HPV is able to outsmart your immune system, in part because it’s so good at hiding.**Thanks to Brilliant for supporting this SciShow video! As a SciShow viewer, you can keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription at Brilliant.org/SciShow. If you’ve had the vaccine for human papillomavirus, you might know that it dramatically reduces your risk of certain cancers. What you might not know is how efficiently HPV has both our immune system and our cancer defenses figured out. While many versions of this virus are mostly harmless, some are actual biological supervillains. And like the best supervillains, they know how to hit the heroes where it hurts. It’s an almost perfect model of how badly our cells need their anti-cancer toolkit… and what happens when that toolkit is taken away. So let’s talk about what makes HPV such a unique entry in our biological rogues’ gallery.
[♪ INTRO] Cancer is when a person’s cells begin to multiply rapidly and uncontrollably, like a rebellion of certain cells against the body itself. But our cells have a whole host of checks to that rebellion, though. If cancer is uncontrolled cell division, it follows that cell division is normally controlled. We have many of these so-called tumor suppressors, genes that keep normal, healthy cell division chugging along. The most notable of these heroes are p53 and the retinoblastoma protein, or RB. p53 is basically the guardian of your genes. Its job is to patrol the nucleus of the cell, looking for any suspicious activity. This includes searching for damaged DNA, which can turn a cell cancerous. If p53 finds damaged DNA, it offers the cell a harsh ultimatum: either you get well again fast, or I’ll send you to the gallows! That is, p53 figures out which cells can be repaired, and which should be killed. It has the ability to temporarily suspend cell division and let the cell attempt to repair its DNA. If the repair is successful, p53 allows division to go ahead, but if not, p53 sends for proteins that will initiate programmed cell death instead.
The other key tumor suppressor we mentioned, the retinoblastoma protein, functions more like a general. That’s because RB is in charge of keeping the cell cycle chugging along at the perfect pace. The cell cycle is simply the multi-phase process by which cells divide, often represented sort of like a clock. RB prevents the cell from duplicating its DNA, which is the point of no return for the cell cycle. But once it receives enough signals from its lieutenants that everything is ok to go ahead, RB will allow other proteins to deactivate it, and cell division can go ahead. So when RB dishes out tight-fisted orders to its troops, it’s only to make sure the cells don’t replicate too fast and spin out of control, thereby becoming cancerous. And much like p53, if the cells don’t listen, RB can order them to be executed.
It’s hard to overstate how important these two microscopic heroes are to human beings, because over 50 percent of all human cancers feature a glitch in one or both of these proteins. Almost like Batman in Gotham and Superman in Metropolis, these tumor suppressors use different methods to watch over their domains and keep everyone safe. So, if you were trying to engineer a cancer, you’d have to find a way to get p53 and RB out of the way, right? Well, that brings us back to that villian HPV.
While there are many varieties of HPV, and many clear up quickly without causing serious problems, types 16 and 18 are the main cause of most cervical and certain throat cancers worldwide. HPV infiltrates the body through a tiny wound or abrasion. It then dives deep into the skin, and hijacks the nucleus of a stem cell living there. And then, like the worst AirBNB renter, it starts using the cell’s own equipment to replicate and spread copies of itself to neighboring cells. Now, normally, your immune system would be the first line of defense against a virus, but that’s where this virus gets especially nasty. HPV is able to outsmart your immune system, in part because it’s so good at hiding. HPV has developed a way to avoid the immune system by producing two proteins, E6 and E7, which can bind to healthy cellular proteins, including tumor suppressors, and turn them off. This allows cells to divide without limit and become cancerous. Fortunately, the CDC recommends a vaccine for young people and scientists are working on an mRNA vaccine to provide the immune system with instructions to fight HPV-tumor cells directly. To learn more about coding and giving instructions to a computer, check out Brilliant’s Programming with Python course. You can get a free trial and 20% off an annual premium subscription by using the link in the description.