Retroviruses: Can you catch cancer?
In daily life, most people talk about cancer as something you get from environmental factors, like smoking or living in an area contaminated by harmful chemicals, or alternatively as a disease that you get from unexplainable bad luck. However, new research is finding that many cancers are linked to viral infections. During infection, viruses like Hepatitis C and B, Herpes, Epstein-Barr (the same one that causes "Mono", or the "kissing disease" mononucleosis), and HPV (human papillomavirus) mess with human proteins that normally keep cell growth under control. In other words, the effect of infection isn't so much like pouring gasoline on a fire; it's more like removing the brakes in a car.
These are not the only viruses that are known to cause cancer in humans. In fact, one virus is actually named for its carcinogenic (cancer-causing) effects: Human T-lymphotropic virus (HTLV), a "cousin" of HIV. HTLV targets T-cells, similarly to HIV, and the result of infection is often leukemia or lymphoma, both cancers of the immune system.
HIV and HTLV are similar in yet another interesting way: they are both retroviruses. This means that the viral genome, or the sum of all its genes, is composed of RNA - and the virus makes DNA from this RNA during infections. Before we proceed, I want to highlight how incredible this fact is. Remember that our genome is made of DNA: all of our genes, like the genes of all other animals on the planet, are encoded in this "DNA language". Retroviruses like HTLV and HIV use a completely different language to write the library of genes that makes them what they are.
You might also remember that in a past MM, we talked about the central dogma of biology. This central dogma holds that DNA is 'transcribed' (a sort of translation from one type of biological molecule to another) into RNA. RNA is then respectively used as a blueprint to build protein, the machines that permit the dynamism of life. For many years, scientists thought that this was the only way that biological information flowed: from DNA, to RNA, to protein. Discovering that retroviruses send information the other way was like finding a river flowing up a mountain, against gravity.
Although HIV is by far the most famous retrovirus, HTLV was actually the first human-infecting retrovirus ever discovered. The same busy scientist, Robert Gallo, discovered both viruses within a few years. In a recent interview that took place in light of the rising rates of HTLV infection in Australia, Dr. Gallo commented that he hopes that more attention will be paid to HTLV in the coming years. He thinks that part of the reason more attention has been paid to HIV is because it is more infectious. This means that HIV is transmitted more efficiently that HTLV from one person to another in a given encounter. For instance, if you have unprotected sex with a person infected with HIV, you're more likely to end up with a retroviral infection than if you have unprotected sex with somebody infected with HTLV. However, despite its lower infectivity, HTLV is still causing high rates of cancer in heavily infected populations - and mostly in poorer populations who have trouble paying for good medical care - and so it definitely deserves some more scientific attention in the coming years.
The good news in all this? Firstly, HTLV, like HIV, is transmitted sexually and by sharing needles. This means that you can protect yourself against it by practicing the safest possible sex and drug use. Secondly, if you're a student looking for a topic for a research proposal, I've just served you one that sorely needs your attention on a silver platter.
Until next week -