Negative selection of immature B cells by receptor editing or deletion is determined by site of antigen encounter.
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Immature B cells that encounter self-antigen are eliminated from the immune repertoire by negative selection. Negative selection has been proposed to take place by two distinct mechanisms: deletion by apoptosis or alteration of the antigen receptor specificity by receptor editing. While convincing evidence exists for each, the two models are inherently contradictory. In this paper, we propose a resolution to this contradiction by demonstrating that the site of first antigen encounter dictates which mechanism of negative selection is utilized. We demonstrate that the bone marrow microenvironment provides signals that block antigen-induced deletion and promote RAG reinduction. In the periphery, the absence of these signals allows the immature B cell to default to apoptosis as a result of BCR engagement. (+info)
Overexpression of Bcl-2 enhances metastatic potential of human bladder cancer cells.
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We investigated the effect of Bcl-2 expression on the metastatic process of bladder cancer cells by using the Bcl-2-transfected human bladder cancer cell lines (KoTCC-1/BH) and the control vector only-transfected cell line (KoTCC-1/C), which were generated in our previous study (Miyake et al (1998) Oncogene 16: 933-934). When they were injected intravenously into athymic nude mice, KoTCC-1/BH formed more than three times as many tumour nodules in the lungs as did KoTCC-1/C. In addition, tumour progression, including lymph node metastasis and haemorrhagic ascites, was observed to be more advanced after the implantation of KoTCC-1/BH cells into the bladder wall of nude mice than after implantation of KoTCC-1/C cells. These enhanced malignant progression of KoTCC-1/BH cells were well correlated with anti-apoptotic activity under anchorage-independent conditions in in vitro experimental models. In contrast, there were no significant differences among these cell lines in their growth rates both in vitro and in vivo, invasive ability and cell motility. These findings suggest that, if it is overexpressed, Bcl-2 prolongs cell survival under unfavourable conditions encountered in the metastatic process, resulting in the enhanced metastatic potential of bladder cancer. (+info)
Caspase I-related protease inhibition retards the execution of okadaic acid- and camptothecin-induced apoptosis and PAI-2 cleavage, but not commitment to cell death in HL-60 cells.
(51/11751)
We have previously reported that the putative cytoprotective protease inhibitor, plasminogen activator inhibitor type 2 (PAI-2), is specifically cleaved during okadaic acid-induced apoptosis in a myeloid leukaemic cell line (Br J Cancer (1994) 70: 834-840). HL-60 cells exposed to okadaic acid and camptothecin underwent morphological and biochemical changes typical of apoptosis, including internucleosomal DNA fragmentation and PAI-2 cleavage. Significant endogenous PAI-2 cleavage was observed 9 h after exposure to okadaic acid; thus correlating with other signs of macromolecular degradation, like internucleosomal DNA fragmentation. In camptothecin-treated cells, PAI-2 cleavage was an early event, detectable after 2 h of treatment, and preceding internucleosomal DNA fragmentation. The caspase I selective protease inhibitor, YVAD-cmk, inhibited internucleosomal DNA fragmentation and PAI-2 cleavage of okadaic acid and camptothecin-induced apoptotic cells. YVAD-cmk rather sensitively and non-toxically inhibited camptothecin-induced morphology, but not okadaic acid-induced morphology. In in vitro experiments recombinant PAI-2 was not found to be a substrate for caspase I. The results suggest that caspase I selective protease inhibition could antagonize parameters coupled to the execution phase of okadaic acid- and camptothecin-induced apoptosis, but not the commitment to cell death. (+info)
Phenylarsine oxide and ethanol prevent cell death of porcine polymorphonuclear leucocytes induced by phorbol myristate acetate.
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In this study, we report that phenylarsine oxide and ethanol, both of which suppress a number of polymorphonuclear leucocyte functions including superoxide production, prevented the phorbol myristate acetate-induced cell death in a dose-dependent manner. These reagents had an inhibitory effect even after polymorphonuclear leucocytes were stimulated to produce superoxide by treatment with phorbol myristate acetate. The results indicate that activation of protein kinase C and subsequent superoxide release do not directly cause phorbol myristate acetate-induced cell death. Phenylarsine oxide or ethanol prevents cell death by affecting pathways downstream from those involved in the superoxide production. (+info)
Macrophages kill capillary cells in G1 phase of the cell cycle during programmed vascular regression.
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Programmed capillary regression occurs during normal development of the eye and serves as a useful model for assessing the forces that drive vascular involution. Using a combination of S-phase labeling and liposome-mediated macrophage elimination, we show that during regression, macrophages induce apoptosis of both pericytes and endothelial cells in a cell cycle stage-dependent manner. Target cells are signaled to die by macrophages approximately 15 hours after S-phase labeling and this corresponds to a point in mid-G1 phase of the cell cycle. The tight correlation between the restriction point of the cell cycle and the point where the macrophage death signal is received suggests that the mitogen, matrix and cytoskeletal signals essential for cell-cycle progression may be inhibited by macrophages as a means of inducing cell death. Furthermore, these experiments show that cells from two distinct lineages are induced to die as a consequence of macrophage action, and this provides evidence that macrophage-induced cell death may be a general phenomenon during development and homeostasis. (+info)
Control of digit formation by activin signalling.
(54/11751)
Major advances in the genetics of vertebrate limb development have been obtained in recent years. However, the nature of the signals which trigger differentiation of the mesoderm to form the limb skeleton remains elusive. Previously, we have obtained evidence for a role of TGFbeta2 in digit formation. Here, we show that activins A and B and/or AB are also signals involved in digit skeletogenesis. activin betaA gene expression correlates with the initiation of digit chondrogenesis while activin betaB is expressed coincidently with the formation of the last phalanx of each digit. Exogenous administration of activins A, B or AB into the interdigital regions induces the formation of extra digits. follistatin, a natural antagonist of activins, is expressed, under the control of activin, peripherally to the digit chondrogenic aggregates marking the prospective tendinous blastemas. Exogenous application of follistatin blocks physiological and activin-induced digit formation. Evidence for a close interaction between activins and other signalling molecules, such as BMPs and FGFs, operating at the distal tip of the limb at these stages is also provided. Chondrogenesis by activins is mediated by BMPs through the regulation of the BMP receptor bmpR-1b and in turn activin expression is upregulated by BMP signalling. In addition, AER hyperactivity secondary to Wnt3A misexpression or local administration of FGFs, inhibits activin expression. In correlation with the restricted expression of activins in the course of digit formation, neither activin nor follistatin treatment affects the development of the skeletal components of the stylopod or zeugopod indicating that the formation of the limb skeleton is regulated by segment-specific chondrogenic signals. (+info)
p53 mediated death of cells overexpressing MDM2 by an inhibitor of MDM2 interaction with p53.
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The p53 tumour suppressor is frequently inactivated in human tumours. One form of inactivation results from overexpression of MDM2, that normally forms a negative auto-regulatory loop with p53 and inhibits its activity through complex formation. We have investigated whether disrupting the MDM2-p53 complex in cells that overexpress MDM2 is sufficient to trigger p53 mediated cell death. We find that expression of a peptide homologue of p53 that binds to MDM2 leads to increased p53 levels and transcriptional activity. The consequences are increased expression of the downstream effectors MDM2 and p21WAF1/CIP1, inhibition of colony formation, cell cycle arrest and cell death. There is also a decrease in E2F activity, that might have been due to the known physical and functional interactions of MDM2 with E2F1/DP1. However, this decrease is p53 dependent, as are also colony formation, cell cycle arrest and cell death. These results show that a peptide homologue of p53 is sufficient to induce p53 dependent cell death in cells overexpressing MDM2, and support the notion that disruption of the p53-MDM2 complex is a target for the development of therapeutic agents. (+info)
Neurogenesis, cell death and regeneration in the adult gymnotiform brain.
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Gymnotiform fish, like all teleosts examined thus far, are distinguished by their enormous potential for the production of new neurons in the adult brain. In Apteronotus leptorhynchus, on average 10(5) cells, corresponding to approximately 0.2 % of the total population of cells in the adult brain, are in S-phase within any period of 2 h. At least a portion of these newly generated cells survive for the rest of the fish's life. This long-term survival, together with the persistent generation of new cells, leads to a continuous growth of the brain during adulthood. Zones of high proliferative activity are typically located at or near the surface of the ventricular, paraventricular and cisternal systems. In the central posterior/ prepacemaker nucleus, for example, new cells are generated, at very high rates, in areas near the wall of the third ventricle. At least some of these cells differentiate into neurons, express immunoreactivity against the neuropeptide somatostatin and migrate into more lateral areas of this complex. Approximately 75 % of all new brain cells are generated in the cerebellum. In the corpus cerebelli and the valvula cerebelli, they are produced in the molecular layers, whereas in the eminentia granularis the newborn cells stem from proliferation zones in the pars medialis. Within the first few days of their life, these cells migrate towards specific target areas, namely the associated granule cell layers. At least some of them develop into granule neurons. The high proliferative activity is counterbalanced by apoptosis, a mechanism that resembles the processes known from embryonic development of the vertebrate brain. Apoptosis also appears to be used as an efficient mechanism for the removal of cells damaged through injury in the brain of adult Apteronotus leptorhynchus. Since apoptosis is not accompanied by the side effects known from necrosis, this 'clean' type of cell death may, together with the enormous proliferative activity in the brain, explain, at least partially, the tremendous capability of teleost fish to replace damaged neurons with newly generated ones. One factor that appears to play a major role in the generation of new cells and in their further development is the neuropeptide somatostatin. In the caudal cerebellum of the gymnotiform brain, somatostatin-binding sites are expressed, at extremely high densities, at sites corresponding to the areas of origin, migration and differentiation of the newborn cells. This pattern of expression resembles the expression pattern in the rat cerebellum, where somatostatin immunoreactivity and somatostatin-binding sites are transiently expressed at the time when the granule cells of the cerebellum are generated. Moreover, after mechanical lesions of the corpus cerebelli, the expression of somatostatin-like immunoreactivity is tremendously increased in several cell types (presumably astrocytes, microglia and granule cell neurons) near the path of the lesion; the time course of this expression coincides with the temporal pattern underlying the recruitment of new cells incorporated at the site of the lesion. (+info)