Exam 4 Flashcards
cell cycle
highly regulated process cells use to decide when and how to divide
why is cell division so tightly regulated?
defects in cell cycle regulation cause:
1) mutations (un-fixed errors)
2) cancer (too much proliferation, too little cell death)
3) atrophy (too little proliferation, too much cell death)
4) aneuploidy (too many or too few chromosomes)
major regulators of the animal cell cycle
1) secreted growth factors (environmental)
2) DNA integrity (intrinsic)
3) cell volume (intrinsic)
4) cell density (environmental)
major regulators of the animal cell cycle:
secreted growth factors
ligand from ER in cell signaling that does not get metabolized;
regulates cell proliferation, migration, survival/apoptosis;
intracellular response of cell that causes some change
major regulators of the animal cell cycle:
DNA integrity
lesions (from intrinsic or extrinsic carcinogens or errors in DNA replication) block replication progress and impair chromosome separation
major regulators of the animal cell cycle:
cell volume
cells know how big they are to help maintain cellular tissue integrity;
cell cycle and growth are interdependent (cells add constant volume each cell cycle, independent of initial size)
major regulators of the animal cell cycle:
cell density
cells are mindful of their neighbors (CAMs help recognize each other and environment);
contact inhibition of proliferation results in mitotic arrest and promotes differentiation
euk cell cycle phases
interphase (G1, S, G2) and M phase (prophase, metaphase, anaphase, telophase)
interphase
prep stages: cell grows, duplicates chromosomes, synthesizes machinery for replication;
every stage checks for DNA integrity
interphase:
G1
increase in cell volume, RNA and ribosome synthesis, protein synthesis for DNA replication
interphase:
S
chromosome and centrosome duplication, histone synthesis
interphase:
G2
protein synthesis for M phase
M phase:
prophase
centrosomes migrate to opposite poles, chromosome condensation, mitotic spindle formation, microtubule polymerization, NE breaks down
M phase:
metaphase
kinetochore alignment and attachment to chromosomes, tension builds across spindle
M phase:
anaphase
chromosome separation to two poles
M phase:
telophase
nuclear membrane reforms around both, cytokinesis begins (ends by G1), actin-myosin contractile ring
typical human cell division
every 24 ish hours, 95 % of cell cycle is spend in interphase;
budding yeast division takes 90 minutes, cells in early embryo take 30 minutes (skip growth stages)
G0
life outside the cell cycle where cells are not dividing or preparing to divide;
three distinct cell types
cell types in G0
1) quiescent
2) senescent
3) differentiated
cell types in G0:
quiescent
reversible G0, programmed event;
cells can be stimulated to re-enter the cell cycle
cell types in G0:
senescent
irreversible G0, reactive event (DNA damage, telomere shortening, growth factors);
cells cannot be stimulated to re-enter the cell cycle (except tumor cells);
discovered by Hayflick and Moorhead
Hayflick limit
the number of times a normal, differentiated, somatic cell will divide before stopping
cell types in G0:
differentiated
irreversible G0, programmed event (not damage induced);
cells cannot be stimulated to re-enter the cell cycle (except dedifferentiation or transdifferentiation)
major cell cycle phase-associated checkpoints
1) restriction point
2) G1/S
3) G2/M
4) spindle checkpoint
plus lots of DNA damage checkpoints by Chk1 and Chk2 throughout interphase, p53 in G1
cyclin-dependent kinases (CDKs)
regulate cell cycle entry and progression by phosphorylating targets;
serine/threonine protein kinases;
inactive until bound by co-activator cyclin proteins
CDKs are in molar excess throughout cell cycle…
how do we make sure CDKs are working on the right targets during the right phase?
1) cyclin expression
2) CDK inhibitors
3) inactivating tyrosine phosphorylation
cyclin expression
waves of synthesis and degradation through ubiquitination (APC/C ubiquitin ligase targets cyclins for degradation in late M and G1)
cell cycle entry/continuation
growth factors and nutrients stimulate entry to cell cycle once they reach a certain level;
1) growth factors activate RTKs and ERK MAPK pathway
2) phosphorylated ERK activates TFs for IEGs (Elk1)
3) expression of SRGs including CycD
4) CycD activates CDK4,6
G1 restriction point
the point at which removal of growth factors and nutrients does not stop cell cycle progression (commitment to the cell cycle)
G1 molecular basis of restriction point
phosphorylation of Rb by CDK4,6/CycD;
releases repression of E2F family TFs
G1/S transition
1) E2F transcription
2) increases CycE expression
3) activates CDK2
*positive feedback: CDK2 phosphorylates Rb more
G1/S transition CDK2/CycE inhibition
inhibited early in G1 by p27 and APC/C until…
growth factors decrease p27 synthesis, CDK2/CycE promotes p27 degradation and APC/C inactivation
G1/S transition is promoted by ___
high level of CDK2/CycE promotes loading of prereplication complex (with MCM) on origins to prepare for replication in S
S phase events
1) increased CycA expression, CycE degradation
2) CDK2/CycA phosphorylates MCM helicase proteins at origin to activate
3) high CDK activity stops re-replication
G2/M transition
1) increased CycB expression
2) activates CDK1 in M phase
3) CDK1/CycB (MPF) phosphorylates 1000s of targets including Aurora A and B and polo-like kinases (positive feedback loop)
4) CDK1/CycB initiates activation of APC/C (inhibited by MCC until chromosomes properly align)
1) CDK1/CycA promotes accumulation of CDK1/CycB in nucleus
2) nuclear envelope breakdown
spindle checkpoint
ensures all chromosomes are properly attached to microtubules at their kinetochores during metaphase;
APC/C inhibited until proper attachment
mitotic exit
1) APC/C activation
2) degradation of CycB
3) inactivation of CDK1
4) promotes mitotic exit and cytokinesis
Aurora A and polo mutants
have mono-polar spindle and do not undergo cytokinesis
Aurora B mutants
have partial condensation and disrupted spindle attachment
prophase spindle assembly
1) Aurora A and polo phosphorylation
2) accumulation of pericentriolar material
3) microtubule anchoring proteins hold - ends
4) y-tubulin initiates microtubule polymerization
1) astral microtubules attach to cell cortex
2) centrosomes migrate to opposite poles
prophase NEB (nuclear envelope breakdown)
1) CDK1/CycB phosphorylation
2) NPC disassembly and lamina depolymerization (weakens NE)
3) microtubule polymerization tears and stretches NE
4) NE fragments into vesicles
prophase chromosome condensation
1) cohesin rings applied to sister chromatids in S phase
2) CDK1/CycB and Aurora B phosphorylation on chromatin proteins
3) condensins bind and package chromosomes into loops
4) NEB removes attachments to chromosomes (like springs poised to condense)
prometaphase
1) + end of kinetochore microtubules attach to kinetochore proteins on chromosomes
2) motor proteins (kinesin and dynein) and MT polymerization/depolymerization initiate the shuffle
microtubule orientation to midline and centrosome
+ end at midline
- end at centrosome
metaphase
1) spindle assembly checkpoint
2) formation of MCC complex inhibits APC/C
metaphase spindle assembly checkpoint
monitors the attachment of chromosomes to the spindle, looks for unattached kinetochores and improper tension
metaphase improper assembly
Aurora B turns over improper attachments (phosphorylates kinetochore proteins) and promotes assembly of MCC complex
anaphase transition
1) proper attachments decrease MCC complex formation which activates APC/C
2) chromosomes separate and move to centrosomes at opposite poles
anaphase transition APC/C activation
1) degradation of CycB
2) inactivates CDK1
1) degrades securin
2) releases separase
3) degradation of cohesin
telophase
1) nucleus reforms
2) cytokinesis begins
telophase nucleus reformation
1) vesicles bind to chromosomes
2) vesicles fuse
3) reformation of nuclear lamina
4) chromsome decondensation
5) NPC reestablished
6) nuclear proteins imported
telophase cytokinesis begins
animal cells divide cytoplasm by ingression of cleavage furrow midway between separated chromosomes;
polo-like kinases
telophase cytokinesis polo-like kinases
play major role in localization of contractile ring and initial ingression of spindle;
localizes at the overlap of the interpolar microtubules and promotes tightening of actin-myosin contractile ring
ATR and ATM
protein kinases that recognize damaged DNA throughout interphase
1) activate signaling pathway
2) cell cycle arrest and DNA repair mechanisms
3) cycle progress OR cell death
ATR activated by
1) ss breaks or unreplicated DNA
2) ATR activation
3) phosphorylation (activation) of Chk1
ATM activated by
1) ds breaks
2) ATM activation
3) phosphorylation (activation) of Chk2
Chk1 and Chk2
protein kinases that inhibit Cdc25
1) Chk1 or Chk2 activation
2) phosphorylation of Cdc25 phosphatases
3) inhibits or promotes degradation of Cdc25
Cdc25
cell cycle inhibitor that normally removes inhibitory phosphorylation on Cdk1 and Cdk2
ATM/Chk2 pathway also activates ___
p53
p53
TF in activated form that regulates gene expression
1) ds break
2) ATM
3) Chk2
4) phosphorylation of p53
5) stabilization of p53
6) formation of active p53 tetramers
7) acts as TF at p53-response element sequences in the regulatory region of target genes
p53 targets
100s of targets including p21
p21
CDK inhibitor (CDKi)
1) inhibits Cdk1 and Cdk2
2) cell cycle arrest
less differentiated cell types
1) stem cells
2) cancer cells
stem cells
unspecialized cells that differentiate into specialized cells
1) self renewing
2) potency
cancer cells
include malignant tumors made of anaplastic cells
malignant
fast growing, metastatic (spreading from primary tumor site)
anaplasia
lack differentiation and features of origin tissue (take a step back in differentiation from surrounding cells)
potency
potential to differentiate
1) totipotent
2) pluripotent
3) multipotent
4) unipotent
5) differentiated
totipotent
can become every cell type; not in adult;
fertilized egg/zygote
pluripotent
can become every cell type except placenta; not in adult;
ex. inner cell mass (ICM) of embryo, iPSCs
multipotent
can become limited (multiple) cell types;
often lineage/cell type specific/restricted;
ex. neural, hematopoietic, intestinal stem cells
unipotent
can become only one cell type; aka progenitor cells;
ex. satellite cells in muscle
differentiated
fully specialized, non-stem cells; some quiescent;
ex. fibroblasts, endothelial, liver cells
ways to replace dead/dying cells
1) proliferation of differentiated cells
2) proliferation of stem cells
proliferation of differentiated cells
fully specialized, quiescent (G0) cells can be stimulated to reenter cell cycle (secreted growth factors);
1) fibroblasts
2) endothelial cells
proliferation of differentiated cells:
fibroblasts
rapidly proliferate in response to PDGF (platelet-derived growth factor); secrete new ECM and coordinate contraction at wound site
proliferation of differentiated cells:
endothelial cells
recruited by cells secreting VEGF (vascular endothelial growth factor; proliferation forms new blood vessels to support tissue needs (angiogenesis)
proliferation of stem cells
less specialized, sometimes quiescent (G0) cells that proliferate throughout their lifetime in most tissues; proliferation can be self-renewing and/or make differentiated cells;
asymmetric vs symmetric division;
ex. hematopoietic, intestinal, satellite stem cells
proliferation of stem cells:
asymmetric division
produces one stem daughter cell and one non-stem daughter cell; so we don’t run out of stem cells;
non-stem daughter cells vs transit-amplifying cells
proliferation of stem cells:
asymmetric divsion - non-stem daughter cells
proliferate into transit-amplifying cells
proliferation of stem cells:
asymmetric division - transit-amplifying cells
undifferentiated intermediates that become differentiated cells
proliferation of stem cells:
symmetric division
produces two stem daughter cells OR two non-stem daughter cells;
ex. adult neural stem cells -> two stem daughter cells;
ex. adult intestinal stem cells -> two non-stem daughter cells
proliferation of stem cells:
hematopoietic stem cells
in marrow replenish blood cells (fully differentiated blood cells do not divide)
proliferation of stem cells:
intestinal stem cells
slowly, but continuously divide in the bottom of the intestinal crypts;
fully differentiated surface epithelial cells apoptose and shed into digestive tract
proliferation of stem cells:
satellite stem cells
re-enter cell cycle to form new muscle fibers (unipotent);
normally quiescent, but injury/exercise-induced proliferation
examples of apoptosis
1) removing tissue in development (larval, webbed limbs, neuronal pruning)
2) adulthood tissue homeostasis and healthy cell turnover
3) injury (eliminating DNA damaged cells and promoting healthy cell proliferation at wound)
4) insult (killing virus infected cells
apoptosis looks like:
regulated event (peaceful)
1) cell shrinkage, DNA fragmentation, nuclear fragmentation, plasma membrane blebbing, cell fragmentation
2) rearrangement of PM (phosphatidylserine to outer leaflet)
3) recognized by phagocytic cells that engulf
necrosis looks like:
EXPLOSION (usually because of acute injury) (neighborhood disturbance)
1) swelling, rupture of membranes
2) release of contents into extracellular space
3) triggers inflammatory response
caspase
proteases (cleave proteins) that execute apoptotic events;
c = cysteine at active sites;
asp = cleave after aspartic acid
caspase targets
cleave 100s of target proteins
1) DNase inhibitor -> DNA fragmentation by DNase
2) nuclear lamins -> nuclear fragmentation
3) cytoskeletal proteins -> PM blebbing/cell fragmentation
4) scramblase -> phosphatidylserine translocation
caspase activation
1) synthesized as inactive precursors, kept at bay in normal cells
2) pro-apoptotic signals start bumpin
3) initiator caspases are activated
4) effector caspases are cleaved/activated by initiators
5) activated effectors cleave target proteins
6) apoptosis yaaaaaay
initiator caspases
caspase-8, 9, 10
effector caspases
caspase-3, 7
cell signaling pathways that control apoptosis:
1) intrinsic (mitochondrial/Bcl-2) pathway
2) extrinsic (receptor-mediated) pathway
intrinsic (mitochondrial/Bcl-2) pathway
activated by internal stress, regulated by Bcl-2 family proteins (3 types):
1) pro-survival
2) pro-apoptotic
3) effectors (Bax, Bac)
intrinsic (mitochondrial/Bcl-2) pathway:
pro-survival Bcl-2 proteins
binded to effector to prevent effector activation in normal cells
intrinsic (mitochondrial/Bcl-2) pathway:
pro-apoptotic Bcl-2 proteins
downstream of death signal bind to pro-survival protein to release effector and promote effector activation
intrinsic (mitochondrial/Bcl-2) pathway:
effector Bcl-2 proteins and activation of apoptosis
promote caspase activation (apoptosis)
1) oligomerize to poke holes in mito membrane
2) cyt c leaks into cytoplasm
3) cyt c binds to Apaf-1 to form apoptosome
4) apoptosome activates caspase-9 initiator
5) caspase-9 activates caspase-3 effector
6) apoptosis yaaaaaaaay
intrinsic (mitochondrial/Bcl-2) pathway:
p53 with Bcl-2 effectors
1) DNA damage
2) ATM/Chk2
3) p53
4) cell cycle and DNA repair
5) OR if can’t repair, p53 activates pro-apoptotic Bcl-2 proteins
6) effector Bcl-2 activation
7) apoptosis yaaaaaaay
extrinsic (receptor-mediated) pathway
activated by external secreted ligands binding to death domain (DD) on tumor necrosis factor (TNF) family receptors
extrinsic (receptor-mediated) pathway:
tumor necrosis factor (TNF)
subset of TNF family receptors have a death domain (DD)
extrinsic (receptor-mediated) pathway:
death domain (DD)
cytoplasmic domain on many proteins (not just TNF) that is a platform for self-assembly of the receptor, adaptor proteins, and caspases;
promotes activation of apoptotic caspases and kinases
extrinsic (receptor-mediated) pathway:
activation of apoptosis
1) TNF ligand
2) TNF family receptor binds
3) adaptor protein assembles on DD
4) initiator caspase-8 or 10 binds adaptor protein
5) activation of caspase-8 or 10
6) activation of effector caspases (also activation of intrinsic pathway by Bid)
7) apoptosis yaaaaaaaaay
neoplasm
abnormal growth of cells in any part of the body;
uncoordinated with growth of surrounding tissue;
irreversible growth due to accumulated genetic changes;
can be benign (noncancerous) or malignant (cancerous)
malignant neoplasm
cancerous;
abnormal borders;
less differentiated than origin tissue (anaplastic);
microscopically disorganized (pleomorphic, DNA, mitoses);
evidence of metastasis
malignant neoplasm:
anaplastic
so poorly differentiated they lack specific features
malignant neoplasm:
pleomorphic
variation in nuclear and cell size
malignant neoplasm:
metastasis
spread of tumor through blood, lymph, to body cavities, or directly to adjacent organs;
seed and soil theory
malignant neoplasm:
metastasis - seed and soil theory
metastases are not random, organ-specific metastasis is because of molecular compatibility between metastatic tumor cell “seed” and secondary tissue “soil”
benign neoplasm
noncancerous;
smooth, distinct borders;
microscopically organized (similar sizes, shapes, mitoses, DNA content);
often well differentiated, resembles origin tissue;
non-invasive, lack metastasis;
some benign tumors can undergo malignant transformations
cancer cell features in vitro that contribute to their deadly, invasive properties in vivo
1) loss of density-dependent and contact inhibition
2) autocrine growth stimulation
3) less adhesive to adjacent cells and ECM
4) evade apoptosis
cancer cell features:
loss of density-dependent and contact inhibition
just grow all over each other
cancer cell features:
autocrine growth stimulation
can stimulate own growth, send and receive their own growth factors (what a baller move haha)
cancer cell features:
less adhesive
to adjacent cells and ECM;
float around, don’t stick to surface receptors
carcinogens
cause cancer by changing cells genome (directly or indirectly);
UV radiation, N-nitrosamines, aflatoxin, bacteria, viruses
driver mutations
cancer cell mutations that increase cell’s fitness (ability to survive and reproduce) compared to those around it
1) proto-oncogenes
2) tumor suppressors
driver mutations:
proto-oncogenes
normally growth “accelerators”, pro-survival factors;
activating mutations or over expressed (activation -> cancer);
mutated proto-oncogenes = oncogenes
driver mutations:
tumor suppressors
normally growth “brakes”, pro-apoptotic factors/DNA repair machinery;
inactivating mutations or under expressed (inactivation -> cancer)
passenger mutations
cancer cell mutations that are coincidental to the driver, and confer not fitness change
1) sequence changes
2) epigenetic changes (modifications to expression like methylation)
3) larger structural changes (like aneuploidy, copy-number variations)
tumorigenesis
an evolutionary process
1) the founder
2) clonal expansion
3) genetic diversification
4) subclonal mutations
5) clonal selection
tumorigenesis:
the founder
a few, or even a single cell acquires driver mutation(s) that enable expansion
tumorigenesis:
clonal expansion
proliferation of founder gives rise to clones with the original driver mutation(s)
tumorigenesis:
genetic diversification
mutations occurs as clones expand
tumorigenesis:
subclonal mutations
some may be driver mutations
tumorigenesis:
clonal selection
genetically distinct subclonal populations compete within the tumor, heterogeneity
