Oncogenic mutations sites in relevant proto and oncogenes
Leerstof Oncology Ch7/14
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Ch7 Apoptosis
Examples of exam questions
1. DNA damage induces apoptosis via
A Caspase 9 activation
B Induction of p53 expression
C Caspase 3 activation
D All three of the above mentioned answers are correct
2. Briefly explain how triggering of apoptosis in tumor cells can contribute to new therapies
against cancer and give an example of a therapy.
Definition of apoptosis
Apoptosis is the regulated and orderly destruction of a cell through a genetically encoded
process also known as programmed cell death (PCD) Apoptosis is a type of “cell suicide” that
is intrinsic to the cell. It is a really tightly regulated destruction of the cell.
Apoptotic process
Apoptosis is organized, neat, and tidy, leaving behind little evidence of the preexisting cell.
That way you don’t have an induction of inflammation in the surrounding of these cells.
The cell undergoing apoptosis is swept clean during phagocytosis by macrophages,
neighboring cells that recognize molecular flags (phosphatidyl serine). Phosphatidyl serine
protein was first on the inside of the cell and when the cell becomes apoptotic it flip flops from
the inside of the cell to the outside of the cell. The protein is then recognized by macrophages
and that leads to phagocytosis.
Function of apoptosis
Some people have dysregulation of the apoptotic process.
Active ATP dependent process Physiological in many organs:
❖ developmental morphogenesis
❖ controls cell numbers (every 3-5 days the whole epithelium of the intestines is renewed)
❖ removal of damaged cells
❖ negative and positive selection of lymphocytes
❖cytotoxic effect of radio- and chemotherapy
Due to dysregulation of apoptosis, you can develop syndactyly ( 2 and 3 finger/toe are not
divided correctly)
Apoptosis in humans
Estimation of apoptosis in a human:
25 x 10^6 mitoses per second and 25 x 10^6 apoptosis per second.
2,2 kg cells per day undergo apoptosis.
This process has to be tightly regulated.
,Apoptosis versus Necrosis
Necrosis is mainly induced by external factors like viruses, Ph etc. We also see necrosis in
someone who has a heart attack.
We have to know the steps that occur during apoptosis.
a. here you have a normal
lymphocyte, you can recognize it
by the nucleus and the chromatin.
The lymphocyte also has a small
cytoplasm surrounding it.
b. The lymphocyte is shrinking.
c. It is forming blebbles on the
outside of the membrane, also
called zeiosis.
d. The chromatin is collapsed
e. This results in the formation of
apoptotic bodies
,Apoptosis signaling
• Induction of apoptosis:
– Programmed
– Loss of growth factors, of adhesion
– Death receptors of the TNFR family
– T- and B cell antigen receptors
– CTLs
– DNA damage (irradiation, chemotherapy)
– Stress conditions
• Mitochondrial changes
• Activation of the caspase family
• Proteolytic cleavage of structural and unctional proteins
• Induction of apoptosis morphology
Caspases
Caspases are cysteine-proteases synthesized as zymogens. In healthy cells they are presented
in the procaspase form.
- Requirement for an aspartatic acid at the P1 position
- 14 family members cloned
- Caspases 2, 3, 6, 7, 8, 9 and 10 are involved in apoptosis
- Divided into:
initiators -> 2, 8, 9 and 10
effectors -> 3, 6 and 7
inflammatory -> 1,4 and 5
this caspase is built of 4 domains, the pro-domain,
large subunit domain, spacer, and small subunit
domain.
In the large subunit domain, there is a specific amino
acid sequence that is specific for all the different
caspases. When the domains cleave it will result in the
activation of the caspase. The spacer connects the
small and the large subunit domains.
Partially processed: the small subunit domain binds to the large subunit domain and finally,
the pro-domain is removed, and which results in the activation of the caspase. This is the most
important area where the cleavage will occur.
, Four Apoptosis pathways
1. Intrinsic/stress-induced or mitochondrial apoptosis pathway
2. Extrinsic/Death receptor mediated apoptosis pathway
3. Granzyme B mediated apoptosis pathway
4. ER mediated apoptosis pathway
Two major apoptosis pathways
- Apoptosis induced by internal signals: The intrinsic or mitochondrial pathway
- Apoptosis triggered by external signals: The extrinsic or death receptor pathway
The intrinsic apoptosis pathway is induced by
immunotherapy, oncogene activation, UV light and that
can result in P53 stabilization. The P53 stabilization can
activate the BH3 only proteins and they are a
proapoptotic group of the BCL-2 family members. They
can activate the BAK and BAX protein and translocate
them from the cytoplasm to the mitochondria and then
these proteins will form homo-/heterodimers. Which is
on the outer membrane of the mitochondria and will
result in the release of cytochrome C. Cytochrome C can
bind to the adapter protein Apaf-1 and caspase 9 in the
presence of ATP. After that a whole complex is formed, caspase 9 is activated and this is called
the apoptosome, and caspase 9 can then cleave caspases 3,6 and 7.
The other pathway is called the extrinsic pathway, we need a ligand from another cell to bind
to the receptor which is on the cell that is going under apoptosis. The ligand (TRAIL, FAS, TNF-
a) can bind to its receptors and then it trimerizes. By binding got the adaptor protein FADD it
can recruit pro-caspase 8 and then there is also a complex formed, which is called the TAP
induces signaling complex and then pro-caspase 8 is activated into active caspases. Active
caspase 8 can then also cleave the effector caspases 3,6 and 7. When caspases 3,6 and 7 are
activated there is no going back, the call will definitely go under apoptosis. After the final
caspases are activated cleavage of very important proteins of the cell will occur.
Breakdown of the cell
Results from the proteolysis of target proteins:
✓ nuclear lamins
✓ Cytoskeletal proteins (actin)
✓ Intermediate filaments (cell structure)
✓ Specific kinases for cell signaling
✓ Other enzymes (caspase-activated DNAse)
Caspases 3,6 and 7 all cleave a certain group of very important proteins for your cell.
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