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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.
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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.
See, HPV has developed a way to avoid the immune system
that just so happens to also turn cells cancerous.
Now, I know what you’re thinking: shouldn’t our tumor suppressors
come to rescue the cell from this highjacking?
Unfortunately, it’s not that simple.
Because like all movie villains, HPV has a secret weapon.
The virus starts to make two proteins, E6 and E7.
These goons loiter around the nucleus and the cytoplasm,
looking to cause trouble by binding to certain healthy cellular proteins.
They’re especially good at sticking to our tumor suppressors,
p53 and RB, and inactivating them.
So when they meet, our heroes are as powerless
against these proteins as Superman facing kryptonite.
To add insult to injury, E6 then turns on telomerase.
This little enzyme keeps the ends of our chromosomes
stocked with enough genetic material to constantly replicate.
So, with the body’s caped crusaders neutralized,
and cells able to ignore all damage and divide without limit,
the result is an astonishingly efficient route to cancer!
And the only thing that’s necessary is an extremely common virus.
But if that sounds terrifying to you, there’s still reason to be optimistic.
The CDC recommends that most young people get vaccinated in their
preteen years, before they’re likely to be
exposed to sexually transmitted infections.
And even if you never got the shot as a child,
scientists are working on another tool to give our bodies’ hard-working defenses
a hand: it’s an mRNA vaccine, like many of us got for COVID-19.
Instead of injecting a weakened version of HPV,
this type of shot actually provides the immune system with the instructions for
how to recognise E6 and E7, so the immune cells
can fight HPV-tumor cells directly.
Shutting down the virus’s key weapons gives your body the ability to
fight back against the malignant cells,
so it’s kind of like a cure for cancer in a handy shot.
Which is exactly the kind of strategy we need to fight a supervillain like HPV.
This SciShow video was supported by Brilliant.
Brilliant offers online courses in math, science, and computer science,
like their Programming with Python course.
After just 19 lessons, you’ll know how to give
instructions to a computer in a whole new language!
Kind of like how the HPV shot gives your body instructions
for how to fight E6 and E7 proteins.
And after taking this Brilliant course, you’ll have the tools to do so much more,
from coding video games to visualizing data.
To get started, head to Brilliant.org/SciShow
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And thank you for watching this SciShow video!
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