Involvement of caspase-4(-like) protease in Fas-mediated apoptotic pathway

A Review on Caspases: Key Regulators of Biological Activities and Apoptosis

Caspases are proteolytic enzymes that belong to the cysteine protease family and play a crucial role in homeostasis and programmed cell death. Caspases have been broadly classified by their known roles in apoptosis (caspase-3, caspase-6, caspase-7, caspase-8, and caspase-9 in mammals) and in inflammation (caspase-1, caspase-4, caspase-5, and caspase-12 in humans, and caspase-1, caspase-11, and caspase-12 in mice). Caspases involved in apoptosis have been subclassified by their mechanism of action as either initiator caspases (caspase-8 and caspase-9) or executioner caspases (caspase-3, caspase-6, and caspase-7). Caspases that participate in apoptosis are inhibited by proteins known as inhibitors of apoptosis (IAPs). In addition to apoptosis, caspases play a role in necroptosis, pyroptosis, and autophagy, which are non-apoptotic cell death processes. Dysregulation of caspases features prominently in many human diseases, including cancer, autoimmunity, and neurodegenerative disorders, and increasing evidence shows that altering caspase activity can confer therapeutic benefits. This review covers the different types of caspases, their functions, and their physiological and biological activities and roles in different organisms.

Sidestream Smoke Extracts from Harm-Reduction and Conventional Camel Cigarettes Inhibit Osteogenic Differentiation via Oxidative Stress and Differential Activation of intrinsic Apoptotic Pathways

Epidemiological studies suggest cigarette smoking as a probable environmental factor for a variety of congenital anomalies, including low bone mass, increased fracture risk and poor skeletal health. Human and animal in vitro models have confirmed hypomineralization of differentiating cell lines with sidestream smoke being more harmful to developing cells than mainstream smoke. Furthermore, first reports are emerging to suggest a differential impact of conventional versus harm-reduction tobacco products on bone tissue as it develops in the embryo or in vitro. To gather first insight into the molecular mechanism of such differences, we assessed the effect of sidestream smoke solutions from Camel (conventional) and Camel Blue (harm-reduction) cigarettes using a human embryonic stem cell osteogenic differentiation model. Sidestream smoke from the conventional Camel cigarettes concentration-dependently inhibited in vitro calcification triggered by high levels of mitochondrially generated oxidative stress, loss of mitochondrial membrane potential, and reduced ATP production. Camel sidestream smoke also induced DNA damage and caspase 9-dependent apoptosis. Camel Blue-exposed cells, in contrast, invoked only intermediate levels of reactive oxygen species insufficient to activate caspase 3/7. Despite the absence of apoptotic gene activation, damage to the mitochondrial phenotype was still noted concomitant with activation of an anti-inflammatory gene signature and inhibited mineralization. Collectively, the presented findings in differentiating pluripotent stem cells imply that embryos may exhibit low bone mineral density if exposed to environmental smoke during development.

Over Fifty Years of Life, Death, and Cannibalism: A Historical Recollection of Apoptosis and Autophagy

Research in biomedical sciences has changed dramatically over the past fifty years. There is no doubt that the discovery of apoptosis and autophagy as two highly synchronized and regulated mechanisms in cellular homeostasis are among the most important discoveries in these decades. Along with the advancement in molecular biology, identifying the genetic players in apoptosis and autophagy has shed light on our understanding of their function in physiological and pathological conditions. In this review, we first describe the history of key discoveries in apoptosis with a molecular insight and continue with apoptosis pathways and their regulation. We touch upon the role of apoptosis in human health and its malfunction in several diseases. We discuss the path to the morphological and molecular discovery of autophagy. Moreover, we dive deep into the precise regulation of autophagy and recent findings from basic research to clinical applications of autophagy modulation in human health and illnesses and the available therapies for many diseases caused by impaired autophagy. We conclude with the exciting crosstalk between apoptosis and autophagy, from the early discoveries to recent findings.

Telomerase activator-65 and pomegranate peel improved the health status of the liver in aged rats; multi-targets involved

OBJECTIVES

This study was undertaken to investigate the efficacy of telomerase activator-65 (Ta-65) and pomegranate peel against aging-induced deteriorations in the liver.

MATERIALS AND METHODS

The rats were divided into four groups: control, aged, aged rats treated with Ta-65, and pomegranate orally for two months.

RESULTS

Aging significantly increased the serum levels of total protein, globulins, and protein carbonyl and reduced the insulin-like growth factor 1 (IGF-1). It also elevated the hepatic malondialdehyde and decreased the hepatic glutathione S-transferase (GST) activity. Aging elevated the expression of thioredoxin reductase1, telomerase reverse transcriptase, and cytochrome 3a1 in the liver; it increased the p53 protein level and elevated the activity of caspase-3 in the liver indicating the occurrence of apoptosis. The architecture of the liver deteriorated in the aged rats, as shown by both light and electron microscopy examinations. The liver of the aged rats had many apoptotic hepatocytes with shrunken nuclei. Many hepatocytes had dilated rough endoplasmic reticulum, many lysosomes, and many fat droplets. Administration of Ta-65 and pomegranate to the aged rats normalized most of the previous biochemical parameters and improved the liver architecture.

CONCLUSION

Ta-65 and pomegranate have anti-aging activity through targeting multiple cellular pathways. It is also noteworthy that Ta-65 was superior to pomegranate in its alleviative effects.

Necroptosis, pyroptosis and apoptosis: an intricate game of cell death

Cell death is a fundamental physiological process in all living organisms. Its roles extend from embryonic development, organ maintenance, and aging to the coordination of immune responses and autoimmunity. In recent years, our understanding of the mechanisms orchestrating cellular death and its consequences on immunity and homeostasis has increased substantially. Different modalities of what has become known as 'programmed cell death' have been described, and some key players in these processes have been identified. We have learned more about the intricacies that fine tune the activity of common players and ultimately shape the different types of cell death. These studies have highlighted the complex mechanisms tipping the balance between different cell fates. Here, we summarize the latest discoveries in the three most well understood modalities of cell death, namely, apoptosis, necroptosis, and pyroptosis, highlighting common and unique pathways and their effect on the surrounding cells and the organism as a whole.

Synthesis of new oxadiazol-phthalazinone derivatives with anti-proliferative activity; molecular docking, pro-apoptotic, and enzyme inhibition profile

Background and aim: The current study reports the synthesis and biological evaluation of two novel series of 4-(5-mercapto-1,3,4-oxadiazol-2-yl)phthalazin-1(2H)-one derivatives. Methods: The synthetic reactions were carried out under both conventional and ultrasonic irradiation conditions. The anti-proliferative activity of the newly synthesized compounds against two human epithelial cell lines; liver (HepG2) and breast (MCF-7) in addition to normal fibroblasts (WI-38) was investigated. In addition to molecular docking studies, the possible mechanism(s) of action were also explored. Results: In general, an improvement in synthetic rates and yields was observed when reactions were carried out under sonication compared with classical conditions. The structures of the products were established based on analytical and spectral data. Derivatives 2e and 7d, in addition to compound 1, had significant and selective anti-proliferative activity against liver and breast cancer cell lines without harming normal fibroblasts. These derivatives arrested the cell cycle progression and/or induced apoptosis. This has been manifested by the elevation in the expression of p53 and caspase 3, down-regulation of cdk1, and a reduction in the concentrations of MAPK and Topo II at submicromolar concentrations. The latter results confirmed the molecular docking study. Conclusions: Compound 1 had the best profile on the gene and protein levels (arresting cell cycle and inducing apoptosis). The ability of compounds 1 and 2e to inhibit both MAPK and Topo II nominates these derivatives as potential candidates for further anticancer and antitumor studies.

Caspase-4 is essential for saikosaponin a-induced apoptosis acting upstream of caspase-2 and γ-H2AX in colon cancer cells

Saikosaponin a (SSa), a bioactive phytochemical from Bupleurum, triggers sequential caspase-2 and caspase-8 activation, and thereby induces caspase-mediated apoptosis in human colon carcinoma (HCC) cells. However, the upstream mechanism of caspase-2 activation remains unknown. Therefore, we investigated the signaling mechanisms underlying SSa-induced caspase activation and apoptosis in HCC cells. SSa treatment triggered marked antitumor effects, especially in HCC cells, in a cell culture model and a mouse xenograft model. SSa also induced the activation of several endoplasmic reticulum (ER) stress signals. Specifically, caspase-4, a critical regulator of ER stress-induced apoptosis, was activated significantly after SSa treatment. Mechanistically, selective inhibition of caspase-4 suppressed SSa-induced apoptosis, colony inhibition, and the activation of caspase-3, -8, and -2, but not vice versa. Consistent with the important role of caspase-2 in the DNA damage response, SSa induced DNA damage, as evidenced by a cytokinesis-block micronucleus assay, single-cell gel electrophoresis, and an increase in the levels of γ-H2AX, a DNA damage marker. Moreover, inhibition of caspase-4 activation inhibited SSa-induced histone H2AX phosphorylation. Taken together, these results suggest that caspase-4 is an upstream regulator of SSa-induced DNA damage and caspase activation in HCC cells. Given that SSa-induced apoptosis appeared to be specific to certain cell types including HCC cells, SSa may be a promising cancer therapy agent in certain types of cancer.

Proteasome Stress Triggers Death of SH-SY5Y and T98G Cells via Different Cellular Mechanisms

Overload or dysfunction of ubiquitin-proteasome system (UPS) is implicated in mechanisms of neurodegeneration associated with neurodegenerative diseases, e.g. Parkinson and Alzheimer disease, and ischemia-reperfusion injury. The aim of this study was to investigate the possible association between viability of neuroblastoma SH-SY5Y and glioblastoma T98G cells treated with bortezomib, inhibitor of 26S proteasome, and accumulation of ubiquitin-conjugated proteins with respect to direct cytotoxicity of aggregates of ubiquitin-conjugated proteins. Bortezomib-induced death of SH-SY5Y cells was documented after 24 h of treatment while death of T98G cells was delayed up to 48 h. Already after 4 h of treatment of both SH-SY5Y and T98G cells with bortezomib, increased levels of both ubiquitin-conjugated proteins with molecular mass more than 150 kDa and Hsp70 were observed whereas Hsp90 was elevated in T98G cells and decreased in SH-SY5Y cells. With respect to the cell death mechanism, we have documented bortezomib-induced activation of caspase 3 in SH-SY5Y cells that was probably a result of increased expression of pro-apoptotic proteins, PUMA and Noxa. In T98G cells, bortezomib-induced expression of caspase 4, documented after 24 h of treatment, with further activation of caspase 3, observed after 48 h of treatment. The delay in activation of caspase 3 correlated well with the delay of death of T98G cells. Our results do not support the possibility about direct cytotoxicity of aggregates of ubiquitin-conjugated proteins. They are more consistent with a view that proteasome inhibition is associated with both transcription-dependent and -independent changes in expression of pro-apoptotic proteins and consequent cell death initiation associated with caspase 3 activation.

Correlation between NF-κB signal pathway-mediated caspase-4 activation and Kawasaki disease

The aim of the study was to investigate the role and mechanisms of action of nuclear factor-κB (NF-κB)-mediated caspase-4 activation in the induction of inflammatory cytokines during Kawasaki disease (KD) and coronary artery endothelial cell injury. Peripheral blood mononuclear cells (PBMCs) were isolated from KD patients and healthy controls and cultured. Double antibody sandwich enzyme-linked immunosorbent assay (ELISA) was applied to detect tumor necrosis factor (TNF)-α levels in activated PBMC-conditioned culture media. To establish a culture model for human coronary artery endothelial cells (HCAECs), we employed KD patient-origin PBMC culture-conditioned media to induce HCAEC transformation and detected the nuclear activation of NF-κB p65 and intracellular caspase-4 protein concentrations using western blot analysis. We also investigated the nuclear transfer of NF-κB p65 using immunofluorescence, as well as HCAEC interleukin (IL)-6 and IL-1β secretion using ELISA. Finally, we investigated HCAEC apoptosis using using Annexin V/PI double staining. After PBMCs were stimulated in vitro, TNF-α secretion was significantly higher in the KD group versus controls (P<0.01). HCAEC cells treated with supernatant conditioned by cells from KD patients showed a significant elevation of NF-κB p65 and caspase-4 protein expression versus HCAEC cells treated with supernatant conditioned by control cells (P<0.01). Similarly, IL-6 and IL-1β secretion, as well as apoptotic rate, were significantly elevated (P<0.01). SN50, an NF-κB inhibitor, significantly attenuated caspase-4 expression, secretion of IL-6, IL-1β, and TNF-α, as well as HCAEC apoptosis in cells treated with KD patient PBMC-conditioned media. NF-κB can induce the generation of various inflammatory factors including IL-6 and IL-1β, mediate the expression of caspase-4 in HCAEC cells, and affect apoptosis and injury of HCAEC cells. Therefore, the expression of caspase-4, mediated by NF-κB signal pathway, plays a critical role in KD.

NF-κB regulates caspase-4 expression and sensitizes neuroblastoma cells to Fas-induced apoptosis

Found in neurons and neuroblastoma cells, Fas-induced apoptosis and accompanied activation of NF-κB signaling were thought to be associated with neurodegenerative diseases. However, the detailed functions of NF-κB activation in Fas killing and the effect of NF-κB activation on its downstream events remain unclear. Here, we demonstrated that agonistic Fas antibody induces cell death in a dose-dependent way and NF-κB signaling is activated as well, in neuroblastoma cells SH-EP1. Unexpectedly, NF-κB activation was shown to be pro-apoptotic, as suggested by the reduction of Fas-induced cell death with either a dominant negative form of IκBα (DN-IκBα) or an IκB kinase-specific inhibitor. To our interest, when analyzing downstream events of NF-κB signaling, we found that DN-IκBα only suppressed the expression of caspase-4, but not other caspases. Vice versa, enhancement of NF-κB activity by p65 (RelA) overexpression increased the expression of caspase-4 at both mRNA and protein levels. More directly, results from dual luciferase reporter assay demonstrated the regulation of caspase-4 promoter activity by NF-κB. When caspase-4 activity was blocked by its dominant negative (DN) form, Fas-induced cell death was substantially reduced. Consistently, the cleavage of PARP and caspase-3 induced by Fas was also reduced. In contrast, the cleavage of caspase-8 remained unaffected in caspase-4 DN cells, although caspase-8 inhibitor could rescue Fas-induced cell death. Collectively, these data suggest that caspase-4 activity is required for Fas-induced cell apoptosis and caspase-4 may act upstream of PARP and caspase-3 and downstream of caspase-8. Overall, we demonstrate that NF-κB can mediate Fas-induced apoptosis through caspase-4 protease, indicating that caspase-4 is a new mediator of NF-κB pro-apoptotic pathway in neuroblastoma cells.

TIMP-3 promotes apoptosis in nonadherent small cell lung carcinoma cells lacking functional death receptor pathway

Tissue inhibitor of metalloproteinases-3 (TIMP-3) has previously been identified as a tumor suppressor for adherent malignant and normal cells. TIMP-3 inhibits adhesion of cells to extracellular matrix and promotes apoptosis through death receptor-activated, caspase-8-mediated pathway. Here, we have studied the effect of adenovirally mediated overexpression of TIMP-3 on small cell lung cancer (SCLC) cell lines SW2 and N417, which grow in suspension and lack functional caspase-8. The results show that adenoviral delivery of TIMP-3 promotes apoptotic cell death in SCLC cells in the absence of caspase-8 activation. These results suggest TIMP-3 as a promising therapeutic anticancer protein also in nonadherent malignant cells lacking functional death receptor signaling.

TNFA deletion alters apoptosis as well as caspase 3 and 4 expression during otitis media

Background

Tumor necrosis factor (TNFA) is the canonical member of the TNF superfamily, which plays a major role in both inflammation and apoptosis. To evaluate the role of TNFs in otitis media (OM), the most common disease of childhood, we evaluated middle ear (ME) expression of genes encoding the TNF and TNF receptor superfamilies during bacterial OM in the mouse, characterized OM in TNFA-deficient mice, and assessed apoptosis during OM in normal versus TNF-deficient MEs.

Results

TNFs and TNF receptors were broadly regulated during OM, with TNFA showing the highest level of up-regulation. TNF deficient mice exhibited mucosal hyperplasia even in the absence of infection and exuberant growth of the mucosa during OM, including the formation of mucosal polyps. Mucosal recovery during OM was also delayed, in parallel with a delay in mucosal apoptosis and reduced caspase gene expression.

Conclusions

The TNF and TNF receptor superfamilies mediate both inflammation and apoptosis during OM. TNF appears to be critical for the maintenance of mucosal architecture in both the normal and infected ME, since excessive accumulation of mucosal tissue is seen in TNFA^-/- MEs both before and after bacterial inoculation of the ME. TNFA is also required for appropriate regulation of caspase genes.

TRAIL-induced apoptosis of human melanoma cells involves activation of caspase-4

Although it is conventionally regarded as an inflammatory caspase, recent studies have shown that caspase-4 plays a role in induction of apoptosis by endoplasmic reticulum (ER) stress. We report here that activation of caspase-4 is also involved in induction of apoptosis by TNF-related apoptosis-inducing ligand (TRAIL) in human melanoma cells. Treatment with TRAIL resulted in activation of caspase-4. This appeared to be mediated by caspase-3, in that caspase-4 was activated later than caspase-8, -9, and -3, and that inhibition of caspase-3 blocked TRAIL-induced caspase-4 activation. Notably, TRAIL triggered ER stress in melanoma cells as shown by up-regulation of the GRP78 protein and the spliced form of XBP-1 mRNA. This seemed to be necessary for activation of caspase-4, as activation of caspase-3 by agents that did not trigger ER stress did not cause activation of caspase-4. Importantly, inhibition of caspase-4 also partially blocked caspase-3 activation, suggesting that activation of caspase-4 may be positive feed-back mechanism to further enhance caspase-3 activation. Collectively, these results show that activation of caspase-4 contributes to TRAIL-induced apoptosis and is associated with induction of ER stress by TRAIL in melanoma cells, and may have important implications for improving therapeutic efficacies of TRAIL in melanoma.

Memory B and memory plasma cells

Vaccination provides a powerful means to control infections. It exploits and exemplifies the ability of the immune system to preserve the information that a specific pathogen has been encountered in the past. The cells and molecular mechanisms of immunological memory are still being discussed controversially. Here, we review the current concepts of memory B cells, the signals involved in their maintenance, and their role in enhanced secondary reactions. Memory plasma cells, secreting protective antibodies over lifetime, have been recognized only recently. Their characterization as cells resting in terms of proliferation and migration, and surviving in dedicated stromal niches, in the absence of antigen, has generated new concepts of how memory cells in general are organized by stroma cells, the 'resting memory'. In autoimmunity and chronic inflammation, memory B cells and memory plasma cells can be essential players, and they require special attention, as they do not respond to most conventional therapies. Their selective targeting will depend on a molecular understanding of their lifestyle.

Arsenic trioxide induces endoplasmic reticulum stress-related events in neutrophils

We recently reported that the endoplasmic reticulum (ER)-induced cell pathway of apoptosis is operational in human neutrophils and that some ER stressors can accelerate this process. Recent data suggest that arsenic trioxide (As(2)O(3) or ATO), may also act as an ER stressor. The aims of the present study were to elucidate if other ER stress-related events occur in ATO-induced neutrophils, and to determine the role of caspase-4 in the proapoptotic activity of ATO. We found that ATO induced ubiquitination of proteins, and increased calcium concentration and gene expression of calcineurin in neutrophils. In addition to caspase-4, activities of caspase-3, -8 and -9 were increased by ATO. The processing of caspase-4 was reversed by a caspase-8 inhibitor, indicating that caspase-4 activation requires the action of upstream initiator components, questioning on the role of caspase-4 in ATO-induced ER stress-mediated cell apoptosis. Using caspase-4 deficient THP-1 cells, we demonstrated that the proapoptotic effect of ATO was similar to that of control caspase-4-positive cells. We conclude that ATO is an ER stressor that can induce cell apoptosis by a mechanism which does not require caspase-4. In addition, we conclude that caspase-4 activation in ATO-induced neutrophils could be involved in functions other than apoptosis.

Dual involvement of caspase-4 in inflammatory and ER stress-induced apoptotic responses in human retinal pigment epithelial cells

PURPOSE

To investigate the functional involvement of caspase-4 in human retinal pigment epithelial (hRPE) cells.

METHODS

Expression and activation of caspase-4 in hRPE cells were measured after stimulation with proinflammatory agents IL-1beta (2 ng/mL), TNF-alpha (20 ng/mL), lipopolysaccharide (1000 ng/mL), interferon-gamma (500 U/mL), or monocyte coculture in the absence or presence of immunomodulating agent cyclosporine (3 or 30 ng/mL), dexamethasone (10 microM), or IL-10 (100 U/mL) and endoplasmic reticulum (ER) stress inducer thapsigargin (25 nM) or tunicamycin (3 or 10 microM). The onset of ER stress was determined by expression of GRP78. The involvement of caspase-4 in inflammation and apoptosis was further examined by treating the cells with caspase-4 inhibitor Z-LEVD-fmk, caspase-1 and -4 inhibitor Z-YVAD-fmk, and pan-caspase inhibitor Z-VAD-fmk.

RESULTS

Caspase-4 mRNA expression and protein activation were induced by all the proinflammatory agents and ER stress inducers tested in this study. Caspase-4 activation was blocked or reduced by dexamethasone and IL-10. Elevated ER stress by proinflammatory agents and ER stress inducers was shown by increased expression of the ER stress marker GRP78. The induced caspase-4 and caspase-3 activities by tunicamycin and the stimulated IL-8 protein expression by IL-1beta were markedly reduced by caspase-4 inhibitor Z-LEVD-fmk. Although caspase-4 inhibitor Z-LEVD-fmk and caspase-1 and -4 inhibitor Z-YVAD-fmk reduced tunicamycin-induced hRPE apoptotic cell death by 59% and 86%, respectively, pan-caspase inhibitor Z-VAD-fmk completely abolished the induced apoptosis.

CONCLUSIONS

Caspase-4 is dually involved in hRPE proinflammatory and proapoptotic responses. Various proinflammatory stimuli and ER stress induce hRPE caspase-4 mRNA synthesis and protein activation. ER stress-induced hRPE cell death is caspase and, in part, caspase-4 dependent.

Evidence that endoplasmic reticulum (ER) stress and caspase-4 activation occur in human neutrophils

Apoptosis can result from activation of three major pathways: the extrinsic, the intrinsic, and the most recently identified endoplasmic reticulum (ER) stress-mediated pathway. While the two former pathways are known to be operational in human polymorphonuclear neutrophils (PMNs), the existence of the ER stress-mediated pathway, generally involving caspase-4, has never been reported in these cells. Recently, we have documented that arsenic trioxide (ATO) induced apoptosis in human PMNs by a mechanism that needs to be further investigated. In this study, using immunofluorescence and electron microscopy, we present evidence of ER alterations in PMNs activated by the ER stress inducer arsenic trioxide (ATO). Several key players of the unfolded protein response, including GRP78, GADD153, ATF6, XBP1 and eIF2alpha are expressed and activated in PMNs treated with ATO or other ER stress inducers. Although caspase-4 is expressed and activated in neutrophils, treatment with a caspase-4 inhibitor did not attenuate the pro-apoptotic effect of ATO at a concentration that reverses caspase-4 processing and activation. Our results demonstrate for the first time that the ER stress-mediated apoptotic pathway operates in human neutrophils.

Caspases: evolutionary aspects of their functions in vertebrates

Caspases (cysteine-dependent aspartyl-specific protease) belong to a family of cysteine proteases that mediate proteolytic events indispensable for biological phenomena such as cell death and inflammation. The first caspase was identified as an executioner of apoptotic cell death in the worm Caenorhabditis elegans. Additionally, a large number of caspases have been identified in various animals from sponges to vertebrates. Caspases are thought to play a pivotal role in apoptosis as an evolutionarily conserved function; however, the number of caspases that can be identified is distinct for each species. This indicates that species-specific functions or diversification of physiological roles has been cultivated through caspase evolution. Furthermore, recent studies suggest that caspases are also involved in inflammation and cellular differentiation in mammals. This review highlights vertebrate caspases in their universal and divergent functions and provides insight into the physiological roles of these molecules in animals.

The endoplasmic reticulum in apoptosis and autophagy: role of the BCL-2 protein family

Apoptosis is essential for normal development and maintenance of homeostasis, and disruption of apoptotic pathways is associated with multiple disease states, including cancer. Although initially identified as central regulators of apoptosis at the level of mitochondria, an important role for BCL-2 proteins at the endoplasmic reticulum is now well established. Signaling pathways emanating from the endoplasmic reticulum (ER) are involved in apoptosis initiated by stimuli as diverse as ER stress, oncogene expression, death receptor (DR) ligation and oxidative stress, and the BCL-2 family is almost invariably implicated in the regulation of these pathways. This also includes Ca(2+)-mediated cross talk between ER and mitochondria during apoptosis, which contributes to the mitochondrial dynamics that support the core mitochondrial apoptosis pathway. In addition to the regulation of apoptosis, BCL-2 proteins at the ER also regulate autophagy, a survival pathway that limits metabolic stress, genomic instability and tumorigenesis. In cases where apoptosis is inhibited, however, prolonged autophagy can lead to cell death. This review provides an overview of ER-associated apoptotic and autophagic signaling pathways, with particular emphasis on the BCL-2 family proteins.

Tumor necrosis factor-alpha can provoke cleavage and activation of sterol regulatory element-binding protein in ethanol-exposed cells via a caspase-dependent pathway that is cholesterol insensitive

Ethanol induces the development of hepatic steatosis, increasingly recognized as causing vulnerability to subsequent liver injury. Ethanol has been shown to activate SREBP-1 (sterol regulatory element-binding protein) processing through the conventional cholesterol-sensitive pathway (1). The present study demonstrates that ethanol can also bring about SREBP-1 cleavage and activation through a novel pathway dependent on the endoplasmic reticulum-localized caspases-4 and -12. Evidence is presented that tumor necrosis factor can stimulate caspase-4 and -12 activation in ethanol-exposed cells, which cleaves SREBP-1 to a transcriptionally active form to induce the synthesis of lipogenic enzymes and triglycerides. Moreover, the caspase-4 and -12-dependent activation of SREBP-1 is insensitive to the normal negative feedback exerted by cholesterol and is mediated by the translocation of the scaffolding protein, TRAF-2, to the endoplasmic reticulum.

Mechanisms of colorectal and lung cancer prevention by vegetables: a genomic approach

Colorectal cancer (CRC) and lung cancer (LC) occur at high incidence, and both can be effectively prevented by dietary vegetable consumption. This makes these two types of cancer highly suitable for elucidating the underlying molecular mechanisms of cancer chemoprevention. Numerous studies have shown that vegetables exert their beneficial effects through various different mechanisms, but effects on the genome level remain mostly unclear. This review evaluates current knowledge on the mechanisms of CRC and LC prevention by vegetables, thereby focusing on the modulation of gene and protein expressions. The majority of the effects found in the colon are changes in the expression of genes and proteins involved in apoptosis, cell cycle, cell proliferation and intracellular defense, in favor of reduced CRC risk. Furthermore, vegetables and vegetable components changed the expression of many more genes and proteins involved in other pathways for which biologic meaning is less clear. The number of studies investigating gene and protein expression changes in the lungs is limited to only a few in vitro and animal studies. Data from these studies show that mostly genes involved in biotransformation, apoptosis and cell cycle regulation are affected. In both colon and lungs, genomewide analyses of gene and protein expression changes by new genomics and proteomics technologies, as well as the investigation of whole vegetables, are few in number. Further studies applying these 'omics' approaches are needed to provide more insights on affected genetic/biologic pathways and, thus, in molecular mechanisms by which different chemopreventive compounds can protect against carcinogenesis. Particularly studies with combinations of phytochemicals and whole vegetables are needed to establish gene expression changes in the colon, but especially in the lungs.

Identification of differentially expressed genes in human lymphoblastoid cells exposed to irradiation and suppression of radiation-induced apoptosis with antisense oligonucleotides against caspase-4

To identify candidate genes in response to ionizing radiation (IR) and discover new targets for basic research and radiation protection, whole human genome bioarrays were used to examine gene expression profiles in human lymphoblastoid AHH-1 cells exposed to IR. The results were confirmed by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR). In addition, the effects of ionizing radiation on cell growth, cell cycles and apoptosis were also examined. The microarray analysis revealed a set of IR responsive genes, including 906 genes at 4 hours and 789 genes at 24 hours after exposure to 5 Gy IR. The processes of cell cycles, apoptosis, signal transduction, and DNA repair involved a high percentage of IR responsive genes, among which, caspase-4 was most strongly induced by irradiation. Consistent with this, downregulation of caspase-4 expression by antisense oligonucleotides significantly increased cell viability and protected cells from undergoing apoptosis induced by IR. Taken together, the results suggested that caspase-4 plays an important role in radiation-induced apoptosis.

Distinct mechanism of cell death is responsible for tunicamycin-induced ER stress in SK-N-SH and SH-SY5Y cells

In order to elucidate underlying mechanism of cell death pathways in neuronal cells in humans, we studied responsible pathways involved in the endoplasmic reticulum (ER) stress-induced cell death in neuroblastoma cells, SK-N-SH and its neuroblast-type subclone SH-SY5Y cells. A time-dependent induction of ER chaperons, glucose regulated protein (GRP)78 and GRP94, was observed after treatment with tunicamycin (TM), and cell death was also induced concomitantly in both cells. Although the pro-caspase-12-like protein was defined in both cells, a decrease in the protein was observed in only SH-SY5Y cells after exposure to TM. In contrast, pro-caspase-4 was detected in only SK-N-SH cells, and the cleaved-form was induced by the treatment with TM. A caspase-4 inhibitor, Z-LEVD-FMK attenuated TM-induced cell death in SK-N-SH cells. Calpain- and caspase-3-mediated proteolysis of alpha II-spectrin was also increased after the treatment with TM in both cells. A calpain inhibitor, calpeptin, repressed TM-induced cell death in only SK-N-SH cells. GADD153/C/EBP homologous protein (CHOP) was significantly induced after exposure to TM in only SH-SY5Y cells and RNA interference to GADD153/CHOP repressed TM-induced cell death. These results demonstrate that induction of GADD153/CHOP plays a pivotal role in mechanism of ER stress-induced cell death in SH-SY5Y cells, on the other hand, cleavage of pro-caspase-4 by activation of calpain play a crucial role in SK-N-SH cells. It is also suggested that the relevance of caspase-4 to ER stress is cell-specific even between human-origin cell lines.

Nine procaspases are expressed in normal human epidermis, but only caspase-14 is fully processed

BACKGROUND

During normal stratification of the epidermis, keratinocytes undergo a complex programme of terminal differentiation. This programmed cell death results in corneocyte accumulation to form the stratum corneum (SC). Terminal differentiation and apoptosis share numerous features such as elimination of nuclei and organelles, changes in cell shape, and activation of transglutaminases and proteases. Caspases are cysteine proteases that play a central role in apoptosis. Therefore they may also be involved in the terminal differentiation of keratinocytes.

OBJECTIVES

To identify the caspases expressed in normal human epidermis and to define their pattern of expression and activation.

METHODS

We analysed mRNAs from human epidermis by reverse transcription-polymerase chain reaction (RT-PCR), skin cryosections by immunohistological methods, and epidermal protein extracts by Western blotting.

RESULTS

The mRNAs encoding caspase-1, -2, -3, -4, -6, -7, -8, -9, -10 and -14 were detected by RT-PCR. Accordingly, the immunohistological analyses showed clear expression in the epidermis of the corresponding proteins except caspase-2 and caspase-8, with only a weak expression of caspase-9. Moreover, procaspase-1, -2, -3, -4, -6, -7, -9, -10 and -14, and the fully processed caspase-14, were immunodetected in total epidermis extracts. However, only procaspase-1 and the processed caspase-14 were detected in extracts of superficial SC. In addition to these two proteins, procaspase-4 was detected in extracts of superficial SC obtained from lesional psoriatic skin.

CONCLUSIONS

This study, the first exhaustive description of caspase expression and processing in normal human epidermis, indicates that in vivo granular keratinocytes express nine procaspases, and in addition the activated form of caspase-14. This confirms that only caspase-14 is involved in keratinocyte differentiation, and suggests that keratinocytes are ready to induce apoptosis in response to cutaneous damage.

The inflammatory caspases: key players in the host response to pathogenic invasion and sepsis

Caspases are cysteinyl-aspartate-specific proteinases known for their role in apoptosis (cell death or apoptotic caspases) and proinflammatory cytokine maturation (inflammatory caspases). The inflammatory caspases were among the first to be discovered, but only recently have the mechanisms leading to their activation and inhibition begun to be elucidated. In this review, we examine the biochemistry, substrates, and function of this unique family of inflammatory proteases, highlight the most recent findings regarding their regulatory mechanisms, and discuss what remains to be understood about their roles in health and disease.

The inflammatory caspases: guardians against infections and sepsis

Innate immunity is the primary host defense against invading microorganisms. Pathogen recognition, mediated through an elaborate 'microbial sensing' system comprising the Toll-like and Nod-like receptor families results in the activation of caspase-1, which is a prerequisite for pathogen clearance. Tight regulation of caspase-1 is necessary to control the magnitude of the innate immune response and protect the organism from possible damaging effects such as sepsis. Recent findings from population studies and animal models of infectious diseases and sepsis have uncovered a role for full-length caspase-12 in blocking the inflammatory response initiated by caspase-1, thus predisposing the organism to severe sepsis and sepsis-related lethality. In this review, we re-examine the relationship among the Group I caspases, their known substrates and their proposed role in apoptosis. We further discuss their function in inflammation and bacterial clearance, with an emphasis on their regulatory mechanisms during the innate immune response.

Protective role of Cop in Rip2/caspase-1/caspase-4-mediated HeLa cell death

CARD only protein (Cop) was recently identified as a protein with significant homology with the CARD of caspase-1. We have conducted functional studies on Cop and report on its role as an inhibitor of cell death in a broad range of cell death paradigms. A notable exception in the ability of Cop to inhibit cell death pertains to its inability to inhibit ER stress-mediated cell death. Furthermore, in addition to the known interaction of Cop and caspase-1, we demonstrated a novel interaction of Cop with caspase-4. We propose that Cop's action to prevent TNF-alpha-induced cell death may operate independently of the mitochondrial death pathway. Furthermore, Cop overexpression inhibits Bid cleavage. In summary, Cop inhibition of cell death, at least to a certain extent, results from its interference with the activation of caspase-1 and caspase-4. Understanding the mechanistic details modulating caspase cell death pathways should provide important information for the development of therapies for diseases featuring aberrant caspase activation. Cop, as an inhibitor of an important apical caspase cell death axis, may provide a tool for modulating pathological cell death.

PANDER-induced cell-death genetic networks in islets reveal central role for caspase-3 and cyclin-dependent kinase inhibitor 1A (p21)

PANcreatic DERived factor is an islet-specific cytokine that promotes apoptosis in primary islets and islet cell lines. To elucidate the genetic mechanisms of PANDER-induced cell death we performed expression profiling using the mouse PancChip version 5.0 in conjunction with Ingenuity Pathway Analysis. Murine islets were treated with PANDER and differentially expressed genes were identified at 48 and 72 h post-treatment. 64 genes were differentially expressed in response to PANDER treatment. 22 genes are associated with cell death. In addition, the genes with the highest fold change were linked with cell death or apoptosis. The most significantly affected gene at 48 h was the downregulated cyclin-dependent kinase inhibitor 1A (CDKN1A or p21). Approximately half of the genes impacted at 72 h were linked to cell death. Cell death differentially expressed genes were confirmed by quantitative RT-PCR. Further analysis identified cell death genetic networks at both time points with 21 of the 22 cell death genes related in various biological pathways. Caspase-3 (CASP3) was biologically linked to CDKN1A in several genetic networks and these two genes were further examined. Elevated cleaved CASP3 levels in PANDER-treated beta-TC3 insulinoma cells were found to abrogate CDKN1A expression. Levels of CDKN1A were not affected in the absence of cleaved CASP3. PANDER-induced downregulation of CDKN1A expression coupled with induced CASP3-activation may serve a central role in islet cell death and offers further insight into the mechanisms of cytokine-induced beta-cell apoptosis.

Scutellariae radix extracts suppress ethanol-induced caspase-11 expression and cell death in N(2)a cells

Scutellariae radix is a Chinese herbal medicine that has been used to treat disease conditions accompanying inflammation and oxidative stress. In the present study, we examined the effect of Scutellariae radix extracts during acute ethanol exposure in N(2)a neuroblastoma. The Scutellariae radix extracts effectively inhibited ethanol-induced apoptosis and caspase-3/-7 activation. Ethanol induced the expression of caspase-11 that has been known as a dual regulator of pathological apoptosis and inflammatory response. The ethanol-induced caspase-11 expression was suppressed by pretreatment of the Scutellariae radix extracts. Furthermore, the activation of caspase-3/-7 and apoptosis were significantly inhibited in caspase-11-/- mouse embryonic fibroblasts following ethanol treatment. These results suggest that caspase-11 has a regulatory role in ethanol-induced apoptosis, and the suppression of caspase-11 may be a mechanism by which Scutellariae radix exerts its cytoprotective effect.

Cleavage of p53-vimentin complex enhances tumor necrosis factor-related apoptosis-inducing ligand-mediated apoptosis of rheumatoid arthritis synovial fibroblasts

Rheumatoid arthritis synovial fibroblasts (RASFs) contribute to arthritic cartilage degradation. Although RASFs are normally resistant to apoptosis, Apo2L/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-based gene therapy has been successfully used in a mouse model of arthritis. We investigated this further by treating human RASFs with nontoxic doses of the proteasome inhibitor lactacystin. Treatment induced cytosolic accumulation of p53 and enhanced the susceptibility of RASFs to apoptosis mediated by TRAIL-R2 (DR5) but not Fas. A specific role for p53 in TRAIL-R2-mediated apoptosis was indicated by the ability of p53 siRNA to significantly reduce RASF apoptosis and by the reduced apoptosis of RASFs bearing p53 mutations on treatment with anti-DR5 antibody or anti-DR5 antibody plus lactacystin. p53 immunoprecipitation followed by mass spectrometry identified a vimentin-p53 complex, an interaction that was confirmed by reciprocal vimentin-p53 immunoprecipitation and by co-immunofluorescence. Interestingly, human caspase-4 cleaved human vimentin, and blockade of caspase-4 with a chemical inhibitor or with specific siRNA significantly inhibited TRAIL-R2-mediated apoptosis of RASFs. Furthermore, blockade of caspase-4 was paralleled by persistence of a cytosolic pattern of p53 and absence of p53 translocation to the nucleus. Taken together, our findings suggest a unique role for caspase-4 in cleaving vimentin and releasing cytosolic p53 for nuclear translocation, events that may regulate the sensitivity of RASFs to receptor-mediated apoptosis.

Proteomics analysis of H-RAS-mediated oncogenic transformation in a genetically defined human ovarian cancer model

RAS is a small GTP binding protein mutated in approximately 30% human cancer. Despite its important role in the initiation and progression of human cancer, the underlying mechanism of RAS-induced human epithelial transformation remains elusive. In this study, we probe the cellular and molecular mechanisms of RAS-mediated transformation, by profiling two human ovarian epithelial cell lines. One cell line was immortalized with SV40 T/t antigens and the human catalytic subunit of telomerase (T29), while the second cell line was transformed with an additional oncogenic ras(V12) allele (T29H). In total, 32 proteins associated with RAS-mediated transformation have been identified using peptide mass fingerprinting. These protein targets are involved in several cellular pathways, including metabolism, redox balance, calcium signaling, apoptosis, and cellular methylation. One such target, the 40 kDa procaspase 4 is significantly upregulated at the protein level in RAS-transformed T29H cells, related directly to signaling through MEK, but not PI3 kinase. Cellular caspase 4 activity is, however, suppressed in the T29H cells, suggesting that the maturation process of caspase 4 is abrogated in RAS-transformed T29H cells. Consistent with this notion, transformed T29H cells were less susceptible to the toxic effects of anti-Fas antibody than were immortalized, nontransformed T29 cells, associated with less activation of caspase 4. This study demonstrates that functional proteomic analysis of a genetically defined cancer model provides a powerful approach toward systematically identifying cellular targets associated with oncogenic transformation.

Oxidative stress-induced apoptosis in neurons correlates with mitochondrial DNA base excision repair pathway imbalance

Neurodegeneration can occur as a result of endogenous oxidative stress. Primary cerebellar granule cells were used in this study to determine if mitochondrial DNA (mtDNA) repair deficiencies correlate with oxidative stress-induced apoptosis in neuronal cells. Granule cells exhibited a significantly higher intracellular oxidative state compared with primary astrocytes as well as increases in reductants, such as glutathione, and redox sensitive signaling molecules, such as AP endonuclease/redox effector factor-1. Cerebellar granule cultures also exhibited an increased susceptibility to exogenous oxidative stress. Menadione (50 μM) produced twice as many lesions in granule cell mtDNA compared with astrocytes, and granule cell mtDNA repair was significantly less efficient. A decreased capacity to repair oxidative mtDNA damage correlates strongly with mitochondrial initiated apoptosis in these neuronal cultures. Interestingly, the mitochondrial activities of initiators for base excision repair (BER), the bifunctional glycosylase/AP lyases as well as AP endonuclease, were significantly higher in cerebellar granule cells compared with astrocytes. The increased mitochondrial AP endonuclease activity in combination with decreased polymerase γ activity may cause an imbalance in oxidative BER leading to an increased production and persistence of mtDNA damage in neurons when treated with menadione. This study provides evidence linking neuronal mtDNA repair capacity with oxidative stress-related neurodegeneration.

Molecular Mechanism of Hepatic Injury in Coinfection with Hepatitis C Virus and HIV

We have previously shown that hepatocytes exposed to hepatitis C virus (HCV) and human immunodeficiency virus (HIV) envelope proteins undergo apoptosis. In this article, we further elucidate the signaling mechanisms that mediate this effect. We found that, in human hepatocellular carcinoma (HepG2) cells, HCV E2 protein and HIV glycoprotein (gp) 120 significantly up-regulated the Fas ligand (FasL) and enhanced the formation of the Fas death-inducing signaling complex downstream of Fas receptor activation. Moreover, after stimulation with HCV E2 and HIV gp120, enhanced expression of caspases 2 and 7 and increased caspase 3 activity were observed. In addition, we showed up-regulation of the proapoptotic molecule Bid and its association with caspase 8 after treatment with these envelope proteins. We also found that HCV E2 and HIV gp120 induced a partial translocation of Bid to the mitochondria, which resulted in the release of cytochrome C and the apoptosis-inducing factor. Thus, the results of this study suggest that FasL and Bid play an important role in HCV and HIV envelope protein-induced apoptosis.

Interferon-regulatory factor-1 is critical for tamoxifen-mediated apoptosis in human mammary epithelial cells

Unlike estrogen receptor-positive (ER(+)) breast cancers, normal human mammary epithelial cells (HMECs) typically express low nuclear levels of ER (ER poor). We previously demonstrated that 1.0 microM tamoxifen (Tam) promotes apoptosis in acutely damaged ER-poor HMECs through a rapid, 'nonclassic' signaling pathway. Interferon-regulatory factor-1 (IRF-1), a target of signal transducer and activator of transcription-1 transcriptional regulation, has been shown to promote apoptosis following DNA damage. Here we show that 1.0 microM Tam promotes apoptosis in acutely damaged ER-poor HMECs through IRF-1 induction and caspase-1/3 activation. Treatment of acutely damaged HMEC-E6 cells with 1.0 microM Tam resulted in recruitment of CBP to the gamma-IFN-activated sequence element of the IRF-1 promoter, induction of IRF-1, and sequential activation of caspase-1 and -3. The effects of Tam were blocked by expression of siRNA directed against IRF-1 and caspase-1 inhibitors. These data indicate that Tam induces apoptosis in HMEC-E6 cells through a novel IRF-1-mediated signaling pathway that results in activated caspase-1 and -3.

Pathways of caspase-mediated apoptosis in autosomal-dominant polycystic kidney disease (ADPKD)

BACKGROUND

We have recently demonstrated an increase in apoptosis in Han:SPRD rat kidneys with autosomal-dominant polycystic kidney disease (ADPKD). Caspase-3 and caspase-7 are major mediators of apoptosis. There are two pathways of caspase-3 and caspase-7-mediated apoptosis: (1) the "extrinsic" pathway involving the death receptor Fas, Fas ligand (FasL), and caspase-8 and (2) the "mitochondrial" or "intrinsic" pathway involving Bcl-2 proteins, caspase-2, cytochrome c release, and caspase-9. The aim of the present study was to investigate the pathways of apoptosis in 3-week-old Han:SPRD rats with ADPKD.

METHODS

Fluorescent substrates were used to measure caspase activity. mRNA and protein was determined by ribonuclease protection assays and immunoblotting, respectively. The effect of caspase inhibitors on caspase activity in polycystic kidneys was determined.

RESULTS

Caspase-3 and caspase-7 activity was more than 100% increased in homozygous (Cy/Cy) compared to heterozygous (Cy/+) and normal littermate control (+/+) kidneys. Ribonuclease protection assays demonstrated no difference in caspase-3 mRNA. On immunoblotting, there was an increase in the proform of caspase-3 and caspase-7 in Cy/Cy compared to +/+ and Cy/+ kidneys. Caspase-8 and caspase-9 activity was more than 100% increased in Cy/Cy compared to Cy/+ and +/+ kidneys. On immunoblotting, there was an increase of the proform of both caspase-8 and caspase-9 in Cy/Cy kidneys. There was also an increase in cytochrome c release into the cytosol and an increase in caspase-2 protein and activity in Cy/Cy kidneys. On ribonuclease protection assay there was no difference in FasL mRNA between +/+, Cy/+, and Cy/Cy kidneys. Short-term treatment of Cy/Cy rats with the caspase inhibitor IDN-8050 resulted in inhibition of caspase-3 and caspase-7 activity in the kidney.

CONCLUSION

In Cy/Cy kidneys with ADPKD, there was an increase of the proform of caspase-9, an increase in cytochrome c release into the cytosol, and an increase in caspase-2 protein and activity demonstrating involvement of the intrinsic pathway. There was an increase in the proform of caspase-8 demonstrating involvement of the extrinsic pathway. No differences in FasL mRNA were seen suggesting that the extrinsic pathway is independent of the death receptor ligand, FasL.

Cocaine-induced changes in the expression of apoptosis-related genes in the fetal mouse cerebral wall

It has been demonstrated that exposure to cocaine increases cell death in the fetal CNS. To examine the molecular mechanisms of this effect, we employed mouse oligo microarrays followed by real-time reverse transcriptase-polymerase chain reaction (real-time RT-PCR) to compare expressions of apoptosis-related genes in the cerebral wall of 18-day-old (E18) fetuses from cocaine-treated (20 mg/kg cocaine, s.c., b.i.d., E8th-E18th) and drug-naive (saline, s.c.) mice. Out of approximately 400 relevant genes in the arrays, 53 showed alterations in expression in cocaine-exposed fetuses. Upregulation was observed in 35 proapoptotic and 8 antiapoptotic genes; 4 proapoptotic and 6 antiapoptotic genes were down-regulated. The affected genes encode a wide range of apoptosis-related proteins, including death receptors (NTF-R1, NTF-R2, DR3, DR5, LTbeta-R, GITR, P57 TR-1) and their adaptor and regulatory proteins (MASGE-D1, TRAF-2, SIVA, MET, FLIP, FAIM, IAP1, ATFA), members of transcription regulatory pathways (JNK, NF-kappaB, P53), members of BCL-2 family of proteins (BID, BAD, BAX, BIK, NIP21, NIP3, NIX, BCL-2), DNA damage sensor (PARP-1), caspases and their substrates and regulatory proteins (caspases 8, 4, 9, and 3, ACINUS, CIDE-A, CIDE-B, GAS2), mitochondrially released factors (cytochrome c, AIF, PRG3), specific endoplasmic reticulum- and oxidative stress-associated factors (BACH2, ABL1, ALG2, CHOP), members of cell survival AKT and HSP70 pathways (PIK3GA, PTEN, HSP70, BAG1, BAG2), and others. This suggests that cocaine affects survival of developing cerebral cells via multiple apoptosis-regulating mechanisms.

Plakin proteins are coordinately cleaved during apoptosis but preferentially through the action of different caspases

In epithelial cells, cell-cell and cell-matrix junctions, desmosomes and hemidesmosomes, provide anchorage sites for the keratin-intermediate filaments. The plakin proteins desmoplakin (DP), plectin, and periplakin represent intracellular constituents of these adhesion junctions. In staurosporine-treated apoptotic HaCaT cells, DP, plectin, and periplakin became cleaved coordinately with the elimination of keratins 10 and 14, while involucrin, actin, and keratin 18 displayed considerable stability. The caspase inhibitor zVAD-fmk prevented both the cell detachment and protein cleavage, indicating the function of caspases in these events. Closer examination in vitro revealed that while caspases 2 and 4 most efficiently cleaved DP, and plectin served as a target for caspases 3 and 7, periplakin as well as keratins were cleaved by caspase 6. The involvement of multiple caspases in the destruction of epithelial cell integrity ensures the efficient elimination of cytoskeleton, but also provides specificity for selectively targeting individual adhesion molecules.

Sclerostin promotes the apoptosis of human osteoblastic cells: a novel regulation of bone formation

A null mutation in the SOST gene is associated with sclerosteosis, an inherited disorder characterized by a high bone mass phenotype. The protein product of the SOST gene, sclerostin, is a bone morphogenetic protein (BMP) antagonist that decreases osteoblast activity and reduces the differentiation of osteoprogenitors. We sought to delineate the mechanism by which sclerostin modulated osteoblastic function by examining the effects of the protein on differentiating cultures of human mesenchymal stem cells (hMSC). Sclerostin significantly decreased alkaline phosphatase (ALP) activity and the proliferation of hMSC cells. In addition, hMSC cells treated with sclerostin displayed a marked increase in caspase activity. Elevated levels of fragmented histone-associated DNA in these cells were detected by ELISA and by TUNEL staining. Other BMP antagonists including noggin, Chordin, Gremlin, and Twisted gastrulation did not affect caspase activity. The sclerostin-mediated increase in caspase activity was blocked by caspase-1 and caspase-3 inhibitors. Sclerostin-induced changes in ALP activity and the survival of hMSC cells were partially restored by BMP-6, suggesting the involvement of additional growth factors. These findings show that sclerostin selectively controls the apoptosis of bone cells. The ability of sclerostin to interact with important growth factors such as BMPs likely serves as the basis by which it modulates the survival of osteoblasts. By making these growth factors unavailable for cell function, sclerostin promotes the apoptosis of bone cells, providing a novel level of control in the regulation of bone formation.

Expression patterns of cell cycle and apoptosis-related genes in a multidrug-resistant human colon carcinoma cell line

BACKGROUND

An in vitro multidrug resistance (MDR) system from a human colonic cancer cell line (SW620-MDR) has been established. To further study the mechanisms at molecular level and prevention of multidrug resistance in clinical practice, it was demonstrated that the expressions of several apoptosis-related and cell cycle regulator genes were changed in the cells.

METHODS

A multidrug-resistant colonic cell line (SW620-MDR) was established, and the Atlas human cDNA expression array was used for studying the pattern of gene expression in this cell line. Furthermore, Northern hybridization or real-time PCR analysis confirmed the pattern of gene expression.

RESULTS

In the SW620-MDR cell line the pro-apoptosis genes, CASP4, BIK, PDCD2, and TACE were expressed with decreased levels, and the antiapoptosis genes CD27-L and IGFBP2 were over-expressed. Furthermore, the cell cycle regulator genes such as CDK6, CCND1, CDC27HS, CDC16HS, Wee1Hu, MAPKK1, and IGFBP6 were expressed with decreased levels in the drug-resistant cell line.

CONCLUSIONS

It is worthwhile investigating whether the differentially expressed pattern of the aforementioned genes exists in the drug-resistant cancer specimens, and to further understand their functions in the cancer drug-resistance mechanism.

Interferon-gamma induces caspase-8 in neuroblastomas without affecting methylation of caspase-8 promoter

BACKGROUND

The expression of caspase-8, a cysteine protease that is crucial for the apoptotic cascade, is absent in a high percentage of neuroblastomas, the most frequent extracranial solid tumor of infants and children. Resistance of neuroblastomas to death-receptor (eg, tumor necrosis factor alpha (TNF-alpha) receptor)--mediated apoptosis is thought to be caused by loss of caspase-8 expression. Gene silencing by hypermethylation of caspase-8 promoter has been proposed for the loss of caspase-8 expression in neuroblastoma cells.

METHODS

To further evaluate the role of caspase-8 in neuroblastoma, we assessed the induction of caspase-8 expression in neuroblastoma cells by treating the cells with a physiologic agent such as interferon-gamma.

RESULTS

The authors found that interferon-gamma induces caspase-8 expression in neuroblastoma cells irrespective of the gene silenced by hypermethylation of caspase-8 promoter. The authors show that interferon-gamma also regulates other apoptosis related gene expression. Moreover, they show that interferon-gamma treatment in combination with TNF-alpha decreases neuroblastoma cell proliferation.

CONCLUSIONS

Interferon-gamma induces procaspase-8 expression in neuroblastoma cells, and this induction is not dependent on demethylation of the caspase-8 promoter. Therapies aimed at inducing caspase-8 expression by adjunctive treatment, such as interferon-gamma, may increase the effectiveness of current chemotherapeutic regimens.

A novel approach in the treatment of neuroendocrine gastrointestinal tumours. Targeting the epidermal growth factor receptor by gefitinib (ZD1839)

Therapeutic options to inhibit the growth and spread of neuroendocrine (NE) gastrointestinal tumours are still limited. Since gefitinib (4-(3-chloro-4-fluoroanilino)-7-methoxy-6-(3-morpholinopropoxy)quinazoline), an inhibitor of epidermal growth factor receptor-sensitive tyrosine kinase (EGFR-TK), had been shown to suppress potently the growth of various non-NE tumour entities, we studied the antineoplastic potency of gefitinib in NE gastrointestinal tumour cells. In human insulinoma (CM) cells, in human pancreatic carcinoid (BON) cells and in NE tumour cells of the gut (STC-1), gefitinib induced a time- and dose-dependent growth inhibition by almost 100%. The antiproliferative potency of gefitinib correlated with the proliferation rate of the tumour cells. So the IC₅₀ value of gefitinib was 4.7±0.6 μM in the fast-growing CM cells, still 16.8±0.4 μM in the moderate-growing BON cells, and up to 31.5±2.5 μM in the slow-growing STC-1 cells. Similarly, the induction of apoptosis and cell-cycle arrest by gefitinib differed according to growth characteristics: fast-growing CM cells displayed a strong G0/G1 arrest in response to gefitinib, while no significant cell-cycle alterations were seen in the slow-growing STC-1. Vice versa, the proapoptotic effects of gefitinib, as determined by caspase-3 activation and DNA fragmentation, were most pronounced in the slow-growing STC-1 cells. Using cDNA microarrays, we found extensive changes in the expression of genes involved in the regulation of apoptosis and cell cycle after incubation with gefitinib. Among them, an upregulation of the growth arrest and DNA damage-inducible gene GADD153 was observed. Phosphorylation of ERK1/2, which inhibits GADD153 expression, was reduced in a time-dependent manner. However, no gefitinib-induced activation of the GADD153-inducing p38 mitogen-activated protein kinase was detected. Our data demonstrate that the inhibition of EGFR-TK by gefitinib induces growth inhibition, apoptosis and cell-cycle arrest in NE gastrointestinal tumour cells. Thus, EGFR-TK inhibition appears to be a promising novel approach for the treatment of NE tumour disease.

Intracellular determination of activated caspases (IDAC) by flow cytometry using a pancaspase inhibitor labeled with FITC

BACKGROUND

Flow cytometry-based methods of simultaneous detection of multiple activated caspases in single cells are of diagnostic value and remain to be fully explored.

METHODS

Genomic DNA fragmentation was determined by agarose gel electrophoresis and flow cytometry. Whole cells were incubated with the cell-permeable pancaspase inhibitor, FITC-Val-Ala-Asp-fluoro-methyl-Rerone (FITC-VAD-FMK), and propidium iodide (PI) and analyzed for intracellular activated caspases and plasma membrane integrity, respectively, by flow cytometry.

RESULTS

Two distinct populations of apoptotic cells were identified by flow cytometry: an early apoptotic population indicated by FITC-VAD-FMK binding and the late apoptotic cells characterized by FITC-VAD-FMK staining and permeability to PI. The binding of FITC-VAD-FMK to apoptotic cells was time dependent and concurred with DNA fragmentation. Pretreatment with the pancaspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-methyl-fluoro-methyl-kerone (Z-VAD (OMe)-FMK), coordinately attenuated apoptosis induction and activation of caspases. The pancaspase inhibitor also competitively blocked the binding of FITC-VAD-FMK to early apoptotic cells in vitro. Significantly, the use of FITC-VAD-FMK permitted apoptosis determination in a number of cell lines including the caspase-3 gene-deleted MCF-7 responding to various apoptotic stimuli.

CONCLUSIONS

Apoptosis detection based on FITC-VAD-FMK binding is specific and easily performed by flow cytometry in a variety of cells. This novel technique has implications for detecting apoptosis in pathophysiologic conditions.

Fas-associated factor 1, FAF1, is a member of Fas death-inducing signaling complex

FAF1 has been introduced as a Fas-binding protein. However, the function of FAF1 in apoptotic execution is not established. Based on the fact that FAF1 is a Fas-binding protein, we asked if FAF1 interacted with other members of the Fas-death-inducing signaling complex (Fas-DISC) such as Fas-associated death domain protein (FADD) and caspase-8. FAF1 could interact with caspase-8 and FADD in vivo as well as in vitro. The death effector domains (DEDs) of caspase-8 and FADD interacted with the amino acid 181-381 region of FAF1, previously known to have apoptotic potential. Considering that FAF1 directly binds to Fas and caspase-8, FAF1 shows similar protein-interacting characteristics to that of FADD. In the coimmunoprecipitation with an anti-Fas antibody (APO-1) in Jurkat cells, endogenous FAF1 was associated with the precipitates in which caspase-8 was present. By confocal microscopic analysis, both Fas and FAF1 were detected in the cytoplasmic membrane before Fas activation, and in the cytoplasm after Fas activation. FADD and caspase-8 colocalized with Fas in Jurkat cells validating the presence of FAF1 in the authentic Fas-DISC. Overexpression of FAF1 in Jurkat cells caused significant apoptotic death. In addition, the FAF1 deletion mutant lacking the N terminus where Fas, FADD, and caspase-8 interact protected Jurkat cells from Fas-induced apoptosis demonstrating dominant-negative phenotype. Cell death by overexpression of FAF1 was suppressed significantly in both FADD- and caspase-8-deficient Jurkat cells when compared with that in their parental Jurkat cells. Collectively, our data show that FAF1 is a member of Fas-DISC acting upstream of caspase-8.

Gene networks in glucocorticoid-evoked apoptosis of leukemic cells

To discover the genes responsible for the apoptosis evoked by glucocorticoids in leukemic lymphoid cells, we have begun gene array analysis on microchips. Three clones of CEM cells were compared: C7-14, C1-15 and C1-6. C7-14 and C1-15 are subclones from the original clones C7 (sensitive to apoptosis by glucocorticoids) and C1 (resistant). C1-6 is a spontaneous revertant to sensitivity from the C1 clone. Previously we presented data on the sets of genes whose expression is altered in these cell clones after 20 h exposure to dexamethasone (Dex). The two sensitive clones, which respond by undergoing apoptosis starting about 24h after Dex is added, both showed >2.5-fold induction of 39 genes and 2-fold reduction of expressed levels from 21 genes. C1-15, the resistant clone, showed alterations in a separate set of genes. In this paper, we present further analysis of the data on genes regulated in these cell clones after 20 h Dex and compare them with the genes regulated after 12h Dex. Some, but not all the genes found altered at 20 h are altered at 12h, consistent with our hypothesis that sequential gene regulation eventually provokes full apoptosis. We also compare the levels of basal gene expression in the three clones. At the basal level no single gene stands out, but small sets of genes differ >2-fold in basal expression between the two sensitive and the resistant clone. A number of the genes basally higher in the resistant clone are potentially anti-apoptotic. This is consistent with our hypothesis that the resistant cells have undergone a general shift in gene expression.

Frameshift mutations in caspase-5 and other target genes in leukemia and lymphoma cell lines having microsatellite instability

Microsatellite instability (MSI) was examined in 49 lymphoid leukemia/lymphoma cell lines. Frameshift mutations within eight MSI target genes were analyzed in the 12 cell lines and nine childhood acute lymphoblastic leukemia (ALL) samples with MSI. Six cell lines (50%) showed mutations within the coding repeats of the BLM, caspase-5, TCF-4, and PTEN genes. No mutations were identified in the nine childhood ALL samples with MSI. This is the first report that describes mutations of these genes in hematological malignancies. Mutations, presumably caused by an abnormality of the DNA repair genes, may be selected for during the establishment of cell lines.

Identification of genes responsible for osteoblast differentiation from human mesodermal progenitor cells

Single human bone marrow-derived mesodermal progenitor cells (MPCs) differentiate into osteoblasts, chondrocytes, adipocytes, myocytes, and endothelial cells. To identify genes involved in the commitment of MPCs to osteoblasts we examined the expressed gene profile of undifferentiated MPCs and MPCs induced to the osteoblast lineage for 1-7 days by cDNA microarray analysis. As expected, growth factor, hormone, and signaling pathway genes known to be involved in osteogenesis were activated during differentiation. In addition, 41 transcription factors (TFs) were differentially expressed over time, including TFs with known roles in osteoblast differentiation and TFs not known to be involved in osteoblast differentiation. As the latter group of TFs coclustered with osteogenesis-specific TFs, they may play a role in osteoblast differentiation. When we compared the gene expression profile of MPCs induced to differentiate to chondroblasts and osteoblasts, significant differences in the nature and/or timing of gene activation were seen. These studies indicate that in vitro differentiation cultures in which MPCs are induced to one of multiple cell fates should be very useful for defining signals important for lineage-specific differentiation.

Caspase inhibitors as anti-inflammatory and antiapoptotic agents

The striking efficacy of Z-VAD-fmk in the various animal models presented above may reflect its ability to inhibit multiple enzymes including caspases. In accord with this, more selective, reversible inhibitors usually show low efficacy in multifactorial models such as ischaemia, but may offer some protection against NMDA-induced excitotoxicity and hepatitis. Importantly, caspase inhibitors may exhibit significant activity in vivo even when they are applied post insult. As far as the CNS is concerned, the first systemically active inhibitors have emerged. Functional recovery could be achieved in some ischaemia models, but long-term protection by caspase inhibitors is still being questioned. Recent developments in drug design enabled the first caspase inhibitors to enter the clinic. Although initially directed towards peripheral indications such as rheumatoid arthritis, caspase inhibitors will no doubt eventually be used to target CNS disorders. For this purpose the peptidic character of current inhibitors will have to be further reduced. Small molecule, nonpeptidic caspase inhibitors, which have appeared recently, indicate that this goal can be accomplished. Unfortunately, many fundamental questions still remain to be addressed. In particular, the necessary spectrum of inhibitory activity required to achieve the desired effect needs to be determined. There is also a safety aspect associated with prolonged administration. Therefore, the next therapeutic areas for broader-range caspase inhibitors are likely to involve acute treatment. Recent results with synergistic effects between MK-801 and caspase inhibitors in ischaemia suggest that caspase inhibitors may need to be used in conjunction with other drugs. It can be expected that, in the near future, research on caspases and their inhibitors will remain a rapidly developing area of biology and medicinal chemistry. More time, however, may be needed for the first caspase inhibitors to appear on the market.