CANCER-CAUSING viruses undergo genetic changes as their host cells become malignant. The finding could allow doctors to predict when people infected with a virus will develop cancer, and possibly points to new treatments.
It is already known that cells turning cancerous accumulate chemical 鈥渃aps鈥�, called methyl groups, on crucial tumour-suppressor genes. These caps silence the genes, often speeding up the onset of cancer.
, an epigenetics researcher at the Bellvitge Institute for Biomedical Research in Barcelona, Spain, wondered whether similar methylations were taking place on viral genes as their host cells turned cancerous.
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To investigate, Esteller and his colleagues totted up the methylations on the entire genome of various types of cancer-causing virus. These included strains 16 and 18 of the human papilloma virus (HPV), which can cause cervical cancer, and hepatitis B virus, which can lead to liver tumours. They also looked for methylations in Epstein-Barr virus, which is associated with some types of lymphoma.
For each virus, the team obtained three sets of samples: from people who were carriers but had no cancer symptoms, from those who had precancerous lesions, and from people with full-blown cancer.
In all four viruses, the degree of methylation correlated with disease progression. One gene found in HPV-16, for example, was not methylated in any of 10 asymptomatic carriers, but was in 21 of 60 people with precancerous lesions, and 16 of 17 with cervical cancer (Genome Research, ). 鈥淲hen you start to get methylation, you start to get tumorigenesis,鈥� says Esteller.
鈥淲hen you start to get methylation on viral genes, you start to get cancer developing鈥�
He suggests that doctors could start monitoring the methylation status of these viruses in order to predict when the infection is progressing towards cancer.
, a cancer biologist at the University of California, Los Angeles, commends the work but points out that it doesn鈥檛 show whether viral methylation triggers cancer or is merely a by-product of the methlyation that occurs in already cancerous cells.
If methylation plays a causative role, demethylating agents 鈥� already part of the chemotherapy regime for some other cancers 鈥� could be used against virally induced tumours as well, says Esteller.