cancer bio final review daniel
Which stage does EMT occur?
gives cell migration ability, occurs before intravasation (before entering bloodstream)
What happens in CML?
granulocytes over-proliferate and eventually blast cells take over the blood
How does p53 carry out its function?
high expression of p53 induced by stress, transcription factor that enhances the expression of other proteins that slow down the cell cycle to let it carry out DNA repair or induce apoptosis
Stages of CML
1. Chronic Stage: elevated WBC counts, less that 10% of cells are blast cells 2. Accelerated Stage: less than 20% of blood cell counts are blast cells (start noticing symptoms) 3. Blast Crisis: more than 20% of cells in the blood are immature granulocytes
Evidence for Multistep Hypothesis
7 pieces of evidence that show carcinogenesis is a multistep process
How is telomerase related to cancer?
All immortalized cells must turn on telomerase
Drug used to treat targeted therapy of CML in Gleevec-resistant CML patients?
Dasatinib
Bic/Bim?
Antagonizes BCL-2 interaction with these two proteins
What is the difference between apoptosis and necrosis?
Apoptosis is shrinking, Necrosis is swelling
What does Bcl2 do in apoptosis?
BCL inhibits the release of cytochrome C from mitochondria by binding Bax and Bak to block pore formation in the mitochondrial membrane
What is the effect of this translocation
BCR region attaches to ABL region
What is the Ph chromosome
Balanced translocation of the Chr9 to Chr22
What did PLX 4032 target?
Braf^V600E
How do patients still develop resistance to Zelboraf?
Cancer upregulates PDGFR or co-opt N-Ras to do the job that B-RAF can't do. This is not the same mechanism of resistance to Gleevec. Resistance to Gleevec comes from the upregulation of BCR-ABL or a mutation on it.
What do we call it when the telomeres have run out?
Crisis or Hayflick limit
What's the only cyclin affected by external factors?
Cyclin D
Why would the body use apoptosis?
Cyto-T Cells, control cell amounts, get rid of old cells, kill mutating ones
How do oncoproteins from DNA tumor viruses interact with Rb proteins?
E1A, E7, and large T-antigen bind to Rb protein and block the Rb protein function
Tissue invasion and metastasis
EMT/MET thing,
What is it not necessarily true that mutating a gene was enough to cause tumors? (Mice)
Gene mutations were tested in immortalized strains or immortalized residue injected into mice
Drug used for targeted therapy of CML?
Gleevec (imatinib), Gleevec is a tyrosine kinase inhibitor, 98% complete response, most patients last for years but drug resistance develops in 10-15% of patients
Resistance difference between Gleevec and Zelboraf?
Gleevec - resistance comes from upregulation of BCR-ABL or a mutation on it Zelboraf - regulation of PDGFR or makes N-ras do the job B-Raf can't do
What does Cyclin D need to start?
Growth factors, EGF ***
How is the function of the Rb protein (to bind to the E2F transcription factor and preventing E2F from binding to DNA) regulated?
Hypo before R point binds E2F Hyper releases E2F
What proteins are responsible for the hyperphosphorylation and hypophosphorylation of Rb?
Hypo: Cyclin D and CDK4/6 Hyper: Cyclin E and CDK2
What do mice studies tell us about immortalized cells?
Immortalized cells have already taken steps to become tumors
What dual roles does overexpression of myc play in regulating cell number?
It stimulates both proliferation and apoptosis
Cancer is more common in older people, what does this signify?
It takes time for mutations to occur
LOH
Loss of heterozygosity, you lose the wild type, you cant lose heterozygosity twice
What can circumvent these anti-growth signals?
Mitogens ***
What occurs in 60% of these patients?
Mutation in the B-raf signaling molecule so that it is constitutively active. The name is because at the 600th V is swapped with E.
Are apoptosis and necrosis caused by the same thing?
No, apoptosis is controlled by the cell, necrosis is due to external factors.
Does the cycle need any other inputs after Cyclin D levels are sufficient?
No, everything is automatic afterwards. It is automatic because you don't want to stop it because it is a waste of energy.
For someone with a familial inheritance allele, how do they get the other defective Rb allele?
Over the course of the cell cycle, something can happen to screw up the Rb gene to create a defective Rb allele
Blast cell?
Partially differentiated stem cell; white blood cell pre-cursor, myeloblast
Most common cause of CML
Ph chromosome
What about if a person has a gene that makes them susceptible to polyps (lots of polyps)?
THey are more likely to develop cancer because they are further ahead on the clock
Stem cells have infinite replicative potential. Why?
Telomerase (enzyme)
What do our statistical/quantitative models show us about cancer?
There are about 4-7 mutations necessary in order to start tumorigenesis.
What do we see when we gene sequence tumors at different points in time?
There are more mutations in older tumors
What happens to cells in crisis?
They do not divide anymore and die slowly
What significantly increases a person's chance of developing the Rb tumor?
They need to have 2 copies (homozygous) for the mutant Rb allele.
Sustained angiogenesis
Tumor begins producing VEGF which tells nearby blood vessels to start forming new ones around the tumor, prevent blood vessel degradation.
Metastatic Melanoma?
Tumors arising from skin pigment cells, melanocytes are mutated
How long does Rb stay hyperphosphorylated for?
Until the end of mitosis
How was PLX4032 more effective than Gleevec?
distinguished between wild type and mutated cells and more effective than Gleevec
Does a polyp in the colon immediately turn into colon cancer?
We can see morphological changes before it turns into a full blown tumor. Essentially there is a clock from when the polyp first forms to when it turns into a tumor.
How are inhibitors activated?
When DNA damage is detected p21 is sent out to stop the cyclin cycle after it starts.
When does p53 cause apoptosis?
When damage is severe enough, mdm2 will no longer be able to keep levels of p53 in check and a high enough concentration will initiate the apoptosis pathway; long term exposure to the stresses, inability to fix stress
When and how does Rb release E2F?
When the cell needs to move past the R point, it hyperphosphorylated Rb. It changes the shape. It OCCURS RIGHT AFTER R POINT. ***
If we remove the polyp do we "reset the clock"?
Yes
Was B-raf also inhibited by PLX 4032?
Yes, but at a 10X higher drug concentration.
Was PLX 4032 effective in treating metastatic melanoma?
Yes, but many resistances developed (60%)
Why is there such a long time between smoking your first cig and getting lung cancer?
Your body's natural repair system will fight it. It takes time for carcinogens to occur.
What is the function of the Rb protein?
bind to E2F transcription factor, prevent E2F from binding to DNA
How are levels of p15^INK48 protein controlled?
binding of TGF-beta to p15^INK48 increases the expression of p15^INK48
EDGFR
causes differentiation, survival, growth, more EDGFR = more ligand binds to more receptors
What maintains a balanced number of cells in a tissue?
cell proliferation, cell differentiation, apoptosis
What are morphological steps in apoptosis?
cell shrinkage, chromatin condensation, budding and phagocytosis
CML?
chronic myelogenous leukemia, cancer of the blood cells; lots of granulocytes, genetic alteration responsible is the chromosomal translocation (balanced) between chromosomes 9 and 22, which makes the Philadelphia Chromosome, oncogene produced is Bcr-abl
CML symptoms
death, pain under the ribs (due to enlarged spleen), weight loss, tiredness and fever
Insensitivity to anti-growth signals
delete the gene for the inhibitor, turn on an alternate pathway that the inhibitor doesn't target
How can the regulation of the cell cycle clock be disrupted (Rb)? Also these help the tumor to achieve insensitivity.
deletion of Rb gene, deletion of p15^INK48, overexpression of E2F, infection with HPV
How is a retinoblastoma developed?
deletion of the Rb gene on both chromosomes, 2 types familial and sporadic
Caspases
enzymes that cause apoptosis
Is a familial retinoblastoma or sporadic retinoblastoma more likely to get the disease first?
familial inheritance, because they only have one functional copy to start with
Bax/Bak do?
form pores on the mitochondria that release cytochrome C
transfecting oncogenes into different fibroblasts in mice
immortalized mose/rat = RAS gives transformed in culture and tumors primary mouse/rat = myc + ras gives transformed tumors immortalized human = ras gives transformed human = myc + ras gives no transformed
What does p15^INK48 do in Rb activity?
inhibits activity of CDK4/6, slows the hyperphosphorylation of Rb protein
Telomeres
junk DNA at the end of chromosomes that get shorter with every replication, takes 50-70 replications to get rid of
Smac / DIABLO pathway of apoptosis
last resort bathway when there is catastrophic damage to the cell
How does Gleevec become resistance in patients?
more Bcr-abl genes, Bcr-abl become mutated and decreases Gleevec binding affinity
Self-sufficiency in growth signals
mutate a constitutively active receptor, manufactures growth signals in cell, overexpress receptors, recruit other proteins to the same signaling pathway
What happened in the mice that we genetically modified to overexpress only myc or only ras?
myc = survival factor, causes immortalization of cells, need ras and myc for cancer formation, you need a survival factor and an oncodriver/proliferation factor to cause cancer, you get cancer fasted when you have both ras and myc
What is MDM2?
negatively regulates the p53 tumour suppressor, p53 encodes for the transcription of MDM2, causes p53 levels to degrade, is in a negative feedback loop
What is BCR-ABL?
non-receptor tyrosine kinase
What does the fact that there needs to be two mutant Rb alleles in order to get the disease tell us?
normal allele is dominant over the mutant one, confirmed with studies, this means the Rb alleles are RECESSIVE
How does a tumor evade apoptosis?
overexpress Bcl2, delete or inactivate p53, overexpress MDM2
What are two methods tumor cells avoid apoptosis?
overexpress Bcl2, delete p53 gene or inactivate mutations of p53 (occurs in 50% of all tumors)
Avoid apoptosis
overexpress survival factors, delete./ mutate apoptotic factors
Sources of stress for the cell
oxidative stress, chemical stress, hypoxia, radiation (UV, gamma, xray), double stranded breaks (DNA damage in general) ***
What are some types of stresses on cells?
p53 increases protein levels in times of stress: oxidative stress, hypoxia, oncogene activation, double strand breaks
BCL2?
prevents the release of cytochrome C, survival factor
TGF-beta?
primary anti-growth receptor, activates p15 to stop CDK4/6
PLX 4032?
primary drug in clinical trial for treating metastatic melanoma, tyrosine kinase inhibitor, called Zelboraf, targets tyrosine kinase
FAS?
receptor, activated by Fas Ligand, Fas activates caspases, extracellular signal that starts apoptosis
6 traits required for a full blown metastatic tumor
self sufficiency in growth signals, insensitivity to antigrowth signals, evasion of apoptosis, limitless replication potential, sustained angiogenesis, tissue invasion and metastasis
RAF?
signaling molecule, MAPKKK-MAPKK-MAPK, survival growth and division
What did cell fusion experiments tell us about cancer causing genes?
some tumor forming genes are dominant (oncogenes) and others are recessive (tumor suppressor genes)
Cytochrome C
start cascade of caspase signalling, oxidative agent released from the mitochondria
Myc?
stimulates both proliferation and apoptosis
How does BCL-2 interact with Bax/Bak?
stops them from forming pores
Limitless replicative potential
telomerase activation, myc
What kind of gene is p53?
tumor suppressor gene
What is p53?
tumor suppressor gene, mutated in 50% of tumor; normally helps with DNA repair, angiogenesis
What is the Rb gene?
tumor suppressor gene, phosphoprotein, only ONE copy is sufficient for normal function, need to lose both copies to develop the tumor, 105kDa, normally phosphorylated and bound to E2F proteins
How did tumors develop resistance to PLX 4032?
upregulation of PDGFR-Beta receptors = activated a new survival pathway, mutation of N-ras = stimulated c-Raf to reactivate the MAPK survival pathway which leads to MAPK dependent survival N-Ras --> c-Raf --> MEK1/2 --> ERK1/2 --> MAPK-dependent survival
When does p53 cause growth arrest?
when the cell detects damage has been done to the DNA by hypoxia, UV radiation, p53 steps in and stops the cell cycle
Granulocyte?
white blood cells: mast cells, basophils, neutrophils, eosinophils
How do you immortalize human fibroblasts or epithelial cells?
you insert gene for telomerase into cells