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effector caspases Apoptosis DNA damage ATM Chk2 P P
levels of p53 p53 PP PP p53p53 response to growth factor stimulation. These signaling pathways control
the fate of a wide variety of cells whose survival is dependent on extracellular growth factors or cell-cell interactions. As already noted, a well-characterized example of programmed cell death in development is provided by
the vertebrate nervous system. About 50% of neurons die by apoptosis,
with the survivors having received sufficient amounts of survival signals
from their target cells. These survival signals are polypeptide growth factors related to nerve growth factor (NGF), which induces both neuronal
survival and differentiation by activating a receptor protein-tyrosine kinase.
Other types of cells are similarly dependent upon growth factors or cell
contacts that activate nonreceptor protein-tyrosine kinases associated with
integrins. Indeed, most cells in higher animals are programmed to undergo
apoptosis unless cell death is actively suppressed by survival signals from
One of the major intracellular signaling pathways responsi...
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