Question

In the case of Rous Sarcoma virus, how does the virus cause cancer? Towards the end of his career Rous was very influential in the scientific community and he personally drove the accepted wisdom of the time that all cancers have a viral origin. Was he correct? Why or why not?

Answer 1

In this case, it is important to mention that most of the genes of retroviruses are encoded in RNA and not DNA. But, in this particular case, the Ros Sarcoma Virus has a reverse transcriptase which is used as a DNA polymerase that takes the RNA as a template.

When the virus infects the host cell, the transcriptase will be able to produce more DNA copies of the virus genome. In fact, the DNA copies will enter the nucleus and they will insert in random segment of the chromosome.

Now, we have a cell that is able to produce a mRNA that comes from the virus and producing newly proteins on the host cell.

Which makes this virus oncogenic is one specific gene of its RNA, the src gene. This gene codes for a tyrosine kinase which is involved in a bunch of signaling pathways of cell proliferation. Once the gene is overexpressed in the host cell, it will start the cancer cells proliferation.

Now, the statement of Ros about that the origin of cancer having a viral origin could be incorrect. Of course, at that time It could be the more logic explanation. However, nowadays we know that our of genome could be generate cancer if in some point a specific mutation occurs in the moment and in the correct gene. Of course, there are some onco viruses that affects human, it is not so common. The cancer disease is a multifactorial disease, it depends on a bunch of things such as life style, stress, alimentation, habits and inheritance.