Exam 2 Flashcards
apoptosis
programmed cell death
p53
homotetramer transcription factor for apoptosis genes and repair mechanisms (binds DNA and responds to stress/damage)
describe why it is important to know that p53 is a homotetramer
only 1/16 of all possible combos is functional because need all 4 WT and no mutation
why is it better to have the p53+/- genotype than the p53+/m
absent, phenotype is mostly normal but mutation, the phenotype is that there is no p53 function
p53 turns on what genes…
mdm2, cell cycle arrest genes (p21/27), DNA repair genes, apoptosis genes
stressors that can turn on p53
lack of nucleotides, UV radiation, ionizing radiation, oncogene signaling, hypoxia, blockage of transcription
why is it an advantage that p53 is constantly expressed in all cells all the time
energy consuming but beneficial because it allows rapid response to stress and a fast way to turn off proliferation
mdm2 function
regulates p53 via negative feedback
how does mdm2 regulate p53 via negative feedback
- lots of copies of p53
- some p53 P even when not stressed so p53 binds DNA—> translate Mdm2 protein
- Mdm2 then feeds back and initiates degradation of un-P p53 by ubiquitination
when is p53 P
stress
how is was signaling involved in p53 expression and function
GF–> Ras–> Mapk/Erk1/2 —> proliferation
overaction GF/Ras signaling will increase Mdm2 expression so there will be very little or no p53 and no regulation
how can we prevent the consequence of overactive Ras signaling and not enough p53
ARF (only transcribed if signaling on “too long”)
describe ARF signaling pathway
ARF negatively regulates Mdm2 and therefore helps p53 because p53 won’t be inhibited by Mdm2
TFs for ARF
E2F when Rb hyper P
Erk 1/2 (AP1 and Ets)
how does ARF inhibit Mdm2`
binds Mdm1 and hides/sequesters Mdm2 into nucleus–> Mdm2 and ARF can’t bind p53, so p53 will accumulate, allows p53 to get P by stress sensing kinase
apoptosis vs necrosis
apoptosis: neat and ordered, usually doesn’t impact neighboring cells, everything stays contained in plasma membrane
necrosis: a lot of cells, messier (explosion), broad neg impacts –> inflammation
extrinsic apoptosis
- death receptor proteins
- no mitochondria
- death signal from diff cell
- no p53
intrinsic apoptosis
- mitochondria
- stuff inside cell signal apoptosis
- p53
explain how cancer cells get past apoptosis
apoptosis in early stages of cancer develop is important (50% cancer has mut p53) so big advantage for cancer cells to lose intrinsic apoptosis because able to survive and reproduce
initiator vs executioner caspases
initiator only cuts proteases and executioner cuts other procaspases and cuts death substrates
cell with no p53 activation
receives survival signals, has stable Bcl-2 levels, cytochrome C in mitochondria
cell with p53 activation
induce p53 to transcribe Bax
Bax
can form a pore to release cytochrome C, pro-apoptotic
Bcl2
anti-apoptotic, binds to Bax to prevent it from forming a pore
what happens when there is more Bax than Bcl2?
apoptosis, Bax prefers to bind to Bcl2 than the mitochondrial membrane but when not enough Bcl2, forms pores so cytochrome C is released into the cytoplasm to induce apoptosis
what happens once cytochrome C leaves the mitochondria and is in the cytoplasm?
- cytochrome C forms apoptosome
- apoptosome will cleave procaspase–> caspase
extrinsic apoptosis steps
- signal from neighboring cell
- extrinsic signals lead to cytochrome C being released
- apoptosome
- initiator and executioner caspases
what kind of signal leads to extrinsic apoptosis
either small protein or cell surface protein on killing cell
targeted therapies
trying to kill cancer cells and not healthy cells
target therapy for cancer cells that are avoiding apoptosis
inhibit Bcl2
- prevent from binding pro-apoptotic
- useful for cancer cells overexpress Bcl2 (drug in binding pocket so pro-apoptotic go into mitochondria instead of bind bcl2)
why does cancer occur?
- drug resistance
- avoid intrinsic/extrinsic
- mutation eliminate protein in pathway (pro-apoptotic, etc)
- mutations lead to a lot of variation
- natural selection
what is the problem that occurs at the end of replication?
after each round of replication of linear DNA, the DNA will be a bit shorter, ds ends of linear DNA look like ds breaks, nuclease destroy end linear DNA
what is the solution to the end replication problem?
telomeres and telomerase
telomere DNA
long 3’ end of dsDNA, short repeated seq allows for looping
telomere protein
facilitate the looping, hide 5’ and 3’ ends so not degraded, repeated hexamer seq, regulate telomerase function
telomerase RNA
hTR
telomerase protein
hTERT
job of telomerase protein
synthesize DNA, 6 nucleotides at a time to extend 3’ end DNA, then DNA poly and primer can extend 5’ end
which cells have telomerase?
- stem cells (long lived, replicate a lot)
- some immune cells (T cells and B cells during infection need a lot)
- germ cells (long lived)
once telomere is gone…
end of DNA looks like ds break which leads to p53 activation and apoptosis
once telomere is gone but no p53 present
fusion of unprotected chromosome ends, chromosome break, crisis, cell death even without p53 or cancer cell turns on telomerase
define hyperplasia
a lot of normal cells
evidence for why cancer takes decades to develop
30 year lag between increase in cigarette consumption and increase in smoking related lung cancer, autopsies
colon cancer multi-step tumorigenesis
normal epithelium–>(loss of APC) hyper plastic epithelium—> (DNA hypomethylation) early–> (activation of K-ras) intermediate adenomas–> (loss of 18q TSG) late –> (loss of p53) carcinoma–> invasion and metastasis
common mutations in colon cancer
- loss of APC TSG function (too much epithelial cell prolif)
- DNA hypomethylation
- oncogene activation of Ras
- loss of unknown TSG
- loss of p53
DNA hypomethylation colon cancer mutation
problems with regulation of gene expression, DNA methylation makes it more difficult to express a region of DNA
oncogene activation of Ras colon cancer mutation
Ras is “on” when it shouldn’t be, too much prolif, p53 activate
step wise cancer
initiating mutation (1st clonal expansion)-> second mutation (2nd clonal)—> –> increase mutation rate due to fast rate of prolif–> multiple independent mutations (multiple parallel clonal expansions–> sub pop gain ability to metastasize –> metastatic cancer
step wise cancer and natural selection
each step inc ability for cancer cells to survive and reproduce, “most fit” metastasize
acute inflammation
short time period, caused by infection, goes away after immune system eliminates virus/bacteria
chronic inflammation
long time period, infections can’t be cleared, autoimmune problems
multi-step tumorigenesis and hep B
- immune cells enter liver
- immune cells prolif and tell liver cells to prolif
- release ROS
- tumor initiating mutations can occur
autoimmunity - hepatitis B virus:
- infects liver cells (chronic inflammation)
- high rates liver cancer
autoimmunity- chron’s disease/UC/IBD
- chronic inflammation in gut
- high rates colon cancer
inflammation on molecular level
pathogen–>
1) immune cells prolif (immune cells produce and respond GF)
2) immune cells to site infection
3) immune cells kill pathogen or pathogen infected cells (secrete apoptosis mol)
cytokines are
GF that tell immune cells and epithelial cells to prolif
chronic inflammation and cytokines
high levels of IL6/TNFa
1) DNA damage (DNA rep mistake)
2) constant prolif of epithelial
immune cells create
ROS to kill pathogen but this leads to DNA damage
cancer stem cells
- not necessarily normal stem cells that have turned into cancer stem cells
- cells that prolif to give rise to more and more tumor cells
- most resistant to treatment
cancer stem cell sub-population
acquire mut that allows them to be really good at prolif
genomic integrity
2 copies of each 23 chromosomes functional
loss of genomic integrity
DNA repair mechanisms messed up and apoptosis not happening
normal cells DNA damage
p53 activation (halt cell cycle, repair, apoptosis)
cancer cells DNA damage
loss of p53 common or problems downstream p53
dsDNA break
HDR, NHEJ
HDR
homology directed repair
NHEJ
non homologous end joining
dsDNA break can lead to
chromosomal translocation (proto-onco)
HDR
- end S/G2
- need sister chromatid pairing
- use undamaged sister chromatid as template to repair damaged chromatid
- involves BRCA1/2 proteins
when can HDR not happen?
without BRCA1/2 or if dsDNA break during G1 so no sister for template
NHEJ
- randomish bp
- worse than HDR but not as bad as 2 diff chromosomes getting stitched together (happens if >1 ds break present)
aneuploidy
abnormal # chromosomes
aneuploidy caused by
DNA damage or mitosis problems
why is aneuploidy bad?
loss of TSG, LOH mech and gain copies of proto-oncogenes
what are some problems that can lead to aneuploidy?
- mis-attach microtubules to kinetochores
- chromosomal translocation (due to NHEJ)
- abnormal number kinetochores
spindle assembly checkpoint
metaphase to anaphase transition
-chromosomes won’t pull apart until all evenly connected to mitotic spindles
spindle assembly checkpoint not effective
chromosomes don’t pull apart correctly and aneuploidy occurs
how does the spindle assembly checkpoint work
- sister chromatids attached with protein called cohesion
- once cohesin degraded, chromatids pull apart
“signaling” pathway of SAC
CDC20 activated by cyclins/CDks –> degrades securin which is in binding pocket of separate but once degraded separase can degrade cohesion –> chromatids pull apart
all chromatids have to be attached evenly before
cohesin degraded
what inhibits CDC20?
BUBR1
mutation with BUBR1
SAC broken and advantageous for cancer cells because leads to aneuploidy
how does BUBR1 inhibit CDC20?
BUBR1 attached to chromatids and kinetochore, once spindles present BUBR1 removed by kinetochore and no longer inhibiting
over expression of BUBR1
no aging, random mistakes such as BUBR1 accidentally falling off prevented and decrease aneuploidy because fewer random mistakes
heterotypic signaling
signals being shared between diff cell types
carcinoma
epithelial originating cancer
cell types involved in carcinoma
cancer cells stromal/mesenchymal cells (non cancer, non epithelial, support) fibroblasts (create ECM) endothelial (form blood vessels) macrophages (support tumors)
what signals are sent from non-cancer cells to cancer cells?
- growth and survival
- angiogenic
- signals that allow for metastasis
- cancer cells need to grow blood vessels and move
what signals allow for metastasis
- require non cancer
- ability for epithelial cell to move
angiogenic signals
growing new blood vessels
non cancerous wound healing main steps
wound–>damage vasculature–> bleeding –> recruit platelets–> blood clot
non cancerous wound healing, what happens between damage vasculature and bleeding?
hypoxia
hypoxia in non cancer leads to
VEGF production
VEGF
recruits macrophages and leads to angiogenesis
macrophages (non-cancer)
degrade ECM, release sequestered GF, lead to EMT
after recruiting platelets in non-cancer what happens?
release PDGF which tells fibroblasts and endothelial cells to grow new blood vessels
what is a key difference between non-cancer and cancer carcinoma cells
cancer go through EMT but not MET so they remain invasive and metastasize
angiogenesis
used for wound healing, growth, pregnancy
angiogenesis is important for
- growth of new blood vessels
- deliver O2, nutrients
- take away CO2, waste
hypoxic area of tumor
cells signal growth of new blood vessels
steps to make more blood vessels
- in blood supply, endothelial progenitor cells (EPCs)
- VEGF recruits EPCs out of circulation and into tissue
- VEGF tells EPCs to prolif and differentiate into endothelial cells
- new blood vessels branch off of existing blood vessels
anti-angiogenesis therapies
anti-VEGF antibody binds VEGF and prevents signaling or drug inhibits VEGF receptors and prevents signaling
benign
- not yet metastatic
- still contain in BM
malignant
metastatic
metastasis steps
1) leave primary tissue
2) colonize a new tissue
leave primary tissue metastasis step
- BM degraded
- EMT
- carcinoma cell moves into bloodstream or lymphatic system
how is the basement membrane degraded?
cancer cells and macrophages secrete an enzyme, MMPs
EMT
epithelial to mesenchymal transition allows carcinoma cells to move
colonize new tissue step
- many cancer cells die in circulation
- often cancer cells caught in lung capillaries
- not all cancer cells survive in the new tissue
other common sites for cancer cells besides lungs
bone, brain, liver
which cancer cells don’t die in circulation?
hearty ones really good at prolif and survival
EMT physical changes
motility
EMT gene exp changes
change from expressing E cadherin to expressing N cadherin
E cadherin
binds epithelial cells together (tight)
N cadherin
binds stromal and endothelial cells together (not tight)
EMT
epithelial stops binding other epithelial because E cadherin signal lost when TGFbeta binds to cells to induce EMT
TGFbeta
- stromal cells produce
- cancer cells can amplify production
- macrophages can help produce
TWIST
- overexpress leads to EMT
- without twist, a lot of E cadherin
- with TWIStT, a lot of N cadherin
