Our studies have led us to conclude that senescent cells respond to growth factors in much the same way, in part, as young cells. The receptor systems are largely unchanged with age, although some subtle modifications do occur. Furthermore, many of the early growth factor initiated events occur in a similar way in both young and old cells. This has led us to theorize that senescent cells are not arrested like mitogen-deprived young cells. Rather, they become blocked at a new arrest point in late G1 just prior to entry into DNA synthesis.

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