SLIDE 1
Cell Growth Control
Peter Takizawa peter.takizawa@yale.edu
SLIDE 2 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
SLIDE 3
Cell division requires cell growth, chromosome duplication and separation.
Cell Cycle
SLIDE 4
Cell cycle is divided into separate phases.
G1 S G2 M C G0
SLIDE 5
Cyclins and cyclin dependent kinases (CDK) drive cell cycle events.
G1 G2 M S CDK Cyclin
SLIDE 6
Different cyclin CDK complexes initiate and control the phases of the cell cycle.
G1 S G2 M G1 Start G2/M Metaphase/ Anaphase CDK Off CDK On CDK Off Cdk2 Cyclin E Cyclin A Cyclin B APC A C
SLIDE 7
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 G1 A C
SLIDE 8
Positive feedback loops increase the amount of active cyclin-CDK.
Cyclin CDK Cdc25 inactive Cdc25 active Activating Inactivating Wee1 CAK Active
SLIDE 9 Switch-like activation of CDKs ensures rapid and irreversible initiation of cell cycle events.
+
Wee1 Cdc25
time protein concentration CDK activity
CDK protein C y c l i n p r
e i n CDK activity
+
time protein concentration CDK activity
CDK protein Cyclin protein CDK activity
Positive Feedback Cyclin CDK CDK Cyclin
SLIDE 10
Ubiquitylation and proteosome are required to digest cyclins and decrease CDK activity.
Ubiquitin Proteosome CDK Cyclin
SLIDE 11
Start and the Decision to Divide
SLIDE 12
Start marks the initiation of DNA replication and an irreversible commitment to cell division.
S Start Anti-mitogens Mitogens G2 M C G1 Cyclin D Cdk4 Cyclin E Cdk2 Cyclin A Cdk2
SLIDE 13
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
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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 Myc Transcription Cyclin D EGF
SLIDE 15
Anti-mitogens activate signaling pathways that inhibit formation of cyclin D-Cdk complexes.
Smad Phosphorylation Transcription TGF-β Smad4 Ink4 Cdk4 Cyclin D Receptor tyrosine kinases
SLIDE 16
E2F proteins regulate expression of cyclin E.
Cyclin E Enhancer Repressor Cyclin E Enhancer Repressor
X
E2F1 or E2F2 or E2F3 E2F4 or E2F5 Cyclin E
SLIDE 17
pRB inhibits cell division by promoting binding of E2F to repressor and inhibiting binding to
X X
E2F1 pRb E2F4 pRb Cyclin E Enhancer Repressor
SLIDE 18
Cyclin D/CDK inactivate pRB to allow E2F to stimulate transcription of cyclin E.
Cyclin E Enhancer Repressor
X
CDK4 Cyclin D Cyclin E E2F1 pRb E2F1 E2F1 pRb E2F4 E2F4 pRb
SLIDE 19
Positive feedback loop keeps cyclin E - CDK active.
Transcription Phosphorylation Phosphorylation CDK4 Cyclin D Cyclin E CDK2 Positive Feedback Loop E2F1 pRb E2F1 pRb E2F1 pRb
SLIDE 20
Mitogens and Increase in Cell Size
SLIDE 21
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
SLIDE 22
Mitogen-activated signaling pathways can turn on TOR complexes to promote cell growth.
Receptor Tyrosine Kinase Adaptor PI3 Kinase PDK AKT TSC1/2 Inactive Mitogen mTORC Active rheb-GDP rheb-GTP
SLIDE 23
Checkpoints in the Cell Cycle
SLIDE 24
Checkpoints ensure completion of one stage of cell cycle before starting the next.
G1/S-CDK S-CDK M-CDK APC DNA Damage Unreplicated DNA DNA Damage Unattached Chromosomes G1 S G2 M G1 A C
SLIDE 25
DNA damage activates p53 to arrest the cell cycle.
Damaged DNA Cyclin E CDK2 Mdm2 p53 Mdm2 p53 p53 p53 p21 p53 Enhancer p21 Mdm2 Mdm2 ATM/ATR kinases Chk1/Chk2 kinases
SLIDE 26
DNA damage also triggers degradation of Cdc25 to slow the cell cycle.
Damaged DNA ATM/ATR kinases Chk1/Chk2 kinases Cdc25 Proteosome Ubiquitin Ligase
SLIDE 27
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-ARF Mdm2
Inactive
SLIDE 28 P53 triggers apoptosis by inducing release of cytochrome c from mitochondria.
p53
Bax
Cytochrome c
Apoptosis
SLIDE 29
Mitosis
SLIDE 30 Mitosis proceeds in several defined stages that involve changes in microtubule organization.
CF CS
Interphase Metaphase Prophase Prometaphase Anaphase A Anaphase B Telophase Cytokinesis
SLIDE 31
Three types of microtubules comprise the mitotic spindle.
Chromosomes Astral microtubules Interpolar microtubules Kinetichore Microtubules Centrosome Kinesin
SLIDE 32
Mitotic Checkpoint
SLIDE 33
Incomplete or incorrect attachment of microtubules arrests cells in metaphase.
Metaphase Arrest
High cyclin B-CDK2 activity
Transition to Anaphase
Decrease in cyclin B-CDK2 activity
SLIDE 34
Cohesins tether sister chromatids to prevent premature separation.
Sister Chromatids Cohesins Sister Chromatids Histones
SLIDE 35
Unattached chromosomes prevent activation of anaphase promoting complex.
Anaphase- promoting complex, inactive Cdc20 Anaphase- promoting complex, active Metaphase Arrest
SLIDE 36
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
SLIDE 37
Separase digests cohesins which allows tension from the spindle to separate chromosomes.
Separase
SLIDE 38 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
