Thioredoxin reductase mediates cell death effects of the combination of beta interferon and retinoic acid

4-Methylumbelliferone Targets Revealed by Public Data Analysis and Liver Transcriptome Sequencing

4-methylumbelliferone (4MU) is a well-known hyaluronic acid synthesis inhibitor and an approved drug for the treatment of cholestasis. In animal models, 4MU decreases inflammation, reduces fibrosis, and lowers body weight, serum cholesterol, and insulin resistance. It also inhibits tumor progression and metastasis. The broad spectrum of effects suggests multiple and yet unknown targets of 4MU. Aiming at 4MU target deconvolution, we have analyzed publicly available data bases, including: 1. Small molecule library Bio Assay screening (PubChemBioAssay); 2. GO pathway databases screening; 3. Protein Atlas Database. We also performed comparative liver transcriptome analysis of mice on normal diet and mice fed with 4MU for two weeks. Potential targets of 4MU public data base analysis fall into two big groups, enzymes and transcription factors (TFs), including 13 members of the nuclear receptor superfamily regulating lipid and carbohydrate metabolism. Transcriptome analysis revealed changes in the expression of genes involved in bile acid metabolism, gluconeogenesis, and immune response. It was found that 4MU feeding decreased the accumulation of the glycogen granules in the liver. Thus, 4MU has multiple targets and can regulate cell metabolism by modulating signaling via nuclear receptors.

The Skeleton and Biomineralization Mechanism as Part of the Innate Immune System of Stony Corals

Stony corals are among the most important calcifiers in the marine ecosystem as they form the coral reefs. Coral reefs have huge ecological importance as they constitute the most diverse marine ecosystem, providing a home to roughly a quarter of all marine species. In recent years, many studies have shed light on the mechanisms underlying the biomineralization processes in corals, as characterizing the calicoblast cell layer and genes involved in the formation of the calcium carbonate skeleton. In addition, considerable advancements have been made in the research field of coral immunity as characterizing genes involved in the immune response to pathogens and stressors, and the revealing of specialized immune cells, including their gene expression profile and phagocytosis capabilities. Yet, these two fields of corals research have never been integrated. Here, we discuss how the coral skeleton plays a role as the first line of defense. We integrate the knowledge from both fields and highlight genes and proteins that are related to biomineralization and might be involved in the innate immune response and help the coral deal with pathogens that penetrate its skeleton. In many organisms, the immune system has been tied to calcification. In humans, immune factors enhance ectopic calcification which causes severe diseases. Further investigation of coral immune genes which are involved in skeleton defense as well as in biomineralization might shed light on our understanding of the correlation and the interaction of both processes as well as reveal novel comprehension of how immune factors enhance calcification.

Prognostic roles of metabolic reprogramming-associated genes in patients with hepatocellular carcinoma

Metabolic reprogramming for adaptation to the tumor microenvironment is recognized as a hallmark of cancer. Although many altered metabolic genes have been reported to be associated with tumor pathological processes, systematic analysis of metabolic genes implicated in hepatocellular carcinoma prognosis remains rare. The aim of this study was to identify key metabolic genes related to hepatocellular carcinoma, and to explore their clinical significance. We downloaded mRNA expression profiles and clinical hepatocellular carcinoma data from The Cancer Genome Atlas database to explore the prognostic roles of metabolic genes. Five prognosis-associated metabolic genes, including POLA1, UCK2, ACYP1, ENTPD2, and TXNRD1, were screened via univariate Cox regression analysis and a LASSO Cox regression model, which divided patients into high- and low-risk groups. Furthermore, gene set enrichment analysis revealed that significantly-enriched gene ontology terms and pathways involving high-risk patients were focused on regulation of nucleic and fatty acid metabolism. Taken together, our study identified five metabolic genes related to survival, which can be used to predict the prognosis of patients with hepatocellular carcinoma. These genes may play essential roles in metabolic microenvironment regulation, and represent potentially important candidate targets in metabolic therapy.

Oxidants, Antioxidants and Thiol Redox Switches in the Control of Regulated Cell Death Pathways

It is well appreciated that biological reactive oxygen and nitrogen species such as hydrogen peroxide, superoxide and nitric oxide, as well as endogenous antioxidant systems, are important modulators of cell survival and death in diverse organisms and cell types. In addition, oxidative stress, nitrosative stress and dysregulated cell death are implicated in a wide variety of pathological conditions, including cancer, cardiovascular and neurological diseases. Therefore, much effort is devoted to elucidate the molecular mechanisms linking oxidant/antioxidant systems and cell death pathways. This review is focused on thiol redox modifications as a major mechanism by which oxidants and antioxidants influence specific regulated cell death pathways in mammalian cells. Growing evidence indicates that redox modifications of cysteine residues in proteins are involved in the regulation of multiple cell death modalities, including apoptosis, necroptosis and pyroptosis. In addition, recent research suggests that thiol redox switches play a role in the crosstalk between apoptotic and necrotic forms of regulated cell death. Thus, thiol-based redox circuits provide an additional layer of control that determines when and how cells die.

Cerebral mitochondrial electron transport chain dysfunction in multiple system atrophy and Parkinson's disease

Multiple system atrophy (MSA) is a neurodegenerative disease characterised by glial cytoplasmic inclusions (GCIs), containing α-synuclein. Mutated COQ2, encoding an enzyme essential for co-enzyme Q10 (CoQ10) biosynthesis, has been associated with MSA. CoQ10 is an electron carrier in the mitochondrial electron transport chain (ETC) and antioxidant. It has been shown to be deficient in MSA brain tissue, thus implicating mitochondrial dysfunction in MSA. To investigate mitochondrial dysfunction in MSA further we examined ETC activity in MSA and control brain tissue, compared with Parkinson's disease (PD) where mitochondrial dysfunction is known to be important. Using cerebellar and occipital white matter ETC complex I, II/III and IV activities were measured spectrophotometrically, selected individual components of the ETC were assessed by immunoblotting and cellular complex IV activity was analysed by enzyme histochemistry. We show decreased complex II/III activity with increased complex I and IV activity in MSA cerebellar white matter. This corresponds with the deficit in CoQ10 previously described in MSA and reflects the high regional pathological burden of GCIs. This study highlights mitochondrial dysfunction in MSA pathogenesis, suggests an influence on selective regional vulnerability to disease and points to shared disease mechanisms in α-synucleinopathies.

Redox regulation of protein kinase C by selenometabolites and selenoprotein thioredoxin reductase limits cancer prevention by selenium

The cancer-preventive mechanism of selenium should address the way low concentrations of selenometabolites react with cellular targets without being diffused from the sites of generation, the way selenium selectively kills tumor cells, and the intriguing U-shaped curve that is seen with dietary supplementation of selenium and cancer prevention. Protein kinase C (PKC), a receptor for tumor promoters, is well suited for this mechanism. Due to the catalytic redox cycle, low concentrations of methylselenol, a postulated active metabolite of selenium, react with the tumor-promoting lipid hydroperoxide bound to PKC to form methylseleninic acid (MSA), which selectively reacts with thiol residues present within the vicinity of the PKC catalytic domain to inactivate it. Given that lipid hydroperoxide levels are high in promoting cells, PKC inactivation selectively leads to death in these cells. A biphasic effect of MSA in inducing cell death was observed in certain prostate cancer cell lines; lower concentrations of MSA induced cell death, while higher concentrations failed to do so. Lower concentrations of selenium inactivate more sensitive antiapoptotic isoenzymes of PKC (ε and α), sparing less sensitive proapoptotic isoenzymes (PKCδ and PKCζ). Higher concentrations of selenium also inactivate proapoptotic isoenzymes and consequently make tumor cells resistant to apoptosis. Due to a high-affinity binding of thioredoxin to the PKC catalytic domain, this thiol oxidation is explicitly reversed by thioredoxin reductase (TXNRD), a selenoprotein. Therefore, overexpression of TXNRD in advanced tumor cells could make them resistant to selenium-induced death. Conceivably, this mechanism, at least in part, explains why selenium prevents cancer only in certain cases.

GRIM-19: A master regulator of cytokine induced tumor suppression, metastasis and energy metabolism

Cytokines induce cell proliferation or growth suppression depending on the context. It is increasingly becoming clear that success of standard radiotherapy and/or chemotherapeutics to eradicate solid tumors is dependent on IFN signaling. In this review we discuss the molecular mechanisms of tumor growth suppression by a gene product isolated in our laboratory using a genome-wide expression knock-down strategy. Gene associated with retinoid-IFN-induced mortality -19 (GRIM-19) functions as non-canonical tumor suppressor by antagonizing oncoproteins. As a component of mitochondrial respiratory chain, GRIM-19 influences the degree of "Warburg effect" in cancer cells as many advanced and/or aggressive tumors show severely down-regulated GRIM-19 levels. In addition, GRIM-19 appears to regulate innate and acquired immune responses in mouse models. Thus, GRIM-19 is positioned at nodes that favor cell protection and/or prevent aberrant cell growth.

Imbalance in Protein Thiol Redox Regulation and Cancer-Preventive Efficacy of Selenium

Although several experimental studies showed cancer-preventive efficacy of supplemental dietary selenium, human clinical trials questioned this efficacy. Identifying its molecular targets and mechanism is important in understanding this discrepancy. Methylselenol, the active metabolite of selenium, reacts with lipid hydroperoxides bound to protein kinase C (PKC) and is oxidized to methylseleninic acid (MSA). This locally generated MSA selectively inactivates PKC by oxidizing its critical cysteine sulfhydryls. The peroxidatic redox cycle occurring in this process may explain how extremely low concentrations of selenium catalytically modify specific membrane-bound proteins compartmentally separated from glutathione and selectively induce cytotoxicity in promoting cells. Mammalian thioredoxin reductase (TR) is itself a selenoenzyme with a catalytic selenocysteine residue. Together with thioredoxin (Trx), it catalyzes reduction of selenite and selenocystine by NADPH generating selenide which in the presence of oxygen redox cycles producing reactive oxygen species. Trx binds with high affinity to PKC and reverses PKC inactivation. Therefore, established tumor cells overexpressing TR and Trx may escape the cancer-preventive actions of selenium. This suggests that in some cases, certain selenoproteins may counteract selenometabolite actions. Lower concentrations of selenium readily inactivate antiapoptotic PKC isoenzymes e and a which have a cluster of vicinal thiols, thereby inducing apoptosis. Higher concentrations of selenium also inactivate proapoptotic enzymes such as proteolytically activated PKCd fragment, holo-PKCz, caspase-3, and c-Jun N-terminal kinase, which all have a limited number of critical cysteine residues and make tumor cells resistant to selenium-induced apoptosis. This may explain the intriguing U-shaped curve that is seen with dietary selenium intake and the extent of cancer prevention.

Decreased expression of GRIM-19 by DNA hypermethylation promotes aerobic glycolysis and cell proliferation in head and neck squamous cell carcinoma

To identify novel tumor suppressor genes that are down-regulated by promoter hypermethylation in head and neck squamous cell carcinoma (HNSCC), genome-wide methylation profiling was performed using a methylated DNA immunoprecipitation (MeDIP) array in HNSCC and normal mucosa tissue samples. Promoter hypermethylation of the candidate gene, gene associated with retinoid-interferon induced mortality-19 (GRIM-19), was confirmed in HNSCC cell lines. Multivariate regression analysis determined that GRIM-19 hypermethylation was an independent significant factor for HNSCC diagnosis (OR:125.562; P < 0.001). HNSCC patients with lower ratio of GRIM-19/ACTB hypermethylation had increased overall and disease free survival. Furthermore, the optimal cutoff provided 90% sensitivity and 77% specificity of GRIM-19 hypermethylation as a diagnostic marker for HNSCC. Ectopic expression of GRIM-19 in HNSCC cells led to increased oxygen consumption, reduced glycolysis and decreased cell proliferation. HNSCC cells ectopically expressing GRIM-19 displayed increased p53 activity as well as decreased Stat3 and HIF-1α activities. Moreover, GRIM-19 knockdown not only resulted in decreased oxygen consumption and increased aerobic glycolysis but also promoted cell proliferation and tumorigenic capacity in HNSCC cells. Our data indicate that decreased GRIM-19 expression due to promoter hypermethylation may be important in head and neck carcinogenesis by promoting cell proliferation and regulating metabolic activity.

Mutation in NDUFA13/GRIM19 leads to early onset hypotonia, dyskinesia and sensorial deficiencies, and mitochondrial complex I instability

Mitochondrial complex I (CI) deficiencies are causing debilitating neurological diseases, among which, the Leber Hereditary Optic Neuropathy and Leigh Syndrome are the most frequent. Here, we describe the first germinal pathogenic mutation in the NDUFA13/GRIM19 gene encoding a CI subunit, in two sisters with early onset hypotonia, dyskinesia and sensorial deficiencies, including a severe optic neuropathy. Biochemical analysis revealed a drastic decrease in CI enzymatic activity in patient muscle biopsies, and reduction of CI-driven respiration in fibroblasts, while the activities of complex II, III and IV were hardly affected. Western blots disclosed that the abundances of NDUFA13 protein, CI holoenzyme and super complexes were drastically reduced in mitochondrial fractions, a situation that was reproduced by silencing NDUFA13 in control cells. Thus, we established here a correlation between the first mutation yet identified in the NDUFA13 gene, which induces CI instability and a severe but slowly evolving clinical presentation affecting the central nervous system.

Unlocking the potential of retinoic acid in anticancer therapy

All-trans-retinoic acid (ATRA) is a physiologically active metabolite of vitamin A. Its antitumour activities have been extensively studied in a variety of model systems and clinical trials; however, to date the only malignancy responsive to ATRA treatment is acute promyelocytic leukaemia (APL) where it induces complete remission in the majority of cases when administered in combination with light chemotherapy and/or arsenic trioxide. After decades of studies, the efficacy of ATRA to treat other acute myeloid leukaemia (AML) subtypes and solid tumours remains poor. Recent studies directed to improve ATRA responsiveness in non-APL AML seem to indicate that the lack of effective ATRA response in these tumours may be primarily due to aberrant epigenetics, which negatively affect ATRA-regulated gene expression and its antileukaemic activity. Epigenetic reprogramming could potentially restore therapeutic effects of ATRA in all AML subtypes. This review discusses the current progresses in the understanding how ATRA can be utilised in the therapy of non-APL AML and other cancers.

Overexpression of nuclear apoptosis-inducing factor 1 altered the proteomic profile of human gastric cancer cell MKN45 and induced cell cycle arrest at G1/S phase

Nuclear apoptosis-inducing factor 1 (NAIF1) was previously reported to induce apoptosis. Moreover, the expression of NAIF1 was significantly down-regulated in human gastric cancer tissues compared to adjacent normal tissues. However, the mechanism by which the NAIF1 gene induces apoptosis is not fully understood. Our results show that NAIF1 was minimally expressed in all the tested gastric cancer cell lines. Our data also demonstrates that NAIF1 is localized in the nuclei of cells as detected by monitoring the green fluorescence of NAIF1-GFP fusion protein using fluorescent confocal microscopy. Next, a comparative proteomic approach was used to identify the differential expression of proteins between gastric cancer cell lines MKN45/NAIF1 (−) and MKN45/NAIF1 (+). We found five proteins (proteasome 26S subunit 2, proteasome 26S subunit 13, NADH dehydrogenase Fe-S protein 1, chaperonin containing TCP1 subunit 3 and thioredoxin reductase 1) that were up-regulated and three proteins (ribonuclease inhibitor 1, 14-3-3 protein epsilon isoform and apolipoprotein A-I binding protein) that were down-regulated in the MKN45 cells overexpressing NAIF1. We also discovered that NAIF1 could induce cell cycle arrest at G1/S phase by altering the expression of cell cycle proteins cyclinD1, cdc2 and p21. The differentially expressed proteins identified here are related to various cellular programs involving cell cycle, apoptosis, and signal transduction regulation and suggest that NAIF1 may be a tumor suppressor in gastric cancer. Our research provides evidence that elucidates the role of how NAIF1 functions in gastric cancer.

Regulation of snoRNAs in cancer: close encounters with interferon

The interferon (IFN) family of cytokines regulates many cellular processes, such as transcription, translation, post-translational modifications, and protein degradation. IFNs induce growth inhibition and/or cell death, depending on the cell type, by employing different proteins. This review describes a novel growth-suppressive pathway employed by IFNs that affects rRNA levels. Maturation of rRNA involves numerous noncoding small regulatory RNA-guided processes. These regulatory RNAs, called small nucleolar RNA (snoRNAs), function as a ribonucleoprotein particle (RNP) in the nucleolus. The biogenesis of snoRNPs is dependent on core protein and assembly factors. Our laboratory recently isolated a growth-suppressive protein gene associated with retinoid-IFN-induced mortality (GRIM)-1 using a genetic screen. IFN-inducible GRIM-1 (SHQ1) is an assembly factor that controls one arm of the snoRNP machinery. GRIM-1 inhibits sno/scaRNP formation to induce growth suppression via reduction in mature rRNA levels. Loss of GRIM-1 observed in certain cancers implicates it to be a novel tumor suppressor. Certain snoRNAs have been reported to act as either oncogenes or tumor suppressors in vitro. Recent studies have shown that certain sno/scaRNAs are further processed into micro RNA-like molecules to control translation of protein-coding RNAs. We present a model as to how these small regulatory RNAs influence cell growth and a potential role for GRIM-1 in this process.

GRIM-19 mutations fail to inhibit v-Src-induced oncogenesis

The non-receptor tyrosine kinase Src is a major player in multiple physiological responses including growth, survival and differentiation. Overexpression and/or oncogenic mutation in the Src gene have been documented in human tumors. The v-Src protein is an oncogenic mutant of Src, which promotes cell survival, migration, invasion and division. GRIM-19 is an anti-oncogene isolated using a genome-wide knockdown screen. GRIM-19 binds to transcription factor STAT3 and ablates its pro-oncogenic effects while v-Src activates STAT3 to promote its oncogenic effects. However, we found that GRIM-19 inhibits the pro-oncogenic effects of v-Src independently of STAT3. Here, we report the identification of functionally inactivating GRIM-19 mutations in a set of Head and Neck cancer patients. While wild-type GRIM-19 strongly ablated v-Src-induced cell migration, cytoskeletal remodeling and tumor metastasis, the tumor-derived mutants (L⁷¹P, L⁹¹P and A⁹⁵T) did not. These mutants were also incapable of inhibiting the drug resistance of v-Src-transformed cells. v-Src down regulated the expression of Pag1, a lipid raft-associated inhibitor of Src, which was restored by wild-type GRIM-19. The tumor-derived mutant GRIM-19 proteins failed to upregulate Pag1. These studies show a novel mechanism that deregulates Src activity in cancer cells.

GRIM-19 inhibits the STAT3 signaling pathway and sensitizes gastric cancer cells to radiation

Gastric cancer is one of the most common malignancies, and radiation resistance is one of the key obstacles in gastric cancer treatment. In this study, we demonstrate that "genes associated retinoid-IFN induced mortality-19" (GRIM-19) expression was lower in patients with radiotherapy-resistant tumors compared to patients with radiotherapy-sensitive tumors. In order to further investigate the effects of GRIM-19 expression on the radiation response in gastric cancer cells, we established BGC-803 clones stably expressing exogenous GRIM-19. We found that the percentage of apoptotic cells was higher in cells expressing GRIM-19 than untransfected cells post-radiation treatment. Furthermore, caspase-3, -8, and -9 activity was significantly increased in GRIM-19-expressing cells compared to untransfected cells after radiation. Finally, we demonstrate that expression of GRIM-19 in BGC-803 cells suppresses accumulation of STAT3. Collectively, these data show that GRIM-19 expression sensitizes BGC-803 cells to radiation, and this is likely due to suppression of STAT3 accumulation. In summary, our results indicate that GRIM-19 expression might be a useful therapy to enhance apoptosis in gastric cancer cells in response to radiation treatment.

Downregulation of GRIM-19 promotes growth and migration of human glioma cells

It has become increasingly clear that there are notable parallels between normal development and tumorigenesis. Glioma is a classic model that links between tumorigenesis and development. We evaluated the expression of GRIM-19, a novel gene essential for normal development, in various grades of gliomas and several human glioma cell lines. We showed that GRIM-19 mRNA and protein expression were markedly lower in gliomas than in control brain tissues and negatively correlated with the malignancy of gliomas. Downregulation of GRIM-19 in glioma cells significantly enhanced cell proliferation and migration, whereas overexpression of GRIM-19 showed the opposite effects. We also showed that the activation of signal transducer and activator of transcription 3 (STAT3) and the expression of many STAT3-dependent genes were regulated by the expression of GRIM-19. In addition, GRIM-19 exerted its role probably through the non-STAT3 signaling pathway. Collectively, our data suggest that most gliomas expressed GRIM-19 at low levels, which may play a major role in tumorigenesis in the brain.

GRIM-1, a novel growth suppressor, inhibits rRNA maturation by suppressing small nucleolar RNAs

We have recently isolated novel IFN-inducible gene, Gene associated with Retinoid-Interferon-induced Mortality-1 (GRIM-1), using a genetic technique. Moderate ectopic expression of GRIM-1 caused growth inhibition and sensitized cells to retinoic acid (RA)/IFN-induced cell death while high expression caused apoptosis. GRIM-1 depletion, using RNAi, conferred a growth advantage. Three protein isoforms (1α, 1β and 1γ) with identical C-termini are produced from GRIM-1 mRNA. We show that GRIM-1 isoforms interact with NAF1 and DKC1, two essential proteins required for box H/ACA sno/sca RNP biogenesis and suppresses box H/ACA RNA levels in mammalian cells by delocalizing NAF1. Suppression of these small RNAs manifests as inefficient rRNA maturation and growth suppression. Interestingly, yeast Shq1p also caused growth suppression in mammalian cells. Consistent with its growth-suppressive property, GRIM-1 expression is lost in a number of human primary prostate tumors. Our observations support a recent study that GRIM-1 might act as a co-tumor suppressor in the prostate.

The viral interferon regulatory factors of KSHV: immunosuppressors or oncogenes?

Kaposi’s sarcoma-associated herpesvirus (KSHV) is a large double-stranded DNA gammaherpesvirus, and the etiological agent for three human malignancies: Kaposi’s sarcoma, primary effusion lymphoma, and multicentric Castleman’s disease. To establish and maintain infection, KSHV has evolved unique mechanisms to evade the host immune response. Cellular interferon regulatory factors (IRFs) are a critical part of the host anti-viral immune response. KSHV encodes four homologs of IRFs, vIRF1–4, which inhibit the activity of their cellular counterparts. vIRF1, 2, and 3 have been shown to interact directly with cellular IRFs. Additionally, the vIRFs have other functions such as modulation of Myc, p53, Notch, transforming growth factor-β, and NF-κB signaling. These activities of vIRFs may contribute to KSHV tumorigenesis. KSHV vIRF1 and vIRF3 have been implicated as oncogenes, making the understanding of KSHV vIRF function vital to understanding KSHV pathogenesis.

Identification and characterization of GRIM-1, a cell-death-associated gene product

Using a genome-wide technical knockout, we isolated a newly identified set of GRIM (genes associated with retinoid-interferon-induced mortality) genes; GRIM genes mediate IFN- and retinoic-acid (RA)-induced cell death. Here, we describe the isolation and characterization of one such gene, GRIM-1. Three proteins, with identical C-termini, were produced from the GRIM-1 open reading frame when this gene was transcribed and translated in vitro. These protein isoforms, designated GRIM-1alpha, GRIM-1beta and GRIM-1gamma, differentially suppressed growth via apoptosis in various cell lines. We also show that a caspase-dependent mechanism generates the proapoptotic GRIM-1 isoforms. Lastly, GRIM-1 isoforms differentially blocked maturation of 18S ribosomal RNA, consistent with their respective growth-suppressive ability. Together, these studies identified a novel protein involved in growth suppression and cell death.

GRIM-19 Expression and Function in Human Gliomas

OBJECTIVE

We determined whether the expression of GRIM-19 is correlated with pathologic types and malignant grades in gliomas, and determined the function of GRIM-19 in human gliomas.

METHODS

Tumor tissues were isolated and frozen at -80 just after surgery. The tissues consisted of normal brain tissue (4), astrocytomas (2), anaplastic astrocytomas (2), oligodendrogliomas (13), anaplastic oligodendrogliomas (11), and glioblastomas (16). To profile tumor-related genes, we applied RNA differential display using a Genefishing DEG kit, and validated the tumor-related genes by reverse transcription polymerase chain reaction (RT-PCR). A human glioblastoma cell line (U343MG-A) was used for the GRIM-19 functional studies. The morphologic and cytoskeletal changes were examined via light and confocal microscopy. The migratory and invasive abilities were investigated by the simple scratch technique and Matrigel assay. The antiproliferative activity was determined by thiazolyl blue Tetrazolium bromide (MTT) assay and FACS analysis.

RESULTS

Based on RT-PCR analysis, the expression of GRIM-19 was higher in astrocytic tumors than oligodendroglial tumors. The expression of GRIM-19 was higher in high-grade tumors than low-grade tumors or normal brain tissue; glioblastomas showed the highest expression. After transfection of GRIM-19 into U343MG-A, the morphology of the sense-transfection cells became larger and more spindly. The antisense-transfection cells became smaller and rounder compared with wild type U343MG-A. The MTT assay showed that the sense-transfection cells were more sensitive to the combination of interferon-beta and retinoic acid than U343MG-A cells or antisense-transfection cells; the anti-proliferative activity was related to apoptosis.

CONCLUSION

GRIM-19 may be one of the gene profiles which regulate cell death via apoptosis in human gliomas.

Cytokine-induced tumor suppressors: a GRIM story

Cytokines belonging to the IFN family are potent growth suppressors. In a number of clinical and preclinical studies, vitamin A and its derivatives like retinoic acid (RA) have been shown to exert synergistic growth-suppressive effects on several tumor cells. We have employed a genome-wide expression-knockout approach to identify the genes critical for IFN/RA-induced growth suppression. A number of novel genes associated with Retinoid-Interferon-induced Mortality (GRIM) were isolated. In this review, we will describe the molecular mechanisms of actions of one, GRIM-19, which participates in multiple pathways for exerting growth control and/or cell death. This protein is emerging as a new tumor suppressor. In addition, GRIM-19 appears to participate in innate immune responses as its activity is modulated by several viruses and bacteria. Thus, GRIMs seem to couple with multiple biological responses by acting at critical nodes.

Ubiquitin B: an essential mediator of trichostatin A-induced tumor-selective killing in human cancer cells

Although histone deacetylase inhibitors (HDACis) are emerging as a new class of anticancer agents, the mechanism of tumor-selective killing by HDACi is not well understood. We used suppression of mortality by antisense rescue technique (SMART) to screen the key genes responsible for the tumor-selective killing by trichostatin A (TSA). Twenty-four genes were identified, the most significant of which was ubiquitin B (UbB). The expression of UbB was selectively upregulated by TSA in tumor cells, but not non-malignant cells. Further observation indicated that TSA induced a substantial dissipation of mitochondrial transmembrane potential, release of cytochrome c into the cytosol, and proteolytic cleavage of caspases-3/9 in HeLa cells, which was apparently mediated by ubiquitylation and the subsequent degradation of mitochondrial membrane proteins including BCL-2 and MCL-1. In contrast, knockdown of UbB expression inhibited the TSA-induced apoptotic cascade by abolishing TSA-induced ubiquitylation and the subsequent degradation of mitochondrial membrane proteins. Furthermore, apicidine, another HDACi, exhibited activity similar to that of TSA. Interestingly, TSA induced UbB-dependent proteasomal degradation of BCR-ABL fusion protein in K562 leukemic cells. Thus, our findings highlight the essential role of UbB and UbB-dependent proteasomal protein degradation in HDACi-induced tumor selectivity. The mechanism provides a novel starting point for dissecting the molecular mechanism underlying the tumor selectivity of HDACi.

JS-K, a nitric oxide prodrug, has enhanced cytotoxicity in colon cancer cells with knockdown of thioredoxin reductase 1

BACKGROUND

The selenoenzyme thioredoxin reductase 1 has a complex role relating to cell growth. It is induced as a component of the cellular response to potentially mutagenic oxidants, but also appears to provide growth advantages to transformed cells by inhibiting apoptosis. In addition, selenocysteine-deficient or alkylated forms of thioredoxin reductase 1 have also demonstrated oxidative, pro-apoptotic activity. Therefore, a greater understanding of the role of thioredoxin reductase in redox initiated apoptotic processes is warranted.

METHODOLOGY

The role of thioredoxin reductase 1 in RKO cells was evaluated by attenuating endogenous thioredoxin reductase 1 expression with siRNA and then either inducing a selenium-deficient thioredoxin reductase or treatment with distinct redox challenges including, hydrogen peroxide, an oxidized lipid, 4-hydroxy-2-nonenol, and a nitric oxide donating prodrug. Thioredoxin redox status, cellular viability, and effector caspase activity were measured.

CONCLUSIONS/SIGNIFICANCE

In cells with attenuated endogenous thioredoxin reductase 1, a stably integrated selenocysteine-deficient form of the enzyme was induced but did not alter either the thioredoxin redox status or the cellular growth kinetics. The oxidized lipid and the nitric oxide donor demonstrated enhanced cytotoxicity when thioredoxin reductase 1 was knocked-down; however, the effect was more pronounced with the nitric oxide prodrug. These results are consistent with the hypothesis that attenuation of the thioredoxin-system can promote apoptosis in a nitric oxide-dependent manner.

Identification of LIV1, a putative zinc transporter gene responsible for HDACi-induced apoptosis, using a functional gene screen approach

Histone deacetylase inhibitors (HDACi) show promise as a novel class of antitumoral agents and have shown the ability to induce apoptosis of tumor cells. To gain a better understanding of the action of HDACi, we conducted a functional gene screen approach named suppression of mortality by antisense rescue technique to identify the key genes responsible for the tumor-selective killing trichostatin A. Over 20 genes associated with HDACi-induced mortality were identified. One of the confirmed positive hits is LIV1, a putative zinc transporter. LIV1 is significantly induced by treatment with HDACi in a number of tumor cells, but not in normal cells. Knockdown of LIV1 suppressed apoptosis induced by HDACi in tumor cells. Although HDACi induced a slight increase in the free intracellular zinc concentration, knockdown of LIV1 significantly enhanced the intracellular zinc level, which was associated with resistance to apoptosis. On the other hand, pretreatment of the cells with a specific zinc chelator TPEN reversed the apoptosis resistance conferred by knockdown of LIV1. However, the biological effects of TPEN were abolished by addition of physiologic concentrations of zinc. Taken together, the present study identifies LIV1 as a critical mediator responsible for HDACi-induced apoptosis. The effect of LIV1 is, at least in part, mediated by affecting intracellular zinc homeostasis, which may be related to alteration of the catalytic activity of the Caspase 3 and expression of some BCL-2 family genes. As such, these findings highlight a novel mechanism underlying the action of HDACi that could be potentially useful in the clinical setting.

Focus on mammalian thioredoxin reductases--important selenoproteins with versatile functions

Thioredoxin systems, involving redox active thioredoxins and thioredoxin reductases, sustain a number of important thioredoxin-dependent pathways. These redox active proteins support several processes crucial for cell function, cell proliferation, antioxidant defense and redox-regulated signaling cascades. Mammalian thioredoxin reductases are selenium-containing flavoprotein oxidoreductases, dependent upon a selenocysteine residue for reduction of the active site disulfide in thioredoxins. Their activity is required for normal thioredoxin function. The mammalian thioredoxin reductases also display surprisingly multifaceted properties and functions beyond thioredoxin reduction. Expressed from three separate genes (in human named TXNRD1, TXNRD2 and TXNRD3), the thioredoxin reductases can each reduce a number of different types of substrates in different cellular compartments. Their expression patterns involve intriguingly complex transcriptional mechanisms resulting in several splice variants, encoding a number of protein variants likely to have specialized functions in a cell- and tissue-type restricted manner. The thioredoxin reductases are also targeted by a number of drugs and compounds having an impact on cell function and promoting oxidative stress, some of which are used in treatment of rheumatoid arthritis, cancer or other diseases. However, potential specific or essential roles for different forms of human or mouse thioredoxin reductases in health or disease are still rather unclear, although it is known that at least the murine Txnrd1 and Txnrd2 genes are essential for normal development during embryogenesis. This review is a survey of current knowledge of mammalian thioredoxin reductase function and expression, with a focus on human and mouse and a discussion of the striking complexity of these proteins. Several yet open questions regarding their regulation and roles in different cells or tissues are emphasized. It is concluded that the intriguingly complex regulation and function of mammalian thioredoxin reductases within the cellular context and in intact mammals strongly suggests that their functions are highly fi ne-tuned with the many pathways involving thioredoxins and thioredoxin-related proteins. These selenoproteins furthermore propagate many functions beyond a reduction of thioredoxins. Aberrant regulation of thioredoxin reductases, or a particular dependence upon these enzymes in diseased cells, may underlie their presumed therapeutic importance as enzymatic targets using electrophilic drugs. These reductases are also likely to mediate several of the effects on health and disease that are linked to different levels of nutritional selenium intake. The thioredoxin reductases and their splice variants may be pivotal components of diverse cellular signaling pathways, having importance in several redox-related aspects of health and disease. Clearly, a detailed understanding of mammalian thioredoxin reductases is necessary for a full comprehension of the thioredoxin system and of selenium dependent processes in mammals.

Cell death by SecTRAPs: thioredoxin reductase as a prooxidant killer of cells

BACKGROUND

SecTRAPs (selenium compromised thioredoxin reductase-derived apoptotic proteins) can be formed from the selenoprotein thioredoxin reductase (TrxR) by targeting of its selenocysteine (Sec) residue with electrophiles, or by its removal through C-terminal truncation. SecTRAPs are devoid of thioredoxin reductase activity but can induce rapid cell death in cultured cancer cell lines by a gain of function.

PRINCIPAL FINDINGS

Both human and rat SecTRAPs killed human A549 and HeLa cells. The cell death displayed both apoptotic and necrotic features. It did not require novel protein synthesis nor did it show extensive nuclear fragmentation, but it was attenuated by use of caspase inhibitors. The redox active disulfide/dithiol motif in the N-terminal domain of TrxR had to be maintained for manifestation of SecTRAP cytotoxicity. Stopped-flow kinetics showed that NADPH can reduce the FAD moiety in SecTRAPs at similar rates as in native TrxR and purified SecTRAPs could maintain NADPH oxidase activity, which was accelerated by low molecular weight substrates such as juglone. In a cellular context, SecTRAPs triggered extensive formation of reactive oxygen species (ROS) and consequently antioxidants could protect against the cell killing by SecTRAPs.

CONCLUSIONS

We conclude that formation of SecTRAPs could contribute to the cytotoxicity seen upon exposure of cells to electrophilic agents targeting TrxR. SecTRAPs are prooxidant killers of cells, triggering mechanisms beyond those of a mere loss of thioredoxin reductase activity.

GRIM-19: A Double-edged Sword that Regulates Anti-Tumor and Innate Immune Responses

Gene associated with retinoid-interferon-β-induced mortality (GRIM)-19, was originally identified as a critical regulatory protein necessary for Interferon-β-Retinoic acid-induced cell death. Overexpression of GRIM-19 activates cell death and its suppression or inactivation promotes cell growth. GRIM-19 targets multiple proteins/pathways for exerting growth control and cell death. However, GRIM-19 is also required for normal cellular processes. In addition, viruses 'hijack' GRIM-19 for their survival. Intracellular bacterial infections and bacterial products have been reported to induce the expression of GRIM-19. In this review, we will discuss the current status of GRIM-19 in growth control and innate immune response.

Tumor suppressive protein gene associated with retinoid-interferon-induced mortality (GRIM)-19 inhibits src-induced oncogenic transformation at multiple levels

Interferons (IFNs) inhibit the growth of infectious pathogens and tumor development. Although IFNs are potent tumor suppressors, they modestly inhibit the growth of some human solid tumors. Their weak activity against such tumors is augmented by co-treatment with differentiation-inducing agents such as retinoids. Previous studies from our laboratory identified a novel gene product, gene associated with retinoid-interferon-induced mortality (GRIM)-19, as an IFN/all-trans retinoic acid-induced growth suppressor. However, the mechanisms of its growth suppressive actions are unclear. The src-family of tyrosine kinases is important regulators of various cell growth responses. Mutational activation of src causes cellular transformation by altering transcription and cytoskeletal properties. In this study, we show that GRIM-19 suppresses src-induced cellular transformation in vitro and in vivo by down-regulating the expression of a number of signal transducer and activator of transcription-3 (STAT3)-dependent cellular genes. In addition, GRIM-19 inhibited the src-induced cell motility and metastasis by suppressing the tyrosyl phosphorylation of focal adhesion kinase, paxillin, E-cadherin, and gamma-catenin. Effects of GRIM-19 on src-induced cellular transformation are reversible in the presence of specific short hairpin RNA, indicating its direct effect on transformation. GRIM-19-mediated inhibition of the src-induced tyrosyl phosphorylation of cellular proteins, such as focal adhesion kinase and paxillin, seems to occur independently of the STAT3 protein. GRIM-19 had no significant effect on the cellular transformation induced by other oncogenes such as myc and Ha-ras. Thus, GRIM-19 not only blocks src-induced gene expression through STAT3 but also the activation of cell adhesion molecules.

Conversion of Fas-resistant to Fas-sensitive MCF-7 Breast Cancer Cells by the Synergistic Interaction of Interferon-γ and all-TransRetinoic Acid

The membrane receptor Fas (Apo-1/CD95) is an important initiator of programmed cell death induced by anti-Fas antibody or Fas ligand. MCF-7 human breast cancer cells have low levels of Fas receptor (FasR) and are resistant to anti-FasR antibody mediated apoptosis, however two naturally occurring substances, interferon and all-trans retinoic acid (AT), act synergistically to enhance antiproliferative processes in these cells, suggesting this combination may also be an effective means for enhancing FasR expression. When this was studied, it was found that IFN-gamma and AT in combination acted synergistically to induce expression of FasR mRNA and FasR protein in a time-dependent and dose-dependent manner. This induction required continuous protein synthesis, and STAT1 protein, but not PKR or TR1 protein, was induced in a manner quantitatively and temporally related to FasR protein induction, and consistent with STAT1 mediation of the synergistic effect of IFN-gamma and AT on FasR expression. FasR-induced cells were resistant to stimulation of apoptosis by anti-FasR antibody, however treatment with cycloheximide rendered these cells sensitive to antibody-induced apoptosis, suggesting endogenous blockade to signaling. These cells did not express caspase 3, or FLIP(L), but strongly expressed the endogenous inhibitor of apoptosis Bcl-2, indicating a type II Fas signaling pathway. Expression of these proteins was not modulated by IFN/AT, however treatment of Fas-induced cells with Bcl-2 specific small interfering RNA (SiRNA) downregulated Bcl-2 protein expression and rendered these cells sensitive to the cytotoxic effects of anti-Fas antibody. These findings indicate that IFN-gamma+AT in combination modulate Fas signaling and provide a novel mechanism for the promotion of cell death in breast cancer cells.

Somatic and germline mutation in GRIM-19, a dual function gene involved in mitochondrial metabolism and cell death, is linked to mitochondrion-rich (Hurthle cell) tumours of the thyroid

Oxyphil or Hurthle cell tumours of the thyroid are characterised by their consistent excessive number of mitochondria. A recently discovered gene, GRIM-19 has been found to fulfil two roles within the cell: as a member of the interferon-beta and retinoic acid-induced pathway of cell death, and as part of the mitochondrial Complex I assembly. In addition, a gene predisposing to thyroid tumours with cell oxyphilia (TCO) has been mapped to chromosome 19p13.2 in one family. A cluster of genes involved in mitochondrial metabolism occurs in this region; one of these is GRIM-19. We have searched for GRIM-19 mutations in a series of 52 thyroid tumours. Somatic missense mutations in GRIM-19 were detected in three of 20 sporadic Hurthle cell carcinomas. A germline mutation was detected in a Hurthle cell papillary carcinoma arising in a thyroid with multiple Hurthle cell nodules. No mutations were detected in any of the 20 non-Hurthle cell carcinomas tested, nor in any of 96 blood donor samples. In one of the sporadic Hurthle cell papillary carcinomas positive for GRIM-19 mutation, we have also detected a ret/PTC-1 rearrangement. No GRIM-19 mutations were detected in any of the six cases of known familial Hurthle cell tumour tested, so that our results do not support the identification of GRIM-19 as the TCO gene. The GRIM-19 mutations we have detected are the first nuclear gene mutations specific to Hurthle cell tumours to be reported to date; we propose that such mutations can be involved in the genesis of sporadic or familial Hurthle cell tumours through the dual function of GRIM-19 in mitochondrial metabolism and cell death.

The GRIMs: a new interface between cell death regulation and interferon/retinoid induced growth suppression

Cytokines and vitamins play a central role in controlling neoplastic cell growth. The interferon (IFN) family of cytokines regulates antiviral, anti-tumor, antimicrobial, differentiation, and immune responses in mammals. Significant advances have been made with respect to IFN-induced signal transduction pathways and antiviral responses. However, the IFN-induced anti-tumor actions are poorly defined. Although IFNs themselves inhibit tumor growth, combination of IFNs with retinoids (a class of Vitamin A related compounds) strongly potentiates the IFN-regulated anti-tumor action in a number of cell types. To define the molecular mechanisms involved in IFN/retinoid (RA)-induced apoptosis we have employed a genetic approach and identified several critical genes. In this review, I provide the current picture of IFN- RA- and IFN/RA-regulated growth suppressive pathways. In particular, I focus on a novel set of genes, the genes-associated with retinoid-interferon induced mortality (GRIM). GRIMs may be novel types of tumor suppressors, useful as biological response markers and potentially novel targets for drug development.

Overexpression of Enzymatically Active Human Cytosolic and Mitochondrial Thioredoxin Reductase in HEK-293 Cells

The mammalian thioredoxin reductases (TrxR) are selenoproteins containing a catalytically active selenocysteine residue (Sec) and are important enzymes in cellular redox control. The cotranslational incorporation of Sec, necessary for activity, is governed by a stem-loop structure in the 3'-untranslated region of the mRNA and demands adequate selenium availability. The complicated translation machinery required for Sec incorporation is a major obstacle in isolating mammalian cell lines stably overexpressing selenoproteins. In this work we report on the development and characterization of stably transfected human embryonic kidney 293 cells that overexpress enzymatically active selenocysteine-containing cytosolic TrxR1 or mitochondrial TrxR2. We demonstrate that the overexpression of selenium-containing TrxR1 results in lower expression and activity of the endogenous selenoprotein glutathione peroxidase and that the activity of overexpressed TrxRs, rather than the protein amount, can be increased by selenium supplementation in the cell growth media. We also found that the TrxR-overexpressing cells grew slower over a wide range of selenium concentrations, which was an effect apparently not related to increased apoptosis nor to fatally altered intracellular levels of reactive oxygen species. Most surprisingly, the TrxR1- or TrxR2-overexpressing cells also induced novel expression of the epithelial markers CK18, CK-Cam5.2, and BerEP4, suggestive of a stimulation of cellular differentiation.

GRIM-19, a cell death regulatory protein, is essential for assembly and function of mitochondrial complex I

Mitochondria play essential roles in cellular energy production via the oxidative phosphorylation system (OXPHOS) consisting of five multiprotein complexes and also in the initiation of apoptosis. NADH:ubiquinone oxidoreductase (complex I) is the largest complex that catalyzes the first step of electron transfer in the OXPHOS system. GRIM-19 was originally identified as a nuclear protein with apoptotic nature in interferon (IFN)- and all-trans-retinoic acid (RA)-induced tumor cells. To reveal its biological role, we generated mice deficient in GRIM-19 by gene targeting. Homologous deletion of GRIM-19 causes embryonic lethality at embryonic day 9.5. GRIM-19(-/-) blastocysts show retarded growth in vitro and, strikingly, display abnormal mitochondrial structure, morphology, and cellular distribution. We reexamined the cellular localization of GRIM-19 in various cell types and found its primary localization in the mitochondria. Furthermore, GRIM-19 is detected in the native form of mitochondrial complex I. Finally, we show that elimination of GRIM-19 destroys the assembly and electron transfer activity of complex I and also influences the other complexes in the mitochondrial respiratory chain. Our result demonstrates that GRIM-19, a gene product with a specific role in IFN-RA-induced cell death, is a functional component of mitochondrial complex I and is essential for early embryonic development.

An Alternative Splicing Variant of the Selenoprotein Thioredoxin Reductase Is a Modulator of Estrogen Signaling

The selenoprotein thioredoxin reductase (TrxR1) is an integral part of the thioredoxin system. It serves to transfer electrons from NADPH to thioredoxin leading to its reduction. Interestingly, recent work has indicated that thioredoxin reductase can regulate the activity of transcription factors such as p53, hypoxia-inducible factor, and AP-1. Here, we describe that an alternative splicing variant of thioredoxin reductase (TrxR1b) containing an LXXLL peptide motif, is implicated in direct binding to nuclear receptors. In vitro interaction studies revealed direct interaction of the TrxR1b with the estrogen receptors alpha and beta. Confocal microscopy analysis showed nuclear colocalization of the TrxR1b with both estrogen receptor alpha and beta in estradiol-17beta-treated cells. Transcriptional studies demonstrated that TrxR1b can affect estrogen-dependent gene activation differentially at classical estrogen response elements as compared with AP-1 response elements. Based on these results, we propose a model where thioredoxin reductase directly influences the estrogen receptor-coactivator complex assembly on non-classical estrogen response elements such as AP-1. In summary, our results suggest that TrxR1b is an important modulator of estrogen signaling.

Alternate interferon signaling pathways

More than a half a century ago, interferons (IFN) were identified as antiviral cytokines. Since that discovery, IFN have been in the forefront of basic and clinical cytokine research. The pleiotropic nature of these cytokines continues to engage a large number of investigators to define their actions further. IFN paved the way for discovery of Janus tyrosine kinase (JAK)-signal transducing activators of transcription (STAT) pathways. A number of important tumor suppressive pathways are controlled by IFN. Several infectious pathogens counteract IFN-induced signaling pathways. Recent studies indicate that IFN activate several new protein kinases, including the MAP kinase family, and downstream transcription factors. This review not only details the established IFN signaling paradigms but also provides insights into emerging alternate signaling pathways and mechanisms of pathogen-induced signaling interference.

Regulation of the mammalian selenoprotein thioredoxin reductase 1 in relation to cellular phenotype, growth, and signaling events

Reactive oxygen species (ROS) are generated as toxic by-products of aerobic metabolism, but are also essential biomolecules in cell signaling. The thioredoxin (Trx) system is a major enzymatic system modulating ROS levels and is important for redox regulation of cellular function. It consists of Trx and thioredoxin reductase (TrxR), which reduces Trx using NADPH. Most, if not all, of the functions of Trx depend on the activity of TrxR. Mammalian TrxR enzymes are selenoproteins with broad substrate specificities, and alteration of cytosolic TrxR1 expression and activity is likely to be an important determinant for the control of cellular redox regulation. TrxR1 activity in cells seems to be modulated by an intricate interplay, involving a housekeeping type promoter in combination with alternative splice variants and transcriptional start sites, posttranscriptional regulation through AU-rich elements, inactivation by electrophilic agents and by itself modulating the effects of several key signaling molecules. TrxR1 activity is also intimately linked with several aspects of selenium metabolism, and hence selenoprotein function in general. Here, we summarize the current knowledge of these different levels of TrxR1 regulation in diverse cell types and in response to growth and signaling events.

Thioredoxin reductase 1 expression in colon cancer: discrepancy between in vitro and in vivo findings

Thioredoxin and thioredoxin reductase 1 (TR1) are redox proteins that have been implicated in cellular events such as proliferation, transformation, and apoptosis. Analysis of the expression and localization of TR1 in different normal and cancer cell lines and in colon tissues (normal, neoplastic, or inflamed) was performed using reverse transcription-PCR and in situ hybridization. TR1 mRNA was expressed in all analyzed tissues with TR mRNA-positive cells restricted to the stroma of colon crypts, partly being CD3 or CD56 positive. In neoplastic areas of colonic cancer tissue, a loss of TR was obvious. None of the epithelial cells in colonic mucosa expressed TR mRNA, whereas more than 70% of HT-29 cells grown in monolayer were positive for TR. In contrast, HT-29 cells, grown as spheroids or as tumors in SCID mice, were negative for TR. In contrast to these in vitro findings and previous studies, there is no evidence that TR plays a significant role in vivo in normal cell growth in colonic epithelial cells. The mechanism underlying the loss of TR1-positive/CD3-positive/CD56-positive cells or the biologic consequence of this phenomenon observed in neoplastic colonic tissue remains to be clarified.

Identification and characterization of a cell cycle and apoptosis regulatory protein-1 as a novel mediator of apoptosis signaling by retinoid CD437

CD437, a novel retinoid, causes cell cycle arrest and apoptosis in a number of cancer cells including human breast carcinoma (HBC) by utilizing an undefined retinoic acid receptor/retinoid X receptor-independent mechanism. To delineate mediators of CD437 signaling, we utilized a random antisense-dependent functional knockout genetic approach. We identified a cDNA that encodes approximately 130-kDa HBC cell perinuclear protein (termed CARP-1). Treatments with CD437 or chemotherapeutic agent adriamycin, as well as serum deprivation of HBC cells, stimulate CARP-1 expression. Reduced levels of CARP-1 result in inhibition of apoptosis by CD437 or adriamycin, whereas increased expression of CARP-1 causes elevated levels of cyclin-dependent kinase inhibitor p21WAF1/CIP1 and apoptosis. CARP-1 interacts with 14-3-3 protein as well as causes reduced expression of cell cycle regulatory genes including c-Myc and cyclin B1. Loss of c-Myc sensitizes cells to apoptosis by CARP-1, whereas expression of c-Myc or 14-3-3 inhibits CARP-1-dependent apoptosis. Thus, apoptosis induction by CARP-1 involves sequestration of 14-3-3 and CARP-1-mediated altered expression of multiple cell cycle regulatory genes. Identification of CARP-1 as a key mediator of signaling by CD437 or adriamycin allows for delineation of pathways that, in turn, may prove beneficial for design and targeting of novel antitumor agents.

The cell death regulator GRIM-19 is an inhibitor of signal transducer and activator of transcription 3

GRIM-19 (gene associated with retinoid-IFN-induced mortality 19), isolated as a cell death activator in a genetic screen used to define mechanisms involved in IFN-beta- and retinoic acid-induced cell death, codes for a approximately 16-kDa protein that induces apoptosis in a number of cell lines. Antisense ablation of GRIM-19 caused resistance to cell death induced by IFN plus retinoic acid and conferred a growth advantage to cells. To understand the molecular bases for its cell death regulatory activity, we used a yeast two-hybrid screen and identified that the transcription factor STAT3 (signal transducer and activator of transcription 3) binds to GRIM-19. GRIM-19 inhibits transcription driven by activation of STAT3, but not STAT1. It neither inhibits the ligand-induced activation of STAT3 nor blocks its ability to bind to DNA. Mutational analysis indicates that the transactivation domain of STAT3, especially residue S727, is required for GRIM-19 binding. Because GRIM-19 does not bind significantly to other STATs, our studies identify a specific inhibitor of STAT3. Because constitutively active STAT3 up-regulates antiapoptotic genes to promote tumor survival, its inhibition by GRIM-19 also demonstrates an antioncogenic effect exerted by biological therapeutics.

Rapid induction of cell death by selenium-compromised thioredoxin reductase 1 but not by the fully active enzyme containing selenocysteine

Mammalian thioredoxin reductases are selenoproteins. For native catalytic activity, these enzymes utilize a C-terminal -Gly-Cys-Sec-Gly-COOH sequence (where Sec is selenocysteine) forming a redox active selenenylsulfide/selenolthiol motif. A range of cellular systems depend upon or are regulated by thioredoxin reductase and its major protein substrate thioredoxin, including apoptosis signal-regulating kinase 1, peroxiredoxins, methionine sulfoxide reductase, and several transcription factors. Cytosolic thioredoxin reductase 1 (TrxR1) is moreover inhibited by various electrophilic anticancer compounds. TrxR1 is hence generally considered to promote cell viability. However, several recent studies have suggested that TrxR1 may promote apoptosis, and the enzyme was identified as GRIM-12 (gene associated with retinoid interferon-induced mortality 12). Transient transfection with GRIM-12/TrxR1 was also shown to directly induce cell death. To further analyze such effects, we have here employed lipid-mediated delivery of recombinant TrxR1 preparations into human A549 cells, thereby bypassing selenoprotein translation to facilitate assessment of the protein-related effects on cell viability. We found that selenium-deficient TrxR1, having a two-amino acid-truncated C-terminal -Gly-Cys-COOH motif, rapidly induced cell death (38 +/- 29% apoptotic cells after 4 h; p < 0.005 compared with controls). Cell death induction was also promoted by selenium-compromised TrxR1 derivatized with either cis-diamminedichloroplatinum (II) (cisplatin) or dinitrophenyl moieties but not by the structurally related non-selenoprotein glutathione reductase. In contrast, TrxR1 with intact selenocysteine could not promote cell death. The direct cellular effects of selenium-compromised forms of TrxR1 may be important for the pathophysiology of selenium deficiency as well as for the efficacy of antiproliferative drugs targeting the selenocysteine moiety of this enzyme.

GRIM-19, a death-regulatory gene product, suppresses Stat3 activity via functional interaction

Signal transducer and activator of transcription 3 (Stat3) is a latent cytoplasmic transcription factor that can be activated by cytokines and growth factors. Stat3 plays important roles in cell growth, anti-apoptosis and cell transformation, and is constitutively active in various cancers. We examined its potential regulators by yeast two-hybrid screening. GRIM-19, a gene product related to interferon-beta- and retinoic acid-induced cancer cell death, was identified and demonstrated to interact with Stat3 in various cell types. The interaction is specific for Stat3, but not for Stat1 and Stat5a. The interaction regions in both proteins were mapped, and the cellular localization of the interaction was examined. GRIM-19 itself co-localizes with mitochondrial markers, and forms aggregates at the perinulear region with co-expressed Stat3, which inhibits Stat3 nuclear translocation stimulated by epidermal growth factor (EGF). GRIM-19 represses Stat3 transcriptional activity and its target gene expression, and also suppresses cell growth in Src-transformed cells and a Stat3-expressing cell line. Our data suggest that GRIM-19 is a novel negative regulator of Stat3.

The mammalian cytosolic selenoenzyme thioredoxin reductase reduces ubiquinone. A novel mechanism for defense against oxidative stress

The selenoprotein thioredoxin reductase (TrxR1) is an essential antioxidant enzyme known to reduce many compounds in addition to thioredoxin, its principle protein substrate. Here we found that TrxR1 reduced ubiquinone-10 and thereby regenerated the antioxidant ubiquinol-10 (Q10), which is important for protection against lipid and protein peroxidation. The reduction was time- and dose-dependent, with an apparent K(m) of 22 microm and a maximal rate of about 12 nmol of reduced Q10 per milligram of TrxR1 per minute. TrxR1 reduced ubiquinone maximally at a physiological pH of 7.5 at similar rates using either NADPH or NADH as cofactors. The reduction of Q10 by mammalian TrxR1 was selenium dependent as revealed by comparison with Escherichia coli TrxR or selenium-deprived mutant and truncated mammalian TrxR forms. In addition, the rate of reduction of ubiquinone was significantly higher in homogenates from human embryo kidney 293 cells stably overexpressing thioredoxin reductase and was induced along with increasing cytosolic TrxR activity after the addition of selenite to the culture medium. These data demonstrate that the selenoenzyme thioredoxin reductase is an important selenium-dependent ubiquinone reductase and can explain how selenium and ubiquinone, by a combined action, may protect the cell from oxidative damage.

Characterization of monoclonal antibodies against GRIM-19, a novel IFN-beta and retinoic acid-activated regulator of cell death

A combination of interferon-beta (IFN-beta) and all-trans retinoic acid (IFN/RA) induces tumor cell apoptosis via some unknown mechanisms. Apoptosis is a gene-directed process that limits the proliferation of undesired cells. Several genes are required to regulate cell death in the higher-order animals. Earlier, we employed a gene expression knockout technique to isolate cell death-related genes. A novel gene, the gene associated with retinoid-interferon-induced mortality-19 (GRIM-19), was found to be essential for tumor cell death induced by IFN/RA. Here, we describe the development and characterization of three monoclonal antibodies (mAbs) against GRIM-19. GRIM-19 is present in the nucleus and cytoplasm. Its expression is induced by the IFN/RA combination. We also show that GRIM-19 inhibits the cell-transforming property of viral oncogenic protein viral IFN regulatory factor-1 (vIRF-1) via a physical interaction. mAbs developed in this study should be useful for studying the other physiologic roles of GRIM-19 and serve as a potent tool for studying tumor responses to IFN/RA therapy.

Protein kinase C as a molecular target for cancer prevention by selenocompounds

Selenium is a very effective cancer-preventive agent, suppressing tumor promotion and early stages of tumor progression. However, the mechanisms by which selenium exerts these cancer-preventive actions are not known. Protein kinase C (PKC) is a receptor for certain tumor promoters and also plays a crucial role in events related to tumor progression. Therefore, it is not only a potential target for the cancer-preventive activity of selenium, but also it has the structural basis for interaction with selenium. Redox-active selenocompounds can inactivate PKC, particularly the Ca(2+)-dependent isozymes, by reacting with the critical cysteine-rich regions present within the catalytic domain while, in some cases, also reacting with the cysteine residues present within the zinc-fingers of the regulatory domain. The selenoprotein thioredoxin reductase (TR), acting through thioredoxin, reverses the inactivation of PKC induced by selenometabolites. Furthermore, TR, through a direct interaction involving its selenosulfur center with the zinc-thiolates of PKC, can reverse the redox modification of this kinase induced by selenometabolites. Thus the selenometabolite-induced toxicity is reversed by a selenoprotein, and therefore an interrelationship exists between these two mechanisms of selenium actions. Moreover, this also explains how a resistance to selenium develops in advanced tumor cells probably due to an overexpression of functional TR. Selenium-induced inactivation of PKC may, at least in part, be responsible for the selenium-induced inhibition of tumor promotion, cell growth, invasion, and metastasis, as well as for the induction of apoptosis.

Viral interferon regulatory factor 1 of Kaposi's sarcoma-associated herpesvirus interacts with a cell death regulator, GRIM19, and inhibits interferon/retinoic acid-induced cell death

Kaposi's sarcoma-associated herpesvirus (KSHV) plays a significant role in the development of Kaposi's sarcoma, primary effusion lymphoma, and some forms of multicentric Castleman's disease. The KSHV open reading frame K9 encodes the viral interferon (IFN) factor 1 (vIRF1), which downregulates IFN- and IRF-mediated transcriptional activation, and leads to cellular transformation in rodent fibroblasts and induction of tumors in nude mice. Using the yeast two-hybrid assay, we identified genes associated with retinoid-IFN-induced mortality-19 (GRIM19), which interacts directly with vIRF1, both in vivo and in vitro. The N-terminal region of vIRF1 is required for binding GRIM19. Colocalization of vIRF1 and GRIM19 was observed in 293T cells. The vIRF1 protein deregulates GRIM19-induced apoptosis in the presence of IFN/all-trans-retinoic acid (RA) and inhibits IFN/RA-induced cell death. Another DNA tumor viral protein, human papillomavirus type 16 E6, also binds GRIM19, suggesting that this is a general target of viral proteins. Our results collectively indicate that vIRF1 modulates IFN/RA-cell death signals via interactions with GRIM19.

Retinoids in combination therapies for the treatment of cancer: mechanisms and perspectives

Retinoid derivatives have been of special interest in cancer research because of their antiproliferative and differentiation-inducing activities in premalignant and malignant cells. Some retinoids are clinically effective in cancer therapy and prevention, and all-trans-retinoic acid is being used for the treatment of acute promyelocytic leukemia. Unfortunately, classical retinoids are not effective against most advanced solid tumors and cause undesirable side effects, which have limited the full development of retinoids as chemopreventive and chemotherapeutic drugs. The recent identification of selective retinoid derivatives capable of inducing apoptosis and their combination with other anticancer therapies promises a more effective and less toxic manner to the successful use of retinoids in cancer therapy.

Mutational analysis of human thioredoxin reductase 1. Effects on p53-mediated gene expression and interferon and retinoic acid-induced cell death

The interferon (IFN)-beta and all-trans-retinoic acid combination suppresses tumor growth by inducing apoptosis in several tumor cell lines. A genetic technique permitted the isolation of human thioredoxin reductase (TR) as a critical regulator of IFN/all-trans-retinoic acid-induced cell death. Our recent studies have shown that TR1:thioredoxin 1-regulated cell death is effected in part through the activation of p53-dependent responses. To understand its death regulatory function, we have performed a mutational analysis of TR. Human TR1 has three major structural domains, the FAD binding domain, the NADPH binding domain, and an interface domain (ID). Here, we show that the deletion of the C-terminal interface domain results in a constitutive activation of TR-dependent death responses and promotes p53-dependent gene expression. TR mutant without the ID still retains its dependence on thioredoxin for promoting these responses. Thus, our data suggest that TR-ID acts as a regulatory domain.