Genomes-L6- Cancer genomics, epigenomics and implications for treatment

what are oncogenes- what do they do when mutated to proteins and the promotors?

a gain of function mutant for proteins:

• mutate coding sequence

• promotor- enhance expression of protein

• enhance stability of protein- doesn’t degrade at fast- proteins re usually degraded after use by phosphorylation or uiquitation

example of oncogene

epidermal growth factor 2-HER2/ERB2-oncogene amplified in breast cancer

discuss P53 and how it works in relation to before DNA damage and after DNA damage

normal:no DNA damage

• p53 always made but little detected as when its made its tagged with ubiquitin

• ubiquitin- marks proteins for degradation by proteasome

• p53- short half life

DNA damage:8 hours later

• p53 increases as it is PROTECTED from degradation

• DNA damage activates kinases ATM- which phosphorylated P53- no ubiquitin

• p53 is sta

how are proteins altered?

1. increase expression

2. alter amino acid and stop it from being targeted by ubiquitination- no degradation

3. mutation at active site- more open

transformed cell features

1. Can live in cultures

2. Disorganised anchorage independent

3. Contact inhibition

4. And form tumours when injected into mice

5. Disobey Hayflick limit- don’t stop dividing after 30-35

what is cellular transformation assay?

• DNA packaged into a plasmid with 1 gene

• introduce this to normal cells and look for transformed cell

to look at which gene can cause tranformation- an oncogene

what did Peyton Rous discover?

that viruses can cause tumours- discovered oncogenes

• took a chicken breast sarcoma and chopped it and filtered it

• injected into healthy tissues- transformed cells in a tissue

• caused by a virus- RSV virus

how did RSV cause cancer- what gene was discovered and how?

• viruses have small genomes and makes it easy too see which gene caused transformation

• in RSV- discovered a gene called SRC- first oncogene

• researchers discovered SRC is similar to a normal chicken gene- was hijacked

• SRC sits close to genome region- to carry host genomes and the virus and have it selected for- integrate genome

why do viruses want to trigger cell division? what do they target?

• viruses want to integrate their genome into ours

• must open the nuclear envelope to do so- a barrier

• cell division- nuclear envelope breaks down and allows virus in

target proteins proteins that regulate cell division to allow it to divide and break down nuclear envelope and allow viral genome in

what human virus can cause cancer?

papillomavirus HPV causes cervical cancer by triggering cell division

explain the Ras/Raf signalling pathway

1. epidermal GF- binds to ligand- 2 receptors come together and phosphorylates the tail

2. binding site for downstream proteins- Grb2 and Sos

3. sos- GTP/GDP exchange factor- for Ras and Raf

4. GDP bound Ras, GTP bound-Raf

5. GTP bound Raf is a kinase and phosphorylates proteins(cascade) to allow cell division cycle to happen

why is the Ras/Raf pathway tightly regulated?

• to prevent uncontrolled cell division- in normal cells the cell would be killed if dividing without the normal signals

how did complex pathways evolve? and why are they so complex?

• step by step through random mutations that were selected for

• system isn’t perfect- but complex

• multiple steps gives many control points through:

• 1)molecules can regulate Ras, 2)feedback loops and 3)one mutation won’t break the system- robustness

what is mutant Ras found and what happens to it? does it cause cancer alone?

• found in 30% of cancers

• usually around GTP binding pocket

• causes it to be bound to TTP for longer and remain ON

doesn’t cause cancer alone as cell apoptosis still in place- increases PROBABILITY

what is B-raf? what happens when it is mutated?

• family of Raf proteins- A,B, C types

• important in SKIN cells

mutated form: position 600 in protein.

• valine at 600

• mutated to glutamic acid V600E mutation

  makes B-Raf 500 more times active than norma

why is B Raf a drug target?

B-Raf is a kinase- enzymes have catalytic pockets where they bind to atp

• drugs can fit into this catalytic site and BLOCK B-raf activity

what are targeted therapies for B-Raf?

Vemurafenib or Zelboraf

differences between chemotherapy and targeted therapy

• chemo: uses chemicals that destroy DNA and kill rapidly dividing cells - effect healthy and cancerous

• targetted- such as Zelboraf- specifically target mutations

what is a target therapy for breast cancer? what does it do? challenges?

• Herceptin- antibody neutralises receptors as too many are expressed

• shut down cells that have too much HERCEPTIN

challenges: when a lot of the tumour is killed- some new mutations arise and can escape effects such as amplifying Ras