Nitric Oxide Regulates Cell Sensitivity to Cisplatin-Induced Apoptosis throughS-Nitrosylation and Inhibition of Bcl-2 Ubiquitination

Pristimerin Induces Apoptosis in Prostate Cancer Cells by Down-regulating Bcl-2 through ROS-dependent Ubiquitin-proteasomal Degradation Pathway

Pristimerin is a quinonemethide triterpenoid with the potential of a promising anticancer agent. Pristimerin (PM) has shown anticancer activity against a range of cancer cell lines, but its activity for prostate cancer has not been adequately investigated. In the present study we have examined the underlying mechanisms of the apoptotic response of the hormone-sensitive (LNCaP) and hormone-refractory (PC-3) prostate cancer cell lines to PM. Treatment with PM induced apoptosis in both cell lines as characterized by increased annexin V-binding and cleavage of PARP-1 and procaspases-3 and -9. It also induced mitochondrial depolarization, cytochrome c release from mitochondria and generation of reactive oxygen species (ROS). Response to PM is regulated by Bcl-2 since it down-regulated Bcl-2 expression and overexpression of Bcl-2 rendered prostate cancer cells resistant to PM. ROS plays a role in down-regulation of Bcl-2, since treatment with PM in the presence of various ROS modulators, e.g., n-acetylcysteine (NAC), a general purpose antioxidant; diphenylene iodonium (DPI), a NADPH inhibitor; rotenone (ROT), a mitochondrial electron transport chain interrupter rotenone or MnTBAP, a O₂ scavenger, attenuated the down-regulation of Bcl-2. Furthermore, ROS is also involved in the ubiquitination and proteasomal degradation of Bcl-2 as both of these events were blocked by O ₂^- scavenger MnTBAP. Thus, pristimerin induces apoptosis in prostate cancer cells predominately through the mitochondrial apoptotic pathway by inhibiting antiapoptic Bcl-2 through a ROS-dependent ubiquitin-proteasomal degradation pathway.

SNObase, a database for S-nitrosation modification

S-Nitros(yl)ation is a ubiquitous redox-based post-translational modification of protein cysteine thiols by nitric oxide or its derivatives, which transduces the bioactivity of nitric oxide (NO) by regulation of protein conformation, activity, stability, localization and protein-protein interactions. These years, more and more S-nitrosated proteins were identified in physiological and pathological processes and the number is still growing. Here we developed a database named SNObase ( http://www.nitrosation.org ), which collected S-nitrosation targets extracted from literatures up to June 1st, 2012. SNObase contained 2561 instances, and provided information about S-nitrosation targets, sites, biological model, related diseases, trends of S-nitrosation level and effects of S-nitrosation on protein function. With SNObase, we did functional analysis for all the SNO targets: In the gene ontology (GO) biological process category, some processes were discovered to be related to S-nitrosation ("response to drug", "regulation of cell motion") besides the previously reported related processes. In the GO cellular component category, cytosol and mitochondrion were both enriched. From the KEGG pathway enrichment results, we found SNO targets were enriched in different diseases, which suggests possible significant roles of S-nitrosation in the progress of these diseases. This SNObase means to be a database with precise, comprehensive and easily accessible information, an environment to help researchers integrate data with comparison and relevancy analysis between different groups or works, and also an SNO knowledgebase offering feasibility for systemic and global analysis of S-nitrosation in interdisciplinary studies.

Is S-nitrosylation of cochlear proteins a critical factor in cisplatin-induced ototoxicity?

S-nitrosylation is a redox-sensitive protein modification, which is a highly specific, but reversible mechanism that regulates several signal transduction cascades. Oxidative stress plays a causal role in the ototoxic effects of an anti-neoplastic drug, cisplatin. Despite emerging evidence implicating nitroxidative stress as a critical factor in cisplatin toxicity, the significance of the cochlear protein S-nitrosylation in cisplatin ototoxicity is yet to be understood. In the present study, a 16-mg/kg dose of cisplatin, induced a significant shift in the amplitudes of distortion product otoacoustic emissions, a measure of outer hair cell activity, in Wistar rats, 3 days post-treatment. These ototoxic effects were accompanied by significant increases in the S-nitrosylation of at least three cochlear proteins. Biological significance of these S-nitrosylated proteins was indicated by their immunolocalization in organ of Corti, stria vascularis, and spiral ganglions, which are known cochlear targets of cisplatin toxicity. In addition, co-treatment with Trolox, an inhibitor of peroxynitrite, attenuated cisplatin-induced S-nitrosylation of cochlear proteins and prevented the associated hearing loss. The cisplatin-induced S-nitrosylation of inner ear proteins, their sensitive cochlear localization, and their potential association with cisplatin-induced hearing loss suggests that S-nitrosylation of cochlear proteins might play a crucial role in mediating cisplatin ototoxicity.

The good and bad effects of cysteine S-nitrosylation and tyrosine nitration upon insulin exocytosis: a balancing act

As understanding of the mechanisms driving and regulating insulin secretion from pancreatic beta cells grows, there is increasing and compelling evidence that nitric oxide (•NO) and other closely-related reactive nitrogen species (RNS) play important roles in this exocytic process. •NO and associated RNS, in particular peroxynitrite, possess the capability to effect signals across both intracellular and extracellular compartments in rapid fashion, affording extraordinary signaling potential. It is well established that nitric oxide signals through activation of guanylate cyclase-mediated production of cyclic GMP. The intricate intracellular redox environment, however, lends credence to the possibility that •NO and peroxynitrite could interact with a wider variety of biological targets, with two leading mechanisms involving 1) Snitrosylation of cysteine, and 2) nitration of tyrosine residues comprised within a variety of proteins. Efforts aimed at delineating the specific roles of •NO and peroxynitrite in regulated insulin secretion indicate that a highly-complex and nuanced system exists, with evidence that •NO and peroxynitrite can contribute in both positive and negative regulatory ways in beta cells. Furthermore, the ultimate biochemical outcome within beta cells, whether to compensate and recover from a given stress, or not, is likely a summation of contributory signals and redox status. Such seeming regulatory dichotomy provides ample opportunity for these mechanisms to serve both physiological and pathophysiologic roles in onset and progression of diabetes. This review focuses attention upon recent accumulating evidence pointing to roles for nitric oxide induced post-translational modifications in the normal regulation as well as the dysfunction of beta cell insulin exocytosis.

MDA-7/IL-24 induces Bcl-2 denitrosylation and ubiquitin-degradation involved in cancer cell apoptosis

MDA-7/IL-24 was involved in the specific cancer apoptosis through suppression of Bcl-2 expression, which is a key apoptosis regulatory protein of the mitochondrial death pathway. However, the underlying mechanisms of this regulation are unclear. We report here that tumor-selective replicating adenovirus ZD55-IL-24 leads to Bcl-2 S-denitrosylation and concomitant ubiquitination, which take part in the 26S proteasome degradation. IL-24-siRNA completely blocks Bcl-2 ubiquitination via reversion of Bcl-2 S-denitrosylation and protects it from proteasomal degradation which confirmed the significant role of MDA-7/IL-24 in regulating posttranslational modification of Bcl-2 in cancer cells. Nitric oxide (NO) is a key regulator of protein S-nitrosylation and denitrosylation. The NO donor, sodium nitroprusside (SNP), down-regulates Bcl-2 S-denitrosylation, attenuates Bcl-2 ubiquitination and subsequently counteracts MDA-7/IL-24 induced cancer cell apoptosis, whereas NO inhibitor 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxy-3-oxide (PTIO) shows the opposite effect. At the same time, these NO modulators fail to affect Bcl-2 phosphorylation, suggesting that NO regulates Bcl-2 stability in a phosphorylation-independent manner. In addition, Bcl-2 S-nitrosylation reduction induced by ZD55-IL-24 was attributed to both iNOS decrease and TrxR1 increase. iNOS-siRNA facilitates Bcl-2 S-denitrosylation and ubiquitin-degradation, whereas the TrxR1 inhibitor auranofin prevents Bcl-2 from denitrosylation and ubiquitination, thus restrains the caspase signal pathway activation and subsequent cancer cell apoptosis. Taken together, our studies reveal that MDA-7/IL-24 induces Bcl-2 S-denitrosylation via regulation of iNOS and TrxR1. Moreover, denitrosylation of Bcl-2 results in its ubiquitination and subsequent caspase protease family activation, as a consequence, apoptosis susceptibility. These findings provide a novel insight into MDA-7/IL-24 induced growth inhibition and carcinoma apoptosis.

Protein S-nitrosylation and cancer

Protein S-nitrosylation is a covalent post-translational modification through coupling of a nitric oxide (NO) moiety with the reactive thiol group of a protein cysteine residue to form an S-nitrosothiol (SNO). S-nitrosylation is a key mechanism in the transmission of NO-based cellular signals in the vital cellular processes, including transcription regulation, DNA repair, and apoptosis. Contemporary research has implicated dysregulation of S-nitrosylation in severe pathological events, including cancer onset, progression, and treatment resistance. The S-nitrosylation status may be directly linked to many cancer therapy outcomes as well as therapeutic-resistance, emphasizing the need to develop S-nitrosylation-related anti-cancer therapeutics. The role of S-nitrosylated proteins in the development and progression of cancer are varied, generating a critical need for a thorough review of the current dynamic research in this area.

Growth-inhibitory and chemosensitizing effects of the glutathione-S-transferase-π-activated nitric oxide donor PABA/NO in malignant gliomas

Glutathione-S-transferases (GSTs) are upregulated in malignant gliomas and contribute to their chemoresistance. The nitric oxide (NO) donor PABA/NO (O(2) -{2,4-dinitro-5-[4-(N-methylamino)benzoyloxy]phenyl} 1-(N,N-dimethylamino)diazen-1-ium-1,2-diolate) generates NO upon selective enzymatic activation by GST-π-inducing selective biological effects in tumors. Tumor cell killing and chemosensitization were observed in a variety of tumors after exposure to GST-activated NO donor drugs. In our project, cytotoxic and chemosensitizing effects of PABA/NO in combination with carboplatin (CPT) and temozolomide (TMZ) were studied in human U87 glioma cells in vitro and in vivo. U87 glioma cells were exposed to PABA/NO alone or in combination with CPT or TMZ for 24 hr. Cell viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay after 24-hr incubation and 48 hr after drug removal. The antiproliferative effect of PABA/NO was assessed in an intracranial U87 glioma nude rat model comparing subcutaneous administration and intratumoral delivery by convection-enhanced delivery. PABA/NO monotherapy showed a strong dose-dependent growth-inhibitory effect in U87 glioma cells in vitro, and a strong synergistic effect was observed after concomitant treatment with TMZ, but not with CPT. Systemic and intratumoral PABA/NO administration significantly reduced cell proliferation, but this did not result in prolonged survival in nude rats with intracranial U87 gliomas. PABA/NO has potent antiproliferative effects, sensitizes U87 glioma cells to TMZ in vitro and shows some in vivo efficacy. Further studies are still required to consolidate the role of NO donor therapy in glioma treatment.

Multi-arm polymeric nanocarrier as a nitric oxide delivery platform for chemotherapy of head and neck squamous cell carcinoma

Nitric oxide is a cell signaling molecule that can be a potent inducer of cell death in cancers at elevated concentrations. However, NO is also toxic to normal tissues and chronic exposure at low levels can induce tumor growth. We have designed a polymeric carrier system to deliver nitric oxide locoregionally to tumorigenic tissues at micromolar concentrations. A highly water solubility and biodegradable multi-arm polymer nanocarrier, sugar poly-(6-O-methacryloyl-d-galactose), was synthesized using MADIX/RAFT polymerization, and utilized to deliver high concentrations of nitric oxide to xenografts of human head and neck squamous cell carcinoma (HNSCC). The in vitro release of the newly synthesized nitric oxide donor, O(2)-(2,4-dinitrophenyl) 1-[4-(2-hydroxy)ethyl]-3-methylpiperazin-1-yl]diazen-1-ium-1,2-diolate and its corresponding multi-arm polymer-based nanoconjugate demonstrated a 1- and 2.3-fold increase in half-life, respectively, compared to the release half-life of the nitric oxide-donor prodrug JS-K. When administered to tumor-bearing nude mice, the subcutaneously injected multi-arm polymer nitric oxide nanoparticles resulted in 50% tumor inhibition and a 7-week extension of the average survival time, compared to intravenous JS-K therapy. In summary, we have developed an effective nitric oxide anti-cancer chemotherapy that could be administered regionally to provide the local disease control, improving prognosis for head and neck cancers.

Nitrosothiol Signaling in Anoikis Resistance and Cancer Metastasis

Nitric oxide (NO) has been widely recognized as an important cell-signaling molecule that regulates various physiological and pathological processes. S-nitrosylation, or covalent attachment of NO to protein sulfhydryl groups, is a key mechanism by which NO regulates protein functions and cellular processes. In this article we discuss the various roles of NO and protein nitrosylation in cancer development, with a focus on cell invasion and anoikis resistance, both of which are key determinants of cancer metastasis. We specially address some of the mechanisms by which NO-mediated S-nitrosylation modulates substrates that have putative effects on key steps of metastasis. We propose that nitrosothiol signaling is a key regulatory mechanism common to several pathways involved in cancer progression and metastasis, and identifying such a mechanism will improve our understanding of the disease process and aid in the development of novel anticancer therapeutics.

Protective effect of Glycine max and Chrysanthemum indicum extracts against cisplatin-induced renal epithelial cell death

Although cisplatin is one of the most efficient chemotherapeutic agents for the treatment of solid tumors, frequently observed nephrotoxicity has limited its use in several patients.

MATERIALS AND METHODS

The protective effect of Glycine max (GM) and Chrysanthemum indicum (CM) extracts on cisplatin-induced apoptosis in human proximal tubular HK-2 cells was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), Hoechst 33342, and propidium iodide assays. Reactive oxygen species (ROS) were determined by flow cytometry with 2,7-dichlorofluorescein diacetate (DCFH(2)-DA).

RESULTS

Cisplatin-induced renal cell toxicity through the induction of hydrogen peroxide (H(2)O(2)) and hydroxyl radical (OH(•-)). CM extract protected cisplatin-induced apoptosis by its anti-oxidant activity against H(2)O(2) and OH(•-), while GM extract scavenged only H(2)O(2). Furthermore, GM and CM extracts protect renal cells without significant interfering effect on cisplatin toxicity in lung cancer H460 and melanoma G361 cells.

CONCLUSION

GM and CM extracts exhibited a promising protective effect on cisplatin-induced nephrotoxicity which could benefit the development for nephroprotective approaches.

A journey under the sea: the quest for marine anti-cancer alkaloids

The alarming increase in the global cancer death toll has fueled the quest for new effective anti-tumor drugs thorough biological screening of both terrestrial and marine organisms. Several plant-derived alkaloids are leading drugs in the treatment of different types of cancer and many are now being tested in various phases of clinical trials. Recently, marine-derived alkaloids, isolated from aquatic fungi, cyanobacteria, sponges, algae, and tunicates, have been found to also exhibit various anti-cancer activities including anti-angiogenic, anti-proliferative, inhibition of topoisomerase activities and tubulin polymerization, and induction of apoptosis and cytotoxicity. Two tunicate-derived alkaloids, aplidin and trabectedin, offer promising drug profiles, and are currently in phase II clinical trials against several solid and hematologic tumors. This review sheds light on the rich array of anti-cancer alkaloids in the marine ecosystem and introduces the most investigated compounds and their mechanisms of action.

Hydroxyl radical mediates cisplatin-induced apoptosis in human hair follicle dermal papilla cells and keratinocytes through Bcl-2-dependent mechanism

Induction of massive apoptosis of hair follicle cells by chemotherapy has been implicated in the pathogenesis of chemotherapy-induced alopecia (CIA), but the underlying mechanisms of regulation are not well understood. The present study investigated the apoptotic effect of cisplatin in human hair follicle dermal papilla cells and HaCaT keratinocytes, and determined the identity and role of specific reactive oxygen species (ROS) involved in the process. Treatment of the cells with cisplatin induced ROS generation and a parallel increase in caspase activation and apoptotic cell death. Inhibition of ROS generation by antioxidants inhibited the apoptotic effect of cisplatin, indicating the role of ROS in the process. Studies using specific ROS scavengers further showed that hydroxyl radical, but not hydrogen peroxide or superoxide anion, is the primary oxidative species responsible for the apoptotic effect of cisplatin. Electron spin resonance studies confirmed the formation of hydroxyl radicals induced by cisplatin. The mechanism by which hydroxyl radical mediates the apoptotic effect of cisplatin was shown to involve down-regulation of the anti-apoptotic protein Bcl-2 through ubiquitin-proteasomal degradation. Bcl-2 was also shown to have a negative regulatory role on hydroxyl radical. Together, our results indicate an essential role of hydroxyl radical in cisplatin-induced cell death of hair follicle cells through Bcl-2 regulation. Since CIA is a major side effect of cisplatin and many other chemotherapeutic agents with no known effective treatments, the knowledge gained from this study could be useful in the design of preventive treatment strategies for CIA through localized therapy without compromising the chemotherapy efficacy.

FKBP38-Bcl-2 interaction: a novel link to chemoresistance

FKBP38, a noncanonical member of the immunosuppressive drug FK506 binding protein (FKBP) family members, possesses an inducible rotamase. FKBP38 interacts with several proteins and regulates multiple signaling pathways such as cell survival, apoptosis, proliferation, and metastasis. Deregulation of apoptosis is associated with chemoresistance and tumor relapse. The antiapoptotic protein Bcl-2 is a key player for increasing the apoptotic threshold in response to various cytotoxic drugs. The molecular interaction of Bcl-2 with FKBP38 potentiates the biological function of Bcl-2 and contributes to tumorigenesis and chemoresistance. Here, we discuss recent advances in the role of FKBP38 in connection with Bcl-2 and its possible link to chemotherapeutic resistance.

Synthesis and Evaluation of the α-D-/α-L-Rhamnosyl and Amicetosyl Digitoxigenin Oligomers as Anti-tumor Agents

A highly regio- and stereo-selective asymmetric synthesis of rhamnosyl- and amicetosyl-digitoxigenin analogues has been established via palladium-catalyzed glycosylation followed by bis-/tris-dihydroxylation or bis-/tris-diimide reduction. The α-l-rhamnose and α-l-amicetose digitoxin monosaccharide analogues displayed stronger apoptosis inducing activity and cytotoxicity against non-small cell human lung cancer cells (NCI-H460) than its d-diastereomeric isomers in a sugar-chain length dependent manner.

C5'-Alkyl Substitution Effects on Digitoxigenin α-l-Glycoside Cancer Cytotoxicity

A highly regio- and stereo-selective asymmetric synthesis of various C5'-alkyl side chains of rhamnosyl- and amicetosyl-digitoxigenin analogs has been established via palladium-catalyzed glycosylation with post-glycosylated dihydroxylation or diimide reduction. The C5'-methyl group in both α-l-rhamnose and α-l-amicetose digitoxin analogs displayed a steric directed apoptosis induction and tumor growth inhibition against non-small cell human lung cancer cells (NCI-H460). The anti-tumor activity is significantly reduced when the steric hindrance is increased at C5'-stereocenter.

KiSS1 mediates platinum sensitivity and metastasis suppression in head and neck squamous cell carcinoma

Although surgery and radiotherapy have been the standard treatment modalities for head and neck squamous cell carcinoma (HNSCC), the integration of cisplatin (CDDP)-based therapy has led to improvements in local and regional control of disease for patients. However, many trials show that only 10-20% of patients benefit from this treatment intensification, which can result in profound treatment-associated morbidity and mortality. Moreover, the marginal survival improvement suggests that CDDP resistance is an innate characteristic of HNSCC. To elucidate the biological mechanisms underpinning CDDP resistance in HNSCC, we utilized an experimental model of CDDP resistance in this disease. We first observed significant enhancements in local tumor growth and metastasis, as well as adverse survival, in CDDP-resistant (CR) tumors compared with sensitive tumors. To elucidate the molecular mechanisms of this phenotype, we undertook a systems biology-based approach utilizing high-throughput PCR arrays, and we identified a significant suppression of KiSS1 mRNA and protein expression in the CR cells, but no significant regions of genomic loss with array comparative genomic hybridization. Genetic suppression of KiSS1 in CDDP-sensitive cell lines rendered them CR, an observation that was mechanistically linked to alterations in glutathione S-transferase-π expression and function. We next confirmed that, in human HNSCC tumors, loss of KiSS1 expression was associated with metastatic human HNSCC tumors compared with non-metastatic tumors. Genetic reconstitution of KiSS1 in CR cells abrogated cellular migration and induced CDDP sensitivity. To confirm these findings in a murine model, either CR or KiSS1-transfected CR cells were studied in an orthotopic model of HNSCC, or survival studies revealed significant improvement in survival of the mice bearing CR-KiSS1 tumors. Mechanistically, alterations in apoptotic pathways and CDDP metabolism contributed to KiSS1-associated chemotherapy sensitization. These studies provided further direct evidence for the role of KiSS1 loss in biologically aggressive HNSCC and suggest potential targets for therapy in CR cancers.

Activation of GluR6-containing kainate receptors induces ubiquitin-dependent Bcl-2 degradation via denitrosylation in the rat hippocampus after kainate treatment

We previously showed that Bcl-2 (B-cell lymphoma 2) is down-regulated in a kainate (KA)-induced rat epileptic seizure model. The underlying mechanism had remained largely unknown, but we here report for the first time that denitrosylation and ubiquitination are involved. Our results show that the S-nitrosylation levels of Bcl-2 are down-regulated after KA injection and that the GluR6 (glutamate receptor 6) antagonist NS102 can inhibit the denitrosylation of Bcl-2. Moreover, the ubiquitin-dependent degradation of Bcl-2 was found to be promoted after KA treatment, which could be suppressed by the proteasome inhibitor MG132 and the NO donors, sodium nitroprusside and S-nitrosoglutathione. In addition, experiments based on siRNA transfections were performed in the human SH-SY5Y neuroblastoma cell line to verify that the stability of Bcl-2 is causal to neuronal survival. At the same time, it was found that the exogenous NO donor GSNO could protect neurons when Bcl-2 is targeted. Subsequently, these mechanisms were morphologically validated by immunohistochemistry, cresyl violet staining, and in situ TUNEL staining to analyze the expression of Bcl-2 as well as the survival of CA1 and CA3/DG pyramidal neurons. NS102, GSNO, sodium nitroprusside, and MG132 contribute to the survival of CA1 and CA3/DG pyramidal neurons by attenuating Bcl-2 denitrosylation. Taken together, our data reveal that Bcl-2 ubiquitin-dependent degradation is induced by Bcl-2 denitrosylation during neuronal apoptosis after KA treatment.

The nitric oxide prodrug JS-K is effective against non-small-cell lung cancer cells in vitro and in vivo: involvement of reactive oxygen species

Non-small-cell lung cancer is among the most common and deadly forms of human malignancies. Early detection is unusual, and there are no curative therapies in most cases. Diazeniumdiolate-based nitric oxide (NO)-releasing prodrugs are a growing class of promising NO-based therapeutics. Here, we show that O(2)-(2,4-dinitrophenyl)-1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K) is a potent cytotoxic agent against a subset of human non-small-cell lung cancer cell lines both in vitro and as xenografts in mice. JS-K treatment led to 75% reduction in the growth of H1703 lung adenocarcinoma cells in vivo. Differences in sensitivity to JS-K in different lung cancer cell lines seem to be related to their endogenous levels of reactive oxygen species (ROS)/reactive nitrogen species (RNS). Other related factors, levels of peroxiredoxin 1 (PRX1) and 8-oxo-deoxyguanosine glycosylase (OGG1), also correlated with drug sensitivity. Treatment of the lung adenocarcinoma cells with JS-K resulted in oxidative/nitrosative stress in cells with high basal levels of ROS/RNS, which, combined with the arylating properties of the compound, was reflected in glutathione depletion and alteration in cellular redox potential, mitochondrial membrane permeabilization, and cytochrome c release. Inactivation of manganese superoxide dismutase by nitration was associated with increased superoxide and significant DNA damage. Apoptosis followed these events. Taken together, the data suggest that diazeniumdiolate-based NO-releasing prodrugs may have application as a personalized therapy for lung cancers characterized by high levels of ROS/RNS. PRX1 and OGG1 proteins, which can be easily measured, could function as biomarkers for identifying tumors sensitive to the therapy.

Tumor and host factors that may limit efficacy of chemotherapy in non-small cell and small cell lung cancer

While chemotherapy provides useful palliation, advanced lung cancer remains incurable since those tumors that are initially sensitive to therapy rapidly develop acquired resistance. Resistance may arise from impaired drug delivery, extracellular factors, decreased drug uptake into tumor cells, increased drug efflux, drug inactivation by detoxifying factors, decreased drug activation or binding to target, altered target, increased damage repair, tolerance of damage, decreased proapoptotic factors, increased antiapoptotic factors, or altered cell cycling or transcription factors. Factors for which there is now substantial clinical evidence of a link to small cell lung cancer (SCLC) resistance to chemotherapy include MRP (for platinum-based combination chemotherapy) and MDR1/P-gp (for non-platinum agents). SPECT MIBI and Tc-TF scanning appears to predict chemotherapy benefit in SCLC. In non-small cell lung cancer (NSCLC), the strongest clinical evidence is for taxane resistance with elevated expression or mutation of class III beta-tubulin (and possibly alpha tubulin), platinum resistance and expression of ERCC1 or BCRP, gemcitabine resistance and RRM1 expression, and resistance to several agents and COX-2 expression (although COX-2 inhibitors have had minimal impact on drug efficacy clinically). Tumors expressing high BRCA1 may have increased resistance to platinums but increased sensitivity to taxanes. Limited early clinical data suggest that chemotherapy resistance in NSCLC may also be increased with decreased expression of cyclin B1 or of Eg5, or with increased expression of ICAM, matrilysin, osteopontin, DDH, survivin, PCDGF, caveolin-1, p21WAF1/CIP1, or 14-3-3sigma, and that IGF-1R inhibitors may increase efficacy of chemotherapy, particularly in squamous cell carcinomas. Equivocal data (with some positive studies but other negative studies) suggest that NSCLC tumors with some EGFR mutations may have increased sensitivity to chemotherapy, while K-ras mutations and expression of GST-pi, RB or p27kip1 may possibly confer resistance. While limited clinical data suggest that p53 mutations are associated with resistance to platinum-based therapies in NSCLC, data on p53 IHC positivity are equivocal. To date, resistance-modulating strategies have generally not proven clinically useful in lung cancer, although small randomized trials suggest a modest benefit of verapamil and related agents in NSCLC.

Oxidative and nitrosative stress in the metastatic microenvironment

Metastases that are resistant to conventional therapies are the main cause of most cancer-related deaths in humans. Tumor cell heterogeneity, which associates with genomic and phenotypic instability, represents a major problem for cancer therapy. Additional factors, such as the attack of immune cells or organ-specific microenvironments, also influence metastatic cell behavior and the response to therapy. Interaction of cancer and endothelial cells in capillary beds, involving mechanical contact and transient adhesion, is a critical step in the initiation of metastasis. This interaction initiates a cascade of activation pathways that involves cytokines, growth factors, bioactive lipids and reactive oxygen and nitrogen species (ROS and RNS) produced by either the cancer cell or the endothelium. Vascular endothelium-derived NO and H₂O₂ are cytotoxic for the cancer cells, but also help to identify some critical molecular targets that appear essential for survival of invasive metastatic cell subsets. Surviving cancer cells that extravasate and start colonization of an organ or tissue can still be attacked by macrophages and be influenced by specific intraorgan microenvironment conditions. At all steps; from the primary tumor until colonization of a distant organ; metastatic cells undergo a dynamic process of constant adaptations that may lead to the survival of highly resistant malignant cell subsets. In this sequence of molecular events both ROS and RNS play key roles.

FKBP38 protects Bcl-2 from caspase-dependent degradation

The cellular processes that regulate Bcl-2 at the posttranslational levels are as important as those that regulate bcl-2 synthesis. Previously we demonstrated that the suppression of FK506-binding protein 38 (FKBP38) contributes to the instability of Bcl-2 or leaves Bcl-2 unprotected from degradation in an unknown mechanism. Here, we studied the underlying molecular mechanism mediating this process. We first showed that Bcl-2 binding-defective mutants of FKBP38 fail to accumulate Bcl-2 protein. We demonstrated that the FKBP38-mediated Bcl-2 stability is specific as the levels of other anti-apoptotic proteins such as Bcl-X(L) and Mcl-1 remained unaffected. FKBP38 enhanced the Bcl-2 stability under the blockade of de novo protein synthesis, indicating it is posttranslational. We showed that the overexpression of FKBP38 attenuates reduction rate of Bcl-2, thus resulting in an increment of the intracellular Bcl-2 level, contributing to the resistance of apoptotic cell death induced by the treatment of kinetin riboside, an anticancer drug. Caspase inhibitors markedly induced the accumulation of Bcl-2. In caspase-3-activated cells, the knockdown of endogenous FKBP38 by small interfering RNA resulted in Bcl-2 down-regulation as well, which was significantly recovered by the treatment with caspase inhibitors or overexpression of FKBP38. Finally we presented that the Bcl-2 cleavage by caspase-3 is blocked when Bcl-2 binds to FKBP38 through the flexible loop. Taken together, these results suggest that FKBP38 is a key player in regulating the function of Bcl-2 by antagonizing caspase-dependent degradation through the direct interaction with the flexible loop domain of Bcl-2, which contains the caspase cleavage site.

Protein denitrosylation: enzymatic mechanisms and cellular functions

S-Nitrosylation, the redox-based modification of Cys thiol side chains by nitric oxide, is a common mechanism in signal transduction. Dysregulated S-nitrosylation contributes to a range of human pathologies. New roles for protein denitrosylation in regulating S-nitrosylation are being revealed. Recently, several denitrosylases - the enzymes that mediate Cys denitrosylation - have been discovered, of which two enzyme systems in particular, the S-nitrosoglutathione reductase and thioredoxin systems, have been shown to be physiologically relevant. These highly conserved enzymes regulate signalling through multiple classes of receptors and influence diverse cellular responses. In addition, they protect from nitrosative stress in microorganisms, mammals and plants, thereby exerting profound effects on host-microbe interactions and innate immunity.

Protein S-nitrosylation in health and disease: a current perspective

Protein S-nitrosylation constitutes a large part of the ubiquitous influence of nitric oxide on cellular signal transduction and accumulating evidence indicates important roles for S-nitrosylation both in normal physiology and in a broad spectrum of human diseases. Here we review recent findings that implicate S-nitrosylation in cardiovascular, pulmonary, musculoskeletal and neurological (dys)function, as well as in cancer. The emerging picture shows that, in many cases, pathophysiology correlates with hypo- or hyper-S-nitrosylation of specific protein targets rather than a general cellular insult due to loss of or enhanced nitric oxide synthase activity. In addition, it is increasingly evident that dysregulated S-nitrosylation can not only result from alterations in the expression, compartmentalization and/or activity of nitric oxide synthases, but can also reflect a contribution from denitrosylases, including prominently the S-nitrosoglutathione (GSNO)-metabolizing enzyme GSNO reductase. Finally, because exogenous mediators of protein S-nitrosylation or denitrosylation can substantially affect the development or progression of disease, potential therapeutic agents that modulate S-nitrosylation could well have broad clinical utility.

Nitric oxide regulates lung carcinoma cell anoikis through inhibition of ubiquitin-proteasomal degradation of caveolin-1

Anoikis, a detachment-induced apoptosis, is a principal mechanism of inhibition of tumor cell metastasis. Tumor cells can acquire anoikis resistance which is frequently observed in metastatic lung cancer. This phenomenon becomes an important obstacle of efficient cancer therapy. Recently, signaling mediators such as caveolin-1 (Cav-1) and nitric oxide (NO) have garnered attention in metastasis research; however, their role and the underlying mechanisms of metastasis regulation are largely unknown. Using human lung carcinoma H460 cells, we show that NO impairs the apoptotic function of the cells after detachment. The NO donors sodium nitroprusside and diethylenetriamine NONOate inhibit detachment-induced apoptosis, whereas the NO inhibitors aminoguanidine and 2-(4-carboxyphenyl) tetramethylimidazoline-1-oxyl-3-oxide promote this effect. Resistance to anoikis in H460 cells is mediated by Cav-1, which is significantly down-regulated after cell detachment through a non-transcriptional mechanism involving ubiquitin-proteasomal degradation. NO inhibits this down-regulation by interfering with Cav-1 ubiquitination through a process that involves protein S-nitrosylation, which prevents its proteasomal degradation and induction of anoikis by cell detachment. These findings indicate a novel pathway for NO regulation of Cav-1, which could be a key mechanism of anoikis resistance in tumor cells.

Cyanide-induced death of dopaminergic cells is mediated by uncoupling protein-2 up-regulation and reduced Bcl-2 expression

Cyanide is a potent inhibitor of mitochondrial oxidative metabolism and produces mitochondria-mediated death of dopaminergic neurons and sublethal intoxications that are associated with a Parkinson-like syndrome. Cyanide toxicity is enhanced when mitochondrial uncoupling is stimulated following up-regulation of uncoupling protein-2 (UCP-2). In this study, the role of a pro-survival protein, Bcl-2, in cyanide-mediated cell death was determined in a rat dopaminergic immortalized mesencephalic cell line (N27 cells). Following pharmacological up-regulation of UCP-2 by treatment with Wy14,643, cyanide reduced cellular Bcl-2 expression by increasing proteasomal degradation of the protein. The increased turnover of Bcl-2 was mediated by an increase of oxidative stress following UCP-2 up-regulation. The oxidative stress involved depletion of mitochondrial glutathione (mtGSH) and increased H2O2 generation. Repletion of mtGSH by loading cells with glutathione ethyl ester reduced H2O2 generation and in turn blocked the cyanide-induced decrease of Bcl-2. To determine if UCP-2 mediated the response, RNAi knock down was conducted. The RNAi decreased cyanide-induced depletion of mtGSH, reduced H2O2 accumulation, and inhibited down-regulation of Bcl-2, thus blocking cell death. To confirm the role of Bcl-2 down-regulation in the cell death, it was shown that over-expression of Bcl-2 by cDNA transfection attenuated the enhancement of cyanide toxicity after UCP-2 up-regulation. It was concluded that UCP-2 up-regulation sensitizes cells to cyanide by increasing cellular oxidative stress, leading to an increase of Bcl-2 degradation. Then the reduced Bcl-2 levels sensitize the cells to cyanide-mediated cell death.

Cisplatin-induced nitrosylation of p53 prevents its mitochondrial translocation

The cellular response to DNA damage has been reported to involve rapid transcription-independent translocation of p53 to mitochondria. We show here that the DNA-damaging cisplatin-derived anticancer agent oxaliplatin induced both mitochondrial translocation and subsequent Bcl-xL interaction, whereas cisplatin did neither. The differential response was due to nitrosative modification of p53. Thus, cisplatin, but not oxaliplatin, induced increased expression of inducible nitric oxide synthase (iNOS). Cisplatin treatment in the presence of an iNOS inhibitor (1400W) allowed p53 mitochondrial translocation. Conversely, oxaliplatin-induced translocation of p53 was prevented by cotreatment with an exogenous NO donor. In cisplatin-treated cells, nuclear but not mitochondrial p53 showed nitrotyrosinylation that was inhibitable by 1400W. We conclude that nitrosative protein modification is more prominent in the response to cisplatin than oxaliplatin and that nitrosative modification of p53 is a major determinant of p53 subcellular location.

The role of Bcl-x(L) protein in nucleotide excision repair-facilitated cell protection against cisplatin-induced apoptosis

Many anticancer drugs target the genomic DNA of cancer cells by generating DNA damage and inducing apoptosis. DNA repair protects cells against DNA damage-induced apoptosis. Although the mechanisms of DNA repair and apoptosis have been extensively studied, the mechanism by which DNA repair prevents DNA damage-induced apoptosis is not fully understood. We studied the role of the antiapoptotic Bcl-x(L) protein in nucleotide excision repair (NER)-facilitated cell protection against cisplatin-induced apoptosis. Using both normal human fibroblasts (NF) and NER-defective xeroderma pigmentosum group A (XPA) and group G (XPG) fibroblasts, we demonstrated that a functional NER is required for cisplatin-induced transcription of the bcl-x(l) gene. The results obtained from our Western blots revealed that the cisplatin treatment led to an increase in the level of Bcl-x(L) protein in NF cells, but a decrease in the level of Bcl-x(L) protein in both XPA and XPG cells. The results of our immunofluorescence staining indicated that a functional NER pathway was required for cisplatin-induced translocation of NF-kappaB p65 from cytoplasm into nucleus, indicative of NF-kappaB activation. Given the important function of NF-kappaB in regulating transcription of the bcl-x(l) gene and the Bcl-x(L) protein in preventing apoptosis, these results suggest that NER may protect cells against cisplatin-induced apoptosis by activating NF-kappaB, which further induces transcription of the bcl-x(l) gene, resulting in an accumulation of Bcl-x(L) protein and activation of the cell survival pathway that leads to increased cell survival under cisplatin treatment.

The role of the ubiquitin proteasome system in ischemia and ischemic tolerance

Ubiquitin modification targets a protein for rapid degradation by the proteasome. However, polyubiquitination of proteins can result in multiple functions depending on the topology of the ubiquitin chain. Therefore, ubiquitin signaling offers a more complex and versatile biology compared with many other posttranslational modifications. One area of potential for the application of this knowledge is the field of ischemia-induced brain damage, as occurs following a stroke. The ubiquitin proteasome system may exert a dual role on neuronal outcome following ischemia. Harmful ischemia results in an overload of the ubiquitin proteasome system, and blocking the proteasome reduces brain infarction following ischemia. However, the rapid and selective degradation of proteins following brief ischemia results in endogenous protection against ischemia. Therefore, further understanding of the molecular signaling mechanisms that regulate the ubiquitin proteasome system may reveal novel therapeutic targets to reduce brain damage when ischemia is predicted or reduce the activation of the cell death mechanisms and the inflammatory response following stroke. The aim of this review is to discuss some of the recent advances in the understanding of protein ubiquitination and its implications for novel stroke therapies.

Detection of protein S-nitrosylation with the biotin-switch technique

Protein S-nitrosylation, the posttranslational modification of cysteine thiols to form S-nitrosothiols, is a principle mechanism of nitric oxide-based signaling. Studies have demonstrated myriad roles for S-nitrosylation in organisms from bacteria to humans, and recent efforts have greatly advanced our scientific understanding of how this redox-based modification is dynamically regulated during physiological and pathophysiological conditions. The focus of this review is the biotin-switch technique (BST), which has become a mainstay assay for detecting S-nitrosylated proteins in complex biological systems. Potential pitfalls and modern adaptations of the BST are discussed, as are future directions for this assay in the burgeoning field of protein S-nitrosylation.

Superoxide-mediated proteasomal degradation of Bcl-2 determines cell susceptibility to Cr(VI)-induced apoptosis

Hexavalent chromium [Cr(VI)] compounds are redox cycling environmental carcinogens that induce apoptosis as the primary mode of cell death. Defects in apoptosis regulatory mechanisms contribute to carcinogenesis induced by Cr(VI). Activation of apoptosis signaling pathways is tightly linked with the generation of reactive oxygen species (ROS). Likewise, ROS have been implicated in the regulation of Cr(VI)-induced apoptosis and carcinogenicity; however, its role in Cr(VI)-induced apoptosis and the underlying mechanism are largely unknown. We report that ROS, specifically superoxide anion (.O(-)(2), mediates Cr(VI)-induced apoptosis of human lung epithelial H460 cells. H460 rho(0) cells that lack mitochondrial DNA demonstrated a significant decrease in ROS production and apoptotic response to Cr(VI), indicating the involvement of mitochondrial ROS in Cr(VI)-induced apoptosis. In agreement with this observation, we found that Cr(VI) induces apoptosis mainly through the mitochondrial death pathway via caspase-9 activation, which is negatively regulated by the antiapoptotic protein Bcl-2. Furthermore, .O(-)(2) induced apoptosis in response to Cr(VI) exposure by downregulating and degrading Bcl-2 protein through the ubiquitin-proteasomal pathway. This study reveals a novel mechanism linking .O(-)(2) with Bcl-2 stability and provides a new dimension to ROS-mediated Bcl-2 downregulation and apoptosis induction.

Dependence of reactive oxygen species and FLICE inhibitory protein on lipofectamine-induced apoptosis in human lung epithelial cells

Cationic liposomes such as lipofectamine (LF) are widely used as nonviral gene delivery vectors; however, their clinical application is limited by their cytotoxicity. These agents have been shown to induce apoptosis as the primary mode of cell death, but their mechanism of action is not well understood. The present study investigated the mechanism of LF-induced apoptosis and examined the role of reactive oxygen species (ROS) in this process. We found that LF induced apoptosis of human epithelial H460 cells through a mechanism that involves caspase activation and ROS generation. Inhibition of caspase activity by pan-caspase inhibitor (z-VAD-fmk) or by specific caspase-8 inhibitor (z-IETD-fmk) or caspase-9 inhibitor (z-LEHD-fmk) inhibited the apoptotic effect of LF. Overexpression of FLICE-inhibitory protein (FLIP) or B-cell lymphoma-2, which are known inhibitors of the extrinsic and intrinsic death pathways, respectively, similarly inhibited apoptosis by LF. Induction of apoptosis by LF was shown to require ROS generation because its inhibition by ROS scavengers or by ectopic expression of antioxidant enzyme superoxide dismutase and glutathione peroxidase strongly inhibited the apoptotic effect of LF. Electron spin resonance studies showed that LF induced multiple ROS; however, superoxide was found to be the primary ROS responsible for LF-induced apoptosis. The mechanism by which ROS mediate the apoptotic effect of LF involves down-regulation of FLIP through the ubiquitination pathway. In demonstrating the role of FLIP and ROS in LF death signaling, we document a novel mechanism of apoptosis regulation that may be exploited to decrease cytotoxicity and increase gene transfection efficiency of cationic liposomes.

Nitric oxide-induced resistance or sensitization to death in tumor cells

This report summarizes the present state of our knowledge pertaining to the NO-induced resistance or sensitization of tumor cell death. The effects of NO and its synergy with members of the TNF family, with cytotoxic drugs, and with ionizing radiations have been investigated. The dual effect of NO-induced resistance or sensitization and the underlying molecular mechanisms are discussed.

Role of S-nitrosylation in apoptosis resistance and carcinogenesis

Nitric oxide (NO) has been widely recognized as a positive regulator of tumorigenesis and cancer progression through its ability to regulate important proteins in various signal transduction pathways. S-Nitrosylation, or covalent attachment of NO to protein sulphydryl groups, has gained prominence as an important mechanism by which NO modulates physiologic and pathologic cellular responses. In this article, we discuss S-nitrosylation of two key apoptosis-regulatory proteins of the intrinsic and extrinsic death pathways, namely B-cell lymphoma-2 (Bcl-2) and FLICE-inhibitory protein (FLIP). These proteins have been shown to be upregulated in a variety of tumors and have been implicated with cancer chemoresistance through dysregulation of apoptosis. S-Nitrosylation of these proteins precludes their ubiquitination and subsequent degradation by the proteasome, thus accentuating their anti-apoptotic effect which is critical in the context of tumorigenic potential and cancer progression. We propose that such post-translational modifications of proteins by NO may be a general mechanism that tumor cells exploit to tilt the scales towards survival and proliferation by evading cell death.

Post-translational modifications induced by nitric oxide (NO): implication in cancer cells apoptosis

Post-translational modifications of proteins can regulate the balance between survival and cell death signals. It is increasingly recognized that nitric oxide (NO) and reactive oxygen species (ROS)-induced post-translational modifications could play a role in cell death. This review provides an introduction of current knowledge of NO proteins modifications promoting or inhibiting cell death with special attention in cancer cells.

Effect of artemisinins and other endoperoxides on nitric oxide-related signaling pathway in RAW 264.7 mouse macrophage cells

Artemisinin is the active principle of the Chinese herb Artemisia annua L. In addition to its anti-malarial activity, artemisinin and its derivatives have been shown to exert profound anti-cancer activity. The endoperoxide moiety in the chemical structure of artemisinin is thought to be responsible for the bioactivity. Here, we analyzed the cytotoxicity and the ability of artemisinin, five of its derivatives, and two other endoperoxides to inhibit generation of nitric oxide (NO). In the RAW 264.7 mouse macrophage cell line, the well-established model cell line to analyze NO generation, artesunate revealed the highest ability to inhibit NO production among all compounds tested. In cytotoxicity assays (XTT assay), the IC(50) value of RAW 264.7 cells for artesunate was determined to be 3.1+/-0.7 microM. In order to associate the cytotoxic effects with specific alteration in gene expression related to NO metabolism and signaling, whole genome mRNA microarray analyses were conducted. RAW 264.7 cells were treated with artesunate using DMSO as vehicle control followed by microarray analysis. A total of 36 genes related to NO metabolism and signaling were found to be differentially expressed upon exposure to artesunate. Apart from NO-related genes, the expression of genes associated with other functional groups was also analyzed. Out of 24 functional groups, differential expression was most prominent in genes involved in cell-to-cell signaling and interactions. Further refinement of this analysis showed that the pathways for cAMP-mediated signaling and Wnt/beta-catenin signaling were most closely related to changes in mRNA expression. In conclusion, NO generation and signaling play a role in exhibiting cytotoxic activity of artesunate. In addition, other signaling pathways also contribute to the inhibitory effect of artesunate towards RAW 264.7 cells pointing to a multi-factorial mode of action of artesunate.

Peroxide is a key mediator of Bcl-2 down-regulation and apoptosis induction by cisplatin in human lung cancer cells

Susceptibility to apoptosis is an essential prerequisite for successful eradication of tumor cells by chemotherapy. Consequently, resistance to apoptosis has been established as one of the mechanisms responsible for the failure of therapeutic approaches in many types of cancers. In the present study, we investigated the susceptibility of human lung cancer H460 cells to apoptotic cell death induced by cisplatin and determined its regulatory mechanisms. Treatment of the cells with cisplatin induced rapid generation of multiple oxidative species and a concomitant increase in apoptotic cell death. Apoptosis induced by cisplatin was mediated through the mitochondrial death pathway, which requires caspase-9 activation and is regulated by Bcl-2. Cisplatin induced down-regulation of Bcl-2 through a process that involves dephosphorylation and ubiquitination of the protein, which facilitates its degradation by proteasome. This down-regulation was inhibited by antioxidant enzymes catalase and glutathione peroxidase (H(2)O(2) scavenger), but not by superoxide dismutase (O(2)(.) scavenger) or deferoxamine (OH. inhibitor). Electron spin resonance and flow cytometric analyses showed the formation of H(2)O(2) along with O(2)(.) and OH. radicals after cisplatin treatment. H(2)O(2) was generated in part by dismutation of O(2)(.) and served as a precursor for OH.. Together, our results indicate an essential role of H(2)O(2) in the regulation of Bcl-2 and apoptotic cell death induced by cisplatin. Because aberrant expression of Bcl-2 has been associated with death resistance of cancer cells to chemotherapy, the results of this study could be used to aid the design of more effective strategies for cancer treatment.

Ubiquitin-proteasome system as a modulator of cell fate

The ubiquitin-proteasome system is the major non-lysosymal system for degrading proteins in the cell; the work leading to its discovery was awarded the Nobel Prize in Chemistry in 2004. In addition to small ubiquitin-like modifiers (e.g. Sumo and Nedd8), ubiquitin is involved in the complex regulation of the levels and function of many proteins and signaling pathways involved in determining cell fate. The cell death regulatory proteins, such as Bcl-2 family proteins and caspases are targeted for degradation by the ubiquitin proteasome system (UPS). In addition to mediating the degradation of proteins, the UPS regulates function and translocation of proteins, many of which play a role in the determination of cell fate. For example the UPS can regulate the activity of transcription factors, such as P53, NF-kappaB and HIF-1 alpha, which control the expression of protein mediators of cell death. Aberrant UPS function has been reported in multiple neuropathologies including Parkinson's diseases and ischemia. With the number of ubiquitin conjugating and de-conjugating enzymes reaching close to the levels of protein kinases and phosphatases, it is clear that ubiquitination is an important biological regulatory step for proteins.

Nitric oxide boosts chemoimmunotherapy via inhibition of acid sphingomyelinase in a mouse model of melanoma

Cisplatin is one of the most effective anticancer drugs, but its severe toxic effects, including depletion of immune-competent cells, limit its efficacy. We combined the systemic treatment with cisplatin with intratumor delivery of dendritic cells (DC) previously treated ex vivo with a pulse of nitric oxide (NO) released by the NO donors (z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]-diazen-1-ium-1,2-diolate or isosorbide dinitrate. We found that this chemoimmunotherapy, tested in the B16 mouse model of melanoma, was significantly more efficacious than cisplatin alone, leading to tumor regression and animal survival at low doses of cisplatin that alone had no effect. Tumor cure was not observed when combining cisplatin with DCs not exposed to NO donors, indicating the key role of the pretreatment with NO. We investigated the mechanisms responsible for the synergic effect of NO-treated DCs and cisplatin and found that NO-treated DCs were protected both in vitro and in vivo from cisplatin-induced cytotoxicity. Cisplatin triggered DC apoptosis through increased expression and activation of acid sphingomyelinase; pretreatment of DCs with NO donors prevented such activation and inhibited activation of the downstream proapoptotic events, including generation of ceramide, activation of caspases 3 and 9, and mitochondrial depolarization. The effects of NO were mediated through generation of its physiologic messenger, cyclic GMP. We conclude that NO and NO generating drugs represent promising tools to increase the efficacy of chemoimmunotherapies in vivo, promoting the survival and increasing the function of injected cells by targeting a key pathway in cisplatin-induced cytotoxicity.

Mechanisms of resistance to cisplatin and carboplatin

While cisplatin and carboplatin are active versus most common cancers, epithelial malignancies are incurable when metastatic. Even if an initial response occurs, acquired resistance due to mutations and epigenetic events limits efficacy. Resistance may be due to excess of a resistance factor, to saturation of factors required for tumor cell killing, or to mutation or alteration of a factor required for tumor cell killing. Platinum resistance could arise from decreased tumor blood flow, extracellular conditions, reduced platinum uptake, increased efflux, intracellular detoxification by glutathione, etc., decreased binding (e.g., due to high intracellular pH), DNA repair, decreased mismatch repair, defective apoptosis, antiapoptotic factors, effects of several signaling pathways, or presence of quiescent non-cycling cells. In lung cancer, flattening of dose-response curves at higher doses suggests that efficacy is limited by exhaustion of something required for cell killing, and several clinical observations suggest epigenetic events may play a major role in resistance.

EGF receptor activity modulates apoptosis induced by inhibition of the proteasome of vascular smooth muscle cells

The observation that intracellular protein turnover rates participate directly in cell viability led to the development and clinical use of potent proteasome inhibitors. This study determined that the mechanism of apoptosis that is induced by inhibition of the proteasome of vascular smooth muscle cells (VSMC) was related to the intracellular accumulation of Bad, a BH3-only member of the Bcl-2 family of apoptosis regulators. Experiments confirmed that the apoptotic process was mitochondria- and caspase-dependent. Ubiquitination and accumulation of Bad in VSMC followed inhibition of the proteasome, and depletion of Bad using RNA interference prevented apoptosis that was induced by proteasome inhibition with PS-341. EGF receptor (EGFR) activation produced posttranslational modifications of Bad, providing the pro-survival signals that prevented apoptosis of smooth muscle cells during proteasome inhibition. Antagonists of the EGFR potentiated the apoptotic rate. In summary, the activities of the EGFR and the proteasome focused on Bad and the intrinsic apoptotic pathway and were involved integrally in determining viability of VSMC. These findings might prove useful in the management of diseases in which proliferation of vascular smooth muscle cells plays a central role.

Reactive oxygen species mediate caspase activation and apoptosis induced by lipoic acid in human lung epithelial cancer cells through Bcl-2 down-regulation

The antioxidant alpha-lipoic acid (LA) is a naturally occurring compound that has been shown to possess promising anticancer activity because of its ability to preferentially induce apoptosis and inhibit proliferation of cancer cells relative to normal cells. However, the molecular mechanisms underlying the apoptotic effect of LA are not well understood. We report here that LA induced reactive oxygen species (ROS) generation and a concomitant increase in apoptosis of human lung epithelial cancer H460 cells. Inhibition of ROS generation by ROS scavengers or by overexpression of antioxidant enzymes glutathione peroxidase and superoxide dismutase effectively inhibited LA-induced apoptosis, indicating the role of ROS, especially hydroperoxide and superoxide anion, in the apoptotic process. Apoptosis induced by LA was found to be mediated through the mitochondrial death pathway, which requires caspase-9 activation. Inhibition of caspase activity by the pan-caspase inhibitor (z-VAD-FMK) or caspase-9-specific inhibitor (z-LEHD-FMK) completely inhibited the apoptotic effect of LA. Likewise, the mitochondrial respiratory chain inhibitor rotenone potently inhibited the apoptotic and ROS-inducing effects of LA, supporting the role of mitochondrial ROS in LA-induced cell death. LA induced down-regulation of mitochondrial Bcl-2 protein through peroxide-dependent proteasomal degradation, and overexpression of the Bcl-2 protein prevented the apoptotic effect of LA. Together, our findings indicate a novel pro-oxidant role of LA in apoptosis induction and its regulation by Bcl-2, which may be exploited for the treatment of cancer and related apoptosis disorders.

S-nitrosylation of Bcl-2 inhibits its ubiquitin-proteasomal degradation. A novel antiapoptotic mechanism that suppresses apoptosis

Bcl-2 is a key apoptosis regulatory protein of the mitochondrial death pathway whose function is dependent on its expression levels. Although Bcl-2 expression is controlled by various mechanisms, post-translational modifications, such as ubiquitination and proteasomal degradation, have emerged as important regulators of Bcl-2 function. However, the underlying mechanisms of this regulation are unclear. We report here that Bcl-2 undergoes S-nitrosylation by endogenous nitric oxide (NO) in response to multiple apoptotic mediators and that this modification inhibits ubiquitin-proteasomal degradation of Bcl-2. Inhibition of NO production by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and by NO synthase inhibitor aminoguanidine effectively inhibited S-nitrosylation of Bcl-2, increased its ubiquitination, and promoted apoptotic cell death induced by chromium (VI). In contrast, the NO donors dipropylenetriamine NONOate and sodium nitroprusside showed opposite effects. The effect of NO on Bcl-2 stability was shown to be independent of its dephosphorylation. Mutational analysis of Bcl-2 further showed that the two cysteine residues of Bcl-2 (Cys158 and Cys229) are important in the S-nitrosylation process and that mutations of these cysteines completely inhibited Bcl-2 S-nitrosylation. Treatment of the cells with other stress inducers, including Fas ligand and buthionine sulfoxide, also induced Bcl-2 S-nitrosylation, suggesting that this is a general phenomenon that regulates Bcl-2 stability and function under various stress conditions. These findings indicate a novel function of NO and its regulation of Bcl-2, which provides a key mechanism for the control of apoptotic cell death and cancer development.