The Telomerase Enzyme and Immortality

Description: Professor Robert Weinberg explains how normal cells can
only double a certain limited number of times; and cancer cells
have to learn how to proliferate indefinitely, i.e, they have to
become immortalized.
Transcript: Cells have a lifespan. The age of a cell and its ability to
divide is related to structures – telomeres – found at the
ends of chromosomes. Robert Weinberg, Ph.D.,
Whitehead Institute for Biomedical Research: "Normal
cells can only double a certain limited finite number of times;
cancer cells have to learn how to proliferate indefinitely, that
i.e, they have to become immortalized. The machinery for
controlling how often a cell may grow and divide, how many
generations a lineage of cells may pass through, is carried in
the telomeric DNAs at the ends of chromosomes. The
telomeres are specialized sequences at the ends of each
chromosome and they operate to prevent end-to-end fusion of
chromosomes. These telomeres protect the ends of
chromosomal DNA from such accidents. And as was
learned in a number of laboratories, when normal cells go
through cycles of growth and division their telomeric DNA
gets shorter and shorter and shorter and ultimately so short
it can no longer protect the ends of chromosomal DNA.
Telomeres start fusing. Chromosomes start fusing in those
cells, and those cells die. Cancer cells must avoid that
problem because they want to grow indefinitely, and what do
they do? They turn on an enzyme called telomerase that is
normally expressed only early in embryologic development
and in a small number of so-called stem cells in the body.
The telomerase enzyme is able to extend the telomeres,
making them longer and longer thereby enabling the cancer cell
to go through many, many cycles of growth and division
without worrying about the imminent collapse of its telomeres.
The telomerase ensures the telomeres stay very long." In
2000, Douglas Hanahan (shown below) and Robert
Weinberg published a paper in Cell, "The Hallmarks of
Cancer," which identified some organizing principles of cancer
cell development. "The nature of the replication machinery is
that chromosomes get smaller every time they divide. And we
now appreciate that specialized cells in the body have a way to
counteract this telomere shorting and that's using several
strategies of which the most prominent is an enzyme known as
telomerase that protects the ends of chromosomes from this
erosion."
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