Death effector domain-containing proteins DEDD and FLAME-3 form nuclear complexes with the TFIIIC102 subunit of human transcription factor IIIC

Rotenone-driven DNA hypermethylation of the miR-6991-3p promoter induces death of mouse brain organoids

Rotenone has potential chemical toxicity in the nervous system of both insects and mammals, but its deep molecular biological mechanisms have not been clarified. Here, the epigenetic regulatory mechanism underlying the toxicity of rotenone was studied using murine brain organoids (mBOs). Transmission electron microscopy indicated that rotenone destroyed mBOs'mitochondrial structure. RRBS-Seq showed that some promoter regions from the DLK1-DIO3 imprinted microRNA clusters were hypomethylated. But, rotenone stimulated hypermethylation significantly on the promoter DNA of miR-6991-3p. MiR-6991-3p in the rotenone-treated mBOs had the greatest decreased miRNA expression compared with the control. Meanwhile, luciferase report assay indicated that miR-6991-3p induced a decrease in luciferase activity via binding to specific sites on the 3'UTR of DEDD2 gene. To overexpression of miR-6991-3p attenuated mBO proliferated inhibition and cell death, accumulation for lipid peroxidation products significantly by rotenone inducing. Subsequently, results of cell staining and molecular biology experiment revealed that overexpression for miR-6991-3p significantly weakened expression levels of death-related genes (DEDD2, caspase-8, caspase-3, and caspase-1), but significantly elevated expression levels of cell proliferation-related genes (Ki67 and BCL2) in rotenone treated mBOs group. Here, we reveal a novel epigenetic mechanism of rotenone-induced neuronal death, in which rotenone induced promoter DNA hypermethylation of miR-6991-3p in the DLK1-DIO3 imprinted cluster. This caused miR-6991-3p transcriptional activity to be downregulated, which subsequently significantly increased the expression of its target gene, DEDD2, ultimately leading to neural organoid cell death.

Bacterial death and TRADD-N domains help define novel apoptosis and immunity mechanisms shared by prokaryotes and metazoans

Several homologous domains are shared by eukaryotic immunity and programmed cell-death systems and poorly understood bacterial proteins. Recent studies show these to be components of a network of highly regulated systems connecting apoptotic processes to counter-invader immunity, in prokaryotes with a multicellular habit. However, the provenance of key adaptor domains, namely those of the Death-like and TRADD-N superfamilies, a quintessential feature of metazoan apoptotic systems, remained murky. Here, we use sensitive sequence analysis and comparative genomics methods to identify unambiguous bacterial homologs of the Death-like and TRADD-N superfamilies. We show the former to have arisen as part of a radiation of effector-associated α-helical adaptor domains that likely mediate homotypic interactions bringing together diverse effector and signaling domains in predicted bacterial apoptosis- and counter-invader systems. Similarly, we show that the TRADD-N domain defines a key, widespread signaling bridge that links effector deployment to invader-sensing in multicellular bacterial and metazoan counter-invader systems. TRADD-N domains are expanded in aggregating marine invertebrates and point to distinctive diversifying immune strategies probably directed both at RNA and retroviruses and cellular pathogens that might infect such communities. These TRADD-N and Death-like domains helped identify several new bacterial and metazoan counter-invader systems featuring underappreciated, common functional principles: the use of intracellular invader-sensing lectin-like (NPCBM and FGS), transcription elongation GreA/B-C, glycosyltransferase-4 family, inactive NTPase (serving as nucleic acid receptors), and invader-sensing GTPase switch domains. Finally, these findings point to the possibility of multicellular bacteria-stem metazoan symbiosis in the emergence of the immune/apoptotic systems of the latter.

Analysis of Argonaute Complex Bound mRNAs in DU145 Prostate Carcinoma Cells Reveals New miRNA Target Genes

Posttranscriptional gene regulation by microRNAs (miRNAs) contributes to the induction and maintenance of prostate carcinoma (PCa). To identify mRNAs enriched or removed from Ago2-containing RISC complexes, these complexes were immunoprecipitated from normal prostate fibroblasts (PNFs) and the PCa line DU145 and the bound mRNAs were quantified by microarray. The analysis of Ago complexes derived from PNFs or DU145 confirmed the enrichment or depletion of a variety of mRNAs already known from the literature to be deregulated. Novel potential targets were analyzed by luciferase assays with miRNAs known to be deregulated in PCa. We demonstrate that the mRNAs of the death effector domain-containing protein (DEDD), the tumor necrosis factor receptor superfamily, member 10b protein (TNFRSF10B), the tumor protein p53 inducible nuclear protein 1 (TP53INP1), and the secreted protein, acidic, cysteine-rich (SPARC; osteonectin) are regulated by miRNAs miR-148a, miR-20a, miR-24, and miR-29a/b, respectively. Therefore, these miRNAs represent potential targets for therapy. Surprisingly, overexpression of miR-24 induced focus formation and proliferation of DU145 cells, while miR-29b reduced proliferation. The study confirms genes deregulated in PCa by virtue of their presence/absence in the Ago2-complex. In conjunction with the already published miRNA profiles of PCa, the data can be used to identify miRNA-regulated mRNAs.

Ectodermal dysplasia-like syndrome with mental retardation due to contiguous gene deletion: further clinical and molecular delineation of del(2q32) syndrome

We report on a patient with an interstitial deletion of the long arm of chromosome 2 at 2q31.2q33.2. She had prenatal and postnatal growth retardation, microcephaly, facial dysmorphism, cleft palate, camptodactyly, bilateral talipes equinovarus, severe intellectual disability, and ectodermal anomalies. She showed thin, atrophic skin, sparse, brittle, slowly growing hair, oligodontia with abnormally shaped teeth, normal sweating, and normal fingernails, consistent with a diagnosis of ectodermal dysplasia. Array CGH analysis (Agilent 44K) showed the deletion to span 26 Mb, between cytogenetic bands 2q31.2 and 2q33. The deletion leads to hemizygosity for the HOXD cluster and its regulatory elements, COL3A1/COL5A2, GTF3C3, CASP8, CASP10, and SABT2 could perhaps interfere with long range control of DLX1 and DLX2 expression. This girl confirms the existence of a clinically recognizable 2q32 microdeletion syndrome, as recently delineated by Van Buggenhout et al. and confirms a novel putative locus for ectodermal dysplasia on chromosome 2q31q33. We recommend considering cytogenetic and/or molecular screening for del(2q32) in patients with developmental disability and ectodermal dysplasia-like phenotype, including thin skin, oligodontia, dysplastic teeth, and sparse hair.

Modulation of Wnt signaling by the nuclear localization of cellular FLIP-L

Cellular FLIP (cFLIP) inhibits the apoptosis signaling initiated by death receptor ligation. We previously reported that a long form of cFLIP (cFLIP-L) enhances Wnt signaling via inhibition of beta-catenin ubiquitylation. In this report, we present evidence that cFLIP-L translocates into the nucleus, which could have a role in modulation of Wnt signaling. cFLIP-L has a functional bipartite nuclear localization signal (NLS) at the C-terminus. Wild-type cFLIP-L (wt-FLIP-L) localizes in both the nucleus and cytoplasm, whereas NLS-mutated cFLIP-L localizes predominantly in the cytoplasm. cFLIP-L also has a nuclear export signal (NES) near the NLS, and leptomycin B, an inhibitor of CRM1-dependent nuclear export, increases the nuclear accumulation of cFLIP-L, suggesting that it shuttles between the nucleus and cytoplasm. Expression of mutant cFLIP-L proteins with a deletion or mutations in the NLS and NES confers resistance to Fas-mediated apoptosis, as does wt-FLIP-L, but they do not enhance Wnt signaling, which suggests an important role of the C-terminus of cFLIP-L in Wnt-signaling modulation. When wt-FLIP-L is expressed in the cytoplasm by conjugation with exogenous NES (NES-FLIP-L), Wnt signaling is not enhanced, whereas the NES-FLIP-L increases cytoplasmic beta-catenin as efficiently as wt-FLIP-L. cFLIP-L physically interacts with the reporter plasmid for Wnt signaling, but not with the control plasmid. These results suggest a role for nuclear cFLIP-L in the modulation of Wnt signaling.

Transcription regulation of caspase-1 by R393 of HIPPI and its molecular partner HIP-1

Earlier we have shown that exogenous expression of HIPPI, a molecular partner of Huntingtin interacting protein HIP-1, induces apoptosis and increases expression of caspases-1, -8 and -10 in HeLa and Neuro2A cells. The C-terminal pseudo death effector domain of HIPPI (pDED-HIPPI) specifically interacts with the putative promoter sequences of these genes. In the present manuscript, we predict from structural modeling of pDED-HIPPI that R393 of HIPPI is important for such interaction. R393E mutation in pDED-HIPPI decreases the interaction with the putative promoter of caspase-1 in cells. Expression of caspase-1 is decreased in cells expressing mutant pDED-HIPPI in comparison to that observed in cells expressing wild type pDED-HIPPI. Using HIP-1 knocked down cells as well as over expressing HIP-1 with mutation at its nuclear localization signal and other deletion mutations, we demonstrate that translocation of HIPPI to the nucleus is mediated by HIP-1 for the increased expression of caspase-1. HIPPI-HIP-1 heterodimer is detected in cytoplasm as well as in the nucleus and is associated with transcription complex in cells. Taking together, we are able to show the importance of R393 of HIPPI and the role of HIPPI-HIP-1 heterodimer in the transcription regulation of caspase-1.

Influenza A virus matrix protein 1 interacts with hTFIIIC102-s, a short isoform of the polypeptide 3 subunit of human general transcription factor IIIC

Influenza A virus matrix protein 1 (M1) is a multifunctional protein that plays important roles during replication, assembly and budding of the virus. To search for intracellular protein components that interact with M1 protein and explore the potential roles of these interactions in the pathogenesis of influenza virus infection, 11 independent proteins, including hTFIIIC102-s protein, encoding a short isoform of the TFIIIC102 subunit of the human TFIIIC transcription factor, were screened from a human cell cDNA library using a yeast two-hybrid technique. The interaction between M1 protein and hTFIIIC102-s was studied in more detail. Mapping assays showed that the N-terminal globular region (amino acids 1-164) of the M1 protein and the five tandem tetratricopeptide repeats (TPR1-5, amino acids 149-362) in hTFIIIC102-s were necessary for the interaction. The interaction was confirmed by both glutathione-S-transferase (GST) pull-down assays and coimmunoprecipitation assays. In addition, coexpression of hTFIIIC102-s with M1 in HeLa cells inhibited the translocation of M1 into the nucleus. Taken together, the present data indicate that hTFIIIC102-s can interact with the structural M1 protein of the influenza virus, which provides a novel clue toward further understanding of the roles of M1 protein in the interactions between influenza virus and host cells.

Bortezomib induces caspase-dependent apoptosis in Hodgkin lymphoma cell lines and is associated with reduced c-FLIP expression: A gene expression profiling study with implications for potential combination therapies

The Hodgkin cells and Reed-Sternberg cells (HRS) of classical Hodgkin lymphoma (CHL) are derived from germinal center B cells. The pathogenesis of CHL is unclear but constitutive activation of NFkappaB may contribute. Proteasome inhibition aimed at inhibiting NFkappaB has been shown to result in apoptosis in HRS cells. Here we investigated the effects of bortezomib, a proteasome inhibitor, in HRS cells with a combination of functional assays and gene expression profiling (GEP). Exposure of KMH2 and L428 cells to bortezomib resulted in inhibition of proliferation and induction of apoptosis. Gene expression analysis of KMH2 cells by oligonucleotide cDNA microarrays showed that a limited set of genes were differentially expressed involving several key cellular pathways including cell cycle and apoptosis. Among them, the caspase 8 inhibitor cFLIP was down-regulated and confirmed by Q-PCR. Given the evidence that cFLIP in HRS cells contribute to cells' insensitive to death receptor-mediated apoptosis, we combined bortezomib and TRAIL. This combination caused further down-regulation of cFLIP protein and increased apoptosis in CHL cells demonstrated by PARP p85 immunohistochemistry and immunoblotting. Such apoptotic effects were inhibited by caspase inhibitor z-VAD-FMK, confirming the pro-apoptotic effects of bortezomib and TRAIL are caspase-dependent. Bortezomib has no detectable effect on expression of TRAIL receptor DR4/DR5 in these two cell lines. Tissue microarray analysis of primary Hodgkin lymphomas displayed that 82% cases (95/116) expressed cFLIP in Reed-Sternberg cells. The discovery of apoptotic pathways that can be manipulated by proteasome inhibition provides rationale for the combination of bortezomib and agents such as TRAIL in CHL treatment.

Interactions of HIPPI, a molecular partner of Huntingtin interacting protein HIP1, with the specific motif present at the putative promoter sequence of the caspase-1, caspase-8 and caspase-10 genes

To investigate the mechanism of increased expression of caspase-1 caused by exogenous Hippi, observed earlier in HeLa and Neuro2A cells, in this work we identified a specific motif AAAGACATG (- 101 to - 93) at the caspase-1 gene upstream sequence where HIPPI could bind. Various mutations in this specific sequence compromised the interaction, showing the specificity of the interactions. In the luciferase reporter assay, when the reporter gene was driven by caspase-1 gene upstream sequences (- 151 to - 92) with the mutation G to T at position - 98, luciferase activity was decreased significantly in green fluorescent protein-Hippi-expressing HeLa cells in comparison to that obtained with the wild-type caspase-1 gene 60 bp upstream sequence, indicating the biological significance of such binding. It was observed that the C-terminal 'pseudo' death effector domain of HIPPI interacted with the 60 bp (- 151 to - 92) upstream sequence of the caspase-1 gene containing the motif. We further observed that expression of caspase-8 and caspase-10 was increased in green fluorescent protein-Hippi-expressing HeLa cells. In addition, HIPPI interacted in vitro with putative promoter sequences of these genes, containing a similar motif. In summary, we identified a novel function of HIPPI; it binds to specific upstream sequences of the caspase-1, caspase-8 and caspase-10 genes and alters the expression of the genes. This result showed the motif-specific interaction of HIPPI with DNA, and indicates that it could act as transcription regulator.

Death effector domain DEDa, a self-cleaved product of caspase-8/Mch5, translocates to the nucleus by binding to ERK1/2 and upregulates procaspase-8 expression via a p53-dependent mechanism

Activation of the apical caspase-8 is crucial to the extrinsic apoptotic pathway. Although the death effector domain (DED) of caspase-8 has been reported to be involved in death-inducing signaling complex formation, the detailed mechanism of how DED functions in regulating apoptosis remains largely unknown. Here, we demonstrate that the prodomain of the caspase-8/Mch5 can be further cleaved between two tandemly repeated DEDs (DEDa-DEDb) at the amino-acid residue Asp129 by caspase-8 itself. The DEDa fragment generated from the endogenous caspase-8 was detected in isolated nucleoli upon treatment with TRAIL (tumor necrosis factor-related apoptosis-inducing ligand). Cleaved DEDa appears to translocate into the nucleus by association with extracellular signal-regulated protein kinases-1/2 (ERK1/2). Elimination of ERK1/2 expression by RNA interference resulted in a significant attenuation of nuclear entry of DEDa and reduced caspase-8-dependent apoptosis. In the nucleus, DEDa interacts with TOPORS, a p53 and topoisomerase I binding protein, and possibly displaces p53 from TOPORS, allowing p53 to stimulate caspase-8 gene expression. In summary, we postulate a positive feedback loop involving DEDa, which enables the continual replenishment of procaspase-8 during apoptosis.

Death-effector domain-containing protein DEDD is an inhibitor of mitotic Cdk1/cyclin B1

Accumulating evidence has shown that many molecules, including some cyclin-dependent kinases (Cdks) and cyclins, as well as the death-effector domain (DED)-containing FADD, function for both apoptosis and cell cycle. Here we identified that DEDD, which also possesses the DED domain, acts as a novel inhibitor of the mitotic Cdk1/cyclin B1 complex. DEDD associates with mitotic Cdk1/cyclin B1 complexes via direct binding to cyclin B1 and reduces their function. In agreement, kinase activity of nuclear Cdk1/cyclin B1 in DEDD-null (DEDD-/-) embryonic fibroblasts is increased compared with that in DEDD+/+ cells, which results in accelerated mitotic progression, thus exhibiting a shortened G2/M stage. Interestingly, DEDD-/- cells also demonstrated decreased G1 duration, which perhaps enhanced the overall reduction in rRNA amounts and cell volume, primarily caused by the rapid termination of rRNA synthesis before cell division. Likewise, DEDD-/- mice show decreased body and organ weights relative to DEDD+/+ mice. Thus, DEDD is an impeder of cell mitosis, and its absence critically influences cell and body size via modulation of rRNA synthesis.

Cloning, expression, purification, crystallization and preliminary crystallographic analysis of pseudo death-effector domain of HIPPI, a molecular partner of Huntingtin-interacting protein HIP-1

The formation of a heterodimer between Huntingtin-interacting protein-1 (HIP-1) and its novel partner HIPPI (HIP-1 protein interactor) through their pseudo death-effector domains (pDEDs) is a key step that recruits caspase-8 and initiates apoptosis. This could be one of the pathways by which apoptosis is increased in Huntington's disease (HD). A construct consisting of the pDED of HIPPI has been cloned and overexpressed as 6NH-tagged protein and purified by Ni-NTA affinity chromatography. Crystals of the pDED of HIPPI were grown in space group P4(1), with unit-cell parameters a = b = 77.42, c = 33.31 A and a calculated Matthews coefficient of 1.88 A3 Da(-1) (33% solvent content) with two molecules per asymmetric unit.

Vanishin is a novel ubiquitinylated death-effector domain protein that blocks ERK activation

The ERK (extracellular-signal regulated-kinase)/MAPK (mitogen-activated protein kinase) pathway can regulate transcription, proliferation, migration and apoptosis. The small DED (death-effector domain) protein PEA-15 (phosphoprotein enriched in astrocytes-15) binds ERK and targets it to the cytoplasm. Other DED-containing proteins including cFLIP and DEDD can also regulate signal transduction events and transcription in addition to apoptosis. In the present study, we report the identification of a novel DED-containing protein called Vanishin. The amino acid sequence of Vanishin is closest in similarly to PEA-15 (61% identical). Vanishin mRNA is expressed in several mouse tissues and in both mouse and human cell lines. Interestingly, Vanishin is regulated by ubiquitinylation and subsequent degradation by the 26 S proteasome. The ubiquitinylation is complex and occurs at both the internal lysine residues and the N-terminus. We further show that Vanishin binds ERK/MAPK but not the DED proteins Fas-associated death domain, caspase 8 or PEA-15. Vanishin is present in both the nucleus and Golgi on overexpression and forces increased ERK accumulation in the nucleus in the absence of ERK stimulation. Moreover, Vanishin expression inhibits ERK activation and ERK-dependent transcription in cells, but does not alter MAPK/ERK activity. Therefore Vanishin is a novel regulator of ERK that is controlled by ubiquitinylation.

Screening of genes differentially expressed in HepG2 cells transfected with non-structural protein 4B ofhepatitis C virus

AIM: To screen genes differently expressed in human hepatoblastoma cell line HepG2 transfected with non-structural protein 4B (NS4B) of hepatitis C virus (HCV) , and to further elucidate the molecular biological mechanism of NS4B in chronic hepatitis C and carcinogenesis, and progression of hepatoma.

METHODS: Sequence-specific primers of HCV NS4B were designed and synthesized. The plasmid pBRTM3011, in which the full length of HCV-H cDNA genome was contained, was treated as the template to amplify the NS4B-coded DNA fragment with polymerase chain reaction (PCR) technique. The expressive vector of pcDNA3.1(-)-NS4B was constructed by routine molecular biological methods. The technology of cDNA microarray was adopted to detect the mRNA extracted from the HepG2 cells transfected with pcDNA3.1(-)-NS4B and pcDNA3.1(-) using lipofectamine, respectively. The expression of NS4B protein in the transfected vector was confirmed by Western blot with single chain variable region antibody.

RESULTS: The expressive vector was constructed and confirmed after restriction enzyme digestion and DNA sequencing analysis. The expression of NS4B protein in the transfected vector was confirmed by Western blot with single chain variable region antibody. High quality mRNA and cDNA were prepared. Among 1 152 genes of the DNA microarray, we found 56 genes were differently expressed in HepG2 cells transfected with NS4B, in which 22 genes were significantly up-regulated and 34 were significantly down-regulated.

CONCLUSION: Differently expressed genes are successfully screened in HepG2 cells transfected with NS4B by cDNA microarray, which may help to further elucidate the molecular mechanism of NS4B in HCV infection and development of hepatocellular carcinoma.

FLIP protein and TRAIL-induced apoptosis

Death ligands (such as Fas/CD95 ligand and TRAIL?Apo2L) and death receptors (such as Fas/CD95, TRAIL-R1?DR4, and TRAIL-R2/DR5) are involved in immune-mediated neutralization of activated or autoreactive lymphocytes, virus-infected cells, and tumor cells. Consequently, dysregulation of death receptor-dependent apoptotic signaling pathways has been implicated in the development of autoimmune diseases, immunodeficiency, and cancer. Moreover, the death ligand TRAIL has gained considerable interest as a potential anticancer agent, given its ability to induce apoptosis of tumor cells without affecting most types of untransformed cells. The FLICE-inhibitory protein (FLIP) potently blocks TRAIL-mediated cell death by interfering with caspase-8 activation. Pharmacologic down-regulation of FLIP might serve as a therapeutic means to sensitize tumor cells to apoptosis induction by TRAIL.

The death effector domain protein family

Apoptosis signaling is regulated and executed by specialized proteins that often carry protein/protein interaction domains. One of these domains is the death effector domain (DED) that is predominantly found in components of the death-inducing signaling complex, which forms at the members of the death receptor family following their ligation. Both proapoptotic- and antiapoptotic-DED-containing proteins have been identified, which makes these proteins exquisitely suited to the regulation of apoptosis. Aside from their pivotal role in the control of the apoptotic program, DED-containing proteins have recently been demonstrated to exert their influence on other cellular processes as well, including cell proliferation. These data highlight the multiple roles for the members of this family, suggesting that they are suited to control both life and death decisions of cells. Additionally, because they can act proapoptotically, antiapoptotically, or in the regulation of the cell cycle, this family of proteins may be excellent candidates for cancer therapy targets. Oncogene (2003) 22, 8634-8644. doi:10.1038/sj.onc.1207103

Regulation of apoptosis by ubiquitination

Cell elimination through apoptosis, or programmed cell death, is an evolutionarily conserved central tenet of biology from embryological development to immune homeostasis. While many of the apoptotic signaling pathways have been elucidated, the relationship between ubiquitin and apoptosis is only beginning to be defined. In the past decade, many reports of polyubiquitin conjugation of key pro- and anti-apoptotic molecules have characterized ubiquitin as an essential regulatory modification targeting proteins for proteasomal degradation. However, recent work relating monoubiquitination and nonclassical polyubiquitin conjugation to apoptotic molecules has added an additional level of diversity to the role of ubiquitin in apoptotic regulation beyond degradation. This review focuses on the direct effects of ubiquitination on apoptosis-signaling molecules.

Fas-associated death domain protein interacts with methyl-CpG binding domain protein 4: a potential link between genome surveillance and apoptosis

Fas-associated death domain protein (FADD) is an adaptor protein bridging death receptors with initiator caspases. Thus, its function and localization are assumed to be cytoplasmic, although the localization of endogenous FADD has not been reported. Surprisingly, the data presented here demonstrate that FADD is mainly nuclear in several adherent cell lines. Its accumulation in the nucleus and export to the cytoplasm required the phosphorylation site Ser-194, which was also required for its interaction with the nucleocytoplasmic shuttling protein exportin-5. Within the nucleus, FADD interacted with the methyl-CpG binding domain protein 4 (MBD4), which excises thymine from GT mismatches in methylated regions of chromatin. The MBD4-interacting mismatch repair factor MLH1 was also found in a complex with FADD. The FADD-MBD4 interaction involved the death effector domain of FADD and a region of MBD4 adjacent to the glycosylase domain. The FADD-binding region of MBD4 was downstream of a frameshift mutation that occurs in a significant fraction of human colorectal carcinomas. Consistent with the idea that MBD4 can signal to an apoptotic effector, MBD4 regulated DNA damage-, Fas ligand-, and cell detachment-induced apoptosis. The nuclear localization of FADD and its interaction with a genome surveillance/DNA repair protein that can regulate apoptosis suggests a novel function of FADD distinct from direct participation in death receptor signaling complexes.

DEDD and DEDD2 associate with caspase-8/10 and signal cell death

An apoptotic signal triggered by cell surface death receptors is disseminated to intracellular compartments through protein-protein interactions mediated by conserved domains such as the death effector domain (DED). A unique family of single DED-containing proteins, including DEDD and DEDD2, is targeted to the nucleolus. However, the role of DEDD/DEDD2 in apoptosis remains less understood. Here we show that DEDD and DEDD2 are highly conserved in diverse species, and that they are potent inducers of apoptosis in various cell types. Deletion analysis indicates that both the N-terminal DED domain and the C-terminal region of DEDD2 can induce apoptosis. The cell death activity of this family appears to be related to their nuclear localization. DEDD and DEDD2 bind to two tandem DED-containing caspases, caspase -8 and -10, that are engaged by death receptors. Consistent with the nuclear localization of this family, caspase-8 translocates to the nucleus during CD95-induced apoptosis. DEDD and DEDD2 also readily associate with themselves and with each other. These results suggest that DEDD and DEDD2 may be important mediators for death receptors and that they may target caspases to the nucleus.

Recognition of ERK MAP kinase by PEA-15 reveals a common docking site within the death domain and death effector domain

PEA-15 is a multifunctional protein that modulates signaling pathways which control cell proliferation and cell death. In particular, PEA-15 regulates the actions of the ERK MAP kinase cascade by binding to ERK and altering its subcellular localization. The three-dimensional structure of PEA-15 has been determined using NMR spectroscopy and its interaction with ERK defined by characterization of mutants that modulate ERK function. PEA-15 is composed of an N-terminal death effector domain (DED) and a C-terminal tail of irregular structure. NMR 'footprinting' and mutagenesis identified elements of both the DED and tail that are required for ERK binding. Comparison of the DED-binding surface for ERK2 with the death domain (DD)-binding surface of Drosophila Tube revealed an unexpected similarity between the interaction modes of the DD and DED motifs in these proteins. Despite a lack of functional or sequence similarity between PEA-15 and Tube, these proteins utilize a common surface of the structurally similar DD and DED to recognize functionally diverse targets.

Apoptosis: biochemical aspects and clinical implications

Apoptosis and necrosis represent two distinct types of cell death. Apoptosis possesses unique morphologic and biochemical features which distinguish this mechanism of programmed cell death from necrosis. Extrinsic apoptotic cell death is receptor-linked and initiates apoptosis by activating caspase 8. Intrinsic apoptotic cell death is mediated by the release of cytochrome c from mitochondrial and initiates apoptosis by activating caspase 3. Cancer chemotherapy utilizes apoptosis to eliminate tumor cells. Agents which bind to the minor groove of DNA, like camptothecin and Hoechst 33342, inhibit topoisomerase I, RNA polymerase II, DNA polymerase and initiate intrinsic apoptotic cell death. Hoechst 33342-induced apoptosis is associated with disruption of TATA box binding protein/TATA box complexes, replication protein A/single-stranded DNA complexes, topoisomerase I/DNA cleavable complexes and with an increased intracellular concentration of E2F-1 transcription factor and nitric oxide concentration. Nitric oxide and transcription factor activation or respression also regulate the two apoptotic pathways. Some human diseases are associated with excess or deficient rates of apoptosis, and therapeutic strategies to regulate the rate of apoptosis include inhibition or activation of caspases, mRNA antisense to reduce anti-apoptotic factors like Bcl-2 and survivin and recombinant TRAIL to activate pro-apoptotic receptors, DR4 and DR5.

DEDD regulates degradation of intermediate filaments during apoptosis

Apoptosis depends critically on regulated cytoskeletal reorganization events in a cell. We demonstrate that death effector domain containing DNA binding protein (DEDD), a highly conserved and ubiquitous death effector domain containing protein, exists predominantly as mono- or diubiquitinated, and that diubiquitinated DEDD interacts with both the K8/18 intermediate filament network and pro-caspase-3. Early in apoptosis, both cytosolic DEDD and its close homologue DEDD2 formed filaments that colocalized with and depended on K8/18 and active caspase-3. Subsequently, these filamentous structures collapsed into intracellular inclusions that migrated into cytoplasmic blebs and contained DEDD, DEDD2, active caspase-3, and caspase-3-cleaved K18 late in apoptosis. Biochemical studies further confirmed that DEDD coimmunoprecipitated with both K18 and pro-caspase-3, and kinetic analyses placed apoptotic DEDD staining prior to caspase-3 activation and K18 cleavage. In addition, both caspase-3 activation and K18 cleavage was inhibited by expression of DEDDDeltaNLS1-3, a cytosolic form of DEDD that cannot be ubiquitinated. Finally, siRNA mediated DEDD knockdown cells exhibited inhibition of staurosporine-induced DNA degradation. Our data suggest that DEDD represents a novel scaffold protein that directs the effector caspase-3 to certain substrates facilitating their ordered degradation during apoptosis.