[Show abstract][Hide abstract] ABSTRACT: Osteoblast apoptosis plays an important role in bone development and maintenance, and is in part responsible for osteoporosis in sex steroid deficiency, glucocorticoid excess, and aging. Although Bcl2 subfamily proteins, including Bcl2 and Bcl-XL, inhibit apoptosis, the physiological significance of Bcl2 in osteoblast differentiation has not been fully elucidated. To investigate this, we examined Bcl2-deficient (Bcl2(-/-)) mice. In Bcl2(-/-) mice, bromodeoxyuridine (BrdU)-positive osteoblasts were reduced in number, while terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive osteoblasts were increased. Unexpectedly, osteoblast differentiation was accelerated in Bcl2(-/-) mice as shown by the early appearance of osteocalcin-positive osteoblasts. Osteoblast differentiation was also accelerated in vitro when primary osteoblasts were seeded at a high concentration to minimize the reduction of the cell density by apoptosis during culture. FoxO transcription factors, whose activities are negatively regulated through the phosphorylation by Akt, play important roles in multiple cell events, including proliferation, death, differentiation, longevity, and stress response. Expressions of FasL, Gadd45a, and Bim, which are regulated by FoxOs, were upregulated; the expression and activity of FoxOs were enhanced; and the phosphorylation of Akt and that of FoxO1 and FoxO3a by Akt were reduced in Bcl2(-/-) calvariae. Further, the levels of p53 mRNA and protein were increased, and the expression of p53-target genes, Pten and Igfbp3 whose proteins inhibit Akt activation, was upregulated in Bcl2(-/-) calvariae. However, Pten but not Igfbp3 was upregulated in Bcl2(-/-) primary osteoblasts, and p53 induced Pten but not Igfbp3 in vitro. Silencing of either FoxO1 or FoxO3a inhibited and constitutively-active FoxO3a enhanced osteoblast differentiation. These findings suggest that Bcl2 deficiency induces and activates FoxOs through Akt inactivation, at least in part, by upregulating Pten expression through p53 in osteoblasts, and that the enhanced expression and activities of FoxOs may be one of the causes of accelerated osteoblast differentiation in Bcl2(-/-) mice.
PLoS ONE 01/2014; 9(1):e86629. · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Extensive studies have unveiled the intracellular molecular signaling pathways of cell death. To better understand cell death in tissues, it is important to investigate the influence of neighboring cells on the response to death stimuli. By time-lapse microscopy, we found that cells in couplets (two hepatocytes attached to each other) died independently when stimulated with anti-Fas antibody and staurosporine, whereas acetaminophen (APAP) and aryl alcohol caused synchronized cell death although its timing varied among different couplets. Synchronized death of couplets was not caused by APAP when hepatocytes were deficient in both Connexin26 and Connexin32, indicating a crucial role of gap junctions in the synchronized death process. We also demonstrated that APAP-sensitive male hepatocytes were protected by attachment to APAP-insensitive female hepatocytes, with this protection being dependent on gap junctions. These findings indicate that APAP-induced and aryl alcohol-induced necrotic death of hepatocytes is modulated by attached neighboring cells via gap junctions.
[Show abstract][Hide abstract] ABSTRACT: IL-10-deficient mice spontaneously develop intestinal inflammation, which has many similarities to Crohn's disease. Several reports suggest that epithelial cell death may increase the severity of colitis; however, decisive evidence is lacking. In the present report, we addressed whether and how epithelial cell death plays a role in the development of chronic colitis. We first examined the morphological characteristics of intestines of IL-10-deficient mice and found two forms of epithelial cell death (typical apoptosis and necrosis-like cell death) in colitis. To elucidate the pathological roles of epithelial cell death, we crossbred IL-10-deficient knockout mice with Bcl-2 transgenic mice, in which the anti-apoptosis protein Bcl-2 was overexpressed in intestinal epithelial cells, but not in immune cells. Epithelial cell-specific Bcl-2 protected IL-10 deficiency-induced colitis and markedly reduced their symptoms. Interestingly, morphological analysis revealed that Bcl-2 suppressed apoptosis and necrosis-like cell death, and better maintained mucosal barrier in IL-10-deficient mice. From the immunological aspect, Bcl-2 did not alter the activation of T-helper cell 1 but inhibited the growth of T-helper cell 17, suggesting that mucosal integrity may control the immune responses. These results provide genetic evidence demonstrating that epithelial cell death is crucial for the development of chronic colitis.
American Journal Of Pathology 12/2013; 183(6):1936-1944. · 4.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: KillerRed, a red fluorescent protein, is a photosensitizer that efficiently generates reactive oxygen species (ROS) when irradiated with green light. Because KillerRed is genetically encoded, it can be expressed in a spatially and temporally regulated manner under control of a chosen promoter and thus is a powerful tool for studying the downstream cellular effects of ROS. However, information is still limited about the effects of KillerRed-mediated production of ROS inside the mitochondria (mtROS). Therefore, we investigated whether mtROS generated by KillerRed could trigger mitochondrial damage and cell death by generating human cell lines (HEK293T and HeLa cells) that stably expressed mitochondria-targeting KillerRed (mtKillerRed). We found that mtROS generated by mtKillerRed caused depolarization of the mitochondrial membrane and morphological changes, which were partly due to the mitochondrial permeability transition (MPT), as well as inducing both caspase-dependent cell death (apoptosis) and caspase-independent cell death. In order to study the pathological processes initiated by mtROS in animals, transgenic Caenorhabditis elegans expressing mtKillerRed in muscle tissue were generated. Transgenic larvae showed developmental delay following light irradiation, suggesting that mtROS influenced the development of C. elegans larvae. In conclusion, our studies demonstrated that the photosensitizer KillerRed is effective at inducing oxidative damage in the mitochondria, and indicated that our experimental systems may be useful for studying the downstream cellular effects of mtROS.
Journal of photochemistry and photobiology. B, Biology 08/2012; 117:1–12. · 3.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although cell death research has progressed rapidly over the two decades with emphasis on the study of apoptosis, non-apoptotic forms of cell death have recently attracted more attention. In the present short review, I will describe how this transition is occurring and emphasize the importance of investigating non-apoptotic forms of cell death as well as apoptosis to fully understand the spectrum of death in eukaryotic cells. The aim is not to list all published forms of cell death, but to indicate the necessity for a conceptual paradigm shift, so I will only introduce a limited number of cell death mechanisms.
[Show abstract][Hide abstract] ABSTRACT: Mast cells release a variety of mediators, including arachidonic acid (AA) metabolites, to regulate allergy, inflammation,
and host defense, and their differentiation and maturation within extravascular microenvironments depend on the stromal cytokine
stem cell factor. Mouse mast cells express two major intracellular phospholipases A2 (PLA2s), namely group IVA cytosolic PLA2 (cPLA2α) and group VIA Ca2+-independent PLA2 (iPLA2β), and the role of cPLA2α in eicosanoid synthesis by mast cells has been well documented. Lipidomic analyses of mouse bone marrow-derived mast cells
(BMMCs) lacking cPLA2α (Pla2g4a−/−) or iPLA2β (Pla2g6−/−) revealed that phospholipids with AA were selectively hydrolyzed by cPLA2α, not by iPLA2β, during FcϵRI-mediated activation and even during fibroblast-dependent maturation. Neither FcϵRI-dependent effector functions
nor maturation-driven phospholipid remodeling was impaired in Pla2g6−/− BMMCs. Although BMMCs did not produce prostaglandin E2 (PGE2), the AA released by cPLA2α from BMMCs during maturation was converted to PGE2 by microsomal PGE synthase-1 (mPGES-1) in cocultured fibroblasts, and accordingly, Pla2g4a−/− BMMCs promoted microenvironmental PGE2 synthesis less efficiently than wild-type BMMCs both in vitro and in vivo. Mice deficient in mPGES-1 (Ptges−/−) had an augmented local anaphylactic response. These results suggest that cPLA2α in mast cells is functionally coupled, through the AA transfer mechanism, with stromal mPGES-1 to provide anti-anaphylactic
PGE2. Although iPLA2β is partially responsible for PGE2 production by macrophages and dendritic cells, it is dispensable for mast cell maturation and function.
Journal of Biological Chemistry 10/2011; 286(43):37249-37263. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mast cells release a variety of mediators, including arachidonic acid (AA) metabolites, to regulate allergy, inflammation, and host defense, and their differentiation and maturation within extravascular microenvironments depend on the stromal cytokine stem cell factor. Mouse mast cells express two major intracellular phospholipases A(2) (PLA(2)s), namely group IVA cytosolic PLA(2) (cPLA(2)α) and group VIA Ca(2+)-independent PLA(2) (iPLA(2)β), and the role of cPLA(2)α in eicosanoid synthesis by mast cells has been well documented. Lipidomic analyses of mouse bone marrow-derived mast cells (BMMCs) lacking cPLA(2)α (Pla2g4a(-/-)) or iPLA(2)β (Pla2g6(-/-)) revealed that phospholipids with AA were selectively hydrolyzed by cPLA(2)α, not by iPLA(2)β, during FcεRI-mediated activation and even during fibroblast-dependent maturation. Neither FcεRI-dependent effector functions nor maturation-driven phospholipid remodeling was impaired in Pla2g6(-/-) BMMCs. Although BMMCs did not produce prostaglandin E(2) (PGE(2)), the AA released by cPLA(2)α from BMMCs during maturation was converted to PGE(2) by microsomal PGE synthase-1 (mPGES-1) in cocultured fibroblasts, and accordingly, Pla2g4a(-/-) BMMCs promoted microenvironmental PGE(2) synthesis less efficiently than wild-type BMMCs both in vitro and in vivo. Mice deficient in mPGES-1 (Ptges(-/-)) had an augmented local anaphylactic response. These results suggest that cPLA(2)α in mast cells is functionally coupled, through the AA transfer mechanism, with stromal mPGES-1 to provide anti-anaphylactic PGE(2). Although iPLA(2)β is partially responsible for PGE(2) production by macrophages and dendritic cells, it is dispensable for mast cell maturation and function.
Journal of Biological Chemistry 08/2011; 286(43):37249-63. · 4.65 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Infantile neuroaxonal dystrophy (INAD) is a fatal neurodegenerative disease characterized by the widespread presence of axonal swellings (spheroids) in the CNS and PNS and is caused by gene abnormality in PLA2G6 [calcium-independent phospholipase A(2)β (iPLA(2)β)], which is essential for remodeling of membrane phospholipids. To clarify the pathomechanism of INAD, we pathologically analyzed the spinal cords and sciatic nerves of iPLA(2)β knock-out (KO) mice, a model of INAD. At 15 weeks (preclinical stage), periodic acid-Schiff (PAS)-positive granules were frequently observed in proximal axons and the perinuclear space of large neurons, and these were strongly positive for a marker of the mitochondrial outer membrane and negative for a marker of the inner membrane. By 100 weeks (late clinical stage), PAS-positive granules and spheroids had increased significantly in the distal parts of axons, and ultrastructural examination revealed that these granules were, in fact, mitochondria with degenerative inner membranes. Collapse of mitochondria in axons was accompanied by focal disappearance of the cytoskeleton. Partial membrane loss at axon terminals was also evident, accompanied by degenerative membranes in the same areas. Imaging mass spectrometry showed a prominent increase of docosahexaenoic acid-containing phosphatidylcholine in the gray matter, suggesting insufficient membrane remodeling in the presence of iPLA(2)β deficiency. Prominent axonal degeneration in neuroaxonal dystrophy might be explained by the collapse of abnormal mitochondria after axonal transportation. Insufficient remodeling and degeneration of mitochondrial inner membranes and presynaptic membranes appear to be the cause of the neuroaxonal dystrophy in iPLA(2)β-KO mice.
Journal of Neuroscience 08/2011; 31(31):11411-20. · 6.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bis (Bag3) is known to be involved in cell survival, migration, the regulating of chaperones, and protein quality control. We reported recently on the production of bis gene-deleted mice, which show early lethality within 3 wk after birth with a phenotype showing severe malnutrition and shrinkage of the thymus. In this report, we provide evidence to show that an intrinsic problem of adrenal gland is the the primary cause for the severe atrophy of the thymus in bis(-/-) mice. The bis(-/-) mice show significantly higher levels of corticosterone, but CRH and ACTH levels were considerably lower than those of wild littermates. The transcription of steroidogenic enzymes was increased in the adrenal glands of bis(-/-) mice, accompanied by an increase in the thickness of the zona reticularis. An analysis of thymus tissue from bis(-/-) mice revealed that the severe atrophy of the thymus is due to the specific loss of immature double-positive (CD4(+)CD8(+)) cortical thymocytes by apoptosis, as evidenced by immunohistochemical examination and flow cytometric analysis, which were restored by injection of an inhibitor of glucocorticoid synthesis. In vitro cultures of thymocytes with increasing doses of dexamethasone exhibited a similar degree of apoptosis between wild and bis(-/-) thymocytes. The corticosterone levels from fasted wild littermates were one-half those of bis(-/-) mice, although serum glucose levels were similar. Thus, the deletion of the bis gene resulted in the intrinsic defect in the adrenal gland, leading to a marked increase in glucocorticoid levels, probably upon starvation stress, which accounts for the massive apoptosis of the thymus.
AJP Endocrinology and Metabolism 05/2011; 301(1):E223-31. · 4.51 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The proapoptotic Bcl-2 family proteins Bak and Bax serve as an essential gateway to the mitochondrial pathway of apoptosis. When activated by BH3-only proteins, Bak/Bax triggers mitochondrial outer membrane permeabilization leading to release of cytochrome c followed by activation of initiator and then effector caspases to dismantle the cells. Hepatocytes are generally considered to be type II cells because, upon Fas stimulation, they are reported to require the BH3-only protein Bid to undergo apoptosis. However, the significance of Bak and Bax in the liver is unclear. To address this issue, we generated hepatocyte-specific Bak/Bax double knockout mice and administered Jo2 agonistic anti-Fas antibody or recombinant Fas ligand to them. Fas-induced rapid fulminant hepatocyte apoptosis was partially ameliorated in Bak knockout mice but not in Bax knockout mice, and was completely abolished in double knockout mice 3 hours after Jo2 injection. Importantly, at 6 hours, double knockout mice displayed severe liver injury associated with repression of XIAP, activation of caspase-3/7 and oligonucleosomal DNA breaks in the liver, without evidence of mitochondrial disruption or cytochrome c-dependent caspase-9 activation. This liver injury was not ameliorated in a cyclophilin D knockout background nor by administration of necrostatin-1, but was completely inhibited by administration of a caspase inhibitor after Bid cleavage. CONCLUSION: Whereas either Bak or Bax is critically required for rapid execution of Fas-mediated massive apoptosis in the liver, delayed onset of mitochondria-independent, caspase-dependent apoptosis develops even in the absence of both. The present study unveils an extrinsic pathway of apoptosis, like that in type I cells, which serves as a backup system even in type II cells.
[Show abstract][Hide abstract] ABSTRACT: We report the construction and application of a mammalian genome-wide RNAi library. The oligodeoxynucleotides encoding approximately 200,000 shRNA sequences that targeted 47,400 human transcripts were inserted into a lentivirus vector pFIV-H1-puro, and a pool of pseudovirus particles with a complexity of approximately 200,000 were used to infect target cells. From the cells surviving apoptogenic Fas stimulation, four candidate shRNA sequences were obtained that provided resistance to Fas-induced cell death, including two shRNAs for caspase-8, an shRNA for Bid, and an shRNA for Fas. The reconstructed shRNAs with these sequences were shown to reduce expression of the respective gene products and increase survival after Fas stimulation. When similar selection was performed for tunicamycin-induced apoptosis, no shRNA strongly inhibiting tunicamycin-induced cell death was isolated, although a few reconstructed shRNAs led to a slight increase of survival. Thus, this genome-wide shRNA library proved useful for selection of genes that are involved in cell death, but some limitation was also revealed.
Journal of Biochemistry 08/2010; 148(2):157-70. · 3.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Programmed cell death is a crucial process in the normal development and physiology of metazoans, and it can be divided into several categories that include type I death (apoptosis) and type II death (autophagic cell death). The Bcl-2 family proteins are well-characterized regulators of apoptosis, among which multidomain pro-apoptotic members (such as Bax and Bak) function as a mitochondrial gateway at which various apoptotic signals converge. Although embryonic fibroblasts from Bax/Bak double-knockout (DKO) mice are resistant to apoptosis, we have previously reported that these cells still die by autophagy in response to various death stimuli. In this study, we found that jun N-terminal kinase (JNK) was activated in etoposide- and staurosporine-treated, but not serum-starved, Bax/Bak DKO cells, and that autophagic cell death was suppressed by the addition of a JNK inhibitor and by a dominant-negative mutant of JNK. Studies with sek1(-/-)mkk7(-/-) cells revealed that disruption of JNK prevented the induction of autophagic cell death. Co-activation of JNK and autophagy induced autophagic cell death. Activation of JNK occurred downstream of the induction of autophagy, and was dependent on the autophagic process. These results indicate that JNK activation is crucial for the autophagic death of Bax/Bak DKO cells.
[Show abstract][Hide abstract] ABSTRACT: Parkinson's disease (PD) is a common neurodegenerative disorder. The motor neuron degeneration 2 mutant (mnd2) mouse exhibits loss of striatal neurons, muscle wasting, weight loss, and death within 40days of birth, and is considered to be a useful animal model of PD. mnd2 was identified as an autosomal recessive mutation in the HtrA2/Omi gene, which encodes a mitochondrial serine protease. Omi-deficient mitochondria are more sensitive to mitochondrial permeability transition (mPT), which raises the possibility that mPT plays a role in motor neurodegeneration in mnd2 mice. Given that cyclophilin D (CypD)-deficient mitochondria are resistant to mPT, we examined whether CypD-dependent mPT is involved in the pathogenesis of neurodegenerative disorders in mnd2 mice by generating CypD-deficient mnd2 mice. Brain mitochondria isolated from CypD-deficient mnd2 mice were more resistant to Ca(2+)-induced mPT than those of mnd2 mice. However, both mnd2 mice and CypD-deficient mnd2 mice showed similar survival periods and phenotypes, including the lack of weight gain, muscle wasting, and resting tremor. Our data suggest that CypD-dependent mPT does not play a major role in neurodegeneration in mnd2 mice.
Biochemical and Biophysical Research Communications 03/2010; 393(2):264-7. · 2.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Oxidative stress induces apoptosis or necrosis of many cell types, which can cause tissue injury. Hydrogen peroxide (H(2)O(2)) induced apoptotic death of Jurkat cells. This effect was inhibited by overexpression of human Bcl-2, by silencing of cytochrome c, and by ablation of Bax/Bak, indicating that H(2)O(2)-induced apoptosis was mediated by the mitochondrial pathway in Jurkat cells. Treatment with H(2)O(2) caused an increase of Noxa protein, via activating transcription factor 4-dependent accumulation of Noxa mRNA and inhibition of Noxa protein degradation. H(2)O(2)-induced apoptosis was strongly suppressed by silencing of Noxa, indicating that Noxa plays a crucial role in this form of apoptosis.
[Show abstract][Hide abstract] ABSTRACT: In the present paper, we introduce a transgenic mouse line whose sperm express green fluorescent protein (GFP) in their acrosome and red fluorescent protein (RFP) in their mitochondria [B6D2F1- Tg(CAG/su9-DsRed2, Acr3-EGFP)RBGS002Osb]. The dual fluorescent sperm showed normal fertilizing ability in both in vivo and in vitro fertilization and the sperm could be observed through uterine and oviductal walls when female reproductive tracts were dissected out and placed under excitation light. This characteristic could facilitate examination of sperm migration inside the female reproductive tract as well as facilitating in situ live imaging of the acrosome reaction, the details of which have remained elusive.
[Show abstract][Hide abstract] ABSTRACT: Macroautophagy is a process that leads to the bulk degradation of subcellular constituents by producing autophagosomes/autolysosomes. It is believed that Atg5 (ref. 4) and Atg7 (ref. 5) are essential genes for mammalian macroautophagy. Here we show, however, that mouse cells lacking Atg5 or Atg7 can still form autophagosomes/autolysosomes and perform autophagy-mediated protein degradation when subjected to certain stressors. Although lipidation of the microtubule-associated protein light chain 3 (LC3, also known as Map1lc3a) to form LC3-II is generally considered to be a good indicator of macroautophagy, it did not occur during the Atg5/Atg7-independent alternative process of macroautophagy. We also found that this alternative process of macroautophagy was regulated by several autophagic proteins, including Unc-51-like kinase 1 (Ulk1) and beclin 1. Unlike conventional macroautophagy, autophagosomes seemed to be generated in a Rab9-dependent manner by the fusion of isolation membranes with vesicles derived from the trans-Golgi and late endosomes. In vivo, Atg5-independent alternative macroautophagy was detected in several embryonic tissues. It also had a function in clearing mitochondria during erythroid maturation. These results indicate that mammalian macroautophagy can occur through at least two different pathways: an Atg5/Atg7-dependent conventional pathway and an Atg5/Atg7-independent alternative pathway.
[Show abstract][Hide abstract] ABSTRACT: Mitochondrial membrane permeabilization is central to apoptotic signaling and is directly regulated by the Bcl-2 family of proteins, consisting of anti-apoptotic members and pro-apoptotic members, although the precise mechanisms involved remain elusive. When cells are deficient in both pro-apoptotic multidomain members of this family (Bax and Bak), mitochondrial membrane permeabilization does not occur in response to various apoptotic stimuli. We have previously reported that the voltage-dependent anion channel (VDAC or porin) plays a role in apoptotic mitochondrial membrane permeabilization by interacting with Bcl-2 family members. Here, we have provided additional evidence that VDAC2 is required for pro-apoptotic activity of Bax in the absence of Bak. In the absence of Bak, VDAC2-deficient cells showed strong resistance to various apoptotic stimuli, whereas re-introduction of the Vdac2 gene restored their apoptotic response. Consistently, silencing of VDAC2 in Bak-deficient cells, but not Bax-deficient cells, also conferred resistance to various apoptotic stimuli. In the absence of VDAC2 and Bak, the activation of Bax (assessed by mitochondrial membrane integration, conformational changes and oligomerization) was markedly impaired. Taken together, these findings indicate that VDAC2 is required for pro-apoptotic activity of Bax in the absence of Bak.
[Show abstract][Hide abstract] ABSTRACT: Cyclophilin D (Cyp D) is implicated in cell death pathway and blockade of Cyp D could be a potent therapeutic strategy for degenerative disorders such as Alzheimer's disease, ischemia, and multiple sclerosis, but physiological role of Cyp D remains elusive. Here, we investigated the ability of learning and memory in several behavioral tasks in mice that lacked Cyp D (Cyp D(-/-)) and the relationship between ability of learning and memory and hippocampal architecture or neuronal transmission in Cyp D(-/-) mice. Cyp D(-/-) mice showed impairments of short-term memory in the Y-maze, object recognition memory in the novel-object recognition test, reference memory in the water maze test, and associative learning in the conditioned fear learning test. Hippocampal infusion of Cyclosporine A, which binds to Cyp D, replicated the defect in hippocampus-dependent cognition observed in Cyp D(-/-) mice. The Cyp D(-/-) mice did not show histopathological abnormalities upon Nissl staining and GFAP immunostaining or irregular expression of neuronal and glial marker proteins on Western blotting. However, release of glutamate and acetylcholine was decreased from the hippocampus in response to high-potassium treatment in the Cyp D(-/-) mice than in the wild-type mice. These results suggest a physiological role for Cyp D in learning and memory via the regulation of neurotransmission.
[Show abstract][Hide abstract] ABSTRACT: The mechanisms of cell death induced by hypoxia or ischemia are not yet fully understood. We have previously demonstrated that cell death induced by hypoxia occurs independently of caspases, and is mediated by phospholipase A(2) (PLA(2)). Here, we show that p38 mitogen-activated protein kinase is activated under hypoxia. A selective inhibitor of p38 or decrease in the p38alpha protein level prevents hypoxia-induced cell death. The p38 inhibitor abolishes PLA(2) activation by hypoxia, indicating that p38 acts upstream of PLA(2). The antioxidant N-acetyl-cysteine inhibits activation of p38 and cell death induced by hypoxia, indicating that reactive oxygen species (ROS) are responsible for p38 activation. These results demonstrate that the ROS/p38/PLA(2) signaling axis has a crucial role in caspase-independent cell death induced by hypoxia.
[Show abstract][Hide abstract] ABSTRACT: We previously reported that the CA-repeat sequence in the 3'-untranslated region (3'UTR) of bcl-2 mRNA is involved in the decay of bcl-2 mRNA. However, the trans-acting factor for the CA element in bcl-2 mRNA remains unidentified. The heterogeneous nuclear ribonucleoprotein L (hnRNP L), an intron splicing factor, has been reported to bind to CA repeats and CA clusters in the 3'UTR of several genes. We reported herein that the CA repeats of bcl-2 mRNA have the potential to form a distinct ribonuclear protein complex in cytoplasmic extracts of MCF-7 cells, as evidenced by RNA electrophoretic mobility shift assays (REMSA). A super-shift assay using the hnRNP L antibody completely shifted the complex. Immunoprecipitation with the hnRNP L antibody and MCF-7 cells followed by RT-PCR revealed that hnRNP L interacts with endogenous bcl-2 mRNA in vivo. Furthermore, the suppression of hnRNP L in MCF-7 cells by the transfection of siRNA for hnRNP L resulted in a delay in the degradation of RNA transcripts including CA repeats of bcl-2 mRNA in vitro, suggesting that the interaction between hnRNPL and CA repeats of bcl-2 mRNA participates in destabilizing bcl-2 mRNA.
Biochemical and Biophysical Research Communications 04/2009; 382(3):583-7. · 2.28 Impact Factor