Potentially groundbreaking research at the University of Maryland School of Medicine has shown for the first time how a bacterial infection contributes to the development of cancer.
The discovery, made by Institute of Human Virology researchers, explains how certain bacteria interfere with infected cells’ ability to respond to and repair DNA, a problem that can cause cancer. The team plans to work next to determine whether there are similar connections between other types of bacteria and cancer development.
The finding offers the possibility of an avenue for research that eventually could allow doctors to reduce the incidence of cancers associated with bacteria and perhaps even prevent them, said Dr. Robert Gallo, co-founder and director of the institute.
“This is really exciting and really has the potential for being something groundbreaking,” said Gallo, one of the authors of the study published this week in the journal Proceedings of the National Academy of Sciences.
Until now, research had linked some bacteria with cancer, but “they could never pin it down,” he said.
The study examined the effect of mycoplasma — a family of bacteria known to be associated with cancers, particularly in HIV patients — on lymphoma development in mice.
In humans, some mycoplasma infections also can cause pneumonia, the sexually transmitted disease MGen, urinary tract infections and pelvic inflammatory disease.
The new study shows how a bacterial protein called DnaK in mycoplasma interferes with a cell’s ability to repair DNA in infected cells and disrupts cancer drugs meant to promote a gene that responds to defective DNA. Damaged DNA is a known cause of cancer.
Researchers used mice with compromised immune systems to analyze the effect of mycoplasma infection on the development of lymphoma by comparing how quickly the cancer developed in mice infected with mycoplasma versus those that were not infected.
They found that mice infected with the bacteria — a strain of mycoplasma from an HIV patient — developed lymphoma earlier in life than those mice that were not infected.
The researchers also determined that neither the infection nor the protein needed to be present to trigger cancer — a phenomenon Gallo referred to as “hit-and-run” that laid the foundation for cancer development long after the infection subsided.
About a fifth of all cancers are thought to be caused by infection, many of which are due to viruses, according to Gallo, one of the doctors who discovered HIV.
Mycoplasmas aren’t the only type of bacteria that have been linked to cancer. The bacteria Helicobacter pylori has been associated to stomach cancer, for example, and the sexually transmitted bacteria Chlamydia trachomatis can increase women’s risk of developing cervical cancer, according to the American Cancer Society.
Amino acids — the building blocks of protein — within the DnaK of other bacteria associated with cancer have similar sequences to the DnaK in mycoplasma, said Hervé Tettelin, an associate professor of microbiology and immunology at the University of Maryland School of Medicine’s Institute for Genome Sciences, in a statement.
“This raises the possibility that other bacteria have the same cancer-promoting ability,” he said.
The researchers are in the process of applying for grants to study whether other bacteria associated with cancer have the same effect.
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“Our theory is that bacteria with the sequence that give us this kind of DnaK is important for several human cancers … and we’re going to try to prove that in the coming year,” Gallo said.
Dr. Mark Kaplan, professor emeritus of infectious diseases at Michigan Medicine, the University of Michigan’s medical school, called the research “kind of major.” He said it helps paint a better picture of the origins of some cancer tumors.
“A lot of the solid tumors — breast cancer, prostate cancer, colon cancer — we don’t have any clue as to how did those cancers come about,” Kaplan said. “You’re beginning to get an emerging story of something important about bacteria that may be an important factor in inducing solid tumors.”
But Kaplan cautioned that the study should not cause alarm about the harmful effects of bacteria.
“It’s pretty scary to think that bacteria can induce cancer, but it’s only certain bacteria. We have tremendous immunity to bacteria,” he said. “What it means for an ordinary patient is not to be scared of all bacteria because we’re already too scared of bacteria.”
Gallo and Tettelin worked with Davide Zella, an assistant professor of biochemistry and molecular biology for the Institute of Human Virology, and other colleagues on the research. Morgan State University also participated in the study, which was partially funded by the Maryland Cigarette Restitution Fund Program.
The team had been researching the effect of DnaK protein on cancer intensively for about the last three years, though Gallo said the first experiments began eight or nine years ago at the Institute for Human Virology. The institute works to combine research and epidemiology to combat deadly viral and immune disorders, particularly HIV.