Xenotropic MuLV-related virus

Xenotropic MuLV-related virus (XMRV) is a newly identified and provisionally named gammaretrovirus which may be involved in the pathology of familial prostate cancer. Its name refers to its similarity to xenotropic murine leukemia viruses, although it does show some substantial differences. It is though to be linked to prostate cancer by ribonuclease L, part of the cell’s natural defense against viruses. When activated, RNase L destroys RNA in an effort to halt viral gene expression. R462Q is a mutation that results in a decreased level of RNase L function, and this mutation’s presence in prostate tumors shows a strong correlation with the presence of XMRV.

The virus was discovered in cancerous prostate tissues using a microarray containing samples of genetic material from over 1000 viruses. The screen revealed the presence of a gammaretrovirus in a substantial number of the homozygous R462Q cells, but very few of the heterozygous or wild type cells. An expanded screen showed the virus present in 40% of men homozygous for R462Q and only 1.5% of those not, and also demonstrated that each case showed the same virus. In another study, the viral genome was reconstructed from prostate mRNA and used to infect prostate tissues in vitro. The researchers were able to show that RNase L deficient lines were more susceptible to infection. These data do not necessarily show that XMRV causes prostate cancer, but they do show that RNase L deficiency makes prostate tissue more susceptible to the virus. This in turn suggests the possibility of a link between the virus and the disease.