Fabian cancer biology slide 41-80 Flashcards
What drug can impact the targeting of BCR/ABL?
What does this drug do?
Where does the drug fit?
-imatinib (Gleevac)
-it prevents tyrosine kinase to activate the BCR-Abl protein which can prevent chronic myelogenous leukemia
-it fits into the ATP binding pocket which prevents activation
What does imatinib do to prevent Bcr-Abl activation?
What does it prevent, what does this lead to
-imatinib binds to the bcr-abl pocket, competitively binds to site and inhibits the protein
-this prevents downstream binding and the substrate cannot enter kinase site, so the tumor cannot proliferate
What is another cellular oncogene
-erbb2/HER2
What type of signaling molcule is erbB2?
What does it respond do?
What is it also known as?
-Receptor Tyrosine Kinase.
* Responds to epidermal growth factor.
-aka neuro/glioblastoma derived oncogene homolog (neu)
* Aka human epidermal growth
factor receptor 2 (HER2).
What activates erbB2?
What can it cause when activated?
Dimerization activates proliferation and survival gene expression signaling pathways
-can cause signal transduction cascades when activated, on growth/proliferaiton and survival paths
What is an RTK example (receptor tyrosine kinase)?
where does the ectodomain protrude into?
RTKs (e.g. epidermal growth factor receptor, EGFR).
* Ectodomain protrudes in extracellular space to recognize and bind ligand.
WHere does the hydrophobic domain of RTK thread through?
Where does kinase domain sit?
- Hydrophobic transmembrane domain threads through plasma membrane lipid bilayer.
- Kinase domain sits inside cell.
What leads to RTK dimerization?
What can mutations result in?
- Hydrophobic transmembrane domain threads through plasma membrane lipid bilayer.
- Kinase domain sits inside cell.
What can RTK overexpression cause?
What type of tumor can overespression lead to?
-RTK overexpression (e.g. ERBB2) may cause cell to become hyper-responsive to low growth factor concentrations and/or cause ligand-independent RTK dimerization due to mass action effect.
-leads to 30% of breat adenocarcinomas
What does amplification of erbB2 signaling cause/
-amplification decreases survival rate by alot
What method can we use to asses gene copy number?
What should we normally see when doing FISH analysis?
WHat about when we have ERBB2 amplification?
-by using fluorescense in situ hybridization (FISH)
-we should see 2 copies of chromosome per cell?
-there are many copies in the cell, which is sign of breat carcinoma
What can we use for analysis of ERBB2/HER2+ in breast cancer cells?
What does antibody bind to get staining?
How can we see the different stages of amplification of Her2 with IHC?
-we use immunohistochemistry (IHC) to visualize
-antibody bind to HER2 then secondary antibody binds on top to get staining
-the staining will appear alot more dark
What does trazuzumab (herceptin) do?
When should this drug be given?
What is this an example of?
-binds to an extracellular domain of this receptor and inhibits HER2
homodimerization, thereby preventing HER2-mediated signaling
-should only be givent patients with ErbB2 amplification
-a personalize medical approach, typically given to breat cancer patients
What is the 3rd type of cellular oncogene?
Ras
What are the 3 types of Ras?
What type of protein is Ras, when is it active?
What can lead to Ras only being active and not turning off?
Three Ras genes (K-Ras, H-Ras, N-Ras).
* Is a GTP (G) protein that is
activated when bound to GTP.
-point mutation change single amino acids which can only lead to Ras activation
How does ras use its GTPase function?
How does it turn itself on/off?
It then uses it’s GTPase function to hydrolyze (cleave) GTP to GDP thereby inactivating itself.
Turns itself on and off like a light
What can Ras regulate?
What activates and inactivates Ras?
it can regulate growth, survival and proliferation
-GAP inactivates Ras into its GDP form
-GEF activates Ras into its GTP form
What is the most highly mutated gene in cancer?
What turns Ras from a protooncogen to an oncogene?
What type of feedback does the oncogene inactivate
-ras, the mutation is typically missense (causing point mutations along the way)
-Missense mutations in G12 and 61 turn Ras from a proto-oncogene into an oncogene.
* Lead to GTPase negative-feedback mechanism being
inactivated
What type of cancers are Ras mutations found in, what are some mutated Ras genes?
what causes this?
-Mutated RAS genes (KRAS, HRAS, NRAS) are found in many cancers, in particular 50% of colorectal cancers and 95% of pancreatic cancers
-Ras point mutation
What do proto oncogene function to regulate?
What do alterations that upregulate their expression lead to?
What do oncogenes drive?
Proto-oncogenes function to regulate normal cell proliferation and differentiation.
-Alterations that upregulate their expression or mutations that alter their structure can lead to overly active growth-promoting genes, which appear in cancer cells as activated oncogenes
What do oncogenes drive?
once formed, oncogenes drive cell proliferation
and play a central role in the pathogenesis of
cancer.
What is a tumor supressor gene?
A gene that when inactivated or lost leads to an increase in the selective growth advantage of the cell in which it resides (e.g. Rb and p53)
How does retinoblastoma arise?
When is it diagnosed/
Arises from photoreceptor cell precursors in 1 in 20,000 children.
* Diagnosed from birth to 8 years of age
What can diagnosed people with no family history vs people who have family history have affected?
-Diagnosed children with no family history (Sporadic form) can have single tumor in one eye, with radiation and surgery generally being effective.
-Diagnosed children with family history (familial form) often have multiple foci of tumors in both eyes (bilateral retinoblastoma).
What does bilateral retinoblastoma increase?
-what do children with retinoblastoma have ahigher risk of
-increases risk of cancer spreading
-While radiation/surgery can treat bilateral retinoblastoma, these children have higher risk of bone cancers (osteosarcomas) as well as other tumors later in life.
What is the knudson 2 hit hypothesis?
What is a hit?
rate of appearance of familial was consistent with one random
event, whereas sporadic was consistent with two random events.–a hit is a mutation event that affects DNA
What is the quiescent state?
-when cells decide not to replicate but are still metabolically active
what is the restriction point in the cell cycle?
What is Rb?
restriction (R) point denotes the point in time when the cell must make the commitment to advance through the remainder of the cell cycle through M phase, to remain in G1, or to retreat from the active cell cycle into G0
–it is the cell cycle gate keeper
What type of protein is Rb?
What can Rb act as?
-nuclear protein that can be phosphorylated by a number of mitogenic signaling pathways.
* Rb acts as a transcriptional repressor that determines if cells will enter S phase.
What is the phosphorylation level in early/mid G1? In late g1? and in S phase?
-early/mid G1 is slightly phosphor.
-late G1 is very phosphor. which allows the cell cycle to proceed
-in S phase there is no E2F2/E2F1
What is the mitogenic pathway and transcription factors?
What is an example of transcription factor?
Mitogenic pathways: pathways that regulate/stimulate mitosis.
Transcription factors: proteins involved in the process of converting, or transcribing, DNA into RNA
-E2f is a TF
What happens if cells are no phoshphor in the cell cycle?
What happens if the cells are phosphor.?
-they cant bind transcription factors
-it can bind TF and doesnt bind E2F2 to go into S phase
What happens in familial retinoblastoma?
What does the first somatic mutation event lead to in familial retinoblastoma?
what does bilateral retinoblastoma lead to more of?
-you are born with one mutant copy of Rb already, so the first hit has already occured
-you get 2 mutant Rb gene copies which leads to loss of heterozygosity (LOH)
-tumors will pop up quicker and will most likelt have bilateral and cancers outside of the eye
How many mutations do you need to have 2 mutant Rb copies in sporadic retinoblastoma?
-you need 2 somatic mutations to have loss of hetereozygosity in sporadic retino.
What can many familial cancers be explained by?
-What does early stage cancer find ways to eliminate, by doing what?
-Many familial cancers can be explained by inheritance of
mutant tumor suppressor genes.
* Early stage cancer cells find ways to eliminate wild-type copies of TSGs (e.g. mitotic recombination can lead to LOH)
in what phase can loss of wild type copies of tumor suppressor genes be done?
-Can occur during G2 phase of the cell cycle.
– Subsequent segregation of chromatics may yield a pair daughter cells that have undergone LOH
What are some of the mechanisms of LOH and inactivation of TSG?
-
What can chromatin do?
-chromatin can come in and transcribe genes
What is heterochromatin and euchromatin?
What is methylation used for?
-heterochromatin is transcriptionally silent and can be caused by DNA methylation
-euchromatin is transcriptionally active and does not have lots of methlation and RNA pol can bind+transcribe
-methylation is used for genetic control
what can lead to TSG inactivation?
What is this an example of?
What does epigentic mean?
What does hypermethylation cause?
-Promoter methylation can lead to TSG inactivation without mutation.
* Example of EPIGENETIC SILENCING
-control gene activity without changing the DNA sequence
-it causes inactivation of TSG which is a property of tumoral cells
What does promoter methylation lead to?
What does DNMT1 and DNMT3b cooperate to do?
Promoter methylation can lead to TSG inactivation without
mutation
-it silences genes in human cancer cells
What does 5-methylcytosine cause?
What can prevent DNA methylation?
What does high levels of DNMT3B (methyltransferase) causes
-causes inactivation when it is in DNA
-azacitibine and decitabine
-the more that is present the more aggressive the cancers
What does p53 regulate?
What leads to p53 stabilization?
what does p53 form to function?
regulates cell cycle control, and it is relatively unstable
-DNA damage and dysregulated growth signals lead to p53 stabilization.
p53 forms a homotetramer to function
What does p53 function as?
What do p53 targets include?
-Functions as a transcription factor that halts cell cycle.
p53 target genes include growth arrest genes, DNA repair genes, regulators of apoptosis
What does cell cycle arrest lead to?
What does p53 not follow?
senescense or return to proliferation
-does not follow the knudson-2 hit model
What is tumor suppressor (TSG) haploinsuffiency?
-when one gene is not enough becasue loss of single TSG allele yields to abnormal phenotypes
What does dominant negative mean?
When does this usually occur?
A mutation whose gene product adversely affects the normal, wild-type gene product within the same cell .
-This usually occurs if the product can still interact with the same elements as the wild-type product, but block some aspect of its function
What does p53 work as?
What happens when one unit of p53 is mutated?
What does mutant p53 normally carry?
-p53 normally works as a tetramer.
-if you have one unit thay is mutant, it will affect the whole tetramer (dominant negative)
* mutant p53 found in many human tumors usually carries amino acid substitutions in its DNA-binding domain.
What do TSG regulate?
What is the theme that unites the TSG mechanisms?
What does TSG act as?
TSGs regulate cell proliferation through many mechanisms
-Only theme that unites them is the fact that the loss of any one of them increases a cell’s selective growth advantage.
-acts as the gatekeepers
What does TSG loss usually affect, and when?
-Tumor suppressor gene loss usually affects cell
phenotype only when both copies of such a gene are lost (although there are exceptions)
What type of pharmocoligical approach would you use to target tumor suppressor gene mutants?
would use a synthetic lethal approach to killing cancer cells
what is the concept of synthetic lethality?
What was it developed from?
-the combined effects of two alleles, each of which is nonlethal but which, when acting in combination, result in lethality (when there are 2 mutants)
-developed from genetic studies in model organisms (yeast, fruit flies)
