Week 4 Flashcards
What % of mutations are acquired?
90%
What causes DNA mutations?
Chemicals, radiation, viruses
3 different types of cancer causing somatic cell mutations?
- Activation of growth promoting oncogenes
- Inactivation of tumor suppressor genes
- Alterations in genes that regulate apoptosis
What is angiogenesis?
The development of new blood supply from preexisting vessels to an area that need more O2
Early stages of vascular-genesis
General steps of cancer?
Mutation Clonal expansion Angiogenesis More mutations Escape from immunity Tumor progression Malignant neoplasm Invasion and metastasis
Neoplastic progression?
A. Tumor growth B. Angiogenesis C. Invasion and metastasis D Evasion of immune system E. Evasion of Senescence (aging of cell line aka shortening telomeres)
7 hallmarks or cancer?
Limitless replicative potential Sustained angiogenesis Evading Apoptosis Self-sufficiency in growth signals Insensitivity to antigrowth signals Evading immune surveillance Tissue invasion and metastasis disease
Are tumors always one mutated cell line?
No they are often and mix of or variety of different mutated cell lines stemming from one mutation.
What is the strongest most powerful carcinogen? Aka what causes most cancers?
Inflammation
When does a tumor need to start angiogenesis aka develop its own blood supply?
When it gets bigger than 2 microns
Is doubling time for a tumor cell shorter or longer than a normal cell?
Longer due to the DNA damage usually making them inefficient at replication
If doubling time is longer then why do tumors grow so quickly sometimes?
More cancer cells are in replication cycle
Cancer cells are shed at a lower rate aka they dies less
Limitless replication potential
Normal cell cycle versus tumor?
Normal- Division, acquires mutation, apoptosis
Cancer- division, acquire mutation, division, acquire another mutation, division etc usually by 4th mutation there is uncontrollable growth
3 things that happen in tumors?
- Activation of oncogenes
- Inactivation of tumor suppressor genes
- Alterations in gene that code for apoptosis
What is a oncogene?
Gene that codes a protein that causes transformation to a neoplastic phenotypes when activated or over expressed. Mutations in oncogenes are dominant on a cell level ie one mutation over expresses enough protein to cause uncontrolled cell proliferation
Names 4 examples of Oncogenes?
erb-B2- amplification of growth factor receptors, Breast and ovarian
ras- signal transduction due to point mutations, lung colon and pancreatic
myc- nuclear regulatory proteins are translocated, Burkett lymphoma
cyclin D- cell cycle regulators that are amplified or translocated, Mantle cell lymphoma breast and esophageal
What are tumor suppressor genes?
Genes that encode a protein that causes a transformation to a neoplastic phenotype when inactivated or under-expressed.
Mutations are recessive on a cell level one normal genes makes enough protein to keep things in check.
Name 6 examples of tumor suppressor genes?
APC- in cytosol inhibition of signal transduction
Rb-cell cycle regulation in nucleus
P53- response to DNA damage work in nucleus regulating cell cycle and apoptosis
BRCA-1- in nucleus regulation DNA repair
p16- CDK inhibitors
p21- CDK inhibitors
What do oncogenes and tumor suppressors do to cell cycle pathways?
Oncogenes- turn on
Tumor suppressors- turn off
What part of the cell cycle is not involved in cancer proliferation?
G-naught- that is a holding pattern not in active replication
What happens when a CDK (cyclin dependent kinase) and a cyclin bind together?
The make an active cyclin/CDK complex that phosphorylates target proteins and drives cell proliferation
Describe levels of cyclin and CDK and CDK inhibitors during cell cycle?
CDKs are stable in the amount but activity goes up and down due to associations with cyclones and inhibitors
CDK inhibitors vary due to environmental signals
Cyclin varies according to cell cycle progression- higher at restriction points to drive them past…
Both cyclin and CDK are only active when associated with each other.
What does the CDK/cyclin complex do?
Regulates transcription factors and replication factors by phosphorylation
What happens in cyclin over expression and how does it fit into pathway with tumor suppressor genes Rb, p21 and p16?
Cyclin is an oncogene and over expression means high levels of cyclin protein which is now around to bind to CDK and make a complex that separates a tumor suppressor Rb from E2F gene that drive cell cycle and replication aka
Increases transcription DNA synthesis genes such a EF2
Example-
- Rb tumor suppressor gene is bound to E2F protein which helps with DNA synthesis and…
- p16 or P21 hold CDK complex in check until it is time to move forward in cell cycle when they are inactivated.
If they are mutated or turned off then CDK complex is free.
- Free CDK/cyclin complex phosphorylates Rb releasing E2F to help with DNA synthesis is cell replication
Describe where the 4 oncogenes she wants us to know fit into the growth factor signal transduction pathway?
- erb-B2 a receptor tyrosine kinase is phosphorylated when receives signal
- Ras is activated by erb-B2 and then it travels through cytoplasm to nuclear wall
- Myc receives signal from Ras and translocates to nucleus and activated Cyclin D which is made and then complexes with CDK which activates growth.
If any part of the pathway is mutation to being always on then unregulated tumor cell proliferation happens
What gene is implicated in 50% of cancers?
p53
Quick description of what p53 does?
It receives the DNA damage signal from a complex pathway and depending on level of damage that signals triggers p53 increase transcription of one of 2 choices:
- Apoptosis genes if damage is bad via Bax activation which activates Cytc or
- Activate p21 to freeze cell cycle and initiate DNA repair
Two p53 pathways and genes in them.
DNA repair p53 to p21
Apoptosis p53 to Bax
What is chromosomal translocation?
When one part of the tip of a chromosome switches with another chromosome tip
How can chromosomal translocation affect cancer?
A oncogene can get placed next to an enhancer or activator or the translocation can makes new oncogene that is the result of the fusion of two separate genes.
Alone they are harmless but together they code for a cancer causing protein
How are translocations noted?
Small t and parentheses with each chromosome number ie
t(14,18) or t(9,22)
Name the two translocations she wants us to know?
t(14,18) and
t(9,22)
What happens in t(14,18) ie what genes, what do they do, and what cancer?
The anti apoptosis oncogene bc12 on 18 is relocated to 14 next to the IgH enhancer. This results in over expression of bc12 causing Follicular Lymphoma
What does bc12 do?
Stops apoptosis signal to Bax in the case of DNA damage
The cell doesn’t die when it should but continues to live
What happens in t(9,22) ie what genes, what do they do, and what cancer?
The Philadelphia Chromosome
The 5’ Bcr gene from chromosome 22 relocates to chromosome 9 right next to the 3’ end of the Abl gene.
The two genes fuse and create an oncogenic tyrosine kinase that phosphorylated P13K creating a cascade that activates cell cycle progression, growth and proliferation
This is tied to CML aka Chronic Myelogenous Leukemia
What is the Philadelphia Chromosome and what cancer?
t(9,22)
CML Chronic Myelogenous Leukemia
How can tumor suppressor genes be recessive at the cell level and dominant at the organismal level?
1 copy is enough to suppress the cancers but often in the life of an organism the one remaining copy is mutated and inactivated
So at some point the organism carrying the 1 copy will lose it and get cancer.
So if a kid inherited the broken gene from one parent and a working copy from the parent 2 when parent 2’s breaks they get cancer
What is Knudsen’s hypothesis?
The “two hit hypothesis”
- One Hit is inherited ie 50% get a broken gene and heterozygous and phenotypically normal
- Second hit is when the one working copy breaks and they become homozygous for the mutant
- Inheritance pattern is dominant because the chance at least one cell will mutate and lose heterozygosity is really really high- everyone with the one broken gene with eventually break the 2nd working gene.
- Non inherited tumor suppressor associated cancers the person has to break both genes.
What is the APC gene?
Adenomatous Polyposis Coli
It is a tumor suppressor that leads to FAP- Familia Adenomatous Polyposis aka colon polyps and cancer
How does the APC gene work?
APC tags beta-catenins for degradation when they a released from keeping cell to cell contacts when the cell is getting ready to divide
If there is no APC to suppress the beta-catenins and tag them for destruction then they go on to change gene expression to cause cancer then there is proto-oncogene mutations then other cancer mutations and carcinoma
What angiogenic signals do tumor sub clones produce?
VEGF
What does VEGF do and how is it regulated?
In hypoxia conditions and when growth factors are around VEGF is made in cancer cells.
VEGF stimulates endothelial cell proliferation, migration and maturation aka new blood vessels made from EPCs from bone marrow, ECM remodeling, vascular permeability and new capillary sprouting
In short new blood supply of O2 to tumors
True or false
Cancer need to create new blood vessels to get big ie undergo angiogenic switch
True
What need to happens for tumors to invade new spaces?
They need to go through the basement membrane and into the stroma.
What are the 4 steps of invasion?
- Detach from neighboring cells
- Bind tighter to basement membrane via receptors such as laminin and fibronectin receptors
- Release MMPs aka metalomatrix proteases such as Type IV collagenase to cleave collagen in basement membrane
- Migration and invasion using fibronection interactions and autocrine motility factors
Do our immune systems recognize tumor cells?
Yes they can and if they do the patient has a better chance but tumors can hide from immune system by:
- not making antigens
- Not displaying them since they don’t have the genes
- Producing immune cell cytokines that suppress t-cells
What sites metastasize most commonly?
Liver, brain, bone, lungs
Then breast, prostate, colon, pancreatic
What cancers don’t metastasize easily?
Basal cell carcinoma and squamous cell carcinoma aka skin cancers