Antiviral enzyme behind several forms of cancer identified

Scientists have discovered that a human antiviral enzyme causes DNA mutations that lead to several forms of cancer.
The discovery by researchers at the University of Minnesota in US follows the team's earlier finding that the enzyme, called APOBEC3B, is responsible for more than half of breast cancer cases.
"We are very excited about this discovery because it indicates that a single enzyme is one of the largest known contributors to cancer mutation, possibly even eclipsing sources such as UV rays from the sun and chemicals from smoking," said lead researcher Reuben Harris, a professor of biochemistry, molecular biology and biophysics based in the College of Biological Sciences.

For the current study, Harris, along with colleagues Michael Burns and Alpay Temiz, analysed tumour samples from 19 different types of cancer for the presence of APOBEC3B and 10 related proteins.
Results showed that APOBEC3B alone was significantly elevated in six types (bladder, cervix, two forms of lung cancer, head & neck, and breast). Levels of the enzyme, which is present in low levels in most healthy tissues, were elevated in several other types of cancer as well.
A second key finding was that the mutational signature of APOBEC3B is a close match to the actual mutation pattern in these cancers.

"Much like we each have unique written signatures, these enzymes each leave a unique mark," Harris said.

Findings from both studies are counterintuitive because the enzyme, which is produced by the immune system, is supposed to protect cells from HIV and other viruses, not harm our own genomic DNA.
While it's well known that sunlight and chemical carcinogens can mutate DNA, and that mutations are essential for cancer to develop, Harris is the first to discover that this human enzyme is a major cause mutation in cancer.
He believes that APOBEC3B is a biological "double-edged sword" that protects some cells from viruses such as HIV and produces mutations that give rise to cancer in others.

Harris hopes to find a way to block APOBEC3B from mutating DNA, just as sunscreen blocks mutations that lead to melanoma. It's also possible that a simple test for APOBEC3B could be used to detect cancer earlier.
The study was published in the journal Nature Genetics.