'Virus Chip' Detects New Virus in Prostate Tumors
UCSF and Cleveland Clinic scientists have discovered a new virus in human prostate tumors. The type of virus, closely related to viruses typically found in mice, has never been detected in humans. The virus's link to human disease is still unclear and more study is needed to determine the relationship between the virus and cancer, if any, the scientists say.
The discovery was made with the same DNA-hunting "virus chip" used to confirm the identity of the SARS virus three years ago.
While the genetics of prostate cancer are complex, one of the first genes implicated in the disease was RNASEL, a gene that serves as an important defense against viruses. Given the anti-viral role of this gene, some scientists have speculated that a virus could be involved in some types of prostate cancers in men with mutated RNASEL genes.
In the new study, the researchers discovered the novel virus far more often in human prostate tumors with two copies of the RNASEL gene mutation than in those with at least one normal copy.
"This is a virus that has never been seen in humans before," said Eric Klein, M.D., a collaborator in the research and head of urologic oncology at the Glickman Urologic Institute of Cleveland Clinic. "This is consistent with previous epidemiologic and genetic research that has suggested that prostate cancer may result from chronic inflammation, perhaps as a response to infection."
"The power of the virus chip resides in its ability to simultaneously screen for all viruses, without preconceptions or bias," said Joe DeRisi, Ph.D, a Howard Hughes Medical Institute (HHMI) investigator at UCSF who developed the chip with colleagues in his lab. "In the case of these prostate tissues, no one would have suspected a virus of this class." DeRisi is a UCSF associate professor of biochemistry and co-leader of the study with Don Ganem, M.D., also an HHMI investigator at UCSF and a professor of microbiology and immunology.
Klein reported the discovery today (Feb. 24) at the American Society of Clinical Oncology (ASCO) prostate symposium in San Francisco. A full report of the discovery is in press in the journal PLoS Pathogens.
The new finding further validates the strategy of using the virus chip to discover previously unknown viruses and potentially uncover new viral causes for disease, the researchers say. While most other virus identification techniques require researchers to look for only a small number of candidates, the virus chip represents an unbiased search, since all known viruses are tested simultaneously.
The study is part of an on-going effort launched two years ago by DeRisi and Ganem at UCSF, using the chip, or microarray, to search for new viruses associated with a wide range of human disease. So far, the chip has been used to search for novel viruses in about 300 cases of respiratory infections and about 50 cases of meningitis, as well as a dozen or more cases of severe encephalitis, and hepatitis and leukemia.
Because the virus was probably originally acquired from another species, it is known as a xenotropic retrovirus; in this case, a xenotropic murine-like retrovirus, or XMRV. This is not the first virus of this family to be discovered, but it appears to be the first one found in humans, the scientists report.
The new virus is 96 percent identical to a class of known endogenous mouse retroviruses