increased expression and decreased degradation of MAPK phosphatase 1

The sIgG(+) lymphoblastoid B cell line CESS spontaneously produces a high amount of nerve growth factor (NGF) and expresses both high affinity (p140(Trk-A)) and low affinity (p75(NTR)) NGF receptors. Autocrine production of NGF maintains the survival of CESS cells through the continuous deactivation of p38 MAPK, an enzyme able to induce Bcl-2 phosphorylation and subsequent cytochrome c release and caspase activation. In this paper, we show that NGF induces transcriptional activation and synthesis of MAPK phosphatase 1 (MKP-1), a dual specificity phosphatase that dephosphorylates p38 MAPK, thus preventing Bcl-2 phosphorylation. Furthermore, NGF increases MKP-1 protein stability by preventing its degradation through the proteasome pathway. Following NGF stimulation, MKP-1 protein mainly localizes on mitochondria, suggesting an interaction with p38 MAPK in this compartment. Incubation of CESS cells with MKP-1-specific antisense oligonucleotides induces cell death, which was not prevented by exogenous NGF. By contrast, overexpression of native MKP-1, but not of its catalytically impaired form, inhibits apoptosis induced by NGF neutralization in CESS cells. Thus, the molecular mechanisms underlying the survival function of NGF in CESS B cell line predominantly consist in maintaining elevated levels of MKP-1 protein, which controls p38 MAPK activation.

Sphingosine-1-Phosphate Inhibition of Apoptosis Requires Mitogen-Activated Protein Kinase Phosphatase-1 in Mouse Fibroblast C3H10T½ Cells

The roles of extracellular regulated kinase (ERK) activation and mitogen-activated protein kinase phosphatase-1 (MKP-1) were examined in sphingosine-1-phosphate (S1P)-mediated inhibition of apoptosis in C3H10T 1/2 fibroblast cells. Apoptosis induced by the ceramide analog, C8-ceramine, was inhibited by S1P (ceramine/S1P). Stress activated protein kinase or c-Jun N-terminal kinase (SAPK/JNK) activation was significantly higher after ceramine and ceramine/S1P treatments. Ceramine/S1P treatment also significantly increased ERK activation and MKP-1 protein levels. ERK activation was required for the inhibition of apoptosis by S1P as shown using the mitogen-activated protein kinase kinase inhibitor, PD98059. Transfection with a dominant negative mutant construct of the MKP-1 gene prevented S1P inhibition of apoptosis and resulted in sustained SAPK/JNK activity. The MKP-1 mutant did not affect ERK activity, indicating that MKP-1 preferentially down-regulates SAPK/JNK in C3H10T 1/2 cells. Finally, the S1P activation of ERK and inhibition of apoptosis were reduced by pertussis toxin treatment, suggesting that G-protein-coupled receptors, such as the endothelial differentiation gene (EDG) receptor, play a role. Thus, both ERK activation and MKP-1, which down-regulates SAPK/JNK, are required for S1P-mediated inhibition of apoptosis.

Parathyroid hormone-related protein induces insulin expression through activation of MAP kinase-specific phosphatase-1 that dephosphorylates c-Jun NH2-terminal kinase in pancreatic beta-cells

Parathyroid hormone-related protein (PTHrP) increases the content and mRNA level of insulin in a mouse beta-cell line, MIN6, and primary-cultured mouse islets. We examined the mechanism of PTHrP-induced insulin expression. The PTHrP effect was markedly augmented by SB203580, a mitogen-activated protein (MAP) kinase inhibitor, and SB203580 itself increased insulin expression extensively, even without PTHrP. Because SB203580 inhibits both p38 and c-jun NH(2)-terminal kinases (JNKs), we investigated the JNK-specific inhibitor SP600125. SP600125 also increased insulin content and its mRNA level. PTHrP induced dephosphorylation of JNK1/2, and PTHrP-induced insulin expression was blocked by a dominant-negative type JNK-APF. We suspected that dual specificity MAP kinase phosphatases (MKPs) may be involved in the PTHrP-induced insulin expression by inactivating JNK1/2. MIN6 cells contained at least five MKPs, among which only MKP-1 was inducible by PTHrP. PTHrP-induced insulin expression was blocked by the MKP-1 expression inhibitor Ro-31-8220, indicating that the PTHrP effect is mediated by MKP-1. Indeed, adenoviral MKP-1 expression increased insulin expression by decreasing a phosphorylation form of JNKs and a resulting phosphorylated form of c-jun in MIN6 cells. The phosphorylated form of c-jun is known to repress cAMP-dependent insulin gene promoter activity. Thus, MKP-1 controls the insulin expression by downregulating a JNK/c-jun pathway.

TNF-alpha-induced cell death in ethanol-exposed cells depends on p38 MAPK signaling but is independent of Bid and caspase-8

Alcoholic liver disease is associated with an increase in the number of necrotic and apoptotic liver parenchymal cells. Part of this injury is mediated by TNF-alpha. Ethanol exposure sensitizes cells to the cytotoxic effects of TNF-alpha. This may be due, in part, to the increased propensity of the mitochondria in ethanol-exposed cells to induction of mitochondrial permeability transition (MPT) by various agents, including the proapoptotic protein Bax. This idea is supported by the observation that increased cell death induced by TNF-alpha in ethanol-exposed cells was dependent on development of the MPT. In the present study, we elucidate the pathways through which ethanol exposure enhances TNF-alpha induction of the MPT and the resulting cytotoxicity. Specifically, ethanol-exposed cells display caspase-8- and Bid-independent cell killing during TNF-alpha treatment. Moreover, the ethanol-enhanced pathway is dependent on p38 MAPK signaling, which brings about caspase-3 activation, mitochondrial depolarization, accumulation of cytochrome c in the cytosol, and the translocation of Bax to the mitochondria. Additionally, ethanol-exposed cells display a blunting of TNF-alpha-induced Akt activation and Bcl-2 antagonist of cell death phosphorylation that may account, in part, for the increased sensitivity of the mitochondria to Bax-mediated damage.

Role of 4-hydroxynonenal in stress-mediated apoptosis signaling

In this mini review we summarize recent studies from our laboratory, which show the involvement of 4-hydroxynonenal (4-HNE) in cell cycle signaling. We demonstrate 4-HNE induced apoptosis in various cell lines is accompanied with c-Jun-N-terminal kinase and caspase-3 activation. Cells exposed to mild, transient, heat or oxidative stress acquire capacity to exclude intracellular 4-HNE at a faster rate by inducing hGST5.8 which conjugate 4-HNE to GSH, and RLIP76 which mediates the ATP-dependent transport of the GSH-conjugate of 4-HNE. The cells preconditioned with mild transient stress acquire resistance to H(2)O(2) and 4-HNE induced apoptosis by excluding intracellular 4-HNE at an accelerated pace. Furthermore, a decrease in intracellular concentration of 4-HNE achieved by transfecting cells with mGSTA4-4 or hGSTA4-4 results in a faster growth rate. These studies strongly suggest a role of 4-HNE in stress mediated signaling.

Inhibition of taurolithocholate 3-sulfate-induced apoptosis by cyclic AMP in rat hepatocytes involves protein kinase A-dependent and -independent mechanisms

The mechanisms underlying the inhibition of bile acid-induced apoptosis by cyclic AMP (cAMP) were studied in 24-h-cultured rat hepatocytes. Taurolithocholate 3-sulfate (TLCS, 100 micromol/l) led to a sustained activation of mitogen activated protein (MAP) kinases (JNK, p38(MAPK), and ERKs), dephosphorylation of protein kinase B (PKB), activation of caspases 3 and 8, and hepatocyte apoptosis. cAMP prevented TLCS-induced apoptosis, shifted the persistent TLCS-induced MAP kinase response to a transient pattern, and prevented PKB dephosphorylation. TLCS-induced CD95 and TRAIL receptor-2 trafficking to the plasma membrane were significantly inhibited. Blockade of protein kinase A (PKA) abolished the inhibitory effect of cAMP on TLCS-induced CD95 membrane targeting, but not TRAIL receptor-2 membrane targeting, PKB and MAP kinase responses. H89, an inhibitor of PKA, had no effect on cAMP-induced inhibition of TLCS-triggered poly(ADP) ribose polymerase (PARP) cleavage and caspase activation, but abolished the cAMP-induced inhibition of TLCS-triggered TUNEL- and Annexin V staining. It is concluded that cAMP inhibits bile acid-induced apoptosis via PKA-dependent and -independent mechanisms.

Tumor necrosis factor signaling

A single mouse click on the topic tumor necrosis factor (TNF) in PubMed reveals about 50,000 articles providing one or the other information about this pleiotropic cytokine or its relatives. This demonstrates the enormous scientific and clinical interest in elucidating the biology of a molecule (or rather a large family of molecules), which began now almost 30 years ago with the description of a cytokine able to exert antitumoral effects in mouse models. Although our understanding of the multiple functions of TNF in vivo and of the respective underlying mechanisms at a cellular and molecular level has made enormous progress since then, new aspects are steadily uncovered and it appears that still much needs to be learned before we can conclude that we have a full comprehension of TNF biology. This review shortly covers some general aspects of this fascinating molecule and then concentrates on the molecular mechanisms of TNF signal transduction. In particular, the multiple facets of crosstalk between the various signalling pathways engaged by TNF will be addressed.

Negative regulation of phosphatidylinositol 3-kinase and Akt signalling pathway by PKC

Although substantial studies have begun to explore the regulation of phosphatidylinositol 3-kinase/Akt cascade by different signalling pathways, whether protein kinase C (PKC) activity plays a crucial role remains as yet unclear. In this study, we found that in A549 and HEK293 cells non-selective PKC inhibitors Ro 31-8220 and bisindolylmaleimide VIII, and PKCbeta inhibitor LY 379196, caused Akt/PKB phosphorylation at Ser 473 and increased the upstream activator, integrin-linked kinase (ILK) activity. The increased Akt phosphorylation was blocked by phosphatidylinositol 3-kinase inhibitor wortmannin and the newly identified PIP(3)-dependent kinases (PDK) inhibitor SB 203580. In contrast to the Akt stimulation caused by PKC inhibitors, PMA attenuated Akt/PKB phosphorylation. We also found that this stimulating effect on Akt phosphorylation by PKC inhibitors was not the result of phosphatase inhibition, since treatment with PP2A, PP2B and tyrosine phosphatase inhibitors (okadaic acid, FK506 and sodium orthovanadate, respectively) had no effect. We conclude that phosphatidylinositol 3-kinase/Akt signalling pathway is regulated by PKC in a negative manner.

Brain genomic response following hypoxia and re-oxygenation in the neonatal rat. Identification of genes that might contribute to hypoxia-induced ischemic tolerance

Hypoxic preconditioning (8% O2, 3 h) produces tolerance 24 h after hypoxic-ischemic brain injury in neonatal rats. To better understand the ischemic tolerance mechanisms induced by hypoxia, we used oligonucleotide microarrays to examine genomic responses in neonatal rat brain following 3 h of hypoxia (8% O2) and either 0, 6, 18, or 24 h of re-oxygenation. The results showed that hypoxia-inducible factor (HIF)-1- but not HIF-2-mediated gene expression may be involved in brain hypoxia-induced tolerance. Among the genes regulated by hypoxia, 12 genes were confirmed by real time reverse transcriptase-PCR as follows: VEGF, EPO, GLUT-1, adrenomedullin, propyl 4-hydroxylase alpha, MT-1, MKP-1, CELF, 12-lipoxygenase, t-PA, CAR-1, and an expressed sequence tag. Some genes, for example GLUT-1, MT-1, CELF, MKP-1, and t-PA did not show any hypoxic regulation in either astrocytes or neurons, suggesting that other cells are responsible for the up-regulation of these genes in the hypoxic brain. These genes were expressed in normal and hypoxic brain, heart, kidney, liver, and lung, with adrenomedullin, MT-1, and VEGF being prominently induced in brain by hypoxia. These results suggest that a number of endogenous molecular mechanisms may explain how hypoxic preconditioning protects against subsequent ischemia, and may provide novel therapeutic targets for treatment of cerebral ischemia.

Bisindolylmaleimide VIII enhances DR5-mediated apoptosis through the MKK4/JNK/p38 kinase and the mitochondrial pathways

Bisindolylmaleimide VIII (Bis VIII) has been previously shown to enhance Fas-mediated apoptosis through a protein kinase C-independent mechanism. In the present study, we examined the effect of Bis VIII on apoptosis induced by DR5 (TRAIL-R2), using an agonistic anti-human DR5 monoclonal antibody, TRA-8. Our results demonstrated that Bis VIII was able to enhance the apoptosis-inducing activity of TRA-8 both in vitro and in vivo. The combination of TRA-8 and Bis VIII led to a synergistic and sustained activation of the c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase, which was mediated by MAPK kinase 4 and was caspase-8-dependent. The mitochondrial pathway is involved in the synergistic induction of apoptosis by Bis VIII and TRA-8. Bis VIII alone induced the loss of mitochondrial membrane potential in a caspase-independent fashion without subsequent release of cytochrome c. However, in the presence of Bis VIII, TRA-8 induced more profound loss of mitochondrial membrane potential and release of cytochrome c. These results suggest that the enhanced and persistent activation of the JNK/p38 and the decreased mitochondrial membrane potential play a crucial role in synergistic induction of the death receptor-mediated apoptosis by Bis VIII. The unique ability of Bis VIII to enhance DR5-mediated apoptosis signal transduction discloses a potential utility of this compound in combination with anti-DR5 antibody in cancer therapy.

The carboxyl-terminal domains of MKP-1 and MKP-2 have inhibitory effects on their phosphatase activity

Both the mitogen-activated protein kinase (MAPK) phosphatases MKP-1 and MKP-2 exert important feedback control of MAPK-mediated signaling events. The function of MKP-1 and MKP-2 is regulated via complex mechanisms, ranging from increased transcription of the MKP-1 and MKP-2 genes to post-translational catalytic activation of MKP-1 and MKP-2 proteins upon binding to their substrate MAPKs. In addition, MKP-1 stability increases upon ERK-dependent phosphorylation of two serine residues in its C-terminus. The C-terminal regions of MKP-1 and MKP-2, but not those of other MKPs, are homologous. To investigate the role of this domain, we have deleted the C-terminal tails from MKP-1 and MKP-2 and examined the effect of these deletions on their enzymatic activity. C-terminally truncated MKP-1 and MKP-2 exhibited, both in vivo and in vitro, substantially greater phosphatase activity towards their substrate MAPKs than did the full-length counterparts. However, C-terminal truncations did not significantly change either their substrate affinity, or their substrate-mediated catalytic activation. Basal phosphatase activity of the truncated proteins was also significantly higher than that of the wild-type counterparts. Collectively, these results suggest that the C-terminal domain may potentially play a role in the regulation of MKP-1 and MKP-2.

p38beta MAP kinase protects rat mesangial cells from TNF-alpha-induced apoptosis

p38 MAP kinases (p38) and c-Jun N-terminal protein kinases (JNK) have been associated with TNF-alpha-induced apoptosis. However, recent studies indicate that an early but brief activation of JNK and/or p38 may actually protect some cells from TNF-alpha-induced apoptosis. Whether the activation of JNK and p38 provides a pro- or anti-apoptotic signal for TNF-alpha has been controversial. In this study, we investigated the role of p38 in the regulation of TNF-alpha cytotoxicity in rat mesangial cells. Treatment of the cells with TNF-alpha alone had little effect on their viability, but they became very sensitive to apoptosis when treated with TNF-alpha in the presence of the p38 inhibitor SB 203580. These results suggested that the p38 pathway is critical for mesangial cells to survive the toxic effect of TNF-alpha. Using adenovirus-mediated gene transfer technique, we further demonstrated that p38beta, but not p38alpha, is essential to protect the cells from TNF-alpha toxicity. It has been speculated that there is a synergetic interaction between the p38 and the nuclear factor-kappaB (NF-kappaB) pathways in protecting certain cells from apoptosis. However, expression of neither p38beta nor its dominant negative mutant in mesangial cells interfered with TNF-alpha-induced translocation of NF-kappaB, the initial step of NF-kappaB activation. While it is unclear whether p38beta regulates NF-kappaB transcription activity at other steps, it is apparent that p38beta does not affect TNF-alpha-induced NF-kappaB activation at the stage of nuclear translocation.

Involvement of DNA-dependent protein kinase in regulation of stress-induced JNK activation

DNA-dependent protein kinase (DNA-PK) is composed of a 460-kDa catalytic subunit and the regulatory subunits Ku70 and Ku80. The complex is activated on DNA damage and plays an essential role in double-strand-break repair and V(D)J recombination. In addition, DNA-PK is involved in S-phase checkpoint arrest following irradiation, although its role in damage-induced checkpoint arrest is not clear. In an effort to understand the role of DNA-PK in damage signaling, human and mouse cells containing the DNA-PK catalytic subunit (DNA-PKcs proficient) were compared with those lacking DNA-PKcs for c-Jun N-terminal kinase (JNK) activity that mediates physiologic responses to DNA damage. The DNA-PKcs-proficient cells showed much tighter regulation of JNK activity after DNA damage, while the level of JNK protein in both cell lines remained unchanged. The JNK proteins physically associated with DNA-PKcs and Ku70/Ku80 heterodimer, and the interaction was significantly stimulated after DNA damage. Various JNK isoforms not only contained a DNA-PK phosphorylation consensus site (serine followed by glutamine) but also were phosphorylated by DNA-PK in vitro. Together, our results suggest that DNA damage induces physical interaction between DNA-PK and JNK, which may in turn negatively affect JNK activity through JNK phosphorylation by DNA-PK.

p38-mediated regulation of an Fas-associated death domain protein-independent pathway leading to caspase-8 activation during TGFbeta-induced apoptosis in human Burkitt lymphoma B cells BL41

On binding to its receptor, transforming growth factor beta (TGFbeta) induces apoptosis in a variety of cells, including human B lymphocytes. We have previously reported that TGFbeta-mediated apoptosis is caspase-dependent and associated with activation of caspase-3. We show here that caspase-8 inhibitors strongly decrease TGFbeta-mediated apoptosis in BL41 Burkitt's lymphoma cells. These inhibitors act upstream of the mitochondria because they inhibited the loss of mitochondrial membrane potential observed in TGFbeta-treated cells. TGFbeta induced caspase-8 activation in these cells as shown by the cleavage of specific substrates, including Bid, and the appearance of cleaved fragments of caspase-8. Our data show that TGFbeta induces an apoptotic pathway involving sequential caspase-8 activation, loss of mitochondrial membrane potential, and caspase-9 and -3 activation. Caspase-8 activation was Fas-associated death domain protein (FADD)-independent because cells expressing a dominant negative mutant of FADD were still sensitive to TGFbeta-induced caspase-8 activation and apoptosis. This FADD-independent pathway of caspase-8 activation is regulated by p38. Indeed, TGFbeta-induced activation of p38 and two different inhibitors specific for this mitogen-activated protein kinase pathway (SB203580 and PD169316) prevented TGFbeta-mediated caspase-8 activation as well as the loss of mitochondrial membrane potential and apoptosis. Overall, our data show that p38 activation by TGFbeta induced an apoptotic pathway via FADD-independent activation of caspase-8.

MAP kinase phosphatase-1 gene transcription in rat neuroendocrine cells is modulated by a calcium-sensitive block to elongation in the first exon

Transcriptional elongation of many eukaryotic, prokaryotic, and viral genes is tightly controlled, which contributes to gene regulation. Here we describe this phenomenon for the MAP kinase phosphatase 1 (MKP-1) immediate early gene. In rat GH4C1 pituitary cells, MKP-1 mRNA is rapidly and transiently induced by the thyrotropin-releasing hormone (TRH) and the epidermal growth factor EGF via transcriptional activation of the gene. Ca(2+) signals are necessary for the induction of MKP-1 in response to TRH but not to EGF. Reporter gene analysis with the newly cloned rat promoter sequence shows only limited induction in response to various stimuli, including TRH or EGF. By nuclear run-on assays we demonstrate that in basal conditions, a strong block to elongation in the first exon regulates the MKP-1 gene and that stimulation with either TRH or EGF overcomes the block. Ca(2+) signals are important to release the MKP-1 elongation block in a manner similar to the c-fos oncogene. These results suggest that a common mechanism of intragenic regulation may be conserved between MKP-1 and c-fos in mammalian cells.

Transfection of mGSTA4 in HL-60 cells protects against 4-hydroxynonenal-induced apoptosis by inhibiting JNK-mediated signaling

The mammalian alpha-class glutathione S-transferase (GST) isozymes mGSTA4-4, rGSTA4-4, and hGSTA4-4 are known to utilize 4-hydroxynonenal (4HNE) as a preferred substrate. During the present studies, we have examined the effect of transfecting human myeloid HL-60 cells with mGSTA4, on 4-HNE-induced apoptosis and the associated signaling mechanisms. Results of these studies show that treatment of the wild-type or vector-only-transfected HL-60 cells with 20 microM 4-HNE caused apoptosis within 2 h. The cells transfected with mGSTA4 did not undergo apoptosis under these conditions even after 4 h. In the wild-type and vector-transfected cells, apoptosis was preceded by JNK activation and c-Jun phosphorylation within 30 min, and an increase in AP-1 binding within 2 h of treatment with 20 microM 4-HNE. In mGSTA4-transfected cells, JNK activation and c-Jun phosphorylation were observed after 1 h, and increased AP-1 binding was observed after 8 h under these conditions. In the control cells, 20 microM 4-HNE caused caspase 3 activation and poly(ADP-ribose) polymerase cleavage within 2 h, while in mGSTA4-transfected cells, a lesser degree of these effects was observed even after 8 h. Transfection with mGSTA4 also provided protection to the cells from 4-HNE and doxorubicin cytotoxicity (1.6- and 2.6-fold, respectively). These results show that 4-HNE mediates apoptosis through its effects on JNK and caspase 3, and that 4-HNE metabolizing GST isozyme(s) may be important in the regulation of this pathway of oxidative-stress-induced apoptosis.

HSP72 can protect cells from heat-induced apoptosis by accelerating the inactivation of stress kinase JNK

The major heat shock protein Hsp72 prevents heat-induced apoptosis. We have previously demonstrated that transiently expressed Hsp72 exerts its anti-apoptotic effect by suppressing the activity of stress-kinase JNK, an early component of the apoptotic pathway initiated by heat shock. On the other hand, constitutive expression of Hsp72 does not lead to suppression of heat-induced JNK activation, yet still efficiently prevents apoptosis. To address this apparent contradiction, we studied the effects of constitutively expressed Hsp72 on activation of JNK and apoptosis in Rat-1 fibroblasts. We found that the level of heat-induced apoptosis directly correlated with the duration rather than the magnitude of JNK activity following heat shock. Constitutively expressed Hsp72 strongly reduced the duration of JNK while it did not suppress initial JNK activation. These effects were due to Hsp72-mediated acceleration of JNK dephosphorylation. Addition of vanadate to inhibit JNK phosphatase activity completely prevented the anti-apoptotic action of Hsp72. Therefore, suppression of heat-induced apoptosis by Hsp72 could be fully accounted for by its effects on JNK activity.

Antioxidant therapy attenuates JNK activation and apoptosis in the remote noninfarcted myocardium after large myocardial infarction

We hypothesized that the concomitant occurrence of increased oxidative stress, JNK activation, and myocyte apoptosis in the remote myocardium (RM) following a large myocardial infarction (MI) are causally related. Three days following coronary ligation, rats were randomized to treatment with probucol and PDTC (MI-T) or vehicle (MI). Control rats (C) underwent sham operation. At 7 weeks, TBARS assay showed increased level of lipid-peroxidation within the RM in the MI group vs C, which was completely inhibited in the MI-T group. Similarly, Western blot analysis showed a twofold increase in p-JNK in the MI group, vs C, which was attenuated in MI-T, a result confirmed by a JNK-kinase activity. Furthermore, apoptosis was increased within the RM in MI vs C, while this was inhibited in MI-T. We conclude that long-term antioxidant therapy with probucol and PDTC attenuates oxidative stress, JNK activation, and myocyte apoptosis within the RM after large MI.

Map kinase phosphatases (MKP's) are early responsive genes during induction of cerulein hyperstimulation pancreatitis

Mitogen-activated protein kinase (MAPK) family members such as c-jun N-terminal kinase (JNK) may act as signal transducers early during pancreatitis development and evidence indicates that MAPK phosphatases (MKP) downregulate MAPK. We therefore investigated expression and regulation of pancreatic MKP in vivo. Pancreatic MKP mRNA levels were near or below the detection threshold in unstimulated animals. Cerulein hyperstimulation strongly induced MKP-1, MKP-3, and MKP-5 expression, peaking 30 to 60 min after treatment. Thus, MKP's clearly are early responsive genes during pancreatitis induction. Interestingly, inhibition of MKP-1 expression by Ro-31-8220 maximally induced activation of JNK but not of p38 and ERK in acutely isolated acini. These effects indicate that JNK may indeed be a preferred MKP-1 substrate in vivo.

Effect of calcium channel blockers, nifedipine and benidipine, on death of cultured mouse mesangi al cells

We examined the effects of the short-acting calcium channel blocker (CCB) nifedipine and the long-acting CCB benidipine on the death of mouse cultured mesangial cells induced by tumor necrosis factor alpha (TNF-alpha) and/or cycloheximide (CHX). Cell death was evaluated by a morphological study using semithin sections. The dead cells were divided into three types, i.e., apoptotic cells (type 1), necrotic cells (type 3) and other types of dead cells, the so-called 'secondary necrotic cells' or 'postapoptotic necrotic cells' (type 2). In the morphological study with semithin sections, cells in the presence of TNF-alpha or CHX and nifedipine or benidipine showed low percentages of all dead cell types with 24 h incubation. Both nifedipine and benidipine have protective effects against TNF-alpha or CHX. It is postulated that CCB might inhibit the apoptotic or necrotic processes by TNF-alpha or CHX with 24 h incubation. With 36 h incubation, CCB increased the percentages of all types of dead cells except for treatment with 1x10(-5) M benidipine and CHX. It appears that these cell-protective effects might be decreased after treatment with TNF-alpha or CHX and CCB for 36 h. In conclusion, the short-acting CCB nifedipine and the long-acting CCB benidipine have protective effects on mouse cultured mesangial cells against TNF-alpha or CHX. However, nifedipine and benidipine did not inhibit specific types of cell death using semithin sections in this study.

mkp-1 encoding mitogen-activated protein kinase phosphatase 1, a verotoxin 1 responsive gene, detected by differential display reverse transcription-PCR in Caco-2 cells

The major cytotoxic effect of the verotoxins (VTs) produced by strains of VT-producing Escherichia coli is the inhibition of host-cell protein synthesis, but VTs are also suspected to play a role in apoptotic cell signaling and cytokine release. Four differentially expressed genes, including mkp-1 (encoding mitogen-activated protein kinase phospatase 1), were detected by differential display reverse transcription-PCR (DD RT-PCR) stimulated by VT1 in Caco-2 cells. Northern blot analysis showed the induction of mkp-1 mRNA 6 h after VT1 stimulation. Neither mutant VT1 (mutVT1), harboring two mutations in the A subunit (E167Q-R170L), nor cycloheximide induced mkp-1 mRNA, but mkp-1 mRNA was detected with both wild-type VT1 (wtVT1) and anisomycin, a 28S rRNA inhibitor. Therefore, we concluded that the A subunit of VT1 was essential for mkp-1 induction. Increased amounts of phosphorylated c-Jun protein were also found with wtVT1 and anisomycin. Although the precise mechanism of induction of MKP-1 is unknown, we hypothesized that 28S rRNA not only was a sensor for ribotoxic stress, but also was involved in the signal cascade of MKP-1. This is the first report of detection by DD RT-PCR of cellular genes induced by bacterial toxins.

Glucagon-induced expression of the MAP kinase phosphatase MKP-1 in rat hepatocytes

BACKGROUND & AIMS

Glucagon exerts pleiotropic effects on liver function, but the underlying signal transduction is incompletely understood. We investigated the effect of glucagon on the mitogen-activated protein (MAP) kinase phosphatase MKP-1 expression.

METHODS

The effect of glucagon on MKP-1 expression was studied in cultured rat hepatocytes.

RESULTS

Glucagon (10-100 nmol/L) and 8-CPT-cAMP (10 or 50 micromol/L) stimulated in rat hepatocytes the expression of MKP-1 messenger RNA and protein, which became maximal within 30 minutes and declined to nearly basal levels after 60 minutes. MKP-1 induction by glucagon was sensitive to inhibition of adenylate cyclase and protein kinase A. The protein kinases G and C, Ca(2+), MAP kinases, reactive oxygen intermediates, and cellular dehydration were not involved in the glucagon-induced signaling to MKP-1. MKP-1 expression correlated with glucagon-induced antagonization of MAP kinase phosphorylation by epidermal growth factor in hepatocytes.

CONCLUSIONS

The MKP-1 response to glucagon produces an additional level of interaction with MAP kinase-dependent processes, which may contribute to the regulation of liver function by glucagon or other cAMP-elevating agents.