TRAIL-TRAIL Flashcards
What are the two types of regulated necrosis
Necroptosis and pyroptosis
How does necrosis differ to apoptosis>
Necrosis: There is an opening in the plasma membrane of the cell, followed by the release of cytoplasmic proteins into the extracellular space. Apoptosis: Cell dies, becomes packaged into apoptotic bodies which can be taken up by neighboring cells or phagocytes
Which type of cell death gives off an alarm signal to the immune system
Necrosis
What are the orderly succession of morphological changes in apoptosis
Shrinkage, Nuclear fragmentation, chromatin condensation, apoptotic bodies segregate, DNA cleavage and phagocytosis
what is secondary necrosis>
If no macrophages or other surrounding cells are available to the apoptotic cell, secondary necrosis occurs which is the release of intracellular contents into the extracellular space
What is TNF?
Tumour necrosis factor
What is TRAIL?
An apoptosis-inducing member of the TNF family.
What is the difference between TRAIL receptors 1,2,3 and 4?
TRAIL receptors 1 and 2 (DR4/5) have a full, intracellular death domain. TRAIL -R3 has no intracellular death domain at all. TRAIL-R4 has a truncated death domain. Therefore TRAIL-R3/4 are considered to be apoptosis inhibiting receptors
In what structure does TRAIL exist? How does it activate TRAIL-Rs?
As a homotrimer which crosslinks three TRAIL receptors.
What happens following crosslinking of TRAIL-R1/2?
The death domains of the receptors adopt a conformation that allows for the recruitment of FADD via its death domain. Via its death effector domain; FADD recruits pro-caspase 8. Procaspase 8 homodimerisation within the DISC leads to cleavage and release of active caspase-8 from the DISC.
What structural domains does FADD have?
It has a death domain and a death effector domain
What molecule prevents the homodimerisation and subsequent activation of procaspase-8 (long form)
c-FLIP long - Very similar to procaspase-8 structure so dimerises with procaspase-8. Cleavage of a single procaspase and c-FLIP long then occurs
What is the method of procaspase-8 inhibition exhibited by c-FLIP short
The caspase domain of procaspase-8 is unable to dimerise with anything so there is a complete inhibition of procaspase-8 at the DISC
How do you distinguish which c-FLIP structure is present
By looking at the fragments of caspase-8 at the DISC when immunoprecipitated from a cell. If it’s full length then c-FLIP short is responsible. If it is p43 of caspase 8 it is due to c-FLIP long.
What does active caspase 8 do to induce death.
It cleaves the molecules Bid and (pro)caspase-3.
What subsequent changes have to occur to procaspase-3 following caspase-8 mediated cleavage to induce its full activity?
A maturation step which requires the activity of caspase-3 itself.
What molecule blocks the maturation step of procaspase-3
XIAP - XIAP binds to procaspase-3 and prevents its intrinsic cleavage. It also inhibits the activity of caspase-9 in the apoptosome.
What is Bid? What is tBid?
A proapoptotic member of the Bcl-2 family. tBid is the active form of Bid following cleavage by caspase-8. It activates to Bax and Bak at the mitochondria which form pores in the mitochondrial membrane so proteins in the intermembranal space of the mitochondria are released.
What are two important compunds released from the intermembranal space in mitochondria during apoptosis?
Cytochrome c and Smac/DIABLO
What is the role of cytochrome c in apoptosis?
It forms the apoptosome with caspase-9 (requires Apaf-1). The apoptosome then induces the pre-activation of procaspase-3
What is the role of Smac/DIABLO in apoptosis?
It binds to the surface of XIAP which removes the inhibition of procaspase-3 and caspase-9, inducing apoptosis.
How does a cancer cell overcome apoptosis following chemo/radiotherapy?
Upregulation of Bcl-2/Bcl-xL - antiapoptotic members of the Bcl-2 family of proteins.
What are BH3 mimetics?
They activate Bax/Bak directly or inactivate Bcl-2/Bcl-xL (antiapoptotic Bcl-2 family members) which induces the permeabilisation of the mitochondrial membrane.
How do Smac mimetics work?
Either leads to autodegredation of XIAP or the removal of the inhibitory action of XIAP by releasing the caspase-3/9
What three methods are there to induce apoptosis therapeutically>
- Targeting the death receptor (antibodies or TRAIL)
- Targeting XIAP via Smac mimetics
- BH3 mimetics which either activate Bax/Bak or inactivate Bcl-2/Bcl-xL/Mcl-1
What is the role of Cdk9
Forms part of the transcription elongation factor b. it phosphorylates RNA pol II allowing for elongation. Blocking of Cdk9 therefore stops transcription.
How does Cdk9 inhibition sensitize cancer cells to TRAIL induced apoptosis?
Loss of Cdk9 inhibits the expression of cFLIP and Mcl-1. (Mcl-1 is another antiapoptotic Bcl-2 family member)
Why does global Cdk9 inhibition only effect Mcl-1 and cFLIP)?
Because they have a high turnover, so transcriptional repression significantly inhibits their production compared to other proteins.
