Robert Weinberg's The Biology of Cancer has a great chapter on the early history of cancer research and its connection with virology and a chance occurrence leading to discovery.
There was a chicken breeder who noticed that some of his birds were getting tumors and he brought them to Rous, who exposed healthy bird cells to an extract of the tumor. He was able to figure out that in this case cancer was being transmitted by a virus. Later analysis showed that the virus itself doesn't cause cancer, but that this particular strain was "lucky" and picked up an oncogene (basically took a normal tyrosine kinase gene that is involved in the cell cycle from a chicken and incorporated it into the virus, making cell replication more rapid).
This happens all the time with retroviruses in the wild. I find it interesting because the key to the virus' ability to cause tumors actually lies in using the normal cells' own machinery. Sort of like uncovering an ancient archeological site and decoding a text only to see it is about your civilization!
My claim is a bit of a stretch, 37% may be attributable. Mechanistic cause is still a bit shaky.
G C Buehring, H M Shen, H M Jensen, D L Jin, M Hudes, G Block. Exposure to Bovine Leukemia Virus Is Associated with Breast Cancer: A Case-Control Study. PLoS One. 2015 Sep 2;10(9):e0134304.
G C Buehring, H M Shen, H M Jensen, K Y Choi, D Sun, G Nuovo. Bovine leukemia virus DNA in human breast tissue. Emerg Infect Dis. 2014 May;20(5):772-82.
K Alibek, A Kakpenova, A Mussabekova, M Sypabekova, N Karatayeva. Role of viruses in the development of breast cancer. Infect Agent Cancer. 2013 Sep 2;8:32.
J Akhter, M A Ali Aziz, A Al Ajlan, A Tulbah, M Akhtar. Breast cancer: is there a viral connection? Adv Anat Pathol. 2014 Sep;21(5):373-81.
G C Buehring, S M Philpott, K Y Choi. Humans have antibodies reactive with Bovine leukemia virus. AIDS Res Hum Retroviruses. 2003 Dec;19(12):1105-13.
J S Lawson, B Heng. Viruses and breast cancer. Cancers (Basel). 2010 Apr 30;2(2):752-72.
(Author unknown) Bovine Leukosis Virus (BLV) on U.S. Dairy Operations, 2007.Veterinary ServicesCenters for Epidemiology and Animal Health. APHIS Info Sheet.
J F Ferrer, S J Kenyon, P Gupta. Milk of dairy cows frequently contains a leukemogenic virus. Science. 1981 Aug 28;213(4511):1014-6.
G C Buehring, P M Kramme, R D Schultz. Evidence for bovine leukemia virus in mammary epithelial cells of infected cows. Lab Invest. 1994 Sep;71(3):359-65.
A PLOS one paper showing evidence of this virus in 59% of breast cancers sampled compared to 29% in non cancerous breast tissue of other women. N size was 239.
I think this deserves future study to see why there is this apparent association but the above poster's claim that this shows that it 'causes 39% of breast cancer' is simply not credible at this time.
I didn't see anything in the article that referenced this, but why is the assumption being made that the virus acquired the genes from black widows and not the other way around?
This article by Ed Yong in The Atlantic contains the following paragraph about this [1]: It’s possible that the spiders got the latrotoxin gene from the virus, or that the two evolved their copies independently. But by comparing the various versions of latrotoxin, the Bordensteins think that it’s most likely that the virus got the gene from spiders. It certainly had the right opportunity, since Wolbachia, its host microbe, does indeed infect black widows. The phage could have picked up spider DNA directly from the creature’s own cells. Or Wolbachia could have picked up spider DNA and then transferred it to the phage. Or other as-yet-unidentified viruses and bacteria could have acted as intermediaries.
Unless the virus injected the gene into the black widows' gametes, the introduced gene would leave the spider population when that individual spider died. It's possible, but lowers the odds of an already unlikely process.
Meanwhile, viruses slurp up DNA from their hosts all the time.
For one thing, it's a lot easier and more common for the transfer to go in that direction. If you think about the life cycles and what would have to happen in each case, one is just a lot more likely than the other.
> The researchers think the virus uses latrotoxin to enter animal cells and reach the bacteria that it targets.
How would it do that? The phage can't synthesize latrotoxin itself, so it would need to instruct its bacterial host to produce it. Can bacteria even produce this toxin properly, with all proper post-translational modifications?
Secondly, how is it even obtaining the spider DNA when it infects the bacteria. I've heard of viruses packing extra nucleic acid from their hosts into their particulate forms when they replicate, but how does the spider DNA get into the bacteria so that this can happen?
Post translationally processing is done by the eukaryotic host cell. The section "Toxin activation by eukaryotic furin cleavage" has details - http://www.nature.com/articles/ncomms13155.
Evolution has some very interesting ways to increase chances of survival. Still most of the species that ever lived are extinct today. Those alive have beaten great odds.
Viruses are the enigma of evolution. Are they just chemicals, or living?
> Viruses are the enigma of evolution. Are they just chemicals, or living?
Biology is full of edge cases like this. For a few more examples, google "species problem". Human beings often like to classify things into discrete groups, but that doesn't necessarily map onto the natural world all that well.
I seem to recall this being the reason the sexual reproduction definition of species is considered problematic. It's a convenient definition for animals but breaks down for most other things, and even the animal kingdom has some funky edge cases, like the https://en.wikipedia.org/wiki/Zebroid.
There was a chicken breeder who noticed that some of his birds were getting tumors and he brought them to Rous, who exposed healthy bird cells to an extract of the tumor. He was able to figure out that in this case cancer was being transmitted by a virus. Later analysis showed that the virus itself doesn't cause cancer, but that this particular strain was "lucky" and picked up an oncogene (basically took a normal tyrosine kinase gene that is involved in the cell cycle from a chicken and incorporated it into the virus, making cell replication more rapid).
This happens all the time with retroviruses in the wild. I find it interesting because the key to the virus' ability to cause tumors actually lies in using the normal cells' own machinery. Sort of like uncovering an ancient archeological site and decoding a text only to see it is about your civilization!