Apoptosis active process

The powerful cancer suppressor, p53, which is also described in Box 11-D, in some way senses DNA damage. It prevents passage through the G checkpoint and also through the G2 checkpoint if the DNA has not been adequately repaired.496 497 Protein p53, whose three-dimensional structure is known,500 501 binds to DNA and also induces transcription of genes that cause arrest of the cell cycle. It may also induce cell death (apoptosis), a process that may also require the protein product of protooncogene c-mi/c.502 505 A variety of protein kinases and phosphatases act on p53 and influence its activity.506... 

Apoptosis Apoptosis is an ordered, active process that brings about the death of a cell as an important part of the maintenance of organismal homeostasis. Apoptosis can be assayed, in flow cytometry, by, for example, looking at the expression of phosphatidylserine on the cell surface, by looking for nuclei with less-than-normal (sub-GO/Gl) amounts of DNA, and by looking for an increase in DNA fragment termini. 

In contrast to cell necrosis, apoptosis is a process by which cells are systematically destroyed and removed. The nuclear body and organelles within the cell become enclosed in a membrane to form residues called apoptotic bodies. These are then said to be phagocytosed as they are enclosed within membranes and actively removed from the site of the injury. Apoptosis is an active process for eliminating dead cellular material. 

A common feature of many animal viruses is their capacity to induce programmed cell death (apoptosis), a process characterized by cell shrinkage, nuclear condensation, and DNA fragmentation (Shen and Shenk, 1995). Apoptosis may serve as a host defense to limit virus growth, or it may promote virus spread or enhance viral replication via activation of one or more signaling pathways involved in apoptosis induction (Teodoro and Branton, 1997). 

Upon SAg challenge in vivo, there is massive proliferation of the activated T cells and the number of V(3-specific T cells increases dramatically. Later on, their number is reduced due to activation-induced apoptosis. This process involves the typical DNA fragmentation, and affects preferentially V(3-specific CD4+ T cells [72], Stimulation with specific antigen and proinflammatory mediators, such as lipopolysaccharide, rescues T cells from death and promotes survival of SAg-stimulated T cells [80, 81]. The mechanism that triggers T cell apoptosis after SAg challenge is not well understood, but several events can contribute to it impaired IL-2 production, massive glucocorticoid release... 

Under some circumstances, such as when DNA damage is extensive, p53 also activates expression of genes that lead to apoptosis, the process of programmed cell death that... 

In a continuation of our efforts to delineate a mechanism for attenuation of DHA-induced skin hyperproliferation by 135-HODE and 155-HETrE, we assayed for activator protein (AP)-l, which has been associated with cell proliferation and apoptosis (a process of programmed cell death). We evaluated the topical effects of 135-HODE and 155-HETrE on hyperproliferative skin as a possible marker of how dietary nutrients can alter the expression of a nuclear transcription factor (AP-1). Our data revealed that topical application of DHA alone on normal skin epidermis elicits a time-dependent cutaneous hyperproliferation, which paralleled the time-dependent alteration of AP-1 expression. For further information, we assayed for two major subunits of AP-1 (c-fos and c-jun), which revealed a selective upregu-lation of c-fos (35). The topical application of 135-HODE and 155-HETrE to the DHA-induced hyperproliferating skin revealed alterations of the c-fos. 

Apoptosis, or programmed cell death, is a concerted, active process involving the coordination of multiple signaling cascades [53]. Discrete signaling cascades are activated in response to specific proapoptotic stimuli, although there may be a degree of cross-talk between the apoptotic pathways. Key determinants of apoptosis include the nature of proapoptotic stimulus, cell type, cellular redox status, and preexisting activation state of the pro- versus antiapoptotic biochemical machinery. 

In apoptotic cell death, several factors such as growth factors, NO, the tumor suppressor gene p53, and the protein encoded by this gene contribute to the process that leads to cell death. One of the functions of p53 protein is the activation of apoptosis if a cell is transformed to a malignant cell. Apoptosis typically leads to the formation of smaller membrane-encapsulated particles within the cell. Apoptotic cell death begins in the nucleus and proceeds to other parts of the cell. The death process may be quite advanced before it can... 

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