Intercellular transfer of apoptotic signals via electrofusion
ABSTRACT We determined whether cells that are induced to undergo anoikis by matrix detachment can initiate apoptosis in healthy cells following electroporation-induced fusion. Separate populations of MDCK cells undergoing anoikis and stained with FITC-annexin or viable MDCK cells that were labeled with spectrally discrete fluorescent beads were electroporated. Cells were analyzed by flow cytometry for enumeration of viable cells with beads, apoptotic cells or fused cells. Electroporation promoted a 49-fold increase of the percentage of viable cells that had fused with apoptotic cells. Apoptotic cell-viable cell fusions were 8-fold more likely to not attach to cell culture plastic and 2.3-fold less likely to proliferate after 24hr incubation than viable cell fusion controls. These data demonstrate that apoptotic signals can be transferred between cells by electrofusion, possibly suggesting a novel investigative approach for optimizing targeted cell deletion in cancer treatment.
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ABSTRACT: Summaryi. Degenerations of embryonic cells have either been reported as such or have been misinterpreted by various authors as ‘mitotic metabolites’ or blood cells.2. There is ample support for the morphological identification of dying cells from the following considerations: the degeneration ‘granules’ are initially Feulgen-positive and have thus originated from nuclear constituents; the stages of cell deaths seen in normal embryos are identical with those produced experimentally and with those observed directly in tissue cultures; degenerating cells react in the same manner to supravital stains in vivo and in vitro.3. The process of degeneration varies with the degree of specialization of the cell, with its functional state (e.g. mitosis), with the type of animal and under experimental conditions with the causative agents.4. Cell death may take from less than 1 hr. to about 7 hr. when only a small proportion of a living tissue dies, but may be prolonged to days when numerous cells die simultaneously and their resorption is delayed.5. Degenerations have been found during the normal development in embryos of all vertebrate animals examined. The occurrence of necrosis in embryos of pure genetical lines is excluded from this article.6. The incidence of embryonic cell deaths according to site, tissue, developmental stage or process and type of animal is summarized in Table 1.7. While some degenerations have no obvious function in embryonic development, others seem to play a significant role in embryonic processes, e.g. the morphogenesis and histogenesis of tissues and organs, and the representation and regression of phylogenetic steps (Table 2).8. Morphogenetic degenerations precede changes in the form of epithelial organs, e.g. during the invagination of the optic cup, the formation of the crystalline lens, the olfactory pit, the neural tube, etc. They bring about the separation of rudiments such as that of the neural tube and the lens from the ectoderm. They reduce the excessive thickening of uniting edges such as those of the body wall and of the mandibles. They are involved in the production of lumina in the solid rudiments of glands and the intestinal tract. In the mesenchyme they precede and make possible the influx of specialized tissue such as the sternal plates or the ingrowth of myogenic tissue in the mandible.9. Histiogenetic degenerations are related to the differentiation of tissues and organs. The differentiation of the three cell layers of the frog tadpole retina, for instance, is accompanied by three waves of degeneration. Similar cell deaths of early neuroblasts are found in the spinal ganglia outside the limb regions. In amphibia a partial sarcolysis during metamorphosis provides a blastema for the permanent musculature. Sex differentiation of the individual involves the partial degeneration of the Mullerian or Wolffian ducts. Cell deaths also occur in relation to fibre formation and to the appearance of bone and cartilage matrix. Their role in these and in evocatory processes needs further elucidation. Whether cell deaths in the central nervous system and the sense organs at the time of vascularization and neurotization are related to these phenomena remains to be further investigated.10. Phylogenetic cell deaths are of two types: those which represent a vestigial organ such as the paraphysis or the second muscle stage in higher vertebrates, and those concerned with the regression of larval structures such as the conjunctival papilla, parts of the ganglia of branchial nerves, of the pro- and mesonephros. Some of these larval organs have a function in embryonic development, viz. the apical ridge on the limb buds.11. The causation of the distinctly localized morphogenetic degenerations is obscure. Vascular or nutritional disturbances are unlikely to be responsible for these cell deaths which precede changes in form and appear in the same localizations and amounts in the vascularized tissue of the intact embryo and after explantation in tissue cultures.. Most of the histiogenetic and phylogenetic cell deaths, as well as some of the not strictly localized morphogenetic degenerations, may be due to the fading out of stimuli for their proliferation or for the completion of their differentiation. If such cells fail to divide, they age and die on reaching the end of their normal life span. This conception assumes that stimuli for the formation of embryonic tissues and organs act for limited periods only and extend over a field of cells. Some of these cells respond fully to stimulation, while others are late to react or do so only partially or receive only a fraction of the whole stimulus. The partial differentiation of cells unfits them for division, for dedifferentiation and redifferentiation in another direction.12. The localized morphogenetic degenerations are correlated with the incidence and orientation of mitosis and of cell movements, and changes in the form of embryonic organs are brought about by the integration of these three cellular activities. Cell deaths are abundant wherever the regular arrangement and close packing of cells prevent free cell movements; they are rare or absent when, as, for instance, in the tadpole eye, a loose arrangement of cells and a decrease in cell volume (by resorption of yolk) allow of free cell movements.14. Cell degeneration in vertebrate ontogeny is an important mechanism of integration of cells into tissues and organs by helping to shape the form of organs, by the removal of superfluous cells or by the preparation of a dedifferentiated blastema in histio- and phylogenesis.Biological Reviews 01/2008; 26(1):59 - 86. DOI:10.1111/j.1469-185X.1951.tb00774.x · 9.79 Impact Factor
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ABSTRACT: Anoikis (or cell-detachment-induced apoptosis) is a self-defense strategy that organisms use to eliminate 'misplaced' cells, i.e. cells that are in an inappropriate location. Occasionally, detached or misplaced cells can overcome anoikis and survive for a certain period of time in the absence of the correct signals from the extracellular matrix (ECM). If cells are able to adapt to their new environment, then they have probably become anchorage-independent, which is one of the hallmarks of cancer cells. Anoikis resistance and anchorage-independency allow tumor cells to expand and invade adjacent tissues, and to disseminate through the body, giving rise to metastasis. Thus, overcoming anoikis is a crucial step in a series of changes that a tumor cell undergoes during malignant transformation. Tumor cells have developed a variety of strategies to bypass or overcome anoikis. Some strategies consist of adaptive cellular changes that allow the cells to behave as they would in the correct environment, so that induction of anoikis is aborted. Other strategies aim to counteract the negative effects of anoikis induction by hyperactivating survival and proliferative cascades. The recently discovered processes of autophagy and entosis also highlight the contribution of these mechanisms to rendering the cells in a dormant state until they receive a signal initiated at the ECM, thereby circumventing anoikis. In all situations, the final outcome is the ability of the tumor to grow and metastasize. A better understanding of the mechanisms underlying anoikis resistance could help to counteract tumor progression and prevent metastasis formation.Journal of Cell Science 10/2011; 124(Pt 19):3189-97. DOI:10.1242/jcs.072165 · 5.33 Impact Factor
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ABSTRACT: We have previously reported that the drs gene, whose mRNA expression is downregulated by retroviral oncogenes such as v-src and v-K-ras, has the ability to suppress transformation by v-src in a rat cell line F2408. We have now isolated a human homolog of this gene (h-drs) and found that the expression of h-drs mRNA is markedly downregulated in a variety of human cancer cell lines including those of the colon, bladder, and ovary. To investigate the function of the drs gene as a tumor suppressor in human cancer cells, we constructed recombinant amphotropic retrovirus containing the drs gene, introduced this virus into human cancer cell lines whose drs expression was downregulated and found that drs has the ability to suppress anchorage-independent growth of these cells without disturbing cell proliferation. Analyses with deletion mutants of the drs gene revealed that both the C-terminal region inside the transmembrane domain and three consensus repeats in the N-terminal region are essential for the suppression of anchorage-independent growth of the cells. We also found that the G1-S progression of the cell cycle and expression of cyclin A mRNA were significantly suppressed in T24 cells expressing the drs gene under non-adhesion culture conditions. In contrast, the expression of cyclin D and E and the phosphorylation of Rb protein were not affected by ectopic expression of the drs gene, suggesting that an Rb-independent downregulation of cyclin A is involved in the suppression of anchorage-independent growth by means of the drs gene.Oncogene 09/1999; 18(34):4777-87. DOI:10.1038/sj.onc.1202852 · 8.56 Impact Factor