ROS mediates 4HPR-induced posttranscriptional expression of the Gadd153 gene

The impact of physical activity on promoter-specific methylation of genes involved in the redox-status and disease progression: A longitudinal study on post-surgery female breast cancer patients undergoing medical treatment

Most anticancer treatments act on oxidative-stress pathways by producing reactive oxygen species (ROS) to kill cancer cells, commonly resulting in consequential drug-induced systemic cytotoxicity. Physical activity (PA) has arisen as an integrative cancer therapy, having positive health effects, including in redox-homeostasis. Here, we investigated the impact of an online supervised PA program on promoter-specific DNA methylation, and corresponding gene expression/activity, in 3 antioxidants- (SOD1, SOD2, and CAT) and 3 breast cancer (BC)-related genes (BRCA1, L3MBTL1 and RASSF1A) in a population-based sample of women diagnosed with primary BC, undergoing medical treatment. We further examined mechanisms involved in methylating and demethylating pathways, predicted biological pathways and interactions of exercise-modulated molecules, and the functional relevance of modulated antioxidant markers on parameters related to aerobic capacity/endurance, physical fatigue and quality of life (QoL). PA maintained levels of SOD activity in blood plasma, and at the cellular level significantly increased SOD2 mRNA (≈+77 %), contrary to their depletion due to medical treatment. This change was inversely correlated with DNA methylation in SOD2 promoter (≈-20 %). Similarly, we found a significant effect of PA only on L3MBTL1 promoter methylation (≈-25 %), which was inversely correlated with its mRNA (≈+43 %). Finally, PA increased TET1 mRNA levels (≈+15 %) and decreased expression of DNMT3B mRNA (≈-28 %). Our results suggest that PA-modulated DNA methylation affects several signalling pathways/biological activities involved in the cellular oxidative stress response, chromatin organization/regulation, antioxidant activity and DNA/protein binding. These changes may positively impact clinical outcomes and improve the response to cancer treatment in post-surgery BC patients.

Desmoglein-2 Affects Vascular Function in Moyamoya Disease by Interacting with MMP-9 and Influencing PI3K Signaling

The pathogenesis and development of Moyamoya disease are still unclear. This study aimed to investigate the effect of desmoglein-2 (DSG2) on Moyamoya disease and determine the inhibitory effect of DSG2 in vascular remodeling in Moyamoya disease.RNA sequencing, immunohistochemistry (IHC), and western blotting were used to detect the expression of DSG2 in the superficial temporal artery (STA) tissues of Moyamoya disease. The association between DSG2 and endothelial cells' biological activities was investigated by cell counting kit-8 (CCK-8), migration assay, tube formation assay, flow cytometry with Annexin V-FITC/PI staining, and TUNEL apoptotic cell detection kit. Pathways affected by overexpression or knockdown of DSG2 were identified in endothelial cells.The expression of DSG2 in the STA tissues of Moyamoya disease was lower than that in normal controls. Overexpression of DSG2 inhibits the proliferation and migration but promotes apoptosis in endothelial cells, and low DSG2 levels result in impaired angiogenesis. In addition, there was an interaction between DSG2 and MMP-9, and DSG2 acted through the PI3K signaling in endothelial cells.Our results indicate that DSG2 affects PI3K signaling in vascular endothelial cells, and MMP-9 is involved in DSG2-mediated vascular changes in Moyamoya disease.

Online Home-Based Physical Activity Counteracts Changes of Redox-Status Biomarkers and Fitness Profiles during Treatment Programs in Postsurgery Female Breast Cancer Patients

Breast cancer (BC) is one of the most commonly diagnosed types of cancer in women. Oxidative stress may contribute to cancer etiology through several mechanisms. A large body of evidence indicates that physical activity (PA) has positive effects on different aspects of BC evolution, including mitigation of negative effects induced by medical treatment. With the aim to verify the capacity of PA to counteract negative effects of BC treatment on systemic redox homeostasis in postsurgery female BC patients, we have examined the modulation of circulating levels of oxidative stress and inflammation markers. Moreover, we evaluated the impacts on physical fitness and mental well-being by measuring functional parameters, body mass index, body composition, health-related quality of life (QoL), and fatigue. Our investigation revealed that PA was effective in maintaining plasma levels of superoxide dismutase (SOD) activity and tGSH, as well as peripheral blood mononuclear cells' (PBMCs) mRNA levels of SOD1 and heat-shock protein 27. Moreover, we found a significant decrease in plasma interleukin-6 (≈0.57 ± 0.23-fold change, p < 0.05) and increases in both interleukin-10 (≈1.15 ± 0.35-fold change, p < 0.05) and PBMCs' mRNA level of SOD2 (≈1.87 ± 0.36-fold change, p < 0.05). Finally, PA improves functional parameters (6 min walking test, ≈+6.50%, p < 0.01; Borg, ≈-58.18%, p < 0.01; sit-and-reach, ≈+250.00%, p < 0.01; scratch right, ≈-24.12%, and left, ≈-18.81%, p < 0.01) and body composition (free fat mass, ≈+2.80%, p < 0.05; fat mass, ≈-6.93%, p < 0.05) as well as the QoL (physical function, ≈+5.78%, p < 0.05) and fatigue (cognitive fatigue, ≈-60%, p < 0.05) parameters. These results suggest that a specific PA program not only is effective in improving functional and anthropometric parameters but may also activate cellular responses through a multitude of actions in postsurgery BC patients undergoing adjuvant therapy. These may include modulation of gene expression and protein activity and impacting several signaling pathways/biological activities involved in tumor-cell growth; metastasis; and inflammation, as well as moderating distress symptoms known to negatively affect QoL.

The double-edged roles of ROS in cancer prevention and therapy

Reactive oxygen species (ROS) serve as cell signaling molecules generated in oxidative metabolism and are associated with a number of human diseases. The reprogramming of redox metabolism induces abnormal accumulation of ROS in cancer cells. It has been widely accepted that ROS play opposite roles in tumor growth, metastasis and apoptosis according to their different distributions, concentrations and durations in specific subcellular structures. These double-edged roles in cancer progression include the ROS-dependent malignant transformation and the oxidative stress-induced cell death. In this review, we summarize the notable literatures on ROS generation and scavenging, and discuss the related signal transduction networks and corresponding anticancer therapies. There is no doubt that an improved understanding of the sophisticated mechanism of redox biology is imperative to conquer cancer.

Fenretinide induces a new form of dynamin-dependent cell death in pediatric sarcoma

Alveolar rhabdomyosarcoma (aRMS) is a highly malicious childhood malignancy characterized by specific chromosomal translocations mostly encoding the oncogenic transcription factor PAX3-FOXO1 and therefore also referred to as fusion-positive RMS (FP-RMS). Previously, we have identified fenretinide (retinoic acid p-hydroxyanilide) to affect PAX3-FOXO1 expression levels as well as FP-RMS cell viability. Here, we characterize the mode of action of fenretinide in more detail. First, we demonstrate that fenretinide-induced generation of reactive oxygen species (ROS) depends on complex II of the mitochondrial respiratory chain, since ROS scavenging as well as complexing of iron completely abolished cell death. Second, we co-treated cells with a range of pharmacological inhibitors of specific cell death pathways including z-vad (apoptosis), necrostatin-1 (necroptosis), 3-methyladenine (3-MA) (autophagy), and ferrostatin-1 (ferroptosis) together with fenretinide. Surprisingly, none of these inhibitors was able to prevent cell death. Also genetic depletion of key players in the apoptotic and necroptotic pathway (BAK, BAX, and RIPK1) confirmed the pharmacological data. Interestingly however, electron microscopy of fenretinide-treated cells revealed an excessive accumulation of cytoplasmic vacuoles, which were distinct from autophagosomes. Further flow cytometry and fluorescence microscopy experiments suggested a hyperstimulation of macropinocytosis, leading to an accumulation of enlarged early and late endosomes. Surprisingly, pharmacological inhibition as well as genetic depletion of large dynamin GTPases completely abolished fenretinide-induced vesicle formation and subsequent cell death, suggesting a new form of dynamin-dependent programmed cell death. Taken together, our data identify a new form of cell death mediated through the production of ROS by fenretinide treatment, highlighting the value of this compound for treatment of sarcoma patients including FP-RMS.

ROS in cancer therapy: the bright side of the moon

Reactive oxygen species (ROS) constitute a group of highly reactive molecules that have evolved as regulators of important signaling pathways. It is now well accepted that moderate levels of ROS are required for several cellular functions, including gene expression. The production of ROS is elevated in tumor cells as a consequence of increased metabolic rate, gene mutation and relative hypoxia, and excess ROS are quenched by increased antioxidant enzymatic and nonenzymatic pathways in the same cells. Moderate increases of ROS contribute to several pathologic conditions, among which are tumor promotion and progression, as they are involved in different signaling pathways and induce DNA mutation. However, ROS are also able to trigger programmed cell death (PCD). Our review will emphasize the molecular mechanisms useful for the development of therapeutic strategies that are based on modulating ROS levels to treat cancer. Specifically, we will report on the growing data that highlight the role of ROS generated by different metabolic pathways as Trojan horses to eliminate cancer cells.

Highly reactive molecules called reactive oxygen species (ROS), which at low levels are natural regulators of important signaling pathways in cells, might be recruited to act as “Trojan horses” to kill cancer cells. Researchers in Italy led by Bruno Perillo of the Institute of Food Sciences in Avelllino review the growing evidence suggesting that stimulating production of natural ROS species could become useful in treating cancer. Although ROS production is elevated in cancer cells it can also promote a natural process called programmed cell death. This normally regulates cell turnover, but could be selectively activated to target diseased cells. The authors discuss molecular mechanisms underlying the potential anti-cancer activity of various ROS-producing strategies, including drugs and light-stimulated therapies. They expect modifying the production of ROS to have potential for developing new treatments.

ROS-modulated therapeutic approaches in cancer treatment

PURPOSE

Reactive oxygen species (ROS) are produced in cancer cells as a result of increased metabolic rate, dysfunction of mitochondria, elevated cell signaling, expression of oncogenes and increased peroxisome activities. Certain level of ROS is required by cancer cells, above or below which lead to cytotoxicity in cancer cells. This biochemical aspect can be exploited to develop novel therapeutic agents to preferentially and selectively target cancer cells.

METHODS

We searched various electronic databases including PubMed, Web of Science, and Google Scholar for peer-reviewed english-language articles. Selected articles ranging from research papers, clinical studies, and review articles on the ROS production in living systems, its role in cancer development and cancer treatment, and the role of microbiota in ROS-dependent cancer therapy were analyzed.

RESULTS

This review highlights oxidative stress in tumors, underlying mechanisms of different relationships of ROS and cancer cells, different ROS-mediated therapeutic strategies and the emerging role of microbiota in cancer therapy.

CONCLUSION

Cancer cells exhibit increased ROS stress and disturbed redox homeostasis which lead to ROS adaptations. ROS-dependent anticancer therapies including ROS scavenging anticancer therapy and ROS boosting anticancer therapy have shown promising results in vitro as well as in vivo. In addition, response to cancer therapy is modulated by the human microbiota which plays a critical role in systemic body functions.

Cancer drug resistance: redox resetting renders a way

Disruption of redox homeostasis is a crucial factor in the development of drug resistance, which is a major problem facing current cancer treatment. Compared with normal cells, tumor cells generally exhibit higher levels of reactive oxygen species (ROS), which can promote tumor progression and development. Upon drug treatment, some tumor cells can undergo a process of 'Redox Resetting' to acquire a new redox balance with higher levels of ROS accumulation and stronger antioxidant systems. Evidence has accumulated showing that the 'Redox Resetting' enables cancer cells to become resistant to anticancer drugs by multiple mechanisms, including increased rates of drug efflux, altered drug metabolism and drug targets, activated prosurvival pathways and inefficient induction of cell death. In this article, we provide insight into the role of 'Redox Resetting' on the emergence of drug resistance that may contribute to pharmacological modulation of resistance.

Redox signaling: Potential arbitrator of autophagy and apoptosis in therapeutic response

Redox signaling plays important roles in the regulation of cell death and survival in response to cancer therapy. Autophagy and apoptosis are discrete cellular processes mediated by distinct groups of regulatory and executioner molecules, and both are thought to be cellular responses to various stress conditions including oxidative stress, therefore controlling cell fate. Basic levels of reactive oxygen species (ROS) may function as signals to promote cell proliferation and survival, whereas increase of ROS can induce autophagy and apoptosis by damaging cellular components. Growing evidence in recent years argues for ROS that below detrimental levels acting as intracellular signal transducers that regulate autophagy and apoptosis. ROS-regulated autophagy and apoptosis can cross-talk with each other. However, how redox signaling determines different cell fates by regulating autophagy and apoptosis remains unclear. In this review, we will focus on understanding the delicate molecular mechanism by which autophagy and apoptosis are finely orchestrated by redox signaling and discuss how this understanding can be used to develop strategies for the treatment of cancer.

Commensal microbiota is hepatoprotective and prevents liver fibrosis in mice

Translocation of bacteria and their products across the intestinal barrier is common in patients with liver disease, and there is evidence that experimental liver fibrosis depends on bacterial translocation. The purpose of our study was to investigate liver fibrosis in conventional and germ-free (GF) C57BL/6 mice. Chronic liver injury was induced by administration of thioacetamide (TAA) in the drinking water for 21 wk or by repeated intraperitoneal injections of carbon tetrachloride (CCl4). Increased liver fibrosis was observed in GF mice compared with conventional mice. Hepatocytes showed more toxin-induced oxidative stress and cell death. This was accompanied by increased activation of hepatic stellate cells, but hepatic mediators of inflammation were not significantly different. Similarly, a genetic model using Myd88/Trif-deficient mice, which lack downstream innate immunity signaling, had more severe fibrosis than wild-type mice. Isolated Myd88/Trif-deficient hepatocytes were more susceptible to toxin-induced cell death in culture. In conclusion, the commensal microbiota prevents fibrosis upon chronic liver injury in mice. This is the first study describing a beneficial role of the commensal microbiota in maintaining liver homeostasis and preventing liver fibrosis.

Modulation of oxidative stress as an anticancer strategy

The regulation of oxidative stress is an important factor in both tumour development and responses to anticancer therapies. Many signalling pathways that are linked to tumorigenesis can also regulate the metabolism of reactive oxygen species (ROS) through direct or indirect mechanisms. High ROS levels are generally detrimental to cells, and the redox status of cancer cells usually differs from that of normal cells. Because of metabolic and signalling aberrations, cancer cells exhibit elevated ROS levels. The observation that this is balanced by an increased antioxidant capacity suggests that high ROS levels may constitute a barrier to tumorigenesis. However, ROS can also promote tumour formation by inducing DNA mutations and pro-oncogenic signalling pathways. These contradictory effects have important implications for potential anticancer strategies that aim to modulate levels of ROS. In this Review, we address the controversial role of ROS in tumour development and in responses to anticancer therapies, and elaborate on the idea that targeting the antioxidant capacity of tumour cells can have a positive therapeutic impact.

Comparative analysis of the activation of unfolded protein response by spike proteins of severe acute respiratory syndrome coronavirus and human coronavirus HKU1

BACKGROUND

Whereas severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) is associated with severe disease, human coronavirus HKU1 (HCoV-HKU1) commonly circulates in the human populations causing generally milder illness. Spike (S) protein of SARS-CoV activates the unfolded protein response (UPR). It is not understood whether HCoV-HKU1 S protein has similar activity. In addition, the UPR-activating domain in SARS-CoV S protein remains to be identified.

RESULTS

In this study we compared S proteins of SARS-CoV and HCoV-HKU1 for their ability to activate the UPR. Both S proteins were found in the endoplasmic reticulum. Transmembrane serine protease TMPRSS2 catalyzed the cleavage of SARS-CoV S protein, but not the counterpart in HCoV-HKU1. Both S proteins showed a similar pattern of UPR-activating activity. Through PERK kinase they activated the transcription of UPR effector genes such as Grp78, Grp94 and CHOP. N-linked glycosylation was not required for the activation of the UPR by S proteins. S1 subunit of SARS-CoV but not its counterpart in HCoV-HKU1 was capable of activating the UPR. A central region (amino acids 201-400) of SARS-CoV S1 was required for this activity.

CONCLUSIONS

SARS-CoV and HCoV-HKU1 S proteins use distinct UPR-activating domains to exert the same modulatory effects on UPR signaling.

Rotavirus infection induces the unfolded protein response of the cell and controls it through the nonstructural protein NSP3

The unfolded protein response (UPR) is a cellular mechanism that is triggered in order to cope with the stress caused by the accumulation of misfolded proteins in the endoplasmic reticulum (ER). This response is initiated by the endoribonuclease inositol-requiring enzyme 1 (IRE1), activating transcription factor 6 (ATF6), and PKR-like ER kinase, which increase the expression of the genes involved in the folding and degradation processes and decrease the protein input into the ER by inhibiting translation. It has been shown that viruses both induce and manipulate the UPR in order to protect the host cells from an ER stress-mediated death, thus permitting the translation of viral proteins and the efficient replication of the virus. To understand the cellular events that occur during the rotavirus replication cycle, we examined the activation of the three UPR arms following infection, using luciferase reporters driven by promoters of the ER stress-responsive genes and real-time reverse transcription-PCR to determine the levels of the stress-induced mRNAs. Our findings indicated that during rotavirus infection two of the three arms of the UPR (IRE1 and ATF6) become activated; however, these pathways are interrupted at the translational level by the general inhibition of protein synthesis caused by NSP3. This response seems to be triggered by more than one viral protein synthesized during the replication of the virus, but not by the viral double-stranded RNA (dsRNA), since cells transfected with psoralen-inactivated virions, or with naked viral dsRNA, did not induce UPR.

SelK is a novel ER stress-regulated protein and protects HepG2 cells from ER stress agent-induced apoptosis

Selenoprotein K (SelK), an endoplasmic reticulum (ER) resident protein, its biological function has been less-well studied. To investigate the role of SelK in the ER stress response, effects of SelK gene silence and ER stress agents on expression of SelK and cell apoptosis in HepG2 cells were studied. The results showed that SelK was regulated by ER stress agents, Tunicamycin (Tm) and beta-Mercaptoethanol (beta-ME), in HepG2 cells. Moreover, the SelK gene silence by RNA interference could significantly aggravate HepG2 cell death and apoptosis induced by the ER stress agents. These results suggest that SelK is an ER stress-regulated protein and plays an important role in protecting HepG2 cells from ER stress agent-induced apoptosis.

The SARS Coronavirus 3a protein causes endoplasmic reticulum stress and induces ligand-independent downregulation of the type 1 interferon receptor

The Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) is reported to cause apoptosis of infected cells and several of its proteins including the 3a accessory protein, are pro-apoptotic. Since the 3a protein localizes to the endoplasmic reticulum (ER)-Golgi compartment, its role in causing ER stress was investigated in transiently transfected cells. Cells expressing the 3a proteins showed ER stress based on activation of genes for the ER chaperones GRP78 and GRP94. Since ER stress can cause differential modulation of the unfolded protein response (UPR), which includes the inositol-requiring enzyme 1 (IRE-1), activating transcription factor 6 (ATF6) and PKR-like ER kinase (PERK) pathways, these were individually tested in 3a-expressing cells. Only the PERK pathway was found to be activated in 3a-expressing cells based on (1) increased phosphorylation of eukaryotic initiation factor 2 alpha (eIF2α) and inhibitory effects of a dominant-negative form of eIF2α on GRP78 promoter activity, (2) increased translation of activating transcription factor 4 (ATF4) mRNA, and (3) ATF4-dependent activation of the C/EBP homologous protein (CHOP) gene promoter. Activation of PERK affects innate immunity by suppression of type 1 interferon (IFN) signaling. The 3a protein was found to induce serine phosphorylation within the IFN alpha-receptor subunit 1 (IFNAR1) degradation motif and to increase IFNAR1 ubiquitination. Confocal microscopic analysis showed increased translocation of IFNAR1 into the lysosomal compartment and flow cytometry showed reduced levels of IFNAR1 in 3a-expressing cells. These results provide further mechanistic details of the pro-apoptotic effects of the SARS-CoV 3a protein, and suggest a potential role for it in attenuating interferon responses and innate immunity.

Oxidative folding: cellular strategies for dealing with the resultant equimolar production of reactive oxygen species

All eukaryotic cells possess an endoplasmic reticulum (ER), which is the site for synthesizing proteins that populate the cell surface or extracellular space. The environment of the ER is oxidizing, which supports the formation of intra- and interchain disulfide bonds that serve to stabilize the folding and assembly of nascent proteins. Recent experimental data reveal that the formation of disulfide bonds does not occur spontaneously but results from the enzymatic transfer of disulfide bonds through a number of intermediate proteins, with molecular oxygen serving as the terminal electron acceptor. Thus, each disulfide bond that forms during oxidative folding should produce a single reactive oxygen species (ROS). Dedicated secretory tissues like the pancreas and plasma cells have been estimated to form up to 3-6 million disulfide bonds per minute, which would be expected to result in the production of the same number of molecules of ROS. Although the methods used to deal with this amount of oxidative stress are not well understood, recent research suggests that different types of cells use distinct strategies and that the unfolded protein response (UPR) is a critical component of the defense.

Hepatocyte necrosis induced by oxidative stress and IL-1 alpha release mediate carcinogen-induced compensatory proliferation and liver tumorigenesis

Hepatocyte I kappaB kinase beta (IKK beta) inhibits hepatocarcinogenesis by suppressing accumulation of reactive oxygen species (ROS) and liver damage, whereas JNK1 activation promotes ROS accumulation, liver damage, and carcinogenesis. We examined whether hepatocyte p38 alpha, found to inhibit liver carcinogenesis, acts similarly to IKK beta in control of ROS metabolism and cell death. Hepatocyte-specific p38 alpha ablation enhanced ROS accumulation and liver damage, which were prevented upon administration of an antioxidant. In addition to elevated ROS accumulation, hepatocyte death, augmented by loss of either IKK beta or p38 alpha, was associated with release of IL-1 alpha. Inhibition of IL-1 alpha action or ablation of its receptor inhibited carcinogen-induced compensatory proliferation and liver tumorigenesis. IL-1 alpha release by necrotic hepatocytes is therefore an important mediator of liver tumorigenesis.

The signaling mechanism of ROS in tumor progression

Reactive oxygen species (ROS) are recently proposed to be involved in tumor metastasis which is a complicated processes including epithelial-mesenchymal transition (EMT), migration, invasion of the tumor cells and angiogenesis around the tumor lesion. ROS generation may be induced intracellularly, in either NADPH oxidase- or mitochondria-dependent manner, by growth factors and cytokines (such as TGFbeta and HGF) and tumor promoters (such as TPA) capable of triggering cell adhesion, EMT and migration. As a signaling messenger, ROS are able to oxidize the critical target molecules such as PKC and protein tyrosine phosphates (PTPs), which are relevant to tumor cell invasion. PKC contain multiple cysteine residues that can be oxidized and activated by ROS. Inactivation of multiple PTPs by ROS may relieve the tyrosine phosphorylation-dependent signaling. Two of the down-stream molecules regulated by ROS are MAPK and PAK. MAPKs cascades were established to be a major signal pathway for driving tumor cell metastasis, which are mediated by PKC, TGF-beta/Smad and integrin-mediated signaling. PAK is an effector of Rac-mediated cytoskeletal remodeling that is responsible for cell migration and angiogenesis. There are several transcriptional factors such as AP1, Ets, Smad and Snail regulating a lot of genes relevant to metastasis. AP-1 and Smad can be activated by PKC activator and TGF-beta1, respectively, in a ROS dependent manner. On the other hand, Est-1 can be upregulated by H2O2 via an antioxidant response element in the promoter. The ROS-regulated genes relevant to EMT and metastasis include E-cahedrin, integrin and MMP. Comprehensive understanding of the ROS-triggered signaling transduction, transcriptional activation and regulation of gene expressions will help strengthen the critical role of ROS in tumor progression and devising strategy for chemo-therapeutic interventions.

N-(4-hydroxyphenyl)retinamide induces apoptosis in human retinal pigment epithelial cells: retinoic acid receptors regulate apoptosis, reactive oxygen species generation, and the expression of heme oxygenase-1 and Gadd153

N-(4-hydroxyphenyl)retinamide (4HPR, fenretinide), a retinoic acid (RA) derivative and a potential cancer preventive agent, is known to exert its chemotherapeutic effects in cancer cells through induction of apoptosis. Earlier work from our laboratory has shown that relatively low concentrations of 4HPR induce neuronal differentiation of cultured human retinal pigment epithelial (ARPE-19) cells (Chen et al., 2003, J Neurochem 84:972-981). However, at higher concentrations of 4HPR, these cells showed morphological changes including cell shrinkage and cell death. Here we demonstrate that ARPE-19 cells treated with 4HPR exhibit a dose- and time-dependent induction of apoptosis as evidenced by morphological changes, mono- and oligonucleosome generation, and increased activity of caspases 2 and 3. The 4HPR-induced apoptosis as well as the activation of caspases 2 and 3 were blocked by both retinoic acid receptors (RAR) pan-antagonists, AGN193109 and AGN194310, and by an RARalpha-specific antagonist AGN194301. 4HPR treatment also increased reactive oxygen species (ROS) generation in ARPE-19 cells in a time-dependent manner as determined from the oxidation of 2',7'-dichlorofluorescin. In addition, the increase in the expression of heme oxygenase-1 (HO-1), a stress response protein, and the growth arrest and DNA damage-inducible transcription factor 153 (Gadd153) in response to the ROS generation were also blocked by these receptor antagonists. Pyrrolidine dithiocarbamate (PDTC), a free-radical scavenger, inhibited 4HPR-induced ROS generation, the expression of its downstream mediator, Gadd153, and apoptosis in the pretreated cells. Therefore, our results, clearly demonstrate that 4HPR induces apoptosis in ARPE-19 cells and that RARs mediate this process by regulating ROS generation as well as the expression of Gadd153 and HO-1.

Modulation of the unfolded protein response by the severe acute respiratory syndrome coronavirus spike protein

Perturbation of the function of endoplasmic reticulum (ER) causes stress leading to the activation of cell signaling pathways known as the unfolded protein response (UPR). Severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) uses ER as a site for synthesis and processing of viral proteins. In this report, we demonstrate that infection with SARS-CoV induces the UPR in cultured cells. A comparison with M, E, and NSP6 proteins indicates that SARS-CoV spike (S) protein sufficiently induces transcriptional activation of several UPR effectors, including glucose-regulated protein 78 (GRP78), GRP94, and C/EBP homologous protein. A substantial amount of S protein accumulates in the ER. The expression of S protein exerts different effects on the three major signaling pathways of the UPR. Particularly, it induces GRP78/94 through PKR-like ER kinase but has no influence on activating transcription factor 6 or X box-binding protein 1. Taken together, our findings suggest that SARS-CoV S protein specifically modulates the UPR to facilitate viral replication.