NFAT but not NF-kappaB is critical for transcriptional induction of the prosurvival gene A1 after IgE receptor activation in mast cells.

FcepsilonRI-activation-induced survival of mast cells is dependent on the expression and function of the prosurvival protein A1. The expression of A1 in lymphocytes and monocytes has previously been described to be transcriptionally regulated by NF-kappaB. Here we demonstrate that the expression of A1 in mast cells is not dependent on NF-kappaB but that NFAT plays a crucial role.

The BCL-2 protein family: opposing activities that mediate cell death.

BCL-2 family proteins, which have either pro- or anti-apoptotic activities, have been studied intensively for the past decade owing to their importance in the regulation of apoptosis, tumorigenesis and cellular responses to anti-cancer therapy. They control the point of no return for clonogenic cell survival and thereby affect tumorigenesis and host-pathogen interactions and regulate animal development. Recent structural, phylogenetic and biological analyses, however, suggest the need for some reconsideration of the accepted organizational principles of the family and how the family members interact with one another during programmed cell death.

Deletion of the BH3-only protein puma protects motoneurons from ER stress-induced apoptosis and delays motoneuron loss in ALS mice.

BH3-only proteins couple diverse stress signals to the evolutionarily conserved mitochondrial apoptosis pathway. Previously, we reported that the activation of the BH3-only protein p53-up-regulated mediator of apoptosis (Puma) was necessary and sufficient for endoplasmic reticulum (ER) stress- and proteasome inhibition-induced apoptosis in neuroblastoma and other cancer cells. Defects in protein quality control have also been suggested to be a key event in ALS, a fatal neurodegenerative condition characterized by motoneuron degeneration.

Puma is a dominant regulator of oxidative stress induced Bax activation and neuronal apoptosis.

Oxidative stress has been implicated as a key trigger of neuronal apoptosis in stroke and neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. The Bcl-2 homology 3 (BH3)-only subfamily of Bcl-2 genes consists of multiple members that can be activated in a cell-type- and stimulus-specific manner to promote cell death. In the present study, we demonstrate that, in cortical neurons, oxidative stress induces the expression of the BH3-only members Bim, Noxa, and Puma.

ABT-737 is a useful component of combinatory chemotherapies for chronic myeloid leukaemias with diverse drug-resistance mechanisms.

The effect of ABT-737, a BH3-mimicking inhibitor for anti-apoptotic Bcl-2 and Bcl-X(L), but not Mcl-1, against Bcr-Abl-positive (Bcr-Abl(+)) leukaemic cells was examined. ABT-737 potently induced apoptosis in Bcr-Abl(+) chronic myeloid leukaemia (CML) cell lines and primary CML samples in vitro and prolonged the survival of mice xenografted with BV173 cells, a CML cell line. Higher expression of anti-apoptotic Bcl-2 proteins reduced cell killing by ABT-737 in each cell line, but there was no correlation between the sensitivities to ABT-737 and the specific expression patterns of Bcl-2 family proteins among cell lines.

What do we know about the mechanisms of elimination of autoreactive T and B cells and what challenges remain.

Tolerance to self-antigens within the adaptive immune system is safeguarded, at least in part, through deletion of autoreactive T and B lymphocytes. This deletion can occur during the development of these cells in primary lymphoid organs, the thymus or bone marrow, respectively, or at the mature stage in peripheral lymphoid tissues. Deletion of autoreactive lymphocytes is achieved to a large extent through apoptotic cell death.

Gefitinib-induced killing of NSCLC cell lines expressing mutant EGFR requires BIM and can be enhanced by BH3 mimetics.

Background: The epidermal growth factor receptor (EGFR) plays a critical role in the control of cellular proliferation, differentiation, and survival. Abnormalities in EGF-EGFR signaling, such as mutations that render the EGFR hyperactive or cause overexpression of the wild-type receptor, have been found in a broad range of cancers, including carcinomas of the lung, breast, and colon. EGFR inhibitors such as gefitinib have proven successful in the treatment of certain cancers, particularly non-small cell lung cancers (NSCLCs) harboring activating mutations within the EGFR gene, but the molecular mechanisms leading to tumor regression remain unknown.

Proapoptotic BH3-only protein Bim is essential for developmentally programmed death of germinal center-derived memory B cells and antibody-forming cells.

T cell-dependent B-cell immune responses induce germinal centers that are sites for expansion, diversification, and selection of antigen-specific B cells. During the immune response, antigen-specific B cells are removed in a process that favors the retention of cells with improved affinity for antigen, a cell death process inhibited by excess Bcl-2. In this study, we examined the role of the BH3-only protein Bim, an initiator of apoptosis in the Bcl-2-regulated pathway, in the programmed cell death accompanying an immune response.

Tumor growth need not be driven by rare cancer stem cells.

The cancer stem cell hypothesis postulates that tumor growth is driven by a rare subpopulation of tumor cells. Much of the supporting evidence for this intriguing idea is derived from xenotransplantation experiments in which human leukemia cells are grown in immunocompromised mice. We show that, when lymphomas and leukemias of mouse origin are transplanted into histocompatible mice, a very high frequency (at least 1 in 10) of the tumor cells can seed tumor growth.

The BH3-only protein Puma plays an essential role in cytokine deprivation induced apoptosis of mast cells.

Mast cells play critical roles in the regulation of inflammation. One characteristic feature of mast cells is their relatively long lifespan in vivo. Members of the Bcl-2 protein family are regulators of cell survival and apoptosis, where the BH3-only proteins are critical proapoptotic proteins.

Interleukin 15-mediated survival of natural killer cells is determined by interactions among Bim, Noxa and Mcl-1.

Interleukin 15 (IL-15) promotes the survival of natural killer (NK) cells by preventing apoptosis through mechanisms unknown at present. Here we identify Bim, Noxa and Mcl-1 as key regulators of IL-15-dependent survival of NK cells. IL-15 suppressed apoptosis by limiting Bim expression through the kinases Erk1 and Erk2 and mechanisms dependent on the transcription factor Foxo3a, while promoting expression of Mcl-1, which was necessary and sufficient for the survival of NK cells.

ER stress triggers apoptosis by activating BH3-only protein Bim.

Endoplasmic reticulum (ER) stress caused by misfolded proteins or cytotoxic drugs can kill cells and although activation of this pathway has been implicated in the etiology of certain degenerative disorders its mechanism remains unresolved. Bim, a proapoptotic BH3-only member of the Bcl-2 family is required for initiation of apoptosis induced by cytokine deprivation or certain stress stimuli. Its proapoptotic activity can be regulated by several transcriptional or posttranslational mechanisms, such as ERK-mediated phosphorylation, promoting its ubiquitination and proteasomal degradation.

Hrk/DP5 contributes to the apoptosis of select neuronal populations but is dispensable for haematopoietic cell apoptosis.

The pro-apoptotic BH3-only members of the Bcl2 family, crucial initiators of cell death, are activated by a diverse array of developmental cues or experimentally applied stress stimuli. We have investigated, through gene targeting in mice, the biological roles for the BH3-only family member HRK (also known as DP5) in apoptosis regulation. Hrk gene expression was found to be restricted to cells and tissues of the central and peripheral nervous systems.

Two molecular pathways initiate mitochondria-dependent dopaminergic neurodegeneration in experimental Parkinson's disease.

Dysfunction of mitochondrial complex I is associated with a wide spectrum of neurodegenerative disorders, including Parkinson's disease (PD). In rodents, inhibition of complex I leads to degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNpc), as seen in PD, through activation of mitochondria-dependent apoptotic molecular pathways. In this scenario, complex I blockade increases the soluble pool of cytochrome c in the mitochondrial intermembrane space through oxidative mechanisms, whereas activation of pro-cell death protein Bax is actually necessary to trigger neuronal death by permeabilizing the outer mitochondrial membrane and releasing cytochrome c into the cytosol.

The BH3-only protein bid is dispensable for DNA damage- and replicative stress-induced apoptosis or cell-cycle arrest.

Bid, a caspase-activated proapoptotic BH3-only protein, is essential for Fas-induced hepatocyte destruction. Recent studies published in Cell produced conflicting results, indicating that loss of Bid either protects or enhances apoptosis induced by DNA damage or replicative stress. To resolve this controversy, we generated novel Bid-deficient mice on an inbred C57BL/6 background and removed the drug-selection cassette from the targeted locus.

FcepsilonRI aggregation promotes survival of connective tissue-like mast cells but not mucosal-like mast cells.

Mast cells play a critical role in IgE-dependent immediate hypersensitivity reactions. This is facilitated by their capacity to release inflammatory mediators and to undergo activation-induced survival upon cross-linking of the high-affinity IgE-receptor (FcepsilonRI). Due to their heterogeneity, mast cells can be divided into two major groups: the connective tissue mast cells and the mucosal mast cells.

Endogenous bcl-2 is not required for the development of Emu-myc-induced B-cell lymphoma.

Although myc and bcl-2 synergize in tumor development, particularly lymphomagenesis, it is not known whether endogenous bcl-2 is required for myc-induced tumorigenesis. To investigate the role of endogenous Bcl-2 in myc-induced lymphomagenesis, we bypassed the early death of Bcl-2-deficient mice by reconstituting lethally irradiated wild-type (wt) mice with a hematopoietic system from fetal liver-derived stem cells of Emu-myc/bcl-2(-/-) or control Emu-myc transgenic embryos. In premalignant (healthy) recipients, loss of Bcl-2 caused a moderate decrease in pre-B and immature B cells, and a dramatic reduction of mature B lymphocytes expressing the Emu-myc transgene.

Multiple triggers of cell death in sepsis: death receptor and mitochondrial-mediated apoptosis.

Lymphocyte apoptosis plays a central role in the pathophysiology of sepsis. Lymphocyte apoptosis was examined in mice with defective death receptor pathways due to transgenic expression of a dominant negative mutant of Fas-associated death domain (FADD-DN) or Bid-/- and in mice with defective mitochondrial-mediated pathways due to loss of Bim-/-, Puma-/-, or Noxa-/-. FADD-DN transgenic and Bid-/- mice had significant albeit incomplete protection, and this protection was associated with increased survival.

Ultraviolet radiation triggers apoptosis of fibroblasts and skin keratinocytes mainly via the BH3-only protein Noxa.

To identify the mechanisms of ultraviolet radiation (UVR)-induced cell death, for which the tumor suppressor p53 is essential, we have analyzed mouse embryonic fibroblasts (MEFs) and keratinocytes in mouse skin that have specific apoptotic pathways blocked genetically. Blocking the death receptor pathway provided no protection to MEFs, whereas UVR-induced apoptosis was potently inhibited by Bcl-2 overexpression, implicating the mitochondrial pathway. Indeed, Bcl-2 overexpression boosted cell survival more than p53 loss, revealing a p53-independent pathway controlled by the Bcl-2 family.

BIM regulates apoptosis during mammary ductal morphogenesis, and its absence reveals alternative cell death mechanisms.

The adult, virgin mammary gland is a highly organized tree-like structure formed by ducts with hollowed lumen. Although lumen formation during pubertal development appears to involve apoptosis, the molecular mechanisms that regulate this process are not known. Here, we demonstrate that disruption of the BH3-only proapoptotic factor Bim in mice prevents induction of apoptosis in and clearing of the lumen in terminal end buds during puberty.

Puma cooperates with Bim, the rate-limiting BH3-only protein in cell death during lymphocyte development, in apoptosis induction.

The physiological role of B cell lymphoma 2 (Bcl-2) homology 3-only proteins has been investigated in mice lacking the individual genes identifying rate-limiting roles for Bim (Bcl-2-interacting mediator of cell death) and Puma (p53-up-regulated modulator of apoptosis) in apoptosis induction. The loss of Bim protects lymphocytes from apoptosis induced by cytokine deprivation and deregulated Ca++ flux and interferes with the deletion of autoreactive lymphocytes and the shutdown of immune responses. In contrast, Puma is considered the key mediator of p53-induced apoptosis.

Loss of Mcl-1 protein and inhibition of electron transport chain together induce anoxic cell death.

How cells die in the absence of oxygen (anoxia) is not understood. Here we report that cells deficient in Bax and Bak or caspase-9 do not undergo anoxia-induced cell death. However, the caspase-9 null cells do not survive reoxygenation due to the generation of mitochondrial reactive oxygen species.

Bim and Bad mediate imatinib-induced killing of Bcr/Abl+ leukemic cells, and resistance due to their loss is overcome by a BH3 mimetic.

Cell killing is a critical pharmacological activity of imatinib to eradicate Bcr/Abl+ leukemias. We found that imatinib kills Bcr/Abl+ leukemic cells by triggering the Bcl-2-regulated apoptotic pathway. Imatinib activated several proapoptotic BH3-only proteins: bim and bmf transcription was increased, and both Bim and Bad were activated posttranslationally.