Cell homeostasis

The activation of specihc immune responses involves the proliferation of lymphocytes. For T-cells, the stimulatory agent can be a combination of anti-CD3 and anti-CD28 or mitogens such PHA or ConA. Dysregulation of cell homeostasis may have severe adverse effects on immune functions, increasing susceptibility to infections and cancer, as well as favoring the development of autoimmune diseases. 

Marleau, A.M. and Sarvetnick, N., T cell homeostasis in tolerance and immunity, J. Leukoc. 

The prototype of a small pore-forming toxin is the S. aureus a-toxin, also called ct-hemolysin, that has been extensively investigated hy Bhakdi and coworkers. Monomers of ct-hemolysin (33 kDa) hind to the surface of erythrocytes, and after lateral diffusion within the lipid hilayer, seven monomers oligomerize to form pores in the cell membrane. The ct-hemolysin forms mushroom-shaped pores with an outer diameter of lOnm and an inner diameter of approximately 2.5 nm. Small molecules can pass through the pore and diffuse into/out of the cytosol, along with water. As a consequence of such movement, cell homeostasis is greatly disturbed and pushed into an unhealthy state. In animals, the a-hemolysin represents a major virulence factor of S. aureus which causes hemolysis as well as tissue destruction. ... 

Apoptosis. Apoptosis— programmed cell death—involves elimination of damaged cells and maintenance of cell homeostasis. Homeostasis can be defined as the ability of living cells to regulate themselves in a dynamic manner. When apoptosis is deregulated, diseases such as cancers, immune... 

Bortezomib is the hrst therapeutic proteasome inhibitor. It inhibits the activity of the 26S-proteasoom protein complex which regulates protein expression and function and thus plays a role for cell homeostasis. It is used for the treatment of relapsed mulh-ple myeloma. Following intravenous administrahon bortezomib is mainly metabolised with an elimina-hon halflife of 5-15 h. It is frequently associated with somehmes irreversable neuropathy. Myelosuppression may be dose limiting. 

The response of cells to stress (including ROS and reactive metabolites) includes the upregulation of synthesis of stress proteins, which play a role in cell survival and thus serve a protective function. These are at a low level in the normal cell but help to maintain cell homeostasis. 

The replacement of an abnormal gene with a normal copy of the same gene may restore the cell capacity to produce functional proteins, contributing to cell homeostasis (Figure 21.5B). This type of gene therapy is one of the... 

Bile acids that escape enterohepatic circulation and pass to the colon can be cytotoxic to colonocytes. Damaged cells undergo apoptosis and are shed into the lumen. To maintain cell homeostasis, new cells must be produced. This replacement can result in an increase in cell proliferation rate that can increase the risk of mutations in tumor-related genes and lead to carcinoma development. Moschetta et al. (2000) showed that sphingomyelin protected against bile acid-induced cytotoxicity in human CaCo-2 colon cancer cells, a common model for studying intestinal cell function. 

The larger biomolecules that have potential Al3+ binding sites are phosphate-bearing biomolecules such as ATP, membrane phospholipids and nucleic acids. It is important to recognize that the metal coordination of these biomolecules might lead to serious disgorges in central biological processes necessary to cell homeostasis and consequently for its overall healthy condition [21]. 

This competitive recruitment hypothesis explains how TNF-R2, a survival receptor, could induce apoptosis (Fig. 12B). It has been observed that mice deficient in TNF-R2 showed decreased cell death following TNF treatment (Erickson et at., 1994), while overexpression of TNF-R2 could lead to increased sensitivity to TNF-induced apoptosis (Chan and Lenar-do, 2000 Haridas et at., 1998 Heller et at., 1992 Vandenabeele et at, 1995 Weiss et at., 1997). Moreover, TNF-induced apoptosis of activated primary T lymphocytes has also been shown to require TNF-R2 (Sarin et at., 1995 Zheng et at., 1995). Functionally, this may be important for Fas-indepen-dent peripheral deletion of T lymphocytes and the regulation of mature T-cell homeostasis. 

Haugliey NJ, Natli A, Chan SL, Borchard AC, Rao MS, Mattson MP (2002) Disi uption of neurogenesis by amyloid beta-pephde, and pertuT bed neur al progenitor cell homeostasis, in models of... 

In bacterial cells homeostasis is achieved by a combination of passive and active mechanisms (Hill, O Driscoll, and Booth, 1995). 

It is proposed that anions are actively extruded from cells to account for lower intracellular concentration. In theory, if anions are extruded from the cell, they would reassociate when exposed to the lower external pH and freely diffuse back into the cell, resulting in a futile cycle without resistance development. However, adapted yeast cells can reduce the diffusion coefficient of preservatives across the plasma membrane, and the diffusion of weak acids into the cell is then reduced. This adaptive mechanism is based on the efflux of preservative anions by Pdrl2. Efflux of anions together with a reduction in the diffusion coefficient of the membrane will result in the maintenance of cell homeostasis, which will enable the organism to survive and grow (Holyoak et al., 1999). 

The very simple systein therefore simulates the various kinetic pathways of a living cell homeostasis, death, and growth/ self-reproduction. It is the simplest possible chemical rendering of the chemical behavior of a living cell. 

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