Presentation of nitric oxide regulates monocyte survival through effects on caspase-9 and caspase-3 activation

Nitric oxide and thioredoxin modulate the activity of caspase 9 in HepG2 cells

The interdependent and finely tuned balance between the well-established redox-based modification, S-nitrosylation, and its counteractive mechanism of S-nitrosothiol degradation, i.e., S-denitrosylation of biological protein or non-protein thiols defines the cellular fate in the context of redox homeostasis. S-nitrosylation of cysteine residues by S-nitrosoglutathione, S-nitroso-L-cysteine-like physiological and S-nitroso-L-cysteine ethyl ester-like synthetic NO donors inactivate Caspase-3, 8, and 9, thereby hindering their apoptotic activity. However, spontaneous restoration of their activity upon S-denitrosylation of S-nitrosocaspases into their reduced, free thiol active states, aided by the members of the ubiquitous cellular redoxin (thioredoxin/ thioredoxin reductase/ NADPH) and low molecular weight dithiol (lipoic acid/ lipoamide dehydrogenase/ dihydrolipoic acid/ NADPH) systems imply a direct relevance to their proteolytic activities and further downstream signaling cascades. Additionally, our previous and current findings offer crucial insight into the concept of redundancy between thioredoxin and lipoic acid systems, and the redox-modulated control of the apoptotic and proteolytic activity of caspases, triggering their cyto- and neurotoxic effects in response to nitro-oxidative stress. Thus, this might lay the foundation for the exogenous introduction of precise and efficient NO or related donor drug delivery systems that can directly participate in catering to the S-(de)-nitrosylation-mediated functional outcomes of the cysteinyl proteases in pathophysiological settings.

Iron-Sulfur Cluster Repair Contributes to Yersinia pseudotuberculosis Survival within Deep Tissues

To successfully colonize host tissues, bacteria must respond to and detoxify many different host-derived antimicrobial compounds, such as nitric oxide (NO). NO has direct antimicrobial activity through attack on iron-sulfur (Fe-S) cluster-containing proteins. NO detoxification plays an important role in promoting bacterial survival, but it remains unclear if repair of Fe-S clusters is also important for bacterial survival within host tissues.

To successfully colonize host tissues, bacteria must respond to and detoxify many different host-derived antimicrobial compounds, such as nitric oxide (NO). NO has direct antimicrobial activity through attack on iron-sulfur (Fe-S) cluster-containing proteins. NO detoxification plays an important role in promoting bacterial survival, but it remains unclear if repair of Fe-S clusters is also important for bacterial survival within host tissues. Here we show that the Fe-S cluster repair protein YtfE contributes to the survival of Yersinia pseudotuberculosis within the spleen following nitrosative stress. Y. pseudotuberculosis forms clustered centers of replicating bacteria within deep tissues, where peripheral bacteria express the NO-detoxifying gene hmp. ytfE expression also occurred specifically within peripheral cells at the edges of microcolonies. In the absence of ytfE, the area of microcolonies was significantly smaller than that of the wild type (WT), consistent with ytfE contributing to the survival of peripheral cells. The loss of ytfE did not alter the ability of cells to detoxify NO, which occurred within peripheral cells in both WT and ΔytfE microcolonies. In the absence of NO-detoxifying activity by hmp, NO diffused across ΔytfE microcolonies, and there was a significant decrease in the area of microcolonies lacking ytfE, indicating that ytfE also contributes to bacterial survival in the absence of NO detoxification. These results indicate a role for Fe-S cluster repair in the survival of Y. pseudotuberculosis within the spleen and suggest that extracellular bacteria may rely on this pathway for survival within host tissues.

Caspase-9: structure, mechanisms and clinical application

As the most intensively studied initiator caspase, caspase-9 is a key player in the intrinsic or mitochondrial pathway which is involved in various stimuli, including chemotherapies, stress agents and radiation. Caspase-9 is activated on the apoptosome complex to remain catalytic status and is thought of involving homo-dimerization monomeric zymogens. Failing to activate caspase-9 has profound physiological and pathophysiological outcomes, leading to degenerative and developmental disorders even cancer. To govern the apoptotic commitment process appropriately, plenty of proteins and small molecules involved in regulating caspase-9. Therefore, this review is to summarize recent pertinent literature on the comprehensive description of the molecular events implicated in caspase-9 activation and inhibition, as well as the clinical trials in progress to give deep insight into caspase-9 for suppressing cancer. We hope that our concerns will be helpful for further clinical studies addressing the roles of caspase-9 and its regulators demanded to identify more effective solutions to overcome intrinsic apoptosis-related diseases especially cancer.

Protein coingestion with alcohol following strenuous exercise attenuates alcohol-induced intramyocellular apoptosis and inhibition of autophagy

Alcohol ingestion decreases postexercise rates of muscle protein synthesis, but the mechanism(s) (e.g., increased protein breakdown) underlying this observation is unknown. Autophagy is an intracellular "recycling" system required for homeostatic substrate and organelle turnover; its dysregulation may provoke apoptosis and lead to muscle atrophy. We investigated the acute effects of alcohol ingestion on autophagic cell signaling responses to a bout of concurrent (combined resistance- and endurance-based) exercise. In a randomized crossover design, eight physically active males completed three experimental trials of concurrent exercise with either postexercise ingestion of alcohol and carbohydrate (12 ± 2 standard drinks; ALC-CHO), energy-matched alcohol and protein (ALC-PRO), or protein (PRO) only. Muscle biopsies were taken at rest and 2 and 8 h postexercise. Select autophagy-related gene (Atg) proteins decreased compared with rest with ALC-CHO (P < 0.05) but not ALC-PRO. There were parallel increases (P < 0.05) in p62 and PINK1 commensurate with a reduction in BNIP3 content, indicating a diminished capacity for mitochondria-specific autophagy (mitophagy) when alcohol and carbohydrate were coingested. DNA fragmentation increased in both alcohol conditions (P < 0.05); however, nuclear AIF accumulation preceded this apoptotic response with ALC-CHO only (P < 0.05). In contrast, increases in the nuclear content of p53, TFEB, and PGC-1α in ALC-PRO were accompanied by markers of mitochondrial biogenesis at the transcriptional (Tfam, SCO2, and NRF-1) and translational (COX-IV, ATPAF1, and VDAC1) level (P < 0.05). We conclude that alcohol ingestion following exercise triggers apoptosis, whereas the anabolic properties of protein coingestion may stimulate mitochondrial biogenesis to protect cellular homeostasis.

S-nitrosoglutathione reduces tau hyper-phosphorylation and provides neuroprotection in rat model of chronic cerebral hypoperfusion

We have previously reported that treatment of rats subjected to permanent bilateral common carotid artery occlusion (pBCCAO), a model of chronic cerebral hypoperfusion (CCH), with S-nitrosoglutathione (GSNO), an endogenous nitric oxide carrier, improved cognitive functions and decreased amyloid-β accumulation in the brains. Since CCH has been implicated in tau hyperphosphorylation induced neurodegeneration, we investigated the role of GSNO in regulation of tau hyperphosphorylation in rat pBCCAO model. The rats subjected to pBCCAO had a significant increase in tau hyperphosphorylation with increased neuronal loss in hippocampal/cortical areas. GSNO treatment attenuated not only the tau hyperphosphorylation, but also the neurodegeneration in pBCCAO rat brains. The pBCCAO rat brains also showed increased activities of GSK-3β and Cdk5 (major tau kinases) and GSNO treatment significantly attenuated their activities. GSNO attenuated the increased calpain activities and calpain-mediated cleavage of p35 leading to production of p25 and aberrant Cdk5 activation. In in vitro studies using purified calpain protein, GSNO treatment inhibited calpain activities while 3-morpholinosydnonimine (a donor of peroxynitrite) treatment increased its activities, suggesting the opposing role of GSNO vs. peroxynitrite in regulation of calpain activities. In pBCCAO rat brains, GSNO treatment attenuated the expression of inducible nitric oxide synthase (iNOS) expression and also reduced the brain levels of nitro-tyrosine formation, thereby indicating the protective role of GSNO in iNOS/nitrosative-stress mediated calpain/tau pathologies under CCH conditions. Taken together with our previous report, these data support the therapeutic potential of GSNO, a biological NO carrier, as a neuro- and cognitive-protective agent under conditions of CCH.

Protective role of S-nitrosoglutathione (GSNO) against cognitive impairment in rat model of chronic cerebral hypoperfusion

Chronic cerebral hypoperfusion (CCH), featuring in most of the Alzheimer's disease spectrum, plays a detrimental role in brain amyloid-β (Aβ) homeostasis, cerebrovascular morbidity, and cognitive decline; therefore, early management of cerebrovascular pathology is considered to be important for intervention in the impending cognitive decline. S-nitrosoglutathione (GSNO) is an endogenous nitric oxide carrier modulating endothelial function, inflammation, and neurotransmission. Therefore, the effect of GSNO treatment on CCH-associated neurocognitive pathologies was determined in vivo by using rats with permanent bilateral common carotid artery occlusion (BCCAO), a rat model of chronic cerebral hypoperfusion. We observed that rats subjected to permanent BCCAO showed a significant decrease in learning/memory performance and increases in brain levels of Aβ and vascular inflammatory markers. GSNO treatment (50 μg/kg/day for 2 months) significantly improved learning and memory performance of BCCAO rats and reduced the Aβ levels and ICAM-1/VCAM-1 expression in the brain. Further, in in vitro cell culture studies, GSNO treatment also decreased the cytokine-induced proinflammatory responses, such as activations of NFκB and STAT3 and expression of ICAM-1 and VCAM-1 in endothelial cells. In addition, GSNO treatment increased the endothelial and microglial Aβ uptake. Additionally, GSNO treatment inhibited the β-secretase activity in primary rat neuron cell culture, thus reducing secretion of Aβ, suggesting GSNO mediated mechanisms in anti-inflammatory and anti-amyloidogenic activities. Taken together, these data document that systemic GSNO treatment is beneficial for improvement of cognitive decline under the conditions of chronic cerebral hypoperfusion and suggests a potential therapeutic use of GSNO for cerebral hypoperfusion associated mild cognitive impairment in Alzheimer's disease.

Increased S-nitrosylation and proteasomal degradation of caspase-3 during infection contribute to the persistence of adherent invasive Escherichia coli (AIEC) in immune cells

Adherent invasive Escherichia coli (AIEC) have been implicated as a causative agent of Crohn’s disease (CD) due to their isolation from the intestines of CD sufferers and their ability to persist in macrophages inducing granulomas. The rapid intracellular multiplication of AIEC sets it apart from other enteric pathogens such as Salmonella Typhimurium which after limited replication induce programmed cell death (PCD). Understanding the response of infected cells to the increased AIEC bacterial load and associated metabolic stress may offer insights into AIEC pathogenesis and its association with CD. Here we show that AIEC persistence within macrophages and dendritic cells is facilitated by increased proteasomal degradation of caspase-3. In addition S-nitrosylation of pro- and active forms of caspase-3, which can inhibit the enzymes activity, is increased in AIEC infected macrophages. This S-nitrosylated caspase-3 was seen to accumulate upon inhibition of the proteasome indicating an additional role for S-nitrosylation in inducing caspase-3 degradation in a manner independent of ubiquitination. In addition to the autophagic genetic defects that are linked to CD, this delay in apoptosis mediated in AIEC infected cells through increased degradation of caspase-3, may be an essential factor in its prolonged persistence in CD patients.

Stimulation of Toll-like receptor-1/2 combined with Velcade increases cytotoxicity to human multiple myeloma cells

An increasing body of evidence supports the important role of adhesion to bone marrow microenvironment components for survival and drug resistance of multiple myeloma (MM) cells. Previous studies suggested that stimulation of Toll-like receptors by endogenous ligands released during inflammation and tissue damage may be pro-tumorigenic, but no studies have been performed in relation to modulation of cell adhesion and drug cytotoxicity. Here, we investigated the effect of TLR1/2 activation on adhesion of human myeloma cells to fibronectin, and their sensitivity to the proteasome inhibitor Velcade. It was found that TLR1/2 activation with Pam3CSK4 increased the cytotoxicity of Velcade in L363, OPM-2 and U266 human myeloma cells. This effect was not related to a decreased adhesion of the cells to fibronectin, but TLR1/2 activation stimulated the caspase-3 activity in Velcade-treated myeloma cells, which may be responsible for the enhanced cell death. Inhibitors of NF-κB and MAPK reduced the stimulatory effect. These findings indicate that TLR activation of MM cells could bypass protective effects of cell adhesion and suggest that TLR signaling may also have antitumorigenic potential.

sRAGE induces human monocyte survival and differentiation

The receptor for advanced glycation end products (RAGE) is produced either as a transmembrane or soluble form (sRAGE). Substantial evidence supports a role for RAGE and its ligands in disease. sRAGE is reported to be a competitive, negative regulator of membrane RAGE activation, inhibiting ligand binding. However, some reports indicate that sRAGE is associated with inflammatory disease. We sought to define the biological function of sRAGE on inflammatory cell recruitment, survival, and differentiation in vivo and in vitro. To test the in vivo impact of sRAGE, the recombinant protein was intratracheally administered to mice, which demonstrated monocyte- and neutrophil-mediated lung inflammation. We also observed that sRAGE induced human monocyte and neutrophil migration in vitro. Human monocytes treated with sRAGE produced proinflammatory cytokines and chemokines. Our data demonstrated that sRAGE directly bound human monocytes and monocyte-derived macrophages. Binding of sRAGE to monocytes promoted their survival and differentiation to macrophages. Furthermore, sRAGE binding to cells increased during maturation, which was similar in freshly isolated mouse monocytes compared with mature tissue macrophages. Because sRAGE activated cell survival and differentiation, we examined intracellular pathways that were activated by sRAGE. In primary human monocytes and macrophages, sRAGE treatment activated Akt, Erk, and NF-kappaB, and their activation appeared to be critical for cell survival and differentiation. Our data suggest a novel role for sRAGE in monocyte- and neutrophil-mediated inflammation and mononuclear phagocyte survival and differentiation.

Palmitate-induced NO production has a dual action to reduce cell death through NO and accentuate cell death through peroxynitrite formation

The objective of this study was to determine the role of palmitate-induced stimulation of nitric oxide synthase (NOS) on palmitate-induced cell death, specifically distinguishing the effects of the subtype NOS2 from NOS3, defining the effect of NO on mitochondria death pathways, and determining whether palmitate induces peroxynitrite formation which may impact cardiomyocyte cell survival. Cardiomyocytes from embryonic chick hearts were treated with palmitate 300-500 microM. Cell death was assessed by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay. The ability of palmitate to induce NO production and its consequences were tested by using the NOS inhibitor 7-nitroindazole (7-N) and the peroxynitrite scavenger (5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III) chloride) (FeTPPS). The effect of palmitate on the mitochondria was assessed by Western blotting for cytochrome c release into the cytosol, and assessment of mitochondrial transmembrane potential (DeltaPsi(m)) by 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl-benzimidazolyl-carbocyanine iodide staining and immunocytochemistry. The NOS inhibitor 7-N, which is selective for NOS2 and not for NOS3, significantly (p<0.05) increased palmitate-induced cell death. In contrast, 7-N did not alter cell death produced by the combination of potassium cyanide and deoxyglucose, which, respectively, inhibit glycolysis and oxidative phosphorylation. The mitochondrial actions of palmitate, specifically palmitate-induced translocation of mitochondrial cytochrome c to cytosol and loss of mitochondrial transmembrane potential, were not altered by pretreatment with 7-N. FeTPPS, which isomerizes peroxynitrite to nitrate and thereby reduces the toxic effects of peroxynitrite, produced a significant reduction in palmitate-induced cell death. In summary, these data suggest that palmitate stimulates NO production, which has a dual action to protect against cell death or to induce cell death. Palmitate-induced cell death is mediated, in part, through NO generation, which leads to peroxynitrite formation. The protective effect of NO is operative through stimulation of NOS2 but not NOS3. The actions of NO on palmitate-induced cell death are independent of mitochondrial cell death pathways.

Inhibitory effect of polyphenol cyanidin on TNF-α-induced apoptosis through multiple signaling pathways in endothelial cells

The aim of this study was to investigate the inhibitory effect of non-aglycone cyanidin on TNF-alpha-induced endothelial cell apoptosis and its mechanism through enhancing expression of thioredoxin in endothelial cells. We found that exposure of the serum-starved BAECs to TNF-alpha increased significantly the number of dead cells, the cleaved caspase-3 and cleaved poly(ADP-ribose)polymerase (RARP)assayed by Western blot, whereas supplementation with cyanidin considerably suppressed these events. Inhibitors of the Akt, ERK1/2, Src kinase and transfection with a dominant-negative Akt cDNA blocked the inhibitory effect of cyanidin on cleaved caspase-3. Cyanidin significantly elevated expression of endothelial nitric oxide synthase (eNOS) and thioredoxin (Trx). The increased Trx expression was blocked by siRNA transfection of cGMP-dependent protein kinase (PKG) and by using a PKG inhibitor, KT5823. Cyanidin also ameliorated TNF-alpha-induced decrease of Trx S-nitrosylation and intracellular glutathione and elevation of 4-hydroxynonenal (4-HNE), a major aldehydic product of lipid peroxidation. Furthermore, cyanidin also restored S-nitrosylation of caspase-3 and reduced the rise in expression and acetylation of tumor suppression gene p53. However, KT5823 or L-NAME, an inhibitor of eNOS, removed the preventive effects of cyanidin. Our data show that inhibitory effect of cyanidin on TNF-alpha-induced apoptosis involves multiple pathways, such as Akt activation, eNOS and thioredoxin expression in endothelial cells.

Requirement of transmembrane transport for S-nitrosocysteine-dependent modification of intracellular thiols

S-nitrosothiols have been implicated as intermediary transducers of nitric oxide bioactivity; however, the mechanisms by which these compounds affect cellular functions have not been fully established. In this study, we have examined the effect of S-nitrosothiol transport on intracellular thiol status and upon the activity of a target protein (caspase-3), in bovine aortic endothelial cells. We have previously demonstrated that the specific transport of amino acid-based S-nitrosothiols (S-nitroso-L-cysteine and S-nitrosohomocysteine) occurs via amino acid transport system L to generate high levels of intracellular protein S-nitrosothiols (Zhang, Y., and Hogg, N. (2004) Proc. Natl. Acad. Sci. U. S. A. 101, 7891-7896). In this study, we demonstrate that the transport of S-nitrosothiols is essential for these compounds to affect intracellular thiol levels and to modify intracellular protein activity. Importantly, the ability of these compounds to affect intracellular processes occurs independently of nitric oxide formation. These findings suggest that the major action of these compounds is not to liberate nitric oxide in the extracellular space but to be specifically transported into cells where they are able to modify cellular functions through nitric oxide-independent mechanisms.

VEGF-E activates endothelial nitric oxide synthase to induce angiogenesis via cGMP and PKG-independent pathways

Vascular endothelial growth factor-A (VEGF), which binds to both VEGF receptor-1 (Flt1) and VEGFR-2 (KDR/Flk-1), requires nitric oxide (NO) to induce angiogenesis in a cGMP-dependent manner. Here we show that VEGF-E, a VEGFR-2-selective ligand stimulates NO release and tube formation in human umbilical vein endothelial cells (HUVEC). Inhibition of phospholipase Cgamma (PLCgamma) with U73122 abrogated VEGF-E induced endothelial cell migration, tube formation and NO release. Inhibition of endothelial nitric oxide synthase (eNOS) using l-NNA blocked VEGF-E-induced NO release and angiogenesis. Pre-incubation of HUVEC with the soluble guanylate cyclase inhibitor, ODQ, or the protein kinase G (PKG) inhibitor, KT-5823, had no effect on angiogenesis suggesting that the action of VEGF-E is cGMP-independent. Our data provide the first demonstration that VEGFR-2-mediated NO signaling and subsequent angiogenesis is through a mechanism that is dependent on PLCgamma but independent of cGMP and PKG.

OxLDL–IgG Immune Complexes Induce Survival of Human Monocytes

OBJECTIVE

Immune complexes containing oxidatively modified low-density lipoprotein (oxLDL) particles are deposited in human atherosclerotic lesions during atherogenesis. Here we studied whether OxLDL-IgG immune complexes (OxLDL-IgG ICs) affect survival of human monocytes.

METHODS AND RESULTS

As demonstrated by light microscopy, and analysis of cell proliferation, caspase-3 activity, and DNA fragmentation, OxLDL-IgG ICs promoted survival of cultured human monocytes by decreasing their spontaneous apoptosis. OxLDL-IgG ICs induced a concentration-dependent production of the major monocyte growth factor, monocyte colony-stimulating factor (M-CSF), by the monocytes, but its inhibition was without effect on OxLDL-IgG IC-induced monocyte survival. Rather, OxLDL-IgG ICs induced rapid phosphorylation of Akt, suggesting a direct anti-apoptotic effect mediated by cross-linking of Fcgamma receptors. Experiments with receptor blocking antibodies revealed that the OxLDL-IgG IC-induced monocyte survival was mediated by Fcgamma receptor I.

CONCLUSIONS

The results show that OxLDL-IgG ICs promote survival of monocytes by cross-linking Fcgamma receptor I and activating Akt-dependent survival signaling. The results reveal a novel mechanism by which an immune reaction toward oxLDL can play a role in the accumulation of macrophages in human atherosclerotic lesions.

Role of nitric oxide-induced mtDNA damage in mitochondrial dysfunction and apoptosis

An increasing body of evidence suggests that nitric oxide (NO) can be cytotoxic and induce apoptosis. NO can also be genotoxic and cause DNA damage and mutations. It has been shown that NO damages mitochondrial DNA (mtDNA) to a greater extent than nuclear DNA. Previously, we reported that conditional targeting of the DNA repair protein hOGG1 into mitochondria using a mitochondria targeting sequence (MTS) augmented mtDNA repair of oxidative damage and enhanced cellular survival. To determine whether enhanced repair resulting from augmented expression of hOGG1 could also protect against the deleterious effects of NO, we used HeLa TetOff/MTS-OGG1-transfected cells to conditionally express hOGG1 in mitochondria. The effects of additional hOGG1 expression on repair of NO-induced mtDNA damage and cell survival were evaluated. These cells, along with vector transfectants, in either the presence or absence of doxycycline (Dox), were exposed to NO produced by the rapid decomposition of 1-propanamine, 3-(2-hydroxy-2-nitroso-1-propylhydrazino) (PAPA NONOate). Functional studies revealed that cells expressing recombinant hOGG1 were more proficient at repairing NO-induced mtDNA damage, which led to increased cellular survival following NO exposure. Moreover, the results described here show that conditional expression of hOGG1 in mitochondria decreases NO-induced inhibition of ATP production and protects cells from NO-induced apoptosis.

Chemical considerations and biological selectivity of protein nitrosation: implications for NO-mediated signal transduction

Nitric oxide (NO) is a diatomic free radical that plays an important role in the homeostatic regulation of the central nervous, immune, and cardiovascular systems. In addition to its interaction with guanylate cyclase, which results in the production of the second messenger cyclic GMP, there is now a large body of literature indicating that many of the effects associated with the production of NO are due to the nitrosation of cysteine residues in proteins. In this review, we outline the primary chemical pathways that may account for protein nitrosation in cells and tissues. The functional implications of protein nitrosation are discussed by using the p21(ras) subfamily of small monomeric GTPases and the cysteine-containing aspartate-specific proteases (caspases) as prototypical examples. Overall, in addition to the well characterized NO/O(2) reaction, there may exist multiple pathways accounting for protein nitrosation in cells. These include acid- and free radical-mediated mechanisms. Although protein nitrosation may not be limited to cysteine residues, there is now ample evidence that nitrosation reactions, in a fashion similar to oxidative modifications, may modulate the structure, activity, association, and localization of a specific subset of proteins in cells and tissues.

Regulation of monocyte apoptosis by the protein kinase Cdelta-dependent phosphorylation of caspase-3

Monocytes are central components of the innate immune response and normally circulate for a short period of time before undergoing spontaneous apoptosis. During inflammation, differentiation, or oncogenic transformation, the life span of monocytes is prolonged by preventing the activation of the apoptotic program. Here we showed that caspase-3, a cysteine protease required for monocyte apoptosis, is a phosphoprotein. We identified protein kinase Cdelta (PKCdelta) as a member of the protein kinase C family that associates with and phosphorylates caspase-3. The PKCdelta-dependent phosphorylation of caspase-3 resulted in an increase in the activity of caspase-3. This effect of PKCdelta is specific to caspase-3, as evidenced by the absence of similar effects on caspase-9. The activity of PKCdelta precedes the activation of caspase-3 during spontaneous monocyte apoptosis and in monocyte-induced apoptosis. We found that the overexpression of PKCdelta resulted in an increase of apoptosis, whereas its inhibition blocked caspase-3 activity and decreased apoptosis. Our results provided evidence that the PKCdelta-dependent phosphorylation of caspase-3 provided a novel pro-apoptotic mechanism involved in the regulation of monocyte life span.

Nitric oxide-modulated marker gene expression of signal transduction pathways in lung endothelial cells

Nitric oxide (NO) is a signal molecule involved in regulation of physiological and pathophysiological functions of the vascular endothelium such as apoptosis. We examined whether NO-modulates marker gene expression of signal transduction pathways in cultured pulmonary artery endothelial cell (PAEC). Cells were exposed to a NO donor, 1 mM NOC-18, for 0.5, 5, and 24 h, thereafter, expression levels of 96 marker genes associated with 18 signal transduction pathways were assessed using a signal transduction pathway-finder microarray analysis system. NO modulation of apoptotic pathways and nuclear factor (NF) microarray were further analyzed. Gene array analyses revealed that 17 genes in 13 signal pathways were up- or down-regulated in cells exposed to NO, four of which were significantly altered by NO and are associated with apoptotic pathways. Apoptotic pathways resulted in identification of 11 genes in this group. Nuclear factor microarray studies demonstrated that NO-modulated expression of these signal transduction genes was associated with regulation of NF-binding activities. Gel shift analysis verified the effects of NO on DNA-binding activity of NF. These results demonstrated that NO signaling modulates at least 13 signal transduction pathways including apoptosis-related families in PAEC.

Involvement of iNOS-dependent NO production in the stimulation of osteoclast survival by TNF-alpha

Osteoclasts, cells primarily responsible for bone resorption, differentiate from hematopoietic progenitor cells under the influence of various hormones, cytokines, and differentiation factors. Once fully differentiated, osteoclasts rapidly die in the absence of any survival factor. We have previously shown that tumor necrosis factor alpha (TNF-alpha) promotes the survival of differentiated osteoclasts. The expression of inducible nitric oxide synthase (iNOS) and consequent NO production is often stimulated under inflammatory conditions. In this study, we found that TNF-alpha, but not receptor activator of nuclear factor kappa B ligand and interleukin 1, increased the expression of iNOS both at the mRNA and protein levels. Subsequently, an enhanced NO level was detected both inside the cells and the culture medium of TNF-alpha-stimulated osteoclasts. Blocking NOS activity with L-NAME prevented TNF-alpha-induced NO generation by osteoclasts and the osteoclast survival stimulated by TNF-alpha. The iNOS selective inhibitor L-NIL also suppressed TNF-alpha-induced osteoclast survival, whereas low concentrations of NO releaser NOC-18 were sufficient to promote osteoclast survival. Furthermore, antiapoptotic and caspase suppressive effects of TNF-alpha on osteoclasts were abolished by L-NAME. Our findings indicate that iNOS-dependent NO generation contributes to the survival-promoting function of TNF-alpha in osteoclasts.

Apoptosis: The Sculptor of Development

Apoptosis is a programmed mechanism of cell death recognized by its characteristic morphological and biochemical changes. Over the last decade, our understanding of the biochemistry of apoptosis has flourished. However, the physiological relevance of apoptosis remains elusive. Here, I propose that the process of programmed cell death plays an essential role in structural development. From pioneering studies almost a century ago to recent findings using modern technology, similar conclusions have emerged that highlight the fundamental role of apoptosis in vascular development. This review will recount these classic and modern studies as I survey evidence that implicates apoptosis in other aspects of development and ask how cell death can possibly contribute to homeostasis and development of the immune system. I briefly consider the mechanisms that may determine the fate of cells within the vasculature and propose new roles for the contribution of apoptosis to development and differentiation. More provocatively, I explore the possibilities that arise from this growing field of study, including prevention of developmental defects and even abnormal development after birth, such as neoplastic development. To realize these end points, the biochemical bases of apoptosis must be thoroughly understood.

Tumor stroma interactions induce chemoresistance in pancreatic ductal carcinoma cells involving increased secretion and paracrine effects of nitric oxide and interleukin-1beta

Pancreatic ductal carcinoma is characterized by a profound chemoresistance. As we have shown previously, these tumor cells can develop chemoresistance by interleukin (IL)-1beta in an autocrine and nuclear factor-kappaB-dependent fashion. Because pancreatic ductal carcinoma contains many mesenchymal stromal cells, we further investigated how tumor-stroma interactions contribute to chemoresistance by using a transwell coculture model, including murine pancreatic fibroblasts and the chemosensitive human pancreatic carcinoma cell lines T3M4 and PT45-P1. If cultured with fibroblast-conditioned medium or kept in coculture with fibroblasts, both cell lines became much less sensitive toward treatment with etoposide than cells cultured under standard conditions. Furthermore, the secretion of IL-1beta in T3M4 and PT45-P1 cells was increased by the fibroblasts, and IL-1beta-receptor blockade abolished the resistance-inducing effect during cocultivation. This stimulated IL-1beta secretion could be attributed to nitric oxide (NO) released by the fibroblasts as an IL-1beta-inducing factor. Although both tumor cells secreted only little NO, which was in line with undetectable inducible nitric oxide synthase (iNOS) expression, fibroblasts exhibited significant iNOS expression and NO secretion that could be further induced by the tumor cells. Incubation of T3M4 and PT45-P1 cells with the NO donor S-Nitroso-N-acetyl-D,L-penicillamine up-regulated IL-1beta secretion and conferred resistance toward etoposide-induced apoptosis. Conversely, the resistance-inducing effect of the fibroblasts was significantly abolished, when the specific iNOS inhibitor aminoguanidine was added during coculture. Immunohistochemistry on tissue sections from human pancreatic ductal carcinoma also revealed iNOS expression in stromal cells and IL-1beta expression in tumor cells, thus supporting the in vitro findings. These data clearly demonstrate that fibroblasts contribute to the development of chemoresistance in pancreatic carcinoma cells via increased secretion of NO, which in turn leads to an elevated release of IL-1beta by the tumor cells. These findings substantiate the implication of tumor-stromal interactions in the chemoresistance of pancreatic carcinoma.

Metal and redox modulation of cysteine protein function

In biological systems, the amino acid cysteine combines catalytic activity with an extensive redox chemistry and unique metal binding properties. The interdependency of these three aspects of the thiol group permits the redox regulation of proteins and metal binding, metal control of redox activity, and ligand control of metal-based enzyme catalysis. Cysteine proteins are therefore able to act as "redox switches," to sense concentrations of oxidative stressors and unbound zinc ions in the cytosol, to provide a "storage facility" for excess metal ions, to control the activity of metalloproteins, and to take part in important regulatory and signaling pathways. The diversity of cysteine's multiple roles in vivo is equally as fascinating as it is promising for future biochemical and pharmacological research.