Down-regulation of the c-Jun N-terminal kinase (JNK) phosphatase M3/6 and activation of JNK by hydrogen peroxide and pyrrolidine dithiocarbamate

Cuproptosis: A novel therapeutic target for overcoming cancer drug resistance

Cuproptosis is a newly identified form of cell death driven by copper. Recently, the role of copper and copper triggered cell death in the pathogenesis of cancers have attracted attentions. Cuproptosis has garnered enormous interest in cancer research communities because of its great potential for cancer therapy. Copper-based treatment exerts an inhibiting role in tumor growth and may open the door for the treatment of chemotherapy-insensitive tumors. In this review, we provide a critical analysis on copper homeostasis and the role of copper dysregulation in the development and progression of cancers. Then the core molecular mechanisms of cuproptosis and its role in cancer is discussed, followed by summarizing the current understanding of copper-based agents (copper chelators, copper ionophores, and copper complexes-based dynamic therapy) for cancer treatment. Additionally, we summarize the emerging data on copper complexes-based agents and copper ionophores to subdue tumor chemotherapy resistance in different types of cancers. We also review the small-molecule compounds and nanoparticles (NPs) that may kill cancer cells by inducing cuproptosis, which will shed new light on the development of anticancer drugs through inducing cuproptosis in the future. Finally, the important concepts and pressing questions of cuproptosis in future research that should be focused on were discussed. This review article suggests that targeting cuproptosis could be a novel antitumor therapy and treatment strategy to overcome cancer drug resistance.

DUSP8 induces TGF-β-stimulated IL-9 transcription and Th9-mediated allergic inflammation by promoting nuclear export of Pur-α

Dual-specificity phosphatase 8 (DUSP8) is a MAPK phosphatase that dephosphorylates and inactivates the kinase JNK. DUSP8 is highly expressed in T cells; however, the in vivo role of DUSP8 in T cells remains unclear. Using T cell-specific Dusp8 conditional KO (T-Dusp8 cKO) mice, mass spectrometry analysis, ChIP-Seq, and immune analysis, we found that DUSP8 interacted with Pur-α, stimulated interleukin-9 (IL-9) gene expression, and promoted Th9 differentiation. Mechanistically, DUSP8 dephosphorylated the transcriptional repressor Pur-α upon TGF-β signaling, leading to the nuclear export of Pur-α and subsequent IL-9 transcriptional activation. Furthermore, Il-9 mRNA levels were induced in Pur-α-deficient T cells. In addition, T-Dusp8-cKO mice displayed reduction of IL-9 and Th9-mediated immune responses in the allergic asthma model. Reduction of Il-9 mRNA levels in T cells and allergic responses of T-Dusp8-cKO mice was reversed by Pur-α knockout. Remarkably, DUSP8 protein levels and the DUSP8-Pur-α interaction were indeed increased in the cytoplasm of T cells from people with asthma and patients with atopic dermatitis. Collectively, DUSP8 induces TGF-β-stimulated IL-9 transcription and Th9-induced allergic responses by inhibiting the nuclear translocation of the transcriptional repressor Pur-α. DUSP8 may be a T-cell biomarker and therapeutic target for asthma and atopic dermatitis.

The Role of Glutathione in Selected Viral Diseases

During inflammatory processes, immunocompetent cells are exposed to substantial amounts of free radicals and toxic compounds. Glutathione is a cysteine-containing tripeptide that is an important and ubiquitous antioxidant molecule produced in human organs. The intracellular content of GSH regulates the detoxifying capacity of cells, as well as the inflammatory and immune response. GSH is particularly important in the liver, where it serves as the major non-protein thiol involved in cellular antioxidant defense. There are numerous causes of hepatitis. The inflammation of the liver can be caused by a variety of infectious viruses. The relationship between oxidative stress and the hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), and hepatitis E virus (HEV) infection is not fully known. The aim of this study was to examine the relationship between hepatotropic viruses and glutathione status, including reduced glutathione (GSH) and oxidized glutathione (GSSG), as well as antioxidant enzymes, e.g., glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione-S-transferase (GST) in liver diseases.

Cyclooxygenase-2 activates the free radical-mediated apoptosis of polymorphonuclear leukocytes in the maneb- and paraquat-intoxicated rats

Overproduction of free radicals and inflammation could lead to maneb (MB)- and paraquat (PQ)-induced toxicity in the polymorphonuclear leukocytes (PMNs). Cyclooxygenase-2 (COX-2), an inducible COX, is imperative in the pesticides-induced pathological alterations. However, its role in MB- and PQ-induced toxicity in the PMNs is not yet clearly deciphered. The current study explored the contribution of COX-2 in MB- and PQ-induced toxicity in the PMNs and the mechanism involved therein. Combined MB and PQ augmented the production of free radicals, lipid peroxides and activity of superoxide dismutase (SOD) in the rat PMNs. While combined MB and PQ elevated the expression of COX-2 protein, activation of nuclear factor-kappa B (NF-κB) and phosphorylation of c-Jun N-terminal kinase (JNK), release of mitochondrial cytochrome c and levels of procaspase-3/9 were attenuated in the PMNs. Celecoxib (CXB), a COX-2 inhibitor, ameliorated the combined MB and PQ-induced modulations in the PMNs. MB and PQ augmented the free radical generation, COX-2 protein expression, NF-κB activation and JNK phosphorylation and reduced the cell viability of cultured rat PMNs and human leukemic HL60. MB and PQ elevated mitochondrial cytochrome c release and poly (ADP-ribose) polymerase cleavage whilst procaspase-3/9 levels were attenuated in the cultured PMNs. MB and PQ also increased the levels of phosphorylated c-jun and caspase-3 activity in the HL60 cells. CXB; SP600125, a JNK-inhibitor and pyrrolidine dithiocarbamate (PDTC), a NF-κB inhibitor, rescued from MB and PQ-induced changes in the PMNs and HL60 cells. However, CXB offered the maximum protection among the three. The results show that COX-2 activates apoptosis in the PMNs following MB and PQ intoxication, which could be linked to NF-κB and JNK signaling.

Dysregulation of Dual-Specificity Phosphatases by Epstein-Barr Virus LMP1 and Its Impact on Lymphoblastoid Cell Line Survival

The strongest evidence of the oncogenicity of Epstein-Barr virus (EBV) in vitro is its ability to immortalize human primary B lymphocytes into lymphoblastoid cell lines (LCLs). Yet the underlying mechanisms explaining how the virus tempers the growth program of the host cells have not been fully elucidated. The mitogen-activated protein kinases (MAPKs) are implicated in many cellular processes and are constitutively activated in LCLs. We questioned the expression and regulation of the dual-specificity phosphatases (DUSPs), the main negative regulator of MAPKs, during EBV infection and immortalization. Thirteen DUSPs, including 10 typical and 3 atypical types of DUSPs, were tested. Most of them were downregulated after EBV infection. Here, a role of viral oncogene latent membrane protein 1 (LMP1) in limiting DUSP6 and DUSP8 expression was identified. Using MAPK inhibitors, we found that LMP1 activates extracellular signal-regulated kinase (ERK) or p38 to repress the expression of DUSP6 and DUSP8, with corresponding substrate specificity. Morphologically, overexpression of DUSP6 and DUSP8 attenuates the ability of EBV-immortalized LCL cells to clump together. Mechanistically, apoptosis induced by restoring DUSP6 and DUSP8 in LCLs indicated a novel mechanism for LMP1 to provide a survival signal during EBV immortalization. Collectively, this report provides the first description of the interplay between EBV genes and DUSPs and contributes considerably to the interpretation of MAPK regulation in EBV immortalization.IMPORTANCE Infections by the ubiquitous Epstein-Barr virus (EBV) are associated with a wide spectrum of lymphomas and carcinomas. It has been well documented that activation levels of MAPKs are found in cancer cells to translate various external or intrinsic stimuli into cellular responses. Physiologically, the dual-specificity phosphates (DUSPs) exhibit great ability in regulating MAPK activities with respect to their capability of dephosphorylating MAPKs. In this study, we found that DUSPs were generally downregulated after EBV infection. EBV oncogenic latent membrane protein 1 (LMP1) suppressed DUSP6 and DUSP8 expression via MAPK pathway. In this way, LMP1-mediated MAPK activation was a continuous process. Furthermore, DUSP downregulation was found to contribute greatly to prevent apoptosis of EBV-infected cells. To sum up, this report sheds light on a novel molecular mechanism explaining how EBV maintains the unlimited proliferation status of the immortalized cells and provides a new link to understand EBV-induced B cell survival.

Phosphorylation Dynamics of JNK Signaling: Effects of Dual-Specificity Phosphatases (DUSPs) on the JNK Pathway

Protein phosphorylation affects conformational change, interaction, catalytic activity, and subcellular localization of proteins. Because the post-modification of proteins regulates diverse cellular signaling pathways, the precise control of phosphorylation states is essential for maintaining cellular homeostasis. Kinases function as phosphorylating enzymes, and phosphatases dephosphorylate their target substrates, typically in a much shorter time. The c-Jun N-terminal kinase (JNK) signaling pathway, a mitogen-activated protein kinase pathway, is regulated by a cascade of kinases and in turn regulates other physiological processes, such as cell differentiation, apoptosis, neuronal functions, and embryonic development. However, the activation of the JNK pathway is also implicated in human pathologies such as cancer, neurodegenerative diseases, and inflammatory diseases. Therefore, the proper balance between activation and inactivation of the JNK pathway needs to be tightly regulated. Dual specificity phosphatases (DUSPs) regulate the magnitude and duration of signal transduction of the JNK pathway by dephosphorylating their substrates. In this review, we will discuss the dynamics of phosphorylation/dephosphorylation, the mechanism of JNK pathway regulation by DUSPs, and the new possibilities of targeting DUSPs in JNK-related diseases elucidated in recent studies.

Regulation of Dual-Specificity Phosphatase (DUSP) Ubiquitination and Protein Stability

Mitogen-activated protein kinases (MAPKs) are key regulators of signal transduction and cell responses. Abnormalities in MAPKs are associated with multiple diseases. Dual-specificity phosphatases (DUSPs) dephosphorylate many key signaling molecules, including MAPKs, leading to the regulation of duration, magnitude, or spatiotemporal profiles of MAPK activities. Hence, DUSPs need to be properly controlled. Protein post-translational modifications, such as ubiquitination, phosphorylation, methylation, and acetylation, play important roles in the regulation of protein stability and activity. Ubiquitination is critical for controlling protein degradation, activation, and interaction. For DUSPs, ubiquitination induces degradation of eight DUSPs, namely, DUSP1, DUSP4, DUSP5, DUSP6, DUSP7, DUSP8, DUSP9, and DUSP16. In addition, protein stability of DUSP2 and DUSP10 is enhanced by phosphorylation. Methylation-induced ubiquitination of DUSP14 stimulates its phosphatase activity. In this review, we summarize the knowledge of the regulation of DUSP stability and ubiquitination through post-translational modifications.

Recent Advances in Antabuse (Disulfiram): The Importance of its Metal-binding Ability to its Anticancer Activity

BACKGROUND

Considerable evidence demonstrates the importance of dithiocarbamates especially disulfiram as anticancer drugs. However there are no systematic reviews outlining how their metal-binding ability is related to their anticancer activity. This review aims to summarize chemical features and metal-binding activity of disulfiram and its metabolite DEDTC, and discuss different mechanisms of action of disulfiram and their contributions to the drug's anticancer activity.

METHODS

We undertook a disulfiram-related search on bibliographic databases of peerreviewed research literature, including many historic papers and in vitro, in vivo, preclinical and clinical studies. The selected papers were carefully reviewed and summarized.

RESULTS

More than five hundreds of papers were obtained in the initial search and one hundred eighteen (118) papers were included in the review, most of which deal with chemical and biological aspects of Disulfiram and the relationship of its chemical and biological properties. Eighty one (81) papers outline biological aspects of dithiocarbamates, and fifty seven (57) papers report biological activity of Disulfiram as an inhibitor of proteasomes or inhibitor of aldehyde dehydrogenase enzymes, interaction with other anticancer drugs, or mechanism of action related to reactive oxygen species. Other papers reviewed focus on chemical aspects of dithiocarbamates.

CONCLUSION

This review confirms the importance of chemical features of compounds such as Disulfiram to their biological activities, and supports repurposing DSF as a potential anticancer agent.

Structural Basis for the Selective Inhibition of c-Jun N-Terminal Kinase 1 Determined by Rigid DARPin-DARPin Fusions

To untangle the complex signaling of the c-Jun N-terminal kinase (JNK) isoforms, we need tools that can selectively detect and inhibit individual isoforms. Because of the high similarity between JNK1, JNK2 and JNK3, it is very difficult to generate small-molecule inhibitors with this discriminatory power. Thus, we have recently selected protein binders from the designed ankyrin repeat protein (DARPin) library which were indeed isoform-specific inhibitors of JNK1 with low nanomolar potency. Here we provide the structural basis for their isotype discrimination and their inhibitory action. All our previous attempts to generate crystal structures of complexes had failed. We have now made use of a technology we recently developed which consists of rigid fusion of an additional special DARPin, which acts as a crystallization enhancer. This can be rigidly fused with different geometries, thereby generating a range of alternative crystal packings. The structures reveal the molecular basis for isoform specificity of the DARPins and their ability to prevent JNK activation and may thus form the basis of further investigation of the JNK family as well as novel approaches to drug design.

Impaired Dual-Specificity Protein Phosphatase DUSP4 Reduces Corticosteroid Sensitivity

We have reported that phosphorylation of the glucocorticoid receptor (GR) at Ser²²⁶ reduces GR nuclear translocation, resulting in corticosteroid insensitivity in patients with severe asthmas. A serine/threonine protein phosphatase 2A, which regulates c-Jun N-terminal kinase (JNK) 1 and GR-Ser²²⁶ signaling, is involved in this mechanism. Here, we further explored protein kinase dual-specificity phosphatases (DUSPs) with the ability to dephosphorylate JNK, and identified DUSP4 as a phosphatase involved in the regulation of corticosteroid sensitivity. The effects of knocking down DUSPs (DUSP1, 4, 8, 16, and 22) by small interfering RNA (siRNA) were evaluated in a monocytic cell line (U937). Corticosteroid sensitivity was determined by dexamethasone enhancement of FK506-binding protein 51 or inhibition of tumor necrosis factor α (TNFα)-induced interferon γ and interleukin 8 expression and GR translocation from cell cytoplasm to nucleus. The nuclear/cytoplasmic GR, phosphorylation levels of GR-Ser²²⁶ and JNK1, coimmunoprecipitated GR-JNK1-DUSP4, and DUSP4 expression were analyzed by western blotting and/or imaging flow cytometry. Phosphatase activity of immunoprecipitated (IP)-DUSP4 was measured by fluorescence-based assay. Knockdown of DUSP4 enhanced phosphorylation of GR-Ser²²⁶ and JNK1 and reduced GR nuclear translocation and corticosteroid sensitivity. Coimmunoprecipitation experiments showed that DUSP4 is associated with GR and JNK1. In peripheral blood mononuclear cells from severe asthmatics, DUSP4 expression was reduced versus healthy subjects and negatively correlated with phosphorylation levels of GR-Ser²²⁶ and JNK1. Formoterol enhanced DUSP4 activity and restored corticosteroid sensitivity reduced by DUSP4 siRNA. In conclusion, DUSP4 regulates corticosteroid sensitivity via dephosphorylation of JNK1 and GR-Ser²²⁶ DUSP4 activation by formoterol restores impaired corticosteroid sensitivity, indicating that DUSP4 is crucial in regulating corticosteroid sensitivity, and therefore might be a novel therapeutic target in severe asthma.

Myc suppresses tumor invasion and cell migration by inhibiting JNK signaling

Tumor metastasis, but not primary overgrowth, is the leading cause of mortality for cancer patients. During the past decade, Drosophila melanogaster has been well-accepted as an excellent model to address the intrinsic mechanism of different aspects of cancer progression, ranging from tumor initiation to metastasis. In a genetic screen performed in Drosophila, aiming to find novel modulators of tumor invasion, we identified the oncoprotein Myc as a negative regulator. While expression of Myc dramatically blocks tumor invasion and cell migration, loss of Myc promotes cell migration in vivo. The activity of Myc is further enhanced by the co-expression of its transcription partner Max. Mechanistically, we found Myc/Max directly upregulates the transcription of puc, which encodes an inhibitor of JNK signaling crucial for tumor invasion and cell migration. Furthermore, we demonstrated that human cMyc potently suppresses JNK-dependent cell invasion and migration in both Drosophila and lung adenocarcinoma cell lines. These findings provide novel molecular insights into Myc-mediated cancer progression and raise the noteworthy problem in therapeutic strategies as inhibiting Myc might conversely accelerate tumor metastasis.

DUSP8 Regulates Cardiac Ventricular Remodeling by Altering ERK1/2 Signaling

RATIONALE

Mitogen-activated protein kinase (MAPK) signaling regulates the growth response of the adult myocardium in response to increased cardiac workload or pathological insults. The dual-specificity phosphatases (DUSPs) are critical effectors, which dephosphorylate the MAPKs to control the basal tone, amplitude, and duration of MAPK signaling.

OBJECTIVE

To examine DUSP8 as a regulator of MAPK signaling in the heart and its impact on ventricular and cardiac myocyte growth dynamics.

METHODS AND RESULTS

Dusp8 gene-deleted mice and transgenic mice with inducible expression of DUSP8 in the heart were used here to investigate how this MAPK-phosphatase might regulate intracellular signaling and cardiac growth dynamics in vivo. Dusp8 gene-deleted mice were mildly hypercontractile at baseline with a cardiac phenotype of concentric ventricular remodeling, which protected them from progressing towards heart failure in 2 surgery-induced disease models. Cardiac-specific overexpression of DUSP8 produced spontaneous eccentric remodeling and ventricular dilation with heart failure. At the cellular level, adult cardiac myocytes from Dusp8 gene-deleted mice were thicker and shorter, whereas DUSP8 overexpression promoted cardiac myocyte lengthening with a loss of thickness. Mechanistically, activation of extracellular signal-regulated kinases 1/2 were selectively increased in Dusp8 gene-deleted hearts at baseline and following acute pathological stress stimulation, whereas p38 MAPK and c-Jun N-terminal kinases were mostly unaffected.

CONCLUSIONS

These results indicate that DUSP8 controls basal and acute stress-induced extracellular signal-regulated kinases 1/2 signaling in adult cardiac myocytes that then alters the length-width growth dynamics of individual cardiac myocytes, which further alters contractility, ventricular remodeling, and disease susceptibility.

Modulation of Hydrogen Peroxide-Induced Oxidative Stress in Human Neuronal Cells by Thymoquinone-Rich Fraction and Thymoquinone via Transcriptomic Regulation of Antioxidant and Apoptotic Signaling Genes

Nigella sativa Linn. (N. sativa) and its bioactive constituent Thymoquinone (TQ) have demonstrated numerous pharmacological attributes. In the present study, the neuroprotective properties of Thymoquinone-rich fraction (TQRF) and TQ against hydrogen peroxide- (H₂O₂-) induced neurotoxicity in differentiated human SH-SY5Y cells were investigated. TQRF was extracted using supercritical fluid extraction while TQ was acquired commercially, and their effects on H₂O₂ were evaluated using cell viability assay, reactive oxygen species (ROS) assay, morphological observation, and multiplex gene expression. Both TQRF and TQ protected the cells against H₂O₂ by preserving the mitochondrial metabolic enzymes, reducing intracellular ROS levels, preserving morphological architecture, and modulating the expression of genes related to antioxidants (SOD1, SOD2, and catalase) and signaling genes (p53, AKT1, ERK1/2, p38 MAPK, JNK, and NF-κβ). In conclusion, the enhanced efficacy of TQRF over TQ was likely due to the synergism of multiple constituents in TQRF. The efficacy of TQRF was better than that of TQ alone when equal concentrations of TQ in TQRF were compared. In addition, TQRF also showed comparable effects to TQ when the same concentrations were tested. These findings provide further support for the use of TQRF as an alternative to combat oxidative stress insults in neurodegenerative diseases.

Mechanistic basis for protection of differentiated SH-SY5Y cells by oryzanol-rich fraction against hydrogen peroxide-induced neurotoxicity

BACKGROUND

Apoptosis is often the end result of oxidative damage to neurons. Due to shared pathways between oxidative stress, apoptosis and antioxidant defence systems, an oxidative insult could end up causing cellular apoptosis or survival depending on the severity of the insult and cellular responses. Plant bioresources have received close attention in recent years for their potential role in regulating the pathways involved in apoptosis and oxidative stress in favour of cell survival. Rice bran is a bioactive-rich by-product of rice milling process. It possesses antioxidant properties, making it a promising source of antioxidants that could potentially prevent oxidative stress-induced neurodegenerative diseases.

METHODS

Thus, the present study investigated the neuroprotective properties of oryzanol-rich fraction (ORF) against hydrogen peroxide (H2O2)-induced neurotoxicity in differentiated human neuroblastoma SH-SY5Y cells. ORF was extracted from rice bran using a green technology platform, supercritical fluid extraction system. Furthermore, its effects on cell viability, morphological changes, cell cycle, and apoptosis were evaluated. The underlying transcriptomic changes involved in regulation of oxidative stress, apoptosis and antioxidant defence systems were equally studied.

RESULTS

ORF protected differentiated SH-SY5Y cells against H2O2-induced neurotoxicity through preserving the mitochondrial metabolic enzyme activities, thus reducing apoptosis. The mechanistic basis for the neuroprotective effects of ORF included upregulation of antioxidant genes (catalase, SOD 1 and SOD 2), downregulation of pro-apoptotic genes (JNK, TNF, ING3, BAK1, BAX, p21 and caspase-9), and upregulation of anti-apoptotic genes (ERK1/2, AKT1 and NF-Kβ).

CONCLUSION

These findings suggest ORF may be an effective antioxidant that could prevent oxidative stress-induced neurodegenerative disorders.

Dual-specificity phosphatases as molecular targets for inhibition in human disease

SIGNIFICANCE

The dual-specificity phosphatases (DUSPs) constitute a heterogeneous group of cysteine-based protein tyrosine phosphatases, whose members exert a pivotal role in cell physiology by dephosphorylation of phosphoserine, phosphothreonine, and phosphotyrosine residues from proteins, as well as other non-proteinaceous substrates.

RECENT ADVANCES

A picture is emerging in which a selected group of DUSP enzymes display overexpression or hyperactivity that is associated with human disease, especially human cancer, making feasible targeted therapy approaches based on their inhibition. A panoply of molecular and functional studies on DUSPs have been performed in the previous years, and drug-discovery efforts are ongoing to develop specific and efficient DUSP enzyme inhibitors. This review summarizes the current status on inhibitory compounds targeting DUSPs that belong to the MAP kinase phosphatases-, small-sized atypical-, and phosphatases of regenerating liver subfamilies, whose inhibition could be beneficial for the prevention or mitigation of human disease.

CRITICAL ISSUES

Achieving specificity, potency, and bioavailability are the major challenges in the discovery of DUSP inhibitors for the clinics. Clinical validation of compounds or alternative inhibitory strategies of DUSP inhibition has yet to come.

FUTURE DIRECTIONS

Further work is required to understand the dual role of many DUSPs in human cancer, their function-structure properties, and to identify their physiologic substrates. This will help in the implementation of therapies based on DUSPs inhibition.

Innate and adaptive inflammation as a therapeutic target in vascular disease: the emerging role of statins

Atherosclerosis, the main pathophysiological condition leading to cardiovascular disease (CVD), is now considered to be a chronic inflammatory condition. Statins are the most widely used and promising agents in treating CVD and are renowned for their pleiotropic lipid-lowering independent effects. Statins exert their anti-inflammatory effects on the vascular wall through a variety of molecular pathways of the innate and adaptive immune systems, their impact on the circulating levels of pro-inflammatory cytokines, and their effect on adhesion molecules. By inhibiting the mevalonate pathway and isoprenoid formation, statins account for the increase of nitric oxide bioavailability and the improvement of vascular and myocardial redox state by multiple different mechanisms (directly or indirectly through low-density lipoprotein [LDL] lowering). A large number of randomized control trials have shown that statins help in the primary and secondary prevention of cardiovascular events, not only via their lipid-lowering effect, but also due to their anti-inflammatory potential as well. In this paper, we examine the molecular pathways in which statins are implicated and exert their anti-inflammatory effects, and we focus specifically on their impact on innate and adaptive immunity systems. Finally, we review the most important clinical data for the role of statins in primary and secondary prevention of cardiovascular events.

YES1 activation elicited by heat stress is anti-apoptotic in mouse pachytene spermatocytes

Deregulated expression of protein tyrosine phosphorylation has been implicated in testicular response to different stimuli. Herein, YES1, a nonreceptor protein tyrosine kinase, was found to be significantly up-regulated in pachytene spermatocytes (PS) during early recovery from a transient testicular heat stress. Coculture of PS with Sertoli cells (SCs) could enhance the hyperthermia-induced YES1 activation, indicative of a positive regulation of the paracrine signaling. Moreover, SU6656, a selective YES1 inhibitor, was shown to effectively block YES1 activity, thereafter resulting in a dramatic increase of heat stress-induced apoptosis in primary cultured PS. Mechanistically, the antiapoptotic effect of YES1 activation in response to testicular heat insult may mediate via the regulation of extracellular signal-regulated kinase (ERK)/metastasis-associated 1 (MTA1) cascade. From a clinical standpoint, a notably higher level of YES1 expression was observed in the pathological testis from varicocele patients as compared to a negligible staining in the control group. Taken together, our present results provide the first evidence that the YES1/ERK/MTA1/p53 cascade may serve as a naturally occurring, indispensable self-defensive mechanism maintaining apoptotic balance during meiotic heat stress. Our study may have also partially answered the question of how activation of signal pathways at the cell membrane surface interacts with the key regulatory events occurring in the nucleus during testicular heat shock.

Magnolol protects against oxidative stress-mediated neural cell damage by modulating mitochondrial dysfunction and PI3K/Akt signaling

Magnolol, an orally available compound from Magnolia officinalis used widely in traditional herbal medicine against a variety of neuronal diseases, possesses potent antioxidant properties and protects the brain against oxidative damage. The aim of the work is to examine the protective mechanisms of magnolol on human neuroblastoma SH-SY5Y cells against apoptosis induced by the neurotoxin acrolein, which can cause neurodegenerative disorders by inducing oxidative stress. By investigating the effect of magnolol on neural cell damage induced by the neurotoxin acrolein, we found that magnolol pretreatment significantly attenuated acrolein-induced oxidative stress through inhibiting reactive oxygen species accumulation caused by intracellular glutathione depletion and nicotinamide adenine dinucleotide phosphate oxidase activation. We next examined the signaling cascade(s) involved in magnolol-mediated antiapoptotic effects. The results showed that acrolein induced SH-SY5Y cell apoptosis by activating mitochondria/caspase and MEK/ERK signaling pathways. Our findings provide the first evidence that magnolol protects SH-SY5Y cells against acrolein-induced oxidative stress and prolongs SH-SY5Y cell survival through regulating JNK/mitochondria/caspase, PI3K/MEK/ERK, and PI3K/Akt/FoxO1 signaling pathways.

Inhibition of MKK7-JNK by the TOR signaling pathway regulator-like protein contributes to resistance of HCC cells to TRAIL-induced apoptosis

BACKGROUND & AIMS

The TOR signaling pathway regulator-like (TIPRL) protein, the mammalian ortholog of yeast TIP41, was identified in an expression profiling screen for factors that regulate human liver carcinogenesis. We investigated the role of human TIPRL protein in hepatocellular carcinoma (HCC).

METHODS

We measured the level of TIPRL in HCC and adjacent nontumor tissues from patients. We used small interfering RNAs and zebrafish to study the function of TIPRL. We used annexin V propidium iodide staining and immunoblot analyses to measure apoptosis and activation of apoptotic signaling pathways. We used confocal microscopy, coimmunoprecipitation, and glutathione-S transferase pull-down analyses to determine interactions among mitogen-activated protein kinase kinase 7 (MKK7 or MAP2K7), TIPRL, and the protein phosphatase type 2A (PP2Ac). We studied the effects of TIPRL in tumor xenografts in mice.

RESULTS

Levels of TIPRL were higher in HCC tissues and cell lines than nontumor tissues and primary hepatocytes. Knockdown of tiprl expression in zebrafish led to large amounts of apoptosis throughout the embryos. Incubation of HCC cells, but not primary human hepatocytes, with small interfering RNA against TIPRL (siTIPRL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) caused prolonged activation (phosphorylation) of MKK7 and c-Jun N-terminal kinase (JNK) and led to apoptosis, indicated by cleavage of procaspase-8,-3 and of poly-(adenosine diphosphate-ribose) polymerase. TIPRL bound to MKK7 and PP2Ac and promoted the interaction between MKK7 and PP2Ac. In mice, injection of HCC xenograft tumors with siTIPRL and TRAIL led to tumor apoptosis and regression.

CONCLUSIONS

TIPRL is highly up-regulated in human HCC samples and cell lines, compared with noncancerous liver tissues. TIPRL prevents prolonged activation of MKK7 and JNK and TRAIL-induced apoptosis by mediating the interaction between MKK7 and PP2Ac.

DUSPs, to MAP kinases and beyond

Phosphatases are important regulators of intracellular signaling events, and their functions have been implicated in many biological processes. Dual-specificity phosphatases (DUSPs), whose family currently contains 25 members, are phosphatases that can dephosphorylate both tyrosine and serine/threonine residues of their substrates. The archetypical DUSP, DUSP1/MKP1, was initially discovered to regulate the activities of MAP kinases by dephosphorylating the TXY motif in the kinase domain. However, although DUSPs were discovered more than a decade ago, only in the past few years have their various functions begun to be described. DUSPs can be categorized based on the presence or absence of a MAP kinase-interacting domain into typical DUSPs and atypical DUSPs, respectively. In this review, we discuss the current understanding of how the activities of typical DUSPs are regulated and how typical DUSPs can regulate the functions of their targets. We also summarize recent findings from several in vivo DUSP-deficient mouse models that studied the involvement of DUSPs during the development and functioning of T cells. Finally, we discuss briefly the potential roles of DUSPs in the regulation of non-MAP kinase targets, as well as in the modulation of tumorigenesis.

Oxidative stress, endogenous antioxidants, alcohol, and hepatitis C: pathogenic interactions and therapeutic considerations

Hepatitis C virus (HCV) is a blood-borne pathogen that was identified as an etiologic agent of non-A, non-B hepatitis in 1989. HCV is estimated to have infected at least 170 million people worldwide. The majority of patients infected with HCV do not clear the virus and become chronically infected, and chronic HCV infection increases the risk for hepatic steatosis, cirrhosis, and hepatocellular carcinoma. HCV induces oxidative/nitrosative stress from multiple sources, including inducible nitric oxide synthase, the mitochondrial electron transport chain, hepatocyte NAD(P)H oxidases, and inflammation, while decreasing glutathione. The cumulative oxidative burden is likely to promote both hepatic and extrahepatic conditions precipitated by HCV through a combination of local and more distal effects of reactive species, and clinical, animal, and in vitro studies strongly point to a role of oxidative/nitrosative stress in HCV-induced pathogenesis. Oxidative stress and hepatopathogenesis induced by HCV are exacerbated by even low doses of alcohol. Alcohol and reactive species may have other effects on hepatitis C patients such as modulation of the host immune system, viral replication, and positive selection of HCV sequence variants that contribute to antiviral resistance. This review summarizes the current understanding of redox interactions of HCV, outlining key experimental findings, directions for future research, and potential applications to therapy.

Involvement of intracellular oxidative stress-sensitive pathway in phloxine B-induced photocytotoxicity in human T lymphocytic leukemia cells

We investigated the molecular mechanisms underlying phloxine B (PhB)-induced photocytotoxicity in human T lymphocytic leukemia Jurkat cells. In addition to apoptosis-related biochemical events, photo-irradiated PhB generated intracellular reactive oxygen species (ROS), induced phosphorylation of c-Jun-N-terminal kinase (JNK) in an oxidative stress-dependent manner and up-regulated the gene expression of interferon (IFN)-γ, an inducer of diverse apoptosis-related molecules in activated T cells. PhB-induced apoptosis was significantly inhibited by N-acetyl-l-cysteine, but not by catalase, indicating that ROS generation occurred intracellularly, and by SP600125 and AG490, specific inhibitors of JNK and IFN-γ signaling, respectively, confirming their roles in the apoptotic pathway. IFN-γ up-regulation was also inhibited by SP600125, indicating that it was downstream of JNK activation. These results suggest that PhB-induced apoptosis in Jurkat cells partially involves the intracellular oxidative stress-sensitive and T cell-specific IFN-γ pathway. These data present a novel insight into the mechanisms of photocytotoxicity induced by artificial food colorants in human T lymphocytic leukemia cells.

Silencing of nicotinamide nucleotide transhydrogenase impairs cellular redox homeostasis and energy metabolism in PC12 cells

Mitochondrial NADPH generation is largely dependent on the inner-membrane nicotinamide nucleotide transhydrogenase (NNT), which catalyzes the reduction of NADP(+) to NADPH utilizing the proton gradient as the driving force and NADH as the electron donor. Small interfering RNA (siRNA) silencing of NNT in PC12 cells results in decreased cellular NADPH levels, altered redox status of the cell in terms of decreased GSH/GSSG ratios and increased H(2)O(2) levels, thus leading to an increased redox potential (a more oxidized redox state). NNT knockdown results in a decrease of oxidative phosphorylation while anaerobic glycolysis levels remain unchanged. Decreased oxidative phosphorylation was associated with a) inhibition of mitochondrial pyruvate dehydrogenase (PDH) and succinyl-CoA:3-oxoacid CoA transferase (SCOT) activity; b) reduction of NADH availability, c) decline of mitochondrial membrane potential, and d) decrease of ATP levels. Moreover, the alteration of redox status actually precedes the impairment of mitochondrial bioenergetics. A possible mechanism could be that the activation of the redox-sensitive c-Jun N-terminal kinase (JNK) and its translocation to the mitochondrion leads to the inhibition of PDH (upon phosphorylation) and induction of intrinsic apoptosis, resulting in decreased cell viability. This study supports the notion that oxidized cellular redox state and decline in cellular bioenergetics - as a consequence of NNT knockdown - cannot be viewed as independent events, but rather as an interdependent relationship coordinated by the mitochondrial energy-redox axis. Disruption of electron flux from fuel substrates to redox components due to NNT suppression induces not only mitochondrial dysfunction but also cellular disorders through redox-sensitive signaling.

Reactive oxygen species control senescence-associated matrix metalloproteinase-1 through c-Jun-N-terminal kinase

The lifetime exposure of organisms to oxidative stress influences many aging processes which involve the turnover of the extracellular matrix. In this study, we identify the redox-responsive molecular signals that drive senescence-associated (SA) matrix metalloproteinase-1 (MMP-1) expression. Precise biochemical monitoring revealed that senescent fibroblasts increase steady-state (H(2)O(2)) 3.5-fold (13.7-48.6 pM) relative to young cells. Restricting H(2)O(2) production through low O(2) exposure or by antioxidant treatments prevented SA increases in MMP-1 expression. The H(2)O(2)-dependent control of SA MMP-1 is attributed to sustained JNK activation and c-jun recruitment to the MMP-1 promoter. SA JNK activation corresponds to increases and decreases in the levels of its activating kinase (MKK-4) and inhibitory phosphatase (MKP-1), respectively. Enforced MKP-1 expression negates SA increases in JNK phosphorylation and MMP-1 production. Overall, these studies define redox-sensitive signaling networks regulating SA MMP-1 expression and link the free radical theory of aging to initiation of aberrant matrix turnover.

Studies on molecular mechanisms of growth inhibitory effects of thymoquinone against prostate cancer cells: role of reactive oxygen species

Thymoquinone (TQ), an active ingredient of black seed oil ( Nigella Sativa), has been shown to possess antineoplastic activity against a variety of experimental tumors. However, the precise mechanism of action of TQ is not known. We investigated the mechanism of action of TQ in androgen receptor (AR)-independent (C4-2B) and AR naïve (PC-3) prostate cancer cells, as models of aggressive prostate cancers. Exposure (24–48 h) to TQ (25–150 μmol/L) inhibited the growth of both C4-2B and PC-3 cells, with IC50 values of approximately 50 and 80 μmol/L, respectively. Within one hour, TQ increased reactive oxygen species (ROS) levels (3-fold) and decreased glutathione (GSH) levels (60%) in both cell types. Pretreatment with N-acetylcysteine (NAC) inhibited both TQ-induced ROS generation and growth inhibition. TQ did not increase the activity of caspases and the caspase inhibitor, z-VAD-FMK did not decrease TQ-induced apoptosis. Furthermore, although TQ treatment resulted in the activation of Jun kinase (JNK), pretreatment with the JNK inhibitor, SP600125, did not protect cells from TQ. However, TQ significantly up-regulated the expressions of growth arrest and DNA damage inducible gene (GADD45 α) and apoptosis-inducing factor-1 and down-regulated the expressions of several Bc12-related proteins, such as BAG-1, Bcl2, Bcl2A1, Bcl2L1 and BID. In C4-2B cells, TQ dose dependently inhibited both total and nuclear AR levels (4–5 fold) and AR-directed transcriptional activity (10–12 fold). Interestingly, this suppressive effect on AR was not prevented by NAC, which clearly suggested that TQ-induced cytotoxicity is not due to changes in AR regulation. These data suggest that TQ-induced cell death is primarily due to increased ROS generation and decreased GSH levels, and is independent of AR activity.

Activation of c-Jun-N-terminal kinase and decline of mitochondrial pyruvate dehydrogenase activity during brain aging

Mitochondrial dysfunction is often associated with aging and neurodegeneration. c-Jun-N-terminal kinase (JNK) phosphorylation and its translocation to mitochondria increased as a function of age in rat brain. This was associated with a decrease of pyruvate dehydrogenase (PDH) activity upon phosphorylation of the E(1alpha) subunit of PDH. Phosphorylation of PDH is likely mediated by PDH kinase, the protein levels and activity of which increased with age. ATP levels were diminished, whereas lactic acid levels increased, thus indicating a shift toward anaerobic glycolysis. The energy transduction deficit due to impairment of PDH activity during aging may be associated with JNK signaling.

Taxol synergizes with antioxidants in inhibiting hormal refractory prostate cancer cell growth

Taxanes are chemotherapeutic agents commonly used to treat various carcinomas. Dietary antioxidants, such as vitamin E, green tea extracts, and isoflavones have been used against prostate cancer, and exhibit anticancer effects both in vitro and in vivo. We evaluated the combined effect of taxol (paclitaxel) with pyrrolidine dithiocarbamate, vitamin E, epigallocatechin gallate, and genistein in killing hormone-refractory prostate cancer cells. Those agents were tested on the hormone-refractory prostate cancer cell line PC-3, and the viability of the cells was determined using MTT {3 (4, 5-dimethylthiazo-2-yl)-2, 5-diphenyl tetrazolium} assay after drug treatment. PC-3 cells were sensitive to these drugs with 50% inhibitory concentrations of 0.1, 23, 220, 1122, and 260 microM, for taxol, pyrrolidine dithiocarbamate, epigallocatechin gallate, genistein, and vitamin E, respectively. Genistein, pyrrolidine dithiocarbamate, and epigallocatechin gallate showed synergistic cytotoxicity to PC-3 cells when combined with 0.01 microM taxol. Only high concentration of vitamin E showed a synergistic effect with this dose of taxol. Further study revealed that 3 combinations could induce sub-G1 phase of cell cycle, induce apoptosis, and increase caspase activity and decrease Bcl-2 expression simultaneously. In conclusion, in addition to vitamin E, incorporation of these antioxidants with taxan-based cytotoxic therapies offers encouraging strategies for combating hormone-refractory prostate cancers.

Zinc-binding compounds induce cancer cell death via distinct modes of action

Metal-binding compounds have been shown to have anticancer activity and are being evaluated clinically as anticancer agents. We have recently found that a zinc-binding compound, 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol), kills cancer cells by transporting zinc into the cells. We therefore compared the action of clioquinol with two other cytotoxic zinc-binding compounds, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) and pyrrolidine dithiocarbamate (PDTC). We demonstrate that metal-binding compounds can be subclassified based upon the reversibility of their cytotoxicity by metal supplementation and their modes of action. Understanding the mechanisms whereby metal-binding compounds affect cell behavior may aid in their optimization for clinical use.

SHP-1 inhibition by 4-hydroxynonenal activates Jun N-terminal kinase and glutamate cysteine ligase

4-Hydroxy-2-nonenal (HNE), a major lipid peroxidation product, is toxic at high concentrations, but at near-physiological concentrations it induces detoxifying enzymes. Previous data established that in human bronchial epithelial (HBE1) cells, both genes for glutamate cysteine ligase (GCL) are induced by HNE through the c-Jun N-terminal kinase (JNK) pathway. The protein-tyrosine phosphatase SH2 domain containing phosphatase-1 (SHP-1) is thought to play a role as a negative regulator of cell signaling, and has been implicated as such in the JNK pathway. In the present study, SHP-1 was demonstrated to contribute to HNE-induced-gclc expression via regulation of the JNK pathway in HBE1 cells. Treatment of HBE1 cells with HNE induced phosphorylation of mitogen-activated protein kinase kinase 4 (MKK4), JNK, and c-Jun. HNE was able to inhibit protein tyrosine phosphatase activity of SHP-1 through increased degradation of the protein. Furthermore, transfection with small interference RNA SHP-1 showed an enhancement of JNK and c-Jun phosphorylation, but not of MKK4, leading to increased gclc expression. These results demonstrate that SHP-1 plays a role as a negative regulator of the JNK pathway and that HNE activated the JNK pathway by inhibiting SHP-1. Thus, SHP-1 acts as a sensor for HNE and is responsible for an important adaptive response to oxidative stress.

Induction of apoptosis in PA-1 ovarian cancer cells by vitamin K2 is associated with an increase in the level of TR3/Nur77 and its accumulation in mitochondria and nuclei

PURPOSE

We examined the growth-inhibitory and apoptosis-inducing effects of vitamin K(2) (VK(2); menaquinone-4) on various lines of human ovarian cancer cells to study the mechanism of induction of apoptosis by VK(2).

METHODS

Cell proliferation was determined by XTT method, and apoptotic cells were detected by Hoechst staining. TR3, also known as Nur77 and NGFI-B, was detected by immunoblotting and immunofluorescence analysis. Role of TR3 on induction of apoptosis was examined by a siRNA experiment.

RESULTS AND CONCLUSIONS

We found that PA-1 cells were the most sensitive to VK(2) (IC(50) = 5.0 +/- 0.7 microM), while SK-OV-3 cells were resistant to VK(2). Immunoblotting and immunofluorescence analyses indicated that levels of TR3 were elevated in cell lysates 48 h after the start of treatment with 30 microM VK(2). In the VK(2)-treated cells, TR3 accumulated at significant levels in mitochondria, as well as in the nuclei of PA-1 cells. No similar changes were observed in SK-OV-3 cells under the same conditions. Treatment of PA-1 cells with small interfering RNA (siRNA) directed against TR3, and with cycloheximide or SP600125 (an inhibitor of c-jun N-terminal kinase; JNK), separately, inhibited the VK(2)-induced synthesis of TR3 and apoptosis. From these results, we can conclude that an increase in the synthesis of TR3 and the accumulation of TR3 in mitochondria and in nuclei might be involved in the induction of apoptosis by VK(2) and that the synthesis of TR3 might be regulated through a JNK signaling pathway.

Reactive oxygen species mediated apoptosis of esophageal cancer cells induced by marine triprenyl toluquinones and toluhydroquinones

Marine invertebrates, algae, and microorganisms are prolific producers of novel secondary metabolites. Some of these secondary metabolites have the potential to be developed as chemotherapeutic agents for the treatment of a wide variety of diseases, including cancer. We describe here the mechanism leading to apoptosis of esophageal cancer cell lines in the presence of triprenylated toluquinones and toluhydroquinones originally isolated from the Arminacean nudibranch Leminda millecra. Triprenylated toluquinone-induced and toluhydroquinone-induced cell death is mediated via apoptosis after a cell cycle block. Molecular events include production of reactive oxygen species (ROS), followed by induction and activation of c-Jun (AP1) via c-Jun-NH2-kinase-mediated and extracellular signal-regulated kinase-mediated pathways. Partial resistance to these compounds could be conferred by the ROS scavengers Trolox and butylated hydroxyanisol, a c-Jun-NH2-kinase inhibitor, and inhibition of c-Jun with a dominant negative mutant (TAM67). Interestingly, the levels of ROS produced varied between compounds, but was proportional to the ability of each compound to kill cells. Because cancer cells are often more susceptible to ROS, these compounds present a plausible lead for new antiesophageal cancer treatments and show the potential of the South African marine environment to provide new chemical entities with potential clinical significance.

c-Jun N-terminal kinase regulates mitochondrial bioenergetics by modulating pyruvate dehydrogenase activity in primary cortical neurons

This study examines the role of c-jun N-terminal kinase (JNK) in mitochondrial signaling and bioenergetics in primary cortical neurons and isolated rat brain mitochondria. Exposure of neurons to either anisomycin (an activator of JNK/p38 mitogen-activated protein kinases) or H2O2 resulted in activation (phosphorylation) of JNK (mostly p46(JNK1)) and its translocation to mitochondria. Experiments with mitochondria isolated from either rat brain or primary cortical neurons and incubated with proteinase K revealed that phosphorylated JNK was associated with the outer mitochondrial membrane; this association resulted in the phosphorylation of the E(1alpha) subunit of pyruvate dehydrogenase, a key enzyme that catalyzes the oxidative decarboxylation of pyruvate and that links two major metabolic pathways: glycolysis and the tricarboxylic acid cycle. JNK-mediated phosphorylation of pyruvate dehydrogenase was not observed in experiments carried out with mitoplasts, thus suggesting the requirement of intact, functional mitochondria for this effect. JNK-mediated phosphorylation of pyruvate dehydrogenase was associated with a decline in its activity and, consequently, a shift to anaerobic pyruvate metabolism: the latter was confirmed by increased accumulation of lactic acid and decreased overall energy production (ATP levels). Pyruvate dehydrogenase appears to be a specific phosphorylation target for JNK, for other kinases, such as protein kinase A and protein kinase C did not elicit pyruvate dehydrogenase phosphorylation and did not decrease the activity of the complex. These results suggest that JNK mediates a signaling pathway that regulates metabolic functions in mitochondria as part of a network that coordinates cytosolic and mitochondrial processes relevant for cell function.

A cytotoxin isolated from Agkistrodon acutus snake venom induces apoptosis via Fas pathway in A549 cells

ACTX-6 is a protein isolated from Agkistrodon acutus snake venom and demonstrated cytotoxic activity to various cancer cells in vitro. In this paper the exact mechanism in ACTX-6-induced cell death was investigated and it was found that ACTX-6 could induce cell apoptosis. The results of Western blot and RT-PCR showed that ACTX-6 could induce Fas and FasL protein expression. When Fas signaling pathway was blocked by neutralizing antibodies to Fas or FasL, ACTX-6-induced apoptosis was inhibited. DISC formation was also detected by immunoprecipitation. These results suggested that Fas pathway was involved in ACTX-6-induced apoptosis. The activities of caspase-3, 8 and 9 were assayed and the activation of caspase-9 demonstrated that mitochondrial pathway was also involved in ACTX-6-induced apoptosis. Bid cleavage and dissipation of mitochondrial membrane potential (delta psi(m)) verified the involvement of mitochondria. ACTX-6 is an L-amino acid oxidase and can oxidize L-amino acid to generate hydrogen peroxide. The production of ROS in ACTX-6-treated cells was detected and the ROS scavenger catalase could inhibit ACTX-6-induced apoptosis. Western blot analysis showed that JNK was phosphorylated in ACTX-6-treated cells and c-Jun was also activated. JNK inhibitor SP600125 could inhibit ACTX-6-induced apoptosis and catalase could inhibit JNK and c-Jun phosphorylation. It could be concluded that JNK pathway was necessary in ACTX-6-induced apoptosis and the oxidative stress generated by ACTX-6 was responsible for the activation of JNK.

Regulation of MAP kinases by MAP kinase phosphatases

MAP kinase phosphatases (MKPs) catalyze dephosphorylation of activated MAP kinase (MAPK) molecules and deactivate them. Therefore, MKPs play an important role in determining the magnitude and duration of MAPK activities. MKPs constitute a structurally distinct family of dual-specificity phosphatases. The MKP family members share the sequence homology and the preference for MAPK molecules, but they are different in substrate specificity among MAPK molecules, tissue distribution, subcellular localization and inducibility by extracellular stimuli. Our understanding of their protein structure, substrate recognition mechanisms, and regulatory mechanisms of the enzymatic activity has greatly increased over the past few years. Furthermore, although there are a number of MKPs, that have similar substrate specificities, non-redundant roles of MKPs have begun to be identified. Here we focus on recent findings regarding regulation and function of the MKP family members as physiological regulators of MAPK signaling.

Nucleotide receptor signaling in murine macrophages is linked to reactive oxygen species generation

Macrophage activation is critical in the innate immune response and can be regulated by the nucleotide receptor P2X7. In this regard, P2X7 signaling is not well understood but has been implicated in controlling reactive oxygen species (ROS) generation by various leukocytes. Although ROS can contribute to microbial killing, the role of ROS in nucleotide-mediated cell signaling is unclear. In this study, we report that the P2X7 agonists ATP and 3'-O-(4-benzoyl) benzoic ATP (BzATP) stimulate ROS production by RAW 264.7 murine macrophages. These effects are potentiated in lipopolysaccharide-primed cells, demonstrating an important interaction between extracellular nucleotides and microbial products in ROS generation. In terms of nucleotide receptor specificity, RAW 264.7 macrophages that are deficient in P2X7 are greatly reduced in their capacity to generate ROS in response to BzATP treatment (both with and without LPS priming), thus supporting a role for P2X7 in this process. Because MAP kinase activation is key for nucleotide regulation of macrophage function, we also tested the hypothesis that P2X7-mediated MAP kinase activation is dependent on ROS production. We observed that BzATP stimulates MAP kinase (ERK1/ERK2, p38, and JNK1/JNK2) phosphorylation and that the antioxidants N-acetylcysteine and ascorbic acid strongly attenuate BzATP-mediated JNK1/JNK2 and p38 phosphorylation but only slightly reduce BzATP-induced ERK1/ERK2 phosphorylation. These studies reveal that P2X7 can contribute to macrophage ROS production, that this effect is potentiated upon lipopolysaccharide exposure, and that ROS are important participants in the extracellular nucleotide-mediated activation of several MAP kinase systems.

Endogenous production of reactive oxygen species is required for stimulation of human articular chondrocyte matrix metalloproteinase production by fibronectin fragments

The objective of the present study was to determine if reactive oxygen species (ROS) are required as secondary messengers for fibronectin fragment-stimulated matrix metalloproteinase (MMP) production in human articular chondrocytes. Cultured cells were stimulated with 25 microg/ml of the alpha5beta1 integrin-binding 110-kDa fibronectin fragment (FN-f) in the presence and absence of various antioxidants including Mn(III) tetrakis(4-benzoic acid)porphyrin (MnTBAP). FN-f stimulation significantly increased intracellular levels of ROS in articular chondrocytes. Pretreatment of cells with 250 microM MnTBAP or 40 mM N-acetyl-L-cysteine, but not inhibitors of nitric oxide synthase, completely prevented FN-f-stimulated MMP-3, -10, and -13 production. MnTBAP also blocked FN-f-induced phosphorylation of the MAP kinases and NF-kappaB-associated proteins and blocked activation of an NF-kappaB promoter-reporter construct. Overexpression of catalase, superoxide dismutase, or glutathione peroxidase also inhibited FN-f-stimulated MMP-13 production. Preincubation of chondrocytes with rotenone, an inhibitor of the mitochondrial electron transport chain, or nordihydroguaiaretic acid (NDGA), a selective 5-lipoxygenase inhibitor, partially prevented FN-f-stimulated MMP-13 production and decreased MAP kinase and NF-kappaB phosphorylation. These results show that increased production of ROS but not nitric oxide as obligatory secondary messengers in the chondrocyte FN-f signaling pathway leads to the increased production of MMPs, including MMP-13.

Regulation of ceruloplasmin in human hepatic cells by redox active copper: identification of a novel AP-1 site in the ceruloplasmin gene

Cp (ceruloplasmin), a copper containing plasma protein, mainly synthesized in the liver, is known to be functional between the interface of iron and copper metabolism. We have reported previously that Cp is regulated by cellular iron status, but the process of the regulation of Cp by copper still remains a subject for investigation. In the present paper, we show that PDTC (pyrrolidine dithiocarbamate), a thiol compound widely known to increase intracellular redox copper, regulates Cp expression in hepatic cells by a copper-dependent transcriptional mechanism. To find out the mechanism of induction, chimeric constructs of the Cp 5'-flanking region driving luciferase were transfected into human hepatic cells. Deletion and mutational analyses showed the requirement of a novel APRE [AP-1 (activator protein-1) responsive element] present about 3.7 kb upstream of the translation initiation site. The role of AP-1 was confirmed by electrophoretic mobility-shift analysis. Western blot and overexpression studies detected the AP-1 as a heterodimer of c-jun and c-fos proteins. The activation of AP-1 was found to be copper-dependent as a specific extracellular chelator bathocuproine disulfonic acid blocked PDTC-mediated induction of AP-1-DNA binding and increased reporter gene activity. Whereas, in a copper-free medium, PDTC failed to activate either AP-1 or Cp synthesis, supplementation of copper could reverse AP-1 activation and Cp synthesis. Our finding is not only the first demonstration of regulation of Cp by redox copper but may also explain previous findings of increased Cp expression in cancers like hepatocarcinoma, where the intracellular copper level is higher in a redox compromised environment.

Mitochondrial c-Jun NH2-terminal kinase prevents the accumulation of reactive oxygen species and reduces necrotic damage in neural tumor cells that lack trophic support

In response to different stress signals, the c-Jun NH(2)-terminal kinase (JNK) can trigger cell death. However, JNK also facilitates the survival and cell cycle progression of tumor cells by mechanisms that are poorly defined. Here, we show that schwannoma RN22 cells can survive and proliferate under serum-free conditions although serum withdrawal rapidly induces mitochondrial fission and swelling. Although the morphologic changes observed in the mitochondria did not trigger cytochrome c release, they were accompanied by an increase in the mitochondrial membrane potential (DeltaPsi(M)) and of immunoreactivity for active JNK in these organelles. Pharmacologic inhibition of JNK provoked a further increase of the DeltaPsi(M), an increase in reactive oxygen species (ROS) production, and a sustained decrease in cell viability due to necrosis. This increase in necrosis was prevented by the presence of ROS scavengers. Immunoreactivity for active JNK was also observed in the mitochondria of neuroblastoma 1E-115 and neuroblastoma 2a neuroblastoma cell lines on serum withdrawal, whereas active JNK was barely detected in serum-deprived fibroblasts. Accordingly, the reduction in neural tumor cell viability induced by JNK inhibition was largely attenuated in serum-deprived fibroblasts. These data indicate that local activation of JNK in the mitochondria can protect against necrotic cell death associated with ROS production, facilitating the growth of neural tumor cells subjected to serum deprivation.

Lipopolysaccharide-binding protein modulates hepatic damage and the inflammatory response after hemorrhagic shock and resuscitation

Hemorrhagic shock and resuscitation cause endotoxemia and hepatocellular damage. Because lipopolysaccharide-binding protein (LBP) enhances cellular responses to endotoxin, our aim was to determine whether LBP contributes to hemorrhage/resuscitation-induced injury by comparing LBP knockout and wild-type mice. Under pentobarbital anaesthesia, wild-type and LBP-deficient mice were hemorrhaged to 30 mmHg for 3 h and then resuscitated with shed blood plus half the volume of lactated Ringer solution. Serum alanine aminotransferase (ALT) necrosis, neutrophil infiltration, and 4-hydroxynonenal by histology/cytochemistry and stress kinase activation by immunoblot analysis were then determined. ALT in wild-type mice was 2,461 +/- 383 and 1,418 +/- 194 IU/l (means +/- SE), respectively, at 2 and 6 h after resuscitation versus sham ALT of 102 +/- 6 IU/l. In LBP-deficient mice, ALT was blunted at both time points to 1,108 +/- 340 and 619 +/- 171 IU/l (P < 0.05). Liver necrosis after 6 h was also attenuated from 3.5 +/- 0.8% in wild-type mice to 1.3 +/- 0.5% in LBP-deficient mice (P < 0.05). After hemorrhage/resuscitation, neutrophil infiltration increased 71% more in wild-type than LBP knockout mice. Similarly, hepatic 4-hydroxynonenal staining, indicative of lipid peroxidation, decreased from 33.8 +/- 4.5% in wild-type mice to 11.6 +/- 1.9% in knockout mice (P < 0.05). After hemorrhage/resuscitation, activation of MAPKs, JNK and ERK, occurred in wild-type mice, which was largely blocked in LBP-deficient mice. However, endotoxin in portal blood after resuscitation was not significantly different between wild-type and knockout mice. In conclusion, hemorrhagic shock and resuscitation to mice cause severe, LBP-mediated hepatocellular damage. An absence of LBP blunts hepatocellular injury with decreased neutrophil infiltration, oxidative stress, and c-Jun and ERK activation.

Increased stability of P21(WAF1/CIP1) mRNA is required for ROS/ERK-dependent pancreatic adenocarcinoma cell growth inhibition by pyrrolidine dithiocarbamate

We present evidence that pyrrolidine dithiocarbamate (PDTC) inhibits growth of p53-negative pancreatic adenocarcinoma cell lines via cell cycle arrest in the S-phase, while it has no effect on primary fibroblast proliferation. Growth inhibition of cancer cells is dependent on ROS and ERK1/2 induction as indicated by a significantly reduced PDTC-associated growth inhibition by the free radical scavenger N-acetyl-L-cysteine (NAC) or the MEK/ERK1/2 inhibitor (PD98059). Moreover, ERK1/2 induction is dependent on ROS production as demonstrated by a complete removal of PDTC-mediated ERK1/2 phosphorylation by NAC. p21(WAF1/CIP1) activation has a central role in growth inhibition by PDTC, as revealed by P21(WAF1/CIP1) silencing experiments with antisense oligonucleotide, and occurs via increased mRNA stability largely mediated by ROS/ERK induction. Conversely, PDTC does not affect P21(WAF1/CIP1) gene expression in primary fibroblasts, although it is able to activate p53 and the p53-regulated antioxidant SESN2. These results suggest that the resistance of fibroblasts to the cytotoxic action of PDTC may be related to the up-regulation of p53-dependent antioxidant genes. Finally, in vivo studies on PaCa44 cells subcutaneously xenografted in nude mice show that treatment with 100 or 200 mg/kg PDTC reduces of 30% or 60% the tumour volume, respectively, and does not cause any apparent form of toxicity.

Cytokines in Atherosclerosis: Pathogenic and Regulatory Pathways

Atherosclerosis is a chronic disease of the arterial wall where both innate and adaptive immunoinflammatory mechanisms are involved. Inflammation is central at all stages of atherosclerosis. It is implicated in the formation of early fatty streaks, when the endothelium is activated and expresses chemokines and adhesion molecules leading to monocyte/lymphocyte recruitment and infiltration into the subendothelium. It also acts at the onset of adverse clinical vascular events, when activated cells within the plaque secrete matrix proteases that degrade extracellular matrix proteins and weaken the fibrous cap, leading to rupture and thrombus formation. Cells involved in the atherosclerotic process secrete and are activated by soluble factors, known as cytokines. Important recent advances in the comprehension of the mechanisms of atherosclerosis provided evidence that the immunoinflammatory response in atherosclerosis is modulated by regulatory pathways, in which the two anti-inflammatory cytokines interleukin-10 and transforming growth factor-β play a critical role. The purpose of this review is to bring together the current information concerning the role of cytokines in the development, progression, and complications of atherosclerosis. Specific emphasis is placed on the contribution of pro- and anti-inflammatory cytokines to pathogenic (innate and adaptive) and regulatory immunity in the context of atherosclerosis. Based on our current knowledge of the role of cytokines in atherosclerosis, we propose some novel therapeutic strategies to combat this disease. In addition, we discuss the potential of circulating cytokine levels as biomarkers of coronary artery disease.

Multiple thermometers in mammalian cells: why do cells from homeothermic organisms need to measure temperature?

Mammalian cells activate survival signaling pathways and other protective mechanisms or induce apoptotic cell death in response to heat stress at temperatures beyond the range of those that they would ever be expected to encounter in vivo. Recent work has demonstrated that heat shock directly activates the apoptotic proteins Bax and Bak, suggesting that these polypeptides function as cellular thermometers in the mitochondrial apoptotic pathway. Here we review this and other heat-activated signaling pathways and propose a model that postulates that these "cellular thermometers" are not designed to sense physiologically irrelevant temperatures but rather to detect a general buildup of abnormal proteins in the cytosol and other cellular compartments.

The tyrphostin adaphostin interacts synergistically with proteasome inhibitors to induce apoptosis in human leukemia cells through a reactive oxygen species (ROS)-dependent mechanism

Interactions between the tyrphostin adaphostin and proteasome inhibitors (eg, MG-132 and bortezomib) were examined in multiple human leukemia cell lines and primary acute myeloid leukemia (AML) specimens. Cotreatment of Jurkat cells with marginally toxic concentrations of adaphostin and proteasome inhibitors synergistically potentiated mitochondrial damage (eg, cytochrome c release), caspase activation, and apoptosis. Similar interactions occurred in other human leukemia cell types (eg, U937, HL-60, Raji). These interactions were associated with a marked increase in oxidative damage (eg, ROS generation), down-regulation of the Raf/MEK/ERK pathway, and JNK activation. Adaphostin/MG-132 lethality as well as mitochondrial damage, down-regulation of Raf/MEK/ERK, and activation of JNK were attenuated by the free-radical scavenger NAC, suggesting that oxidative damage plays a functional role in antileukemic effects. Ectopic expression of Raf-1 or constitutively active MEK/ERK or genetic interruption of the JNK pathway significantly diminished adaphostin/MG-132-mediated lethality. Interestingly, enforced Raf or MEK/ERK activation partially diminished adaphostin/MG-132-mediated ROS generation, suggesting the existence of an amplification loop. Finally, the adaphostin/MG-132 regimen displayed similar toxicity toward 5 primary AML samples but not normal hematopoietic progenitors (eg, bone marrow CD34+ cells). Collectively, these findings suggest that potentiating oxidative damage by combining adaphostin with proteasome inhibitors warrants attention as an antileukemic strategy.

Hydrogen peroxide induces apoptosis of human spleen cells in vitro

AIM: To investigate the dose- and time-effect of hydrogen peroxide (H₂O₂) on human spleen cells, and to establish a stable apoptotic model of human spleen cells.

METHODS: The human spleen cells, obtained by the method of grinding, were divided into four groups and treated with saline solution or various concentrations of H₂O₂ respectively. The function of mitochondrions was assessed by the 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and the early apoptotic cells were detected by flow cytometry with a combination of Annexin V-FITC/PI.

RESULTS: H₂O₂ affected the mitochondrial function (negatively) and apoptosis (positively) of the human spleen cells in a dose- and time-dependent manner The apoptotic rates were significantly different between different groups (Total: 55.01±9.11%, 44.07±9.00%, 30.20±6.75% and 9.97±1.68% for 100, 50, 25 μmol/L and control group respectively, P<0.05). The apoptotic rate of cells reached the highest value (69.28±3.01)% at the concentration of 100 mmol/L 6 hours after treatment.

CONCLUSION: H₂O₂ can induce the apoptosis of human spleen cells in vitro, which can be used to establish apoptotic model.

Post-irradiation hypoxic incubation of X-irradiated MOLT-4 cells reduces apoptotic cell death by changing the intracellular redox state and modulating SAPK/JNK pathways

To elucidate radiobiological effects of hypoxia on X-ray-induced apoptosis, MOLT-4 cells were treated under four set of conditions: (1) both X irradiation and incubation under normoxia, (2) X irradiation under hypoxia and subsequent incubation under normoxia, (3) X irradiation under normoxia and subsequent incubation under hypoxia, and (4) both X irradiation and incubation under hypoxia, and the induction of apoptosis was examined by fluorescence microscopy. About 28-33% apoptosis was observed in cells treated under conditions 1 and 2, but this value was significantly reduced to around 18-20% in cells treated under conditions 3 and 4, suggesting that post-irradiation hypoxic incubation rather than hypoxic irradiation mainly caused the reduction of apoptosis. The activation and expression of apoptosis signal-related molecules SAPK/JNK, Fas and caspase-3 were also suppressed by hypoxic incubation. Effects of hypoxic incubation were canceled when cells were treated under conditions 3 and 4 with an oxygen-mimicking hypoxic cell radiosensitizer, whereas the addition of N-acetyl-L-cysteine again reduced the induction of apoptosis. From these results it was concluded that hypoxia reduced the induction of apoptosis by changing the intracellular redox state, followed by the regulation of apoptotic signals in X-irradiated MOLT-4 cells.