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
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
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:
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
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
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
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
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:
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)
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)
