|
Aging
and Cancer
By Karen Lurie,
Sciencentral News
October 21, 2003
Of all the possible causes of cancer the biggest is simply growing old.
Scientists trying to understand why are turning to an age-old friend of
bakers—yeast
Cancer
Switch
Aging appears to be a carcinogen. About 77 percent of all cancers
are diagnosed in people of age 55 and older
"In the first 30 or 40 years of your life you normally don't
have any cancer," says Daniel Gottschling, a
researcher at the Fred
Hutchinson Cancer Research Center and professor
of genome sciences at the
University
of
Washington
. "But suddenly as you hit your 50's the incidence of cancer begins
to go up astronomically."
Now, Gottschling and his colleague Michael McMurray report in the
journal Science that the same stuff
that makes bread dough rise can help scientists explain this rise of
cancer with aging.
Simple baker's yeast, a single-celled fungus, is a favorite tool of
scientists for studying aging because of its short lifespan. "Yeast
and humans have a lot of the same things, they have chromosomes, they
divide," says Gottschling. "They have a certain lifespan just
like humans do, but instead of it being 70 years, it's more like about
five days. So we can learn a lot of things about the fundamentals of aging
from this simple organism and it turns out that a lot of that is
translated to humans."
Yeast cells do not get cancer. But, says Gottschling, "one of
the hallmarks of cancer that has been known for a long time is called
chromosomal instability–basically, the chromosomes get all mixed up and
messed up. If yeast get old, they too get chromosomal instability near the
end of their life."
The lifespan of a yeast cell is measured by how many times it
divides. Scientists call a single yeast cell a mother cell. "The
number of daughter cells that she gives off, the number of buds, is her
lifespan," says Gottschling. "A typical yeast will have maybe 30
daughters that she'll give off, and after the 30, she dies."
Recording the age and lifespan of the mothers and daughters is
painstaking work. McMurray used a microscope with a fiber-optic needle to
isolate each daughter cell as it budded. Then he watched each daughter
cell grow up into a colony. Watching for chromosomal instability in the
daughter colonies was easier, thanks to a genetics trick. They genetically
manipulated the yeast cells to change color from white to red if there
were abnormal chromosomes, a sign of genetic instability.
The color changes revealed what Gottschling
calls "an amazing switch" when the mother cells reached middle
age. "In the early stages of her life, the mom was just fine,"
Gottschling explains. "She was going along dividing happily, making
new cells… all her daughters were white, which meant the chromosomes
were all normal. Then later in her life, roughly the equivalent of 50 or
60 years old in a human, we started seeing all this color change. There
was lots of red…starting to appear, indicating all these chromosomal
abnormalities were occurring–late in her lifespan, not early."
"We equate that with the same phenomenon that happens in
humans," he says. "We can make a sort of an equivalent
calculation. That is, the time at which the mother cell first started to
become unstable or making bad daughters is roughly the equivalent to when
a mother, a human mother, is about 50 years old. The other thing we could
see is that the increase was incredibly dramatic, it was about a one
hundred to two hundred-fold increase... and that is roughly equivalent to
what we see in the frequency of cancer in humans late in life as
well."
Even when the researchers used other genetic manipulations to double
the lifespan of yeast, the cancer switch still came on around the
equivalent of age 50 in humans. That suggests that the switch is a
separate phenomenon from other changes of aging. "So for instance,
somebody might die of heart disease first, another person might die of
infection, another person might die due to cancer," Gottschling says.
"If we get rid of the problems of, let's say, heart disease, then my
speculation is that things like cancer will raise their ugly head if we
don't figure out the late onset of that disease as well."
Gottschling hopes this new simple model of aging and cancer will be
useful to researchers testing hypotheses of how cancer develops, as well
as for testing potential anti-cancer drugs or treatments.
This research was funded by the
National Science Foundation
(NSF), the National Institutes of
Health (NIH) and Ellison
Medical Foundation.
Copyright
© 2002 Global Action on Aging
Terms of Use | Privacy
Policy | Contact Us
|
