Biomedical subjects

Marcus E Peter

Publications and source records attributed to Marcus E Peter.

31 records · Page 2Linked to original sources

PubMed2003

Cell cycle effects by C-FADD depend on its C-terminal phosphorylation site.

Expression of a truncated form of the death receptor adaptor FADD (C-FADD) as a transgene in mice blocks T cell proliferation. Here we provide evidence that the C-terminal phosphorylation site Ser194 in C-FADD affects the cell cycle in nonlymphoid cells as well. High expression of wild type C-FADD but not C-FADD with a S194A point mutation arrested the nontumor cell line MCF10A in G2/M but not the tumor cell line MCF7. BJAB as well as MCF10A cells expressing moderate levels of C-FADD with a S194E mutation mimicking phosphorylated C-FADD were more susceptible to a Taxol-induced G2/M arrest than cells expressing C-FADD S194A suggesting that C-FADD S194E lowers the threshold for G2/M arrest. Our data suggest that C-FADD may affect apoptosis sensitivity of cells by interfering with cell cycle progression and not only by binding to death receptors.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Interdimer processing mechanism of procaspase-8 activation.

The execution of apoptosis depends on the hierarchical activation of caspases. The initiator procaspases become autoproteolytically activated through a less understood process that is triggered by oligomerization. Procaspase-8, an initiator caspase recruited to death receptors, is activated through two cleavage events that proceed in a defined order to generate the large and small subunits of the mature protease. Here we show that dimerization of procaspase-8 produces enzymatically competent precursors through the stable homophilic interaction of the procaspase-8 protease domain. These dimers are also more susceptible to processing than individual procaspase-8 molecules, which leads to their cross-cleavage. The order of the two interdimer cleavage events is maintained by a sequential accessibility mechanism: the separation of the large and small subunits renders the region between the large subunit and prodomain susceptible to further cleavage. In addition, the activation process involves an alteration in the enzymatic properties of caspase-8; while procaspase-8 molecules specifically process one another, mature caspases only cleave effector caspases. These results reveal the key steps leading to the activation of procaspase-8 by oligomerization.

Apoptosis↗

PubMed2003

The TNF receptor 1: a split personality complex.

The tumor necrosis factor receptor 1 (TNFR1), a prototypic member of the death receptor family signals both cell survival and apoptosis. In this issue of Cell, report that apoptotic TNFR1 signaling proceeds via the sequential formation of two distinct complexes. Since the first complex can activate survival signals and influence the activity of the second complex, this mechanism provides a checkpoint to control the execution of apoptosis.

Adaptor Proteins, Signal Transducing↗

PubMed2003

Actin dependent CD95 internalization is specific for Type I cells.

CD95 Type I and Type II cells differ in the requirement for mitochondrial contribution to the execution of apoptosis. Mitochondria are required to amplify the apoptosis signal only in Type II cells. Here we show that CD95 internalizes in an actin dependent manner only in Type I cells and that the two CD95 apoptosis cell types differ in their threshold of active caspase-8 required to execute apoptosis. The data suggest that CD95 is linked to the cytoskeleton in different ways in the two cell types and that they have adapted to different levels of active caspase-8 generated at the activated receptor.

Actins↗

PubMed2003

Gadd45 beta mediates the protective effects of CD40 costimulation against Fas-induced apoptosis.

In B lymphocytes, induction of apoptosis or programmed cell death (PCD) by Fas (CD95/APO-1) is suppressed by the triggering of CD40. This suppression controls various aspects of the humoral immune response, including antibody affinity maturation. The opposing effects of these receptors are also crucial to B-cell homeostasis, autoimmune disease, and cancer. Cytoprotection by CD40 involves activation of protective genes mediated by NF-kappa B transcription factors; however, its basis remains poorly understood. Here, we report that, in B cells, Gadd45 beta is induced by CD40 through a mechanism that requires NF-kappa B and that this induction suppresses Fas-mediated killing. Importantly, up-regulation of Gadd45 beta by CD40 precedes Fas-induced caspase activation, as well as up-regulation of other NF-kappa B-controlled inhibitors of apoptosis such as Bcl-xL and c-FLIPL. In the presence of Gadd45 beta, the Fas-induced apoptotic cascade is halted at mitochondria. However, in contrast to Bcl-xL, Gadd45 beta is unable to hamper the "intrinsic" pathway for apoptosis and in fact appears to block Fas cytotoxicity herein by suppressing a mitochondria-targeting mechanism activated by this receptor. These findings identify Gadd45 beta as a critical mediator of the prosurvival response to CD40 stimulation and provide important new insights into the apoptotic mechanism that is triggered by Fas in B cells.

Antigens, Differentiation↗

PubMed2003

The CD95 type I/type II model.

CD95 (APO-1/Fas) has become the prototype of a death domain containing receptor and is the best studied member of the death receptors that activate the extrinsic apoptosis pathway. This pathway is initiated by recruitment and activation of caspase-8, an initiator caspase, in the death-inducing signaling complex (DISC) followed by direct cleavage of downstream effector caspases. In contrast, the intrinsic apoptosis pathway starts from within the cell either by direct activation of caspases or through intracellular changes such as DNA damage resulting in the release of a number of pro-apoptotic factors from the intermembrane space of mitochondria. The release of these factors results in the activation of another initiator caspase, caspase-9, and ultimately in the activation of effector caspases in a protein complex called the apoptosome. In recent years, it has become apparent that there is cross talk between the extrinsic and intrinsic pathway. In the death receptor pathway of apoptosis induction, the best characterized connection between the two pathways is the Bcl-2 family member Bid which translocates to mitochondria after cleavage by caspase-8 causing pro-apoptotic changes. Cells that die through CD95 without help from mitochondria are called Type I cells, whereas cells in which CD95-mediated death relies mostly on the intrinsic pathway are called Type II. This review focuses on recent developments in the delineation of the biochemistry and the physiological function of the two CD95 pathways.

Animals↗

PubMed2003

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.

Animals↗

PubMed2002

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.

Animals↗

PubMed2002

c-FLIP(L) is a dual function regulator for caspase-8 activation and CD95-mediated apoptosis.

Activation of the caspase cascade is a pivotal step in apoptosis and can occur via death adaptor-mediated homo-oligomerization of initiator procaspases. Here we show that c-FLIP(L), a protease-deficient caspase homolog widely regarded as an apoptosis inhibitor, is enriched in the CD95 death-inducing signaling complex (DISC) and potently promotes procaspase-8 activation through hetero-dimerization. c-FLIP(L) exerts its effect through its protease-like domain, which associates efficiently with the procaspase-8 protease domain and induces the enzymatic activity of the zymogen. Ectopic expression of c-FLIP(L) at physiologically relevant levels enhances procaspase-8 processing in the CD95 DISC and promotes apoptosis, while a decrease of c-FLIP(L) expression results in inhibition of apoptosis. c-FLIP(L) acts as an apoptosis inhibitor only at high ectopic expression levels. Thus, c-FLIP(L) defines a novel type of caspase regulator, distinct from the death adaptors, that can either promote or inhibit apoptosis.

Apoptosis↗

PubMed2002

Apoptosis-independent functions of killer caspases.

Caspases are well known for their role in the execution of the apoptotic program by cleaving specific target proteins, leading to the dismantling of the cell, as well as for mediating cytokine maturation. Recent work has highlighted novel non-apoptotic activities of apoptotic caspases. These reports indicate that caspases are much more versatile enzymes than we originally expected. In addition to regulating cell survival and cytokine maturation, caspases may be involved in regulating cell differentiation, cell proliferation, spreading and receptor internalization.

Animals↗

PubMed2002

Two faces of caspase-8.

Explore the source record for details and available documents.

BH3 Interacting Domain Death Agonist Protein↗

PubMed2002

Molecular ordering of the initial signaling events of CD95.

Binding of either ligand or agonistic antibodies to the death receptor CD95 (APO-1/Fas) induces the formation of the death-inducing signaling complex (DISC). We now show that signal initiation of CD95 in type I cells can be further separated into at least four distinct steps. (i) The first step is ligand-induced formation of CD95 microaggregates at the cell surface. (ii) The second step is recruitment of FADD to form a DISC. This step is dependent on actin filaments. (iii) The third step involves formation of large CD95 surface clusters. This event is positively regulated by DISC-generated caspase 8. (iv) The fourth step is internalization of activated CD95 through an endosomal pathway. The latter step is again dependent on the presence of actin filaments. The data indicate that the signal initiation by CD95 is a complex process actively regulated at various levels, providing a number of new drug targets to specifically modulate CD95 signaling.

Actin Cytoskeleton↗

PubMed2001

Inactivation of caspase-8 on mitochondria of Bcl-xL-expressing MCF7-Fas cells: role for the bifunctional apoptosis regulator protein.

Apoptosis induction through CD95 (APO-1/Fas) critically depends on generation of active caspase-8 at the death-inducing signaling complex (DISC). Depending on the cell type, active caspase-8 either directly activates caspase-3 (type I cells) or relies on mitochondrial signal amplification (type II cells). In MCF7-Fas cells that are deficient for pro-caspase-3, even high amounts of caspase-8 produced at the DISC cannot directly activate downstream effector caspases without mitochondrial help. Overexpression of Bcl-x(L) in these cells renders them resistant to CD95-mediated apoptosis. However, activation of caspase-8 in control (vector) and Bcl-x(L) transfectants of MCF7-Fas cells proceeds with similar kinetics, resulting in a complete processing of cellular caspase-8. Most of the cytosolic caspase-8 substrates are not cleaved in the Bcl-x(L) protected cells, raising the question of how Bcl-x(L)-expressing MCF7-Fas cells survive large amounts of potentially cytotoxic caspase-8. We now demonstrate that active caspase-8 is initially generated at the DISC of both MCF7-Fas-Vec and MCF7-Fas-Bcl-x(L) cells and that the early steps of CD95 signaling such as caspase-8-dependent cleavage of DISC bound c-FLIP(L), caspase-8-dependent clustering, and internalization of CD95, as well as processing of pro-caspase-8 bound to mitochondria are very similar in both transfectants. However, events downstream of mitochondria, such as release of cytochrome c, only occur in the vector-transfected MCF7-Fas cells, and no in vivo caspase-8 activity can be detected in the Bcl-x(L)-expressing cells. Our data suggest that, in Bcl-x(L)-expressing MCF7-Fas cells, active caspase-8 is sequestered on the outer mitochondrial surface presumably by association with the protein "bifunctional apoptosis regulator" in a way that does not allow substrates to be cleaved, identifying a novel mechanism of regulation of apoptosis sensitivity by mitochondrial Bcl-x(L).

Breast Neoplasms↗