Apoptosis repressor with caspase recruitment domain, a multifunctional modulator of cell death

Role of apoptosis repressor with caspase recruitment domain in human health and chronic diseases

Apoptosis repressor with caspase recruitment domain (ARC) is a highly potent and multifunctional suppressor of various types of programmed cell death (PCD) (e.g. apoptosis, necroptosis, and pyroptosis) and plays a key role in determining cell fate. Under physiological conditions, ARC is predominantly expressed in terminally differentiated cells, such as cardiomyocytes and skeletal muscle cells. Its expression and activity are tightly controlled by a complicated system consisting of transcription factor (TF), non-coding RNA (ncRNA), and post-translational modification (PTM). ARC dysregulation has been shown to be closely associated with many chronic diseases, including cardiovascular disease, cancer, diabetes, and neurodegenerative disease. However, the detailed mechanisms of ARC involved in the progression of these diseases remain unclear to a large extent. In this review, we mainly focus on the regulatory mechanisms of ARC expression and activity and its role in PCD. We also discuss the underlying mechanisms of ARC in health and disease and highlight the potential implications of ARC in the clinical treatment of patients with chronic diseases. This information may assist in developing ARC-based therapeutic strategies for patients with chronic diseases and expand researchers' understanding of ARC.

Effect of caspase inhibitors on hemodynamics and inflammatory factors in ARDS model rats

To study the effects of caspase inhibitors on hemodynamics and inflammatory factors in acute respiratory distress syndrome (ARDS) model rats. Sixty healthy male Wistar rats were randomly divided into three groups, namely, the control group, ARDS group and ARDS + Caspase inhibitor group, with 20 rats in each group. The control group was intraperitoneally injected with 2 mL/kg saline, and the ARDS model group was established by intraperitoneally injecting 4 mg/kg Lipopolysaccharide (LPS), ARDS + Caspase inhibitor group was adminstered 20 mg/kg caspase inhibitor after intraperitoneal LPS injection. Changes in pulmonary arterial pressure (PAP) and mean arterial pressure (MAP) at 6 and 12 h before and after administration were recorded. Moreover, arterial blood gas was evaluated with a blood gas analyzer and changes in the partial pressure of O2 (PaO2), partial pressure of CO2 (PaCO2), partial pressure of O2/fraction of inspired O2 (PaO2/FiO2) were evaluated. In addition, the lung wet/dry weight (W/D) ratio and inflammatory factor levels in lung tissue were determined. Finally, pathological sections were used to determine the pulmonary artery media thickness (MT), MT percentage (MT%), and the degree of muscle vascularization. The pulmonary arterial pressure of rats was determined at several time points. Compared with the control group, the model group had a significantly increased pulmonary arterial pressure at each time point (P < 0.01), and the mean arterial pressure significantly increased at 6 h (P < 0.05). Compared with that of rats in the model group, the pulmonary arterial pressure of rats in drug administration group was significantly reduced at each time point after administration (P < 0.01), and the mean arterial pressure was significantly reduced at 6 h (P < 0.05). The arterial blood gas analysis showed that compared with those in the control group, PaO2, PaCO2 and PaO2/FiO2 in the model group were significantly reduced (P < 0.01), and PaO2, PaCO2 and PaO2/FiO2 were significantly increased after caspase inhibitor treatment (P < 0.05 or 0.01). The levels of the inflammatory mediators tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) in the model group were significantly higher than those in the control group (P < 0.01), and they were significantly decreased after caspase inhibitor treatment (P < 0.01). In the model group, pulmonary artery MT, MT% and the degree of muscle vascularization were significantly increased (P < 0.05 or 0.01), and pulmonary artery MT and the degree of muscle vascularization were significantly reduced after caspase inhibitor treatment (P < 0.05 or 0.01). Apoptosis Repressor with a Caspase Recuitment Domain (ARC) can alleviate the occurrence and development of pulmonary hypertension (PH) by affecting hemodynamics and reducing inflammation.

Advances in the knowledge on the role of apoptosis repressor with caspase recruitment domain in hemorrhagic stroke

The apoptosis repressor with caspase recruitment domain (ARC) plays a critical role in extrinsic apoptosis initiation via death receptor ligands, physiological stress, infection response in a tissue-dependent manner, endoplasmic reticulum (ER) stress, genotoxic drugs, ionizing radiation, oxidative stress, and hypoxia. Recent studies have suggested that regulating apoptosis-related pathways can improve outcomes for patients with neurological diseases, such as hemorrhagic stroke. ARC expression is significantly correlated with acute cerebral hemorrhage. However, the mechanism by which it mediates the anti-apoptosis pathway remains poorly known. Here, we discuss the function of ARC in hemorrhagic stroke and argue that it could serve as an effective target for the treatment of hemorrhagic stroke.

ALDOC- and ENO2- driven glucose metabolism sustains 3D tumor spheroids growth regardless of nutrient environmental conditions: a multi-omics analysis

BACKGROUND

Metastases are the major cause of cancer-related morbidity and mortality. By the time cancer cells detach from their primary site to eventually spread to distant sites, they need to acquire the ability to survive in non-adherent conditions and to proliferate within a new microenvironment in spite of stressing conditions that may severely constrain the metastatic process. In this study, we gained insight into the molecular mechanisms allowing cancer cells to survive and proliferate in an anchorage-independent manner, regardless of both tumor-intrinsic variables and nutrient culture conditions.

METHODS

3D spheroids derived from lung adenocarcinoma (LUAD) and breast cancer cells were cultured in either nutrient-rich or -restricted culture conditions. A multi-omics approach, including transcriptomics, proteomics, and metabolomics, was used to explore the molecular changes underlying the transition from 2 to 3D cultures. Small interfering RNA-mediated loss of function assays were used to validate the role of the identified differentially expressed genes and proteins in H460 and HCC827 LUAD as well as in MCF7 and T47D breast cancer cell lines.

RESULTS

We found that the transition from 2 to 3D cultures of H460 and MCF7 cells is associated with significant changes in the expression of genes and proteins involved in metabolic reprogramming. In particular, we observed that 3D tumor spheroid growth implies the overexpression of ALDOC and ENO2 glycolytic enzymes concomitant with the enhanced consumption of glucose and fructose and the enhanced production of lactate. Transfection with siRNA against both ALDOC and ENO2 determined a significant reduction in lactate production, viability and size of 3D tumor spheroids produced by H460, HCC827, MCF7, and T47D cell lines.

CONCLUSIONS

Our results show that anchorage-independent survival and growth of cancer cells are supported by changes in genes and proteins that drive glucose metabolism towards an enhanced lactate production. Notably, this finding is valid for all lung and breast cancer cell lines we have analyzed in different nutrient environmental conditions. broader Validation of this mechanism in other cancer cells of different origin will be necessary to broaden the role of ALDOC and ENO2 to other tumor types. Future in vivo studies will be necessary to assess the role of ALDOC and ENO2 in cancer metastasis.

CK2 and the Hallmarks of Cancer

Cancer is a leading cause of death worldwide. Casein kinase 2 (CK2) is commonly dysregulated in cancer, impacting diverse molecular pathways. CK2 is a highly conserved serine/threonine kinase, constitutively active and ubiquitously expressed in eukaryotes. With over 500 known substrates and being estimated to be responsible for up to 10% of the human phosphoproteome, it is of significant importance. A broad spectrum of diverse types of cancer cells has been already shown to rely on disturbed CK2 levels for their survival. The hallmarks of cancer provide a rationale for understanding cancer's common traits. They constitute the maintenance of proliferative signaling, evasion of growth suppressors, resisting cell death, enabling of replicative immortality, induction of angiogenesis, the activation of invasion and metastasis, as well as avoidance of immune destruction and dysregulation of cellular energetics. In this work, we have compiled evidence from the literature suggesting that CK2 modulates all hallmarks of cancer, thereby promoting oncogenesis and operating as a cancer driver by creating a cellular environment favorable to neoplasia.

The Molecular Roles and Clinical Implications of Non-Coding RNAs in Gastric Cancer

Gastric cancer (GC) is one of the most common malignancies in the world. It is also the fifth most common cancer in China. In recent years, a large number of studies have proved that non-coding RNAs (ncRNAs) can regulate cell proliferation, invasion, metastasis, apoptosis, and angiogenesis. NcRNAs also influence the therapeutic resistance of gastric cancer. NcRNAs mainly consist of miRNAs, lncRNAs and circRNAs. In this paper, we summarized ncRNAs as biomarkers and therapeutic targets for gastric cancer, and also reviewed their role in clinical trials and diagnosis. We sum up different ncRNAs and related moleculars and signaling pathway in gastric cancer, like Bcl-2, PTEN, Wnt signaling. In addition, the potential clinical application of ncRNAs in overcoming chemotherapy and radiotherapy resistance in GC in the future were also focused on.

Apoptosis repressor with caspase recruitment domain (ARC) promotes bone regeneration of bone marrow-derived mesenchymal stem cells by activating Fgf-2/PI3K/Akt signaling

Objectives

This study aims to investigate whether apoptosis repressor with caspase recruitment domain (ARC) could promote survival and enhance osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs).

Materials and methods

The lentivirus transfection method was used to establish ARC-overexpressing BMSCs. The CCK-8 method was used to detect cell proliferation. The BD Pharmingen™ APC Annexin V Apoptosis Detection kit was used to detect cell apoptosis. The osteogenic capacity was investigated by OCN immunofluorescence staining, ALP analysis, ARS assays, and RT-PCR analysis. Cells were seeded into calcium phosphate cement (CPC) scaffolds and then inserted subcutaneously into nude mice and the defect area of the rat calvarium. Histological analysis was conducted to evaluate the in vivo cell apoptosis and new bone formation of the ARC-overexpressing BMSCs. RNA-seq was used to detect the possible mechanism of the effect of ARC on BMSCs.

Results

ARC promoted BMSC proliferation and inhibited cell apoptosis. ARC enhanced BMSC osteogenic differentiation in vitro. An in vivo study revealed that ARC can inhibit BMSC apoptosis and increase new bone formation. ARC regulates BMSCs mainly by activating the Fgf-2/PI3K/Akt pathway.

Conclusions

The present study suggests that ARC is a powerful agent for promoting bone regeneration of BMSCs and provides a promising method for bone tissue engineering.

Expression of apoptosis repressor with caspase recruitment domain (ARC) in familial adenomatous polyposis (FAP) adenomas and its correlation with DNA mismatch repair proteins, p53, Bcl-2, COX-2 and beta-catenin

Background

Colorectal familial adenomatous polyposis (FAP) adenomas exhibit a uniform pathogenetic basis caused by a germline mutation in the adenomatous polyposis gene (APC), but the molecular changes leading to their development are incompletely understood. However, dysregulated apoptosis is known to substantially affect the development of colonic adenomas. One of the key regulatory proteins involved in apoptosis is apoptosis repressor with caspase recruitment domain (ARC).

Methods

The expression of nuclear and cytoplasmic ARC in 212 adenomas from 80 patients was analyzed by immunohistochemistry. We also compared expression levels of ARC with the expression levels of p53, Bcl-2, COX-2, and MMR proteins. Statistical analyses were performed by Spearman’s rank correlation and linear regression test.

Results

ARC was overexpressed in the nuclei and cytoplasm of most FAP adenomas investigated. Cytoplasmic ARC staining was moderately stronger (score 2) in 49.1% (n = 104/212) and substantially stronger (score 3) in 32.5% (n = 69/212) of adenomas compared to non-tumorous colorectal mucosa. In 18.4% (n = 39/212) of adenomas, cytoplasmic ARC staining was equivalent to that in non-tumorous mucosa.

Nuclear expression of ARC in over 75% of cells was present in 30.7% (n = 65/212) of investigated adenomas, and nuclear expression in 10–75% of cells was detected in 62.7% (n = 133/212). ARC expression in under 10% of nuclei was found in 6.6% (n = 14/212) of adenomas.

The correlation between nuclear ARC expression and cytoplasmic ARC expression was highly significant (p = 0.001). Moreover, nuclear ARC expression correlated positively with overexpression of Bcl-2, COX-2 p53 and β-catenin. Cytoplasmic ARC also correlated with overexpression of Bcl-2. Sporadic MMR deficiency was detected in very few FAP adenomas and showed no correlation with nuclear or cytoplasmic ARC.

Conclusions

Our results demonstrated that both cytoplasmic and nuclear ARC are overexpressed in FAP adenomas, thus in a homogenous collective. The highly significant correlation between nuclear ARC and nuclear β-catenin suggested that ARC might be regulated by β-catenin in FAP adenomas. Because of its further correlations with p53, Bcl-2, and COX-2, nuclear ARC might play a substantial role not only in carcinomas but also in precursor lesions.

Bioinformatic analysis and functional predictions of selected regeneration-associated transcripts expressed by zebrafish microglia

BACKGROUND

Unlike mammals, zebrafish have a remarkable capacity to regenerate a variety of tissues, including central nervous system tissue. The function of macrophages in tissue regeneration is of great interest, as macrophages respond and participate in the landscape of events that occur following tissue injury in all vertebrate species examined. Understanding macrophage populations in regenerating tissue (such as in zebrafish) may inform strategies that aim to regenerate tissue in humans. We recently published an RNA-seq experiment that identified genes enriched in microglia/macrophages in regenerating zebrafish retinas. Interestingly, a small number of transcripts differentially expressed by retinal microglia/macrophages during retinal regeneration did not have predicted orthologs in human or mouse. We reasoned that at least some of these genes could be functionally important for tissue regeneration, but most of these genes have not been studied experimentally and their functions are largely unknown. To reveal their possible functions, we performed a variety of bioinformatic analyses aimed at identifying the presence of functional protein domains as well as orthologous relationships to other species.

RESULTS

Our analyses identified putative functional domains in predicted proteins for a number of selected genes. For example, we confidently predict kinase function for one gene, cytokine/chemokine function for another, and carbohydrate enzymatic function for a third. Predicted orthologs were identified for some, but not all, genes in species with described regenerative capacity, and functional domains were consistent with identified orthologs. Comparison to other published gene expression datasets suggest that at least some of these genes could be important in regenerative responses in zebrafish and not necessarily in response to microbial infection.

CONCLUSIONS

This work reveals previously undescribed putative function of several genes implicated in regulating tissue regeneration. This will inform future work to experimentally determine the function of these genes in vivo, and how these genes may be involved in microglia/macrophage roles in tissue regeneration.

ARC Is a Critical Protector against Inflammatory Bowel Disease (IBD) and IBD-Associated Colorectal Tumorigenesis

The key functional molecules involved in inflammatory bowel disease (IBD) and IBD-induced colorectal tumorigenesis remain unclear. In this study, we found that the apoptosis repressor with caspase recruitment domain (ARC) protein plays critical roles in IBD. ARC-deficient mice exhibited substantially higher susceptibility to dextran sulfate sodium (DSS)-induced IBD compared with wild-type mice. The inflammatory burden induced in ARC-deficient conditions was inversely correlated with CCL5 and CXCL5 levels in immune cells, especially CD4-positive T cells. Pathologically, ARC expression in immune cells was significantly decreased in clinical biopsy specimens from patients with IBD compared with normal subjects. In addition, ARC levels inversely correlated with CCL5 and CXCL5 levels in human biopsy specimens. ARC interacted with TNF receptor associated factor (TRAF) 6, regulating ubiquitination of TRAF6, which was associated with NF-κB signaling. Importantly, we identified a novel ubiquitination site at lysine 461, which was critical in the function of ARC in IBD. ARC played a critical role in IBD and IBD-associated colon cancer in a bone marrow transplantation model and azoxymethane/DSS-induced colitis cancer mouse models. Overall, these findings reveal that ARC is critically involved in the maintenance of intestinal homeostasis and protection against IBD through its ubiquitination of TRAF6 and subsequent modulation of NF-κB activation in T cells. SIGNIFICANCE: This study uncovers a crucial role of ARC in the immune system and IBD, giving rise to a novel strategy for IBD and IBD-associated colon cancer therapy.

Apoptosis repressor with caspase recruitment domain promotes cell proliferation and phenotypic modulation through 14-3-3ε/YAP signaling in vascular smooth muscle cells

AIMS

In response to vascular injury, vascular smooth muscle cells (VSMC) may change from a contractile phenotype to a proliferative phenotype and consequently become conducive to neointima formation. Apoptosis repressor with caspase recruitment domain (ARC) was initially discovered as an endogenous apoptosis inhibitor, but whether ARC plays a role in VSMCs and whether it can participate in the regulation of atherosclerosis are unknown.

METHODS AND RESULTS

Protein and mRNA levels of ARC in tissues and cells were detected by western blot and quantitative real-time PCR. Immunofluorescence staining was used to detect the protein location, and immunohistochemistry was used to detect protein expression in tissues. VSMC proliferation was analysed using Cell Counting Kit-8 (CCK-8) and EdU assays, while migration was assessed by Transwell assay. Mechanistically, the direct binding between two proteins was verified by immunoprecipitation. We found that ARC expression was stimulated in VSMCs during cell proliferation. Our results also showed that ARC promoted cell proliferation and induced phenotypic modulation of VSMCs in vitro and vivo. Mechanistic studies demonstrated that ARC increased the nuclear localization of Yes associated protein (YAP) by binding to 14-3-3ε and that ARC played a role in promoting cell proliferation and phenotypic modulation. Additionally, the transcription factor p53 negatively regulated ARC expression at the transcriptional level during cell proliferation and phenotypic modulation.

CONCLUSIONS

Our findings define a novel role for ARC in the phenotypic transition of proliferating VSMCs, which may provide a new strategy for regulating neointimal formation.

Modulation of Apoptosis by Plant Polysaccharides for Exerting Anti-Cancer Effects: A Review

Cancer has become a significant public health problem with high disease burden and mortality. At present, radiotherapy and chemotherapy are the main means of treating cancer, but they have shown serious safety problems. The severity of this problem has caused further attention and research on effective and safe cancer treatment methods. Polysaccharides are natural products with anti-cancer activity that are widely present in a lot of plants, and many studies have found that inducing apoptosis of cancer cells is one of their important mechanisms. Therefore, this article reviews the various ways in which plant polysaccharides promote apoptosis of cancer cells. The major apoptotic pathways involved include the mitochondrial pathway, the death receptor pathway, and their upstream signal transduction such as MAPK pathway, PI3K/AKT pathway, and NF-κB pathway. Moreover, the paper has also been focused on the absorption and toxicity of plant polysaccharides with reference to extant literature, making the research more scientific and comprehensive. It is hoped that this review could provide some directions for the future development of plant polysaccharides as anticancer drugs in pharmacological experiments and clinical researches.

Loss of nuclear ARC contributes to the development of cardiac hypertrophy in rats

AIM

Cardiac hypertrophy and myocardial apoptosis are two major factors in heart failure. As a classical regulator of apoptosis, apoptosis repressor with caspase recruitment domain (ARC) has recently also been found to have a protective effect against hypertrophy. However, the mechanism underlying this effect is still not fully understood.

METHODS

In the present study, we established animal and cellular models to monitor the changes in total and nuclear ARC during cardiac hypertrophic processes. The preventive effects of nuclear ARC in cellular hypertrophy were verified by ARC regulation and nuclear export inhibition. To further explore the mechanism for nuclear ARC superficially, we analysed proteins that interact with ARC in the nucleus via Co-IP and mass spectrometry.

RESULTS

The expression of total ARC in hypertrophic myocardial tissue and H9C2 cells remained invariant, while the level of nuclear ARC decreased dramatically. By altering the content of ARC in H9C2 cells, we found that both nuclear ARC transfection and nuclear ARC export blockade attenuated norepinephrine or angiotensin II-induced hypertrophy, while ARC knockdown had an inverse effect. Co-IP data showed that ARC interacted with prohibitin (PHB) in the nucleus and might participate in maintaining the level of PHB in cells.

CONCLUSIONS

These findings suggest a novel mechanism for ARC in cardiac hypertrophy prevention and also indicate that the anti-hypertrophic roles of ARC are probably associated with its localization in nucleus, which imply the nuclear ARC as a potential therapeutic target for cardiac hypertrophy.

Caspase recruitment domains for protein interactions in cellular signaling (Review)

The caspase recruitment domain (CARD), a well-known protein interaction module, belongs to the death domain (DD) superfamily, which includes DDs, death effector domains, and pyrin domains. The DD superfamily mediates the protein interactions necessary for apoptosis and immune cell signaling pathways. Among these domains, the CARD has been studied extensively as it mediates important cellular signaling events that are associated with various human diseases including cancer, neuro-degenerative diseases and immune disorders. Homo-type and hetero-type CARD-CARD interactions mediate the formation of large signaling complexes, including caspase-activating complexes and downstream signaling complexes. The present review summarizes and discusses the results of structural studies of various CARDs and their complexes. These studies shed light on the mechanisms that control the assembly and disassembly of signaling complexes and provide an improved understanding of cellular signaling processes.

Inhibition of ARC decreases the survival of HEI-OC-1 cells after neomycin damage in vitro

Hearing loss is a common sensory disorder mainly caused by the loss of hair cells (HCs). Noise, aging, and ototoxic drugs can all induce apoptosis in HCs. Apoptosis repressor with caspase recruitment domain(ARC) is a key factor in apoptosis that inhibits both intrinsic and extrinsic apoptosis pathways; however, there have been no reports on the role of ARC in HC loss in the inner ear. In this study, we used House Ear Institute Organ of Corti 1 (HEI-OC-1) cells, which is a cochlear hair-cell-like cell line, to investigate the role of ARC in aminoglycoside-induced HC loss. ARC was expressed in the cochlear HCs as well as in the HEI-OC-1 cells, but not in the supporting cells, and the expression level of ARC in HCs was decreased after neomycin injury in both cochlear HCs and HEI-OC-1 cells, suggesting that reduced levels of ARC might correlate with neomycin-induced HC loss. We inhibited ARC expression using siRNA and found that this significantly increased the sensitivity of HEI-OC-1 cells to neomycin toxicity. Finally, we found that ARC inhibition increased the expression of pro-apoptotic factors, decreased the mitochondrial membrane potential, and increased the level of reactive oxygen species (ROS) after neomycin injury, suggesting that ARC inhibits cell death and apoptosis in HEI-OC-1 cells by controlling mitochondrial function and ROS accumulation. Thus the endogenous anti-apoptotic factor ARC might be a new therapeutic target for the prevention of aminoglycoside-induced HC loss.

Data of expression status of miR- 29a and its putative target mitochondrial apoptosis regulatory gene DRP1 upon miR-15a and miR-214 inhibition

Data is about the mitochondrial apoptosis regulatory framework genes PUMA, DRP1 (apoptotic), and ARC (anti-apoptotic) analysis after the employment of their controlling miRNAs inhibitors. The data represents putative conserved targeting of seed regions of miR-15a, miR-29a, and miR-214 with respective target genes PUMA, DRP1, and ARC. Data is of cross interference in expression levels of one miRNA family, miR-29a and its putative target DRP1 upon the inhibitory treatment of other miRNAs 15a and 214.

The effect of ARC ablation on skeletal muscle morphology, function, and apoptotic signaling during aging

Augmented apoptotic signaling can result in degradation of skeletal muscle proteins and loss of myonuclei, ultimately contributing to muscle atrophy and contractile dysfunction. Apoptosis repressor with caspase recruitment domain (ARC) is an anti-apoptotic protein highly expressed in skeletal muscle. Here we examined the role of ARC on age-related skeletal muscle apoptosis and wasting by utilizing an ARC-deficient mouse model. Aged mice displayed a number of morphological, phenotypic, and contractile alterations in both soleus and plantaris muscle with aging. Although no differences were found in proteolytic enzyme activity, ARC protein decreased while several anti-apoptotic proteins (e.g., BCL2, BCLXL, HSP70, and XIAP) and the release of mitochondrial housed protein (i.e., SMAC, AIF) increased in aged muscle. Importantly, ARC KO mice had low muscle weights and fewer fibers in soleus, with 2-year-old ARC KO mice displaying lower mitochondrial BCL2 protein along with augmented release of CYTC and SMAC in red/oxidative muscle. Overall, these results indicate that aged skeletal muscle undergoes atrophy as well as contractile and fiber type composition alterations despite an increase in anti-apoptotic protein expression. Although some mitochondrial-specific apoptotic alterations occurred in skeletal muscle due to ARC ablation over the lifespan, our data suggest that ARC may not have a large influence during skeletal muscle aging.

Inhibition of ARC promoting the apoptosis of rat pulmonary arterial smooth muscle cells after serum deprivation in vitro

Apoptosis has important pathophysiological consequences contributing to pulmonary arterial hypertension (PAH). However, the mechanism underlying apoptosis in PAH remains unknown. Apoptosis repressor with caspase recruitment domain (ARC) is an essential factor in cell apoptosis, and regulates intrinsic and extrinsic apoptosis signaling pathways. It is hypothesized that ARC may be involved in the apoptotic responses of pulmonary arterial smooth muscle cells (PASMCs) following mild chronic injury. In the present study, serum deprivation (SD) was used to induce apoptosis of PASMCs. It was demonstrated that the expression of ARC in PASMCs was significantly increased following SD stimulation within 24 h, and ARC downregulation using small interfering RNA significantly enhanced the apoptosis of PASMCs following SD stimulation. In addition, the results demonstrated that ARC downregulation significantly increased the expression of proapoptotic factors and the level of reactive oxygen species (ROS), and decreased the mitochondrial membrane potential following SD exposure, suggesting ARC regulates the apoptosis of PASMCs via modulating mitochondrial function and ROS accumulation. The results of the present study revealed that ARC inhibition promotes the apoptosis of PASMCs following SD stimulation, and that ARC expression increases in the early stages of SD injury.

Status of Therapeutic Gene Transfer to Treat Cardiovascular Disease in Dogs and Cats

Gene therapy is a procedure resulting in the transfer of a gene into an individual's cells to treat a disease. One goal of gene transfer is to express a functional gene when the endogenous gene is inactive. However, because heart failure is a complex disease characterized by multiple abnormalities at the cellular level, an alternate gene delivery approach is to alter myocardial protein levels to improve function. This article discusses background information on gene delivery, including packaging, administration, and a brief discussion of some of the candidate transgenes likely to alter the progression of naturally occurring heart disease in dogs and cats.

Nicotine plus a high-fat diet triggers cardiomyocyte apoptosis

Cigarette smoking is an important risk factor for diabetes, cardiovascular disease and non-alcoholic fatty liver disease. The health risk associated with smoking can be aggravated by obesity. Smoking might also trigger cardiomyocyte (CM) apoptosis. Given that CM apoptosis has been implicated as a potential mechanism in the development of cardiomyopathy and heart failure, we characterize the key signaling pathways in nicotine plus high-fat diet (HFD)-induced CM apoptosis. Adult C57BL6 male mice were fed a normal diet (ND) or HFD and received twice-daily intraperitoneal (IP) injections of nicotine (0.75 mg/kg body weight [BW]) or saline for 16 weeks. An additional group of nicotine-treated mice on HFD received twice-daily IP injections of mecamylamine (1 mg/kg BW), a non-selective nicotinic acetylcholine receptor antagonist, for 16 weeks. Nicotine when combined with HFD led to a massive increase in CM apoptosis that was fully prevented by mecamylamine treatment. Induction of CM apoptosis was associated with increased oxidative stress and activation of caspase-2-mediated intrinsic pathway signaling coupled with inactivation of AMP-activated protein kinase (AMPK). Furthermore, nicotine treatment significantly (P < 0.05) attenuated the HFD-induced decrease in fibroblast growth factor 21 (FGF21) and silent information regulator 1 (SIRT1). We conclude that nicotine, when combined with HFD, triggers CM apoptosis through the generation of oxidative stress and inactivation of AMPK together with the activation of caspase-2-mediated intrinsic apoptotic signaling independently of FGF21 and SIRT1.

Phosphorylation of apoptosis repressor with caspase recruitment domain by protein kinase CK2 contributes to chemotherapy resistance by inhibiting doxorubicin induced apoptosis

The development of cancer resistance to chemotherapy is the major obstacle to cancer therapy. Here, we identified that the phosphorylation of apoptosis repressor with caspase recruitment domain (ARC) at threonine 149 was essential to inhibit doxorubicin (DOX) induced apoptosis and mitochondrial fission in cancer cells. Our further study showed that casein kinase II (CK2) inhibitors could decrease the phosphorylation levels of ARC and make cancer cells sensitive to undergoing apoptosis. Furthermore, CK2α and CK2α', catalytic subunits of CK2, were observed to translocate into nuclear in cancer cells with the treatment of DOX. Finally, the synergistically therapeutic effect by combining DOX and CK2 inhibitor was confirmed in tumor xenograft model. Taken together, our results revealed that CK2-mediated phosphorylation of ARC contributed to chemotherapy resistance by inhibiting DOX induced apoptosis and combining DOX with CK2 inhibitor could induce apoptosis of cancer cells synergistically by down-regulating the phosphorylation of ARC. Therefore, development of new therapeutic strategies based on ARC and CK2, is promising for overcoming cancer resistance to chemotherapy.

Expression of the apoptosis repressor with caspase recruitment domain (ARC) in liver metastasis of colorectal cancer and its correlation with DNA mismatch repair proteins and p53

INTRODUCTION

Apoptotic signaling is one of the most important processes in the measurement of chemotherapeutic effectiveness. In apoptotic machinery, various pathways and proteins are involved (i.e., mismatch repair proteins, p53). One of the regulatory proteins is ARC, which can inhibit not only the extrinsic but also the intrinsic apoptotic signaling.

MATERIALS AND METHODS

In this study, we investigated the expression levels of ARC in colorectal liver metastasis and compared them with the expression of mismatch repair proteins and p53. Furthermore, we investigated ARC expression level depending on sex, age, tumor grade, mucin production, tumor size and number of liver metastasis.

RESULTS

ARC expression level in colorectal cancer liver metastasis was independent from clinical data (i.e., age, gender, tumor size, tumor number or mucin production) but strongly correlated with MSH2 and MSH6 expression, which further supported the evidence for the regulatory role of MSH2 and MSH6 in apoptosis; i.e., in case of sufficient MSH2 and MSH6 expression, significantly higher ARC level is required to suppress the apoptosis. A regulatory interaction between ARC and p53 has been described, but we found no correlation between p53 expression levels and ARC levels.

CONCLUSION

Further studies are needed to define the exact role of ARC in apoptotic signaling and thus its role in chemoresistance and survival of tumor cells.

Crystal structure of caspase recruiting domain (CARD) of apoptosis repressor with CARD (ARC) and its implication in inhibition of apoptosis

Apoptosis repressor with caspase recruiting domain (ARC) is a multifunctional inhibitor of apoptosis that is unusually over-expressed or activated in various cancers and in the state of the pulmonary hypertension. Therefore, ARC might be an optimal target for therapeutic intervention. Human ARC is composed of two distinct domains, N-terminal caspase recruiting domain (CARD) and C-terminal P/E (proline and glutamic acid) rich domain. ARC inhibits the extrinsic apoptosis pathway by interfering with DISC formation. ARC CARD directly interacts with the death domains (DDs) of Fas and FADD, as well as with the death effector domains (DEDs) of procaspase-8. Here, we report the first crystal structure of the CARD domain of ARC at a resolution of 2.4 Å. Our structure was a dimer with novel homo-dimerization interfaces that might be critical to its inhibitory function. Interestingly, ARC did not exhibit a typical death domain fold. The sixth helix (H6), which was detected at the typical death domain fold, was not detected in the structure of ARC, indicating that H6 may be dispensable for the function of the death domain superfamily.

Expression of the vault RNA protects cells from undergoing apoptosis

Non-protein-coding RNAs are a functionally versatile class of transcripts exerting their biological roles on the RNA level. Recently, we demonstrated that the vault complex-associated RNAs (vtRNAs) are significantly upregulated in Epstein-Barr virus (EBV)-infected human B cells. Very little is known about the function(s) of the vtRNAs or the vault complex. Here, we individually express latent EBV-encoded proteins in B cells and identify the latent membrane protein 1 (LMP1) as trigger for vtRNA upregulation. Ectopic expression of vtRNA1-1, but not of the other vtRNA paralogues, results in an improved viral establishment and reduced apoptosis, a function located in the central domain of vtRNA1-1. Knockdown of the major vault protein has no effect on these phenotypes revealing that vtRNA1-1 and not the vault complex contributes to general cell death resistance. This study describes a NF-κB-mediated role of the non-coding vtRNA1-1 in inhibiting both the extrinsic and intrinsic apoptotic pathways.

Distinct muscle apoptotic pathways are activated in muscles with different fiber types in a rat model of critical illness myopathy

Critical illness myopathy (CIM) is associated with severe muscle atrophy and fatigue in affected patients. Apoptotic signaling is involved in atrophy and is elevated in muscles from patients with CIM. In this study we investigated underlying mechanisms of apoptosis-related pathways in muscles with different fiber type composition in a rat model of CIM using denervation and glucocorticoid administration (denervation and steroid-induced myopathy, DSIM). Soleus and tibialis anterior (TA) muscles showed severe muscle atrophy (40-60% of control muscle weight) and significant apoptosis in interstitial as well as myofiber nuclei that was similar between the two muscles with DSIM. Caspase-3 and -8 activities, but not caspase-9 and -12, were elevated in TA and not in soleus muscle, while the caspase-independent proteins endonuclease G (EndoG) and apoptosis inducing factor (AIF) were not changed in abundance nor differentially localized in either muscle. Anti-apoptotic proteins HSP70, -27, and apoptosis repressor with a caspase recruitment domain (ARC) were elevated in soleus compared to TA muscle and ARC was significantly decreased with induction of DSIM in soleus. Results indicate that apoptosis is a significant process associated with DSIM in both soleus and TA muscles, and that apoptosis-associated processes are differentially regulated in muscles of different function and fiber type undergoing atrophy due to DSIM. We conclude that interventions combating apoptosis with CIM may need to be directed towards inhibiting caspase-dependent as well as -independent mechanisms to be able to affect muscles of all fiber types.

Dihydromyricetin prevents cardiotoxicity and enhances anticancer activity induced by adriamycin

Adriamycin, a widely used anthracycline antibiotic in multiple chemotherapy regimens, has been challenged by the cardiotoxicity leading to fatal congestive heart failure in the worst condition. The present study demonstrated that Dihydromyricetin, a natural product extracted from ampelopsis grossedentat, exerted cardioprotective effect against the injury in Adriamycin-administrated ICR mice. Dihydromyricetin decreased ALT, LDH and CKMB levels in mice serum, causing a significant reduction in the toxic death triggered by Adriamycin. The protective effects were also indicated by the alleviation of abnormal electrocardiographic changes, the abrogation of proliferation arrest and apoptotic cell death in primary myocardial cells. Further study revealed that Dihydromyricetin-rescued loss of anti-apoptosis protein ARC provoked by Adriamycin was involved in the cardioprotection. Intriguingly, the anticancer activity of Adriamycin was not compromised upon the combination with Dihydromyricetin, as demonstrated by the enhanced anticancer effect achieved by Adriamycin plus Dihydromyricetin in human leukemia U937 cells and xenograft models, in a p53-dependent manner. These results collectively promised the potential value of Dihydromyricetin as a rational cardioprotective agent of Adriamycin, by protecting myocardial cells from apoptosis, while potentiating anticancer activities of Adriamycin, thus further increasing the therapeutic window of the latter one.

Crystallization and preliminary X-ray crystallographic analysis of the CARD domain of apoptosis repressor with CARD (ARC)

Apoptosis repressor with caspase-recruiting domain (ARC) is an apoptosis repressor that inhibits both intrinsic and extrinsic apoptosis signalling. Human ARC contains an N-terminal caspase-recruiting domain (CARD domain) and a C-terminal proline- and glutamic acid-rich (P/E-rich) domain. The CARD domain in ARC is the domain that is directly involved in inhibition of the extrinsic pathway. In this study, the N-terminal CARD domain of ARC was overexpressed, purified and crystallized. X-ray diffraction data were collected to a resolution of 2.1 Å and the crystals were found to belong to space group P6(1) or P65, with unit-cell parameters a=98.28, b=98.28, c=51.86 Å, α=90, β=90, γ=120°.

MicroRNA-185 regulates chemotherapeutic sensitivity in gastric cancer by targeting apoptosis repressor with caspase recruitment domain

Gastric cancer remains the second leading cause of cancer deaths worldwide. Resistance to chemotherapy is a significant barrier for effective cancer treatment. Here, we identified miR-185 to be a contributor to chemosensitivity in gastric cancer. We observed low levels of miR-185 in gastric cancer cell lines and clinical tissues, compared with gastric epithelium cell line and noncancerous tissues. Furthermore, enforced expression of miR-185 increased the sensitivity of gastric cancer cells to low-dose chemotherapeutic agents, which alone cannot trigger significant apoptosis. Conversely, knockdown of endogenous miR-185 prevented high-dose chemotherapy-induced apoptosis. In elucidating the molecular mechanism by which miR-185 participated in the regulation of chemosensitivity in gastric cancer, we discovered that apoptosis repressor with caspase recruitment domain (ARC) is a direct target of miR-185. The role of miR-185 was confirmed in gastric tumor xenograft model. The growth of established tumors was suppressed by a combination therapy using enforced miR-185 expression and a low dose of anticancer drugs. Finally, we found that RUNX3 (Runt-related transcription factor) was involved in the activation of miR-185 at the transcriptional level. Taken together, our results reveal that RUNX3, miR-185 and ARC regulate the sensitivity of gastric cancer cells to chemotherapy.

The dual behavior of PCSK9 in the regulation of apoptosis is crucial in Alzheimer's disease progression (Review)

Neuronal apoptosis is crucial in neurodegenerative diseases. However, a lower apoptotic rate of nerve cells is detected in the brain compared to that in other organs in neurodegenerative patients or in animal models, suggesting that neuronal apoptosis induced by any type of risk factors is intricately regulated. Human and animal studies demonstrated that a high concentration of oxidized LDL (ox-LDL) in the brain, which is associated with hyperlipidemia, is one of the key apoptosis inducers in neurodegenerative diseases. However, the mechanism underlying the ox-LDL-mediated regulation of neuronal apoptosis has not been fully elucidated. Recently, we investigated proprotein convertase subtilisin/kexin type 9 (PCSK9), a striking gene involved in lipid metabolism that exhibits a positive correlation with macrophage and endothelial cell apoptosis induced by ox-LDL. Moreover, PCSK9 may degrade β-site amyloid precursor protein-cleaving enzyme 1 (BACE1), the key enzyme cleaving amyloid precursor protein (APP) to generate amyloid β peptide (Aβ). Aβ is another key apoptosis inducer in neurodegenerative diseases. Our findings indicated that PCSK9 may be upregulated by the high levels of ox-LDL in the brain associated with hyperlipidemia and promote neuronal apoptosis through the NF-κB-B-cell lymphoma 2 (Bcl-2)/Bax-caspase 9-caspase 3 signaling pathways. Moreover, increased PCSK9 levels may inhibit the APP/Aβ metabolic pathway and reduce Aβ generation by degrading BACE1, thereby decreasing Aβ-induced neuronal apoptosis. The dual regulation mechanism of PCSK9 on apoptosis maintains neuronal apoptosis induced by risk factors at low levels.

The apoptosis repressor with a CARD domain (ARC) gene is a direct hypoxia-inducible factor 1 target gene and promotes survival and proliferation of VHL-deficient renal cancer cells

The induction of hypoxia-inducible factors (HIFs) is essential for the adaptation of tumor cells to a low-oxygen environment. We found that the expression of the apoptosis inhibitor ARC (apoptosis repressor with a CARD domain) was induced by hypoxia in a variety of cancer cell types, and its induction is primarily HIF1 dependent. Chromatin immunoprecipitation (ChIP) and reporter assays also indicate that the ARC gene is regulated by direct binding of HIF1 to a hypoxia response element (HRE) located at bp -190 upstream of the transcription start site. HIFs play an essential role in the pathogenesis of renal cell carcinoma (RCC) under normoxic conditions, through the loss of the Von Hippel-Lindau gene (VHL). Accordingly, our results show that ARC is not expressed in normal renal tissue but is highly expressed in 65% of RCC tumors, which also express high levels of carbonic anhydrase IX (CAIX), a HIF1-dependent protein. Compared to controls, ARC-deficient RCCs exhibited decreased colony formation and increased apoptosis in vitro. In addition, loss of ARC resulted in a dramatic reduction of RCC tumor growth in SCID mice in vivo. Thus, HIF-mediated increased expression of ARC in RCC can explain how loss of VHL can promote survival early in tumor formation.

Mechanisms of radiation toxicity in transformed and non-transformed cells

Radiation damage to biological systems is determined by the type of radiation, the total dosage of exposure, the dose rate, and the region of the body exposed. Three modes of cell death—necrosis, apoptosis, and autophagy—as well as accelerated senescence have been demonstrated to occur in vitro and in vivo in response to radiation in cancer cells as well as in normal cells. The basis for cellular selection for each mode depends on various factors including the specific cell type involved, the dose of radiation absorbed by the cell, and whether it is proliferating and/or transformed. Here we review the signaling mechanisms activated by radiation for the induction of toxicity in transformed and normal cells. Understanding the molecular mechanisms of radiation toxicity is critical for the development of radiation countermeasures as well as for the improvement of clinical radiation in cancer treatment.

Low-Dose Spironolactone Prevents Apoptosis Repressor With Caspase Recruitment Domain Degradation During Myocardial Infarction

Low-dose mineralocorticoid receptor antagonists reduce morbidity and mortality in patients with heart failure and myocardial infarction, despite normal plasma aldosterone levels. Since apoptosis plays an important role in heart failure and postinfarction left ventricular remodeling, we examined whether low-dose mineralocorticoid receptor antagonists modulate cardiomyocyte death by regulating the apoptosis repressor protein apoptosis repressor with caspase recruitment domain to lessen the extent of apoptosis. Hearts from adult male Sprague-Dawley rats were subjected to regional ischemia followed by reperfusion ex vivo, with mineralocorticoid receptor antagonists added to perfusates before ischemia. Low-dose spironolactone (10 nmol/L) or eplerenone (100 nmol/L) significantly reduced infarct size. Spironolactone also prevented cleavage of the apoptotic chromatin condensation inducer in the nucleus and of the inhibitor of caspase-activated DNAse induced by ischemia-reperfusion, thereby abolishing chromatin condensation and internucleosomal cleavage. Ischemia-reperfusion–induced activation of caspases 2, 3, and 9, but not caspase 8, was prevented by spironolactone, suggesting targeted regulation of the intrinsic pathway. Low-dose spironolactone and eplerenone prevented loss of the apoptosis repressor with the caspase recruitment domain and reduced myocyte death. In H9c2 cells, mineralocorticoid receptor activation by aldosterone resulted in apoptosis repressor with caspase recruitment domain degradation and enhanced apoptosis; these actions were prevented by coadministration of spironolactone. Using a triple lysine mutant we identified that aldosterone enhances posttranscriptional degradation of the apoptosis repressor with a caspase recruitment domain via the ubiquitin-proteasomal pathway. Our data demonstrate that low-dose mineralocorticoid receptor antagonists reduce infarct size and apoptosis in the reperfused myocardium by preventing the apoptosis repressor with caspase recruitment domain degradation.