A first insight into the molecular mechanisms of apoptosis.
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Animals↗
Biomedical subjects
Junying Yuan
Publications and source records attributed to Junying Yuan.
Mechanisms of cell death in polyglutamine expansion diseases.
Abnormal protein aggregation is a hallmark of many neurodegenerative diseases. However, the mechanism by which protein aggregates induce neurodegneration remains controversial. Recently proposed mechanisms of neuronal death in polyglutamine expansion diseases include activation of caspases and associated cell death pathways, interference with transcriptional regulation, downregulation of survival pathways and obstruction of axonal transport. Because the expression of expanded polyglutamine in selected neuronal populations can adversely affect multiple aspects of neuronal survival and function, we propose that effective therapeutic approaches might have to target the upstream mechanism of neurotoxicity by selectively inhibiting the formation of intraneuronal aggregates and increasing the degradation of mutant proteins.
Animals↗
Caspase-11 is not necessary for chemotherapy-induced intestinal mucositis.
Mucositis is a common, dose-limiting toxicity associated with drug and radiation therapy for cancer. The ulcerative lesions of mucositis serve as systemic portals of entry for the micro-organisms that inhabit the mucosa of the gastrointestinal tract and the oral cavity, often leading to systemic infection. The pathogenesis of mucositis is complex, and consists of varying, sequential interactions between pro-inflammatory cytokines, transcription factors, and pro-apoptotic pathways of the mucosal epithelium and the cells and tissues within the submucosa. A possible mechanism for mucositis injury is the activation of caspases, a family of cysteine proteases. Caspase-11, one of 14 members of this enzymatic family, was studied to determine its role in the development of intestinal mucositis after exposure to melphalan in caspase-11 wild-type (+/+) and knockout (-/-) mice. Immunoblots demonstrated the activation of caspase-11 in duodenal and jejunal samples 24 and 48 h after melphalan administration. No significant differences in the level of intestinal cell death or macrophage infiltration, as measured by TUNEL staining and immunohistochemistry, were present between wildtype (+/+) and knockout (-/-) mice. These findings suggest that while caspase-11 activation occurs in response to melphalan, it does not have a primary role in the pathogenesis of intestinal mucositis.
Animals↗
A decade of caspases.
Caspases are a family of cysteine proteases that play important roles in regulating apoptosis. A decade of research has generated a wealth of information on the signal transduction pathways mediated by caspases, the distinct functions of individual caspases and the mechanisms by which caspases mediate apoptosis and a variety of physiological and pathological processes.
Allosteric Regulation↗
Diversity in the mechanisms of neuronal cell death.
Neurons may die as a normal physiological process during development or as a pathological process in diseases. The best-understood mechanism of neuronal cell death is apoptosis, which is regulated by an evolutionarily conserved cellular pathway that consists of the caspase family, the Bcl-2 family, and the adaptor protein Apaf-1. Apoptosis, however, may not be the only cellular mechanism that regulates neuronal cell death. Neuronal cell death may exhibit morphological features of autophagy or necrosis, which differ from that of the canonical apoptosis. This review evaluates the evidence supporting the existence of alternative mechanisms of neuronal cell death and proposes the possible existence of an evolutionarily conserved pathway of necrosis.
Animals↗
The PHD finger of the chromatin-associated protein ING2 functions as a nuclear phosphoinositide receptor.
Phosphoinositides (PtdInsPs) play critical roles in cytoplasmic signal transduction pathways. However, their functions in the nucleus are unclear, as specific nuclear receptors for PtdInsPs have not been identified. Here, we show that ING2, a candidate tumor suppressor protein, is a nuclear PtdInsP receptor. ING2 contains a plant homeodomain (PHD) finger, a motif common to many chromatin-regulatory proteins. We find that the PHD fingers of ING2 and other diverse nuclear proteins bind in vitro to PtdInsPs, including the rare PtdInsP species, phosphatidylinositol 5-phosphate (PtdIns(5)P). Further, we demonstrate that the ING2 PHD finger interacts with PtdIns(5)P in vivo and provide evidence that this interaction regulates the ability of ING2 to activate p53 and p53-dependent apoptotic pathways. Together, our data identify the PHD finger as a phosphoinositide binding module and a nuclear PtdInsP receptor, and suggest that PHD-phosphoinositide interactions directly regulate nuclear responses to DNA damage.
1-Phosphatidylinositol 4-Kinase↗
Bax and Bak can localize to the endoplasmic reticulum to initiate apoptosis.
Bax and Bak play a redundant but essential role in apoptosis initiated by the mitochondrial release of apoptogenic factors. In addition to their presence at the mitochondrial outer membrane, Bax and Bak can also localize to the ER. Agents that initiate ER stress responses can induce conformational changes and oligomerization of Bax on the ER as well as on mitochondria. In wild-type cells, this is associated with caspase 12 cleavage that is abolished in bax-/-bak-/- cells. In bax-/-bak-/- cells, introduction of Bak mutants selectively targeted to either mitochondria or the ER can induce apoptosis. However, ER-targeted, but not mitochondria-targeted, Bak leads to progressive depletion of ER Ca2+ and induces caspase 12 cleavage. In contrast, mitochondria-targeted Bak leads to enhanced caspase 7 and PARP cleavage in comparison with the ER-targeted Bak. These findings demonstrate that in addition to their functions at mitochondria, Bax and Bak also localize to the ER and function to initiate a parallel pathway of caspase activation and apoptosis.
Animals↗
Dissociation between neurodegeneration and caspase-11-mediated activation of caspase-1 and caspase-3 in a mouse model of amyotrophic lateral sclerosis.
Caspase-11 is a key regulator of caspase-1 and caspase-3 activation under pathological conditions. We show here that the expression of caspase-11 is upregulated in the spinal cord of superoxide dismutase 1 (SOD1) G93A transgenic mice, a mouse model of amyotrophic lateral sclerosis (ALS), before the onset of motor dysfunction and remains at the high levels throughout the course of disease. The caspase-1- and caspase-3-like activities, as well as the level of interleukin-1beta, were significantly reduced in the spinal cord of symptomatic caspase-11-/-;SOD1 G93A mice compared with that of caspase-11+/-; SOD1 G93A mice. However, neurodegeneration, inflammatory responses, and the disease onset and progression in SOD1 G93A transgenic mice were not altered by the ablation of caspase-11 gene. Thus, although caspases may contribute to certain aspects of pathology in this mouse model of ALS, their inhibition is not sufficient to prevent neurodegeneration. Our study urges caution when considering the inhibition of caspases as a direct therapeutic method for the treatment of chronic neurodegenerative diseases.
Amyotrophic Lateral Sclerosis↗
Pivotal role of oligomerization in expanded polyglutamine neurodegenerative disorders.
The expansion of a CAG repeat coding for polyglutamine in otherwise unrelated gene products is central to eight neurodegenerative disorders including Huntington's disease. It has been well documented that expanded polyglutamine fragments, cleaved from their respective full-length proteins, form microscopically visible aggregates in affected individuals and in transgenic mice. The contribution of polyglutamine oligomers to neurodegeneration, however, is controversial. The azo-dye Congo red binds preferentially to beta-sheets containing amyloid fibrils and can specifically inhibit oligomerization and disrupt preformed oligomers. Here we show that inhibition of polyglutamine oligomerization by Congo red prevents ATP depletion and caspase activation, preserves normal cellular protein synthesis and degradation functions, and promotes the clearance of expanded polyglutamine repeats in vivo and in vitro. Infusion of Congo red into a transgenic mouse model of Huntington's disease, well after the onset of symptoms, promotes the clearance of expanded repeats in vivo and exerts marked protective effects on survival, weight loss and motor function. We conclude that oligomerization is a crucial determinant in the biochemical properties of expanded polyglutamine that are central to their chronic cytotoxicity.
Adenosine Triphosphate↗
Alpha-synuclein oligomerization: a role for lipids?
Alpha-Synuclein is a core component of the proteinaceous aggregates observed in several neurodegenerative diseases. A central role of alpha-synuclein in neurodegeneration was demonstrated by the discovery of missense alpha-synuclein mutations in familial Parkinson's disease. However, the specific mechanism by which alpha-synuclein contributes to these diseases remains unclear. A recent study by Sharon et al. linked the presence of specific fatty acids to the appearance of alpha-synuclein oligomers in vivo. alpha-Synuclein oligomers might be a first step in the formation of alpha-synuclein aggregates present in a number of neurodegenerative diseases, although their cytotoxicity remains to be directly demonstrated.
Animals↗
Bax, caspase-2, and caspase-3 are required for ovarian follicle loss caused by 4-vinylcyclohexene diepoxide exposure of female mice in vivo.
The industrial chemical, 4-vinylcyclohexene diepoxide (VCD), kills oocytes within immature follicles in the ovaries of mice and rats and is considered a potential occupational health hazard. It has been reported that VCD-induced follicle loss occurs via a cell death process involving elevated expression of Bax, a proapoptotic Bcl-2 family member, and increased caspase-3-like activity. We have previously shown that oocytes lacking acid sphingomyelinase (ASMase; an enzyme that generates the proapoptotic stress sensor ceramide), the aromatic hydrocarbon receptor (Ahr), Bax, or caspase-2 are resistant to apoptosis induced by other chemical toxicants. Therefore, this study was designed to investigate the functional importance of ASMase, Ahr, Bax, and caspase-2 as well as the related executioner enzyme caspase-3 to VCD-induced ovotoxicity in mice using gene knockout technology. For each gene mutant mouse line, wild-type and homozygous-null female siblings derived from heterozygous matings were given once-daily ip injections of either vehicle (sesame oil) or VCD (80 mg/kg body weight) for 15 d (three or four mice per treatment group per genotype). Ovaries were collected 24 h after the final injection and analyzed for the total number of nonatretic primordial and primary follicles remaining per ovary. No differences in the extent of primordial or primary follicle destruction resulting from VCD exposure were observed in wild-type vs. ASMase- or Ahr-deficient mice. By contrast, the extent of VCD-induced primordial follicle depletion in Bax-deficient mice (45 +/- 11%) was significantly (P < 0.05) lower than that in wild-type females (85 +/- 2%). The extent of primary follicle loss in bax-null mice exposed to VCD (3 +/- 22%) was also significantly (P < 0.05) lower than that in their wild-type sisters (86 +/- 4%). In caspase-2-deficient mice, significantly (P < 0.05) fewer oocyte-containing primary follicles were destroyed by VCD (17 +/- 19%) vs. wild-type controls (71 +/- 6%); however, no significant difference in the extent of VCD-induced primordial follicle destruction was observed in caspase-2-null vs. wild-type females. Finally, in caspase-3-deficient mice, significantly (P < 0.05) fewer oocyte-containing primary follicles were destroyed by VCD (33 +/- 3%) vs. wild-type controls (71 +/- 2%); however, no significant difference in the extent of VCD-induced primordial follicle destruction was observed in caspase-3-null vs. wild-type females. We conclude that Bax, caspase-2, and caspase-3, but not ASMase or Ahr, are functionally important in VCD-induced follicle loss. However, as a loss of Bax, caspase-2, or caspase-3 function conveyed only partial protection from the ovotoxic effects of VCD, other cell death pathways that either function independently of Bax, caspase-2, and caspase-3 or are not apoptotic in nature are also involved.
Animals↗
Caspase activation and neuroprotection in caspase-3- deficient mice after in vivo cerebral ischemia and in vitro oxygen glucose deprivation.
Caspase-3 is a major cell death effector protease in the adult and neonatal nervous system. We found a greater number and higher density of cells in the cortex of caspase-3(-/-) adult mice, consistent with a defect in developmental cell death. Caspase-3(-/-) mice were also more resistant to ischemic stress both in vivo and in vitro. After 2 h of ischemia and 48 h of reperfusion, cortical infarct volume was reduced by 55%, and the density of terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling-positive cells was decreased by 36% compared with wild type. When subjected to oxygen-glucose deprivation (2 h), cortical neurons cultured from mice deficient in caspase-3 expression were also more resistant to cell death by 59%. Mutant brains showed caspase-specific poly(ADP-ribose) polymerase cleavage product (85-kDa fragment) in vivo and in vitro, suggesting redundant mechanisms and persistence of caspase-mediated cell death. In the present study, we found that caspase-8 mediated poly(ADP-ribose) polymerase cleavage in caspase-3(-/-) neurons in vivo and in vitro. In addition, mutant neurons showed no evidence of compensatory activation by caspase-6 or caspase-7 after ischemia. Taken together, these data extend the pharmacological evidence supporting an important role for caspase-3 and caspase-8 as cell death mediators in mammalian cortex and indicate the potential advantages of targeting more than a single caspase family member to treat ischemic cell injury.
Animals↗
Caspase cascades in human immunodeficiency virus-associated neurodegeneration.
Many patients infected with human immunodeficiency virus-1 (HIV-1) develop a syndrome of neurologic deterioration known as HIV-associated dementia (HAD). Neurons are not productively infected by HIV-1; thus, the mechanism of HIV-induced neuronal injury remains incompletely understood. Several investigators have observed evidence of neuronal injury, including dendritic degeneration, and apoptosis in CNS tissue from patients with HAD. Caspase enzymes, proteases associated with the process of apoptosis, are synthesized as inactive proenzymes and are activated in a proteolytic cascade after exposure to apoptotic signals. Here we demonstrate that HAD is associated with active caspase-3-like immunoreactivity that is localized to the soma and dendrites of neurons in affected regions of the human brain. Additionally, the cascade of caspase activation was studied using an in vitro model of HIV-induced neuronal apoptosis. Increased caspase-3 proteolytic activity and mitochondrial release of cytochrome c were observed in cerebrocortical cultures exposed to the HIV coat protein gp120. Specific inhibitors of both the Fas/tumor necrosis factor-alpha/death receptor pathway and the mitochondrial caspase pathway prevented gp120-induced neuronal apoptosis. Caspase inhibition also prevented the dendrite degeneration observed in vivo in transgenic mice with CNS expression of HIV/gp120. These findings suggest that pharmacologic interventions aimed at the caspase enzyme pathways may be beneficial for the prevention or treatment of HAD.
AIDS Dementia Complex↗
Upregulation of the Fas receptor death-inducing signaling complex after traumatic brain injury in mice and humans.
Recent studies have implicated Fas in the pathogenesis of inflammatory, ischemic, and traumatic brain injury (TBI); however, a direct link between Fas activation and caspase-mediated cell death has not been established in injured brain. We detected Fas-Fas ligand binding and assembly of death-inducing signaling complexes (DISCs) [Fas, Fas-associated protein with death domain, and procaspase-8 or procaspase-10; receptor interacting protein (RIP)-RIP-associated interleukin-1beta converting enzyme and CED-3 homolog-1/Ced 3 homologous protein with a death domain-procaspase-2] by immunoprecipitation and immunoblotting within mouse parietal cortex after controlled cortical impact. At the time of DISC assembly, procaspase-8 was cleaved and the cleavage product appeared at 48 hr in terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling-positive neurons. Cleavage of caspase-8 was accompanied by caspase-3 processing detected at 48 hr by immunohistochemistry, and by caspase-specific cleavage of poly(ADP-ribose) polymerase at 12 hr. Fas pathways were also stimulated by TBI in human brain, because Fas expression plus Fas-procaspase-8 interaction were robust in contused cortical tissue samples surgically removed between 2 and 30 hr after injury. To address whether Fas functions as a death receptor in brain cells, cultured embryonic day 17 cortical neurons were transfected with an adenoviral vector containing the gene encoding Fas ligand. After 48 hr in culture, Fas ligand expression and Fas-procaspase-8 DISC assembly increased, and by 72 hr, cell death was pronounced. Cell death was decreased by approximately 50% after pan-caspase inhibition (Z-Val-ALa-Asp(Ome)-fluoromethylketone). These data suggest that Fas-associated DISCs assemble in neurons overexpressing Fas ligand as well as within mouse and human contused brain after TBI. Therefore, Fas may function as a death receptor after brain injury.
Adaptor Proteins, Signal Transducing↗
A novel approach for characterizing protein ligand complexes: molecular basis for specificity of small-molecule Bcl-2 inhibitors.
The increasing diversity of small molecule libraries has been an important source for the development of new drugs and, more recently, for unraveling the mechanisms of cellular events-a process termed chemical genetics.(1) Unfortunately, the majority of currently available compounds are mechanism-based enzyme inhibitors, whereas most of cellular activity regulation proceeds on the level of protein-protein interactions. Hence, the development of small molecule inhibitors of protein-protein interactions is important. When screening compound libraries, low-micromolar inhibitors of protein interactions can be routinely found. The enhancement of affinities and rationalization of the binding mechanism require structural information about the protein-ligand complexes. Crystallization of low-affinity complexes is difficult, and their NMR analysis suffers from exchange broadening, which limits the number of obtainable intermolecular constraints. Here we present a novel method of ligand validation and optimization, which is based on the combination of structural and computational approaches. We successfully used this method to analyze the basis for structure-activity relationships of previously selected (2) small molecule inhibitors of the antiapoptotic protein Bcl-xL and identified new members of this inhibitor family.
Acetates↗
Life and death in paradise.
Over 500 researchers participated in a recent American Association for Cancer Research special conference, entitled "Apoptosis and Cancer: Basic Mechanisms and Therapeutic Opportunities in the Post-Genomic Era" (February 13-17, 2002) in sunny Hawaii (Hilton Waikoloa village, Kona, Hawaii). The meeting participants presented the most recent findings on the mechanisms regulating cell death in cancer. In the past decade, apoptosis research has undergone a quantum leap, metamorphosing from a descriptive, phenomenological discipline into a molecularly defined, highly complex signalling field. This transformation was highlighted in the conference's opening talk by meeting co-organizer, John Reed (The Burnham Institute, La Jolla, CA). Reed and colleagues used published protein functional information and bio-informatic mining of the available human genome databases to tabulate the number of human proteins predicted to be involved in regulating apoptosis. The list includes 11 catalytically active caspases, 26 CARD (caspase associated recruitment domain)-, 32 DD (death domain)-, 12 DED (death effector domain)-, 8 BIR (baculovirus inhibitor of apoptosis protein region)-, 24 BH (Bcl-2 homology)-, and 34 PAAD/PYD (pyrin/PAAD)-containing sequences.
Animals↗
Releasing the nerve cell killers.
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14-3-3 Proteins↗
LKB1--a master tumour suppressor of the small intestine and beyond.
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AMP-Activated Protein Kinase Kinases↗