The Role Of The P53 Gene In Apoptosis And Cancer
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3Biol 211 – K. Marr
The Role of the p53 Gene in Apoptosis and Cancer
p53 Gene and Apoptosis
1.
Activation of the p53 Gene in some cells initiates Apoptosis: programmed cell suicide (fig. 1, below and on the left
of fig. 2 page 2)
o
p53 is Activated by
a.
Damage to DNA, e.g. radiation
b.
Cellular invasion, e.g. Viruses
c.
Normal chemical signals during embryonic development
o
Apoptosis helps to prevent the reproduction of genetically damaged cells
2.
Apoptosis removes unneeded cells when activated by normal chemical signals during development (on the left in
fig. 2 on page 2). Some examples….
o
Tail of tadpole during metamorphosis
o
Webbing between fingers during human embryonic development
o
Human lens during embryonic development
o
Human skin cells
o
Uterine lining during menstruation
p53 Gene as a Tumor Suppressor Gene
3.
In some cells the p53 gene acts as a Tumor Suppressor Gene (in the middle in fig. 2 on page 2)
The “normal” p53 gene product inhibits cells from proceeding from the G
o
or G
phases of the cell cycle to
1
o
the “S” phase of the cell cycle
Helps to regulate the cell cycle—i.e. acts as the “brakes” to keep cells from dividing unnecessarily
o
4.
Mutant p53 gene (on the right in fig. 2 on page 2)
o
phases of the cell cycle to the “S”
Mutant gene product does not stop a cell from proceeding from G
or G
1
o
phase of the cell cycle
o
May lead to___________________________________?
Role of p53 in Preventing Skin Cancer
U.V. Light
Over exposure
Repeated exposure
to “minor” amounts
Skin
Skin
Severe Damage
p53 mutates
to DNA
p53 activated
p53 inactive
No Apoptosis
Apoptosis
Skin Peels
No peeling of skin
Adaptive
Possible
signicance?
consequence?
Figure 1. The role of the p53 gene in apoptosis and in helping to prevent skin cancer.
Adapted from Scientific American, 9/96
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