A diverse array of bacteria live in the human mouth as part of a vital ecosystem known as the oral microbiome.
In a new study, researchers found that one of these common bacteria can leave the mouth and potentially cause existing cancer cells in other parts of the body to spread.
These bacteria are believed to predominantly travel through the blood to different sites in the body where they are associated with serious infections of the brain, liver, and heart; preterm birth in pregnant women; and are present in high levels in colon tumors.
Poor oral hygiene could cause the bacteria to migrate to other parts of the body where cancers exist. Also, evidence exists for a link between severe gum disease and colorectal cancer.
The research was conducted by Virginia Tech scientists.
Since 2012, several studies have shown this bacterium, F. nucleatum, directly invades colon tumors, but questions remained as to how this bacterium is contributing to cancer.
To address the potential of F. nucleatum driving metastasis, the team asked the broad question: How do human cells respond when colon cancer cells are infected with F. nucleatum?
Their findings provide a deeper understanding of the critical role bacteria can play in cancer.
At first glance, Fusobacterium nucleatum appears quite unremarkable and lives in harmony with other bacteria under the gums in the oral microbiome.
Despite its role as a common bacterium in the mouth, the correlations with colon cancer were too strong to ignore.
According to the team, there is no evidence that this bacterium is directly initiating cancer. Also, this bacterium does not appear to be releasing molecules that are causing the cancer cells to migrate.
Instead, F. nucleatum sticks to and even enters cancer cells.
This in turn causes cancer cells to release two proteins that are members of the cytokine protein family that play critical roles in immune system activation against infections.
Strikingly, the cytokine combination of the two proteins could induce the spread of cancer cells.
These cytokines released by an infected cell then can talk back to the same cell or those signals can be sent out to other cancer cells, immune cells, and various other cell types that surround a tumor.
In essence, one infected cell could be affecting multiple neighboring cells, so there doesn’t have to be a widespread infection within a tumor for it to be influencing a large surrounding area.
In addition, the two proteins also play roles in inflammation; a hallmark of cancer.
Together, these results provide a deeper understanding of how bacteria influence cancer.
While this process was shown to occur with colorectal cancer cells, the team is exploring if the same process is influencing other types of cancer, including pancreatic cancer, breast cancer, and oral squamous cell carcinoma of the mouth.
One author of the study is Daniel Slade, an assistant professor in the Department of Biochemistry in the College of Agriculture and Life Sciences.
The study is published in Science Signaling.
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