Clearly there can be many mutations in genes
that are involved in cell cycle controls.
There are lots of protein players,
proteins are coded for, by genes on the DNA.
So any mutations could cause loss of cell cycle controls.
We put these sorts of genes into two categories.
There are oncogenes, and oncogenes are genes
that already existed just could cause cancer.
They could cause a gas pedal to be stucked down for example.
And if the gas pedal is stucked,
then there's a potential for that cell to become cancerous.
Proto-oncogenes are genes that we know about,
they are not cancer causing presently,
but they could acquire mutation that causes them
to become a cancerous gene as in p53.
If p53 has a broken gene, we have a non functional protein,
and that results in no checks and balances on the cell cycles
so it's a proto-oncogene. It didn't come into existence as
an oncogene but it could acquire a mutation during life.
So often these proto-oncogenes are things like
growth factors, the signal molecule.
Let's say the signal molecule binds
with more affinity to the receptor.
The receptor tyrosine kinase is always active,
the gas pedal is going to be stucked on.
Or it could be a receptor molecule. Maybe the receptor grabs too
tightly to the growth factor and won't let it go in appropriate time.
And so again, we could have a stucked gas pedal.
We also might see that any of the genes
in those signal transduction pathways could be affected.
Some of them are supposed to inhibit processes,
some of them are supposed to accelerate.
So again, broken genes on any of the proteins involved in these cascades
could result in cancerous cells or uncontrolled cell division.
So you can see that there are many many points
which we could have problems in the cell cycle.
And we're discovering more and more of these proteins,
especially now that we have the sequence of the human genome
we can explore what different pieces of that genome do,
and correlate them with cancer in individuals.
And so more and more and more. It's a very active area presently.
We're learning so much about what the causes of cancer are.
And perhaps in the future, we'll be able to move in
and change some of DNA sequences, so that we don't have
uncontrolled cell division, thus removing the cancer.
So really inspiring research going on in that area.
We explored p53 as a tumor suppressor gene,
and that is going to prevent proliferation of mutated cells.
Some tumor suppressor genes we see, we've discovered p53,
again that comes up in about fifty percent of cancers.
Whether we're talking about breast cancers
or colon cancers or brain cancers,
it's this single enzyme that seems to be broken
in a lot of those cases, not all of them.
Now the first tumor suppresor gene we identified was
the retinoblastoma susceptibility gene.
And if it's working properly,
it's going to suppress proliferation of mutated cells
but it leads to premature form of blindness in children
because the retina will divide uncontrollably.
The key about this is that it was just
the first tumor suppresor gene that we identified.
So caretaker genes would be genes like the p53,
it's taking care or making sure that everything's okay
so we call them caretaker genes.
BRCA 1 and BRCA 2 are examples of caretaker genes.
So because the caretaking is not happening
or not checking the DNA properly,
and so like the p53 issue , we'll have bad cells being allowed to
synthesize DNA, that's a bad copy of the DNA and so on and so forth.
Producing cells that divide uncontrollably and produce a tumor.
So BRCA1 and BRCA 2 involved in breast cancer
result from these broken caretaker genes,
in this case, it's not p53 but p53 would be a caretaker gene.
Then we have genes that we call gatekeeper genes.
So once we have cell division occuring,
there are other genes that produce proteins
that run around and check that everything is okay
to make sure that it's okay for those cells to continue growing.
Otherwise they will be destroyed so that they can
no longer go through synthesis and cell divisions.
So gatekeeper and caretaker genes, we now have basic understanding
of the sorts of proteins or sorts of roles that those genes have.
In the case that we arrive in life,
let's say we've got a hereditary form of cancer
we have a likelihood of having a cancer,
we come into life with one mutated copy of that gene.