LANDMARK DISCOVERY: WE ALL CARRY GENES THAT MAY CAUSE CANCER
Author: By Richard Saltus, Globe Staff
Date: Tuesday, October 10, 1989
Page: 18
Section: NATIONAL/FOREIGN
All of us carry in each cell a set of genes that determine our individual
eye color, height and a thousand other traits. But what astonished the
scientific world in 1975 was the discovery that we also harbor certain genes
that can turn against us and cause cancer.
The landmark finding, which yesterday earned researchers J. Michael Bishop
and Harold E. Varmus the Nobel Prize in Medicine, changed forever the way
scientists view the origins of cancer.
"What we showed is that we carry the seeds of our cancer within us," Bishop
has said.
So instead of seeing cancer as an outside intruder, scientists today take
the view "that cancer is a genetic disease," Bishop said yesterday. "Some
genes get damaged and cause cells to run amok."
The genes can be damaged by outside factors: chemicals, foods, radiation
and other environmental agents.
The landmark finding raised the prospect of ultimately diagnosing, treating
or even preventing cancer by influencing the way these genes behave. But that
is a long-term hope, not yet a reality.
"This will surely produce practical benefits," said Dr. John Cairns, a
cancer specialist at the Harvard School of Public Health. "But I don't think
it has yet, except in one or two cases" where research on oncogenes, or
cancer-causing genes, allows doctors to determine whether an individual's
cancer is a more or less dangerous type, influencing the choice of treatment.
The research by Bishop and Varmus at the University of California in San
Francisco stemmed from work on a particular virus that causes cancer in
chickens.
When the virus infected the chicken cells, it developed a particular virus
that appeared to be the actual cancer-initiating culprit. CLARIFICATION: A
story in Tuesday's Globe explaining the research that won the Nobel Prize in
Medicine contained a misworded sentence about the infection of chicken cells
by a cancer virus. It should have read, "When the virus infected the chicken
cells, it inserted a particular gene that appeared to be the actual cancer-
initiating culprit." But this gene was not one of the virus' normal genes.
Ancestors of the virus must have acquired the gene somewhere during evolution.
Bishop and Varmus discovered that the source of the gene had been the
chickens themselves. An apparantly normal gene was pilfered by the virus, and
was now able to cause cancer when it infected the birds.
The real astonishing discovery was that this gene was found to be
widespread in nature. In fact, laborious experiments carried out by the
scientists and by Dominique Stehelin, then a post-doctoral fellow, showed that
an almost endless variety of animals, and humans as well, carried a copy of
the gene that could become a cancer gene.
But why should evolution perpetuate a cancer-causing gene?
According to Bishop and Varmus, the gene normally has a necessary and
helpful role in cells, such as controlling growth, or regulating some key
chemical process. At this stage, it is a "proto-oncogene" -- a term coined by
Bishop. But when the gene is damaged -- by a virus, a chemical, a broken
chromosome, or other cause -- it becomes an oncogene. Since its genetic
instructions are flawed, it can now trigger the cell it lives in to turn
cancerous.
Since the Bishop-Varmus discovery, scientists examining cancer tumors, such
as those in the breast, colon, bladder and lung, have found more than 50
different types of oncogenes, which are believed to cause the tumors.
Currently, scientists are transferring oncogenes into different animals to
try to determine how they cause tumors. Geneticist Philip Leder and
colleagues at Harvard Medical School used the technique to create the
''Harvard mouse," the first patented animal, which was implanted with a
particular oncogene so that it would develop cancer.
And in the most recent chapter of the story, researchers have discovered at
least six so-called "antioncogenes," genes that normally keep cancer in
check, but when lost or damaged, allow cancer to develop. The presence or
absence of these antioncogenes in an individual's genetic makeup is thought to
be the reason for hereditary predispositions to types of cancer in some
families.
SALTUS;10/09 CORCOR;10/11,19:48 RESEAR10
|
