Transcript The Discovery of Oncogenes

The Discovery of
Oncogenes
张雪、赵颖慧、刘席文
• The discovery of Reverse transcriptase
• Experiment about the discover of src
• Src gene &something about human
oncogene
The discovery of
reverse transcript
History
In 1911 Peyton Rous
a paper less than one page in length
chicken sarcoma
Propagated from one hen to another
By a “filterable virus”
Experiment
Remove the tumor(瘤组织)
→ground→centrifuged
→remove the supernatant
→through filter(滤器)
→inject into recipient hen
Found that a significant percentage of the
injected animals developed the tumor.
1960s
The virus discovered by Rous is an RNAcontaining virus
It could be seen within the tumor cells and
also budding from the cell surface
Figure 1
It transmitted through the fertilized egg from
mother to offspring
These provided evidence that the viral
genome can be inherited through the gametes
Cell to cell
Without having any obvious effect on the
behavior of the cell
Questions
One of the major questions concerning the
vertical transmission of RNA tumor was
whether the viral genome is passed from
parents to progeny(子孙)as
• Free RNA molecules
• Integrated(整合) into the DNA of the host
cell
But
Require the synthesis of DNA
• Howard Temin suggested
tumor viruses occurs by means of a DNA
intermediate-a provirus-a template
• But need a enzyme
In 1970 the enzyme was discovered
After that
• A experiment suggesting that it was part of
the virion itself and not an enzyme donated
by the host cell.
• And the viral RNA was providing the
template for synthesis of a DNA copy.
Overturn
Information in a cell always flowed
from DNA
to RNA
to protein
That is
• Reverse transctiptase(逆转录)
Experiment about
the discover of src
During the 1970
• Genes carried by tumor viruses
Responsible for transformation & the
mechanism of action of the gene products.
• Mutant strain of viruses
retained the ability to grow in host cells,
but unable to transform the cell into
malignant properties.
Thus
The capacity to transform a cell resided in a
restricted portion of the viral genome.
So
The researchers began by isolating mutant
strains of the avian sarcoma virus(ASV)
First
• Deletions of 10 to 20 percent of the genome
that render the virus Unable to induce
sarcomas or to transform fibroblast in
culture
The gene which is missing in these mutant
referred to as src
Second
• The reseachers use the RNA from the
genomes of complete virions was used as
template for the formation of a
radioactively labeled ,single-stranded
complementary (cDNA).Then use the
labeled cDNA fragment hybridized to
RNA obtained from one of the deletion
mutant
• Those DNA fragment that failed to
hybridize to the RNA represent of the
genome that had been deleted from the
transformation-defective mutant
• Thus Presumed to contain the gene required
by the virus to cause transformation.
• Once isolated labeled cDNA hybridizes to
DNA extracted from cells of avian species
contain DNA sequence that is closely
related to src
Find
• That a gene carried by a tumor virus that
cause cell transformation is actully present
in the DNA of normol genome.
• So the result indicated that the viral
genome are not true viral genes
• But rather are cellular genes that were
picked up by RNA tumor viruses during a
previous infection.
• 反转录RNA病毒感染宿主细胞将
病毒RNA反转录成双链DNA，
然后在细胞原癌基因旁整合。病
毒成熟前，病毒DNA转录成
RNA同时原癌基因也转录下来，
后经突变成为病毒RNA一部分。
Conclusion
• The src sequence is present in all of the
avian species and the sequence has been
conserved during avian evolution.
• So the src gene is not only present in the
RNA of the ASV genome but also in the
genome of the chicken cells.
Question
• What is the Function of src gene product
• How does src alter the behavior of normal
cell that already possesses a copy of the
cellular gene
Scr gene
&
something about
human oncogene
Then
• Precipitation the RSV-antibodies
• Synthesis of the protein using the isolated viral
gene as a template
Immunoprecipitation
find src codes for an enzyme that possesses protein
kinase activity.
Antibodies localized on the inner surface of the
plasma membrane.
Src gene product in this part of the cell.
These were the first studies to elucidate(解释) the
function of an oncogene.
Through the experiment found
The viral version of the gene may induce transformation
because it functions at a higher level of activity than the cellular
version.
Cellular genes could be converted into oncogenes in two
different ways:
1.Incorporated into the genome of a virus
2.By carcinogenic chemicals
In1981
• Attention turned to human cancer
• Once the transforming gene from human bladder
cancer cells had been isolated and cloned.
• In the same human genes-RAS-can cause a wide
range of different tumors.
• RAS gene that leads to its activation as an
oncogene.
• The change of amino acid lead the change of the
protein.
• RAS gene is a proto-oncogene that, like
SRC, can be activated by linkage to a viral
promoter.
• RAS induce by two way:
1.increasing its expression
2.altering the amino acid sequence of its
encode polypeptide.
The research led to the realization
• The oncogene is a celluar sequence that is
acquired by the virus
• An oncogene can cause cancer without the
involvement of a viral genome.
We hope that a method would be
found to cure cancer completely !!