Apoptosis

By : najmaldin saki2008

Department of Hematology School of Medical

Sciences Tarbiat Modares University

Caspases

Ligand-induced cell deathLigand-induced cell death

“The death receptors”

Ligand-induced trimerization

Death Domains

Death Effectors

Induced proximity of Caspase 8

Activation of Caspase 8

FasL

Trail

TNF

CASPASES CAN BE INHIBITED BY VIRUSESCASPASES CAN BE INHIBITED BY VIRUSES

... CrmA

... Baculovirüs p35

... Ebstein Barr Virüs BHRFI proteini

... Ebstein Barr Virüs LMP-1 proteini

3 mechanisms of caspase activationa. Proteolytic cleavage e.g. pro-

caspase 3

b. Induced proximity, e.g. pro-caspase 8

c. Oligomerization, e.g. cyt c, Apaf-1 & caspase 9

Back

Bcl-XL

Bad

Bcl-XL

BaxBcl-2

Bax

Bax Bax

Bcl-2

Bad

CELL SURVIVAL

CELL DEATH

Controlling the cell-proliferation Controlling the cell-proliferation and death machineryand death machinery

P53 is able to activate p21

P21 binds to the CDK-cyclin complex and inhibits its protein kinase enzymatic activity

- CDK’s target proteins are not phosphorylated- Cell cycle is unable to progress-When the DNA mismatches have been repaired, the drop of p53 levels & a cessation of inhibition

G1-to-S checkpoint block

The cell cycle: negative intracellular controls

Intracellular signals

-Fail-safe systems (checkpoints) ensure that the cell cycle does not progress until the cell is competent.

The bcl-2 family

BH4 BH3 BH1 BH2 TMN C

Receptor domain

phosphorylation

Raf-1calcineurin Pore

formation

Membraneanchor

Liganddomain

Group I

Group II

Group III

Bcl-2

bax

Badbidbik

Bcl-2 ProteinBcl-2 Protein(with BH3 Peptide)(with BH3 Peptide)Bcl-2 ProteinBcl-2 Protein

65000 papers

Apoptsis in anucleate platelets wa first reported in 1997 by Vanags et al.

It was demonstrated that apoptosis within megakaryocytes & megakaryoblastic is causal for platelet production (NO , TNFα, BCL2)

Models of platelet apoptosis

1. apoptosis of platelets was induced by the calcium ionophores ionomycin , A23187 which induce apoptosis in nucleate cells.

2. apoptosis was provoked by platelet storage in culture where washed platelets were aged by incubation for 18–24 h at 37 C in a culture medium or plasma in capped tubes

3. apoptosis was induced by platelet aging in vitro during storage of leukodepleted platelet concentrates (PCs) under standard blood banking conditions at 22 C

4. apoptosis was associated with platelet aging in vivo in dogs with thrombopoiesis suppressed by estradiol injection .

5. platelet apoptosis was reported in mice with thrombocytopenia caused by malaria infection and induced by injection of TNF or anti-platelet antibodies

Apoptotic changes in platelet morphology

These morphologic changes included:

platelet shrinkagecytoplasm condensationplasma membrane blebbing extension of filopodia.

Originaly , these changes were described as “platelet activation” and only since 1997 did some investigetors begin to consider these morphologic chenges as apoptotic.

Li et al, found that platelets express mRNA for death ligand TRAIL, death receptors TNFR1, DR3, DR4 and DR5, and adapter proteins TRADD and RIP.

In contrast , Fas receptor and Fas ligand were not detected in platelets as determined by mRNA and immunoblot and anti-Fas antibodies had no e ect on platelets.ff

ᴪm

In normal undamaged nucleate cells, mitochondria have a high ᴪm; breakdown of ᴪm is characteristic of early apoptosis .

ᴪm in platelets can be measured by the cell-permeable lipophilic cationic dyes JC-1 and DiOC6 .

Using JC-1 , we have demonstrated depolarization of ᴪm in PCs starting from days

13_14 of storage.

Cytochrome c, Diablo/Smac and Apaf-1.

Cytochrome C and Apaf-1 have been found by immunoblot in whole lysates of fresh nonactivated platelets.