Apoptotic and necrotic cell death induced by death domain receptors

Apoptosis and necrosis are two distinct forms of cell death. Caspases are indispensable as initiators and effectors of apoptotic cell death and are involved in many of the morphological and biochemical features of apoptosis. Major changes in mitochondrial membrane integrity and release of proapoptotic factors, such as cytochrome c from the mitochondrial intermembrane space, play an important sensor and amplifying role during apoptotic cell death. In vitro studies of cell death in cell lines have revealed that inhibition of the classical caspase-dependent apoptotic pathway leads in several cases to necrotic cell death. Thus, the same cell death stimulus can result either in apoptotic or necrotic cell death, depending on the availability of activated caspase. Therefore, death domain receptors may initiate an active caspase-independent necrotic signaling pathway. In this review, we describe what is known about the apoptotic and necrotic cell death pathways. Principal elements of necrosis include mitochondrial oxidative phosphorylation, reactive oxygen production, and non-caspase proteolytic cascades depending on serine proteases, calpains, or cathepsins.     

Lysozyme activates Enterococcus faecium to induce necrotic cell death in macrophages

Enterococci are commensal organisms in the alimentary tract. However, they can cause a variety of life-threatening infections, especially in nosocomial settings. We hypothesized that induction of cell death might enable these facultative pathogenic bacteria to evade the innate immune response and to cause infections of their host. We demonstrate that E. faecium when exposed to lysozyme induces cell death in macrophages in vitro and in vivo. Flow cytometric analyses of J774A.1 macrophages infected with E. faecium revealed loss of cell membrane integrity indicated by uptake of propidium iodide and decrease of the inner mitochondrial transmembrane potential ΔΨ_m. Inhibition of caspases, treatment of macrophages with cytochalasin D, or rifampicin did not prevent cells from dying, suggesting cell death mechanisms that are independent of caspase activation, bacterial uptake, and intracellular bacterial replication. Characteristics of necrotic cell death were demonstrated by both lack of procaspase 3 activation and cell shrinkage, electron microscopy, and release of lactate dehydrogenase. Pretreatment of E. faecium with lysozyme and subsequently with broad spectrum protease considerably reduced cell death, suggesting that a bacterial surface protein is causative for cell death induction. Moreover, in a mouse peritonitis model we demonstrated that E. faecium induces cell death of peritoneal macrophages in vivo. Altogether, our results show that enterococci, under specific conditions such as exposure to lysozyme, induce necrotic cell death in macrophages, which might contribute to disseminated infections by these facultative pathogenic bacteria.     

EGF-induced programmed cell death of human mammary carcinoma MDA-MB-468 cells is preceded by activation of AP-1

MDA-MB-468 is a human mammary adenocarcinoma cell line that overexpresses the epidermal growth factor (EGF) receptor and undergoes programmed cell death (apoptosis) in response to EGF treatment. Programmed cell death was shown to be greatly enhanced when cells were growth-arrested prior to EGF treatment. Apoptosis was characterized by an initial rounding up and detachment of the cells from their substrate starting about 12 h after EGF treatment, followed by chromatin condensation, nuclear fragmentation and oligonucleosomal fragmentation of the DNA at about 24 to 48 h. Cell death was dependent on de novo protein synthesis. We found a rapid induction of c-fos, c-jun and junB at the mRNA level after about 30 min of EGF treatment and a more delayed upregulation of fosB and fra-1. The junD gene was expressed in the absence of EGF, and it was moderately induced within 30 min of growth factor addition. The increase of the different fos and jun mRNAs were paralleled by an increase of activator protein-1 (AP-1) DNA binding activity. A characterization of the AP-1 complex revealed similar levels of several Fos and Jun proteins. Based on the kinetics of AP-1 accumulation and cell death, it seems likely that AP-1 contributes to the apoptotic cell death of EGF receptor-overexpressing MDA-MB-468 cells. Received 21 July 1997; received after revision 6 November 1997; accepted 6 November 1997     

Suppressor of cytokine signaling-1 inhibits caspase activation and protects from cytokine-induced beta cell death

Pancreatic beta cell damage caused by pro-inflammatory cytokines interleukin-1β (IL-1β), interferon-γ (IFNγ) and tumor necrosis factor-α (TNFα) is a key event in the pathogenesis of type 1 diabetes. The suppressor of cytokine signaling-1 (SOCS-1) blocks IFNγ-induced signaling and prevents diabetes in the non-obese diabetic mouse. Here, we investigated if SOCS-1 overexpression in primary beta cells provides protection from cytokine-induced islet cell dysfunction and death. We demonstrate that SOCS-1 does not prevent increase in NO production and decrease in glucose-stimulated insulin secretion in the presence of IL-1β, IFNγ, TNFα. However, it decreases the activation of caspase-3, -8 and -9, and thereby, promotes a robust protection from cytokine-induced beta cell death. Our data suggest that SOCS-1 overexpression may not be sufficient in preventing all the biological activities of IFNγ in beta cells. In summary, we show that interference with IFNγ signal transduction pathways by SOCS-1 inhibits cytokine-stimulated pancreatic beta cell death.     

NDE1 and NDEL1 from genes to (mal)functions: parallel but distinct roles impacting on neurodevelopmental disorders and psychiatric illness

NDE1 (Nuclear Distribution Element 1, also known as NudE) and NDEL1 (NDE-Like 1, also known as NudEL) are the mammalian homologues of the fungus nudE gene, with important and at least partially overlapping roles for brain development. While a large number of studies describe the various properties and functions of these proteins, many do not directly compare the similarities and differences between NDE1 and NDEL1. Although sharing a high degree structural similarity and multiple common cellular roles, each protein presents several distinct features that justify their parallel but also unique functions. Notably both proteins have key binding partners in dynein, LIS1 and DISC1, which impact on neurodevelopmental and psychiatric illnesses. Both are implicated in schizophrenia through genetic and functional evidence, with NDE1 also strongly implicated in microcephaly, as well as other neurodevelopmental and psychiatric conditions through copy number variation, while NDEL1 possesses an oligopeptidase activity with a unique potential as a biomarker in schizophrenia. In this review, we aim to give a comprehensive overview of the various cellular roles of these proteins in a “bottom-up” manner, from their biochemistry and protein–protein interactions on the molecular level, up to the consequences for neuronal differentiation, and ultimately to their importance for correct cortical development, with direct consequences for the pathophysiology of neurodevelopmental and mental illness.     

Rad51 and DNA-PKcs are involved in the generation of specific telomere aberrations induced by the quadruplex ligand 360A that impair mitotic cell progression and lead to cell death

Functional telomeres are protected from non-homologous end-joining (NHEJ) and homologous recombination (HR) DNA repair pathways. Replication is a critical period for telomeres because of the requirement for reconstitution of functional protected telomere conformations, a process that involves DNA repair proteins. Using knockdown of DNA-PKcs and Rad51 expression in three different cell lines, we demonstrate the respective involvement of NHEJ and HR in the formation of telomere aberrations induced by the G-quadruplex ligand 360A during or after replication. HR contributed to specific chromatid-type aberrations (telomere losses and doublets) affecting the lagging strand telomeres, whereas DNA-PKcs-dependent NHEJ was responsible for sister telomere fusions as a direct consequence of G-quadruplex formation and/or stabilization induced by 360A on parental telomere G strands. NHEJ and HR activation at telomeres altered mitotic progression in treated cells. In particular, NHEJ-mediated sister telomere fusions were associated with altered metaphase-anaphase transition and anaphase bridges and resulted in cell death during mitosis or early G1. Collectively, these data elucidate specific molecular and cellular mechanisms triggered by telomere targeting by the G-quadruplex ligand 360A, leading to cancer cell death.     

Metabolism of metopirone and 3-(1,2,3,4-tetrahydro-1-oxo-2 naphthyl)-pyridine in relation to DMBA induced adrenal necrosis

Résumé Nous avons réduit le Su-4885 et le Su-9055 pour étudier l'action de ces substances contre la destruction des adrénales par le DMBA. Les effets inhibiteurs ne peuvent pas Être expliqués par les changements que le foie produit sur le métabolisme du DMBA.     

Effect of metopirone and 3-(1,2,3,4-tetrahydro-1-oxo-2-naphthyl)-pyridine on the metabolism of corticosteroids and DMBA in relation to adrenal necrosis

Résumé Nous avons protegé des rats contre l'action destructive du DMBA sur les adrénales avec des doses de Su-4885 ou de Su-9055 qui n'avaient pas d'effet sur le métabolisme du progestérone et du déoxycorticostérone. Un mécanisme expliquant l'action de ces substances inhibitrices est suggèré.

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We thank Dr.C. W. Murphy, Ciba Co. Dorval, for a generous gift of metopirone and Su-9055. This work was supported by the Medical Research Council and the National Cancer Institute of Canada.