such as "Introduction", "Conclusion"..etc
October 1998 -- Cells die. It's a normal part of development and of
aging. Cell death also plays a role in many deadly diseases such as
cancer, stroke and Alzheimer's disease. The more scientists understand
about the process of cell death, the better able they will be to combat
those and other diseases.
Scientists know that badly damaged cells that cannot be repaired are
slated for programmed cell death known as apotosis. They also know that
in the fruit fly proteins called Reaper, Grim and Hid appear prior to
cell death, but until now, they did not understand their role in
apotosis. Toshinori Hoshi, Ph.D., UI associate professor of physiology
and biophysics, and colleagues at the Beckman Research Institute of the
City of Hope, discovered that these proteins cause over-stimulation of
cells, leading to death. The findings are published in the Sept. 29
issue of the journal Proceedings of the National Academy of Sciences.
Cells become active when they communicate with each other through a
complex "telephone" system where one cell sends an activation message
or impulse to the next, and that cell activates the next and so on. The
impulses that activate each cell usually arise from a chemical message,
Most cells in the body are relatively passive or quiescent until an
impulse excites them to action, but once they have acted they need to
return to the quiet state or die from over excitation. Studying the
protein Reaper, Hoshi and colleagues found that it doesn't allow the
cell to return to the nonactive state, thus exciting itself to death.
When a quiescent cell receives chemical messages spurring it into
action, ions such as sodium or calcium rush inside the cell. After the
message is sent, the cell is ready to return to the quiescent state. To
do so, potassium leaves the cell through special potassium channels.
Hoshi found that Reaper inserts part of its structure into the
pore-like channel, thus clogging the pore and blocking the release of
potassium, preventing the cell from returning to its resting state. The
researchers also found that a mutated Reaper protein that is not able
to jam the potassium channel, did not cause apotosis.
It is not clear why these proteins appear in certain cells, Hoshi said.
It may be the result of stress produced by a heart attack or stroke, or
even the food we eat. But understanding the process by which they
initiate cell death has enormous implications.
"If there isn't enough protein like Reaper to initiate cell death,
abnormal cells, like cancer cells, are not destroyed. If there is too
much, it causes neurodegeneration, or kills cells that shouldn't die,"
Hoshi said. "We think mechanisms like this exist in humans too," Hoshi
added, "and we are now working with mammalian cells in culture."
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