00:01
Okay, this is just an example.
00:02
This is just an example of how proteasomes are important
and how diseases occur when we don't have the appropriate sequence of events.
00:11
So, how do we respond to hypoxia? Low oxygen levels.
00:15
We don't just give up and we don't try to find new oxygen.
00:18
We have cellular ways of responding. How does this happen?
Well, as you might expect, it involves proteasomes.
00:26
So, under normoxic conditions, that is to say 21% as we walk around,
we have regular levels of oxygen, and they interact with a protein factor called,
a transcription factor called HIF-1-alpha.
00:42
Hypoxia inducible factor one, that's what HIF stands for.
00:47
And with high levels or normal levels of oxygen,
we get hydroxylation of that protein, HIF-1-alpha,
and that OH is what you see on the next little one,
and we get a conformational change.
00:58
That conformational change under normal oxygen conditions
is recognized by another protein called Von Hippel-Lindau.
01:05
This is based after the doctor who discovered the disease
associated with the mutated form of this.
01:10
We'll peek back to that in a minute.
01:11
Anyway, Von Hippel-Lindau, that protein binds
to this now rearranged hydroxylated protein,
and targets it for ubiquitin linkage and degradation.
01:24
So, we get rid of the HIF-1-alpha transcription factor.
01:28
That's under normal hypoxic conditions,
so we don't get any signaling through that.
01:32
Perfect, that's when it's working properly.
01:35
And it does that by targeting HIF-1-alpha to the proteasome
and we get our little peptide fragments. Beauteous, nice job.
01:44
Now, under hypoxia, we don't have the normal oxygen levels,
so we don't get the proline hydroxylation.
01:52
And the HIF-1-alpha doesn't have that conformational change,
so Von Hippel-Lindau doesn't bind to it, the ubiquitin doesn't ligate to it,
and we don't target to the proteasomes,
so now the HIF-1-alpha in our bottom slide is present in high levels,
can get across the membrane, joining with its buddy, HIF-1-beta,
bind to hypoxia response elements, that's HRE,
and then we get transcription of proteins
that are going to be important for saving the cell under low oxygen conditions.
02:24
So, that includes changing metabolism from systems
that will utilize oxygen to anaerobic metabolism.
02:34
It also means that we will make more erythropoietin appropriately
so that we get more red blood cells.
02:41
That's an appropriate effect if we're feeling hypoxic.
02:44
It also means that we will induce new blood vessel formation.
02:47
So, there are a variety of effects that happen
when we get HIF-1-alpha getting across into the nucleus
because it didn't undergo that modification.
02:55
Okay, so that's the way it's supposed to work.
02:58
Now, let's mutate it. Let's do what Dr. Von Hippel-Lindau
did when he kind of discovered this disease.