week 18 p1 Flashcards
- What is oncogene
Oncogenes arise from gain-of-function mutations which over-activate genes involved in cell proliferation
Mutated gene whose protein is produced in either higher quanity or altered manner to increase activity
What is protooncogene
• A proto-oncogene is the normal unmutated gene which regulates cell proliferation
- Who discovered SRC
In 1911 Peyton Rous identified the Rous Sarcoma Virus which could be transmitted between chickens causing cancer
- What is The discovery of src (retroviral transfer)
• In 1911 Peyton Rous identified the
Rous Sarcoma Virus which could be
transmitted between chickens
causing cancer.
• In 1941 he transformed normal
cells into tumour cells in culture by
infecting them with the virus
What happen in the 1960s
- In the 1960s everyone was working on RSV (Harry Rubin, Howard Temin, Peter Vogt and Hidesaburo and Teruko Hanafusa)
* They isolated RSV strains that did not transform cells- Other strains could transform but could not replicate themselves
- what did Tentin and the other disover about the gene
- one gene was responsible for the transforming capacity
- and that this was separate from the genes necessary for viral replication
- At the same time another group of scientists found out that the RSV genome was made of RNA not DNA (Crawford, Robinson, Duesberg)
What happened in 1970s
Molecular biology was invented
Temin continued his work using this technology and isolated reverse- transcriptase from RSV
Baltimore and his group simultaneouslyisolated it from another virus This explained how a virus (made of RNA) could integrate into a mammalian genome (made of DNA) becoming a provirus
what else occurred in 1970
This enabled some more ground-breaking scientists (Stehelin and Bishop)
to reverse transcribe the RSV genome and generate labelled probes to the src gene.
How did the SRC originality
avian cellular gene and was “stolen” by the RSV virus and turned into an oncogene by a viral promoter.
Un-mutated chicken src was called a proto-oncogene
How is SRC oncogene is derived from the host genome
- Virus is uncoated on the entry in the host cell
- Reverse transcriptase make DNA copy of the vital genome in the host cell
- Second strand of DNA is made by copying the first
- Viral DNA is integrated into the host chromosomes
- Viral mRNA is transcribed
- Viral proteins are are produced if the retrovirus has been picked up by the mamelian gene, this mean that oncoproteins will be also be produced
- Viral particles are assembled
How does Oncogenes and human cancer
- Retroviral activation of proto-oncogenes is associated with many animal tumours
- However, very few retroviruses are involved in human cancers
- Human tumours contain activated oncogenes without the viral intermediary
what was the discovery of RAS (mammalian cell transfection)
- • Begins with viruses in the 60s again:
* •Lather it became possible to transfect DNA into mammalian cells without viral vectors.
what is DNA transfection assay
• DNA from tumour cell lines collected
• Transfected into mouse cultured cells
• Transformed cells identified by increased growth and loss of contact inhibition
• Transformed cells produce tumours in athymic (nude)
mice
how was Multiple RAS genes exist
Between 1981 and 1984 the human homologues
What are the different Ras
• HRAS was discovered in DNA from the EJ/T24
bladder carcinoma line
• KRAS was discovered in DNA from lung and colon cancers
• NRAS was discovered in DNA from Neuroblastomas
what is Reciprocal translocation in ph chromoskmes
A reciprocal translocation between
Chromosomes 9 and 22
t(9;22)(q34;q11)
• The translocation affects an gene called
ABL on Chr9
• fusing it to the BCR gene on
Chr22.
• The BCR-ABL fusion functions as an
oncogenewhat is MYC (oncogenic amplification)
Double minute chromosomes are “small
chromatin bodies whose origin and
function are uncertain”
• In neuroblastoma (up to 80%) they exist
in multiple copies and contain the gene
N-MYC
What is IDH1 (Next Generation DNA Sequencing)
• Discovered by sequencing 20,661 protein coding genes 22 human glioblastoma (GBS) tumour samples. • In 5 of the tumours they identified a mutated gene not previously known to be mutated in (GBS) – IDH1 • All 5 tumours had the same point mutation • IDH1 has subsequently been found to be mutated in many types of glioma, colon cancer, and AML
- What are Other oncogenes identified by Next Generation DNA Sequencing
The study involving IDH1 took around 3 years – compare that
with >60 for SRC
• Almost all future Oncogenes are likely to be discovered this
way
• Systematic sequencing of cancer genomes is now underway in
may laboratories eg
The Cancer Genome Project
Genomics England, 100,000 genomes project
Other oncogenes found this way include: IDH2, EZH2, and there
will be many more
what is the function of proto-oncogenes
Self sufficient in growth signals
- How does protooncogenes play an role in signal transduction
- Extracellular: growth factors and receptors
- Cytoplasmic: signal transduction
- Nuclear: signal transcription back to cytoplasm
- Signal translation
What are the Growth factor proto-oncogen
• Molecules that stimulate cells to enter the cell cycle
e.g a hormone or vitamin
Oncogenic activation of receptor tyrosine kinases occurs through spefic mutations that leads to tyrosine activation
• Platelet-derived growth factor - (PDGF) - Sarcoma
• Fibroblast growth factor 1-7 - (FGF1-7) Breast Cancer
• Insulin-like growth factor 1-2 - (IGF1-2) - Wilms tumour
• Transforming growth factor - (TGF) a and b -Breast
Cancer
What does growth factor interact with
receptors -receptor tyrosine kinases
what is an example that could occur in Signal transducers
• Eg SRC • non-receptor tyrosine kinase • Associates with activated receptors • These include EGFR and PDGFR\ • It becomes phosphorylated which • activates its own kinase domain It phosphorylates downstream pathways involved in cell proliferation, survival, motility, cell-cell adhesion
demonstrate how KRAS is also e.g. of signal transduction
- Has Small GTPase
- Activated by EGFR receptor
- This leads to GDP molecules on KRAS being replaced by GTP
- KRAS is now active.
- It recruits RAF proteins and activates them so they
- phosphorylate MEK
- Yellow( red circfles in the diagram) highlighted is oncogenes
- Pink (green circle in the diagram )highlight is tumour suppressor gene
How does BRAF I in signal transduction occurs
• Serine threonine kinase
• Activated by GTP-KRAS
• Phosphorylates downstream
kinases MEK and ERK
Give e.g. of transcription factors
• c-MYC
• bind directly to DNA usually at promoters
• Each transcription factor as a specific recognition sequence
• MYC binds at an E Box
• They have multiple target genes
• They often have binding partners (eg MYC and MAX)
• They can activate or repress transcription depending on binding partners, tissue type, context
c-MYC is amplified in Burkitts lymphoma, B-CLL
how is c-JUN an e.g. of transcription factor
• Encodes part of the AP-1 transcription factor
• One binding partner is FOS (another oncogene)
• JUN is overexpressed in multiple cancer types including breast,
skin and liver.
• Overexpression is often caused by gene amplification
how is Activation in human tumours happen
- Activated cellular oncogenes have a DOMINANT gain-of-
- function effect
- Only one allele needs to be mutated.
- (as opposed to the recessive tumour suppressor genes, here both alleles must be mutated
How is oncogene activated
• Genetic mutation resulting in increased expression or stability: Point mutation, Chromosomal translocation
• Amplification: Many copies of the oncogene
Deregulated expression: Normal number of copies of the oncogene, but with abnormal increased expression
how does KRAS cause Genetic mutation (point mutation)
KRAS (lung, colon, pancreas, skin etc)
• KRAS (and NRAS and HRAS) is typically activated by a point
mutation at one of three codons: 12, 13 or 61.
• The position and sequence of the mutation varies between
tissue types and can have therapeutic implications • Mutation at these sites causes a structural alteration which
favours GTP binding causing constitutive activation.
ow can EGFR cause Genetic mutation (point mutation)
• EGFR (multiple cancer types)
• Missense mutations in the ATP binding domain cause over-
activation of the kinase.
how can FGFR3 ECD cause genetic mutation (point mutation) ( uterine cancer)
- specific amino acid substitutions that promote receptor dimerization
- g FGFR3 S249C results in unpaired cysteine residues,
- Allowing abnormal receptor dimerization through intermolecular disulphide bonding .
how does BCR-ABL cause Genetic mutation (translocation)
• c-ABL is a non-receptor tyrosine kinase, a signal transduction protein
• It is normally tightly regulated
• BRC has serine/threonine kinase activity. It’s function
is still not clear.
• The fusion protein has greatly increased kinase activity which
activates multiple known cancer pathways (RAS, AKT, JUN)
• It is also trapped in the cytoplasm preventing it from inducing
apoptosis, a normal function of ABL
how does MYCN (Neuroblastoma) promote Amplification
• Double minute chromosomes are small chromatin bodies
• They exist in multiple copies,sometimes >100 per cell
• Genes on DMs are expressed meaning that MYC expression
is increased in proportion with the number of DMs
how does HER2/ERBB2 (Breast cancer) promote amplification
- Also amplified on DMs
- Or amplified in tandem arrays
- These are detected as homogeneously staining regions (HSR)
how does cMYC (Burkitts lymphoma) cause Deregulation of expression (translocation)
A translocation between chromosome 8 and usually 14
• MYC expression is normal tightly regulated by sequences in the surrounding DNA
• The immunoglobulin (IgH) transcriptional enhancers and
promoters are highly and constitutively active
• On the translocated chromosome the IgH transcriptional
machinery drives high levels of MYC
• Continuous MYC drives continuous proliferation\
