It's not all genetic: Common epigenetic problem doubles cancer risk in mice

February 24, 2005

In experiments with mice, a team of scientists from the United States, Sweden and Japan has discovered that having a double dose of one protein is sufficient to change the normal balance of cells within the lining of the colon, thereby doubling the risk that a cancer-causing genetic mutation will trigger a tumor there. Roughly 10 percent of people have this double protein dose as well.

In the Feb. 24 online version of Science, the researchers report that mice engineered to have a double dose of insulin-like growth factor 2 (IGF2) develop more so-called precursor cells within the lining of the colon than normal mice. When these mice also carried a colon-cancer-causing genetic mutation, they developed twice as many tumors as those with normal IGF2 levels, the researchers report.

"Both clinically and scientifically, this discovery should expand attention in colon cancer research to earlier events, situations present well before tumors appear," says the study's leader, Andrew Feinberg, M.D., M.P.H., professor of medicine and director of the Center for Epigenetics in Common Human Disease at Johns Hopkins.

"In the mice with a double dose of IGF2, everything is pretty normal except for the extra precursor cells," says Christine Iacobuzio-Donahue, M.D., assistant professor of pathology and oncology. "But when the genetic mutation is present, too, we found a clear cost for what otherwise appears to be a benign effect of extra IGF2."

The team's analysis of colon tissue samples from a dozen or so Johns Hopkins patients with suspected colon cancer suggests that IGF2's effect in people may be similar, the researchers report. A larger study of samples from patients with and without suspected colon cancer is underway, Feinberg notes.

In the mice -- as well as in about 30 percent of colon cancer patients and 10 percent of the general population -- the extra IGF2 stems not from a genetic problem, or mutation, but an "epigenetic" problem that improperly turns on the copy of the IGF2 gene that should remain off.

Unlike most genes, the copy of IGF2 that should be silent depends only on which parent it came from, a situation called genomic imprinting. For IGF2, the copy inherited from the mother is always supposed to be turned off.

In the mice and in some people, however, cells lack the epigenetic "marks" that sit on the DNA and keep the maternally inherited copy turned off. As a result, cells make a double dose of the IGF2 protein and are said to have "loss of imprinting" of IGF2.

Although Feinberg and others have already noted an association between loss of imprinting of IGF2 and colon cancer in people, the current experiments were designed to find out whether the loss of imprinting is involved in cancer's development or just in its progression.

"Most researchers, including me, expect epigenetic differences to influence progression -- whether a tumor would grow slowly or quickly, or whether it would spread," says Feinberg. "But, in this case, our results show that loss of imprinting of IGF2 contributes to colon cancer's development in the mice. It doesn't cause tumors directly, but it creates an environment which is ripe for cancer to start."

Because precursor cells in the colon's lining had been identified as a likely starting point for tumors, Feinberg and his team tossed a cancer-causing genetic mutation into the mix. The IGF2 mice were crossed with mice carrying a mutation in a gene called APC, which had been tied to colon cancer by researchers studying families with excessive growths, or polyps, in the colon.

Mice with extra IGF2 and the APC mutation developed twice the number of tumors as mice with the mutation but whose IGF2 levels were normal. The tumors grew at the same rate in both sets of mice, suggesting that more tumors get started in the mice with extra IGF2, notes Feinberg.

"In the mice, loss of imprinting of IGF2 roughly doubles the risk that the genetic mutation will cause a tumor," says postdoctoral fellow Atsushi Kaneda, Ph.D. "Double the risk may not seem like much, but this loss of imprinting is common."

The researchers' mice mirror two situations in people because the double dose of IGF2 was accomplished in two ways. One set of mice, obtained from Shirley Tilghman at Princeton, have a double dose of IGF2 because they are missing another gene, H19, whose sequence overlaps the region that usually shuts off one copy of IGF2. As a result, these mice lack H19 and have double IGF2.

To isolate the effect of the extra IGF2, Rolf Ohlsson at the Uppsala University, Sweden, developed a set of mice missing only the control region for IGF2; their H19 gene was intact. These mice likely mimic the 30 percent of colon cancer patients and 10 percent or so of the human population who have loss of imprinting of IGF2.

Only the Princeton mice have been crossed with the APC mice. Both the Princeton and the Swedish mice have the extra precursor cells in the lining of the colon, suggesting the effect on cancer development would be similar.

Co-author Dan Longo, M.D., of the National Institute on Aging notes that the mice with both double IGF2 and the APC mutation should be a useful animal model to evaluate the impact of colon cancer prevention strategies, including dietary interventions and targeted drugs.
-end-
The researchers were funded by the National Cancer Institute, the National Institute on Aging, The Uehara Memorial Foundation and the Swedish Cancer Research Foundation. Authors on the paper are Kaneda, Feinberg, Iacobuzio-Donahue, Takashi Sakatani and Sten de Boom Witzel of Johns Hopkins; Mark Carter, Minoru Ko and Dan Longo of the National Institute on Aging; Hideyuki Okano of Keio University School of Medicine, Tokyo, Japan; and Ohlsson of Uppsala University.

On the Web:

http://www.sciencemag.org

Johns Hopkins Medicine

Related Cancer Articles from Brightsurf:

New blood cancer treatment works by selectively interfering with cancer cell signalling
University of Alberta scientists have identified the mechanism of action behind a new type of precision cancer drug for blood cancers that is set for human trials, according to research published in Nature Communications.

UCI researchers uncover cancer cell vulnerabilities; may lead to better cancer therapies
A new University of California, Irvine-led study reveals a protein responsible for genetic changes resulting in a variety of cancers, may also be the key to more effective, targeted cancer therapy.

Breast cancer treatment costs highest among young women with metastic cancer
In a fight for their lives, young women, age 18-44, spend double the amount of older women to survive metastatic breast cancer, according to a large statewide study by the University of North Carolina at Chapel Hill.

Cancer mortality continues steady decline, driven by progress against lung cancer
The cancer death rate declined by 29% from 1991 to 2017, including a 2.2% drop from 2016 to 2017, the largest single-year drop in cancer mortality ever reported.

Stress in cervical cancer patients associated with higher risk of cancer-specific mortality
Psychological stress was associated with a higher risk of cancer-specific mortality in women diagnosed with cervical cancer.

Cancer-sniffing dogs 97% accurate in identifying lung cancer, according to study in JAOA
The next step will be to further fractionate the samples based on chemical and physical properties, presenting them back to the dogs until the specific biomarkers for each cancer are identified.

Moffitt Cancer Center researchers identify one way T cell function may fail in cancer
Moffitt Cancer Center researchers have discovered a mechanism by which one type of immune cell, CD8+ T cells, can become dysfunctional, impeding its ability to seek and kill cancer cells.

More cancer survivors, fewer cancer specialists point to challenge in meeting care needs
An aging population, a growing number of cancer survivors, and a projected shortage of cancer care providers will result in a challenge in delivering the care for cancer survivors in the United States if systemic changes are not made.

New cancer vaccine platform a potential tool for efficacious targeted cancer therapy
Researchers at the University of Helsinki have discovered a solution in the form of a cancer vaccine platform for improving the efficacy of oncolytic viruses used in cancer treatment.

American Cancer Society outlines blueprint for cancer control in the 21st century
The American Cancer Society is outlining its vision for cancer control in the decades ahead in a series of articles that forms the basis of a national cancer control plan.

Read More: Cancer News and Cancer Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.