cell growth control - yale universitytbl.med.yale.edu/files/cell_growth_control/slides.pdf ·...
TRANSCRIPT
What we’ll talk about…
• Cyclin and cyclin-dependent kinases and control of the cell cycle
• Start and regulation of cell division
• Signaling pathways that stimulate and inhibit cell division
• Checkpoints and regulation of the cell cycle
• Mitosis
Cell division requires cell growth, chromosome duplication and separation.
CellCycle
Cell cycle is divided into separate phases.
G1
S
G2
MC
G0
Cyclins and cyclin dependent kinases (CDK) drive cell cycle events.
G1
G2
M
S
CDK
Cyclin
Different cyclin CDK complexes initiate and control the phases of the cell cycle.
G1 S G2 M G1
Start G2/MMetaphase/Anaphase
CDK Off CDK On CDK Off
Cdk2
Cyclin E Cyclin A Cyclin B APC
A C
Waves of cyclin expression and degradation mediate ordered progression of cell cycle.
Cdk2
Cyclin E Cyclin A Cyclin B APC
Cyclin E Cyclin A Cyclin B
Cyclin protein level
G1 S G2 M G1A C
Positive feedback loops increase the amount of active cyclin-CDK.
Cyclin
CDK
Cdc25inactive
Cdc25active
Activating
Inactivating
Wee1
CAK
Active
Switch-like activation of CDKs ensures rapid and irreversible initiation of cell cycle events.
+Wee1 Cdc25
time
prot
ein
conc
entr
atio
n
CD
K a
ctiv
ity
CDK protein
Cyclin protein
CDK activity
+
time
prot
ein
conc
entr
atio
n
CD
K a
ctiv
ity
CDK protein
Cyclin protein
CDK activity
Positive Feedback
CyclinCDK
CDK Cyclin
Ubiquitylation and proteosome are required to digest cyclins and decrease CDK activity.
UbiquitinProteosome
CDK
Cyclin
Start and the Decision to Divide
Start marks the initiation of DNA replication and an irreversible commitment to cell division.
SStart
Anti-mitogensMitogens
G2 M CG1
Cyclin D
Cdk4
Cyclin E
Cdk2
Cyclin A
Cdk2
Mitogens activate signaling pathways that lead to expression of Cyclin D.
Signal transduction pathway
Mitogen
Cyclin D
CDK4
CDK2
Cyclin E
DNA replication
Cyclin A
CDK2
Receptor tyrosine kinases activate MAP kinase pathways to increase expression of cyclin D.
Receptor tyrosine kinases
Guanine nucleotide exchange factor
Ras
MAP kinase kinase kinase
MAP kinase kinase
MAP kinase
Phosphorylation
MycTranscription
Cyclin D
EGF
Anti-mitogens activate signaling pathways that inhibit formation of cyclin D-Cdk complexes.
Smad
Phosphorylation
Transcription
TGF-β
Smad4
Ink4Cdk4
Cyclin D
Receptor tyrosine kinases
E2F proteins regulate expression of cyclin E.
Cyclin EEnhancer Repressor
Cyclin EEnhancer Repressor
X
E2F1 or E2F2 or E2F3
E2F4 or E2F5
Cyclin E
pRB inhibits cell division by promoting binding of E2F to repressor and inhibiting binding to
XX
E2F1
pRb
E2F4
pRb
Cyclin EEnhancer Repressor
Cyclin D/CDK inactivate pRB to allow E2F to stimulate transcription of cyclin E.
Cyclin EEnhancer Repressor
X
CDK4Cyclin D
Cyclin E
E2F1
pRbE2F1
E2F1
pRb
E2F4
E2F4
pRb
Positive feedback loop keeps cyclin E - CDK active.
TranscriptionPhosphorylation
Phosphorylation
CDK4Cyclin D
Cyclin ECDK2
Positive Feedback Loop
E2F1pRb
E2F1pRb
E2F1
pRb
Mitogens and Increase in Cell Size
TOR complex integrates the nutritional status of the cell and regulates cell growth.
mTORC Active
Growth Factors[ATP] [Amino Acids]O2
Protein Synthesis Lipid Synthesis
Mitogen-activated signaling pathways can turn on TOR complexes to promote cell growth.
Receptor Tyrosine Kinase
Adaptor
PI3 KinasePDK
AKT
TSC1/2 Inactive
Mitogen
mTORC Activerheb-GDP rheb-GTP
Checkpoints in the Cell Cycle
Checkpoints ensure completion of one stage of cell cycle before starting the next.
G1/S-CDK S-CDK M-CDK APC
DNADamage
Unreplicated DNA
DNADamage
UnattachedChromosomes
G1 S G2 M G1A C
DNA damage activates p53 to arrest the cell cycle.Damaged DNA
Cyclin ECDK2
Mdm2
p53Mdm2
p53
p53
p53
p21p53
Enhancer
p21
Mdm2
Mdm2ATM/ATR kinasesChk1/Chk2 kinases
DNA damage also triggers degradation of Cdc25 to slow the cell cycle.
Damaged DNA
ATM/ATR kinasesChk1/Chk2 kinases
Cdc25
Proteosome
Ubiquitin Ligase
p53 is activated by oncogenes and slows cell division.
Oncogenic Transformation: Ras, Myc, E2F
p53
p21
p14-ARF Cyclin D
Cyclin E
CDK4
CDK2
p14-ARFMdm2
Inactive
P53 triggers apoptosis by inducing release of cytochrome c from mitochondria.
p53 Bax
Cytochrome c
Apoptosis
Mitosis
Mitosis proceeds in several defined stages that involve changes in microtubule organization.
CF
CS
Interphase MetaphaseProphase Prometaphase
Anaphase AAnaphase BTelophaseCytokinesis
Three types of microtubules comprise the mitotic spindle.
Chromosomes Astral microtubules
Interpolar microtubules
Kinetichore Microtubules
CentrosomeKinesin
Mitotic Checkpoint
Incomplete or incorrect attachment of microtubules arrests cells in metaphase.
Metaphase ArrestHigh cyclin B-CDK2 activity
Transition to AnaphaseDecrease in cyclin B-CDK2 activity
Cohesins tether sister chromatids to prevent premature separation.
SisterChromatids
Cohesins
SisterChromatids
Histones
Unattached chromosomes prevent activation of anaphase promoting complex.
Anaphase-promoting complex,inactive
Cdc20
Anaphase-promoting complex,
active
Metaphase Arrest
Anaphase-promoting complex ubiquitylates cyclin B and securin to trigger transition to anaphase.
Cyclin B
Cdk2
Securin
Separase
Ubiquitylation
Ubiquitylation
Proteosome
Anaphase-promoting complex
Cdc20
Separase Active
Separase digests cohesins which allows tension from the spindle to separate chromosomes.
Separase
Take home points
• Cyclins and CDKs initiate different stages of the cell cycle
• Positive feedback is critical for commitment steps in the cell cycle
• Mitogens and anti-mitogens work through signaling pathways to influence the decision to divide
• Oncogenes trigger cell division in the absence of mitogen
• Tumor suppressors slow cell division by inactivating cyclin-CDKs
• Checkpoints monitor the state of the cell and can arrest the cell cycle