week 18 p1

Question 1

1. What is oncogene

Answer 1

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

Question 2

What is protooncogene

Answer 2

• A proto-oncogene is the normal unmutated gene which regulates cell proliferation

Question 3

3. Who discovered SRC

Answer 3

In 1911 Peyton Rous identified the Rous Sarcoma Virus which could be transmitted between chickens causing cancer

Question 4

4. What is The discovery of src (retroviral transfer)

Answer 4

• 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

Question 5

What happen in the 1960s

Answer 5

• 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

Question 6

6. what did Tentin and the other disover about the gene

Answer 6

• 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)

Question 7

What happened in 1970s

Answer 7

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

Question 8

what else occurred in 1970

Answer 8

This enabled some more ground-breaking scientists (Stehelin and Bishop)

to reverse transcribe the RSV genome and generate labelled probes to the src gene.

Question 9

How did the SRC originality

Answer 9

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

Question 10

How is SRC oncogene is derived from the host genome

Answer 10

• 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

Question 11

How does Oncogenes and human cancer

Answer 11

• 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

Question 12

what was the discovery of RAS (mammalian cell transfection)

Answer 12

• • Begins with viruses in the 60s again:

* •Lather it became possible to transfect DNA into mammalian cells without viral vectors.

Question 13

what is DNA transfection assay

Answer 13

• 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

Question 14

how was Multiple RAS genes exist

Answer 14

Between 1981 and 1984 the human homologues

Question 15

What are the different Ras

Answer 15

• 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

Question 16

what is Reciprocal translocation in ph chromoskmes

Answer 16

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
      oncogene

Question 17

what is MYC (oncogenic amplification)

Answer 17

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

Question 18

What is IDH1 (Next Generation DNA Sequencing)

Answer 18

• 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

Question 19

17. What are Other oncogenes identified by Next Generation DNA Sequencing

Answer 19

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

Question 20

what is the function of proto-oncogenes

Answer 20

Self sufficient in growth signals

Question 21

19. How does protooncogenes play an role in signal transduction

Answer 21

• Extracellular: growth factors and receptors
  
  • Cytoplasmic: signal transduction
  • Nuclear: signal transcription back to cytoplasm
  • Signal translation

Question 22

What are the Growth factor proto-oncogen

Answer 22

• 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

Question 23

What does growth factor interact with

Answer 23

receptors -receptor tyrosine kinases

Question 24

what is an example that could occur in Signal transducers

Answer 24

• 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

Question 25

demonstrate how KRAS is also e.g. of signal transduction

Answer 25

* 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

Question 26

How does BRAF I in signal transduction occurs

Answer 26

• Serine threonine kinase • Activated by GTP-KRAS • Phosphorylates downstream kinases MEK and ERK

Question 27

Give e.g. of transcription factors

Answer 27

• 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

Question 28

how is c-JUN an e.g. of transcription factor

Answer 28

• 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

Question 29

how is Activation in human tumours happen

Answer 29

* 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

Question 30

How is oncogene activated

Answer 30

• 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

Question 31

how does KRAS cause Genetic mutation (point mutation)

Answer 31

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.

Question 32

ow can EGFR cause Genetic mutation (point mutation)

Answer 32

• EGFR (multiple cancer types) • Missense mutations in the ATP binding domain cause over- activation of the kinase.

Question 33

how can FGFR3 ECD cause genetic mutation (point mutation) ( uterine cancer)

Answer 33

* specific amino acid substitutions that promote receptor dimerization * g FGFR3 S249C results in unpaired cysteine residues, * Allowing abnormal receptor dimerization through intermolecular disulphide bonding .

Question 34

how does BCR-ABL cause Genetic mutation (translocation)

Answer 34

• 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

Question 35

how does MYCN (Neuroblastoma) promote Amplification

Answer 35

• 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

Question 36

how does HER2/ERBB2 (Breast cancer) promote amplification

Answer 36

* Also amplified on DMs * Or amplified in tandem arrays * These are detected as homogeneously staining regions (HSR)

Question 37

how does cMYC (Burkitts lymphoma) cause Deregulation of expression (translocation)

Answer 37

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\