Showing papers on "Apoptosis published in 1996"
TL;DR: Reintroduction of RelA into RelA−/− fibroblasts resulted in enhanced survival, demonstrating that the presence ofrelA is required for protection from TNF-α.
Abstract: Studies on mice deficient in nuclear factor kappa B (NF-κB) subunits have shown that this transcription factor is important for lymphocyte responses to antigens and cytokine-inducible gene expression. In particular, the RelA (p65) subunit is required for induction of tumor necrosis factor-α (TNF-α)-dependent genes. Treatment of RelA-deficient (RelA−/−) mouse fibroblasts and macrophages with TNF-α resulted in a significant reduction in viability, whereas RelA+/+ cells were unaffected. Cytotoxicity to both cell types was mediated by TNF receptor 1. Reintroduction of RelA into RelA−/− fibroblasts resulted in enhanced survival, demonstrating that the presence of RelA is required for protection from TNF-α. These results have implications for the treatment of inflammatory and proliferative diseases.
3,021 citations
TL;DR: The rapid phosphorylation of BAD following IL-3 connects a proximal survival signal with the BCL-2 family, modulating this checkpoint for apoptosis and enhanced BAD's death-promoting activity.
2,731 citations
TL;DR: The activation of the transcription factor nuclear factor-kappa B by tumor necrosis factor, ionizing radiation, or daunorubicin, was found to protect from cell killing, providing a mechanism of cellular resistance to killing by some apoptotic reagents.
Abstract: Many cells are resistant to stimuli that can induce apoptosis, but the mechanisms involved are not fully understood. The activation of the transcription factor nuclear factor-kappa B (NF-kappaB) by tumor necrosis factor (TNF), ionizing radiation, or daunorubicin (a cancer chemotherapeutic compound), was found to protect from cell killing. Inhibition of NF-kappaB nuclear translocation enhanced apoptotic killing by these reagents but not by apoptotic stimuli that do not activate NF-kappaB. These results provide a mechanism of cellular resistance to killing by some apoptotic reagents, offer insight into a new role for NF-kappaB, and have potential for improvement of the efficacy of cancer therapies.
2,637 citations
TL;DR: In this paper, the sensitivity and kinetics of TNF-α-induced apoptosis were shown to be enhanced in a number of cell types expressing a dominant negative IkappaBalpha (Ikappa-BalphaM).
Abstract: Tumor necrosis factor alpha (TNF-alpha) signaling gives rise to a number of events, including activation of transcription factor NF-kappaB and programmed cell death (apoptosis). Previous studies of TNF-alpha signaling have suggested that these two events occur independently. The sensitivity and kinetics of TNF-alpha-induced apoptosis are shown to be enhanced in a number of cell types expressing a dominant-negative IkappaBalpha (IkappaBalphaM). These findings suggest that a negative feedback mechanism results from TNF-alpha signaling in which NF-kappaB activation suppresses the signals for cell death.
2,515 citations
TL;DR: It is proposed that hypoxia provides a physiological selective pressure in tumours for the expansion of variants that have lost their apoptotic potential, and in particular for cells acquiring p53mutations.
Abstract: Apoptosis is a genetically encoded programme of cell death that can be activated under physiological conditions and may be an important safeguard against tumour development. Regions of low oxygen (hypoxia) and necrosis are common features of solid tumours. Here we report that hypoxia induces apoptosis in oncogenically transformed cells and that further genetic alterations, such as loss of the p53 tumour-suppressor gene or overexpression of the apoptosis-inhibitor protein Bcl-2, substantially reduce hypoxia-induced cell death. Hypoxia also selects for cells with defects in apoptosis, because small numbers of transformed cells lacking p53 overtake similar cells expressing wild-type p53 when treated with hypoxia. Furthermore, highly apoptotic regions strongly correlate with hypoxic regions in transplanted tumours expressing wild-type p53, whereas little apoptosis occurs in hypoxic regions of p53-deficient tumours. We propose that hypoxia provides a physiological selective pressure in tumours for the expansion of variants that have lost their apoptotic potential, and in particular for cells acquiring p53 mutations.
2,266 citations
TL;DR: This work investigated how TNFR1 activates different effector functions; the protein kinase JNK, transcription factor NF-kappaB, and apoptosis, finding that the three responses are mediated through separate pathways.
1,988 citations
TL;DR: CPP32 is shown to play a critical role during morphogenetic cell death in the mammalian brain during embryonic day 12, resulting in a variety of hyperplasias and disorganized cell deployment.
Abstract: Programmed cell death (apoptosis) is a prominent feature of the development of the immune and nervous systems. The identification of the Caenorhabditis elegans cell death gene, ced-3, as a prototype of the interleukin-1beta converting enzyme (ICE) protease family has led to extensive evidence implicating these enzymes in apoptosis. Among the ten or more members of the ICE protease family, CPP32/yama/apopain exhibits the highest similarity to CED-3 in both sequence homology and substrate specificity. To analyse its function in vivo, we generated CPP32-deficient mice by homologous recombination. These mice, born at a frequency lower than expected by mendelian genetics, were smaller than their littermates and died at 1-3 weeks of age. Although their thymocytes retained normal susceptibility to various apoptotic stimuli, brain development in CPP32-deficient mice was profoundly affected, and discernible by embryonic day 12, resulting in a variety of hyperplasias and disorganized cell deployment. These supernumerary cells were postmitotic and terminally differentiated by the postnatal stage. Pyknotic clusters at sites of major morphogenetic change during normal brain development were not observed in the mutant embryos, indicating decreased apoptosis in the absence of CPP32. Thus CPP32 is shown to play a critical role during morphogenetic cell death in the mammalian brain.
1,926 citations
TL;DR: Results suggest that, along with other family members such as Fas/Apo-1 ligand and TNF, Apo-2L may serve as an extracellular signal that triggers programmed cell death.
1,898 citations
TL;DR: It is reported that ceramide initiates apoptosis through the SAPK cascade and evidence is provided for a signalling mechanism that integrates cytokine- and stress-activated apoptosis.
Abstract: The induction of programmed cell death, or apoptosis, involves activation of a signalling system, many elements of which remain unknown. The sphingomyelin pathway, initiated by hydrolysis of the phospholipid sphingomyelin in the cell membrane to generate the second messenger ceramide, is thought to mediate apoptosis in response to tumour-necrosis factor (TNF)-alpha, to Fas ligand and to X-rays. It is not known whether it plays a role in the stimulation of other forms of stress-induced apoptosis. Given that environmental stresses also stimulate a stress-activated protein kinase (SAPK/JNK), the sphingomyelin and SAPK/JNK signalling systems may be coordinated in induction of apoptosis. Here we report that ceramide initiates apoptosis through the SAPK cascade and provide evidence for a signalling mechanism that integrates cytokine- and stress-activated apoptosis.
1,813 citations
TL;DR: Direct evidence is presented indicating that mitochondrial PT constitutes a critical early event of the apoptotic process, and a specific ligand of the mitochondrial adenine nucleotide translocator, bongkreik acid, inhibits PT and reduces apoptosis induction by mitochondria in a cell-free system.
Abstract: Anucleate cells can be induced to undergo programmed cell death (PCD), indicating the existence of a cytoplasmic PCD pathway that functions independently from the nucleus. Cytoplasmic structures including mitochondria have been shown to participate in the control of apoptotic nuclear disintegration. Before cells exhibit common signs of nuclear apoptosis (chromatin condensation and endonuclease-mediated DNA fragmentation), they undergo a reduction of the mitochondrial transmembrane potential (delta psi m) that may be due to the opening of mitochondrial permeability transition (PT) pores. Here, we present direct evidence indicating that mitochondrial PT constitutes a critical early event of the apoptotic process. In a cell-free system combining purified mitochondria and nuclei, mitochondria undergoing PT suffice to induce chromatin condensation and DNA fragmentation. Induction of PT by pharmacological agents augments the apoptosis-inducing potential of mitochondria. In contrast, prevention of PT by pharmacological agents impedes nuclear apoptosis, both in vitro and in vivo. Mitochondria from hepatocytes or lymphoid cells undergoing apoptosis, but not those from normal cells, induce disintegration of isolated Hela nuclei. A specific ligand of the mitochondrial adenine nucleotide translocator (ANT), bongkreik acid, inhibits PT and reduces apoptosis induction by mitochondria in a cell-free system. Moreover, it inhibits the induction of apoptosis in intact cells. Several pieces of evidence suggest that the proto-oncogene product Bcl-2 inhibits apoptosis by preventing mitochondrial PT. First, to inhibit nuclear apoptosis, Bcl-2 must be localized in mitochondrial but not nuclear membranes. Second, transfection-enforced hyperexpression of Bcl-2 directly abolishes the induction of mitochondrial PT in response to a protonophore, a pro-oxidant, as well as to the ANT ligand atractyloside, correlating with its apoptosis-inhibitory effect. In conclusion, mitochondrial PT appears to be a critical step of the apoptotic cascade.
1,423 citations
TL;DR: The identification of genes that control cell death and the appreciation of the role of apoptosis in development and disease has been identified and the characterization of the function of these gene products will help to define the process of cell death at the biochemical level.
Abstract: Apoptosis or programmed cell death is a genetically controlled response for cells to commit suicide. The symptoms of apoptosis are viability loss accompanied by cytoplasmic boiling, chromatin condensation, and DNA fragmentation (Wyllie 1980). Pathologists and developmental biologists have cataloged the occurrences of apoptosis for many years based on these defined morphological features, but what has propelled apoptosis into the forefront of basic research has been the identification of genes that control cell death and the appreciation of the role of apoptosis in development and disease. Regulation of cell death is essential for normal development and is an important defense against viral infection and the emergence of cancer. Too much cell death can lead to impaired development and degenerative diseases, whereas too little cell death car/lead to cancer and persistent and sustained viral infection. The process of apoptosis is controlled through the expression of an increasing number of genes conserved in nematodes through mammals and viruses. Some gene products are activators of apoptosis, whereas others are inhibitors and the characterization of the function of these gene products will help to define the process of cell death at the biochemical level.
TL;DR: In vivo, injection of FasL+ mouse melanoma cells in mice led to rapid tumor formation and tumorigenesis was delayed in Fas-deficient lpr mutant mice in which immune effector cells cannot be killed by FasL.
Abstract: Malignant melanoma accounts for most of the increasing mortality from skin cancer. Melanoma cells were found to express Fas (also called Apo-1 or CD95) ligand (FasL). In metastatic lesions, Fas-expressing T cell infiltrates were proximal to FasL+ tumor cells. In vitro, apoptosis of Fas-sensitive target cells occurred upon incubation with melanoma tumor cells; and in vivo, injection of FasL+ mouse melanoma cells in mice led to rapid tumor formation. In contrast, tumorigenesis was delayed in Fas-deficient lpr mutant mice in which immune effector cells cannot be killed by FasL. Thus, FasL may contribute to the immune privilege of tumors.
TL;DR: It is shown that mitochondria contain a pre-formed approximately 50-kD protein which is released upon delta psi m disruption and which, in a cell-free in vitro system, causes isolated nuclei to undergo apoptotic changes such as chromatin condensation and internucleosomal DNA fragmentation, and the effect of Bcl-2 on the formation, release, and action of AIF.
Abstract: Bcl-2 belongs to a family of apoptosis-regulatory proteins which incorporate into the outer mitochondrial as well as nuclear membranes. The mechanism by which the proto-oncogene product Bcl-2 inhibits apoptosis is thus far elusive. We and others have shown previously that the first biochemical alteration detectable in cells undergoing apoptosis, well before nuclear changes become manifest, is a collapse of the mitochondrial inner membrane potential (delta psi m), suggesting the involvement of mitochondrial products in the apoptotic cascade. Here we show that mitochondria contain a pre-formed approximately 50-kD protein which is released upon delta psi m disruption and which, in a cell-free in vitro system, causes isolated nuclei to undergo apoptotic changes such as chromatin condensation and internucleosomal DNA fragmentation. This apoptosis-inducing factor (AIF) is blocked by N-benzyloxycarbonyl-Val-Ala-Asp.fluoromethylketone (Z-VAD.fmk), an antagonist of interleukin-1 beta-converting enzyme (ICE)-like proteases that is also an efficient inhibitor of apoptosis in cells. We have tested the effect of Bcl-2 on the formation, release, and action of AIF. When preventing mitochondrial permeability transition (which accounts for the pre-apoptotic delta psi m disruption in cells), Bcl-2 hyperexpressed in the outer mitochondrial membrane also impedes the release of AIF from isolated mitochondria in vitro. In contrast, Bcl-2 does not affect the formation of AIF, which is contained in comparable quantities in control mitochondria and in mitochondria from Bcl-2-hyperexpressing cells. Furthermore, the presence of Bcl-2 in the nuclear membrane does not interfere with the action of AIF on the nucleus, nor does Bcl-2 hyperexpression protect cells against AIF. It thus appears that Bcl-2 prevents apoptosis by favoring the retention of an apoptogenic protease in mitochondria.
Journal Article•
TL;DR: Programmed myocyte cell death is the major form of myocardial damage produced by occlusion of a major epicardial coronary artery, whereas necrotic myocytes cell death follows apoptosis and contributes to the progressive loss of cells with time after infarction.
TL;DR: It is described that doxorbicin induces apoptosis via the CD95/CD95–L system in human leukemia T–cell lines and this finding provides a new molecular insight into resistance and sensitivity toward chemotherapy in malignancies.
Abstract: Cytotoxic drugs used in chemotherapy of leukemias and solid tumors cause apoptosis in target cells. In lymphoid cells the CD95 (APO-1/Fas)/CD95 ligand (CD95-L) system is a key regulator of apoptosis. Here we describe that doxorbicin induces apoptosis via the CD95/CD95-L system in human leukemia T-cell lines. Doxorubicin-induced apoptosis was completely blocked by inhibition of gene expression and protein synthesis. Also, doxorbicin strongly stimulates CD95-L messenger RNA expression in vitro at concentrations relevant for therapy in vivo. CEM and jurkat cells resistant to CD95-mediated apoptosis were also resistant to doxorbicin-induced apoptosis . Furthermore, doxorbicin-induced apoptosis was inhibited by blocking F(ab')2 anti-APO-1 (anti-CD95) antibody fragments. Expression of CD95-L mRNA and protein in vitro was also stimulated by other cytotoxic drugs such as methotrexate. The finding that apoptosis caused by anticancer drugs may be mediated via the CD95 system provides a new molecular insight into resistance and sensitivity toward chemotherapy in malignancies.
TL;DR: It is shown that Fas sequentially activates ICE- and CPP32-like proteases, and that downstream CPP 32, together with a component(s) in the cytoplasm, causes apoptosis of nuclei.
Abstract: Binding of Fas ligand or an agonistic anti-Fas antibody induces apoptosis in Fas-bearing cells. The interleukin-1Beta-converting enzyme (ICE) is a cysteine protease that is involved in apoptosis induced by various stimuli, including Fas-mediated apoptosis. Several ICE homologues have been identified, and these are subdivided into three groups (ICE-, CPP32-, and Ich-1-like proteases). We show here that specific inhibitors of ICE- or CPP32-like proteases can inhibit Fas-mediated apoptosis. Transient ICE-like activity was found in the cytosolic fraction of Fas-activated cells, whereas ICE-dependent, CPP32-like activity gradually accumulated in the cytosol. Cell lysates from mouse lymphoma supplemented with either recombinant ICE or CPP32 induced apoptosis of nuclei. The CPP32 inhibitor inhibited ICE- or CPP32-induced apoptosis in the cell-free system, whereas the ICE-inhibitor only inhibited ICE-induced apoptosis. Cell extracts from thymocytes from ICE-null mice induced apoptosis in the cell-free system when it was supplemented with CPP32. These results indicate that Fas sequentially activates ICE- and CPP32-like proteases, and that downstream CPP32, together with a component(s) in the cytoplasm, causes apoptosis of nuclei.
TL;DR: BAX-induced alterations in mitochondrial function and subsequent cell death do not apparently require the known ICE-like proteases.
Abstract: Expression of BAX, without another death stimulus, proved sufficient to induce a common pathway of apoptosis. This included the activation of interleukin 1 beta-converting enzyme (ICE)-like proteases with cleavage of the endogenous substrates poly(ADP ribose) polymerase and D4-GDI (GDP dissociation inhibitor for the rho family), as well as the fluorogenic peptide acetyl-Asp-Glu-Val-Asp-aminotrifluoromethylcoumarin (DEVD-AFC). The inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (zVAD-fmk) successfully blocked this protease activity and prevented FAS-induced death but not BAX-induced death. Blocking ICE-like protease activity prevented the cleavage of nuclear and cytosolic substrates and the DNA degradation that followed BAX induction. However, the fall in mitochondrial membrane potential, production of reactive oxygen species, cytoplasmic vacuolation, and plasma membrane permeability that are downstream of BAX still occurred. Thus, BAX-induced alterations in mitochondrial function and subsequent cell death do not apparently require the known ICE-like proteases.
TL;DR: A Fas counterattack model for immune escape in colon cancer is suggested, whereby the cancer cells resist Fas-mediated T cell cytotoxicity but express functional FasL, an apoptotic death signal to which activated T cells are inherently sensitive.
Abstract: Tumors escape immunological rejection by a diversity of mechanisms. In this report, we demonstrate that the colon cancer cell SW620 expresses functional Fas ligand (FasL), the triggering agent of Fas receptor (FasR)-mediated apoptosis within the immune system. FasL mRNA and cell surface FasL were detected in SW620 cells using reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemical staining, respectively. We show that SW620 kills Jurkat T cells in a Fas-mediated manner. FasR-specific antisense oligonucleotide treatment, which transiently inhibited FasR expression, completely protected Jurkat cells from killing by SW620. FasL-specific antisense oligonucleotide treatment of SW620 inhibited its Jurkat-killing activity. FasL has recently been established as a mediator of immune privilege in mouse retina and testis. Our finding that colon cancer cells express functional FasL suggests it may play an analogous role in bestowing immune privilege on human tumors. HT29 and SW620 colon cancer cells were found to express FasR mRNA and cell surface FasR using RT-PCR and immunofluorescence flow cytometry, respectively. However, neither of these cells underwent apoptosis after treatment by the anti-FasR agonistic monoclonal antibody CH11. Our results therefore suggest a Fas counterattack model for immune escape in colon cancer, whereby the cancer cells resist Fas-mediated T cell cytotoxicity but express functional FasL, an apoptotic death signal to which activated T cells are inherently sensitive.
TL;DR: It is demonstrated that CTLA-4 engagement by antibody cross-linking or binding to B7 inhibits proliferation and accumulation of the primary T cell growth factor, IL-2, by cells stimulated with anti- CD3 and anti-CD28.
Abstract: While interactions between CD28 and members of the B7 family costimulate and enhance T cell responses, recent evidence indicates that the CD28 homologue CTLA-4 plays a downregulatory role. The mechanism by which this occurs is not clear, but it has been suggested that CTLA-4 terminates ongoing responses of activated T cells, perhaps by induction of apoptosis. Here we demonstrate that CTLA-4 engagement by antibody cross-linking or binding to B7 inhibits proliferation and accumulation of the primary T cell growth factor, IL-2, by cells stimulated with anti-CD3 and anti-CD28. This inhibition is not a result of enhanced cell death. Rather it appears to result from restriction of transition from the G1 to the S phase of the cell cycle. Our observation that upregulation of both the IL-2R alpha chain and the CD69 activation antigen are inhibited by CTLA-4 engagement supplies further evidence that CTLA-4 restricts the progression of T cells to an activated state. Together this data demonstrates that CTLA-4 can regulate T cell activation in the absence of induction of apoptotic cell death.
TL;DR: The data revealed the requirement of the JNK pathway in radiation-induced apoptosis and implicated the importance of the duration of JNK activation in determining the cell fates.
TL;DR: Runaway cell death seen in lsd1 plants reflected abnormal accumulation of superoxide and lack of responsiveness to signals derived from it.
Abstract: Reactive oxygen intermediates (ROIs) regulate apoptosis during normal development and disease in animals. ROIs are also implicated in hypersensitive resistance responses of plants against pathogens. Arabidopsislsd1 mutants exhibited impaired control of cell death in the absence of pathogen and could not control the spread of cell death once it was initiated. Superoxide was necessary and sufficient to initiate lesion formation; it accumulated before the onset of cell death and subsequently in live cells adjacent to spreading lsd1 lesions. Thus, runaway cell death seen in lsd1 plants reflected abnormal accumulation of superoxide and lack of responsiveness to signals derived from it.
TL;DR: Testing the effect of a specific inhibitor of PT, bongkrekic acid (BA), a ligand of the mitochondrial adenine nucleotide translocator, on a prototypic model of apoptosis glucocorticoid-induced thymocyte death suggests that a number of apoptotic phenomena are secondary to PT.
Abstract: In a number of experimental systems, the early stage of the apoptotic process, i.e., the stage that precedes nuclear disintegration, is characterized by the breakdown of the inner mitochondrial transmembrane potential (delta psi m). This delta psi m disruption is mediated by the opening of permeability transition (PT) pores and appears to be critical for the apoptotic cascade, since it is directly regulated by Bcl-2 and since mitochondria induced to undergo PT in vitro become capable of inducing nuclear chromatinolysis in a cell-free system of apoptosis. Here, we addressed the question of which apoptotic events are secondary to mitochondrial PT. We tested the effect of a specific inhibitor of PT, bongkrekic acid (BA), a ligand of the mitochondrial adenine nucleotide translocator, on a prototypic model of apoptosis glucocorticoid-induced thymocyte death. In addition to abolishing the apoptotic delta psi m disruption, BA prevents a number of phenomena linked to apoptosis: depletion of nonoxidized glutathione, generation of reactive oxygen species, translocation of NF kappa B, exposure of phosphatidylserine residues on the outer plasma membrane, cytoplasmic vacuolization, chromatin condensation, and oligonucleosomal DNA fragmentation. BA is also an efficient inhibitor of p53-dependent thymocyte apoptosis induced by DNA damage. These data suggest that a number of apoptotic phenomena are secondary to PT. In addition, we present data indicating that apoptotic delta psi m disruption is secondary to transcriptional events. These data connect the PT control point to the p53- and ICE/ Ced 3-regulated control points of apoptosis and place PT upstream of nuclear and plasma membrane features of PCD.
TL;DR: In this paper, As2O3 was shown to trigger NB4 cell apoptosis at micromolar concentration, as proved by morphology, histogramic related nuclear DNA contents, and DNA gel eletrophoresis.
TL;DR: This work reports that an N-terminal truncation of one of these candidate signal transducers, FADD/MORT1, abrogates CD95-induced apoptosis, ceramide generation, and activation of the cell death protease Yama/CPP32.
TL;DR: It is suggested that while certain members of the E2F family may positively regulate cell cycle progression, E1F-1 functions to regulate apoptosis and to suppress cell proliferation.
TL;DR: Three recent papers indicate that ROS are not required for PCD and that Bcl-2 can protect against cell death even under conditions where ROS are unlikely to be produced.
TL;DR: The ability of the appropriate stimulus to drive cardiomyocytes into apoptosis indicated that these cells were primed for apoptosis and were susceptible to clinically relevant apoptotic triggers, such as TNFalpha, suggest that the elevated TNF alpha levels seen in a variety of clinical conditions, including sepsis and ischemic myocardial disorders, may contribute to TNFAlpha-induced cardiac cell death.
Abstract: In the present study, it was shown that physiologically relevant levels of the proinflammatory cytokine TNFalpha induced apoptosis in rat cardiomyocytes in vitro, as quantified by single cell microgel electrophoresis of nuclei ("cardiac comets") as well as by morphological and biochemical criteria. It was also shown that TNFalpha stimulated production of the endogenous second messenger, sphingosine, suggesting sphingolipid involvement in TNFalpha-mediated cardiomyocyte apoptosis. Consistent with this hypothesis, sphingosine strongly induced cardiomyocyte apoptosis. The ability of the appropriate stimulus to drive cardiomyocytes into apoptosis indicated that these cells were primed for apoptosis and were susceptible to clinically relevant apoptotic triggers, such as TNFalpha. These findings suggest that the elevated TNFalpha levels seen in a variety of clinical conditions, including sepsis and ischemic myocardial disorders, may contribute to TNFalpha-induced cardiac cell death. Cardiomyocyte apoptosis is also discussed in terms of its potential beneficial role in limiting the area of cardiac cell involvement as a consequence of myocardial infarction, viral infection, and primary cardiac tumors.
TL;DR: It is shown that a full apoptotic response to p53 requires both its amino and carboxyl terminus, and the data suggest that there is synergism between transcription-dependent and -independent functions of p53 in apoptosis.
Abstract: It is well established that induction of the p53 tumor suppressor protein in cells can lead to either cell cycle arrest or apoptosis. To further understand features of p53 that contribute to these cell responses several p53-null Saos2 and H1299 cell lines were generated that express wild-type or mutant forms of p53, or the cyclin-dependent kinase inhibitor p21/WAF1, under a tetracycline-regulated promoter. Our results show that the cellular level of p53 can dictate the response of the cell such that lower levels of p53 result in arrest whereas higher levels result in apoptosis; nevertheless, DNA damage can heighten the apoptotic response to p53 without altering the protein level of p53 in cells. We also demonstrate that arrest and apoptosis are two genetically separable functions of p53 because a transcriptionally incompetent p53 can induce apoptosis but not arrest, whereas induction of p21/WAF1, which is a major transcriptional target of p53, can induce arrest but not apoptosis. Finally, we show that a full apoptotic response to p53 requires both its amino and carboxyl terminus, and our data suggest that there is synergism between transcription-dependent and -independent functions of p53 in apoptosis. Thus, there are multiple independent cellular responses to p53 that together may account for the extraordinarily high frequency of p53 mutations in diverse types of human tumors. The implications of these results are discussed and a model is proposed.
TL;DR: Galectin-3 is a regulator of cell growth and apoptosis and it may function through a cell death inhibition pathway that involves Bcl-2, a well-characterized suppressor of apoptosis.
Abstract: Galectin-3 is a member (if a large family of beta-galactoside-binding animal lectins. It has been shown that the expression of galectin-3 is upregulated in proliferating cells, suggesting a possible role for this lectin in regulation of cell growth. Previously, we have shown that T cells infected with human T-cell leukemia virus type I express high levels of galectin-3, in contrast to uninfected cells, which do not express detectable amounts of this protein. In this study, we examined growth properties of human leukemia T cells transfected with galectin-3 cDNA, and thus constitutively overexpressing this lectin. Transfectants expressing galectin-3 displayed higher growth rates than control transfectants, which do not express this lectin. Furthermore, galectin-3 expression in these cells confers resistance to apoptosis induced by anti-Fas antibody and staurosporine. Galectin-3 was found to have significant sequence similarity with Bcl-2, a well-characterized suppressor of apoptosis. In particular, the lectin contains the NWGR motif that is highly conserved among members of the Bcl-2 family and shown to be critical for the apoptosis-suppressing activity. We further demonstrated that galectin-3 interacts with Bc1-2 in a lactose-inhibitable manner. We conclude that galectin-3 is a regulator of cell growth and apoptosis and it may function through a cell death inhibition pathway that involves Bcl-2.
Journal Article•
TL;DR: Findings support the use of the anticancer drug taxol for the treatment of b cl-2-positive prostate cancers and other bcl- 2-positive malignancies, such as follicular lymphoma.
Abstract: Treatment of prostate cancer cell lines expressing bcl-2 with taxol induces bcl-2 phosphorylation and programmed cell death, whereas treatment of bcl-2-negative prostate cancer cells with taxol does not induce apoptosis. bcl-2 phosphorylation seems to inhibit its binding to bax since less bax was observed in immunocomplex with bcl-2 in taxol-treated cancer cells. These findings support the use of the anticancer drug taxol for the treatment of bcl-2-positive prostate cancers and other bcl-2-positive malignancies, such as follicular lymphoma.