Retroviruses like to cause cancer. Its kinda their shtick.
Sometimes the viruses themselves code for oncogenes.
Sometimes the retroviral promoters accidentally upregulate an innate oncogene (the cell doesnt know its supposed to stop replicating).
And sometimes a retrovirus accidentally plops down in the middle of an important regulatory gene, and thats how you get uncontrolled replication.
MLV, murine leukemia virus, is a retrovirus that causes… leukemia… in mice.
It has also been implicated in prostate cancer in humans. This is kinda weird (target is immune cells in mice, but prostate stromal/epithelial cells in humans?), but it would be GREAT news if it were true! Women have HPV shots now to help prevent cervical cancer, and guys could theoretically get MLV shots to prevent prostate cancer!
… Unfortunately, though MLV has been associated with prostate cancer in humans, causality hasnt been established.
And its still not established after this latest paper on the topic:
XMRV, xenotropic murine leukemia virus-related virus (for real), is what we call a virus that looks like MLV in humans.
These folks, pathologists, got some really nice images of prostate tumors, clearly staining positive for XMLV proteins. Super pictures, well controlled, its nice.
However, as a virologist, I have some issues with this paper.
1. They made an infectious molecular clone of XMLV. First of its kind. But they did very limited analysis of it, and basically just used it to create antibodies they would use for their pictures. They had a cell line that was permissive to XMLV infection, and one that was not, but were apparently uninterested in figuring out the receptor XMLV is using in humans. Knowing this would move their field forward, and give us an easy yes/no as to which human cells are susceptible to XMLV. If normal prostate stromal/epithelial cells dont have the receptor (maybe the receptor is only expressed after transformation), then we can shut this story down now. But they didnt look. What???
2. The images are just beautiful… but they dont look right. MLV has been shown to prefer cell-to-cell transmission. Yet several images in this paper had punctuated infection of cells– a scattering of infected cells, rather than clusters of infected cells. That makes me furrow my eyebrow. It aint right. Especially when we are talking about cancer. If MLV has transformed a cell, then the cancer is clonal, and every cell in the tumor should be making MLV proteins. But in these images, it isnt.
3. Their PCR is shit. For real. Their characterization of their real-time PCR reagents is great, but their reagents are still shit. There is no way that histology is more sensitive than real-time PCR, unless your primer/probes are crap and you need to move them. You cant believe any of the PCR data in this paper, because you know there are a ton of false negatives. *squint eyes* Boo.
This paper is fine, but we still dont know if XMLV can cause prostate cancer in humans.