EXAM2_L23_L24_Cancer_Biology_Genetics_of_Cancer Flashcards
What is Cancer?
- Genetic Disease (hereditary or spontaneous)
- Result from accumulation of somatic mutations clustered in one cell
- Loss of cell cycle control (g1,s,g2,m)> uncontrolled proliferation
- All cancer due to mutations passed to other cells
- Multi-factorial disease
What are the 1st and 2nd most common cause of death in the USA?
Who is at risk for cancer?
1st- Cardiovascular Disease
2nd- Cancer
OLD PEOPLE
- family history of cancer (10-20% due to inheriting alleles that predispose individual to cancer)
- Men
- individuals from developed countries due to environment
What are the 4 Classes of Tumors?
Where are each derived from?
Which one is most common?
- CARCINOMA (epithelial cells)- 90% malignant tumors
- lung, prostate, breast, skin, colon - SARCOMA (supporting- CT, BV,Fat, Muscle, Bone) 1%
- LYMPHOMA (Immune system cells) solid mass blood cells
- LEUKEMIA (blood-forming tissues-lymph & bone marrow)
- large proliferation of malignant blood cells in bloodstream
What are the 4 major causes of cancer?
- Chemical
- Viruses (HPV)
- Genetic Factors (protooncogenes->oncogenes)
- Point mutations: RAS
- Gene amplification: MYC
- Gene rearrangeent: Burkitt’s lymphoma/philadelphia
chromosome
- Tumor suppressor genes: TP53 & Rb
- Inherited mutations/alleles: (TP53,RB,DNA repair genes) - Obesity
How common is it for humans to get cancer due to exposure to carcinogens?
What are some examples?
How do carcinogens work?
80% of Cancers due to exposure to carcinogens!
- ie:
- UVB- distorts DNA structure
- X/Gamma rays- dsDNA breaks
- Chemicals that interact directly w/ DNA
Tumor Initiators vs Tumor Promoters (examples?)
What will cause cancer?
Initiators are mutagenic (damage DNA)
Promoters stimulate cell proliferation of initiated cells
-repeated exposure of promoter w/ initator will cause cancer
promoter ex: infection, alcohol, drugs, smoke inflammation
Tumor viruses how common? What seen in RNA viruses? What seen in DNA viruses? ex of DNA virus?
15% caused by viruses
-Viral (RNA/DNA) into host genome
RNA- inhibits regulation of cell cycle, apoptosis, and signaling pathways
DNA-inhibit tumor suppressor genes (TP53>p53) & RB
-HPV (DNA virus)> Cervical Cancer
HPV one-two punch
What two proteins does HPV encode?
What do each inhibit?
E6 & E7 inhibit DNA damage control mechanisms
- E6 binds P53 (p53 destroyed)- inhibits STOP of cell cycle and inhibits apoptosis
- E7 binds Rb- (Rb can’t bind/inhibit E2F to STOP at restriction point of G1)
EF2 is FREE to go into S phase and Duplicate DNA
HPV Vaccine? Generic name? What is it? What is it made of? How does it work?
Recombinant HPV Quadrivalent Vaccine: Gardasil
- Vaccine is the “coat proteins” of (HPV16,18-cervical cancer) and (HPV6,11- genital warts)
- immune system will illicit response if encounters real HPV
Genetic Mutations: what types?
Where mostly found?
what two types of genes affected by mutations?
- inherited or spontaneous
- DNA repair enzymes or signal transduction pathway proteins
1. Proto-oncogenes
2. Tumor suppressor genes
Proto-oncogenes & onchogenes
How do proto-oncogenes become oncogenes?
3 ways
proto-oncogenes = normal function
- oncogenes function when they shouldn’t
- gain of function mutations
- point mutation (altered product)
- Amplification (gene overexpression)
- Gene arrangement/translocation
Proto-oncogenes converted to oncogenes:
POINT MUTATIONS:
Point mutation converts proto-oncogene to oncogene
- RAS is stuck ON/ACTIVE (lost ability to take GTP>GDP)
- 1/3 human tumors RAS is converted to oncogene
Proto-oncogenes converted to oncogenes:
GENE AMPLIFICATION:
-DNA replication error increases # gene copies of a TF in a chromosome:
- MYC gene amplified on chromosome
- MYC mRNA transcripts increased
- MYC proteins behave as oncogenes in abnormally large amounts
- NO MUTATION-JUST TOO MUCH OF A GOOD THING
- MYC is an early response TF gene induced when cell gets signal to divide
Proto-oncogenes converted to oncogenes:
GENE ARRANGEMENT
(amplification of MYC due to rearrangement):
What happens?
What is a type of cancer resulting from MYC gene arrangement?
What happens and where?
MYC gene of chromosome is rearranged onto a more active promoter
- BURKITT’s LYMPHOMA t(8;14):
- Translocation of proto-oncogene MYC on Chromosome 8 to highly active promoter on 14.
-EXCESS MYC PROTEIN acts as oncogene
Proto-oncogenes converted to oncogenes: GENE ARRANGEMENT (Translocation of a gene):
Where is translocation? between what chromosomes?
What is the short chromosome called?
Where is it found? How common is it found there?
What is the Fusion Gene created?
What is the oncogene?
t(9;22)
translocation between chromosomes 9 & 22
chrm 22 is SHORT called “PHILADELPHIA” chrmsm
-Found in 95% of chronic Myelogenous leukemia (CML)
BCR-ABL FUSION GENE- (abl(9) fuses to bcr(22))
—FUSION PROTEIN IS ONCOGENIC
MITOGENIC PATHWAY CORRUPTION:
What three points of receptor-tyrosine kinase signaling can become overactive as a result of oncogene mutations?
What will increase in signaling of these three things ultimately increase? What will be the result?
- RTK
- RAS GTPase
- Transcription factor MYC
Increase CYCLIN D- > Allows cells to cross restriction point
RTK
Two types that are OUT OF CONTROL!
Receptor Tyrosine Kinases
Truncated RTK- continuously send growth signal w/o ligand
Amplified RTK- HYPER signal w/ small amounts of ligand
What two types of genes do mutations affect?
- Proto-oncogenes
2. Tumor suppressor Genes
Loss of Function Mutations
TSG= Tumor suppressor Gene
TWO Examples of TSG’s
Mutated TSG are DEACTIVATED
-lose normal function of STOPPING cell cycle
- TP53 (encodes p53) “guardian of the genome”
- – Key in DNA damage response
- Normal conditions (low p53)
- if DNA damage– STOP proteins and high p53 protein
- > 50% human tumors mutated/deleted tp53 gene!
What is normal and mutated function of p53
p53 normally STOPS cell cycle, DNA repair, apoptosis
Mutated- p53 inactive- NO DNA repair, apoptosis. Cant STOP cell cycle