New microarray technology has linked a previously unknown virus to prostate cancer, although the exact relation between the virus and prostate cancer is not yet clear.
The virus, tentatively named XMRV, is similar to leukaemia viruses that infect mice, but seems to infect only human beings. The lack of studies in animals will complicate efforts to determine the virus’ precise role in prostate cancer, says Eric Klein, (Cleveland Clinic, Cleveland, OH, USA) who reported the study at the American Society for Clinical Oncology Prostate Cancer Symposium (San Francisco, CA, USA; Feb 24–26, 2006).
“Identifying the agent does not imply you have identified causality”, cautions Joseph DeRisi (University of California, San Francisco, CA, USA). “Proving causality could take many more years.” DeRisi and colleagues created the virus chip used in the study. The same microarray was used to identify a new coronavirus that causes severe acute respiratory syndrome. Furthermore, the chip is a tool that can be used to investigate any disease of unknown aetiology, especially when the epidemiology of a disease suggests infection is a factor, says DeRisi.
Virus was seen in tissues from patients with prostate cancer who were homozygous for a single nucleotide polymorphism, known as R462Q, which codes for a variant, malfunctioning form of RNase L. These men are at substantially increased risk of prostate cancer. According to Klein, about 15% of the population have this variant. It is associated with about 13% of prostate cancer, he adds, making it the most common gene variant linked to any human cancer. The wildtype enzyme degrades single-stranded RNA in response to interferon or viral infection, preventing propagation of viruses once they have infected the cell, and triggering apoptosis in the host cell.
The chip contains several thousand conserved sequences from every virus known to infect plants, animals, and humans—a total of nearly 1000 viruses. Researchers use these sequences as probes to uncover previously unknown viruses in tissues.
The researchers are also attempting to identify other viruses in cancers—particularly those that occur in patients with compromised immune systems. These include AIDS-related lymphomas and skin cancers associated with solid-organ transplantation.