p38 kinase mediates nitric oxide-induced apoptosis of chondrocytes through the inhibition of protein kinase C zeta by blocking autophosphorylation

Using RSM for Optimum of Optimum Production of Peptides from Edible Bird’s Nest By-Product and Characterization of Its Antioxidant’s Properties

In this research, the neutrase hydrolysis conditions of edible bird’s nest (EBN) by-products were optimized by response surface methodology (RSM). Antioxidant peptides were then isolated from the EBN by-products by ultrafiltration and chromatography taking the DPPH radical scavenging ability as an indicator. The antioxidant activity of the purified peptides was estimated by radical scavenging ability and sodium nitroprusside (SNP)-induced damage model in PC12 cells. When the enzyme concentration was10 kU/g-hydrolysis temperature was 45 °C, and hydrolysis time was 10.30 h, the degree of hydrolysis (DH) of EBN by-product hydrolysate (EBNH) was the highest. The purified peptide exerted strong scavenging ability with EC₅₀ values of 0.51, 1.31, and 0.65 mg/mL for DDPH, ABTS, and O₂⁻ radicals, respectively. In addition, the purified peptides could significantly reduce the SNP-induced oxidative damage of PC12 cells, and twelve peptides that were rich in leucine (Leu), valine (Val), and lysine (Lys) were identified by LC-MS/MS. These results suggested that EBN by-products have potential as new materials for natural antioxidant peptides.

Dihydromyricetin protects HUVECs of oxidative damage induced by sodium nitroprusside through activating PI3K/Akt/FoxO3a signalling pathway

The damage of vascular endothelial cells induced by oxidative stress plays an important role in the pathogenesis of atherosclerosis. Dihydromyricetin (DMY) is considered as a natural antioxidant. However, the mechanism of DMY on endothelial cell injury induced by oxidative stress remains unclear. In this study, we found that DMY could reduce the oxidative damage of HUVECs induced by sodium nitroprusside (SNP), HUVECs pre-treated with DMY suppressed SNP-induced apoptosis by reduced ROS overproduction of intracellular, decreased MDA level and elevated the superoxide dismutase activity. Meanwhile, we found that DMY could promote the expression of phosphorylated FoxO3a and Akt, and affect the nuclear localization of FoxO3a, when treated with the PI3K inhibitor LY294002, the effect of DMY was blocked. These data suggest that DMY protects HUVECs from oxidative stress by activating PI3K/Akt/FoxO3a signalling pathway. Therefore, DMY may have great therapeutic potential as a new drug for atherosclerosis.

Caveolin-1 regulation of Sp1 controls production of the antifibrotic protein follistatin in kidney mesangial cells

BACKGROUND

We previously showed that caveolin-1 (cav-1), an integral membrane protein, is required for the synthesis of matrix proteins by glomerular mesangial cells (MC). In a previous study to understand how cav-1 is involved in regulating matrix production, we had identified significant upregulation of the antifibrotic protein follistatin in cav-1 knockout MC. Follistatin inhibits the profibrotic effects of several members of the transforming growth factor beta superfamily, in particular the activins. Here, we characterize the molecular mechanism through which cav-1 regulates the expression of follistatin.

METHODS

Kidneys from cav-1 wild type and knockout (KO) mice were analyzed and primary cultures of MC from cav-1 wild-type and KO mice were utilized. FST promoter deletion constructs were generated to determine the region of the promoter important for mediating FST upregulation in cav-1 KO MC. siRNA-mediated down-regulation and overexpression of Sp1 in conjunction with luciferase activity assays, immunoprecipitation, western blotting and ChiP was used to assess the role of Sp1 in transcriptionally regulating FST expression. Pharmacologic kinase inhibitors and specific siRNA were used to determine the post-translational mechanism through which cav-1 affects Sp1 activity.

RESULTS

Our results establish that follistatin upregulation occurs at the transcript level. We identified Sp1 as the critical transcription factor regulating activation of the FST promoter in cav-1 KO MC through binding to a region within 123 bp of the transcription start site. We further determined that the lack of cav-1 increases Sp1 nuclear levels and transcriptional activity. This occurred through increased phosphoinositide 3-kinase (PI3K) activity and downstream protein kinase C (PKC) zeta-mediated phosphorylation and activation of Sp1.

CONCLUSIONS

These findings shed light on the transcriptional mechanism by which cav-1 represses the expression of a major antifibrotic protein, and can inform the development of novel antifibrotic treatment strategies.

Extracellular cGMP Reverses Altered Membrane Expression of AMPA Receptors in Hippocampus of Hyperammonemic Rats: Underlying Mechanisms

Chronic hyperammonemia impairs spatial memory by altering membrane expression of GluA1 and GluA2 subunits of AMPA receptors in hippocampus. Intracerebral administration of extracellular cGMP to hyperammonemic rats restores spatial memory and membrane expression of AMPA receptors. The underlying molecular mechanisms remain unknown and cannot be analyzed in vivo. The aims of the present work were to (1) assess whether extracellular cGMP reverses the alterations in membrane expression of GluA1 and GluA2 in hippocampus of hyperammonemic rats ex vivo and (2) identify the underlying mechanisms. To reach these aims, we used freshly isolated hippocampal slices from control and hyperammonemic rats and treated them ex vivo with extracellular cGMP. Extracellular cGMP normalizes membrane expression of GluA2 restoring its phosphorylation in Ser880 because it restores PKCζ activation by Thr560 auto-phosphorylation, which is a consequence of normalization by extracellular cGMP of phosphorylation and activity of p38 which was increased in hyperammonemic rats. Normalization of p38 is a consequence of normalization of membrane expression of the GluN2B subunit of NMDA receptor, mediated by a reduction in its phosphorylation in Tyr1472 due to reduction of Src activation, which was over-activated in hyperammonemic rats. Extracellular cGMP also restores membrane expression of GluA1 increasing its phosphorylation at Ser831 because it restores CaMKII membrane association and phosphorylation in Thr286. All these effects of extracellular cGMP are due to a reduction of hippocampal IL-1β levels in hyperammonemic rats, which reduces IL-1 receptor-mediated Src over-activation. Reduction in IL-1β levels is due to the reduction of microglia activation in hippocampus of hyperammonemic rats.

Hyperammonemia alters membrane expression of GluA1 and GluA2 subunits of AMPA receptors in hippocampus by enhancing activation of the IL-1 receptor: underlying mechanisms

Background

Hyperammonemic rats reproduce the cognitive alterations of patients with hepatic encephalopathy, including altered spatial memory, attributed to altered membrane expression of AMPA receptor subunits in hippocampus. Neuroinflammation mediates these cognitive alterations. We hypothesized that hyperammonemia-induced increase in IL-1β in hippocampus would be responsible for the altered GluA1 and GluA2 membrane expression. The aims of this work were to (1) assess if increased IL-1β levels and activation of its receptor are responsible for the changes in GluA1 and/or GluA2 membrane expression in hyperammonemia and (2) identify the mechanisms by which activation of IL-1 receptor leads to altered membrane expression of GluA1 and GluA2.

Methods

We analyzed in hippocampal slices from control and hyperammonemic rat membrane expression of AMPA receptors using the BS3 cross-linker and phosphorylation of the GluA1 and GluA2 subunits using phosphor-specific antibodies. The IL-1 receptor was blocked with IL-Ra, and the signal transduction pathways involved in modulation of membrane expression of GluA1 and GluA2 were analyzed using inhibitors of key steps.

Results

Hyperammonemia reduces GluA1 and increases GluA2 membrane expression and reduces phosphorylation of GluA1 at Ser831 and of GluA2 at Ser880. Hyperammonemia increases IL-1β, enhancing activation of IL-1 receptor. This leads to activation of Src. The changes in membrane expression of GluA1 and GluA2 are reversed by blocking the IL-1 receptor with IL-1Ra or by inhibiting Src with PP2.

After Src activation, the pathways for GluA2 and GluA1 diverge. Src increases phosphorylation of GluN2B at Tyr14721 and membrane expression of GluN2B in hyperammonemic rats, leading to activation of MAP kinase p38, which binds to and reduces phosphorylation at Thr560 and activity of PKCζ, resulting in reduced phosphorylation at Ser880 and enhanced membrane expression of GluA2.

Increased Src activity in hyperammonemic rats also activates PKCδ which enhances phosphorylation of GluN2B at Ser1303, reducing membrane expression of CaMKII and phosphorylation at Ser831 and membrane expression of GluA1.

Conclusions

This work identifies two pathways by which neuroinflammation alters glutamatergic neurotransmission in hippocampus. The steps of the pathways identified could be targets to normalize neurotransmission in hyperammonemia and other pathologies associated with increased IL-1β by acting, for example, on p38 or PKCδ.

Graphical abstract

IL-1β alters membrane expression of GluA1 and GluA2 AMPA receptor subunits by two difrerent mechanisms in the hippocampus of hyperammonemic rats.

Resveratrol protects against sodium nitroprusside induced nucleus pulposus cell apoptosis by scavenging ROS

Oxidative stress induced disc cell apoptosis plays an important role in intervertebral disc (IVD) degeneration. The present study aims to investigate effects of resveratrol (RV), a natural polyphenol compound, on sodium nitroprusside (SNP) induced nucleus pulposus (NP) cell apoptosis and related mechanism. Rat NP cells were pretreated with RV, N-acetyl cysteine (NAC) and carboxy-PTIO (PTIO) before SNP treatment. Cell Counting Kit-8 assay was carried out for cell viability evaluation. Annexin V/propidium iodide (PI), Hoechst 33258 and Actin‑Tracker Green and Tubulin-Tracker Red staining were conducted to detect NP cell apoptosis and apoptotic structural changes. Mitochondrial membrane potential (ΔΨm) was analyzed with tetramethylrhodamine methyl ester staining. DCFH-DA and DAF-FM DA staining was used to determine intracellular reactive oxygen species (ROS) and nitric oxide (NO) levels. An ex vivo experiment was also carried out followed by TUNEL assay of sections of discs. SNP induced NP cell apoptosis, excessive production of intracellular ROS and NO, reduction of ΔΨm as well as disruption of cytoskeletal and morphological structure. Meanwhile, organ culture results showed that SNP induced NP cell apoptosis ex vivo. RV and NAC siginificantly inhibited SNP induced NP cell apoptosis, production of intracellular ROS, deline of ΔΨm as well as disruption of cytoskeletal and morphological structure, while RV did not suppress NO production. RV and NAC could also suppress SNP induced NP cell apoptosis ex vivo. However, PTIO did not prevent SNP induced NP cell apoptosis, though it scavenged NO significantly. In conclusion, RV protects against SNP induced NP cell apoptosis by scavenging ROS but not NO, suggesting a promising prospect of RV in IVD degeneration retardation.

Annexin A5 suppresses cyclooxygenase-2 expression by downregulating the protein kinase C-ζ-nuclear factor-κB signaling pathway in prostate cancer cells

Annexin A5 (ANXA5) is a member of the annexin protein family. Previous studies have shown that ANXA5 is involved in anti-inflammation and cell death. However, the detailed mechanism of the role of ANXA5 in cancer cells is not well understood. In this study, we investigated the inhibitory effect of ANXA5 on cyclooxygenase-2 (COX-2) in prostate cancer cells. Expression of COX-2 induced by TNF-α was inhibited by overexpression of ANXA5 and inhibition of COX-2 expression by auranofin, which could induce ANXA5 expression, was restored by ANXA5 knockdown. In addition, ANXA5 knockdown induces phosphorylation of NF-κB p65 in prostate cancer cells, indicating that ANXA5 causes COX-2 downregulation through inhibition of p65 activation. We also found that protein kinase C (PKC)-ζ protein levels were upregulated by the inhibition of ANXA5, although the mRNA levels were unaffected. We have shown that upregulated COX-2 expression by inhibition of ANXA5 is attenuated by PKC-ζ siRNA. In summary, this study demonstrates that downregulation of PKC-ζ-NF-κB signaling by ANXA5 may inhibit COX-2 expression in prostate cancer.

Dominant roles of Fenton reaction in sodium nitroprusside-induced chondrocyte apoptosis

Sodium nitroprusside (SNP) has been widely used as an exogenous nitric oxide (NO) donor to explore the molecular mechanism of NO-mediated chondrocyte apoptosis during the latest two decades. We have recently found that NO-independent ROS play a key role in SNP-induced apoptosis in rabbit chondrocytes. This study aims to investigate what kind of ROS and how the reliable ROS mediators mediate the SNP-induced apoptosis. Data shows that SNP and NO-exhausted SNP (SNPex) induced ROS production or cytotoxicity to identically degree. SNP induced a marked increase in iron ions, superoxide anion (O2(•-)), hydrogen peroxide (H2O2) and hydroxyl radical ((•)OH) level. H2O2 scavenger (CAT) and (•)OH scavenger (DMSO) significantly inhibited SNP-induced chondrocyte apoptosis. Iron ions chelator (DFO) entirely prevented SNP-induced chondrocyte apoptosis. In contrast, O2(•-) scavenger (SOD) and glutathione depletion agent (BSO) promoted SNP-induced cytotoxicity. K3[Fe(CN)6] exhibited no cytotoxicity, and H2O2 alone up to 250µM or iron ions alone up to 90µM is non-cytotoxic to chondrocytes. Combination of 25µM FeSO4 and 100µM H2O2 in the presence of BSO induced chondrocyte death similar to SNP treatment. Fetal bovine serum (FBS) enhanced iron ions release from SNP and the cytotoxicity of SNP. Our data shows that the extracellular Fenton reaction between iron ions released from SNP and H2O2 induced by SNP plays a key role in SNP-induced chondrocyte apoptosis. Overall, our results indicate that the potential of SNP to increase iron ions and ROS should be especially considered for some biological functions and, possibly, also for clinical applications of this drug.

ERp57 modulates STAT3 activity in radioresistant laryngeal cancer cells and serves as a prognostic marker for laryngeal cancer

Although targeting radioresistant tumor cells is essential for enhancing the efficacy of radiotherapy, the signals activated in resistant tumors are still unclear. This study shows that ERp57 contributes to radioresistance of laryngeal cancer by activating STAT3. Increased ERp57 was associated with the radioresistant phenotype of laryngeal cancer cells. Interestingly, increased interaction between ERp57 and STAT3 was observed in radioresistant cells, compared to the control cells. This physical complex is required for the activation of STAT3 in the radioresistant cells. Among STAT3-regulatory genes, Mcl-1 was predominantly regulated by ERp57. Inhibition of STAT3 activity with a chemical inhibitor or siRNA-mediated depletion of Mcl-1 sensitized radioresistant cells to irradiation, suggesting that the ERp57-STAT3-Mcl-1 axis regulates radioresistance of laryngeal cancer cells. Furthermore, we observed a positive correlation between ERp57 and phosphorylated STAT3 or Mcl-1 and in vivo interactions between ERp57 and STAT3 in human laryngeal cancer. Importantly, we also found that increased ERp57-STAT3 complex was associated with poor prognosis in human laryngeal cancer, indicating the prognostic role of ERp57-STAT3 regulation. Overall, our data suggest that ERp57-STAT3 regulation functions in radioresistance of laryngeal cancer, and targeting the ERp57-STAT3 pathway might be important for enhancing the efficacy of radiotherapy in human laryngeal cancer.

IL-32θ gene expression in acute myeloid leukemia suppresses TNF-α production

The proinflammatory cytokine TNF-α is highly expressed in patients with acute myeloid leukemia (AML) and has been demonstrated to induce rapid proliferation of leukemic blasts. Thus suppressing the production of TNF-α is important because TNF-α can auto-regulate own expression through activation of NF-κB and p38 mitogen-activated protein kinase (MAPK). In this study, we focused on the inhibitory effect of IL-32θ on TNF-α production in acute myeloid leukemia. Approximately 38% of patients with AML express endogenous IL-32θ, which is not expressed in healthy individuals. Furthermore, plasma samples were classified into groups with or without IL-32θ; then, we measured proinflammatory cytokine TNF-α, IL-1β, and IL-6 levels. TNF-α production was not increased in patients with IL-32θ expression than that in the no-IL-32θ group. Using an IL-32θ stable expression system in leukemia cell lines, we found that IL-32θ attenuated phorbol 12-myristate 13-acetate (PMA)-induced TNF-α production. IL-32θ inhibited phosphorylation of p38 MAPK, inhibitor of κB (IκB), and nuclear factor κB (NF-κB), which are key positive regulators of TNF-α expression, and inhibited nuclear translocation of NF-κB. Moreover, the presence of IL-32θ attenuated TNF-α promoter activity and the binding of NF-κB with the TNF-α promoter. In addition, IL-32γ-induced TNF-α production has no correlation with inhibition of TNF-α via IL-32θ expression. Thus, IL-32θ may serve as a potent inhibitor of TNF-α in patients with AML.

A novel phosphorylation site at Ser130 adjacent to the pseudosubstrate domain contributes to the activation of protein kinase C-δ

Protein kinase C-δ (PKCδ) is a signalling kinase that regulates many cellular responses. Although most studies focus on allosteric mechanisms that activate PKCδ at membranes, PKCδ also is controlled via multi-site phosphorylation [Gong et al. (2015) Mol. Cell. Biol. 35: , 1727-1740]. The present study uses MS-based methods to identify PKCδ phosphorylation at Thr(50) and Ser(645) (in resting and PMA-treated cardiomyocytes) as well as Thr(37), Thr(38), Ser(130), Thr(164), Thr(211), Thr(215), Ser(218), Thr(295), Ser(299) and Thr(656) (as sites that increase with PMA). We focused on the consequences of phosphorylation at Ser(130) and Thr(141) (sites just N-terminal to the pseudosubstrate domain). We show that S130D and T141E substitutions co-operate to increase PKCδ's basal lipid-independent activity and that Ser(130)/Thr(141) di-phosphorylation influences PKCδ's substrate specificity. We recently reported that PKCδ preferentially phosphorylates substrates with a phosphoacceptor serine residue and that this is due to constitutive phosphorylation at Ser(357), an ATP-positioning G-loop site that limits PKCδ's threonine kinase activity [Gong et al. (2015) Mol. Cell. Biol. 35: , 1727-1740]. The present study shows that S130D and T141E substitutions increase PKCδ's threonine kinase activity indirectly by decreasing G loop phosphorylation at Ser(357). A S130F substitution [that mimics a S130F single-nt polymorphism (SNP) identified in some human populations] also increases PKCδ's maximal lipid-dependent catalytic activity and confers threonine kinase activity. Finally, we show that Ser(130)/Thr(141) phosphorylations relieve auto-inhibitory constraints that limit PKCδ's activity and substrate specificity in a cell-based context. Since phosphorylation sites map to similar positions relative to the pseudosubstrate domains of other PKCs, our results suggest that phosphorylation in this region of the enzyme may constitute a general mechanism to control PKC isoform activity.

Resveratrol protects rabbit articular chondrocyte against sodium nitroprusside-induced apoptosis via scavenging ROS

This study aims to investigate the mechanism by which resveratrol (RV) prevents sodium nitroprusside (SNP)-induced chondrocyte apoptosis, which is a characteristic feature of osteoarthritis (OA). Rabbit articular chondrocytes were pre-incubated with 100 μM RV for 18 h before 1.5 mM SNP co-treatment for 6 h. Cell viability was evaluated by CCK-8. Annexin V/PI double staining and Hoechst 33258 staining were used to determine the fashion of SNP-induced chondrocytes death. Mitochondrial membrane potential (ΔΨm) was measured by using flow cytometry (FCM) with TMRM and Rhodamine 123 staining. Intracellular reactive oxygen species (ROS) and nitric oxide (NO) levels were confirmed by FCM analysis with DCFH-DA and DAF-FM DA staining. Cytoskeleton proteins of chondrocytes co-stained with Actin-Trakcer Green and Tubulin-Trakcer Red were validated by confocal microscopy. SNP induced time- and dose-dependent chondrocytes apoptosis with decline of ΔΨm, activation of caspases as well as cytoskeletal remodeling. SNP induced a significant induction of both ROS and NO. RV remarkably prevented SNP-induced ROS production and apoptosis as well as cytoskeletal remodeling, but did not prevent SNP-induced NO production. Pretreatment with NO scavengers did not significantly prevent SNP-induced apoptosis and cytoskeletal remodeling. SNP induces NO-independent ROS production which dominates rabbit articular chondrocyte apoptosis, and RV protects chondrocytes against SNP-induced apoptosis via scavenging ROS instead of NO.

Induction of apoptosis in T lymphoma cells by long-term treatment with thyroxine involves PKCζ nitration by nitric oxide synthase

Thyroid hormones are important regulators of cell physiology, inducing cell proliferation, differentiation or apoptosis, depending on the cell type. Thyroid hormones induce proliferation in short-term T lymphocyte cultures. In this study, we assessed the effect of long-term thyroxine (T4) treatment on the balance of proliferation and apoptosis and the intermediate participants in T lymphoma cells. Treatment with T4 affected this balance from the fifth day of culture, inhibiting proliferation in a time-dependent manner. This effect was associated with apoptosis induction, as characterized through nuclear morphological changes, DNA fragmentation, and Annexin V-FITC/Propidium Iodide co-staining. In addition, increased iNOS gene and protein levels, and enzyme activity were observed. The generation of reactive oxygen species, depolarization of the mitochondrial membrane, and a reduction in glutathione levels were also observed. The imbalance between oxidants and antioxidants species is typically associated with the nitration of proteins, including PKCζ, an isoenzyme essential for lymphoma cell division and survival. Consistently, evidence of PKCζ nitration via proteasome degradation was also observed in this study. Taken together, these results suggest that the long-term culture of T lymphoma cells with T4 induces apoptosis through the increased production of oxidative species resulting from both augmented iNOS activity and the loss of mitochondrial function. These species induce the nitration of proteins involved in cell viability, promoting proteasome degradation. Furthermore, we discuss the impact of these results on the modulation of T lymphoma growth and the thyroid status in vivo.

Resveratrol protects chondrocytes from apoptosis via altering the ultrastructural and biomechanical properties: an AFM study

Osteoarthritis (OA), a degenerative joint disease with high prevalence among older people, occurs from molecular or nanometer level and extends gradually to higher degrees of the ultrastructure of cartilage, finally resulting in irreversible structural and functional damages. This report aims to use atomic force microscopy (AFM) to investigate the protective effects of resveratrol (RV), a drug with good anti-inflammatory properties, on cellular morphology, membrane architecture, cytoskeleton, cell surface adhesion and stiffness at nanometer level in sodium nitroprusside (SNP)-induced apoptotic chondrocytes, a typical cellular OA model. CCK-8 assay showed that 100 μM RV significantly prevented SNP-induced cytotoxicity. AFM imaging and quantitative analysis showed that SNP potently induced chondrocytes changes including shrunk, round, lamellipodia contraction and decrease in adherent junctions among cells, as well as the destruction of biomechanics: 90% decrease in elasticity and 30% decrease in adhesion. In addition, confocal imaging analysis showed that SNP induced aggregation of the cytoskeleton and decrease in the expression of cytoskeletal proteins. More importantly, these SNP-induced damages to chondrocytes could be potently prevented by RV pretreatment. Interestingly, the biomechanical changes occurred before morphological changes could be clearly observed during SNP-induced apoptosis, indicating that the biomechanics of cellular membrane may be a more robust indicator of cell function. Collectively, our data demonstrate that RV prevents SNP-induced apoptosis of chondrocytes by regulating actin organization, and that AFM-based technology can be developed into a powerful and sensitive method to study the interaction mechanisms between chondrocytes and drugs.

CIP2A modulates cell-cycle progression in human cancer cells by regulating the stability and activity of Plk1

Abnormal cell-cycle control can lead to aberrant cell proliferation and cancer. The oncoprotein cancerous inhibitor of protein phosphatase 2A (CIP2A) is an inhibitor of protein phosphatase 2A (PP2A) that stabilizes c-Myc. However, the precise role of CIP2A in cell division is not understood. Herein, we show that CIP2A is required for mitotic progression by regulating the polo-like kinase (Plk1). With mitotic entry, CIP2A translocated from the cytoplasm to the nucleus, where it was enriched at spindle poles. CIP2A depletion delayed mitotic progression, resulting in mitotic abnormalities independent of PP2A activity. Unexpectedly, CIP2A interacted directly with the polo-box domain of Plk1 during mitosis. This interaction was required to maintain Plk1 stability by blocking APC/C-Cdh1-dependent proteolysis, thereby enhancing the kinase activity of Plk1 during mitosis. We observed strong correlation and in vivo interactions between these two proteins in multiple human cancer specimens. Overall, our results established a novel function for CIP2A in facilitating the stability and activity of the pivotal mitotic kinase Plk1 in cell-cycle progression and tumor development.

Exogenous nitric oxide negatively regulates the S-nitrosylation p38 mitogen-activated protein kinase activation during cerebral ischaemia and reperfusion

AIMS

A number of studies have suggested that nitric oxide (NO) plays an important role in the reactive phosphorylation of p38MAPKα (p38). However, whether S-nitrosylation of p38 is activated by NO and the details remain unclear. The aim of the present work was to assess the activation of p38, the S-nitrosylation site and the p38 signalling pathway in rat hippocampus and in HEK293 cell induced by exogenous NO.

METHODS

Primary hippocampal cultures, HEK293 cells and rat model of cerebral ischaemia/reperfusion (brain ischaemia was induced by four-vessel occlusion procedure) were used in this study. Biotin-switch method and immunoblotting were performed to study the S-nitrosylation and phosphorylation of p38, and neuronal loss was observed by histology.

RESULTS

Endogenous NO increased p38 phosphorylation and S-nitrosylation, and the activation of p38 was dependent on the S-nitrosylation of Cys-211, which was critical for the NO-mediated activation of p38. The exogenous NO donor sodium nitroprusside, S-nitrosoglutathione, 7-nitroindazole, the inhibitor of the neuronal nitric oxide synthase, inhibited the activation of p38 signal pathway induced by cerebral ischaemia/reperfusion and attenuated the damage in rat hippocampal neurones. Moreover, the N-methyl-D-aspartate receptor (NMDAR) is probably involved in the p38 activation process of S-nitrosylation and phosphorylation.

CONCLUSION

Endogenous NO induces the S-nitrosylation and phosphorylation of p38 and mediates p38 signalling pathway by NMDAR, and as exogenous NO inhibits this process and is neuroprotective in rat cerebral ischaemia/reperfusion, it may make a contribution to stroke therapy.

Identification of inositol polyphosphate 4-phosphatase type II as a novel tumor resistance biomarker in human laryngeal cancer HEp-2 cells

Although tumor resistance remains a significant impediment to successful radiotherapy, associated regulatory markers and detailed molecular mechanisms underlying this phenomenon are not well defined. In this study, we identified inositol polyphosphate 4-phosphatase type II (INPP4B) as a novel marker of radioresistance by systematically analyzing Unigene libraries of laryngeal cancer. INPP4B was highly expressed in radioresistant laryngeal cancer cells and was induced by treatment with either radiation or anticancer drugs in various types of cancer cells. Ectopic INPP4B overexpression increased radioresistance and anticancer drug resistance by suppressing apoptosis in HEp-2 cells. Conversely, INPP4B depletion with small interfering RNA resensitized HEp-2 as well as A549 and H1299 cells to radiation- and anticancer drug-induced apoptosis. Furthermore, radiation-induced INPP4B expression was blocked by inhibition of extracellular signal-regulated kinase (ERK). INPP4B depletion significantly attenuated radiation-induced increases in Akt phosphorylation, indicating an association of INPP4B-mediated radioresistance with Akt survival signaling. Taken together, our data suggest that ERK-dependent induction of INPP4B triggers the development of a tumor-resistance phenotype via Akt signaling and identify INPP4B as a potentially important target molecule for resolving the radioresistance of cancer cells.

Protein kinase C isoforms: Multi-functional regulators of cell life and death

The protein kinase C (PKC) family consists of 10 related serine/threonine protein kinases some of which are critical regulators of cell proliferation, survival and cell death. While early studies relied on broad spectrum chemical activators or inhibitors of this family, the generation of isoform specific tools has greatly facilitated our understanding of the contribution of specific PKC isoforms to cell proliferation and apoptosis. These studies suggest that PKC-alpha, PKC-epsilon, and the atypical PKC's, PKC-lambda/iota and PKC-zeta, preferentially function to promote cell proliferation and survival, while the novel isoform, PKC-delta is an important regulator of apoptosis. The essential role of this kinase family in both cell survival and apoptosis suggests that specific isoforms may function as molecular sensors, promoting cell survival or cell death depending on environmental cues. Given their central role in cell and tissue homeostasis, it is not surprising that the expression or activity of some of these kinases is altered in human diseases, particularly cancer.

Apoptotic insults to human chondrocytes induced by sodium nitroprusside are involved in sequential events, including cytoskeletal remodeling, phosphorylation of mitogen-activated protein kinase kinase kinase-1/c-Jun N-terminal kinase, and Bax-mitochondria-mediated caspase activation

Nitric oxide (NO) can regulate chondrocyte activities. This study was aimed to evaluate the molecular mechanisms of NO donor sodium nitroprusside (SNP)-induced insults to human chondrocytes. Exposure of human chondrocytes to SNP increased cellular NO levels but decreased cell viability in concentration- and time-dependent manners. SNP time dependently induced DNA fragmentation and cell apoptosis. Treatment with 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide, an NO scavenger, significantly lowered SNP-induced cell injuries. Administration of SNP interrupted F-actin and microtubule cytoskeletons and stimulated phosphorylation of mitogen-activated protein kinase kinase kinase-1 (MEKK1) and c-Jun N-terminal kinase (JNK). Similar to SNP, cytochalasin D, an inhibitor of F-actin formation, disturbed F-actin polymerization and increased MEKK1 and JNK activations. Overexpression of a dominant negative mutant of MEKK1 (dnMEK1) in human chondrocytes significantly ameliorated SNP-induced cell apoptosis. Exposure to SNP promoted Bax translocation from the cytoplasm to mitochondria, but application of dnMEKK1 lowered the translocation. SNP time dependently decreased the mitochondrial membrane potential, complex I NADH dehydrogenase activity, and cellular ATP levels, but increased the release of cytochrome c from mitochondria to the cytoplasm. Activities of caspase-9, -3, and -6 were sequentially increased by SNP administration. This study shows that SNP can induce apoptosis of human chondrocytes through sequential events, including cytoskeletal remodeling, activation of MEKK1/JNK, Bax translocation, mitochondrial dysfunction, cytochrome c release, caspase activation, and DNA fragmentation.

Influence of NO synthase inhibitor L-NAME on parasitemia and survival of Plasmodium berghei infected mice

Accelerated suicidal death or eryptosis of infected erythrocytes may delay development of parasitemia in malaria. Eryptosis is inhibited by nitric oxide (NO). The present study has been performed to explore, whether inhibition of NO synthase by L-NAME modifies the course of malaria. We show here that L-NAME (>or=10 microM) increased phosphatidylserine exposure of Plasmodium falciparum infected human erythrocytes, an effect significantly more marked than in noninfected human erythrocytes. We further show that parasitemia in Plasmodium berghei infected mice was significantly decreased (from 50% to 18% of circulating erythrocytes 20 days after infection) by addition of 1 mg/ml L-NAME to the drinking water. According to CFSE labelling L-NAME treatment accelerated the clearance of both, noninfected and infected, erythrocytes from circulating blood, but did not significantly extend the life span of infected animals. In conclusion, treatment with L-NAME shortens the life span of circulating erythrocytes and thus delays development of parasitemia during malaria.

Chondroitin sulfate inhibits the nuclear translocation of nuclear factor-kappaB in interleukin-1beta-stimulated chondrocytes

Chondroitin sulfate is referred as a symptomatic slow-acting drug for osteoarthritis because it improves articular function, and reduces joint swelling and effusion. In addition, chondroitin sulfate prevents joint space narrowing of the knee. We hypothesized that the anti-inflammatory effect of chondroitin sulfate is associated to a decrease in the activation of mitogen-activated protein kinases (MAPK) and of the transcription factors nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1). Cultured rabbit chondrocytes were stimulated with interleukin-1beta (IL-1beta) in presence of chondroitin sulfate. Nuclear translocation of NF-kappaB and AP-1, and nitrite concentrations (as an index for nitric oxide) was assessed 48 hr later. The effect of chondroitin sulfate on IL-1beta activation of extracellular signal-regulated kinase 1/2 (Erk1/2) and p38MAPK was documented by immunoblot. The effect of chondroitin sulfate on sodium nitroprusside-induced apoptosis was evaluated with the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling assay. Chondroitin sulfate reduced IL-1beta-induced NF-kappaB nuclear translocation, but not AP-1 translocation, it decreased IL-1beta-induced phosphorylation of Erk1/2 and abrogated p38MAPK phosphorylation, but did not prevent IL-1beta-induced increase in nitrite. Finally, chondroitin sulfate decreased nitroprusside-induced apoptosis of the chondrocytes. These results suggest that some of the biological activities of chondroitin sulfate may be associated to the reduction in Erk1/2 and p38MAPK phosphorylation and nuclear transactivation of NF-kappaB.

Cytokine-like 1 (CYTL1) Regulates the Chondrogenesis of Mesenchymal Cells

To identify novel molecules regulating chondrogenesis and cartilage development, we screened a cartilage-specific expressed sequence tag data base. Cytokine-like 1 (Cytl1), a possible cytokine candidate with unknown function that was originally identified in bone marrow-derived CD34-positive cells, was selected for functional characterization. In view of the initial observation that Cytl1 is predominantly expressed in chondrocytes and cartilage, we investigated its possible role in chondrogenesis and hypertrophic maturation of chondrocytes. Cytl1 expression was very low in mesenchymal cells, dramatically increased during chondrogenesis, and decreased during hypertrophic maturation, both in vivo and in vitro. The role of Cytl1 in chondrogenesis and hypertrophic maturation was examined by treating chondrifying mesenchymal cells with exogenous Cytl1 or ectopic expression of Cytl1. Notably, exogenous Cytl1 caused chondrogenic differentiation of mouse limb bud mesenchymal cells during micromass culture. Lentivirus-mediated overexpression of Cytl1 additionally induced chondrogenic differentiation of mesenchymal cells. However, Cytl1 did not affect the hypertrophic maturation of chondrocytes. Cytl1 exerted its chondrogenic effect via stimulation of Sox9 transcriptional activity. In addition, Cytl1 caused expression of insulin-like growth factor 1, which has a capacity to induce chondrogenesis. Thus, our results collectively suggest that chondrocyte-specific Cytl1 regulates chondrogenesis as a novel autocrine factor, but not hypertrophic maturation of chondrocytes during cartilage development.

Nitric oxide differentially regulates the gene expression of caspase genes but not some autophagic genes

Nitric oxide (NO) is fundamentally important molecule which produces a wide range of cellular effects with the most poorly understood one being alteration in the sensitivity to cell death. The objective of this study was to test the hypothesis that NO would differentially affect caspase or autophagy gene expression in a manner that might account for the disparate actions of NO to either enhance or protect against cell death. Neonatal mouse cardiomyocytes in culture were treated with the NO donor SIN-1 (3-morpholinosydnonimine hydrochloride) for up to 20 h. RNA was collected, after either 2, 4 or 20 h, labeled and hybridized to cDNA microarray slides The concentration of SIN-1 was selected after concentration response studies of SIN-1 on cell viability, assessed by the MTT assay. The cDNA microarrays were used that contained the mouse genome version 2.0 with genes for enzymes crucial to apoptosis, namely caspases-1, -2, -3, -6, -7, -8, -9, -11, -12 and -14, as well as for enzymes crucial to autophagy namely beclin-1, Apg5l and Apg12l. Considering the entire 20 h period, treatment with SIN-1 was associated with significant (p<0.05) changes in five caspases. In contrast, there were no changes in the three separate genes involved in autophagy. Time course experiments showed a consistent increase in caspase-8, -11 and -14, and a consistent decrease in caspase-1 and -6. Notably, caspase-1 showed a persistent and marked reduction so that after 20 h of treatment, caspase-1 was dramatically reduced, almost ten fold, to 0.14+/-0.11 of control. In conclusion, these results suggest that: (i) NO regulates the expression of genes involved in apoptotic but not some involved in autophagic cell death; (ii) the more recently discovered caspase-14 may have a role in the heart; (iii) NO-induced alteration of different caspases may explain the ability of NO to either enhance or protect against cell death depending on whether associated factors involve, respectively caspases-8, -11, and -14 or -1 and -6.

Oxidative stress-induced intestinal epithelial cell apoptosis is mediated by p38 MAPK

Free oxygen radicals are involved in the pathogenesis of necrotizing enterocolitis (NEC) in premature infants. The stress-activated p38 mitogen-activated protein kinase (MAPK) has been implicated in gut injury. Here, we found that phosphorylated p38 was detected primarily in the villus tips of normal intestine, whereas it was expressed in the entire mucosa in NEC. H(2)O(2) treatment resulted in a rapid phosphorylation of p38 MAPK and subsequent apoptosis of rat intestinal epithelial (RIE)-1 cells; this induction was attenuated by treatment with SB203580, a selective p38 MAPK inhibitor, or transfection with p38alpha siRNA. Moreover, SB203580 also blocked H(2)O(2)-induced PKC activation. In contrast, the PKC inhibitor (GF109203x) did not affect p38 activation, indicating that p38 MAPK activation occurs upstream of PKC activation in H(2)O(2)-induced apoptosis. H(2)O(2) treatment also decreased mitochondrial membrane potential; pretreatment with SB203580 attenuated this response. Our study demonstrates that the p38 MAPK/PKC pathway plays an important role as a pro-apoptotic cellular signaling during oxidative stress-induced intestinal epithelial cell injury.