L312Spring 2007Lecture 19Drummond March 29

1
L312/Spring 2007 Lecture 19 Drummond March 29
For today Finish Ch. 18 Apoptosis and Growth
(625 - 633) Exams back Today! Hooray! Last
time cell cycle control and checkpoint
arrest Cyclins cdk (cyclin dependent
kinases) regulate key cell cycle
events Ubiquinylation (adding the small
protein ubiquitin) is a signal for the
protein to enter the proteasome cyclins are
degraded by Ubq/proteolysis after cell phase
initiation Again focus on protein/protein
or proteinmodification events that underlie
the specific events in question. Today
Apoptosis! (Programmed Cell Death
PCD) compare microorganisms versus complex
organisms the machinery that degrades the
cell and its regulation (an ordered,
irreversible cascade) Cell growth
signals relationship with apoptosis how
is cell proliferation achieved?
2
It couldnt be that simple phosphorylation
status is crucial to M-cdk
The key here is that phosphorylation at specific
sites is crucial for function. Multiple
required inputs exponentially increases the level
of complexity for regulation. doesnt fire too
soon supports sudden cell cycle progression
multiple sites for input information
3
Activating the activator how is the process
accelerated?
4
M-cyclin regulates initiation of mitosis
How is the very rapid decay Of the M-cyclin
activity achieved?
5
Cyclins and cdks regulate the cell cycle
Not the same Cyclin or cdk!
How might this setup avoid re-replication of DNA?
6
How is replication Triggered in S-phase?
Modulating phosphorylation status is the single
most important switch in the cell (by kinases
and phosphatases)
7
But what happens when something goes wrong in
replication
p53 protein mediates cell cycle arrest and
apoptosis in response to DNA damage
know p53 and p21 function (frequently mutated in
tumors)
(P21 also directly blocks Replication by binding
to PCNA at the fork)
STOP!! Choices?
8
What is apoptosis (and why should you care)?
Embryonic mouse paw
Identify the bright green dots
Using cells as a medium, which is easier carve
a structure from a block of cells, or create a
structure by moving cells? (Which
might be stronger?)
Liver as an example
9
Apoptosis versus necrosis
In tissue
In culture
Identify when each occurs what are the
consequences to neighboring cells
Key events (B/C) in apoptosis Cytoskeleton
(actin) Nuclear lamina (IF) DNA (chromatin)
10
What are the key molecular events that mediate
protein degradation in the cell?
Why a cascade? Relationship with Irreversibility?

• Key hierarchy
• Of caspases --gt
• Hierarchy of targets
• Hierarchy of
• events in the
• breakdown

11
What happens to chromosomal DNA after apoptosis
induction?
Can you draw the products? Where might the
apoptotic nucleases be found?
12
Two key questions What happens to the
mitochondria during apoptosis? What are the roles
of the bcl-2 family of proteins?
Bcl-2
(inhibitor)
mediators
bax
bak
Another key System is always in place
What would happen to a cell with Damaged or
compromised mitochondria?
13
Apoptosis in the normal course of development
Why start out with too many?
Revisit p53 common mediator of apoptosis in
response to DNA damage
14
The other face of the bcl-2 family inhibition
of apoptosis
What kind of signal transduction pathway might
this be?
Revisit the liver model What is a survival factor?
15
Classes of extracellular signals that control
growth and apoptosis

• Death factors
• Binds transmembrane receptor and induces
  apoptosis
• or necrosis (TNF, death ligands)
• Mitogens
• Stimulate cell division (interfere with cyclin
  control)
• 3. Growth factors
• Stimulate growth in cell mass
• (upregulate protein synthesis or prevent
  degradation)
• 4. Survival factors
• Suppress the initiation of apoptosis
• (might induce bcl-2, for example)

16
How do mitogens promote cell proliferation?
Rb retinoblastoma gene/protein What might
mutation that causes cancer be?
Remember generic switch story
17
Growth factors stimulate growth but not
proliferation
18
Growth factors regulate protein and cell
component synthesis and degradation
19
What happens when you inhibit a block inhibition
of growth?
Myostatin normally blocks cellular growth (NOT
proliferation)