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Researchers know that one species of bacteria called Helicobacter pylori (or H. pylori) is a major cause of stomach cancer worldwide. Not everyone who is infected with H. pylori develops stomach cancer, but it is a common infection, especially in developing parts of the world, and results in many cases of the disease.
Yet researchers haven’t understood how these bacteria causes cancer. The stomach lining is exposed to fluids needed for food digestion, and cells are constantly being cleared away with new cells dividing to replace them. Bacteria and other early cancerous cells on the surface of the stomach lining should be removed regularly as well, yet cancer still develops.
Researchers from Germany and California recently published a study that provides an explanation for how these bacteria may cause cancer, and how a population of rapidly dividing stem cells may be at the root of this process.
Stem cells replace specialized cells that are lost
Stem cells are unspecialized cells that can develop into different types of cells that work in different ways. For example, a complex organ like the stomach contains many different types of cells, and all of these types originate from the same group of stem cells. The stomach has many stem cells to replace all the cells that are regularly lost from the stomach lining.
Stomach stem cells need to be able to divide and grow quickly as part of their job – but these are also key features of cancer cells. It does not take much transformation for these cells to become cancerous.
The researchers in this study found that the stem cells are concentrated at the base of the stomach gland, allowing them to do their job protected from the harsh environment in the stomach. Their location also makes it more difficult for bacteria to access these stem cells, and questions remain about how H. pylori may be involved in transforming these cells into cancer.
Two different types of stem cells are found in stomach gland
The researchers studied the stem cell populations in the stomach and found that there are actually 2 distinct groups of stem cells. One group divides slowly and the other divides quickly. Both could specialize into other kinds of stomach cells, but they responded very differently when exposed to a protein called R-spo.
Importantly, the R-spo protein is produced by another type of stomach cell when a person is infected with H. pylori. The researchers found that after infection, the slow-growing group of cells is essentially silenced, while the fast-growing group of stem cells starts dividing more quickly, which thickens the stomach lining and may eventually lead to cancer.
Study provides first explanation of how bacteria causes cancer
This is the first research that helps to explain how H. pylori causes stomach cancer. With a better understanding of how H. pylori can alter stem cells to promote cancer development, researchers may be able to develop new strategies for stomach cancer treatment and prevention.
Eileen Hoftyzer, BSc, and Carolyn Goard, PhD